Research ArticleExperiment and Simulation Study on the Special Phase Behaviorof Huachang Near-Critical Condensate Gas Reservoir Fluid

Dali Hou12 Yang Xiao12 Yi Pan3 Lei Sun3 and Kai Li12

1School of Energy Chengdu University of Technology Chengdu Sichuan 610059 China2State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Chengdu University of Technology ChengduSichuan 610059 China3State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Southwest Petroleum University of TechnologyChengdu Sichuan 610500 China

Correspondence should be addressed to Yang Xiao yangxiao20142015126com

Received 5 November 2015 Revised 16 January 2016 Accepted 10 February 2016

Academic Editor Casimiro Mantell

Copyright copy 2016 Dali Hou et alThis is an open access article distributed under the Creative CommonsAttribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Due to the special phase behavior of near-critical fluid the development approaches of near-critical condensate gas and near-criticalvolatile oil reservoirs differ from conventional oil and gas reservoirs In the near-critical region slightly reduced pressuremay resultin considerable change in gas and liquid composition since a large amount of gas or retrograde condensate liquid is generated It is ofsignificance to gain insight into the composition variation of near-critical reservoir during the depletion development In our studywe performed a series of PVT experiments on a real near-critical gas condensate reservoir fluid In addition to the experimentalstudies a commercial simulator combined with the PREOS model was utilized to study retrograde condensate characteristics andreevaporation mechanism of condensate oil with CO

2injection based on vapor-liquid phase equilibrium thermodynamic theory

The research shows that when reservoir pressure drops below a certain pressure the variation of retrograde condensate liquidsaturation of the residual reservoir fluid exhibits the phase behavior of volatile oil

1 Introduction

In recent years amounts of criticalnear-critical oil andgas reservoirs were both found in China and abroad [1]The phase behavior of near-critical fluid has received closeattention because of its complex and fickle fluid propertiesand a large number of studies were conducted on binary orternary systems the study on a multicomponent reservoirfluid is very scarce [2] Gil et al measured the density of CO

2-

C2H6binary mixture at the critical region and supercritical

region and compared the measured data with the data fromreferences [3] A R Bazaev and E A Bazaev reviewed thePVT parameters of some binary mixtures at the near-criticalregion and measured the PVT parameters of four groups ofbinary mixtures at near-critical region [4] However only afew scholars performed the phase behavior experiments andtheoretical research on multicomponent mixtures at near-critical region [5ndash14] Yang et al measured PVT physicalparameters including deviation factor bubble point and dew

point at the critical region critical point volume fraction ofliquid at the two-phase region and density of gas and fluidphase of real multicomponent formation fluid in reservoirsat the near-critical region through experiments [5] Luo andZhong explained the layering effect of synthetic near-criticalcondensate gas reservoir fluid in PVT cell and demonstratedgraded distribution of near-critical fluid density with heightusing optical principle Results indicate that great compress-ibility of near-critical fluid and gravity result in great densitygradient and that it is hard for fluid to reach balance within ashort time because of wide transition zone area between two-phase fluid at near-critical region and distinct fluctuations[6] Zheng et al measured phase behavior at near-criticalregion of three rich condensate gas pools one is synthetic 6-component rich condensate gas reservoir fluid sample and theother two are fluid samples from real offshore rich condensategas pool and land rich condensate gas pool respectivelyCritical point bubbledew point curve critical opalescencephenomena and phase transition at critical region were

Hindawi Publishing CorporationJournal of ChemistryVolume 2016 Article ID 2742696 10 pageshttpdxdoiorg10115520162742696

2 Journal of Chemistry

tested Test results indicate that two dew points occur at tem-peratures higher than critical point and transition betweendew point and bubble point at temperatures lower thancritical point namely transition from dew point into bubblepoint and behaviors of synthetic fluid sample and realformation fluid sample at near-critical region are differentnear-critical region of real formation fluid sample is widerand becomes wider when paraffin content in fluid is greater[7ndash9] Parra andRemolina used synthetic 4-component near-critical volatile oil fluid to study PVT phase behavior afterinjection of N

2 Results indicate that saturation pressure of

near-critical volatile oil fluid increases with increasing N2

injection ratio and crude oil density decreases with increasinggasoil ratio and near-critical volatile oil fluid transformedinto near-critical condensate gas fluid at N

2injection of

40mol Above results indicate that researches on multi-component near-critical fluid phase behavior were mainlyfocused on synthetic multicomponent fluid and scarcelyfocused on real multicomponent formation fluid what ismore researches onmulticomponent near-critical fluid phasebehavior were mainly focused on experiment and scarcelyfocused on theory and stimulation [10]

Therefore in this paper phase behavior experiment wasperformed on a real near-critical reservoir fluid the phasebehavior experiment includes two-flash experiment constantcomposition expansion experiment and constant volumedepletion experiment In addition we also conducted a seriesof numerical simulations which includes two-flash experi-ment constant composition expansion experiment constantvolume depletion experiment and CO

2-injection swelling

test The experimental and simulation results provide basicdata for further research on phase behavior characteristicsand thermodynamic model of near-critical complex fluidalso provide basic data for determining the minimum mis-cible pressure in CO

2miscible flooding of the near-critical

complex fluid and provide reference for enhancing recoveryof retrograde condensate oil by injecting CO

2in near-critical

condensate gas reservoirs [15]

2 Experiment

21 Sample Preparation Experimental measurements weremade on the Huachang reservoir fluid and the fluid ofH2-3 well was selected which was directly taken from thesurface of the gas-liquid separator of H2-3 well in Huachangoil field in the south of China Under original reservoircondition (1324∘C 2553MPa) and initial gas-oil ratio therepresentative fluid sample was prepared by using the surfaceseparator oil and separator gas All our operations complywith the standard of gas condensate reservoir fluid propertiesanalysis (SYT5542-2009) [16] Table 1 shows the well streamcomposition of reservoir fluid based on the results of gas andoil chromatographic analysis and measured gas-oil ratio Asis shown in Table 1 the content of intermediate hydrocarboncomponents is about 2566mol and combined with thegas-oil ratio (86900m3m3) and the content of condensateoil (70290 gm3) so the reservoir fluid of H2-3 well isconsidered to be a near-critical condensate gas reservoirfluid system with a low gas-oil ratio and high content of

Table 1 Well stream composition for H2-3 well

Component molN2

0636CO2

5228C1

57067C2

11732C3

6224iC4

1075nC4

1756iC5

1207nC5

1086C6

2580C7+

11411Properties of C

7+

Density of C7+ gcm3 0754

Molecular weight of C7+ gmol 1144

intermediate hydrocarbon and high content of condensateoil

22 Apparatus For conducting the PVT experiment of near-critical condensate gas reservoir fluid system a full obser-vation mercury-free high temperature and high pressuremultifunctional reservoir fluid analyzer JEFRI which wasdeveloped and produced by Canadian DBR Company wasadopted A schematic of the apparatus is shown in Figure 1 Itconsists of an injection pump system a 150mL overall visualPVT cell (the temperature ranges from 0∘C to 200∘C withan uncertainty of 01∘C and pressure ranges from 01MPa to70MPawith an uncertainty of 001MPa) a flash separation atemperature control system an oilgas chromatography andan electronic balance The PVT cell is equipped with a tightfit cone piston at the bottom so that a small annular spacevolume is formed between cylinder wall and piston whichcan accurately measure a very small amount of retrogradecondensate liquid dropout of the sample through the externalaltimeter And by way of video it allows us to observe thewhole phase behavior of the near-critical condensate gasreservoir fluid

23 Experimental Procedure

(1) Clean PVT vessel and cells then connect the PVTvessel to cells and evacuate the cells

(2) Prepare the near-critical condensate gas sample andcontrol and maintain the desired temperature usingthe constant temperature air bath

(3) Transfer a certain amount (about 40mL) of thesynthetic near-critical condensate gas sample intoPVT cells at the specified temperature and pressureadjust the oven through thermostat to the reservoirtemperature stir the condensate gas sample for 1 hourand then maintain for 30min and measure the near-critical condensate gas sample volume of the PVTcells

Journal of Chemistry 3

(1)

(2)

(3)

(4)

(5) (6)

(7)

Reservoir fluid

Piston

Pressure transmitting medium

(1) Condensate gas sample

(3) Thermostatic system(4) Oil and gas separation devices and electronic balance

(5) Gasometer(6) Oil and gas chromatography(7) Automatic pump

(2) PVT cell

Figure 1 Schematic diagram of the experimental apparatus

(4) After transferring the prepared sample to PVT cellsunder reservoir condition the stable fluid was slowlyreleased to laboratory temperature and atmosphericconditions from the PVT cells and gas and liquidseparated Record the bled gas volumes using thegasometer and the bled oil volumes using the elec-tronic balance and density meter and remaining gasvolumes of PVT vessel

(5) The following step is prepared for the constant com-position expansion experiment on the remaining gasvolumes of PVT vessel The remaining gas samplein the PVT vessel was depressurized step by stepfrom the reservoir pressure under the formationtemperature record the value of pressure and volume

(6) Finally the constant volume depletion experimentwas conducted It is evenly divided into 6sim8 pres-sure drop between the dew point pressure and theproposed abandonment pressure under the formationtemperature Depressurize to the each desirable pres-sure and balance the system for half an hour or moreand then record the total volume of the sample andthe volume of the condensate oil in the PVT cell

The detailed testing of the process of each experiment andtesting purposes are as follows

(1) Two-flash experiment the testing procedures aredescribed in step (4) Besides chromatographic anal-ysis (HP-6890 gas chromatograph and an Agilent-7890A oil chromatograph) of the separated gas andliquid was conducted to identify composition ofreservoir fluid systemThe testing purpose is to obtainthe well stream components and gas-oil ratio

(2) Constant composition expansion experiment (CCEexperiment) Constant composition expansion exper-iment is also known as 119875-119881 test The testing pur-pose is to provide information on determination of

dew point gas deviation factor and relative vol-ume of the fluid at different pressures The testingprocedures are described in step (5) In the CCEtest the gradual step-down approximation methodis used to determine the dew point pressure whenthe pressure differences between a fine mist dropletexisting and disappearing is less than 01MPa takethe average value of these two pressures for thedew point pressure To test the 119875-119881 relationshipthe sample in the container was pressurized to thereservoir pressure (2553MPa) under the formationtemperature (1324∘C) and sufficiently stirred untilstability Then reduce the pressure step by step atreservoir temperature during which the change involume is obtained When pressure drops below thedew point retrograde condensate liquid drops out

(3) Constant volume depletion experiment (CVD exper-iment) The testing purpose is to predict the changeof the condensate oil saturation the change of pro-duced well stream components and residual liquidwell stream components in the process of depletiondevelopment of the condensate gas reservoir Thetesting procedures are described in step (5) In theCVD test the volume of the sample at dew pointpressure is identified as the constant fluid pore vol-ume of gas condensate reservoir and the volume isexpressed as 119881

119889(it is used to calculate the conden-

sate oil saturation and the condensate oil and gasrecovery) And dew point pressure to zero pressure(gauge pressure 01MPa) is divided into eight pres-sure stages to simulate the depletion process of thereservoir and each time (each pressure stage whichis 2553MPa 2448MPa 22MPa 20MPa 17MPa14MPa 11MPa 8MPa and 5MPa) the system wasallowed to equilibrate Since the pressure reducedthe gas expanded discharging the gas until reachingthe constant volume 119881

119889at each constant pressure

4 Journal of Chemistry

Table 2 Composition of pseudo-components

Pseudo-components molCO2

523N2

064CH4

5707C2H6

1173C3H8

622iC4H10

107nC4H10

176iC5H12

121nC5H12

109C6H14

258C7simC8

774C9simC10

249C11+

118

Repeat the depressurization-exhaust process till thelast stage of pressure The testing process of the lastlevel pressure to zero pressure is described as followsopen the top valve and directly depressurize to zeropressure by gas releasing Subsequently dischargethe residual oil and gas from the cell and take thegas sample to conduct the component analysis andthe density and composition of residual oil weresimultaneously measured

3 Calculations

To verify the laboratory results we utilized the high pre-cision PR equation of state (PREOS78) [17] in WINPROPmodule of the Computer Modeling Group (CMG) simulatorCombinedwith the fluid thermodynamic equilibrium theoryit can accurately describe and predict phase behavior ofcondensate gas reservoir fluid and phase transition near thecritical point Thermodynamic parameters of the PREOS areadjusted to match the experimental measured PVT data Theoriginal well stream composition was split and grouped into13 pseudo-components which is given in Table 2 Criticaltemperatures critical pressures and acentric factors of theplus components and binary interaction parameters (119870

119894119895)

were adjusted to match the experimental data such as thesaturation pressure (the dew point pressure) gas-oil ratiorelative volumes and retrograde condensate liquid satura-tions It is worth mentioning that interaction coefficients(119870119894119895) are introduced to account for the molecular interaction

between dissimilar molecules The values of the interactioncoefficients are obtained by fitting the predicted saturationpressures to experimental data through the PR78 EOS Tables3 and 4 present the adjusted critical temperatures criticalpressures and acentric factors of the plus components andobtained binary interaction parametersThe absolute relativeerror (1) and the average absolute relative error (2) are used toexpress the deviation between the calculated values by usingthe PREOS in this paper and the experimental measuredvalues The objective is to make the deviation between thecalculated value and experimental valueminimumTo extend

the laboratory results on the basis of fitting the experimentaldata a series of simulation calculations were carried out suchas the component variation of remaining fluid condensateoil condensate gas in CVD experiment and reevaporationmechanism of remaining fluid with CO

2injection

ARE =119873

sum

119894=1

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

Cal minus ExpExp

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

119894

times 100 (1)

AARE = 1119873

119873

sum

119894=1

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

Cal minus ExpExp

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

119894

times 100 (2)

4 Results and Discussion

41 Experimental Results and Discussion Prior to constantcomposition expansion (CCE) and constant volume deple-tion (CVD) experiment a two-flash experiment of the reser-voir fluid of H2-3 well was performed Table 5 shows the two-flash experimental data of the reservoir fluid of H2-3 wellReferring to the international standard the fluid is identifiedas near-critical condensate gas reservoir fluid system whichhas high content of condensate oil low condensate oil densityand gas-oil ratio

Constant composition expansion experiment is alsoknown as119875-119881 relationship experiment which provides infor-mation on determination of dew point relative volume of thefluid and retrograde condensate liquid saturation at differentpressures Relative volume is the ratio between the volumeof each pressure and the volume of dew point pressureand the retrograde condensate liquid saturation is the ratiobetween the volume of the retrograde condensate oil and thevolume of the dew point pressure The CCE experimentalresults under reservoir temperature (1324∘C) are showed inTable 6 the reservoir fluid of H2-3 well exhibits a maximumretrograde condensate liquid saturation of 42079 and theretrograde condensate liquid saturation increases first andthen decreases

Meanwhile we observed the phase behavior of H2-3well reservoir fluid in the near-critical region during CCEexperiment Figure 2 presents the phase behavior in thenear-critical region of reservoir fluid in H2-3 well duringpressure drop process Under the formation temperaturewhen pressure reduces from the pressure point in Figure 2(a)to the pressure point in Figures 2(b) 2(c) 2(d) 2(e) and2(f) reservoir fluid in PVT test cell turns from transparentgolden yellow into light brown and then into reddish brownand finally into completely opaque ash black When pressurereduces from the pressure point in Figure 2(f) to the pressurepoint in Figures 2(g) and 2(h) reservoir fluid in PVT test cellturns from completely opaque ash black into reddish brownat bottom and ash black at top and then into light brownat bottom and light ash black at top and does not have theobvious gas-liquid interface When pressure further reducesfrom the pressure point in Figure 2(h) to the pressure pointin Figures 2(i) 2(j) and 2(k) reservoir fluid in PVT testcell turns from light brown at bottom and light ash black attop into golden yellow at bottom and has the obvious gas-liquid interface besides retrograde condensate liquid volume

Journal of Chemistry 5

Table 3 Critical temperatures and critical pressures acentric factors of the plus components

Plus components Critical temperature(∘C) Critical pressure(MPa) Acentric factorC7simC8

28031 30245 0283C9simC10

33685 24608 0368C11+

40139 21066 0477

Table 4 Binary interaction parameters (119870119894119895) and mixing rules for the PREOS in this study

Components CO2

N2

CH4

C2H6

C3H8

iC4H10

nC4H10

iC5H12

nC5H12

C6H14

C7simC8

C9simC10

C11+

CO2

0 00200 01030 01300 01350 01300 01300 01250 01250 01500 01500 01500 01500N2

00200 0 00310 00420 00910 00950 00950 00950 00950 01200 01200 01200 01200CH4

01030 00310 0 00027 00085 00158 00148 00209 00206 00253 00314 00426 00561C2H6

01300 00420 00027 0 00017 00055 00049 00087 00086 00117 00160 00245 00352C3H8

01350 00910 00085 00017 0 00011 00001 00028 00027 00046 00075 00136 00219iC4H10

01300 00950 00158 00055 00011 0 00000 00004 00004 00012 00028 00069 00133nC4H10

01300 00950 00148 00049 00001 00000 0 00006 00005 00015 00033 00077 00143iC5H12

01250 00950 00209 00087 00028 00004 00006 0 00000 00002 00011 00041 00093nC5H12

01250 00950 00206 00086 00027 00004 00005 00000 0 00003 00012 00042 00094C6H14

01500 01200 00253 00117 00046 00012 00015 00002 00003 0 00003 00024 00066C7simC8

01500 01200 00314 00160 00075 00028 00033 00011 00012 00003 0 00009 00039C9simC10

01500 01200 00426 00245 00136 00069 00077 00041 00042 00024 00009 0 00010C11+

01500 01200 00561 00352 00219 00133 00143 00093 00094 00066 00039 00010 0

Table 5 Summary of two-flash experimental data

Gas-oil ratio (m3m3) 86900Gas volume factor 00078Condensate oil density (gcm3) 07244The content of condensate oil (gm3) 70290

increases dramatically to the maximum and then decreasesmildly

The above phenomenon of the color of reservoir fluidchanging from transparent golden yellow into light brownand then into reddish brown and finally into completelyopaque ash black is called critical opalescence which isshown in dotted line position in Figure 2 The criticalopalescence is caused by molecular density fluctuation as aresult of gas-liquid molecular movement in the gas-liquidphase change process The reason of density fluctuation isevaporation of liquid molecules and condensation of gasmolecules and the molecular motion was especially sharpfluctuations when the temperature is near the critical pointAs a result density distribution presents concavo-convexrandomly distributed spatial curved surface instead of lam-inar and on the direction of the light numerous liquid-gas interfaces or gas-liquid interfaces appear As light travelsthrough these interfaces a series of reflection and refractionhappened which reduces light energy gradually resulting incritical opalescence

In the CVD test the sample volume at dew point pressureis identified as the constant pore volume of gas condensatereservoir and dew point pressure to zero pressure (gaugepressure) is divided into six to eight pressure stages tosimulate the depletion process in the reservoir and the

retrograde condensate liquid saturations at each pressureduring the depletion process were measured under theconditions of equilibrium Table 7 presents the retrogradecondensate liquid saturation during the depletion processwhich exhibits a maximum retrograde condensate liquidsaturation of 3404 of 119881

119889at 20MPa

42 Simulated Results and Discussion In order to furtherstudy the phase behavior characteristics of reservoir fluid ofH2-3 well first of all we used the PREOS which adjuststhe parameters to fit the experiment data and the fittingresults are shown in Table 8 and Figures 3 and 4 Table 8presents the matching results of dew point pressure andgas-oil ratio between the experimental data and calculatedvalues Figures 3 and 4 show the matching results of relativevolume and retrograde condensate liquid saturation betweenthe experimental data and calculated values It can be seenfromTable 8 and Figures 3 and 4 that the experimental valuesand the calculated values are very close thus the calculatedresults can be used to guide the phase behavior study At thesame time on the basis of fitting the experimental data 119875-119879phase diagram of theH2-3 well reservoir fluid was calculatedand the calculated results are shown in Figure 5 It can beseen from Figure 5 that the reservoir temperature and criticaltemperature are very close and the reservoir temperaturelocates in the right side of the critical point which showsthat the reservoir fluid of H2-3 wells belongs to the near-critical condensate gas reservoir Secondly to extend thelaboratory results a series of simulation calculations werecarried out such as the component variation of remainingfluid condensate oil condensate gas in CVD experimentand reevaporation mechanism of remaining fluid with CO

2

injection

6 Journal of Chemistry

Table 6 Summary of constant composition expansion experimental data at 1324∘C

Pressure(MPa) Gas volume(mL) Liquid volume(mL) Relative volume(119881119881119889) Retrograde condensate liquid saturation( of 119881

119889)

2553 16023 000 0983 0002448lowast 16308 mdash 1 mdash24 16471 mdash 1009 mdash22 17245 mdash 1057 mdash21 17938 mdash 1099 mdash20 12015 6537 1137 4007919 12785 6375 1175 3908518 14089 6169 1242 3783317 15469 6010 1317 3685215 18853 5763 1509 3533513 24227 5519 1824 3383910 35989 5197 2525 318657 57411 4908 3821 30094lowastSaturation pressuremdash liquid volume is too small and liquid volume is not measured

(a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k)Pressure drop process

Figure 2The critical opalescence phase behavior characteristics in the constant composition expansion experiment at 1324∘C for H2-3 well(a) 2553MPa (b) 25MPa (c) 248MPa (d) 247MPa (e) 246MPa (f) 2448MPa (g) 24MPa (h) 23MPa (i) 20MPa (j) 19MPa and (k)5MPa

Table 7 Summary of constant volume depletion experimental dataat 1324∘C

Pressure(MPa) Retrograde condensateliquid saturation( of 119881

119889)

2553 02448lowast mdash22 mdash20 340417 297714 295811 26838 25225 2129lowastSaturation pressuremdash liquid volume is too small and liquid volume is not measured

Through simulation and calculation of the CVD exper-iment the composition of remaining fluid along with con-densate oil and gas was obtained under different pressures(ranged from 2448MPa (dew point) to 5MPa) and theresults are presented in Tables 9sim11 As is shown in Tables 910 and 11 in the remaining fluid and remaining condensateoil the content of CH

4decreases with decreasing the pres-

sure while in the discharging condensate gas the content ofCH4increases with decreasing the pressure And the content

of 1198622sim119862

6shows a rising trend in the composition of the

remaining fluid remaining condensate oil and dischargingcondensate gas which indicates that once pressure dropsbelow the dew point light hydrocarbons (such as CH

4)

escape from condensate gas system first In the remainingcondensate oil system the content of C

7simC10is up to 7472

and with the decrease of pressure the content of C7simC10

has a slight decrease while the content of C11+

increases

Journal of Chemistry 7

Table 8 Matching results of dew point pressure gas-oil ratio between the experimental data and calculated values

Matching items Experiment Calculation Relative errorDew point pressure(MPa) 2448 2447 0046Gas-oil ratio(m3m3) 869 87112 024

Table 9 Calculated composition of the remaining fluid under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

523 521 519 512 500 480 446 385N2

064 064 063 061 059 055 049 041CH4

5707 5677 5635 5529 5354 5081 4651 3927C2H6

1173 1172 1170 1164 1153 113 1082 976C3H8

622 623 625 63 636 643 645 626iC4H10

107 107 108 110 113 116 121 125nC4H10

176 177 178 182 188 197 209 222iC5H12

121 122 123 127 134 144 158 18nC5H12

109 110 111 115 121 131 146 169C6H14

258 261 266 277 298 330 382 470C7simC8

774 787 806 857 945 1089 1333 178C9simC10

249 254 264 285 323 385 490 688C11+

118 125 132 151 176 219 288 411

Calculated ROVMeasured ROV

5 10 15 20 25 300Pressure (MPa)

