SPE 10127

A Method to Determand Its Applications

by Jose L. Bashbush, * PEMEX-National University of Mexico

●Member SPE.AIME

C) Copy.lghl 1981, Society of Petroleum Engineers of Al ME

This paper was presented at the 56th Annual Fall Technical Conferel,ca and Exhibition of the Society of Petroleum Engineers of AIME, held inSan Antonio, Texas, October 5.7, 1981. The material is subject to correction by the author. Permission to copy is restricted to an abstract ofnot more than 300 words. Write: 6200 N. Central Expressway, Dallas, Texas 75206.

ABSTRACT1

.— Equilibrium Ratios. Various nomograms andcorrelations have been developed, modified

P.etrograde condensate reservoirs and and refined to simplify the volumixtouavolatile oil reservoirs are not amenable to calculation implied in the proposed trialbe studied using traditional material and error procedures.balance methods and simulation techniques.To analize these “variable composition As the result of drilling deeper andhotte.rreservoirs” , it is necessary to obtain a horizons, the number of variable compositionconsistent and reliable set of K-values reservoirs has increased considerably duringwhich might be capable of reproducing the the last few years. These reservoirs, oftenphase behavior of the fluids within the found at temperatures near the criticalreservoir, temperature of the mixture of hydrocarbons

they contain, present a behavior that pr~This paper presents a simple and pract~ vents the use of traditional methods common

cal material balance method by which liquid ly applied in moat reservoirs. The need fo~compositions, K-values and molecular better precision in the forecasting of theweights of the heavy fraction in the liquid behavior of these kinds of reservoirs comp~at different pressures are calculated, based sitional material balance methods7 and comon the data available in a constant volumedepletion lab analysis. Results of the

positional finite difference simulators w~redeveloped.

analyses of three PVT studies are discussedalong with guidelines to evaluate the The fluids of these reservoirs aregoodness of reported experimental data and characterized by having considerable amountsways to correct inconsistencies commonlyfound in the reports.

of intermediate hydrocarbons (C2-C6). Tables1 and 2 present the consolidated compositional analysis of 19 of these reservoirs. The

The corrected K-value table generated Cr,nposition of these fluids and the tempe~

with the method can be directly used in a ature of the reservoirs they are found in,compositional study to predict the reservoir are the reasons for obtaining large retrobehavior. Another use involves the applic~ grade condensations from the gases and h~ghtion of the metliod as a necessary preamble shrinkage in liquid volumes from the oils.to the adjustment of the parameters of anequation of state. This practice will avoid Figure 1 depicts the retrogradethe great deal of time spent in unsucces~ condensate curves obtained in the lab forful attempts to match inconsistent inform~ several of the fluids of Table 1. Figure 2tion includes the liquid phase volum~ curves (re

lated to the volume occupied at the bubble–

INTRODUCTIONpoint) for seven of the volatile oils ofTable 2. The curve of a light black oilwith a bubble point formation volume factor

Several articlesl$2~3$4 and books 5’6 have of 1.6 is also included for comparison. Thedealt with the problem of predicting the difference between this fairly light blackbehavior of reservoirs containing variable oil and the volatile oils is quite evident.composition fluids (volatile oils andretrograde condensate gases), The end The increased sophistication in theresult of all the predictions is the obtai; predictive techniques for these kinds ofment of a consistent set of K-values or reservoirs, underlines the need for a

References and illustrations at end of paper.

2 A METHOD TO DETERMINE K-VALUES FROM LABORATORY DATA AND ITS APPLICATIONS SPE 10127-_-—

procedure that is able to determine K-values PVT cell.capable of reproducing the observed behaviorof fluid samples in the laboratory. Dykstra For volatile oils it is also necessaryand Mueller8published a method that corre- to know the molecular weight of the originallates K-values versus pressure and the char fluid, as well as its density at the bubbleacterization factor of each component. Thi; point pressure.method was successfully used for theprediction of phase behavior in gas injection The analysis of the set of K-valuesprocesses in spite that the correlating obtained in this manner provides the followequation assumes an ideal solution behavior ing additional advantages:and also that the vapor phase follows theperfect gas lawg. Subsequent modifications By plotting the K-values versus pressureto this methodlo~ll have made it suitable it is possible to analize the quality offor its use in the simulation of variable the experimental data. Incorrect meacomposition reservoirs. surements will show as “humps” or –

“inflections” in the K-value curves.Jones and Erbar12 presented a computer

oriented algorithm that adjusts an initially -The method allows to correct the exper~

estimated set of K-values by means of tran~ mental errors by visually altering the

lation andjor rotation of the curves. TheK-values or, in a more adequate form,by

initial estimate is made through the use ofselectively altering the compositions

polynomial approximations to published data13.reported by the lab.

