Scientia Iranica C (2015) 22(6), 2373{2378

Sharif University of TechnologyScientia Iranica

Transactions C: Chemistry and Chemical Engineeringwww.scientiairanica.com

Research Note

Experimental observation and mathematical modelingof immiscible displacement in oil wet reservoirs

E. Kamari�

Department of Petroleum Engineering, Research Institute of Petroleum Industry (RIPI), Tehran, Iran.

Received 22 September 2014; received in revised form 27 January 2015; accepted 4 August 2015

KEYWORDSBreakthrough;Fracture reservoir;Front;Heterogeneous;Immiscibledisplacement;Oil recovery.

Abstract. Here, a series of immiscible displacement processes have been performed on thefractured porous medium developed on glass micro-models in order to investigate the roleof fracture characteristics in oil displacement e�ciency during the immiscible displacementprocess. Oil recoveries were determined from image analyses of continuously recordedpictures during di�erent ooding schemes. A clear bypassing of displacing uid whichresults in premature breakthrough of injected uid due to the fracture has been observed.Moreover, the results showed a decrease in oil recovery when fracture's length increased. Incontrast, an increase in fracture orientation from ow direction increased oil recovery. Theresults of this work may be useful in gaining a thorough understanding of the immiscibledisplacement process as well as the optimal �eld development plans.© 2015 Sharif University of Technology. All rights reserved.

1. Introduction

Fluid ow in porous media is of great interest in manyindustrial applications, such as oil recovery, geologicalsequestration of carbon dioxide, imbibition, and under-ground pollutant remedy application. The dynamicsand stability of immiscible uid- uid displacements inporous media is a subject of interest, both from a fun-damental point of view as a dynamical non-equilibriumprocess and from a technological point of view inindustrial and environmental problems such as oilrecovery, irrigation, and �ltration. This is particularlytrue in the context of oil recovery enhancement fromunderground reservoirs. Such an enhanced oil recoverytypically involves displacement of in-situ oleic phaseby continuous injection of another uid phase whichmay be immiscible (e.g. water injection) or miscible(e.g. CO2 or solvent injection) to the former. Stabilityconsiderations partly a�ect the degree of e�ectivenessof these methods [1-3].

*. Mobile: +98 912 4147996; Fax: +98 21 44739746E-mail address: kamarie@ripi.ir

Experimental [4-6] and theoretical [4,7-13] studieshave revealed that the transient growth pattern ofthe displacement of a non-wetting uid by a wettingone (imbibition), and vice-versa (drainage) dependsstrongly on various factors such as pore morphology,capillary number, viscosity ratio, and wettability.

There is strong evidence that the so-estimatedrelative permeability and capillary pressure curves arecorrelated strongly with capillary number and viscosityratio [12,14-21]. Such correlations have occasionallybeen attributed to the interactive e�ects of various localforces (e.g. capillary, viscous, gravity, etc.) on thedisplacement propagation pattern at the pore networkscale [10,12,15,18,21,22].

Many researchers have used micro-models, whichhave been proved to be useful for studying a variety ofoil recovery processes and for obtaining a better under-standing of transport mechanisms during enhanced oilrecovery phenomena [23-35].

In this study, the micro-model is used for quan-titative measurements as well as qualitative investi-gations. Therefore, a series of experimental testswere conducted in order to investigate the role of

2374 E. Kamari/Scientia Iranica, Transactions C: Chemistry and ... 22 (2015) 2373{2378

Figure 1. Schematic diagram of the experiment setup.

single fracture characteristics (length and orientation)in oil recovery during the immiscible displacementprocess. For this purpose, distilled water was used asan injection uid to displace n-Decane in glass micro-models with di�erent fracture geometries.

2. Materials and experiments

Schematic diagram of the micro-model apparatus isshown in Figure 1. Description of experimental setupand micro-model patterns construction can be foundelsewhere [32-35].

2.1. Experimental procedureAll of the tests were carried out at a temperatureof 21 � 0:5�C. At the �rst step, before startingthe experiments, the micro-model was cleaned withtoluene/ethanol and then de-ionized water to be re-moved of any extra material trapped inside the model.A low ow rate, high-pressure pump was used forcleaning purposes. At the second step, micro-modelswere saturated with n-C10. At the last step, thedistilled water was injected through the inlet port ofthe micro-model at a pre-selected ow rate. During theexperiments, a digital video camera captured imagesfrom the process and saved them in the computerevery 30 seconds. The fractional ow versus porevolume injected at the output of glass micro-modelwas calculated using the captured images and the data

from injection pump; for example, two images of oneof them is shown in Figure 2. Experiments in some ofthe patterns were repeated to check the reproducibilityof results.