00

05

10

15

20

25

30

35

40

Rela

tive v

olum

e

Figure 3 Matching results of relative volume between the experi-mental data and calculated values

which indicates that part of the heavy hydrocarbons (C7simC10)

reevaporate from the condensate oil when depleting to acertain pressure In general with the decrease of pressurethe heavy component shows a rising trend in the remainingfluid

On the basis of composition analysis phase diagramsand retrograde condensate characteristics of reservoir fluidunder different pressures have been simulated and calculatedFigure 6 shows the two-phase boundaries of remaining fluidof different depletion pressure It can be seen from Figure 6that with the decrease of pressure phase diagram becomes

Measured retrograde condensate liquid saturationCalculated retrograde condensate liquid saturation

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

40

5 10 15 20 250Pressure (MPa)

satu

ratio

n (

Vd)

Figure 4 Matching results of retrograde condensate liquid satura-tion between the experimental data and calculated values

more wide and narrow to the right and critical pointmoves tothe lower right And when pressure drops below the 17MPathe critical temperature of the remaining fluid system is abovethe reservoir temperature (1324∘C) and the remaining fluidis considered to shift from condensate gas reservoir systeminto a volatile oil system The variation relationship betweenthe retrograde condensate liquid saturation and pressure isshown in Figure 7 It can be clearly seen that in the remainingfluids at 22MPa 20MPa and 17MPa with the decreaseof pressure the retrograde condensate liquid saturationsincrease at first and then decrease which indicates that theremaining reservoir fluids appear as the phase behavior ofcondensate gas system And when pressure drops below

8 Journal of Chemistry

Table 10 Calculated composition of the remaining condensate oil under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

008 008 008 008 008 008 008N2

000 000 000 000 000 000 000CH4

038 038 038 037 037 036 035C2H6

044 044 044 045 046 047 048C3H8

087 088 090 092 096 102 111iC4H10

039 039 040 041 044 048 053nC4H10

087 088 091 095 101 110 125iC5H12

149 150 154 161 172 187 208nC5H12

170 171 176 183 194 209 229C6H14

841 846 858 879 908 944 973C7simC8

5352 5324 5272 5211 5143 5061 4954C9simC10

2120 2112 2097 2081 2063 2043 2031C11+

1065 1092 1132 1167 1188 1205 1225 there is no remaining condensate oil because the calculated saturation pressure is 2447MPa and the measured saturation pressure is 2448MPa

Table 11 Calculated composition of the discharging condensate gas under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

068 069 071 072 072 072 072N2

608 625 634 631 618 596 557CH4

6252 6393 6518 6582 6592 6534 6350C2H6

1185 1194 1211 1233 1262 1301 1351C3H8

588 582 582 59 608 642 704iC4H10

097 094 093 093 095 101 115nC4H10

154 149 146 145 149 158 182iC5H12

100 095 09 088 089 094 11nC5H12

089 084 079 076 076 081 094C6H14

197 18 163 153 149 154 18C7simC8

503 426 349 297 262 247 27C9simC10

105 071 043 027 017 012 01C11+

053 037 023 015 01 007 006 there is not remaining discharging condensate gas because the calculated saturation pressure is 2447MPa and themeasured saturation pressure is 2448MPa

2-phase boundary5 volume10 volume20 volume

30 volumeCritical pointSaturation pressure

minus100 minus50 0 50 100 150 200 250 300minus150Temperature (∘C)

0

5

10

15

20

25

30

Pres

sure

(MPa

)

Figure 5 Calculated phase diagram of reservoir fluid of H2-3 well

the 17MPa the retrograde condensate liquid saturationsdecrease with decreasing the pressure which indicates thatthe remaining reservoir fluids exhibit the phase behavior ofvolatile oil system

In addition we performed the simulation of phase behav-ior of remaining fluid with CO

2injection and the remaining

fluid at 22MPa is selected Then the remaining fluid wasmixed with CO

2of 20mol 40mol 60mol 70mol

and 80mol respectively The dew point and the retrogradecondensate liquid saturation of the mixed system werecalculated The calculated results are presented in Figures8 and 9 Figures 8 and 9 illustrate that with the increaseof CO

2injected quantity the retrograde condensate liquid

saturation decreases and at 80mol CO2injected quantity

the maximum condensate saturation is only about 247Compared with the original remaining fluid at 22MPathe retrograde condensate liquid saturation is significantlyreduced which explains the reevaporation mechanism of

Journal of Chemistry 9

Critical point trajectory

0

5

10

15

20

25

Pres

sure

(MPa

)

minus100 minus50 0 50 100 150 200 250 300 350 400minus150Temperature (∘C)

2448MPa20MPa14MPa8MPa

22MPa17MPa11MPa5MPa

Figure 6 Calculated two-phase boundaries of resident fluid underdifferent depletion pressures

2448MPa

20MPa

14MPa

8MPa22MPa

17MPa

11MPa

5MPa

Retro

grad

e con

dens

ate l

iqui

d

0102030405060708090

100

5 10 15 20 25 300Temperature (∘C)

satu

ratio

n (

Vd)

Figure 7 Calculated retrograde condensate liquid saturation underdifferent depletion pressures

remaining fluid with CO2injection As to dew point pressure

with the increase of CO2injected quantity the dew point

pressure increases first and then decreases

5 Conclusions

(1) The reservoir fluid of H2-3 well is considered tobe the near-critical condensate gas reservoir systemcombined with the well stream components and 119875-119879phase diagram

(2) In the vicinity of the critical region the reservoirfluid of H2-3 well appears as the ldquocritical opalescencerdquophenomenon and the phenomenon is caused by the

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

5 10 15 20 25 300Pressure (MPa)

80mol CO2

70mol CO2

60mol CO2

40mol CO2

20mol CO2

satu

ratio

n (

Vd)

Figure 8 The variation of calculated retrograde condensate liquidsaturation with CO

2injected quantity

2460

2480

2500

2520

2540

2560

2580

2600

2620D

ew p

oint

pre

ssur

e (M

Pa)

01 02 03 04 05 06 07 08 090CO2 content (mol)

Figure 9 The variation of calculated dew point pressure with CO2

injected quantity

density fluctuations in the gas and liquid molecularmotion during the gas-liquid phase change process

(3) The volume of retrograde condensate liquid satura-tion during the depletion process increases first andthen decreases and when reservoir pressure dropsbelow a certain pressure the variation of retro-grade condensate liquid saturation exhibits the phasebehavior of volatile oil

(4) The reevaporation of remaining fluid consists of twoaspects (1) part of heavy hydrocarbons reevaporatefrom the remaining condensate oil when depleting toa certain pressure (2) the variation characteristics ofretrograde condensate liquid saturation of remainingfluid shift from a condensate gas condensate systeminto a volatile oil system

(5) The recovery of condensate oil and gas is proportionalto the CO

2injected quantity

10 Journal of Chemistry

(6) When implementing CO2injection in the near-

critical condensate gas reservoir the dew point pres-sure of the new mixed fluid system should be takeninto account since it is not simply monotonicallyincreasing or decreasing with the increase of CO

2

injected quantity

Competing Interests

Here all the authors solemnly declare that there are nocompeting interests regarding the publication of this paper

Acknowledgments

The authors wish to acknowledge anonymous reviewersfor constructive comments and suggestions for improvingthis paper The authors also wish to thank the anonymousAssociate Editor for his handling of the paper and addi-tional suggestions This work was supported by Open Fund(PLN1509) of State Key Laboratory of Oil and Gas ReservoirGeology and Exploitation (Southwest Petroleum University)and the Fund of the Department of Education in Sichuan (no15ZB0065)

References

[1] L Sun H Zhao S B Kiselev and C McCabe ldquoPredictingmixture phase equilibria and critical behavior using the SAFT-VRX approachrdquo Journal of Physical Chemistry B vol 109 no 18pp 9047ndash9058 2005

[2] W Yan L-K Wang L-Y Yang and T-M Guo ldquoA systematicexperimental study on the phase behavior of complex fluidmixtures up to near-critical regionrdquo Fluid Phase Equilibria vol190 no 1-2 pp 159ndash178 2001

[3] L Gil J F Martınez-Lopez M Artal et al ldquoVolumetricbehavior of theCO

2(1) +C

2H6(2) system in the subcritical (T =

29315 K) critical and supercritical (T = 30815 K) regionsrdquoTheJournal of Physical Chemistry B vol 114 no 1 pp 5447ndash54692010

[4] A R Bazaev and E A Bazaev ldquoThe thermodynamic propertiesof binary mixtures of technologically important substances inthe near- and supercritical statesrdquo Russian Journal of PhysicalChemistry B vol 4 no 8 pp 1178ndash1187 2010

[5] T YangW-D Chen and T-M Guo ldquoPhase behavior of a near-critical reservoir fluid mixturerdquo Fluid Phase Equilibria vol 128no 1-2 pp 183ndash197 1997

[6] K Luo and T Zhong ldquoA discussion on the layering of near-critical gas condensate in PVT cellrdquo Petroleum Exploration andDevelopment vol 26 no 1 pp 68ndash70 1999

[7] P Shen K Luo X Zheng S Li Z Dai andH Liu ldquoExperimen-tal study of near-critical behavior of gas condensate systemsrdquo inProceedings of the SPE Production and Operations SymposiumSPE 67285 Oklahoma City Okla USA March 2001

[8] X Zheng P Sheng S Li K Luo and Z Dai ldquoExperimentalinvestigation into near-critical phenomena of rich gas conden-sate systemsrdquo inProceedings of the SPE International Oil andGasConference and Exhibition in China (iOGCEC rsquo00) SPE64712pp 459ndash468 Beijing China November 2000

[9] P P Shen X T Zheng S Li K Luo andWY Sun ldquoNear-criticalphenomenal of rich gas condensate system an experimentalinvestigationrdquoActa Petrolei Sinica vol 22 no 3 pp 47ndash51 2001

[10] C-A C Parra and J-C-M E Remolina ldquoExperimental studyand calculations of the near critical behavior of a synthetic fluidin nitrogen injectionrdquo Ciencia Tecnologıa y Futuro vol 3 no 1pp 127ndash137 2005

[11] H-Y Chiu R-F Jung M-J Lee and H-M Lin ldquoVaporndashliquidphase equilibriumbehavior ofmixtures containing supercriticalcarbon dioxide near critical regionrdquo Journal of SupercriticalFluids vol 44 no 3 pp 273ndash278 2008

[12] M N Shehata S-E K Fateen and A Bonilla-PetricioletldquoCritical point calculations of multi-component reservoir fluidsusing nature-inspired metaheuristic algorithmsrdquo Fluid PhaseEquilibria vol 409 pp 280ndash290 2016

[13] H-G Li X-Y Lu and V Yang ldquoA numerical study of fluidinjection and mixing under near-critical conditionsrdquo ActaMechanica Sinica vol 28 no 3 pp 559ndash571 2012

[14] L Mistura ldquoTransport coefficients near a critical point in mul-ticomponent fluid systemsrdquo Il Nuovo Cimento vol 12 no 1 pp35ndash42 1972

[15] J-N Jaubert L Avaullee and C Pierre ldquoIs it still necessaryto measure the minimum miscibility pressurerdquo Industrial ampEngineering Chemistry Research vol 41 no 2 pp 303ndash310 2002

[16] China National Oil and Gas Industry Standards ldquoAnalysis forreservoir fluids physical propertiesrdquo Tech Rep SYT5542-20092009

[17] D-Y Peng and D B Robinson ldquoA new two-constant equationof staterdquo Industrial amp Engineering Chemistry Fundamentals vol15 no 1 pp 59ndash64 1976

Submit your manuscripts athttpwwwhindawicom

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Quantum Chemistry

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CatalystsJournal of

2 Journal of Chemistry

tested Test results indicate that two dew points occur at tem-peratures higher than critical point and transition betweendew point and bubble point at temperatures lower thancritical point namely transition from dew point into bubblepoint and behaviors of synthetic fluid sample and realformation fluid sample at near-critical region are differentnear-critical region of real formation fluid sample is widerand becomes wider when paraffin content in fluid is greater[7ndash9] Parra andRemolina used synthetic 4-component near-critical volatile oil fluid to study PVT phase behavior afterinjection of N

2 Results indicate that saturation pressure of

near-critical volatile oil fluid increases with increasing N2

injection ratio and crude oil density decreases with increasinggasoil ratio and near-critical volatile oil fluid transformedinto near-critical condensate gas fluid at N

2injection of

40mol Above results indicate that researches on multi-component near-critical fluid phase behavior were mainlyfocused on synthetic multicomponent fluid and scarcelyfocused on real multicomponent formation fluid what ismore researches onmulticomponent near-critical fluid phasebehavior were mainly focused on experiment and scarcelyfocused on theory and stimulation [10]

Therefore in this paper phase behavior experiment wasperformed on a real near-critical reservoir fluid the phasebehavior experiment includes two-flash experiment constantcomposition expansion experiment and constant volumedepletion experiment In addition we also conducted a seriesof numerical simulations which includes two-flash experi-ment constant composition expansion experiment constantvolume depletion experiment and CO

2-injection swelling

test The experimental and simulation results provide basicdata for further research on phase behavior characteristicsand thermodynamic model of near-critical complex fluidalso provide basic data for determining the minimum mis-cible pressure in CO

2miscible flooding of the near-critical

complex fluid and provide reference for enhancing recoveryof retrograde condensate oil by injecting CO

2in near-critical

condensate gas reservoirs [15]

2 Experiment

21 Sample Preparation Experimental measurements weremade on the Huachang reservoir fluid and the fluid ofH2-3 well was selected which was directly taken from thesurface of the gas-liquid separator of H2-3 well in Huachangoil field in the south of China Under original reservoircondition (1324∘C 2553MPa) and initial gas-oil ratio therepresentative fluid sample was prepared by using the surfaceseparator oil and separator gas All our operations complywith the standard of gas condensate reservoir fluid propertiesanalysis (SYT5542-2009) [16] Table 1 shows the well streamcomposition of reservoir fluid based on the results of gas andoil chromatographic analysis and measured gas-oil ratio Asis shown in Table 1 the content of intermediate hydrocarboncomponents is about 2566mol and combined with thegas-oil ratio (86900m3m3) and the content of condensateoil (70290 gm3) so the reservoir fluid of H2-3 well isconsidered to be a near-critical condensate gas reservoirfluid system with a low gas-oil ratio and high content of

Table 1 Well stream composition for H2-3 well

Component molN2

0636CO2

5228C1

57067C2

11732C3

6224iC4

1075nC4

1756iC5

1207nC5

1086C6

2580C7+

11411Properties of C

7+

Density of C7+ gcm3 0754

Molecular weight of C7+ gmol 1144

intermediate hydrocarbon and high content of condensateoil

22 Apparatus For conducting the PVT experiment of near-critical condensate gas reservoir fluid system a full obser-vation mercury-free high temperature and high pressuremultifunctional reservoir fluid analyzer JEFRI which wasdeveloped and produced by Canadian DBR Company wasadopted A schematic of the apparatus is shown in Figure 1 Itconsists of an injection pump system a 150mL overall visualPVT cell (the temperature ranges from 0∘C to 200∘C withan uncertainty of 01∘C and pressure ranges from 01MPa to70MPawith an uncertainty of 001MPa) a flash separation atemperature control system an oilgas chromatography andan electronic balance The PVT cell is equipped with a tightfit cone piston at the bottom so that a small annular spacevolume is formed between cylinder wall and piston whichcan accurately measure a very small amount of retrogradecondensate liquid dropout of the sample through the externalaltimeter And by way of video it allows us to observe thewhole phase behavior of the near-critical condensate gasreservoir fluid

23 Experimental Procedure

(1) Clean PVT vessel and cells then connect the PVTvessel to cells and evacuate the cells

(2) Prepare the near-critical condensate gas sample andcontrol and maintain the desired temperature usingthe constant temperature air bath

(3) Transfer a certain amount (about 40mL) of thesynthetic near-critical condensate gas sample intoPVT cells at the specified temperature and pressureadjust the oven through thermostat to the reservoirtemperature stir the condensate gas sample for 1 hourand then maintain for 30min and measure the near-critical condensate gas sample volume of the PVTcells

Journal of Chemistry 3

(1)

(2)

(3)

(4)

(5) (6)

(7)

Reservoir fluid

Piston

Pressure transmitting medium

(1) Condensate gas sample

(3) Thermostatic system(4) Oil and gas separation devices and electronic balance

(5) Gasometer(6) Oil and gas chromatography(7) Automatic pump

(2) PVT cell

Figure 1 Schematic diagram of the experimental apparatus

(4) After transferring the prepared sample to PVT cellsunder reservoir condition the stable fluid was slowlyreleased to laboratory temperature and atmosphericconditions from the PVT cells and gas and liquidseparated Record the bled gas volumes using thegasometer and the bled oil volumes using the elec-tronic balance and density meter and remaining gasvolumes of PVT vessel

(5) The following step is prepared for the constant com-position expansion experiment on the remaining gasvolumes of PVT vessel The remaining gas samplein the PVT vessel was depressurized step by stepfrom the reservoir pressure under the formationtemperature record the value of pressure and volume

(6) Finally the constant volume depletion experimentwas conducted It is evenly divided into 6sim8 pres-sure drop between the dew point pressure and theproposed abandonment pressure under the formationtemperature Depressurize to the each desirable pres-sure and balance the system for half an hour or moreand then record the total volume of the sample andthe volume of the condensate oil in the PVT cell

The detailed testing of the process of each experiment andtesting purposes are as follows

(1) Two-flash experiment the testing procedures aredescribed in step (4) Besides chromatographic anal-ysis (HP-6890 gas chromatograph and an Agilent-7890A oil chromatograph) of the separated gas andliquid was conducted to identify composition ofreservoir fluid systemThe testing purpose is to obtainthe well stream components and gas-oil ratio

(2) Constant composition expansion experiment (CCEexperiment) Constant composition expansion exper-iment is also known as 119875-119881 test The testing pur-pose is to provide information on determination of

dew point gas deviation factor and relative vol-ume of the fluid at different pressures The testingprocedures are described in step (5) In the CCEtest the gradual step-down approximation methodis used to determine the dew point pressure whenthe pressure differences between a fine mist dropletexisting and disappearing is less than 01MPa takethe average value of these two pressures for thedew point pressure To test the 119875-119881 relationshipthe sample in the container was pressurized to thereservoir pressure (2553MPa) under the formationtemperature (1324∘C) and sufficiently stirred untilstability Then reduce the pressure step by step atreservoir temperature during which the change involume is obtained When pressure drops below thedew point retrograde condensate liquid drops out

(3) Constant volume depletion experiment (CVD exper-iment) The testing purpose is to predict the changeof the condensate oil saturation the change of pro-duced well stream components and residual liquidwell stream components in the process of depletiondevelopment of the condensate gas reservoir Thetesting procedures are described in step (5) In theCVD test the volume of the sample at dew pointpressure is identified as the constant fluid pore vol-ume of gas condensate reservoir and the volume isexpressed as 119881

119889(it is used to calculate the conden-

sate oil saturation and the condensate oil and gasrecovery) And dew point pressure to zero pressure(gauge pressure 01MPa) is divided into eight pres-sure stages to simulate the depletion process of thereservoir and each time (each pressure stage whichis 2553MPa 2448MPa 22MPa 20MPa 17MPa14MPa 11MPa 8MPa and 5MPa) the system wasallowed to equilibrate Since the pressure reducedthe gas expanded discharging the gas until reachingthe constant volume 119881

119889at each constant pressure

4 Journal of Chemistry

Table 2 Composition of pseudo-components

Pseudo-components molCO2

523N2

064CH4

5707C2H6

1173C3H8

622iC4H10

107nC4H10

176iC5H12

121nC5H12

109C6H14

258C7simC8

774C9simC10

249C11+

118

Repeat the depressurization-exhaust process till thelast stage of pressure The testing process of the lastlevel pressure to zero pressure is described as followsopen the top valve and directly depressurize to zeropressure by gas releasing Subsequently dischargethe residual oil and gas from the cell and take thegas sample to conduct the component analysis andthe density and composition of residual oil weresimultaneously measured

3 Calculations

To verify the laboratory results we utilized the high pre-cision PR equation of state (PREOS78) [17] in WINPROPmodule of the Computer Modeling Group (CMG) simulatorCombinedwith the fluid thermodynamic equilibrium theoryit can accurately describe and predict phase behavior ofcondensate gas reservoir fluid and phase transition near thecritical point Thermodynamic parameters of the PREOS areadjusted to match the experimental measured PVT data Theoriginal well stream composition was split and grouped into13 pseudo-components which is given in Table 2 Criticaltemperatures critical pressures and acentric factors of theplus components and binary interaction parameters (119870

119894119895)

were adjusted to match the experimental data such as thesaturation pressure (the dew point pressure) gas-oil ratiorelative volumes and retrograde condensate liquid satura-tions It is worth mentioning that interaction coefficients(119870119894119895) are introduced to account for the molecular interaction

between dissimilar molecules The values of the interactioncoefficients are obtained by fitting the predicted saturationpressures to experimental data through the PR78 EOS Tables3 and 4 present the adjusted critical temperatures criticalpressures and acentric factors of the plus components andobtained binary interaction parametersThe absolute relativeerror (1) and the average absolute relative error (2) are used toexpress the deviation between the calculated values by usingthe PREOS in this paper and the experimental measuredvalues The objective is to make the deviation between thecalculated value and experimental valueminimumTo extend

the laboratory results on the basis of fitting the experimentaldata a series of simulation calculations were carried out suchas the component variation of remaining fluid condensateoil condensate gas in CVD experiment and reevaporationmechanism of remaining fluid with CO

2injection

ARE =119873

sum

119894=1

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

Cal minus ExpExp

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

119894

times 100 (1)

AARE = 1119873

119873

sum

119894=1

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

Cal minus ExpExp

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

119894

times 100 (2)

4 Results and Discussion

41 Experimental Results and Discussion Prior to constantcomposition expansion (CCE) and constant volume deple-tion (CVD) experiment a two-flash experiment of the reser-voir fluid of H2-3 well was performed Table 5 shows the two-flash experimental data of the reservoir fluid of H2-3 wellReferring to the international standard the fluid is identifiedas near-critical condensate gas reservoir fluid system whichhas high content of condensate oil low condensate oil densityand gas-oil ratio

Constant composition expansion experiment is alsoknown as119875-119881 relationship experiment which provides infor-mation on determination of dew point relative volume of thefluid and retrograde condensate liquid saturation at differentpressures Relative volume is the ratio between the volumeof each pressure and the volume of dew point pressureand the retrograde condensate liquid saturation is the ratiobetween the volume of the retrograde condensate oil and thevolume of the dew point pressure The CCE experimentalresults under reservoir temperature (1324∘C) are showed inTable 6 the reservoir fluid of H2-3 well exhibits a maximumretrograde condensate liquid saturation of 42079 and theretrograde condensate liquid saturation increases first andthen decreases