Normal boiling points of the heavy components - Even if an equation of state is utilizedare also required in the characterization the method allows to first check if theprocess. PVT results are internally consistent.

If they are not, the application of, theIn a more rigorous way, several methods procedure will render a consistent set

based upon the use of two and three-parameter of K-values. This precaution will avoidequations of state (EOS) have been developed. the great deal of time and difficultyThe most commonly used EOS are the numerous involved in useless or impossible matchmodifications to the Redlich-Kwongl” EOS es to incorrect data.and the Peng-Robinson15 EOS. A recent publ~cation16 summarizes most of these equations. The first stage of a constant volume

depletion test will be briefly reviewed,The use of EOS in phase behavior calc~

lationssince this test is the basic source of info~

presents several advantages over mation for the method.other methods by reducing the use of empir~cal correlations and allowing the calculation of a consistent set of physical prope~ CONSTANT VOLUME DEPLETION TF.STties. Furthermore, once the parameters ofthe equation are adjusted, it is theoretical A constant volume depletion test consistpossible to calculate the whole two-phase of a series of expansions tit constant composjenvelope knowing only the initial fluid tion, equilibrations at constant presure andcomposition. The problem arises during the then withdrawals again at constant pressureadjustment of the equation to experimental all .~f them carried out at reservoir tempers

lab data. The large number of parameters ture. The gas withdrawn from the cell isand the ample range of variation of some of analized and its amount and compositionthem, makes it difficult to know if the match measured.is unique or if it applies to the whole rangeof interest. Figure 3 schematically presents the

first step of a test performed on a sampleA simple and practical method for the of the Gas Condensate ‘8A”. Figure 3a, shows

exact calculation of K-values of a hydroca~ the initial conditions of the cell at thebon mixture with nitrogen, carbon dioxide dew point pressure of 6720 psig. The volumeand/or hydrogen sulfide is presented. The VI occupied by the sample at the saturationinformation required is available in a pressure serves as the basis for the entireroutine constant volume PVT compositional test. Figure 3b represents the end of theanalysis, that is: first expansion. In this case the pressure in

the cell has decreased to 5800 psig. TheInitial fluid composition at the volume of the sample in the cell V2 is pr~saturation pressure, portional to the plz relationships:

Composition of the gas effluentdisplaced during each pressure PI 22

decrement, ‘2 ‘;l@... (1)

Gas deviation factor,

Amount of gas displaced in each step,‘2 =

1.0656 Vl ... (2)and

Volume of the liquid phase in the

SPE 10127 JOSE L. BASHBUSH 3

The two-phase deviation factors are used 3. The number of moles of the vapor phasein this calculation since there are two Ng . is calculated by the application ofphases present in the cell below the satur~ th~ real gas law. The volume of thetion pressure. The first stage is concluded gaseous phase is the difference betweenwith a constant pressure production of the the initial cell volume VI and the volumegas phase G2, until the volume of the sample occupied by the liquid (RLVj) at theis reduced to the original volume VI. See corresponding pressure.Figure 3c. In this test tk,e retrogradecondensate occupies 7.~0% of “Vll and consg The number of moles of the liquid phasequently the gas G2 occupies 92.20% of V . (N~j) is the difference between Nj and

The moles of G2 gas produced are 6.193%1 of Ng..the moles originally present in the cell at J

the saturation pressure. As a way of checking the accuracy of theexperimental data, it is convenient to