Meanwhile we observed the phase behavior of H2-3well reservoir fluid in the near-critical region during CCEexperiment Figure 2 presents the phase behavior in thenear-critical region of reservoir fluid in H2-3 well duringpressure drop process Under the formation temperaturewhen pressure reduces from the pressure point in Figure 2(a)to the pressure point in Figures 2(b) 2(c) 2(d) 2(e) and2(f) reservoir fluid in PVT test cell turns from transparentgolden yellow into light brown and then into reddish brownand finally into completely opaque ash black When pressurereduces from the pressure point in Figure 2(f) to the pressurepoint in Figures 2(g) and 2(h) reservoir fluid in PVT test cellturns from completely opaque ash black into reddish brownat bottom and ash black at top and then into light brownat bottom and light ash black at top and does not have theobvious gas-liquid interface When pressure further reducesfrom the pressure point in Figure 2(h) to the pressure pointin Figures 2(i) 2(j) and 2(k) reservoir fluid in PVT testcell turns from light brown at bottom and light ash black attop into golden yellow at bottom and has the obvious gas-liquid interface besides retrograde condensate liquid volume

Journal of Chemistry 5

Table 3 Critical temperatures and critical pressures acentric factors of the plus components

Plus components Critical temperature(∘C) Critical pressure(MPa) Acentric factorC7simC8

28031 30245 0283C9simC10

33685 24608 0368C11+

40139 21066 0477

Table 4 Binary interaction parameters (119870119894119895) and mixing rules for the PREOS in this study

Components CO2

N2

CH4

C2H6

C3H8

iC4H10

nC4H10

iC5H12

nC5H12

C6H14

C7simC8

C9simC10

C11+

CO2

0 00200 01030 01300 01350 01300 01300 01250 01250 01500 01500 01500 01500N2

00200 0 00310 00420 00910 00950 00950 00950 00950 01200 01200 01200 01200CH4

01030 00310 0 00027 00085 00158 00148 00209 00206 00253 00314 00426 00561C2H6

01300 00420 00027 0 00017 00055 00049 00087 00086 00117 00160 00245 00352C3H8

01350 00910 00085 00017 0 00011 00001 00028 00027 00046 00075 00136 00219iC4H10

01300 00950 00158 00055 00011 0 00000 00004 00004 00012 00028 00069 00133nC4H10

01300 00950 00148 00049 00001 00000 0 00006 00005 00015 00033 00077 00143iC5H12

01250 00950 00209 00087 00028 00004 00006 0 00000 00002 00011 00041 00093nC5H12

01250 00950 00206 00086 00027 00004 00005 00000 0 00003 00012 00042 00094C6H14

01500 01200 00253 00117 00046 00012 00015 00002 00003 0 00003 00024 00066C7simC8

01500 01200 00314 00160 00075 00028 00033 00011 00012 00003 0 00009 00039C9simC10

01500 01200 00426 00245 00136 00069 00077 00041 00042 00024 00009 0 00010C11+

01500 01200 00561 00352 00219 00133 00143 00093 00094 00066 00039 00010 0

Table 5 Summary of two-flash experimental data

Gas-oil ratio (m3m3) 86900Gas volume factor 00078Condensate oil density (gcm3) 07244The content of condensate oil (gm3) 70290

increases dramatically to the maximum and then decreasesmildly

The above phenomenon of the color of reservoir fluidchanging from transparent golden yellow into light brownand then into reddish brown and finally into completelyopaque ash black is called critical opalescence which isshown in dotted line position in Figure 2 The criticalopalescence is caused by molecular density fluctuation as aresult of gas-liquid molecular movement in the gas-liquidphase change process The reason of density fluctuation isevaporation of liquid molecules and condensation of gasmolecules and the molecular motion was especially sharpfluctuations when the temperature is near the critical pointAs a result density distribution presents concavo-convexrandomly distributed spatial curved surface instead of lam-inar and on the direction of the light numerous liquid-gas interfaces or gas-liquid interfaces appear As light travelsthrough these interfaces a series of reflection and refractionhappened which reduces light energy gradually resulting incritical opalescence

In the CVD test the sample volume at dew point pressureis identified as the constant pore volume of gas condensatereservoir and dew point pressure to zero pressure (gaugepressure) is divided into six to eight pressure stages tosimulate the depletion process in the reservoir and the

retrograde condensate liquid saturations at each pressureduring the depletion process were measured under theconditions of equilibrium Table 7 presents the retrogradecondensate liquid saturation during the depletion processwhich exhibits a maximum retrograde condensate liquidsaturation of 3404 of 119881

119889at 20MPa

42 Simulated Results and Discussion In order to furtherstudy the phase behavior characteristics of reservoir fluid ofH2-3 well first of all we used the PREOS which adjuststhe parameters to fit the experiment data and the fittingresults are shown in Table 8 and Figures 3 and 4 Table 8presents the matching results of dew point pressure andgas-oil ratio between the experimental data and calculatedvalues Figures 3 and 4 show the matching results of relativevolume and retrograde condensate liquid saturation betweenthe experimental data and calculated values It can be seenfromTable 8 and Figures 3 and 4 that the experimental valuesand the calculated values are very close thus the calculatedresults can be used to guide the phase behavior study At thesame time on the basis of fitting the experimental data 119875-119879phase diagram of theH2-3 well reservoir fluid was calculatedand the calculated results are shown in Figure 5 It can beseen from Figure 5 that the reservoir temperature and criticaltemperature are very close and the reservoir temperaturelocates in the right side of the critical point which showsthat the reservoir fluid of H2-3 wells belongs to the near-critical condensate gas reservoir Secondly to extend thelaboratory results a series of simulation calculations werecarried out such as the component variation of remainingfluid condensate oil condensate gas in CVD experimentand reevaporation mechanism of remaining fluid with CO

2

injection

6 Journal of Chemistry

Table 6 Summary of constant composition expansion experimental data at 1324∘C

Pressure(MPa) Gas volume(mL) Liquid volume(mL) Relative volume(119881119881119889) Retrograde condensate liquid saturation( of 119881

119889)

2553 16023 000 0983 0002448lowast 16308 mdash 1 mdash24 16471 mdash 1009 mdash22 17245 mdash 1057 mdash21 17938 mdash 1099 mdash20 12015 6537 1137 4007919 12785 6375 1175 3908518 14089 6169 1242 3783317 15469 6010 1317 3685215 18853 5763 1509 3533513 24227 5519 1824 3383910 35989 5197 2525 318657 57411 4908 3821 30094lowastSaturation pressuremdash liquid volume is too small and liquid volume is not measured

(a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k)Pressure drop process

Figure 2The critical opalescence phase behavior characteristics in the constant composition expansion experiment at 1324∘C for H2-3 well(a) 2553MPa (b) 25MPa (c) 248MPa (d) 247MPa (e) 246MPa (f) 2448MPa (g) 24MPa (h) 23MPa (i) 20MPa (j) 19MPa and (k)5MPa

Table 7 Summary of constant volume depletion experimental dataat 1324∘C

Pressure(MPa) Retrograde condensateliquid saturation( of 119881

119889)

2553 02448lowast mdash22 mdash20 340417 297714 295811 26838 25225 2129lowastSaturation pressuremdash liquid volume is too small and liquid volume is not measured

Through simulation and calculation of the CVD exper-iment the composition of remaining fluid along with con-densate oil and gas was obtained under different pressures(ranged from 2448MPa (dew point) to 5MPa) and theresults are presented in Tables 9sim11 As is shown in Tables 910 and 11 in the remaining fluid and remaining condensateoil the content of CH

4decreases with decreasing the pres-

sure while in the discharging condensate gas the content ofCH4increases with decreasing the pressure And the content

of 1198622sim119862

6shows a rising trend in the composition of the

remaining fluid remaining condensate oil and dischargingcondensate gas which indicates that once pressure dropsbelow the dew point light hydrocarbons (such as CH

4)

escape from condensate gas system first In the remainingcondensate oil system the content of C

7simC10is up to 7472

and with the decrease of pressure the content of C7simC10

has a slight decrease while the content of C11+

increases

Journal of Chemistry 7

Table 8 Matching results of dew point pressure gas-oil ratio between the experimental data and calculated values

Matching items Experiment Calculation Relative errorDew point pressure(MPa) 2448 2447 0046Gas-oil ratio(m3m3) 869 87112 024

Table 9 Calculated composition of the remaining fluid under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

523 521 519 512 500 480 446 385N2

064 064 063 061 059 055 049 041CH4

5707 5677 5635 5529 5354 5081 4651 3927C2H6

1173 1172 1170 1164 1153 113 1082 976C3H8

622 623 625 63 636 643 645 626iC4H10

107 107 108 110 113 116 121 125nC4H10

176 177 178 182 188 197 209 222iC5H12

121 122 123 127 134 144 158 18nC5H12

109 110 111 115 121 131 146 169C6H14

258 261 266 277 298 330 382 470C7simC8

774 787 806 857 945 1089 1333 178C9simC10

249 254 264 285 323 385 490 688C11+

118 125 132 151 176 219 288 411

Calculated ROVMeasured ROV

5 10 15 20 25 300Pressure (MPa)

00

05

10

15

20

25

30

35

40

Rela

tive v

olum

e

Figure 3 Matching results of relative volume between the experi-mental data and calculated values

which indicates that part of the heavy hydrocarbons (C7simC10)

reevaporate from the condensate oil when depleting to acertain pressure In general with the decrease of pressurethe heavy component shows a rising trend in the remainingfluid

On the basis of composition analysis phase diagramsand retrograde condensate characteristics of reservoir fluidunder different pressures have been simulated and calculatedFigure 6 shows the two-phase boundaries of remaining fluidof different depletion pressure It can be seen from Figure 6that with the decrease of pressure phase diagram becomes

Measured retrograde condensate liquid saturationCalculated retrograde condensate liquid saturation

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

40

5 10 15 20 250Pressure (MPa)

satu

ratio

n (

Vd)

Figure 4 Matching results of retrograde condensate liquid satura-tion between the experimental data and calculated values

more wide and narrow to the right and critical pointmoves tothe lower right And when pressure drops below the 17MPathe critical temperature of the remaining fluid system is abovethe reservoir temperature (1324∘C) and the remaining fluidis considered to shift from condensate gas reservoir systeminto a volatile oil system The variation relationship betweenthe retrograde condensate liquid saturation and pressure isshown in Figure 7 It can be clearly seen that in the remainingfluids at 22MPa 20MPa and 17MPa with the decreaseof pressure the retrograde condensate liquid saturationsincrease at first and then decrease which indicates that theremaining reservoir fluids appear as the phase behavior ofcondensate gas system And when pressure drops below

8 Journal of Chemistry

Table 10 Calculated composition of the remaining condensate oil under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

008 008 008 008 008 008 008N2

000 000 000 000 000 000 000CH4

038 038 038 037 037 036 035C2H6

044 044 044 045 046 047 048C3H8

087 088 090 092 096 102 111iC4H10

039 039 040 041 044 048 053nC4H10

087 088 091 095 101 110 125iC5H12

149 150 154 161 172 187 208nC5H12

170 171 176 183 194 209 229C6H14

841 846 858 879 908 944 973C7simC8

5352 5324 5272 5211 5143 5061 4954C9simC10

2120 2112 2097 2081 2063 2043 2031C11+

1065 1092 1132 1167 1188 1205 1225 there is no remaining condensate oil because the calculated saturation pressure is 2447MPa and the measured saturation pressure is 2448MPa

Table 11 Calculated composition of the discharging condensate gas under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

068 069 071 072 072 072 072N2

608 625 634 631 618 596 557CH4

6252 6393 6518 6582 6592 6534 6350C2H6

1185 1194 1211 1233 1262 1301 1351C3H8

588 582 582 59 608 642 704iC4H10

097 094 093 093 095 101 115nC4H10

154 149 146 145 149 158 182iC5H12

100 095 09 088 089 094 11nC5H12

089 084 079 076 076 081 094C6H14

197 18 163 153 149 154 18C7simC8

503 426 349 297 262 247 27C9simC10

105 071 043 027 017 012 01C11+

053 037 023 015 01 007 006 there is not remaining discharging condensate gas because the calculated saturation pressure is 2447MPa and themeasured saturation pressure is 2448MPa

2-phase boundary5 volume10 volume20 volume

30 volumeCritical pointSaturation pressure

minus100 minus50 0 50 100 150 200 250 300minus150Temperature (∘C)

0

5

10

15

20

25

30

Pres

sure

(MPa

)

Figure 5 Calculated phase diagram of reservoir fluid of H2-3 well

the 17MPa the retrograde condensate liquid saturationsdecrease with decreasing the pressure which indicates thatthe remaining reservoir fluids exhibit the phase behavior ofvolatile oil system

In addition we performed the simulation of phase behav-ior of remaining fluid with CO

2injection and the remaining

fluid at 22MPa is selected Then the remaining fluid wasmixed with CO

2of 20mol 40mol 60mol 70mol

and 80mol respectively The dew point and the retrogradecondensate liquid saturation of the mixed system werecalculated The calculated results are presented in Figures8 and 9 Figures 8 and 9 illustrate that with the increaseof CO

2injected quantity the retrograde condensate liquid

saturation decreases and at 80mol CO2injected quantity

the maximum condensate saturation is only about 247Compared with the original remaining fluid at 22MPathe retrograde condensate liquid saturation is significantlyreduced which explains the reevaporation mechanism of

Journal of Chemistry 9

Critical point trajectory

0

5

10

15

20

25

Pres

sure

(MPa

)

minus100 minus50 0 50 100 150 200 250 300 350 400minus150Temperature (∘C)

2448MPa20MPa14MPa8MPa

22MPa17MPa11MPa5MPa

Figure 6 Calculated two-phase boundaries of resident fluid underdifferent depletion pressures

2448MPa

20MPa

14MPa

8MPa22MPa

17MPa

11MPa

5MPa

Retro

grad

e con

dens

ate l

iqui

d

0102030405060708090

100

5 10 15 20 25 300Temperature (∘C)

satu

ratio

n (

Vd)

Figure 7 Calculated retrograde condensate liquid saturation underdifferent depletion pressures

remaining fluid with CO2injection As to dew point pressure

with the increase of CO2injected quantity the dew point

pressure increases first and then decreases

5 Conclusions

(1) The reservoir fluid of H2-3 well is considered tobe the near-critical condensate gas reservoir systemcombined with the well stream components and 119875-119879phase diagram

(2) In the vicinity of the critical region the reservoirfluid of H2-3 well appears as the ldquocritical opalescencerdquophenomenon and the phenomenon is caused by the

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

5 10 15 20 25 300Pressure (MPa)

80mol CO2

70mol CO2

60mol CO2

40mol CO2

20mol CO2

satu

ratio

n (

Vd)

Figure 8 The variation of calculated retrograde condensate liquidsaturation with CO

2injected quantity

2460

2480

2500

2520

2540

2560

2580

2600

2620D

ew p

oint

pre

ssur

e (M

Pa)

01 02 03 04 05 06 07 08 090CO2 content (mol)

Figure 9 The variation of calculated dew point pressure with CO2

injected quantity

density fluctuations in the gas and liquid molecularmotion during the gas-liquid phase change process

(3) The volume of retrograde condensate liquid satura-tion during the depletion process increases first andthen decreases and when reservoir pressure dropsbelow a certain pressure the variation of retro-grade condensate liquid saturation exhibits the phasebehavior of volatile oil

(4) The reevaporation of remaining fluid consists of twoaspects (1) part of heavy hydrocarbons reevaporatefrom the remaining condensate oil when depleting toa certain pressure (2) the variation characteristics ofretrograde condensate liquid saturation of remainingfluid shift from a condensate gas condensate systeminto a volatile oil system

(5) The recovery of condensate oil and gas is proportionalto the CO

2injected quantity

10 Journal of Chemistry

(6) When implementing CO2injection in the near-

critical condensate gas reservoir the dew point pres-sure of the new mixed fluid system should be takeninto account since it is not simply monotonicallyincreasing or decreasing with the increase of CO

2

injected quantity

Competing Interests

Here all the authors solemnly declare that there are nocompeting interests regarding the publication of this paper

Acknowledgments

The authors wish to acknowledge anonymous reviewersfor constructive comments and suggestions for improvingthis paper The authors also wish to thank the anonymousAssociate Editor for his handling of the paper and addi-tional suggestions This work was supported by Open Fund(PLN1509) of State Key Laboratory of Oil and Gas ReservoirGeology and Exploitation (Southwest Petroleum University)and the Fund of the Department of Education in Sichuan (no15ZB0065)

References

[1] L Sun H Zhao S B Kiselev and C McCabe ldquoPredictingmixture phase equilibria and critical behavior using the SAFT-VRX approachrdquo Journal of Physical Chemistry B vol 109 no 18pp 9047ndash9058 2005

[2] W Yan L-K Wang L-Y Yang and T-M Guo ldquoA systematicexperimental study on the phase behavior of complex fluidmixtures up to near-critical regionrdquo Fluid Phase Equilibria vol190 no 1-2 pp 159ndash178 2001

[3] L Gil J F Martınez-Lopez M Artal et al ldquoVolumetricbehavior of theCO

2(1) +C

2H6(2) system in the subcritical (T =

29315 K) critical and supercritical (T = 30815 K) regionsrdquoTheJournal of Physical Chemistry B vol 114 no 1 pp 5447ndash54692010

[4] A R Bazaev and E A Bazaev ldquoThe thermodynamic propertiesof binary mixtures of technologically important substances inthe near- and supercritical statesrdquo Russian Journal of PhysicalChemistry B vol 4 no 8 pp 1178ndash1187 2010

[5] T YangW-D Chen and T-M Guo ldquoPhase behavior of a near-critical reservoir fluid mixturerdquo Fluid Phase Equilibria vol 128no 1-2 pp 183ndash197 1997

[6] K Luo and T Zhong ldquoA discussion on the layering of near-critical gas condensate in PVT cellrdquo Petroleum Exploration andDevelopment vol 26 no 1 pp 68ndash70 1999

[7] P Shen K Luo X Zheng S Li Z Dai andH Liu ldquoExperimen-tal study of near-critical behavior of gas condensate systemsrdquo inProceedings of the SPE Production and Operations SymposiumSPE 67285 Oklahoma City Okla USA March 2001

[8] X Zheng P Sheng S Li K Luo and Z Dai ldquoExperimentalinvestigation into near-critical phenomena of rich gas conden-sate systemsrdquo inProceedings of the SPE International Oil andGasConference and Exhibition in China (iOGCEC rsquo00) SPE64712pp 459ndash468 Beijing China November 2000

[9] P P Shen X T Zheng S Li K Luo andWY Sun ldquoNear-criticalphenomenal of rich gas condensate system an experimentalinvestigationrdquoActa Petrolei Sinica vol 22 no 3 pp 47ndash51 2001

[10] C-A C Parra and J-C-M E Remolina ldquoExperimental studyand calculations of the near critical behavior of a synthetic fluidin nitrogen injectionrdquo Ciencia Tecnologıa y Futuro vol 3 no 1pp 127ndash137 2005

[11] H-Y Chiu R-F Jung M-J Lee and H-M Lin ldquoVaporndashliquidphase equilibriumbehavior ofmixtures containing supercriticalcarbon dioxide near critical regionrdquo Journal of SupercriticalFluids vol 44 no 3 pp 273ndash278 2008

[12] M N Shehata S-E K Fateen and A Bonilla-PetricioletldquoCritical point calculations of multi-component reservoir fluidsusing nature-inspired metaheuristic algorithmsrdquo Fluid PhaseEquilibria vol 409 pp 280ndash290 2016

[13] H-G Li X-Y Lu and V Yang ldquoA numerical study of fluidinjection and mixing under near-critical conditionsrdquo ActaMechanica Sinica vol 28 no 3 pp 559ndash571 2012

[14] L Mistura ldquoTransport coefficients near a critical point in mul-ticomponent fluid systemsrdquo Il Nuovo Cimento vol 12 no 1 pp35ndash42 1972

[15] J-N Jaubert L Avaullee and C Pierre ldquoIs it still necessaryto measure the minimum miscibility pressurerdquo Industrial ampEngineering Chemistry Research vol 41 no 2 pp 303ndash310 2002

[16] China National Oil and Gas Industry Standards ldquoAnalysis forreservoir fluids physical propertiesrdquo Tech Rep SYT5542-20092009

[17] D-Y Peng and D B Robinson ldquoA new two-constant equationof staterdquo Industrial amp Engineering Chemistry Fundamentals vol15 no 1 pp 59ndash64 1976

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Theoretical ChemistryJournal of

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Spectroscopy

Analytical ChemistryInternational Journal of

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Quantum Chemistry

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Organic Chemistry International

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CatalystsJournal of

Journal of Chemistry 3

(1)

(2)

(3)

(4)

(5) (6)

(7)

Reservoir fluid

Piston

Pressure transmitting medium

(1) Condensate gas sample

(3) Thermostatic system(4) Oil and gas separation devices and electronic balance

(5) Gasometer(6) Oil and gas chromatography(7) Automatic pump

(2) PVT cell

Figure 1 Schematic diagram of the experimental apparatus

(4) After transferring the prepared sample to PVT cellsunder reservoir condition the stable fluid was slowlyreleased to laboratory temperature and atmosphericconditions from the PVT cells and gas and liquidseparated Record the bled gas volumes using thegasometer and the bled oil volumes using the elec-tronic balance and density meter and remaining gasvolumes of PVT vessel

(5) The following step is prepared for the constant com-position expansion experiment on the remaining gasvolumes of PVT vessel The remaining gas samplein the PVT vessel was depressurized step by stepfrom the reservoir pressure under the formationtemperature record the value of pressure and volume

(6) Finally the constant volume depletion experimentwas conducted It is evenly divided into 6sim8 pres-sure drop between the dew point pressure and theproposed abandonment pressure under the formationtemperature Depressurize to the each desirable pres-sure and balance the system for half an hour or moreand then record the total volume of the sample andthe volume of the condensate oil in the PVT cell

The detailed testing of the process of each experiment andtesting purposes are as follows

(1) Two-flash experiment the testing procedures aredescribed in step (4) Besides chromatographic anal-ysis (HP-6890 gas chromatograph and an Agilent-7890A oil chromatograph) of the separated gas andliquid was conducted to identify composition ofreservoir fluid systemThe testing purpose is to obtainthe well stream components and gas-oil ratio

(2) Constant composition expansion experiment (CCEexperiment) Constant composition expansion exper-iment is also known as 119875-119881 test The testing pur-pose is to provide information on determination of

dew point gas deviation factor and relative vol-ume of the fluid at different pressures The testingprocedures are described in step (5) In the CCEtest the gradual step-down approximation methodis used to determine the dew point pressure whenthe pressure differences between a fine mist dropletexisting and disappearing is less than 01MPa takethe average value of these two pressures for thedew point pressure To test the 119875-119881 relationshipthe sample in the container was pressurized to thereservoir pressure (2553MPa) under the formationtemperature (1324∘C) and sufficiently stirred untilstability Then reduce the pressure step by step atreservoir temperature during which the change involume is obtained When pressure drops below thedew point retrograde condensate liquid drops out

(3) Constant volume depletion experiment (CVD exper-iment) The testing purpose is to predict the changeof the condensate oil saturation the change of pro-duced well stream components and residual liquidwell stream components in the process of depletiondevelopment of the condensate gas reservoir Thetesting procedures are described in step (5) In theCVD test the volume of the sample at dew pointpressure is identified as the constant fluid pore vol-ume of gas condensate reservoir and the volume isexpressed as 119881