The procedure is repeated in succesive calculate the two-phase deviation factorstages until a minimum test pressure is

~~~ $ es for condensates12commonly reported in the PVT

reached (generally 700 psig). For this .pressure, the composition of the gas phase aswell as the composition of the retrograde 4. The number of moles withdrawn in eachliquid remaining in the cell are reported. depletion stage S. ia obtained as a

function of the aAount of mass producedTable 3 contains the corrected compos~ in two succeeding stages.

tional analysis of a depletion study perfo~med dn a sample of Gas Condensate A. The following two steps are applied to each

component or pseudo-component included in theFor a volatile oil, the procedure is PVT analysis:

identical, but in this case the initialpressure is the bubble point pressure and the 5. A material balance for each one of thecell contains liquid and not gas. components renders the equation:

Initial moles of = Noles of ith comp~

DESCRIPTION OF THE METHOD ith component nent in the vaporphase

The equations are developed in AppendixA. Moles of ith comp~ Moles produced

The method consists on the application+ nent in the liquid + of the ith

of a material balance to the moles of fluidphase component ... (3)

originally present in the cell at the satur~tion pressure, (bubble point for an oil or

The above equation is solved in terms of

dew point for a gas). The objective is tothe mol fraction of the ith component in

obtain the liquid composition in the cellthe liquid phase xi, that is the only

with can be used, along with the gas compos~unk~own remaining.

tion obtained in the lab, to calculate theK-values.

6. The equilibrium ratio of the ith component K. at the corresponding pressure—is

The procedure is divided into eightobtain;d dividing the mol fraction of

steps:the ith component in the vapor phase(reported in the PVT analysis) by the mol

1. In the first step the total number offraction of the ith component in the

moles NT in the system is obtained. Thi sliquid phaae calculated in step 5 above.

number 1s a function of the initial cel 17volume V1. However, dcring the calcul~ “

Once all the equilibrium ratios have bee]

tion procedure the volume cancels outcalculated it is convenient to extrap~

and does not enter into the equations.late the curves to obtain the K-valuescorresponding to the saturation pressure

For a volatile oil it is necessary to(either bubble point or dew point). The

know the density at the bubble point and theextrapolated values can be then correcte~

apparent molecular weight of the originalto satisfy the corresponding limitation

reservoir fluid. For a retrograde condensate ,at this pressure, i.e.:

the dew point and the deviation factor su~fice, since the real gas law can be applied.

The sum of the mole concentrations forthe first drop of dew (for gases) or for

Steps 2 through 6 are repeatedlythe first bubble of gas (for oils) shoul~be exactly one.

applied for each depletion level for which anana’lysis of the produced gas is available.

8. The last step consist of the calculation

2. The number of moles remaining in theof the molecular weight of the C7+ fras

cell N. are obtained as a function oftion in the liquid. The molecul~r weight

the amaunt of mass produced up to aand the number of moles of the fluid at

given depletion level (WSPj).the saturation pressure (step 1) areknown. Therefore it is possible to calcy

4 A METHOD TO DETERMINE K-VALUES FROM LABOFQiTORYDATA AND ITS APPLICATIONS SPE 10127

late the mass originally in the cell. than about one percent.This mas is partitioned into a vaporand liquid phases, with the molecular

Another useful plot* can be generated

weight of the vapor phase being measuredwith the calculated liquid compositions

in the test. Then it is possible to vereus pressure. Again, unexpected humps

calculate the molecular weight and the in the curves would be indicative of

mass of the vapor phase. experimental errors.