119889(it is used to calculate the conden-

sate oil saturation and the condensate oil and gasrecovery) And dew point pressure to zero pressure(gauge pressure 01MPa) is divided into eight pres-sure stages to simulate the depletion process of thereservoir and each time (each pressure stage whichis 2553MPa 2448MPa 22MPa 20MPa 17MPa14MPa 11MPa 8MPa and 5MPa) the system wasallowed to equilibrate Since the pressure reducedthe gas expanded discharging the gas until reachingthe constant volume 119881

119889at each constant pressure

4 Journal of Chemistry

Table 2 Composition of pseudo-components

Pseudo-components molCO2

523N2

064CH4

5707C2H6

1173C3H8

622iC4H10

107nC4H10

176iC5H12

121nC5H12

109C6H14

258C7simC8

774C9simC10

249C11+

118

Repeat the depressurization-exhaust process till thelast stage of pressure The testing process of the lastlevel pressure to zero pressure is described as followsopen the top valve and directly depressurize to zeropressure by gas releasing Subsequently dischargethe residual oil and gas from the cell and take thegas sample to conduct the component analysis andthe density and composition of residual oil weresimultaneously measured

3 Calculations

To verify the laboratory results we utilized the high pre-cision PR equation of state (PREOS78) [17] in WINPROPmodule of the Computer Modeling Group (CMG) simulatorCombinedwith the fluid thermodynamic equilibrium theoryit can accurately describe and predict phase behavior ofcondensate gas reservoir fluid and phase transition near thecritical point Thermodynamic parameters of the PREOS areadjusted to match the experimental measured PVT data Theoriginal well stream composition was split and grouped into13 pseudo-components which is given in Table 2 Criticaltemperatures critical pressures and acentric factors of theplus components and binary interaction parameters (119870

119894119895)

were adjusted to match the experimental data such as thesaturation pressure (the dew point pressure) gas-oil ratiorelative volumes and retrograde condensate liquid satura-tions It is worth mentioning that interaction coefficients(119870119894119895) are introduced to account for the molecular interaction

between dissimilar molecules The values of the interactioncoefficients are obtained by fitting the predicted saturationpressures to experimental data through the PR78 EOS Tables3 and 4 present the adjusted critical temperatures criticalpressures and acentric factors of the plus components andobtained binary interaction parametersThe absolute relativeerror (1) and the average absolute relative error (2) are used toexpress the deviation between the calculated values by usingthe PREOS in this paper and the experimental measuredvalues The objective is to make the deviation between thecalculated value and experimental valueminimumTo extend

the laboratory results on the basis of fitting the experimentaldata a series of simulation calculations were carried out suchas the component variation of remaining fluid condensateoil condensate gas in CVD experiment and reevaporationmechanism of remaining fluid with CO

2injection

ARE =119873

sum

119894=1

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

Cal minus ExpExp

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

119894

times 100 (1)

AARE = 1119873

119873

sum

119894=1

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

Cal minus ExpExp

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

119894

times 100 (2)

4 Results and Discussion

41 Experimental Results and Discussion Prior to constantcomposition expansion (CCE) and constant volume deple-tion (CVD) experiment a two-flash experiment of the reser-voir fluid of H2-3 well was performed Table 5 shows the two-flash experimental data of the reservoir fluid of H2-3 wellReferring to the international standard the fluid is identifiedas near-critical condensate gas reservoir fluid system whichhas high content of condensate oil low condensate oil densityand gas-oil ratio

Constant composition expansion experiment is alsoknown as119875-119881 relationship experiment which provides infor-mation on determination of dew point relative volume of thefluid and retrograde condensate liquid saturation at differentpressures Relative volume is the ratio between the volumeof each pressure and the volume of dew point pressureand the retrograde condensate liquid saturation is the ratiobetween the volume of the retrograde condensate oil and thevolume of the dew point pressure The CCE experimentalresults under reservoir temperature (1324∘C) are showed inTable 6 the reservoir fluid of H2-3 well exhibits a maximumretrograde condensate liquid saturation of 42079 and theretrograde condensate liquid saturation increases first andthen decreases

Meanwhile we observed the phase behavior of H2-3well reservoir fluid in the near-critical region during CCEexperiment Figure 2 presents the phase behavior in thenear-critical region of reservoir fluid in H2-3 well duringpressure drop process Under the formation temperaturewhen pressure reduces from the pressure point in Figure 2(a)to the pressure point in Figures 2(b) 2(c) 2(d) 2(e) and2(f) reservoir fluid in PVT test cell turns from transparentgolden yellow into light brown and then into reddish brownand finally into completely opaque ash black When pressurereduces from the pressure point in Figure 2(f) to the pressurepoint in Figures 2(g) and 2(h) reservoir fluid in PVT test cellturns from completely opaque ash black into reddish brownat bottom and ash black at top and then into light brownat bottom and light ash black at top and does not have theobvious gas-liquid interface When pressure further reducesfrom the pressure point in Figure 2(h) to the pressure pointin Figures 2(i) 2(j) and 2(k) reservoir fluid in PVT testcell turns from light brown at bottom and light ash black attop into golden yellow at bottom and has the obvious gas-liquid interface besides retrograde condensate liquid volume

Journal of Chemistry 5

Table 3 Critical temperatures and critical pressures acentric factors of the plus components

Plus components Critical temperature(∘C) Critical pressure(MPa) Acentric factorC7simC8

28031 30245 0283C9simC10

33685 24608 0368C11+

40139 21066 0477

Table 4 Binary interaction parameters (119870119894119895) and mixing rules for the PREOS in this study

Components CO2

N2

CH4

C2H6

C3H8

iC4H10

nC4H10

iC5H12

nC5H12

C6H14

C7simC8

C9simC10

C11+

CO2

0 00200 01030 01300 01350 01300 01300 01250 01250 01500 01500 01500 01500N2

00200 0 00310 00420 00910 00950 00950 00950 00950 01200 01200 01200 01200CH4

01030 00310 0 00027 00085 00158 00148 00209 00206 00253 00314 00426 00561C2H6

01300 00420 00027 0 00017 00055 00049 00087 00086 00117 00160 00245 00352C3H8

01350 00910 00085 00017 0 00011 00001 00028 00027 00046 00075 00136 00219iC4H10

01300 00950 00158 00055 00011 0 00000 00004 00004 00012 00028 00069 00133nC4H10

01300 00950 00148 00049 00001 00000 0 00006 00005 00015 00033 00077 00143iC5H12

01250 00950 00209 00087 00028 00004 00006 0 00000 00002 00011 00041 00093nC5H12

01250 00950 00206 00086 00027 00004 00005 00000 0 00003 00012 00042 00094C6H14

01500 01200 00253 00117 00046 00012 00015 00002 00003 0 00003 00024 00066C7simC8

01500 01200 00314 00160 00075 00028 00033 00011 00012 00003 0 00009 00039C9simC10

01500 01200 00426 00245 00136 00069 00077 00041 00042 00024 00009 0 00010C11+

01500 01200 00561 00352 00219 00133 00143 00093 00094 00066 00039 00010 0

Table 5 Summary of two-flash experimental data

Gas-oil ratio (m3m3) 86900Gas volume factor 00078Condensate oil density (gcm3) 07244The content of condensate oil (gm3) 70290

increases dramatically to the maximum and then decreasesmildly

The above phenomenon of the color of reservoir fluidchanging from transparent golden yellow into light brownand then into reddish brown and finally into completelyopaque ash black is called critical opalescence which isshown in dotted line position in Figure 2 The criticalopalescence is caused by molecular density fluctuation as aresult of gas-liquid molecular movement in the gas-liquidphase change process The reason of density fluctuation isevaporation of liquid molecules and condensation of gasmolecules and the molecular motion was especially sharpfluctuations when the temperature is near the critical pointAs a result density distribution presents concavo-convexrandomly distributed spatial curved surface instead of lam-inar and on the direction of the light numerous liquid-gas interfaces or gas-liquid interfaces appear As light travelsthrough these interfaces a series of reflection and refractionhappened which reduces light energy gradually resulting incritical opalescence

In the CVD test the sample volume at dew point pressureis identified as the constant pore volume of gas condensatereservoir and dew point pressure to zero pressure (gaugepressure) is divided into six to eight pressure stages tosimulate the depletion process in the reservoir and the

retrograde condensate liquid saturations at each pressureduring the depletion process were measured under theconditions of equilibrium Table 7 presents the retrogradecondensate liquid saturation during the depletion processwhich exhibits a maximum retrograde condensate liquidsaturation of 3404 of 119881

119889at 20MPa

42 Simulated Results and Discussion In order to furtherstudy the phase behavior characteristics of reservoir fluid ofH2-3 well first of all we used the PREOS which adjuststhe parameters to fit the experiment data and the fittingresults are shown in Table 8 and Figures 3 and 4 Table 8presents the matching results of dew point pressure andgas-oil ratio between the experimental data and calculatedvalues Figures 3 and 4 show the matching results of relativevolume and retrograde condensate liquid saturation betweenthe experimental data and calculated values It can be seenfromTable 8 and Figures 3 and 4 that the experimental valuesand the calculated values are very close thus the calculatedresults can be used to guide the phase behavior study At thesame time on the basis of fitting the experimental data 119875-119879phase diagram of theH2-3 well reservoir fluid was calculatedand the calculated results are shown in Figure 5 It can beseen from Figure 5 that the reservoir temperature and criticaltemperature are very close and the reservoir temperaturelocates in the right side of the critical point which showsthat the reservoir fluid of H2-3 wells belongs to the near-critical condensate gas reservoir Secondly to extend thelaboratory results a series of simulation calculations werecarried out such as the component variation of remainingfluid condensate oil condensate gas in CVD experimentand reevaporation mechanism of remaining fluid with CO

2

injection

6 Journal of Chemistry

Table 6 Summary of constant composition expansion experimental data at 1324∘C

Pressure(MPa) Gas volume(mL) Liquid volume(mL) Relative volume(119881119881119889) Retrograde condensate liquid saturation( of 119881

119889)

2553 16023 000 0983 0002448lowast 16308 mdash 1 mdash24 16471 mdash 1009 mdash22 17245 mdash 1057 mdash21 17938 mdash 1099 mdash20 12015 6537 1137 4007919 12785 6375 1175 3908518 14089 6169 1242 3783317 15469 6010 1317 3685215 18853 5763 1509 3533513 24227 5519 1824 3383910 35989 5197 2525 318657 57411 4908 3821 30094lowastSaturation pressuremdash liquid volume is too small and liquid volume is not measured

(a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k)Pressure drop process

Figure 2The critical opalescence phase behavior characteristics in the constant composition expansion experiment at 1324∘C for H2-3 well(a) 2553MPa (b) 25MPa (c) 248MPa (d) 247MPa (e) 246MPa (f) 2448MPa (g) 24MPa (h) 23MPa (i) 20MPa (j) 19MPa and (k)5MPa

Table 7 Summary of constant volume depletion experimental dataat 1324∘C

Pressure(MPa) Retrograde condensateliquid saturation( of 119881

119889)

2553 02448lowast mdash22 mdash20 340417 297714 295811 26838 25225 2129lowastSaturation pressuremdash liquid volume is too small and liquid volume is not measured

Through simulation and calculation of the CVD exper-iment the composition of remaining fluid along with con-densate oil and gas was obtained under different pressures(ranged from 2448MPa (dew point) to 5MPa) and theresults are presented in Tables 9sim11 As is shown in Tables 910 and 11 in the remaining fluid and remaining condensateoil the content of CH

4decreases with decreasing the pres-

sure while in the discharging condensate gas the content ofCH4increases with decreasing the pressure And the content

of 1198622sim119862

6shows a rising trend in the composition of the

remaining fluid remaining condensate oil and dischargingcondensate gas which indicates that once pressure dropsbelow the dew point light hydrocarbons (such as CH

4)

escape from condensate gas system first In the remainingcondensate oil system the content of C

7simC10is up to 7472

and with the decrease of pressure the content of C7simC10

has a slight decrease while the content of C11+

increases

Journal of Chemistry 7

Table 8 Matching results of dew point pressure gas-oil ratio between the experimental data and calculated values

Matching items Experiment Calculation Relative errorDew point pressure(MPa) 2448 2447 0046Gas-oil ratio(m3m3) 869 87112 024

Table 9 Calculated composition of the remaining fluid under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

523 521 519 512 500 480 446 385N2

064 064 063 061 059 055 049 041CH4

5707 5677 5635 5529 5354 5081 4651 3927C2H6

1173 1172 1170 1164 1153 113 1082 976C3H8

622 623 625 63 636 643 645 626iC4H10

107 107 108 110 113 116 121 125nC4H10

176 177 178 182 188 197 209 222iC5H12

121 122 123 127 134 144 158 18nC5H12

109 110 111 115 121 131 146 169C6H14

258 261 266 277 298 330 382 470C7simC8

774 787 806 857 945 1089 1333 178C9simC10

249 254 264 285 323 385 490 688C11+

118 125 132 151 176 219 288 411

Calculated ROVMeasured ROV

5 10 15 20 25 300Pressure (MPa)

00

05

10

15

20

25

30

35

40

Rela

tive v

olum

e

Figure 3 Matching results of relative volume between the experi-mental data and calculated values

which indicates that part of the heavy hydrocarbons (C7simC10)

reevaporate from the condensate oil when depleting to acertain pressure In general with the decrease of pressurethe heavy component shows a rising trend in the remainingfluid

On the basis of composition analysis phase diagramsand retrograde condensate characteristics of reservoir fluidunder different pressures have been simulated and calculatedFigure 6 shows the two-phase boundaries of remaining fluidof different depletion pressure It can be seen from Figure 6that with the decrease of pressure phase diagram becomes

Measured retrograde condensate liquid saturationCalculated retrograde condensate liquid saturation

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

40

5 10 15 20 250Pressure (MPa)

satu

ratio

n (

Vd)

Figure 4 Matching results of retrograde condensate liquid satura-tion between the experimental data and calculated values

more wide and narrow to the right and critical pointmoves tothe lower right And when pressure drops below the 17MPathe critical temperature of the remaining fluid system is abovethe reservoir temperature (1324∘C) and the remaining fluidis considered to shift from condensate gas reservoir systeminto a volatile oil system The variation relationship betweenthe retrograde condensate liquid saturation and pressure isshown in Figure 7 It can be clearly seen that in the remainingfluids at 22MPa 20MPa and 17MPa with the decreaseof pressure the retrograde condensate liquid saturationsincrease at first and then decrease which indicates that theremaining reservoir fluids appear as the phase behavior ofcondensate gas system And when pressure drops below

8 Journal of Chemistry

Table 10 Calculated composition of the remaining condensate oil under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

008 008 008 008 008 008 008N2

000 000 000 000 000 000 000CH4

038 038 038 037 037 036 035C2H6

044 044 044 045 046 047 048C3H8

087 088 090 092 096 102 111iC4H10

039 039 040 041 044 048 053nC4H10

087 088 091 095 101 110 125iC5H12

149 150 154 161 172 187 208nC5H12

170 171 176 183 194 209 229C6H14

841 846 858 879 908 944 973C7simC8

5352 5324 5272 5211 5143 5061 4954C9simC10

2120 2112 2097 2081 2063 2043 2031C11+

1065 1092 1132 1167 1188 1205 1225 there is no remaining condensate oil because the calculated saturation pressure is 2447MPa and the measured saturation pressure is 2448MPa

Table 11 Calculated composition of the discharging condensate gas under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

068 069 071 072 072 072 072N2

608 625 634 631 618 596 557CH4

6252 6393 6518 6582 6592 6534 6350C2H6

1185 1194 1211 1233 1262 1301 1351C3H8

588 582 582 59 608 642 704iC4H10

097 094 093 093 095 101 115nC4H10

154 149 146 145 149 158 182iC5H12

100 095 09 088 089 094 11nC5H12

089 084 079 076 076 081 094C6H14

197 18 163 153 149 154 18C7simC8

503 426 349 297 262 247 27C9simC10

105 071 043 027 017 012 01C11+

053 037 023 015 01 007 006 there is not remaining discharging condensate gas because the calculated saturation pressure is 2447MPa and themeasured saturation pressure is 2448MPa

2-phase boundary5 volume10 volume20 volume

30 volumeCritical pointSaturation pressure

minus100 minus50 0 50 100 150 200 250 300minus150Temperature (∘C)

0

5

10

15

20

25

30

Pres

sure

(MPa

)

Figure 5 Calculated phase diagram of reservoir fluid of H2-3 well

the 17MPa the retrograde condensate liquid saturationsdecrease with decreasing the pressure which indicates thatthe remaining reservoir fluids exhibit the phase behavior ofvolatile oil system

In addition we performed the simulation of phase behav-ior of remaining fluid with CO

2injection and the remaining

fluid at 22MPa is selected Then the remaining fluid wasmixed with CO

2of 20mol 40mol 60mol 70mol

and 80mol respectively The dew point and the retrogradecondensate liquid saturation of the mixed system werecalculated The calculated results are presented in Figures8 and 9 Figures 8 and 9 illustrate that with the increaseof CO

2injected quantity the retrograde condensate liquid

saturation decreases and at 80mol CO2injected quantity

the maximum condensate saturation is only about 247Compared with the original remaining fluid at 22MPathe retrograde condensate liquid saturation is significantlyreduced which explains the reevaporation mechanism of

Journal of Chemistry 9

Critical point trajectory

0

5

10

15

20

25

Pres

sure

(MPa

)

minus100 minus50 0 50 100 150 200 250 300 350 400minus150Temperature (∘C)

2448MPa20MPa14MPa8MPa

22MPa17MPa11MPa5MPa

Figure 6 Calculated two-phase boundaries of resident fluid underdifferent depletion pressures

2448MPa

20MPa

14MPa

8MPa22MPa

17MPa

11MPa

5MPa

Retro

grad

e con

dens

ate l

iqui

d

0102030405060708090

100

5 10 15 20 25 300Temperature (∘C)

satu

ratio

n (

Vd)

Figure 7 Calculated retrograde condensate liquid saturation underdifferent depletion pressures

remaining fluid with CO2injection As to dew point pressure

with the increase of CO2injected quantity the dew point

pressure increases first and then decreases

5 Conclusions

(1) The reservoir fluid of H2-3 well is considered tobe the near-critical condensate gas reservoir systemcombined with the well stream components and 119875-119879phase diagram

(2) In the vicinity of the critical region the reservoirfluid of H2-3 well appears as the ldquocritical opalescencerdquophenomenon and the phenomenon is caused by the

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

5 10 15 20 25 300Pressure (MPa)

80mol CO2

70mol CO2

60mol CO2

40mol CO2

20mol CO2

satu

ratio

n (

Vd)

Figure 8 The variation of calculated retrograde condensate liquidsaturation with CO

2injected quantity

2460

2480

2500

2520

2540

2560

2580

2600

2620D

ew p

oint

pre

ssur

e (M

Pa)

01 02 03 04 05 06 07 08 090CO2 content (mol)

Figure 9 The variation of calculated dew point pressure with CO2

injected quantity

density fluctuations in the gas and liquid molecularmotion during the gas-liquid phase change process

(3) The volume of retrograde condensate liquid satura-tion during the depletion process increases first andthen decreases and when reservoir pressure dropsbelow a certain pressure the variation of retro-grade condensate liquid saturation exhibits the phasebehavior of volatile oil

(4) The reevaporation of remaining fluid consists of twoaspects (1) part of heavy hydrocarbons reevaporatefrom the remaining condensate oil when depleting toa certain pressure (2) the variation characteristics ofretrograde condensate liquid saturation of remainingfluid shift from a condensate gas condensate systeminto a volatile oil system

(5) The recovery of condensate oil and gas is proportionalto the CO

2injected quantity

10 Journal of Chemistry

(6) When implementing CO2injection in the near-

critical condensate gas reservoir the dew point pres-sure of the new mixed fluid system should be takeninto account since it is not simply monotonicallyincreasing or decreasing with the increase of CO

2

injected quantity

Competing Interests

Here all the authors solemnly declare that there are nocompeting interests regarding the publication of this paper

Acknowledgments

The authors wish to acknowledge anonymous reviewersfor constructive comments and suggestions for improvingthis paper The authors also wish to thank the anonymousAssociate Editor for his handling of the paper and addi-tional suggestions This work was supported by Open Fund(PLN1509) of State Key Laboratory of Oil and Gas ReservoirGeology and Exploitation (Southwest Petroleum University)and the Fund of the Department of Education in Sichuan (no15ZB0065)

References

[1] L Sun H Zhao S B Kiselev and C McCabe ldquoPredictingmixture phase equilibria and critical behavior using the SAFT-VRX approachrdquo Journal of Physical Chemistry B vol 109 no 18pp 9047ndash9058 2005

[2] W Yan L-K Wang L-Y Yang and T-M Guo ldquoA systematicexperimental study on the phase behavior of complex fluidmixtures up to near-critical regionrdquo Fluid Phase Equilibria vol190 no 1-2 pp 159ndash178 2001

[3] L Gil J F Martınez-Lopez M Artal et al ldquoVolumetricbehavior of theCO

2(1) +C

2H6(2) system in the subcritical (T =

29315 K) critical and supercritical (T = 30815 K) regionsrdquoTheJournal of Physical Chemistry B vol 114 no 1 pp 5447ndash54692010

[4] A R Bazaev and E A Bazaev ldquoThe thermodynamic propertiesof binary mixtures of technologically important substances inthe near- and supercritical statesrdquo Russian Journal of PhysicalChemistry B vol 4 no 8 pp 1178ndash1187 2010

[5] T YangW-D Chen and T-M Guo ldquoPhase behavior of a near-critical reservoir fluid mixturerdquo Fluid Phase Equilibria vol 128no 1-2 pp 183ndash197 1997

[6] K Luo and T Zhong ldquoA discussion on the layering of near-critical gas condensate in PVT cellrdquo Petroleum Exploration andDevelopment vol 26 no 1 pp 68ndash70 1999

[7] P Shen K Luo X Zheng S Li Z Dai andH Liu ldquoExperimen-tal study of near-critical behavior of gas condensate systemsrdquo inProceedings of the SPE Production and Operations SymposiumSPE 67285 Oklahoma City Okla USA March 2001

[8] X Zheng P Sheng S Li K Luo and Z Dai ldquoExperimentalinvestigation into near-critical phenomena of rich gas conden-sate systemsrdquo inProceedings of the SPE International Oil andGasConference and Exhibition in China (iOGCEC rsquo00) SPE64712pp 459ndash468 Beijing China November 2000

[9] P P Shen X T Zheng S Li K Luo andWY Sun ldquoNear-criticalphenomenal of rich gas condensate system an experimentalinvestigationrdquoActa Petrolei Sinica vol 22 no 3 pp 47ndash51 2001

[10] C-A C Parra and J-C-M E Remolina ldquoExperimental studyand calculations of the near critical behavior of a synthetic fluidin nitrogen injectionrdquo Ciencia Tecnologıa y Futuro vol 3 no 1pp 127ndash137 2005

[11] H-Y Chiu R-F Jung M-J Lee and H-M Lin ldquoVaporndashliquidphase equilibriumbehavior ofmixtures containing supercriticalcarbon dioxide near critical regionrdquo Journal of SupercriticalFluids vol 44 no 3 pp 273ndash278 2008

[12] M N Shehata S-E K Fateen and A Bonilla-PetricioletldquoCritical point calculations of multi-component reservoir fluidsusing nature-inspired metaheuristic algorithmsrdquo Fluid PhaseEquilibria vol 409 pp 280ndash290 2016

[13] H-G Li X-Y Lu and V Yang ldquoA numerical study of fluidinjection and mixing under near-critical conditionsrdquo ActaMechanica Sinica vol 28 no 3 pp 559ndash571 2012