The most important and sensitive checkSubtracting the mass of the vapor phase on the consistency of the experimentalfrom the total mass in the cell at the data is a plot of the K-values obtainedbeginning of the corresponding depletion through this procedure (step 6) versusstage, the mass of the liquid phase is pressure. The curves should plot in aobtained. Finally, with the composition(step 5), number of moles (step 3), and

parallel-like trend with no humps orcrossings. The upper curve (higer K-va~

mass of the liquid phase in the cell ues) should correspond to nitrogen,known, it is possible to calculate both, followed by the curves of methane andthe molecular weight of the liquid, and carbon dioxide. Then, either the curvethe molecular weight of the C7+ fraction of ethane or the curve of hydrogen SU1in the liquid. fide (depending on the fluid composition

and reservoir temperature). Underneath,the curves of the rest of the components

CONSISTENCY OF THE EXPERIMENTAL DATA should plot, in order of their molecularweights. The K-values of isobutane and

The consistency of the experimental iso-pentane should always be higher thandata can be revised in several ways. the ones corresponding to the “normal”

components.The first check can be easily done by

plotting* the composition of the produced gasversus pressure. Smooth curves should be the APPLICATIONSnorm. Humps in the plot will usually be anindication of experimental error. To il~tistrate the utilization of the

method, a discussion of t’ne characterizationFor gas-condensate fluids this plot can of three of the ?luids in Tables 1 and 2

be extended to the dew point pressure utili~ follows.ing the composition of the fluid at the dewpoint. However, for volatile oils the plotcan not be extended to the bubble point by CASE 1. GAS CONDENSATE “A”means of the composition of the fluid at thebubble point (a very common mistake). The Gas-Condensate “A” is in a hot (273”F),composition of the first “bubble” of gas deep (15 000’) reservoir with an originsl(consistent with the rest of the data in the pressure over 1 000 psi above the dew pointplot) is very different from the composition pressure. Bottom hole samples were collectedof the oil in the cell at the bubble point. and analized. The maximum retrograde condens~This is the case even for oils near the tion of 19.4 percent of hydrocarbon porecritical conditions. Therefore, the gas comp~ space occurred at a pressure of 31OO psig.sition obtained in the extrapolation of the Table 3 contains the corrected compositionalK-values (step 7) should be used in this case analysis of a constant volume depletion study

at the reservoir temperature. Table 4 has theA second check applicable to retrograde concentrations, modified in Table 3, thatcondensate gases is by means of the two were originally reported by the lab.-phase deviation factor. The calculatedvalues (step 3) should not differ in When the procedure was applied to themore than a unit in the third decimal original data and the K-values were plotted,place in all instances. This condition a few inconsistencies were apparent. Figureis not severe, therefore, satisfying it 4 shows the K-value curves that were thoughtis not a conclusive proof of consistency to indicate errors in the experimental inforof the experimental data, mation. The most notorious are the crossove~s

All of the compositional PVT reports, shown by the curves for iso-butane and normal

include the analysis of the liquid butane, and the ones shown by the curves of

remaining in the cell at the end of the ethane and hydrogen sulfide.

las depletion stage. This compositionshould be compared against the calcula To correct those curves the concentr~

ted composition (step 5). For most – ties originally reported by the lab we~e

components with initial mole conce~ modified until a set of smooth K-value curves

trations greated than 0,4 percent, the was obtained. It wae necessary to make 19

difference between the calculated andchanges of which 12 were beyond the exper~

the measured compositions should be less mental occuracy. Of the other seven, onlyfour resulted in changes greater than one

* semilog coordinate paper

SPE 10127 JOSE L. BASHBUSH 5

percent (and less than one and a half percent) CASE 3. GAS CONDENSATE IIB,!

of the original concentrations.As a contrast to the former two instance~

Table 5 and Figure 5 contain the CalC~ this case is presented to show the usefulnesslated compositions of the retrograde liquid of the procedu?e not only in the characterizecondensed in the cell for each pressure tion of a fluid but also in correcting exper~level. Included in Table 5 is a list ot the mental information inadequately obtained orcalculated two-phase deviation factors. reported.Evidently there is an excellent matchbetween the values measured in the lab and As the basis for an urgent simulationthe ones calculated by this procedure. The study, a first attempt to characterize thecomposition of the first drop of dew, is fluid of Gas Condensate “B” by the methodshown in Table 5 as the composition of theliquid at the dew point of 6720 psig.

presented in this paper failed. Several ofthe calculated compositions for the retrograchliquid were negative and consequently, the

Table 6 shows the calculated equilibrium K-values as well. A thorough analysis of theratios graphically displayed in Figure 6. The information and the calculations, pointed outK-values at the dew point are extrapolations that the major source of error was probablyof the trend shown by the rest of the curves. the original fluid composition. (First columnActually, four different extrapolating of Table 8). The method was applied inequations combined with four different ways several instances until a consistent set ofof forcing the extrapolated values to sat- K-value curves was obtained. The calculatedisfy the dew point condition were used. initial composition after seven trials isTherefore, the numbers on the second columns shown in the second column of Table 8. Withof Tables 5 and 6 were chosen out of 16 these numbers and the calculated K-valuespossible sets. (Figure 9) it was possible to continue the

reservoir study.Figure 7 shows the behavior of the

molecular weight of the heptanes plus frac The third column of Table 8, has thetion. As pressure decreases from the dewp;int, composition modified by the service companythe molecular weight of this fraction de- that performed the PVT study, several weekscreases up to a minimum at around 1300 psig. after they were notified of the error. WithBeyond that, there is a slight increase. As these modifications still several humps werea result of this decrease and of the calcu present in the K-value curves.lated liquid compositions, the apparent m~lecular weight of the retrograde liquid, The compositions of columns 2 and 3 arefirst decreases showing a minimum at about4800 psig, and then increases.

very similar, nonetheless, the compositioncalculated with the outlined procedureresulted in a consistent set of K-values and

Once the PVT data has been analized in allowed the reservoir study to continue in athis manner, it is possible to either use matter of hours.the information directly into a model, or toattempt to calibrate the parameters of anequation of state with the knowledge that CONCLUSIONSthe experimental information is consistentthroughout. Even having fairly good exper~ A method that allows to obtain themental data, as it is the case for Gas equilibrium ratios, liquid compositions and,Condensate “A”, serious difficulties could the molecular weight of the liquid and ofhave arisen in trying to match the behavior the C7+ fraction in the liquid for a variableof the butanes for example, using an composition fluid has been presented. Theequation of state. data required is obtained from a constant

volume depletion test.CASE 2. VOLATILE OIL IICI!

The method is practical and efficientFigure 8 shows the equilibrium ratios even for a desk calculator. The procedure can

calculated from a PVT analysis for VolatileOil “C”.

cut down significantly the time required toThe K-value curves only required characterize a fluid. Furthermore, the