[14] L Mistura ldquoTransport coefficients near a critical point in mul-ticomponent fluid systemsrdquo Il Nuovo Cimento vol 12 no 1 pp35ndash42 1972

[15] J-N Jaubert L Avaullee and C Pierre ldquoIs it still necessaryto measure the minimum miscibility pressurerdquo Industrial ampEngineering Chemistry Research vol 41 no 2 pp 303ndash310 2002

[16] China National Oil and Gas Industry Standards ldquoAnalysis forreservoir fluids physical propertiesrdquo Tech Rep SYT5542-20092009

[17] D-Y Peng and D B Robinson ldquoA new two-constant equationof staterdquo Industrial amp Engineering Chemistry Fundamentals vol15 no 1 pp 59ndash64 1976

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Journal of

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Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

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Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

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Journal of

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Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

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CatalystsJournal of

4 Journal of Chemistry

Table 2 Composition of pseudo-components

Pseudo-components molCO2

523N2

064CH4

5707C2H6

1173C3H8

622iC4H10

107nC4H10

176iC5H12

121nC5H12

109C6H14

258C7simC8

774C9simC10

249C11+

118

Repeat the depressurization-exhaust process till thelast stage of pressure The testing process of the lastlevel pressure to zero pressure is described as followsopen the top valve and directly depressurize to zeropressure by gas releasing Subsequently dischargethe residual oil and gas from the cell and take thegas sample to conduct the component analysis andthe density and composition of residual oil weresimultaneously measured

3 Calculations

To verify the laboratory results we utilized the high pre-cision PR equation of state (PREOS78) [17] in WINPROPmodule of the Computer Modeling Group (CMG) simulatorCombinedwith the fluid thermodynamic equilibrium theoryit can accurately describe and predict phase behavior ofcondensate gas reservoir fluid and phase transition near thecritical point Thermodynamic parameters of the PREOS areadjusted to match the experimental measured PVT data Theoriginal well stream composition was split and grouped into13 pseudo-components which is given in Table 2 Criticaltemperatures critical pressures and acentric factors of theplus components and binary interaction parameters (119870

119894119895)

were adjusted to match the experimental data such as thesaturation pressure (the dew point pressure) gas-oil ratiorelative volumes and retrograde condensate liquid satura-tions It is worth mentioning that interaction coefficients(119870119894119895) are introduced to account for the molecular interaction

between dissimilar molecules The values of the interactioncoefficients are obtained by fitting the predicted saturationpressures to experimental data through the PR78 EOS Tables3 and 4 present the adjusted critical temperatures criticalpressures and acentric factors of the plus components andobtained binary interaction parametersThe absolute relativeerror (1) and the average absolute relative error (2) are used toexpress the deviation between the calculated values by usingthe PREOS in this paper and the experimental measuredvalues The objective is to make the deviation between thecalculated value and experimental valueminimumTo extend

the laboratory results on the basis of fitting the experimentaldata a series of simulation calculations were carried out suchas the component variation of remaining fluid condensateoil condensate gas in CVD experiment and reevaporationmechanism of remaining fluid with CO

2injection

ARE =119873

sum

119894=1

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

Cal minus ExpExp

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

119894

times 100 (1)

AARE = 1119873

119873

sum

119894=1

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

Cal minus ExpExp

1003816

1003816

1003816

1003816

1003816

1003816

1003816

1003816

119894

times 100 (2)

4 Results and Discussion

41 Experimental Results and Discussion Prior to constantcomposition expansion (CCE) and constant volume deple-tion (CVD) experiment a two-flash experiment of the reser-voir fluid of H2-3 well was performed Table 5 shows the two-flash experimental data of the reservoir fluid of H2-3 wellReferring to the international standard the fluid is identifiedas near-critical condensate gas reservoir fluid system whichhas high content of condensate oil low condensate oil densityand gas-oil ratio

Constant composition expansion experiment is alsoknown as119875-119881 relationship experiment which provides infor-mation on determination of dew point relative volume of thefluid and retrograde condensate liquid saturation at differentpressures Relative volume is the ratio between the volumeof each pressure and the volume of dew point pressureand the retrograde condensate liquid saturation is the ratiobetween the volume of the retrograde condensate oil and thevolume of the dew point pressure The CCE experimentalresults under reservoir temperature (1324∘C) are showed inTable 6 the reservoir fluid of H2-3 well exhibits a maximumretrograde condensate liquid saturation of 42079 and theretrograde condensate liquid saturation increases first andthen decreases

Meanwhile we observed the phase behavior of H2-3well reservoir fluid in the near-critical region during CCEexperiment Figure 2 presents the phase behavior in thenear-critical region of reservoir fluid in H2-3 well duringpressure drop process Under the formation temperaturewhen pressure reduces from the pressure point in Figure 2(a)to the pressure point in Figures 2(b) 2(c) 2(d) 2(e) and2(f) reservoir fluid in PVT test cell turns from transparentgolden yellow into light brown and then into reddish brownand finally into completely opaque ash black When pressurereduces from the pressure point in Figure 2(f) to the pressurepoint in Figures 2(g) and 2(h) reservoir fluid in PVT test cellturns from completely opaque ash black into reddish brownat bottom and ash black at top and then into light brownat bottom and light ash black at top and does not have theobvious gas-liquid interface When pressure further reducesfrom the pressure point in Figure 2(h) to the pressure pointin Figures 2(i) 2(j) and 2(k) reservoir fluid in PVT testcell turns from light brown at bottom and light ash black attop into golden yellow at bottom and has the obvious gas-liquid interface besides retrograde condensate liquid volume

Journal of Chemistry 5

Table 3 Critical temperatures and critical pressures acentric factors of the plus components

Plus components Critical temperature(∘C) Critical pressure(MPa) Acentric factorC7simC8

28031 30245 0283C9simC10

33685 24608 0368C11+

40139 21066 0477

Table 4 Binary interaction parameters (119870119894119895) and mixing rules for the PREOS in this study

Components CO2

N2

CH4

C2H6

C3H8

iC4H10

nC4H10

iC5H12

nC5H12

C6H14

C7simC8

C9simC10

C11+

CO2

0 00200 01030 01300 01350 01300 01300 01250 01250 01500 01500 01500 01500N2

00200 0 00310 00420 00910 00950 00950 00950 00950 01200 01200 01200 01200CH4

01030 00310 0 00027 00085 00158 00148 00209 00206 00253 00314 00426 00561C2H6

01300 00420 00027 0 00017 00055 00049 00087 00086 00117 00160 00245 00352C3H8

01350 00910 00085 00017 0 00011 00001 00028 00027 00046 00075 00136 00219iC4H10

01300 00950 00158 00055 00011 0 00000 00004 00004 00012 00028 00069 00133nC4H10

01300 00950 00148 00049 00001 00000 0 00006 00005 00015 00033 00077 00143iC5H12

01250 00950 00209 00087 00028 00004 00006 0 00000 00002 00011 00041 00093nC5H12

01250 00950 00206 00086 00027 00004 00005 00000 0 00003 00012 00042 00094C6H14

01500 01200 00253 00117 00046 00012 00015 00002 00003 0 00003 00024 00066C7simC8

01500 01200 00314 00160 00075 00028 00033 00011 00012 00003 0 00009 00039C9simC10

01500 01200 00426 00245 00136 00069 00077 00041 00042 00024 00009 0 00010C11+

01500 01200 00561 00352 00219 00133 00143 00093 00094 00066 00039 00010 0

Table 5 Summary of two-flash experimental data

Gas-oil ratio (m3m3) 86900Gas volume factor 00078Condensate oil density (gcm3) 07244The content of condensate oil (gm3) 70290

increases dramatically to the maximum and then decreasesmildly

The above phenomenon of the color of reservoir fluidchanging from transparent golden yellow into light brownand then into reddish brown and finally into completelyopaque ash black is called critical opalescence which isshown in dotted line position in Figure 2 The criticalopalescence is caused by molecular density fluctuation as aresult of gas-liquid molecular movement in the gas-liquidphase change process The reason of density fluctuation isevaporation of liquid molecules and condensation of gasmolecules and the molecular motion was especially sharpfluctuations when the temperature is near the critical pointAs a result density distribution presents concavo-convexrandomly distributed spatial curved surface instead of lam-inar and on the direction of the light numerous liquid-gas interfaces or gas-liquid interfaces appear As light travelsthrough these interfaces a series of reflection and refractionhappened which reduces light energy gradually resulting incritical opalescence

In the CVD test the sample volume at dew point pressureis identified as the constant pore volume of gas condensatereservoir and dew point pressure to zero pressure (gaugepressure) is divided into six to eight pressure stages tosimulate the depletion process in the reservoir and the

retrograde condensate liquid saturations at each pressureduring the depletion process were measured under theconditions of equilibrium Table 7 presents the retrogradecondensate liquid saturation during the depletion processwhich exhibits a maximum retrograde condensate liquidsaturation of 3404 of 119881

119889at 20MPa

42 Simulated Results and Discussion In order to furtherstudy the phase behavior characteristics of reservoir fluid ofH2-3 well first of all we used the PREOS which adjuststhe parameters to fit the experiment data and the fittingresults are shown in Table 8 and Figures 3 and 4 Table 8presents the matching results of dew point pressure andgas-oil ratio between the experimental data and calculatedvalues Figures 3 and 4 show the matching results of relativevolume and retrograde condensate liquid saturation betweenthe experimental data and calculated values It can be seenfromTable 8 and Figures 3 and 4 that the experimental valuesand the calculated values are very close thus the calculatedresults can be used to guide the phase behavior study At thesame time on the basis of fitting the experimental data 119875-119879phase diagram of theH2-3 well reservoir fluid was calculatedand the calculated results are shown in Figure 5 It can beseen from Figure 5 that the reservoir temperature and criticaltemperature are very close and the reservoir temperaturelocates in the right side of the critical point which showsthat the reservoir fluid of H2-3 wells belongs to the near-critical condensate gas reservoir Secondly to extend thelaboratory results a series of simulation calculations werecarried out such as the component variation of remainingfluid condensate oil condensate gas in CVD experimentand reevaporation mechanism of remaining fluid with CO

2

injection

6 Journal of Chemistry

Table 6 Summary of constant composition expansion experimental data at 1324∘C

Pressure(MPa) Gas volume(mL) Liquid volume(mL) Relative volume(119881119881119889) Retrograde condensate liquid saturation( of 119881

119889)

2553 16023 000 0983 0002448lowast 16308 mdash 1 mdash24 16471 mdash 1009 mdash22 17245 mdash 1057 mdash21 17938 mdash 1099 mdash20 12015 6537 1137 4007919 12785 6375 1175 3908518 14089 6169 1242 3783317 15469 6010 1317 3685215 18853 5763 1509 3533513 24227 5519 1824 3383910 35989 5197 2525 318657 57411 4908 3821 30094lowastSaturation pressuremdash liquid volume is too small and liquid volume is not measured

(a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k)Pressure drop process

Figure 2The critical opalescence phase behavior characteristics in the constant composition expansion experiment at 1324∘C for H2-3 well(a) 2553MPa (b) 25MPa (c) 248MPa (d) 247MPa (e) 246MPa (f) 2448MPa (g) 24MPa (h) 23MPa (i) 20MPa (j) 19MPa and (k)5MPa

Table 7 Summary of constant volume depletion experimental dataat 1324∘C

Pressure(MPa) Retrograde condensateliquid saturation( of 119881

119889)

2553 02448lowast mdash22 mdash20 340417 297714 295811 26838 25225 2129lowastSaturation pressuremdash liquid volume is too small and liquid volume is not measured

Through simulation and calculation of the CVD exper-iment the composition of remaining fluid along with con-densate oil and gas was obtained under different pressures(ranged from 2448MPa (dew point) to 5MPa) and theresults are presented in Tables 9sim11 As is shown in Tables 910 and 11 in the remaining fluid and remaining condensateoil the content of CH

4decreases with decreasing the pres-

sure while in the discharging condensate gas the content ofCH4increases with decreasing the pressure And the content

of 1198622sim119862

6shows a rising trend in the composition of the

remaining fluid remaining condensate oil and dischargingcondensate gas which indicates that once pressure dropsbelow the dew point light hydrocarbons (such as CH

4)

escape from condensate gas system first In the remainingcondensate oil system the content of C

7simC10is up to 7472

and with the decrease of pressure the content of C7simC10

has a slight decrease while the content of C11+

increases

Journal of Chemistry 7

Table 8 Matching results of dew point pressure gas-oil ratio between the experimental data and calculated values

Matching items Experiment Calculation Relative errorDew point pressure(MPa) 2448 2447 0046Gas-oil ratio(m3m3) 869 87112 024

Table 9 Calculated composition of the remaining fluid under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

523 521 519 512 500 480 446 385N2

064 064 063 061 059 055 049 041CH4

5707 5677 5635 5529 5354 5081 4651 3927C2H6

1173 1172 1170 1164 1153 113 1082 976C3H8

622 623 625 63 636 643 645 626iC4H10

107 107 108 110 113 116 121 125nC4H10

176 177 178 182 188 197 209 222iC5H12

121 122 123 127 134 144 158 18nC5H12

109 110 111 115 121 131 146 169C6H14

258 261 266 277 298 330 382 470C7simC8

774 787 806 857 945 1089 1333 178C9simC10

249 254 264 285 323 385 490 688C11+

118 125 132 151 176 219 288 411

Calculated ROVMeasured ROV

5 10 15 20 25 300Pressure (MPa)

00

05

10

15

20

25

30

35

40

Rela

tive v

olum

e

Figure 3 Matching results of relative volume between the experi-mental data and calculated values

which indicates that part of the heavy hydrocarbons (C7simC10)

reevaporate from the condensate oil when depleting to acertain pressure In general with the decrease of pressurethe heavy component shows a rising trend in the remainingfluid

On the basis of composition analysis phase diagramsand retrograde condensate characteristics of reservoir fluidunder different pressures have been simulated and calculatedFigure 6 shows the two-phase boundaries of remaining fluidof different depletion pressure It can be seen from Figure 6that with the decrease of pressure phase diagram becomes

Measured retrograde condensate liquid saturationCalculated retrograde condensate liquid saturation

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

40

5 10 15 20 250Pressure (MPa)

satu

ratio

n (

Vd)

Figure 4 Matching results of retrograde condensate liquid satura-tion between the experimental data and calculated values

more wide and narrow to the right and critical pointmoves tothe lower right And when pressure drops below the 17MPathe critical temperature of the remaining fluid system is abovethe reservoir temperature (1324∘C) and the remaining fluidis considered to shift from condensate gas reservoir systeminto a volatile oil system The variation relationship betweenthe retrograde condensate liquid saturation and pressure isshown in Figure 7 It can be clearly seen that in the remainingfluids at 22MPa 20MPa and 17MPa with the decreaseof pressure the retrograde condensate liquid saturationsincrease at first and then decrease which indicates that theremaining reservoir fluids appear as the phase behavior ofcondensate gas system And when pressure drops below

8 Journal of Chemistry

Table 10 Calculated composition of the remaining condensate oil under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

008 008 008 008 008 008 008N2

000 000 000 000 000 000 000CH4

038 038 038 037 037 036 035C2H6

044 044 044 045 046 047 048C3H8

087 088 090 092 096 102 111iC4H10

039 039 040 041 044 048 053nC4H10

087 088 091 095 101 110 125iC5H12

149 150 154 161 172 187 208nC5H12

170 171 176 183 194 209 229C6H14

841 846 858 879 908 944 973C7simC8

5352 5324 5272 5211 5143 5061 4954C9simC10

2120 2112 2097 2081 2063 2043 2031C11+

1065 1092 1132 1167 1188 1205 1225 there is no remaining condensate oil because the calculated saturation pressure is 2447MPa and the measured saturation pressure is 2448MPa

Table 11 Calculated composition of the discharging condensate gas under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

068 069 071 072 072 072 072N2

608 625 634 631 618 596 557CH4

6252 6393 6518 6582 6592 6534 6350C2H6

1185 1194 1211 1233 1262 1301 1351C3H8

588 582 582 59 608 642 704iC4H10

097 094 093 093 095 101 115nC4H10

154 149 146 145 149 158 182iC5H12

100 095 09 088 089 094 11nC5H12

089 084 079 076 076 081 094C6H14

197 18 163 153 149 154 18C7simC8

503 426 349 297 262 247 27C9simC10

105 071 043 027 017 012 01C11+

053 037 023 015 01 007 006 there is not remaining discharging condensate gas because the calculated saturation pressure is 2447MPa and themeasured saturation pressure is 2448MPa

2-phase boundary5 volume10 volume20 volume

30 volumeCritical pointSaturation pressure

minus100 minus50 0 50 100 150 200 250 300minus150Temperature (∘C)

0

5

10

15

20

25

30

Pres

sure

(MPa

)

Figure 5 Calculated phase diagram of reservoir fluid of H2-3 well

the 17MPa the retrograde condensate liquid saturationsdecrease with decreasing the pressure which indicates thatthe remaining reservoir fluids exhibit the phase behavior ofvolatile oil system

In addition we performed the simulation of phase behav-ior of remaining fluid with CO

2injection and the remaining

fluid at 22MPa is selected Then the remaining fluid wasmixed with CO

2of 20mol 40mol 60mol 70mol

and 80mol respectively The dew point and the retrogradecondensate liquid saturation of the mixed system werecalculated The calculated results are presented in Figures8 and 9 Figures 8 and 9 illustrate that with the increaseof CO

2injected quantity the retrograde condensate liquid

saturation decreases and at 80mol CO2injected quantity

the maximum condensate saturation is only about 247Compared with the original remaining fluid at 22MPathe retrograde condensate liquid saturation is significantlyreduced which explains the reevaporation mechanism of

Journal of Chemistry 9

Critical point trajectory

0

5

10

15

20

25

Pres

sure

(MPa

)

minus100 minus50 0 50 100 150 200 250 300 350 400minus150Temperature (∘C)

2448MPa20MPa14MPa8MPa

22MPa17MPa11MPa5MPa

Figure 6 Calculated two-phase boundaries of resident fluid underdifferent depletion pressures

2448MPa

20MPa

14MPa

8MPa22MPa

17MPa

11MPa

5MPa

Retro

grad

e con

dens

ate l

iqui

d

0102030405060708090

100

5 10 15 20 25 300Temperature (∘C)

satu

ratio

n (

Vd)

Figure 7 Calculated retrograde condensate liquid saturation underdifferent depletion pressures

remaining fluid with CO2injection As to dew point pressure

with the increase of CO2injected quantity the dew point

pressure increases first and then decreases

5 Conclusions

(1) The reservoir fluid of H2-3 well is considered tobe the near-critical condensate gas reservoir systemcombined with the well stream components and 119875-119879phase diagram

(2) In the vicinity of the critical region the reservoirfluid of H2-3 well appears as the ldquocritical opalescencerdquophenomenon and the phenomenon is caused by the

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

5 10 15 20 25 300Pressure (MPa)

80mol CO2

70mol CO2

60mol CO2

40mol CO2

20mol CO2

satu

ratio

n (

Vd)

Figure 8 The variation of calculated retrograde condensate liquidsaturation with CO

2injected quantity

2460

2480

2500

2520

2540

2560

2580

2600

2620D

ew p

oint

pre

ssur

e (M

Pa)

01 02 03 04 05 06 07 08 090CO2 content (mol)

Figure 9 The variation of calculated dew point pressure with CO2

injected quantity

density fluctuations in the gas and liquid molecularmotion during the gas-liquid phase change process

(3) The volume of retrograde condensate liquid satura-tion during the depletion process increases first andthen decreases and when reservoir pressure dropsbelow a certain pressure the variation of retro-grade condensate liquid saturation exhibits the phasebehavior of volatile oil

(4) The reevaporation of remaining fluid consists of twoaspects (1) part of heavy hydrocarbons reevaporatefrom the remaining condensate oil when depleting toa certain pressure (2) the variation characteristics ofretrograde condensate liquid saturation of remainingfluid shift from a condensate gas condensate systeminto a volatile oil system

(5) The recovery of condensate oil and gas is proportionalto the CO

2injected quantity

10 Journal of Chemistry

(6) When implementing CO2injection in the near-

critical condensate gas reservoir the dew point pres-sure of the new mixed fluid system should be takeninto account since it is not simply monotonicallyincreasing or decreasing with the increase of CO

2

injected quantity

Competing Interests

Here all the authors solemnly declare that there are nocompeting interests regarding the publication of this paper

Acknowledgments

The authors wish to acknowledge anonymous reviewersfor constructive comments and suggestions for improvingthis paper The authors also wish to thank the anonymousAssociate Editor for his handling of the paper and addi-tional suggestions This work was supported by Open Fund(PLN1509) of State Key Laboratory of Oil and Gas ReservoirGeology and Exploitation (Southwest Petroleum University)and the Fund of the Department of Education in Sichuan (no15ZB0065)

References

[1] L Sun H Zhao S B Kiselev and C McCabe ldquoPredictingmixture phase equilibria and critical behavior using the SAFT-VRX approachrdquo Journal of Physical Chemistry B vol 109 no 18pp 9047ndash9058 2005

[2] W Yan L-K Wang L-Y Yang and T-M Guo ldquoA systematicexperimental study on the phase behavior of complex fluidmixtures up to near-critical regionrdquo Fluid Phase Equilibria vol190 no 1-2 pp 159ndash178 2001

[3] L Gil J F Martınez-Lopez M Artal et al ldquoVolumetricbehavior of theCO

2(1) +C

2H6(2) system in the subcritical (T =

29315 K) critical and supercritical (T = 30815 K) regionsrdquoTheJournal of Physical Chemistry B vol 114 no 1 pp 5447ndash54692010

[4] A R Bazaev and E A Bazaev ldquoThe thermodynamic propertiesof binary mixtures of technologically important substances inthe near- and supercritical statesrdquo Russian Journal of PhysicalChemistry B vol 4 no 8 pp 1178ndash1187 2010

[5] T YangW-D Chen and T-M Guo ldquoPhase behavior of a near-critical reservoir fluid mixturerdquo Fluid Phase Equilibria vol 128no 1-2 pp 183ndash197 1997

[6] K Luo and T Zhong ldquoA discussion on the layering of near-critical gas condensate in PVT cellrdquo Petroleum Exploration andDevelopment vol 26 no 1 pp 68ndash70 1999

[7] P Shen K Luo X Zheng S Li Z Dai andH Liu ldquoExperimen-tal study of near-critical behavior of gas condensate systemsrdquo inProceedings of the SPE Production and Operations SymposiumSPE 67285 Oklahoma City Okla USA March 2001

[8] X Zheng P Sheng S Li K Luo and Z Dai ldquoExperimentalinvestigation into near-critical phenomena of rich gas conden-sate systemsrdquo inProceedings of the SPE International Oil andGasConference and Exhibition in China (iOGCEC rsquo00) SPE64712pp 459ndash468 Beijing China November 2000

[9] P P Shen X T Zheng S Li K Luo andWY Sun ldquoNear-criticalphenomenal of rich gas condensate system an experimentalinvestigationrdquoActa Petrolei Sinica vol 22 no 3 pp 47ndash51 2001

[10] C-A C Parra and J-C-M E Remolina ldquoExperimental studyand calculations of the near critical behavior of a synthetic fluidin nitrogen injectionrdquo Ciencia Tecnologıa y Futuro vol 3 no 1pp 127ndash137 2005