three very slight modifications to plot in a method permits to:smooth way. The similarity between themeasured composition of the liquid left in

Detect experimental errors

the cell at 700 psig, and the composition Correct such errorscalculated by the method is remarkable. Themaximum difference between any two cOmPo~ Adjust the parametersof an equation of

itions is less than 0.3 percent (Table 7),state with the certainty that the baseinformation is consistent

The consistency shown by the Volatile - Utilize the calculated K-value tableOil “C” data has been the best shown out of directly into compositional simulation28 PVT analyses characterized to date. packages.

.

NOMENCLATURE

K= equilibrium ratio, dimensionless

N= mass, moles

P= absolute pressure, psia

RLV = liquid volume in the cell, % of Vl

s . amount of mass produced in adepletion stage, moles

T= absolute temperature, ‘Rankine

WSP = total mass produced, % of initialmoles

x= mol fraction in the liquid phase,dimensionless

Y= mol fraction in the gas phase,dimensionless

z . deviation factor, dimensionless

SUBSCRIPTS

1 . saturation pressure conditions

2 . any other pressure

c . calculated

D= dew point

g= gas

i= i-th component

i- iso-

j= j-th depletion stage,

j = 1 at the saturation pressure

L= liquid

n = normal-

r . reservoir conditions

T= total

REFERENCES

1. Jacoby, R.H. y V.J. Berry: “A methodfor Predicting Depletion Performance ofa Reservoir Producing Volatil CrudeOil”. Trans.AIME, v. 21O, 1957.

2. Jacoby, R.H. y V.J. Berry: “A Methodfor Predicting Pressure MaintenancePerformance for Reservoirs ProducingVolatil Crude Oil”. Trans. AIME, v.213,1958.

3. Reudelhuber, F.O. y Hinds R.F.: “ ACompositional Material Balance Method

for Prediction of Recovery from VolatilOil Depletion Drive Reservoirs”, Trans.AIME, V, 210, 1957,

4, Jacoby, R.H. y Koeller R.C.: “Effect ofComposition and Temperature on PhaseBehavior and Depletion Performance ofRich Gas Condensate Systems”, Trans.AIME, v.216, 1959.

5. Standing, M.B.: “Volumetric and PhaseBehavior of Oil Field HydrocarbonSystems”, SPE-AIME 1977. (Publishedoriginally in 1952).

6. Eilerts C.K. et al. : “Phase Relationsof Gas Condensate Fluids”, Monograph 10,Vols. 1 and 2; Bureau of Mines-AmericanGas Association, 1959.

7. Lohrenz, J., Clark G.C. y Francis R.J.:“A Compositional Material Balance forCombination Drive Reservoirs with Gasand Water Injection”, Trans. AIME, 1963,

8. Dykstra, H. y Mueller, T.D.: “Calcu13tion of Phase Compositions and Prope~ties for Lean or Enriched Gas Drive”,SPEJ, Sep. 1965.

9. Hoffmann, A.E., Crump, J.S. y Hocott C.R.: “Equilibrium Constants for a GasCondensate System”, Trans. AIME, v. 198!1953.

10. Scientific Software Corporation, N-COMPUser’s Manual.

11. Abel, W., Jackson, R.F. y Wattenbarger,R.A.: “Simulation of a Partial PressureMaintenance Gas Cycling Project with aCompositional Model, Carson Creek FieldAlbert”a”, JPT, Jan. 1970.

12. Jones , D.M. y Erbar J.: “ComputerDetermination of Data Matched Equili&rium Ratios”, JPT, Aug. 1970.

13. NGSMA , “Engineering Data Book” Tulsa,Okla, 1957.

14. Redlich, O. y Kwong, J.N.: “On theThermodynamics of Solutions, V. A Equ~tion of State. Fugacities of GaseousSolutions”, Chem. Rev., v. 44, 1949.

15. Peng, D.Y. y Robinson, D.B.: “A NewTwo-Constant Equation of State”, Ind.Eng. Chem. Fund., v. 15, 1976.

16. S6nchez, J.C. y Leyva M.A.: “EstudioComparative de Ecuaciones de Estado”,IMP, vol. XII, Abril 1980.

APPENDIX A

The equations of the appendix followthe order delineated in the paper.

1, Obtainment of NT (for gases):

~D

‘T = 10.732 ZD Tr... (Al)

2. Moles of fluid remaining in the j-thdepletion stage

N. = NT (13

- wsPj/loo) ... (A.2)

3. Moles of gas, moles of liquid andcalculated two-phase deviation factor

p. (1 - RLV/100)... (A.3)

(Ng)j=10.732 Z. Tr

J

(N~)j = Nj - (Ng)j ... (A.4) IPj

(z2pc)j =

10.732 Nj Tr

... (A.5)

4. Number of moles withdrawn in the j-thdepletion stage

WSP. - WSP.-ls

... (A.6).=J 100

‘T