[11] H-Y Chiu R-F Jung M-J Lee and H-M Lin ldquoVaporndashliquidphase equilibriumbehavior ofmixtures containing supercriticalcarbon dioxide near critical regionrdquo Journal of SupercriticalFluids vol 44 no 3 pp 273ndash278 2008

[12] M N Shehata S-E K Fateen and A Bonilla-PetricioletldquoCritical point calculations of multi-component reservoir fluidsusing nature-inspired metaheuristic algorithmsrdquo Fluid PhaseEquilibria vol 409 pp 280ndash290 2016

[13] H-G Li X-Y Lu and V Yang ldquoA numerical study of fluidinjection and mixing under near-critical conditionsrdquo ActaMechanica Sinica vol 28 no 3 pp 559ndash571 2012

[14] L Mistura ldquoTransport coefficients near a critical point in mul-ticomponent fluid systemsrdquo Il Nuovo Cimento vol 12 no 1 pp35ndash42 1972

[15] J-N Jaubert L Avaullee and C Pierre ldquoIs it still necessaryto measure the minimum miscibility pressurerdquo Industrial ampEngineering Chemistry Research vol 41 no 2 pp 303ndash310 2002

[16] China National Oil and Gas Industry Standards ldquoAnalysis forreservoir fluids physical propertiesrdquo Tech Rep SYT5542-20092009

[17] D-Y Peng and D B Robinson ldquoA new two-constant equationof staterdquo Industrial amp Engineering Chemistry Fundamentals vol15 no 1 pp 59ndash64 1976

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Journal of Chemistry 5

Table 3 Critical temperatures and critical pressures acentric factors of the plus components

Plus components Critical temperature(∘C) Critical pressure(MPa) Acentric factorC7simC8

28031 30245 0283C9simC10

33685 24608 0368C11+

40139 21066 0477

Table 4 Binary interaction parameters (119870119894119895) and mixing rules for the PREOS in this study

Components CO2

N2

CH4

C2H6

C3H8

iC4H10

nC4H10

iC5H12

nC5H12

C6H14

C7simC8

C9simC10

C11+

CO2

0 00200 01030 01300 01350 01300 01300 01250 01250 01500 01500 01500 01500N2

00200 0 00310 00420 00910 00950 00950 00950 00950 01200 01200 01200 01200CH4

01030 00310 0 00027 00085 00158 00148 00209 00206 00253 00314 00426 00561C2H6

01300 00420 00027 0 00017 00055 00049 00087 00086 00117 00160 00245 00352C3H8

01350 00910 00085 00017 0 00011 00001 00028 00027 00046 00075 00136 00219iC4H10

01300 00950 00158 00055 00011 0 00000 00004 00004 00012 00028 00069 00133nC4H10

01300 00950 00148 00049 00001 00000 0 00006 00005 00015 00033 00077 00143iC5H12

01250 00950 00209 00087 00028 00004 00006 0 00000 00002 00011 00041 00093nC5H12

01250 00950 00206 00086 00027 00004 00005 00000 0 00003 00012 00042 00094C6H14

01500 01200 00253 00117 00046 00012 00015 00002 00003 0 00003 00024 00066C7simC8

01500 01200 00314 00160 00075 00028 00033 00011 00012 00003 0 00009 00039C9simC10

01500 01200 00426 00245 00136 00069 00077 00041 00042 00024 00009 0 00010C11+

01500 01200 00561 00352 00219 00133 00143 00093 00094 00066 00039 00010 0

Table 5 Summary of two-flash experimental data

Gas-oil ratio (m3m3) 86900Gas volume factor 00078Condensate oil density (gcm3) 07244The content of condensate oil (gm3) 70290

increases dramatically to the maximum and then decreasesmildly

The above phenomenon of the color of reservoir fluidchanging from transparent golden yellow into light brownand then into reddish brown and finally into completelyopaque ash black is called critical opalescence which isshown in dotted line position in Figure 2 The criticalopalescence is caused by molecular density fluctuation as aresult of gas-liquid molecular movement in the gas-liquidphase change process The reason of density fluctuation isevaporation of liquid molecules and condensation of gasmolecules and the molecular motion was especially sharpfluctuations when the temperature is near the critical pointAs a result density distribution presents concavo-convexrandomly distributed spatial curved surface instead of lam-inar and on the direction of the light numerous liquid-gas interfaces or gas-liquid interfaces appear As light travelsthrough these interfaces a series of reflection and refractionhappened which reduces light energy gradually resulting incritical opalescence

In the CVD test the sample volume at dew point pressureis identified as the constant pore volume of gas condensatereservoir and dew point pressure to zero pressure (gaugepressure) is divided into six to eight pressure stages tosimulate the depletion process in the reservoir and the

retrograde condensate liquid saturations at each pressureduring the depletion process were measured under theconditions of equilibrium Table 7 presents the retrogradecondensate liquid saturation during the depletion processwhich exhibits a maximum retrograde condensate liquidsaturation of 3404 of 119881

119889at 20MPa

42 Simulated Results and Discussion In order to furtherstudy the phase behavior characteristics of reservoir fluid ofH2-3 well first of all we used the PREOS which adjuststhe parameters to fit the experiment data and the fittingresults are shown in Table 8 and Figures 3 and 4 Table 8presents the matching results of dew point pressure andgas-oil ratio between the experimental data and calculatedvalues Figures 3 and 4 show the matching results of relativevolume and retrograde condensate liquid saturation betweenthe experimental data and calculated values It can be seenfromTable 8 and Figures 3 and 4 that the experimental valuesand the calculated values are very close thus the calculatedresults can be used to guide the phase behavior study At thesame time on the basis of fitting the experimental data 119875-119879phase diagram of theH2-3 well reservoir fluid was calculatedand the calculated results are shown in Figure 5 It can beseen from Figure 5 that the reservoir temperature and criticaltemperature are very close and the reservoir temperaturelocates in the right side of the critical point which showsthat the reservoir fluid of H2-3 wells belongs to the near-critical condensate gas reservoir Secondly to extend thelaboratory results a series of simulation calculations werecarried out such as the component variation of remainingfluid condensate oil condensate gas in CVD experimentand reevaporation mechanism of remaining fluid with CO

2

injection

6 Journal of Chemistry

Table 6 Summary of constant composition expansion experimental data at 1324∘C

Pressure(MPa) Gas volume(mL) Liquid volume(mL) Relative volume(119881119881119889) Retrograde condensate liquid saturation( of 119881

119889)

2553 16023 000 0983 0002448lowast 16308 mdash 1 mdash24 16471 mdash 1009 mdash22 17245 mdash 1057 mdash21 17938 mdash 1099 mdash20 12015 6537 1137 4007919 12785 6375 1175 3908518 14089 6169 1242 3783317 15469 6010 1317 3685215 18853 5763 1509 3533513 24227 5519 1824 3383910 35989 5197 2525 318657 57411 4908 3821 30094lowastSaturation pressuremdash liquid volume is too small and liquid volume is not measured

(a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k)Pressure drop process

Figure 2The critical opalescence phase behavior characteristics in the constant composition expansion experiment at 1324∘C for H2-3 well(a) 2553MPa (b) 25MPa (c) 248MPa (d) 247MPa (e) 246MPa (f) 2448MPa (g) 24MPa (h) 23MPa (i) 20MPa (j) 19MPa and (k)5MPa

Table 7 Summary of constant volume depletion experimental dataat 1324∘C

Pressure(MPa) Retrograde condensateliquid saturation( of 119881

119889)

2553 02448lowast mdash22 mdash20 340417 297714 295811 26838 25225 2129lowastSaturation pressuremdash liquid volume is too small and liquid volume is not measured

Through simulation and calculation of the CVD exper-iment the composition of remaining fluid along with con-densate oil and gas was obtained under different pressures(ranged from 2448MPa (dew point) to 5MPa) and theresults are presented in Tables 9sim11 As is shown in Tables 910 and 11 in the remaining fluid and remaining condensateoil the content of CH

4decreases with decreasing the pres-

sure while in the discharging condensate gas the content ofCH4increases with decreasing the pressure And the content

of 1198622sim119862

6shows a rising trend in the composition of the

remaining fluid remaining condensate oil and dischargingcondensate gas which indicates that once pressure dropsbelow the dew point light hydrocarbons (such as CH

4)

escape from condensate gas system first In the remainingcondensate oil system the content of C

7simC10is up to 7472

and with the decrease of pressure the content of C7simC10

has a slight decrease while the content of C11+

increases

Journal of Chemistry 7

Table 8 Matching results of dew point pressure gas-oil ratio between the experimental data and calculated values

Matching items Experiment Calculation Relative errorDew point pressure(MPa) 2448 2447 0046Gas-oil ratio(m3m3) 869 87112 024

Table 9 Calculated composition of the remaining fluid under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

523 521 519 512 500 480 446 385N2

064 064 063 061 059 055 049 041CH4

5707 5677 5635 5529 5354 5081 4651 3927C2H6

1173 1172 1170 1164 1153 113 1082 976C3H8

622 623 625 63 636 643 645 626iC4H10

107 107 108 110 113 116 121 125nC4H10

176 177 178 182 188 197 209 222iC5H12

121 122 123 127 134 144 158 18nC5H12

109 110 111 115 121 131 146 169C6H14

258 261 266 277 298 330 382 470C7simC8

774 787 806 857 945 1089 1333 178C9simC10

249 254 264 285 323 385 490 688C11+

118 125 132 151 176 219 288 411

Calculated ROVMeasured ROV

5 10 15 20 25 300Pressure (MPa)

00

05

10

15

20

25

30

35

40

Rela

tive v

olum

e

Figure 3 Matching results of relative volume between the experi-mental data and calculated values

which indicates that part of the heavy hydrocarbons (C7simC10)

reevaporate from the condensate oil when depleting to acertain pressure In general with the decrease of pressurethe heavy component shows a rising trend in the remainingfluid

On the basis of composition analysis phase diagramsand retrograde condensate characteristics of reservoir fluidunder different pressures have been simulated and calculatedFigure 6 shows the two-phase boundaries of remaining fluidof different depletion pressure It can be seen from Figure 6that with the decrease of pressure phase diagram becomes

Measured retrograde condensate liquid saturationCalculated retrograde condensate liquid saturation

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

40

5 10 15 20 250Pressure (MPa)

satu

ratio

n (

Vd)

Figure 4 Matching results of retrograde condensate liquid satura-tion between the experimental data and calculated values

more wide and narrow to the right and critical pointmoves tothe lower right And when pressure drops below the 17MPathe critical temperature of the remaining fluid system is abovethe reservoir temperature (1324∘C) and the remaining fluidis considered to shift from condensate gas reservoir systeminto a volatile oil system The variation relationship betweenthe retrograde condensate liquid saturation and pressure isshown in Figure 7 It can be clearly seen that in the remainingfluids at 22MPa 20MPa and 17MPa with the decreaseof pressure the retrograde condensate liquid saturationsincrease at first and then decrease which indicates that theremaining reservoir fluids appear as the phase behavior ofcondensate gas system And when pressure drops below

8 Journal of Chemistry

Table 10 Calculated composition of the remaining condensate oil under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

008 008 008 008 008 008 008N2

000 000 000 000 000 000 000CH4

038 038 038 037 037 036 035C2H6

044 044 044 045 046 047 048C3H8

087 088 090 092 096 102 111iC4H10

039 039 040 041 044 048 053nC4H10

087 088 091 095 101 110 125iC5H12

149 150 154 161 172 187 208nC5H12

170 171 176 183 194 209 229C6H14

841 846 858 879 908 944 973C7simC8

5352 5324 5272 5211 5143 5061 4954C9simC10

2120 2112 2097 2081 2063 2043 2031C11+

1065 1092 1132 1167 1188 1205 1225 there is no remaining condensate oil because the calculated saturation pressure is 2447MPa and the measured saturation pressure is 2448MPa

Table 11 Calculated composition of the discharging condensate gas under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

068 069 071 072 072 072 072N2

608 625 634 631 618 596 557CH4

6252 6393 6518 6582 6592 6534 6350C2H6

1185 1194 1211 1233 1262 1301 1351C3H8

588 582 582 59 608 642 704iC4H10

097 094 093 093 095 101 115nC4H10

154 149 146 145 149 158 182iC5H12

100 095 09 088 089 094 11nC5H12

089 084 079 076 076 081 094C6H14

197 18 163 153 149 154 18C7simC8

503 426 349 297 262 247 27C9simC10

105 071 043 027 017 012 01C11+

053 037 023 015 01 007 006 there is not remaining discharging condensate gas because the calculated saturation pressure is 2447MPa and themeasured saturation pressure is 2448MPa

2-phase boundary5 volume10 volume20 volume

30 volumeCritical pointSaturation pressure

minus100 minus50 0 50 100 150 200 250 300minus150Temperature (∘C)

0

5

10

15

20

25

30

Pres

sure

(MPa

)

Figure 5 Calculated phase diagram of reservoir fluid of H2-3 well

the 17MPa the retrograde condensate liquid saturationsdecrease with decreasing the pressure which indicates thatthe remaining reservoir fluids exhibit the phase behavior ofvolatile oil system

In addition we performed the simulation of phase behav-ior of remaining fluid with CO

2injection and the remaining

fluid at 22MPa is selected Then the remaining fluid wasmixed with CO

2of 20mol 40mol 60mol 70mol

and 80mol respectively The dew point and the retrogradecondensate liquid saturation of the mixed system werecalculated The calculated results are presented in Figures8 and 9 Figures 8 and 9 illustrate that with the increaseof CO

2injected quantity the retrograde condensate liquid

saturation decreases and at 80mol CO2injected quantity

the maximum condensate saturation is only about 247Compared with the original remaining fluid at 22MPathe retrograde condensate liquid saturation is significantlyreduced which explains the reevaporation mechanism of

Journal of Chemistry 9

Critical point trajectory

0

5

10

15

20

25

Pres

sure

(MPa

)

minus100 minus50 0 50 100 150 200 250 300 350 400minus150Temperature (∘C)

2448MPa20MPa14MPa8MPa

22MPa17MPa11MPa5MPa

Figure 6 Calculated two-phase boundaries of resident fluid underdifferent depletion pressures

2448MPa

20MPa

14MPa

8MPa22MPa

17MPa

11MPa

5MPa

Retro

grad

e con

dens

ate l

iqui

d

0102030405060708090

100

5 10 15 20 25 300Temperature (∘C)

satu

ratio

n (

Vd)

Figure 7 Calculated retrograde condensate liquid saturation underdifferent depletion pressures

remaining fluid with CO2injection As to dew point pressure

with the increase of CO2injected quantity the dew point

pressure increases first and then decreases

5 Conclusions

(1) The reservoir fluid of H2-3 well is considered tobe the near-critical condensate gas reservoir systemcombined with the well stream components and 119875-119879phase diagram

(2) In the vicinity of the critical region the reservoirfluid of H2-3 well appears as the ldquocritical opalescencerdquophenomenon and the phenomenon is caused by the

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

5 10 15 20 25 300Pressure (MPa)

80mol CO2

70mol CO2

60mol CO2

40mol CO2

20mol CO2

satu

ratio

n (

Vd)

Figure 8 The variation of calculated retrograde condensate liquidsaturation with CO

2injected quantity

2460

2480

2500

2520

2540

2560

2580

2600

2620D

ew p

oint

pre

ssur

e (M

Pa)

01 02 03 04 05 06 07 08 090CO2 content (mol)

Figure 9 The variation of calculated dew point pressure with CO2

injected quantity

density fluctuations in the gas and liquid molecularmotion during the gas-liquid phase change process

(3) The volume of retrograde condensate liquid satura-tion during the depletion process increases first andthen decreases and when reservoir pressure dropsbelow a certain pressure the variation of retro-grade condensate liquid saturation exhibits the phasebehavior of volatile oil

(4) The reevaporation of remaining fluid consists of twoaspects (1) part of heavy hydrocarbons reevaporatefrom the remaining condensate oil when depleting toa certain pressure (2) the variation characteristics ofretrograde condensate liquid saturation of remainingfluid shift from a condensate gas condensate systeminto a volatile oil system

(5) The recovery of condensate oil and gas is proportionalto the CO

2injected quantity

10 Journal of Chemistry

(6) When implementing CO2injection in the near-

critical condensate gas reservoir the dew point pres-sure of the new mixed fluid system should be takeninto account since it is not simply monotonicallyincreasing or decreasing with the increase of CO

2

injected quantity

Competing Interests

Here all the authors solemnly declare that there are nocompeting interests regarding the publication of this paper

Acknowledgments

The authors wish to acknowledge anonymous reviewersfor constructive comments and suggestions for improvingthis paper The authors also wish to thank the anonymousAssociate Editor for his handling of the paper and addi-tional suggestions This work was supported by Open Fund(PLN1509) of State Key Laboratory of Oil and Gas ReservoirGeology and Exploitation (Southwest Petroleum University)and the Fund of the Department of Education in Sichuan (no15ZB0065)

References

[1] L Sun H Zhao S B Kiselev and C McCabe ldquoPredictingmixture phase equilibria and critical behavior using the SAFT-VRX approachrdquo Journal of Physical Chemistry B vol 109 no 18pp 9047ndash9058 2005

[2] W Yan L-K Wang L-Y Yang and T-M Guo ldquoA systematicexperimental study on the phase behavior of complex fluidmixtures up to near-critical regionrdquo Fluid Phase Equilibria vol190 no 1-2 pp 159ndash178 2001

[3] L Gil J F Martınez-Lopez M Artal et al ldquoVolumetricbehavior of theCO

2(1) +C

2H6(2) system in the subcritical (T =

29315 K) critical and supercritical (T = 30815 K) regionsrdquoTheJournal of Physical Chemistry B vol 114 no 1 pp 5447ndash54692010

[4] A R Bazaev and E A Bazaev ldquoThe thermodynamic propertiesof binary mixtures of technologically important substances inthe near- and supercritical statesrdquo Russian Journal of PhysicalChemistry B vol 4 no 8 pp 1178ndash1187 2010

[5] T YangW-D Chen and T-M Guo ldquoPhase behavior of a near-critical reservoir fluid mixturerdquo Fluid Phase Equilibria vol 128no 1-2 pp 183ndash197 1997

[6] K Luo and T Zhong ldquoA discussion on the layering of near-critical gas condensate in PVT cellrdquo Petroleum Exploration andDevelopment vol 26 no 1 pp 68ndash70 1999

[7] P Shen K Luo X Zheng S Li Z Dai andH Liu ldquoExperimen-tal study of near-critical behavior of gas condensate systemsrdquo inProceedings of the SPE Production and Operations SymposiumSPE 67285 Oklahoma City Okla USA March 2001

[8] X Zheng P Sheng S Li K Luo and Z Dai ldquoExperimentalinvestigation into near-critical phenomena of rich gas conden-sate systemsrdquo inProceedings of the SPE International Oil andGasConference and Exhibition in China (iOGCEC rsquo00) SPE64712pp 459ndash468 Beijing China November 2000

[9] P P Shen X T Zheng S Li K Luo andWY Sun ldquoNear-criticalphenomenal of rich gas condensate system an experimentalinvestigationrdquoActa Petrolei Sinica vol 22 no 3 pp 47ndash51 2001

[10] C-A C Parra and J-C-M E Remolina ldquoExperimental studyand calculations of the near critical behavior of a synthetic fluidin nitrogen injectionrdquo Ciencia Tecnologıa y Futuro vol 3 no 1pp 127ndash137 2005

[11] H-Y Chiu R-F Jung M-J Lee and H-M Lin ldquoVaporndashliquidphase equilibriumbehavior ofmixtures containing supercriticalcarbon dioxide near critical regionrdquo Journal of SupercriticalFluids vol 44 no 3 pp 273ndash278 2008

[12] M N Shehata S-E K Fateen and A Bonilla-PetricioletldquoCritical point calculations of multi-component reservoir fluidsusing nature-inspired metaheuristic algorithmsrdquo Fluid PhaseEquilibria vol 409 pp 280ndash290 2016

[13] H-G Li X-Y Lu and V Yang ldquoA numerical study of fluidinjection and mixing under near-critical conditionsrdquo ActaMechanica Sinica vol 28 no 3 pp 559ndash571 2012

[14] L Mistura ldquoTransport coefficients near a critical point in mul-ticomponent fluid systemsrdquo Il Nuovo Cimento vol 12 no 1 pp35ndash42 1972

[15] J-N Jaubert L Avaullee and C Pierre ldquoIs it still necessaryto measure the minimum miscibility pressurerdquo Industrial ampEngineering Chemistry Research vol 41 no 2 pp 303ndash310 2002

[16] China National Oil and Gas Industry Standards ldquoAnalysis forreservoir fluids physical propertiesrdquo Tech Rep SYT5542-20092009

[17] D-Y Peng and D B Robinson ldquoA new two-constant equationof staterdquo Industrial amp Engineering Chemistry Fundamentals vol15 no 1 pp 59ndash64 1976

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

6 Journal of Chemistry

Table 6 Summary of constant composition expansion experimental data at 1324∘C

Pressure(MPa) Gas volume(mL) Liquid volume(mL) Relative volume(119881119881119889) Retrograde condensate liquid saturation( of 119881

119889)

2553 16023 000 0983 0002448lowast 16308 mdash 1 mdash24 16471 mdash 1009 mdash22 17245 mdash 1057 mdash21 17938 mdash 1099 mdash20 12015 6537 1137 4007919 12785 6375 1175 3908518 14089 6169 1242 3783317 15469 6010 1317 3685215 18853 5763 1509 3533513 24227 5519 1824 3383910 35989 5197 2525 318657 57411 4908 3821 30094lowastSaturation pressuremdash liquid volume is too small and liquid volume is not measured

(a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k)Pressure drop process

Figure 2The critical opalescence phase behavior characteristics in the constant composition expansion experiment at 1324∘C for H2-3 well(a) 2553MPa (b) 25MPa (c) 248MPa (d) 247MPa (e) 246MPa (f) 2448MPa (g) 24MPa (h) 23MPa (i) 20MPa (j) 19MPa and (k)5MPa

Table 7 Summary of constant volume depletion experimental dataat 1324∘C

Pressure(MPa) Retrograde condensateliquid saturation( of 119881

119889)

2553 02448lowast mdash22 mdash20 340417 297714 295811 26838 25225 2129lowastSaturation pressuremdash liquid volume is too small and liquid volume is not measured

Through simulation and calculation of the CVD exper-iment the composition of remaining fluid along with con-densate oil and gas was obtained under different pressures(ranged from 2448MPa (dew point) to 5MPa) and theresults are presented in Tables 9sim11 As is shown in Tables 910 and 11 in the remaining fluid and remaining condensateoil the content of CH

4decreases with decreasing the pres-

sure while in the discharging condensate gas the content ofCH4increases with decreasing the pressure And the content

of 1198622sim119862

6shows a rising trend in the composition of the

remaining fluid remaining condensate oil and dischargingcondensate gas which indicates that once pressure dropsbelow the dew point light hydrocarbons (such as CH

4)

escape from condensate gas system first In the remainingcondensate oil system the content of C

7simC10is up to 7472

and with the decrease of pressure the content of C7simC10

has a slight decrease while the content of C11+

increases

Journal of Chemistry 7

Table 8 Matching results of dew point pressure gas-oil ratio between the experimental data and calculated values

Matching items Experiment Calculation Relative errorDew point pressure(MPa) 2448 2447 0046Gas-oil ratio(m3m3) 869 87112 024

Table 9 Calculated composition of the remaining fluid under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

523 521 519 512 500 480 446 385N2

064 064 063 061 059 055 049 041CH4

5707 5677 5635 5529 5354 5081 4651 3927C2H6

1173 1172 1170 1164 1153 113 1082 976C3H8

622 623 625 63 636 643 645 626iC4H10

107 107 108 110 113 116 121 125nC4H10

176 177 178 182 188 197 209 222iC5H12

121 122 123 127 134 144 158 18nC5H12

109 110 111 115 121 131 146 169C6H14

258 261 266 277 298 330 382 470C7simC8

774 787 806 857 945 1089 1333 178C9simC10

249 254 264 285 323 385 490 688C11+

118 125 132 151 176 219 288 411

Calculated ROVMeasured ROV

5 10 15 20 25 300Pressure (MPa)

00

05

10

15

20

25

30

35

40

Rela

tive v

olum

e

Figure 3 Matching results of relative volume between the experi-mental data and calculated values

which indicates that part of the heavy hydrocarbons (C7simC10)

reevaporate from the condensate oil when depleting to acertain pressure In general with the decrease of pressurethe heavy component shows a rising trend in the remainingfluid

On the basis of composition analysis phase diagramsand retrograde condensate characteristics of reservoir fluidunder different pressures have been simulated and calculatedFigure 6 shows the two-phase boundaries of remaining fluidof different depletion pressure It can be seen from Figure 6that with the decrease of pressure phase diagram becomes

Measured retrograde condensate liquid saturationCalculated retrograde condensate liquid saturation

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

40

5 10 15 20 250Pressure (MPa)

satu

ratio

n (

Vd)

Figure 4 Matching results of retrograde condensate liquid satura-tion between the experimental data and calculated values

more wide and narrow to the right and critical pointmoves tothe lower right And when pressure drops below the 17MPathe critical temperature of the remaining fluid system is abovethe reservoir temperature (1324∘C) and the remaining fluidis considered to shift from condensate gas reservoir systeminto a volatile oil system The variation relationship betweenthe retrograde condensate liquid saturation and pressure isshown in Figure 7 It can be clearly seen that in the remainingfluids at 22MPa 20MPa and 17MPa with the decreaseof pressure the retrograde condensate liquid saturationsincrease at first and then decrease which indicates that theremaining reservoir fluids appear as the phase behavior ofcondensate gas system And when pressure drops below

8 Journal of Chemistry

Table 10 Calculated composition of the remaining condensate oil under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

008 008 008 008 008 008 008N2

000 000 000 000 000 000 000CH4

038 038 038 037 037 036 035C2H6

044 044 044 045 046 047 048C3H8

087 088 090 092 096 102 111iC4H10

039 039 040 041 044 048 053nC4H10

087 088 091 095 101 110 125iC5H12

149 150 154 161 172 187 208nC5H12

170 171 176 183 194 209 229C6H14

841 846 858 879 908 944 973C7simC8

5352 5324 5272 5211 5143 5061 4954C9simC10

2120 2112 2097 2081 2063 2043 2031C11+

1065 1092 1132 1167 1188 1205 1225 there is no remaining condensate oil because the calculated saturation pressure is 2447MPa and the measured saturation pressure is 2448MPa

Table 11 Calculated composition of the discharging condensate gas under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

068 069 071 072 072 072 072N2

608 625 634 631 618 596 557CH4

6252 6393 6518 6582 6592 6534 6350C2H6

1185 1194 1211 1233 1262 1301 1351C3H8

588 582 582 59 608 642 704iC4H10

097 094 093 093 095 101 115nC4H10

154 149 146 145 149 158 182iC5H12

100 095 09 088 089 094 11nC5H12

089 084 079 076 076 081 094C6H14

197 18 163 153 149 154 18C7simC8

503 426 349 297 262 247 27C9simC10

105 071 043 027 017 012 01C11+

053 037 023 015 01 007 006 there is not remaining discharging condensate gas because the calculated saturation pressure is 2447MPa and themeasured saturation pressure is 2448MPa

2-phase boundary5 volume10 volume20 volume

30 volumeCritical pointSaturation pressure

minus100 minus50 0 50 100 150 200 250 300minus150Temperature (∘C)

0

5

10

15

20

25

30

Pres

sure

(MPa

)

Figure 5 Calculated phase diagram of reservoir fluid of H2-3 well

the 17MPa the retrograde condensate liquid saturationsdecrease with decreasing the pressure which indicates thatthe remaining reservoir fluids exhibit the phase behavior ofvolatile oil system

In addition we performed the simulation of phase behav-ior of remaining fluid with CO

2injection and the remaining

fluid at 22MPa is selected Then the remaining fluid wasmixed with CO

2of 20mol 40mol 60mol 70mol

and 80mol respectively The dew point and the retrogradecondensate liquid saturation of the mixed system werecalculated The calculated results are presented in Figures8 and 9 Figures 8 and 9 illustrate that with the increaseof CO

2injected quantity the retrograde condensate liquid

saturation decreases and at 80mol CO2injected quantity

the maximum condensate saturation is only about 247Compared with the original remaining fluid at 22MPathe retrograde condensate liquid saturation is significantlyreduced which explains the reevaporation mechanism of

Journal of Chemistry 9

Critical point trajectory

0

5

10

15

20

25

Pres

sure

(MPa

)

minus100 minus50 0 50 100 150 200 250 300 350 400minus150Temperature (∘C)

2448MPa20MPa14MPa8MPa

22MPa17MPa11MPa5MPa

Figure 6 Calculated two-phase boundaries of resident fluid underdifferent depletion pressures

2448MPa

20MPa

14MPa

8MPa22MPa

17MPa

11MPa

5MPa

Retro

grad

e con

dens

ate l

iqui

d

0102030405060708090

100

5 10 15 20 25 300Temperature (∘C)

satu

ratio

n (

Vd)

Figure 7 Calculated retrograde condensate liquid saturation underdifferent depletion pressures

remaining fluid with CO2injection As to dew point pressure

with the increase of CO2injected quantity the dew point

pressure increases first and then decreases

5 Conclusions

(1) The reservoir fluid of H2-3 well is considered tobe the near-critical condensate gas reservoir systemcombined with the well stream components and 119875-119879phase diagram

(2) In the vicinity of the critical region the reservoirfluid of H2-3 well appears as the ldquocritical opalescencerdquophenomenon and the phenomenon is caused by the

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

5 10 15 20 25 300Pressure (MPa)

80mol CO2

70mol CO2

60mol CO2

40mol CO2

20mol CO2

satu

ratio

n (

Vd)

Figure 8 The variation of calculated retrograde condensate liquidsaturation with CO

2injected quantity

2460

2480

2500

2520

2540

2560

2580

2600

2620D

ew p

oint

pre

ssur

e (M

Pa)

01 02 03 04 05 06 07 08 090CO2 content (mol)

Figure 9 The variation of calculated dew point pressure with CO2

injected quantity

density fluctuations in the gas and liquid molecularmotion during the gas-liquid phase change process

(3) The volume of retrograde condensate liquid satura-tion during the depletion process increases first andthen decreases and when reservoir pressure dropsbelow a certain pressure the variation of retro-grade condensate liquid saturation exhibits the phasebehavior of volatile oil

(4) The reevaporation of remaining fluid consists of twoaspects (1) part of heavy hydrocarbons reevaporatefrom the remaining condensate oil when depleting toa certain pressure (2) the variation characteristics ofretrograde condensate liquid saturation of remainingfluid shift from a condensate gas condensate systeminto a volatile oil system

(5) The recovery of condensate oil and gas is proportionalto the CO

2injected quantity

10 Journal of Chemistry

(6) When implementing CO2injection in the near-

critical condensate gas reservoir the dew point pres-sure of the new mixed fluid system should be takeninto account since it is not simply monotonicallyincreasing or decreasing with the increase of CO

2

injected quantity

Competing Interests

Here all the authors solemnly declare that there are nocompeting interests regarding the publication of this paper

Acknowledgments

The authors wish to acknowledge anonymous reviewersfor constructive comments and suggestions for improvingthis paper The authors also wish to thank the anonymousAssociate Editor for his handling of the paper and addi-tional suggestions This work was supported by Open Fund(PLN1509) of State Key Laboratory of Oil and Gas ReservoirGeology and Exploitation (Southwest Petroleum University)and the Fund of the Department of Education in Sichuan (no15ZB0065)

References

[1] L Sun H Zhao S B Kiselev and C McCabe ldquoPredictingmixture phase equilibria and critical behavior using the SAFT-VRX approachrdquo Journal of Physical Chemistry B vol 109 no 18pp 9047ndash9058 2005

[2] W Yan L-K Wang L-Y Yang and T-M Guo ldquoA systematicexperimental study on the phase behavior of complex fluidmixtures up to near-critical regionrdquo Fluid Phase Equilibria vol190 no 1-2 pp 159ndash178 2001

[3] L Gil J F Martınez-Lopez M Artal et al ldquoVolumetricbehavior of theCO

2(1) +C

2H6(2) system in the subcritical (T =

29315 K) critical and supercritical (T = 30815 K) regionsrdquoTheJournal of Physical Chemistry B vol 114 no 1 pp 5447ndash54692010

[4] A R Bazaev and E A Bazaev ldquoThe thermodynamic propertiesof binary mixtures of technologically important substances inthe near- and supercritical statesrdquo Russian Journal of PhysicalChemistry B vol 4 no 8 pp 1178ndash1187 2010

[5] T YangW-D Chen and T-M Guo ldquoPhase behavior of a near-critical reservoir fluid mixturerdquo Fluid Phase Equilibria vol 128no 1-2 pp 183ndash197 1997

[6] K Luo and T Zhong ldquoA discussion on the layering of near-critical gas condensate in PVT cellrdquo Petroleum Exploration andDevelopment vol 26 no 1 pp 68ndash70 1999

[7] P Shen K Luo X Zheng S Li Z Dai andH Liu ldquoExperimen-tal study of near-critical behavior of gas condensate systemsrdquo inProceedings of the SPE Production and Operations SymposiumSPE 67285 Oklahoma City Okla USA March 2001

[8] X Zheng P Sheng S Li K Luo and Z Dai ldquoExperimentalinvestigation into near-critical phenomena of rich gas conden-sate systemsrdquo inProceedings of the SPE International Oil andGasConference and Exhibition in China (iOGCEC rsquo00) SPE64712pp 459ndash468 Beijing China November 2000

[9] P P Shen X T Zheng S Li K Luo andWY Sun ldquoNear-criticalphenomenal of rich gas condensate system an experimentalinvestigationrdquoActa Petrolei Sinica vol 22 no 3 pp 47ndash51 2001

[10] C-A C Parra and J-C-M E Remolina ldquoExperimental studyand calculations of the near critical behavior of a synthetic fluidin nitrogen injectionrdquo Ciencia Tecnologıa y Futuro vol 3 no 1pp 127ndash137 2005

[11] H-Y Chiu R-F Jung M-J Lee and H-M Lin ldquoVaporndashliquidphase equilibriumbehavior ofmixtures containing supercriticalcarbon dioxide near critical regionrdquo Journal of SupercriticalFluids vol 44 no 3 pp 273ndash278 2008

[12] M N Shehata S-E K Fateen and A Bonilla-PetricioletldquoCritical point calculations of multi-component reservoir fluidsusing nature-inspired metaheuristic algorithmsrdquo Fluid PhaseEquilibria vol 409 pp 280ndash290 2016

[13] H-G Li X-Y Lu and V Yang ldquoA numerical study of fluidinjection and mixing under near-critical conditionsrdquo ActaMechanica Sinica vol 28 no 3 pp 559ndash571 2012

[14] L Mistura ldquoTransport coefficients near a critical point in mul-ticomponent fluid systemsrdquo Il Nuovo Cimento vol 12 no 1 pp35ndash42 1972

[15] J-N Jaubert L Avaullee and C Pierre ldquoIs it still necessaryto measure the minimum miscibility pressurerdquo Industrial ampEngineering Chemistry Research vol 41 no 2 pp 303ndash310 2002

[16] China National Oil and Gas Industry Standards ldquoAnalysis forreservoir fluids physical propertiesrdquo Tech Rep SYT5542-20092009

[17] D-Y Peng and D B Robinson ldquoA new two-constant equationof staterdquo Industrial amp Engineering Chemistry Fundamentals vol15 no 1 pp 59ndash64 1976

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Journal of Chemistry 7

Table 8 Matching results of dew point pressure gas-oil ratio between the experimental data and calculated values

Matching items Experiment Calculation Relative errorDew point pressure(MPa) 2448 2447 0046Gas-oil ratio(m3m3) 869 87112 024

Table 9 Calculated composition of the remaining fluid under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

523 521 519 512 500 480 446 385N2

064 064 063 061 059 055 049 041CH4

5707 5677 5635 5529 5354 5081 4651 3927C2H6

1173 1172 1170 1164 1153 113 1082 976C3H8

622 623 625 63 636 643 645 626iC4H10

107 107 108 110 113 116 121 125nC4H10

176 177 178 182 188 197 209 222iC5H12

121 122 123 127 134 144 158 18nC5H12

109 110 111 115 121 131 146 169C6H14

258 261 266 277 298 330 382 470C7simC8

774 787 806 857 945 1089 1333 178C9simC10

249 254 264 285 323 385 490 688C11+

118 125 132 151 176 219 288 411

Calculated ROVMeasured ROV

5 10 15 20 25 300Pressure (MPa)

00

05

10

15

20

25

30

35

40

Rela

tive v

olum

e

Figure 3 Matching results of relative volume between the experi-mental data and calculated values

which indicates that part of the heavy hydrocarbons (C7simC10)

reevaporate from the condensate oil when depleting to acertain pressure In general with the decrease of pressurethe heavy component shows a rising trend in the remainingfluid

On the basis of composition analysis phase diagramsand retrograde condensate characteristics of reservoir fluidunder different pressures have been simulated and calculatedFigure 6 shows the two-phase boundaries of remaining fluidof different depletion pressure It can be seen from Figure 6that with the decrease of pressure phase diagram becomes

Measured retrograde condensate liquid saturationCalculated retrograde condensate liquid saturation

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

40

5 10 15 20 250Pressure (MPa)

satu

ratio

n (

Vd)

Figure 4 Matching results of retrograde condensate liquid satura-tion between the experimental data and calculated values

more wide and narrow to the right and critical pointmoves tothe lower right And when pressure drops below the 17MPathe critical temperature of the remaining fluid system is abovethe reservoir temperature (1324∘C) and the remaining fluidis considered to shift from condensate gas reservoir systeminto a volatile oil system The variation relationship betweenthe retrograde condensate liquid saturation and pressure isshown in Figure 7 It can be clearly seen that in the remainingfluids at 22MPa 20MPa and 17MPa with the decreaseof pressure the retrograde condensate liquid saturationsincrease at first and then decrease which indicates that theremaining reservoir fluids appear as the phase behavior ofcondensate gas system And when pressure drops below

8 Journal of Chemistry

Table 10 Calculated composition of the remaining condensate oil under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

008 008 008 008 008 008 008N2

000 000 000 000 000 000 000CH4

038 038 038 037 037 036 035C2H6

044 044 044 045 046 047 048C3H8

087 088 090 092 096 102 111iC4H10

039 039 040 041 044 048 053nC4H10

087 088 091 095 101 110 125iC5H12

149 150 154 161 172 187 208nC5H12

170 171 176 183 194 209 229C6H14

841 846 858 879 908 944 973C7simC8

5352 5324 5272 5211 5143 5061 4954C9simC10

2120 2112 2097 2081 2063 2043 2031C11+

1065 1092 1132 1167 1188 1205 1225 there is no remaining condensate oil because the calculated saturation pressure is 2447MPa and the measured saturation pressure is 2448MPa

Table 11 Calculated composition of the discharging condensate gas under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

068 069 071 072 072 072 072N2

608 625 634 631 618 596 557CH4

6252 6393 6518 6582 6592 6534 6350C2H6

1185 1194 1211 1233 1262 1301 1351C3H8

588 582 582 59 608 642 704iC4H10

097 094 093 093 095 101 115nC4H10

154 149 146 145 149 158 182iC5H12

100 095 09 088 089 094 11nC5H12

089 084 079 076 076 081 094C6H14

197 18 163 153 149 154 18C7simC8

503 426 349 297 262 247 27C9simC10

105 071 043 027 017 012 01C11+

053 037 023 015 01 007 006 there is not remaining discharging condensate gas because the calculated saturation pressure is 2447MPa and themeasured saturation pressure is 2448MPa

2-phase boundary5 volume10 volume20 volume

30 volumeCritical pointSaturation pressure

minus100 minus50 0 50 100 150 200 250 300minus150Temperature (∘C)

0

5

10

15

20

25

30

Pres

sure

(MPa

)

Figure 5 Calculated phase diagram of reservoir fluid of H2-3 well

the 17MPa the retrograde condensate liquid saturationsdecrease with decreasing the pressure which indicates thatthe remaining reservoir fluids exhibit the phase behavior ofvolatile oil system

In addition we performed the simulation of phase behav-ior of remaining fluid with CO

2injection and the remaining

fluid at 22MPa is selected Then the remaining fluid wasmixed with CO

2of 20mol 40mol 60mol 70mol

and 80mol respectively The dew point and the retrogradecondensate liquid saturation of the mixed system werecalculated The calculated results are presented in Figures8 and 9 Figures 8 and 9 illustrate that with the increaseof CO

2injected quantity the retrograde condensate liquid

saturation decreases and at 80mol CO2injected quantity

the maximum condensate saturation is only about 247Compared with the original remaining fluid at 22MPathe retrograde condensate liquid saturation is significantlyreduced which explains the reevaporation mechanism of

Journal of Chemistry 9

Critical point trajectory

0

5

10

15

20

25

Pres

sure

(MPa

)

minus100 minus50 0 50 100 150 200 250 300 350 400minus150Temperature (∘C)

2448MPa20MPa14MPa8MPa

22MPa17MPa11MPa5MPa

Figure 6 Calculated two-phase boundaries of resident fluid underdifferent depletion pressures

2448MPa

20MPa

14MPa

8MPa22MPa

17MPa

11MPa

5MPa

Retro

grad

e con

dens

ate l

iqui

d

0102030405060708090

100

5 10 15 20 25 300Temperature (∘C)

satu

ratio

n (

Vd)

Figure 7 Calculated retrograde condensate liquid saturation underdifferent depletion pressures

remaining fluid with CO2injection As to dew point pressure

with the increase of CO2injected quantity the dew point

pressure increases first and then decreases

5 Conclusions

(1) The reservoir fluid of H2-3 well is considered tobe the near-critical condensate gas reservoir systemcombined with the well stream components and 119875-119879phase diagram

(2) In the vicinity of the critical region the reservoirfluid of H2-3 well appears as the ldquocritical opalescencerdquophenomenon and the phenomenon is caused by the

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

5 10 15 20 25 300Pressure (MPa)

80mol CO2

70mol CO2

60mol CO2

40mol CO2

20mol CO2

satu

ratio

n (

Vd)

Figure 8 The variation of calculated retrograde condensate liquidsaturation with CO

2injected quantity

2460

2480

2500

2520

2540

2560

2580

2600

2620D

ew p

oint

pre

ssur

e (M

Pa)

01 02 03 04 05 06 07 08 090CO2 content (mol)

Figure 9 The variation of calculated dew point pressure with CO2

injected quantity

density fluctuations in the gas and liquid molecularmotion during the gas-liquid phase change process

(3) The volume of retrograde condensate liquid satura-tion during the depletion process increases first andthen decreases and when reservoir pressure dropsbelow a certain pressure the variation of retro-grade condensate liquid saturation exhibits the phasebehavior of volatile oil

(4) The reevaporation of remaining fluid consists of twoaspects (1) part of heavy hydrocarbons reevaporatefrom the remaining condensate oil when depleting toa certain pressure (2) the variation characteristics ofretrograde condensate liquid saturation of remainingfluid shift from a condensate gas condensate systeminto a volatile oil system

(5) The recovery of condensate oil and gas is proportionalto the CO

2injected quantity

10 Journal of Chemistry

(6) When implementing CO2injection in the near-

critical condensate gas reservoir the dew point pres-sure of the new mixed fluid system should be takeninto account since it is not simply monotonicallyincreasing or decreasing with the increase of CO

2

injected quantity

Competing Interests

Here all the authors solemnly declare that there are nocompeting interests regarding the publication of this paper

Acknowledgments

The authors wish to acknowledge anonymous reviewersfor constructive comments and suggestions for improvingthis paper The authors also wish to thank the anonymousAssociate Editor for his handling of the paper and addi-tional suggestions This work was supported by Open Fund(PLN1509) of State Key Laboratory of Oil and Gas ReservoirGeology and Exploitation (Southwest Petroleum University)and the Fund of the Department of Education in Sichuan (no15ZB0065)

References

[1] L Sun H Zhao S B Kiselev and C McCabe ldquoPredictingmixture phase equilibria and critical behavior using the SAFT-VRX approachrdquo Journal of Physical Chemistry B vol 109 no 18pp 9047ndash9058 2005

[2] W Yan L-K Wang L-Y Yang and T-M Guo ldquoA systematicexperimental study on the phase behavior of complex fluidmixtures up to near-critical regionrdquo Fluid Phase Equilibria vol190 no 1-2 pp 159ndash178 2001

[3] L Gil J F Martınez-Lopez M Artal et al ldquoVolumetricbehavior of theCO

2(1) +C

2H6(2) system in the subcritical (T =

29315 K) critical and supercritical (T = 30815 K) regionsrdquoTheJournal of Physical Chemistry B vol 114 no 1 pp 5447ndash54692010

[4] A R Bazaev and E A Bazaev ldquoThe thermodynamic propertiesof binary mixtures of technologically important substances inthe near- and supercritical statesrdquo Russian Journal of PhysicalChemistry B vol 4 no 8 pp 1178ndash1187 2010

[5] T YangW-D Chen and T-M Guo ldquoPhase behavior of a near-critical reservoir fluid mixturerdquo Fluid Phase Equilibria vol 128no 1-2 pp 183ndash197 1997

[6] K Luo and T Zhong ldquoA discussion on the layering of near-critical gas condensate in PVT cellrdquo Petroleum Exploration andDevelopment vol 26 no 1 pp 68ndash70 1999

[7] P Shen K Luo X Zheng S Li Z Dai andH Liu ldquoExperimen-tal study of near-critical behavior of gas condensate systemsrdquo inProceedings of the SPE Production and Operations SymposiumSPE 67285 Oklahoma City Okla USA March 2001

[8] X Zheng P Sheng S Li K Luo and Z Dai ldquoExperimentalinvestigation into near-critical phenomena of rich gas conden-sate systemsrdquo inProceedings of the SPE International Oil andGasConference and Exhibition in China (iOGCEC rsquo00) SPE64712pp 459ndash468 Beijing China November 2000

[9] P P Shen X T Zheng S Li K Luo andWY Sun ldquoNear-criticalphenomenal of rich gas condensate system an experimentalinvestigationrdquoActa Petrolei Sinica vol 22 no 3 pp 47ndash51 2001

[10] C-A C Parra and J-C-M E Remolina ldquoExperimental studyand calculations of the near critical behavior of a synthetic fluidin nitrogen injectionrdquo Ciencia Tecnologıa y Futuro vol 3 no 1pp 127ndash137 2005

[11] H-Y Chiu R-F Jung M-J Lee and H-M Lin ldquoVaporndashliquidphase equilibriumbehavior ofmixtures containing supercriticalcarbon dioxide near critical regionrdquo Journal of SupercriticalFluids vol 44 no 3 pp 273ndash278 2008