5. Material balance for the i-th componentin the j-th depletion stage

(Yi)l NT = (Yi)j (Ng)j + (xi)j(N~)j

+ (Yi)j ‘j

solving for xi

... (A.7)

[ 1(yi)lNT - (Yi)j ‘Ng)j + ‘j ,.. (A 8)

:x.)==.

lJ(Nz)j

6. Equilibrium Ratios I

[1YiKi=—

x.1

j

... (A.9)

Steps 5 and 6 are applied for everycomponent in each one of the depletion stages

7. Extrapolation of the K-value curves I8. Mass balance to obtain the molecular

weight of the liquid and the molecularweight of the heavy fraction (C7+) inthe liquid.

TABLE 1

CONSOLIDATED ANALYSES OF SEVERAL GAS CONDENSATE FLUID SYSTEi.lS

(1) (2) (3) (4) (5) (6) (7) (8) (9) (lo)=~ t, ~u GC”E” G~n~n ~~ I*B ,, GC tt~ t, GC’’A1’ .-& ,,~ ,, GC1’1 “ G~ t,J t, ~~o,~t,—— . — — ,_ _ _,

c1 - ‘269.93 70.60 77.22 74.96 71.68 74.51 69.79 67.55 71.02 70.20

C2 - C624.05 22.80 15.71 17.87 20.77 17.83 22.14 23.59 19.23 19.74

032- H2S

‘7+ 6.02 6.60 7.07 7’.17 7.55 7.66 8.07 8.86 9.75 10,06

Reservoir

Temperature 160 271 314 266 266 273 264 237 277 274

(’F)

TABLE 2

CONSOLIDATED ANALYSES OF SEVERAL VOLATILE OiLS

(1) (2) (3) (4) (5) (6) (7) (8) (9)

“~ U~U “~tt~,t “(j ,$~ t’ “~,,or, Vo”c “ “(),,pt, “~wQ1t ~~tt~,, Vo“s “—— —— . . _

% - ‘265.01 50.43 62.13 59.81 S6.33 49.S8 51.79 48.76 30.90

C2 - C6

22.98 35.37 23.3G 23.72 23.58 29.43 26.25 25.80 39.80

co2-~2s

‘7+12.01 14.20 14.49 16.47 20.04 20.99 21.96 25.44 29.30

ReservoirTemperature241 276 279 270 266 318 275 261 286

(°F)

——

CONPONENT

%?sC02

N2

%C2

C3ic4

nC ~

ic5

nC5

C6

c?+

TABLE 3cORRECTED c014poSIT10NAL ANALySES FOR GAS CONDENSATE “A” (MOL, PERCENT)

NW OF c,+ 174

‘G ‘F C7+ .814

Z-FACTO%

EQ. GAS 1.213

TWO-PHASE 1.213

WELI.ISTREAi2PRODUCEDCUM.%OF INIT. .000

RJ3TROGRAOELIQUID .000VOLUME

.110

2.630

1.640

74.450

7.260

3.310

.800

1.355

.660

.680

.700

6.405

153

.799

1.108

1.116

6.193

7.800

.1112.666

1.690

76.020

7.226

3.259

.770

1.”300

.610

.630

.613

5.105

141

.788

1.021

1.033

14.359

14.900

.112

2.700

1.720

77.360

7.236

3.220

.760

1.280

.582

.6oO

.570

3.860

132

.779

,954

.964

25.021

18.200

RESERVOIR PIwSSUlw3 ‘PSIG

~ g“~ ~ 2200. ~ ~ Jo&

.110 .120 .060

2.600

1.590

72.920

7.300

3.360

.830

1.410

.700

.730

.790

7.660

~.113

2.730

1.750

78.329

7.260

3.210

.760

1.280

.570

.588

.550

2.860

124

.771

.917

.910

38.349

19.400

NOTE: The last column contains the equilibrium liquid phase

composition corresponding to the last pressure.

.114 .117

2.760 2.780

1.750 1.710

73.690 78.370

7.420 7.740

3.260 3.450

.780 .830

1.300 1.380

.579 .620

.587 .630

.550 .600

2.210 1.773

118 113

.765 .760

.912 .936

.863 .804

53. s01 70.557

19.300 18.100

TABLE 4

REPORTED LAB CONCENTRATIONS MODIFIED IN TABLE 3, GA!j CONDENSATE “A”

COMPOliENT

H2S

C02

C2

ic4

nC4

1C5

nC5

C6

‘7+

(MOL, PERCENT)

R3sERVOIR PRESSU~ (PSIG)

3100

.11

.59

2200

.11

.58

.59

-

2.790 .710

1.650 .100

76.950 12.430

8.24o 3.280

3.720 2.880

.900 1.030

1.490 2.070

.730 1.620

.740 1.850

.680 3.190

1.990 70.780

111 196

.757 ,830

.962

.710

81.868

5800 4900 _4000

.11 .11

2.66

7.24 7.23

.78

1.36 1.32

.59

.62

6.40 5.06 -

17.100

1300

.12

1.77

I

I

TAE!LE 5

CALCULATED COMPOSITIONS OF RETROGRADE LIQUID CONDENSED IN THE CELL, CONDENSATE “A”

(MOL, PERCENT)

RESERVOIR PRESSURE (PSIG)

CONPONENT

H2S

C02

~2

c1

C2

C31C4

nC4

ic5

nC5

C6

c?+

MW Ol?C7+

MW Ol?LIQUID

Tk!O-PHASE ZFACTOR CHECK----- -

LABORATORY

CALCULATED

~

.106

2.238

.906

52.299

7.096

4.034

1.238

2.158

1.157

1$405

2.013

24.551

292*

91.1

1.213

-----

~

.104

2.179

.889

51.471

7.361

4.061

1,251

2.181

1.261

1.431

2.052

25.259

248.6

82.2

1.116

1.116

4y :

.103

2.128

.873

50.702

7.832

4.084

1.260

2.199

1.343

1.447

2.060

25.969

221.5

76.8

1.033

1.s34

4000.

.098

1,984

.775

45.379

7.724

4.231

1,274

2,233

1.436

1,545

2.176

31.143

201.8

93.7

,964

.964

~

.092

1.795

.574

38.815

7,627

4.334

1.300

2.282

1.541

1.654

2.360

37.623

199.2

106.5

.910

.910

S

.085

1.532

.419

31.915

6.931

4.250

1.279

2.322

1.628

1.800

2.599

45,241

197.4

128.6

1300.-—

.065

1.139

.259

21.609

5.434

3.681

1.189

2.233

1.713

1.918

2.896

57.864

196.9

152.1

Jo&

.043

.715

.102

12.545

3.291

2.877

1.052

2.087

1.625

1.876

3.191

70.596

.863 ,804 .710

,863 .804 .710

* EXTRAPOLATED

TABLE 6

CALCULATED EQUILIBRIUM RATIOS-FOR GAS CONDENSATE “A”

PRESSURE (PSIG)

COMPONENT

H2S

co*

~2

c1

C2

C3ic4

nC4

ic5

nC5

C6

c?+

~

1.0361

1.1616

1.7558

1.3943

0.92457

0.83292

0.67045

0.65353

0.60514

0.51971

0.39236

0.31200

S8Q&

1.058

1.207

1.845

1.446

0.9236

0.8151

0.6397

0,6213

0.5235

0.4752

0.3412

0.2536

4900.

1.079

1.253

1.936

1.499

0.9226

0.7980

0.6110

0.5912

0.4543

0.4354

0.2976

0.1966

&o&

1.143

1.361

2.218

1.705

0.9368

0.7610

0.5965

0.5731

0.4052

0.3884

0.2619

0.1239

~

1.226

1.521

3.046

2.018

0.9518

0.7406

0.5844

0.5608

0.3698

0.3555

0.2330

0.07602

~

1.345

1.801

4.175

2.466

1.071

0.7671

0.6100

0.5599

0.3557

0.3262

0.2115

0.04885

1300.

1.811

2.439

6.611

3.627

1.424

0.9373

0.6983

0.6179

0.3618

O.32(I5

0.2072

0.03064

&

2.823

3.902

16.128

6.134

2.504

1.293

0.8559

0.7138

0.4492

0.3945

0.2131

0.02819

—

.-—

TABLE 7

CALCULATED AND MEASURED COMPOSITIONS FOR THE

LIQUID AT 700 PSIG, VOLATILE OIL “C”

COMPONENT

~A~ljRED

CONPOSITION(Mol. %)

H2S

co ~

N2

c1

C2

C3

1C4

nc5

iC5

nC ~

C6

C7+

.31

.65

.12

11.02

5.01

4.79

1.32

3.30

1.s1

2.42

3.96

65.29

CALCULATEDCOMPOSITION

(Mol.%)

.31

.65

.12

11.05

5.02

4.80

1.32

3.30

1.81

2.42

3.96

65.23

COMPONENT

H2S

Coz

‘2

c1

C2

C3

ic4

nC4

ic5

nC5

C6

DIFFERENCE(%)

100.00 r.o.oo

TABLE 8.

COMPARISON BETWEEN ORIGINAL COMPOSITIC;i S

FOR GAS CONDENSATE “B”

0.27

0.20

0.21

0.09

ORIGINALLYREPORTEDCOMPOS ITION

(Mol.%)

1.27

2,33

0.40

74.56

7.38

3.07

0.61

1.25

0.43

0.62

0.91

CALCUI.ATED NODIFIEDCOMPOSITION C014POSITION

(Mol.%) (Mel.%)

1.27 1.2?

2.33 2,33

0.40 0.40

74.57 74.56

7.38 7,38

3.07 3.07

0.61 0.61

1.25 1.25

0.43 0.43

0.62 0,62

0.91 0.91---------------- --------- --------. --------. --------- ------

C7 0.48 1,00 0.98

C8 0.66 1.21 1.23

C9 1.21 1.03 1.02

Clo 0.93 0,76 0,76

Cll 0.69 0.55 0.55

Clz+ 3.20 2.61 2.63

100.00 100,00 100.00

o

[p~iq]

[%1

I100

I. ...

RETROGRADECONDENSATE

28 /

d>w 24

!?

#20

52Ao>ws(nzg.12z~

u .0 8.a

0,*

E

,,,-

W4 8K +

01000 2000 3 coo 4000 5000 6000 7000 80<

PRESSURE ( PSIG )

fig. l- Retrograde condenaatloncurvaa

6720 5800

10f[%1 —...H

G! v 10656

II

GZ

. . . J.. . . . w 2’ ?.60

7’

[%]

I.

9220

1 1i 80~.

(a) (b)

Fig. 3- Constant volume depletion teat

5800

TG2 Pduced and

[

analked(6.193%)

Gtv

I,2/, . -.,, .

(c)

Fig, 2- Llquidphaae volume cuwe2

3.0 I I I I I I

\ 4

4- $.I Ns GAS CONDENSATE “A”

\

“\\Cg

-———— ————— ._,

\

“c+ -.— —.-./

I720

I I I I I I Io 1000 2000 30QI 400U 300Q 6CQ 7oca

PRESSURE (PSI13)

Fl& 4- Selected K.value cuwes, Orlglnal data

10Q.C

10.C

1.0

0.1 —

“ck4

c,

/ C02

I

GAS CONDENSATE“A”

Hz S

6i

I / I I I I I I I I_ I t I1 Io

&1000 2000 3000 4000 5000’ - 6000

PRESSURE ( PSI]

Fig. 5- Compositon of theretrograde llquld condensed in the cell

X7-’-----l

lx’ GAs CONDENSATE “A”

1

0.02 I I I ~ J~1000 2cmn 3(M 4000 5000 6 COO 7000

PRESSURE ( PSIG)

Fig. 6-Equilibrium raliosfor gaacondensate,-A’s

200 ‘ I II

I I II I I I 1 I 1

n5gA GAS CONDENSATE ‘A”~asoQ uh 150a

uo

&a❑ L3 0

K+

a4 100 —u

. 2Q0 IIJ

ws

d= J

6720 Id

:

so I I 1 I I I t I I I 1 I I I 1501000 2WQ 3000 4000 moo 6000 7000

PRESSURE ( PSIG)

Fig. 7- Molecular waighl behavior

10.(

5.(

1.(

O.:

0,1

0.05

0.02

I I I I I

VOLATILE OIL ‘c”

I I I I I I I1000 2000 3000 4000 5000 6 OC

PRESSURE (PSIG)

Fig. 8- Equilibrium ratios for volatiie oil “C”

10.(

5.1

1.(

“*x\+>II o.!

x-

0.1

0.05

0.01

\l I I I I

“\

\

GAS CONDENSATE “B”

c’

\

IC3

\ iC4II

/c,’ +

I /l I I I1000 2000 3000 4000 5000 6000 70

PRESSURE ( PSIG)

Fig. 9- Equilibrium ratios for gas condensate “~,,