[12] M N Shehata S-E K Fateen and A Bonilla-PetricioletldquoCritical point calculations of multi-component reservoir fluidsusing nature-inspired metaheuristic algorithmsrdquo Fluid PhaseEquilibria vol 409 pp 280ndash290 2016

[13] H-G Li X-Y Lu and V Yang ldquoA numerical study of fluidinjection and mixing under near-critical conditionsrdquo ActaMechanica Sinica vol 28 no 3 pp 559ndash571 2012

[14] L Mistura ldquoTransport coefficients near a critical point in mul-ticomponent fluid systemsrdquo Il Nuovo Cimento vol 12 no 1 pp35ndash42 1972

[15] J-N Jaubert L Avaullee and C Pierre ldquoIs it still necessaryto measure the minimum miscibility pressurerdquo Industrial ampEngineering Chemistry Research vol 41 no 2 pp 303ndash310 2002

[16] China National Oil and Gas Industry Standards ldquoAnalysis forreservoir fluids physical propertiesrdquo Tech Rep SYT5542-20092009

[17] D-Y Peng and D B Robinson ldquoA new two-constant equationof staterdquo Industrial amp Engineering Chemistry Fundamentals vol15 no 1 pp 59ndash64 1976

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

8 Journal of Chemistry

Table 10 Calculated composition of the remaining condensate oil under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

008 008 008 008 008 008 008N2

000 000 000 000 000 000 000CH4

038 038 038 037 037 036 035C2H6

044 044 044 045 046 047 048C3H8

087 088 090 092 096 102 111iC4H10

039 039 040 041 044 048 053nC4H10

087 088 091 095 101 110 125iC5H12

149 150 154 161 172 187 208nC5H12

170 171 176 183 194 209 229C6H14

841 846 858 879 908 944 973C7simC8

5352 5324 5272 5211 5143 5061 4954C9simC10

2120 2112 2097 2081 2063 2043 2031C11+

1065 1092 1132 1167 1188 1205 1225 there is no remaining condensate oil because the calculated saturation pressure is 2447MPa and the measured saturation pressure is 2448MPa

Table 11 Calculated composition of the discharging condensate gas under different depletion pressures

Component(mol) 2448(MPa) 2200(MPa) 2000(MPa) 1700(MPa) 1400(MPa) 1100(MPa) 800(MPa) 500(MPa)CO2

068 069 071 072 072 072 072N2

608 625 634 631 618 596 557CH4

6252 6393 6518 6582 6592 6534 6350C2H6

1185 1194 1211 1233 1262 1301 1351C3H8

588 582 582 59 608 642 704iC4H10

097 094 093 093 095 101 115nC4H10

154 149 146 145 149 158 182iC5H12

100 095 09 088 089 094 11nC5H12

089 084 079 076 076 081 094C6H14

197 18 163 153 149 154 18C7simC8

503 426 349 297 262 247 27C9simC10

105 071 043 027 017 012 01C11+

053 037 023 015 01 007 006 there is not remaining discharging condensate gas because the calculated saturation pressure is 2447MPa and themeasured saturation pressure is 2448MPa

2-phase boundary5 volume10 volume20 volume

30 volumeCritical pointSaturation pressure

minus100 minus50 0 50 100 150 200 250 300minus150Temperature (∘C)

0

5

10

15

20

25

30

Pres

sure

(MPa

)

Figure 5 Calculated phase diagram of reservoir fluid of H2-3 well

the 17MPa the retrograde condensate liquid saturationsdecrease with decreasing the pressure which indicates thatthe remaining reservoir fluids exhibit the phase behavior ofvolatile oil system

In addition we performed the simulation of phase behav-ior of remaining fluid with CO

2injection and the remaining

fluid at 22MPa is selected Then the remaining fluid wasmixed with CO

2of 20mol 40mol 60mol 70mol

and 80mol respectively The dew point and the retrogradecondensate liquid saturation of the mixed system werecalculated The calculated results are presented in Figures8 and 9 Figures 8 and 9 illustrate that with the increaseof CO

2injected quantity the retrograde condensate liquid

saturation decreases and at 80mol CO2injected quantity

the maximum condensate saturation is only about 247Compared with the original remaining fluid at 22MPathe retrograde condensate liquid saturation is significantlyreduced which explains the reevaporation mechanism of

Journal of Chemistry 9

Critical point trajectory

0

5

10

15

20

25

Pres

sure

(MPa

)

minus100 minus50 0 50 100 150 200 250 300 350 400minus150Temperature (∘C)

2448MPa20MPa14MPa8MPa

22MPa17MPa11MPa5MPa

Figure 6 Calculated two-phase boundaries of resident fluid underdifferent depletion pressures

2448MPa

20MPa

14MPa

8MPa22MPa

17MPa

11MPa

5MPa

Retro

grad

e con

dens

ate l

iqui

d

0102030405060708090

100

5 10 15 20 25 300Temperature (∘C)

satu

ratio

n (

Vd)

Figure 7 Calculated retrograde condensate liquid saturation underdifferent depletion pressures

remaining fluid with CO2injection As to dew point pressure

with the increase of CO2injected quantity the dew point

pressure increases first and then decreases

5 Conclusions

(1) The reservoir fluid of H2-3 well is considered tobe the near-critical condensate gas reservoir systemcombined with the well stream components and 119875-119879phase diagram

(2) In the vicinity of the critical region the reservoirfluid of H2-3 well appears as the ldquocritical opalescencerdquophenomenon and the phenomenon is caused by the

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

5 10 15 20 25 300Pressure (MPa)

80mol CO2

70mol CO2

60mol CO2

40mol CO2

20mol CO2

satu

ratio

n (

Vd)

Figure 8 The variation of calculated retrograde condensate liquidsaturation with CO

2injected quantity

2460

2480

2500

2520

2540

2560

2580

2600

2620D

ew p

oint

pre

ssur

e (M

Pa)

01 02 03 04 05 06 07 08 090CO2 content (mol)

Figure 9 The variation of calculated dew point pressure with CO2

injected quantity

density fluctuations in the gas and liquid molecularmotion during the gas-liquid phase change process

(3) The volume of retrograde condensate liquid satura-tion during the depletion process increases first andthen decreases and when reservoir pressure dropsbelow a certain pressure the variation of retro-grade condensate liquid saturation exhibits the phasebehavior of volatile oil

(4) The reevaporation of remaining fluid consists of twoaspects (1) part of heavy hydrocarbons reevaporatefrom the remaining condensate oil when depleting toa certain pressure (2) the variation characteristics ofretrograde condensate liquid saturation of remainingfluid shift from a condensate gas condensate systeminto a volatile oil system

(5) The recovery of condensate oil and gas is proportionalto the CO

2injected quantity

10 Journal of Chemistry

(6) When implementing CO2injection in the near-

critical condensate gas reservoir the dew point pres-sure of the new mixed fluid system should be takeninto account since it is not simply monotonicallyincreasing or decreasing with the increase of CO

2

injected quantity

Competing Interests

Here all the authors solemnly declare that there are nocompeting interests regarding the publication of this paper

Acknowledgments

The authors wish to acknowledge anonymous reviewersfor constructive comments and suggestions for improvingthis paper The authors also wish to thank the anonymousAssociate Editor for his handling of the paper and addi-tional suggestions This work was supported by Open Fund(PLN1509) of State Key Laboratory of Oil and Gas ReservoirGeology and Exploitation (Southwest Petroleum University)and the Fund of the Department of Education in Sichuan (no15ZB0065)

References

[1] L Sun H Zhao S B Kiselev and C McCabe ldquoPredictingmixture phase equilibria and critical behavior using the SAFT-VRX approachrdquo Journal of Physical Chemistry B vol 109 no 18pp 9047ndash9058 2005

[2] W Yan L-K Wang L-Y Yang and T-M Guo ldquoA systematicexperimental study on the phase behavior of complex fluidmixtures up to near-critical regionrdquo Fluid Phase Equilibria vol190 no 1-2 pp 159ndash178 2001

[3] L Gil J F Martınez-Lopez M Artal et al ldquoVolumetricbehavior of theCO

2(1) +C

2H6(2) system in the subcritical (T =

29315 K) critical and supercritical (T = 30815 K) regionsrdquoTheJournal of Physical Chemistry B vol 114 no 1 pp 5447ndash54692010

[4] A R Bazaev and E A Bazaev ldquoThe thermodynamic propertiesof binary mixtures of technologically important substances inthe near- and supercritical statesrdquo Russian Journal of PhysicalChemistry B vol 4 no 8 pp 1178ndash1187 2010

[5] T YangW-D Chen and T-M Guo ldquoPhase behavior of a near-critical reservoir fluid mixturerdquo Fluid Phase Equilibria vol 128no 1-2 pp 183ndash197 1997

[6] K Luo and T Zhong ldquoA discussion on the layering of near-critical gas condensate in PVT cellrdquo Petroleum Exploration andDevelopment vol 26 no 1 pp 68ndash70 1999

[7] P Shen K Luo X Zheng S Li Z Dai andH Liu ldquoExperimen-tal study of near-critical behavior of gas condensate systemsrdquo inProceedings of the SPE Production and Operations SymposiumSPE 67285 Oklahoma City Okla USA March 2001

[8] X Zheng P Sheng S Li K Luo and Z Dai ldquoExperimentalinvestigation into near-critical phenomena of rich gas conden-sate systemsrdquo inProceedings of the SPE International Oil andGasConference and Exhibition in China (iOGCEC rsquo00) SPE64712pp 459ndash468 Beijing China November 2000

[9] P P Shen X T Zheng S Li K Luo andWY Sun ldquoNear-criticalphenomenal of rich gas condensate system an experimentalinvestigationrdquoActa Petrolei Sinica vol 22 no 3 pp 47ndash51 2001

[10] C-A C Parra and J-C-M E Remolina ldquoExperimental studyand calculations of the near critical behavior of a synthetic fluidin nitrogen injectionrdquo Ciencia Tecnologıa y Futuro vol 3 no 1pp 127ndash137 2005

[11] H-Y Chiu R-F Jung M-J Lee and H-M Lin ldquoVaporndashliquidphase equilibriumbehavior ofmixtures containing supercriticalcarbon dioxide near critical regionrdquo Journal of SupercriticalFluids vol 44 no 3 pp 273ndash278 2008

[12] M N Shehata S-E K Fateen and A Bonilla-PetricioletldquoCritical point calculations of multi-component reservoir fluidsusing nature-inspired metaheuristic algorithmsrdquo Fluid PhaseEquilibria vol 409 pp 280ndash290 2016

[13] H-G Li X-Y Lu and V Yang ldquoA numerical study of fluidinjection and mixing under near-critical conditionsrdquo ActaMechanica Sinica vol 28 no 3 pp 559ndash571 2012

[14] L Mistura ldquoTransport coefficients near a critical point in mul-ticomponent fluid systemsrdquo Il Nuovo Cimento vol 12 no 1 pp35ndash42 1972

[15] J-N Jaubert L Avaullee and C Pierre ldquoIs it still necessaryto measure the minimum miscibility pressurerdquo Industrial ampEngineering Chemistry Research vol 41 no 2 pp 303ndash310 2002

[16] China National Oil and Gas Industry Standards ldquoAnalysis forreservoir fluids physical propertiesrdquo Tech Rep SYT5542-20092009

[17] D-Y Peng and D B Robinson ldquoA new two-constant equationof staterdquo Industrial amp Engineering Chemistry Fundamentals vol15 no 1 pp 59ndash64 1976

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Journal of Chemistry 9

Critical point trajectory

0

5

10

15

20

25

Pres

sure

(MPa

)

minus100 minus50 0 50 100 150 200 250 300 350 400minus150Temperature (∘C)

2448MPa20MPa14MPa8MPa

22MPa17MPa11MPa5MPa

Figure 6 Calculated two-phase boundaries of resident fluid underdifferent depletion pressures

2448MPa

20MPa

14MPa

8MPa22MPa

17MPa

11MPa

5MPa

Retro

grad

e con

dens

ate l

iqui

d

0102030405060708090

100

5 10 15 20 25 300Temperature (∘C)

satu

ratio

n (

Vd)

Figure 7 Calculated retrograde condensate liquid saturation underdifferent depletion pressures

remaining fluid with CO2injection As to dew point pressure

with the increase of CO2injected quantity the dew point

pressure increases first and then decreases

5 Conclusions

(1) The reservoir fluid of H2-3 well is considered tobe the near-critical condensate gas reservoir systemcombined with the well stream components and 119875-119879phase diagram

(2) In the vicinity of the critical region the reservoirfluid of H2-3 well appears as the ldquocritical opalescencerdquophenomenon and the phenomenon is caused by the

Retro

grad

e con

dens

ate l

iqui

d

0

5

10

15

20

25

30

35

5 10 15 20 25 300Pressure (MPa)

80mol CO2

70mol CO2

60mol CO2

40mol CO2

20mol CO2

satu

ratio

n (

Vd)

Figure 8 The variation of calculated retrograde condensate liquidsaturation with CO

2injected quantity

2460

2480

2500

2520

2540

2560

2580

2600

2620D

ew p

oint

pre

ssur

e (M

Pa)

01 02 03 04 05 06 07 08 090CO2 content (mol)

Figure 9 The variation of calculated dew point pressure with CO2

injected quantity

density fluctuations in the gas and liquid molecularmotion during the gas-liquid phase change process

(3) The volume of retrograde condensate liquid satura-tion during the depletion process increases first andthen decreases and when reservoir pressure dropsbelow a certain pressure the variation of retro-grade condensate liquid saturation exhibits the phasebehavior of volatile oil

(4) The reevaporation of remaining fluid consists of twoaspects (1) part of heavy hydrocarbons reevaporatefrom the remaining condensate oil when depleting toa certain pressure (2) the variation characteristics ofretrograde condensate liquid saturation of remainingfluid shift from a condensate gas condensate systeminto a volatile oil system

(5) The recovery of condensate oil and gas is proportionalto the CO

2injected quantity

10 Journal of Chemistry

(6) When implementing CO2injection in the near-

critical condensate gas reservoir the dew point pres-sure of the new mixed fluid system should be takeninto account since it is not simply monotonicallyincreasing or decreasing with the increase of CO

2

injected quantity

Competing Interests

Here all the authors solemnly declare that there are nocompeting interests regarding the publication of this paper

Acknowledgments

The authors wish to acknowledge anonymous reviewersfor constructive comments and suggestions for improvingthis paper The authors also wish to thank the anonymousAssociate Editor for his handling of the paper and addi-tional suggestions This work was supported by Open Fund(PLN1509) of State Key Laboratory of Oil and Gas ReservoirGeology and Exploitation (Southwest Petroleum University)and the Fund of the Department of Education in Sichuan (no15ZB0065)

References

[1] L Sun H Zhao S B Kiselev and C McCabe ldquoPredictingmixture phase equilibria and critical behavior using the SAFT-VRX approachrdquo Journal of Physical Chemistry B vol 109 no 18pp 9047ndash9058 2005

[2] W Yan L-K Wang L-Y Yang and T-M Guo ldquoA systematicexperimental study on the phase behavior of complex fluidmixtures up to near-critical regionrdquo Fluid Phase Equilibria vol190 no 1-2 pp 159ndash178 2001

[3] L Gil J F Martınez-Lopez M Artal et al ldquoVolumetricbehavior of theCO

2(1) +C

2H6(2) system in the subcritical (T =

29315 K) critical and supercritical (T = 30815 K) regionsrdquoTheJournal of Physical Chemistry B vol 114 no 1 pp 5447ndash54692010

[4] A R Bazaev and E A Bazaev ldquoThe thermodynamic propertiesof binary mixtures of technologically important substances inthe near- and supercritical statesrdquo Russian Journal of PhysicalChemistry B vol 4 no 8 pp 1178ndash1187 2010

[5] T YangW-D Chen and T-M Guo ldquoPhase behavior of a near-critical reservoir fluid mixturerdquo Fluid Phase Equilibria vol 128no 1-2 pp 183ndash197 1997

[6] K Luo and T Zhong ldquoA discussion on the layering of near-critical gas condensate in PVT cellrdquo Petroleum Exploration andDevelopment vol 26 no 1 pp 68ndash70 1999

[7] P Shen K Luo X Zheng S Li Z Dai andH Liu ldquoExperimen-tal study of near-critical behavior of gas condensate systemsrdquo inProceedings of the SPE Production and Operations SymposiumSPE 67285 Oklahoma City Okla USA March 2001

[8] X Zheng P Sheng S Li K Luo and Z Dai ldquoExperimentalinvestigation into near-critical phenomena of rich gas conden-sate systemsrdquo inProceedings of the SPE International Oil andGasConference and Exhibition in China (iOGCEC rsquo00) SPE64712pp 459ndash468 Beijing China November 2000

[9] P P Shen X T Zheng S Li K Luo andWY Sun ldquoNear-criticalphenomenal of rich gas condensate system an experimentalinvestigationrdquoActa Petrolei Sinica vol 22 no 3 pp 47ndash51 2001

[10] C-A C Parra and J-C-M E Remolina ldquoExperimental studyand calculations of the near critical behavior of a synthetic fluidin nitrogen injectionrdquo Ciencia Tecnologıa y Futuro vol 3 no 1pp 127ndash137 2005

[11] H-Y Chiu R-F Jung M-J Lee and H-M Lin ldquoVaporndashliquidphase equilibriumbehavior ofmixtures containing supercriticalcarbon dioxide near critical regionrdquo Journal of SupercriticalFluids vol 44 no 3 pp 273ndash278 2008

[12] M N Shehata S-E K Fateen and A Bonilla-PetricioletldquoCritical point calculations of multi-component reservoir fluidsusing nature-inspired metaheuristic algorithmsrdquo Fluid PhaseEquilibria vol 409 pp 280ndash290 2016

[13] H-G Li X-Y Lu and V Yang ldquoA numerical study of fluidinjection and mixing under near-critical conditionsrdquo ActaMechanica Sinica vol 28 no 3 pp 559ndash571 2012

[14] L Mistura ldquoTransport coefficients near a critical point in mul-ticomponent fluid systemsrdquo Il Nuovo Cimento vol 12 no 1 pp35ndash42 1972

[15] J-N Jaubert L Avaullee and C Pierre ldquoIs it still necessaryto measure the minimum miscibility pressurerdquo Industrial ampEngineering Chemistry Research vol 41 no 2 pp 303ndash310 2002

[16] China National Oil and Gas Industry Standards ldquoAnalysis forreservoir fluids physical propertiesrdquo Tech Rep SYT5542-20092009

[17] D-Y Peng and D B Robinson ldquoA new two-constant equationof staterdquo Industrial amp Engineering Chemistry Fundamentals vol15 no 1 pp 59ndash64 1976

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

10 Journal of Chemistry

(6) When implementing CO2injection in the near-

critical condensate gas reservoir the dew point pres-sure of the new mixed fluid system should be takeninto account since it is not simply monotonicallyincreasing or decreasing with the increase of CO

2

injected quantity

Competing Interests

Here all the authors solemnly declare that there are nocompeting interests regarding the publication of this paper

Acknowledgments

The authors wish to acknowledge anonymous reviewersfor constructive comments and suggestions for improvingthis paper The authors also wish to thank the anonymousAssociate Editor for his handling of the paper and addi-tional suggestions This work was supported by Open Fund(PLN1509) of State Key Laboratory of Oil and Gas ReservoirGeology and Exploitation (Southwest Petroleum University)and the Fund of the Department of Education in Sichuan (no15ZB0065)

References

[1] L Sun H Zhao S B Kiselev and C McCabe ldquoPredictingmixture phase equilibria and critical behavior using the SAFT-VRX approachrdquo Journal of Physical Chemistry B vol 109 no 18pp 9047ndash9058 2005

[2] W Yan L-K Wang L-Y Yang and T-M Guo ldquoA systematicexperimental study on the phase behavior of complex fluidmixtures up to near-critical regionrdquo Fluid Phase Equilibria vol190 no 1-2 pp 159ndash178 2001

[3] L Gil J F Martınez-Lopez M Artal et al ldquoVolumetricbehavior of theCO

2(1) +C

2H6(2) system in the subcritical (T =

29315 K) critical and supercritical (T = 30815 K) regionsrdquoTheJournal of Physical Chemistry B vol 114 no 1 pp 5447ndash54692010

[4] A R Bazaev and E A Bazaev ldquoThe thermodynamic propertiesof binary mixtures of technologically important substances inthe near- and supercritical statesrdquo Russian Journal of PhysicalChemistry B vol 4 no 8 pp 1178ndash1187 2010

[5] T YangW-D Chen and T-M Guo ldquoPhase behavior of a near-critical reservoir fluid mixturerdquo Fluid Phase Equilibria vol 128no 1-2 pp 183ndash197 1997

[6] K Luo and T Zhong ldquoA discussion on the layering of near-critical gas condensate in PVT cellrdquo Petroleum Exploration andDevelopment vol 26 no 1 pp 68ndash70 1999

[7] P Shen K Luo X Zheng S Li Z Dai andH Liu ldquoExperimen-tal study of near-critical behavior of gas condensate systemsrdquo inProceedings of the SPE Production and Operations SymposiumSPE 67285 Oklahoma City Okla USA March 2001

[8] X Zheng P Sheng S Li K Luo and Z Dai ldquoExperimentalinvestigation into near-critical phenomena of rich gas conden-sate systemsrdquo inProceedings of the SPE International Oil andGasConference and Exhibition in China (iOGCEC rsquo00) SPE64712pp 459ndash468 Beijing China November 2000

[9] P P Shen X T Zheng S Li K Luo andWY Sun ldquoNear-criticalphenomenal of rich gas condensate system an experimentalinvestigationrdquoActa Petrolei Sinica vol 22 no 3 pp 47ndash51 2001

[10] C-A C Parra and J-C-M E Remolina ldquoExperimental studyand calculations of the near critical behavior of a synthetic fluidin nitrogen injectionrdquo Ciencia Tecnologıa y Futuro vol 3 no 1pp 127ndash137 2005

[11] H-Y Chiu R-F Jung M-J Lee and H-M Lin ldquoVaporndashliquidphase equilibriumbehavior ofmixtures containing supercriticalcarbon dioxide near critical regionrdquo Journal of SupercriticalFluids vol 44 no 3 pp 273ndash278 2008

[12] M N Shehata S-E K Fateen and A Bonilla-PetricioletldquoCritical point calculations of multi-component reservoir fluidsusing nature-inspired metaheuristic algorithmsrdquo Fluid PhaseEquilibria vol 409 pp 280ndash290 2016

[13] H-G Li X-Y Lu and V Yang ldquoA numerical study of fluidinjection and mixing under near-critical conditionsrdquo ActaMechanica Sinica vol 28 no 3 pp 559ndash571 2012

[14] L Mistura ldquoTransport coefficients near a critical point in mul-ticomponent fluid systemsrdquo Il Nuovo Cimento vol 12 no 1 pp35ndash42 1972

[15] J-N Jaubert L Avaullee and C Pierre ldquoIs it still necessaryto measure the minimum miscibility pressurerdquo Industrial ampEngineering Chemistry Research vol 41 no 2 pp 303ndash310 2002

[16] China National Oil and Gas Industry Standards ldquoAnalysis forreservoir fluids physical propertiesrdquo Tech Rep SYT5542-20092009

[17] D-Y Peng and D B Robinson ldquoA new two-constant equationof staterdquo Industrial amp Engineering Chemistry Fundamentals vol15 no 1 pp 59ndash64 1976

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of