To change the wettability of micro-models tostrongly oil-wet, the following procedure was con-ducted:

1. Rinse micro-model thoroughly with NaOH solutionfor 1 h;

2. Rinse micro-model thoroughly with distilled waterto remove all residues, and then dry in an oven at200�C for at least 15 min;

3. Prepare a diluted solution of 2% Three ChloroMethyl Silane (TCMS) and 98% dehydrate tolueneby volume (this solution should be prepared freshdaily);

4. Saturate the micro-model with the diluted solutionfor at least 5 min. A thin �lm immediately coatsthe internal surface of micro-model making it waterrepellent;

5. Rinse the micro-model with methanol to removeexcess siliconizing uid;

6. Dry the micro-model in an oven at 100�C for 1 h tocure the silicone coating.

3. Experimental results

When capillary trapping experiments are performed inthe laboratory studies, care must be taken to insurethat laboratory ow conditions are representative ofthe subsurface conditions. The ratio of capillary toviscous forces is quanti�ed by a dimensionless number,the capillary number by which ow phenomena inporous media can be scaled. For systems withoutgravity, we expect di�erent ow regimes dependingon the capillary number [4]. In this study, thedisplacement experiments have been carried out in ahorizontal mounting to ignore the e�ect of gravity.For evaluation of the viscous and capillary forcesthrough the porous medium used in these experiments,we calculated the capillary number for some of the

Figure 2. Flow pattern of glass micro-models for LFD = 0:5 and � = 0�: a) 0.47 injected pore volume; and b) 1.20injected pore volume.

E. Kamari/Scientia Iranica, Transactions C: Chemistry and ... 22 (2015) 2373{2378 2375

tests. For the range of experiments performed here,the capillary number varies from 10�4 to 10�3 andas a result, the e�ect of capillary force can be ne-glected.

3.1. The e�ect of fracture length on recoveryfactor

To investigate the e�ect of fracture length on recoveryof an immiscible oil displacement, micro-models withdi�erent fracture lengths of 3, 4, 5, 6, 8, 10, and11 cm with 0� fracture orientation to ow directionwere used. The results are shown in Figure 3. Thedimensionless fracture length is de�ned by the lengthof fracture divided into injection length, which is thedistance between the injection-production face or thelength of the pattern. Having oil-wet micro-models,distilled water tends to go to the big pores and as aresult, front goes inside the fracture and causes earlierbreakthrough time; also, it needs more pore volumeinjected of distilled water to displace trapped n-Decaneand reach to a recovery factor of one. In addition,Figure 3 shows that the longer fracture in the micro-model causes the earlier breakthrough time and needsmore pore volume injected of displaced uid to attainultimate recovery.

3.2. The e�ect of fracture orientation onrecovery factor

To observe the e�ect of fracture inclination (the angleof fracture with respect to ow direction) on theimmiscible displacement process, several micro-modelpatterns with the same length of fracture and withdi�erent orientations of fracture to the ow directionwere used. The results of the immiscible displacementtests conducted on the above micro-models for LFD =0:5 are shown in Figure 4. This �gure shows that byincreasing the fracture orientation to ow direction, thebreakthrough time increases and therefore the porousmedia will act homogenously. Therefore, if the fractureorientation is 0�, it causes earlier breakthrough timeand lower recovery factor curve versus pore volumeinjected of distilled ware; and if fracture orientation is

Figure 3. E�ect of fracture length on recovery factorcurves.

Figure 4. E�ect of fracture orientation on recovery factorcurves for LFD = 0:5.

90�, it acts like homogeneous porous media (as shownin Figure 4).

4. Modeling: Calculation of recovery factor

The fractional ow model for a fractured porous media,where the capillary and gravity e�ects are neglected,can be written as follows [33]:

fd =1

1 +�krokrd

���d�o

� � 1H

� : (1)

Correlations of Corey were used for relative permeabil-ity calculations:

Relative permeability to oil:

kro = �1(1� sdD)m: (2)

Relative permeability to displacing uid:

krd = �2sndD: (3)

Normalized saturation of displacing uid:

sdD =sd � sid

1� sor � sid ; (4)

where fd is fractional ow of displaced uid, kd isrelative permeability to displaced uid, ko is relativepermeability to oil, �d is viscosity of displaced uid,�o is viscosity of oil, sd is displaced uid saturation,sid is initial displaced uid saturation, sor is residualoil saturation, m is exponent in relative permeabilitycorrelation for oil, and n is exponent in relative perme-ability correlation for displaced uid. m and n are di-mensionless parameters. Also H is heterogeneity factorwhich represents the heterogeneity of a porous mediumin fractional ow model for immiscible displacementdue to the presence of the fractures.

Substituting Eqs. (2), (3), and (4) into Eq. (1)yields:

fd =sndD

sndD +A� 1H

�(1� sdD)m

: (5)

Taking the derivative of Eq. (5), with respect to

2376 E. Kamari/Scientia Iranica, Transactions C: Chemistry and ... 22 (2015) 2373{2378

normalized saturation, gives us:@fd@sdD

=1pvi

=A� 1H

� �nsn�1

dD (1�sdD)m +msndD(1�sdD)m�1��sndD +A

� 1H

�(1� sdD)m

�2 ;(6)

where pvi is pore volume injected and A is de�ned as:

A =�d�o: (7)

Before breakthrough, recovery factor is equal to theinjected pore volume of displacing uid; however, afterbreakthrough of displacing uid, the recovery factor iscalculated as follows:

R.F. = (pvi)bt +pviZ

(pvi)bt

(1� fd)d(pvi); (8)

where R.F. is recovery factor and (pvi)bt is injected porevolume of displacing uid at the breakthrough time.

5. Results and discussion

In this study, more than 40 experiments were con-ducted on several glass micro-model patterns with dif-ferent fracture lengths and orientations. The H valuesfor each of these micro-models have been calculated bythe Kamari et al. [33] method.

In this study, the values of other parameters inEq. (8) are shown in Table 1.

The integration in Eq. (8) was calculated nu-merically by Simpson's rule. The curve of recoveryfactor versus injected pore volume for di�erent valuesof H is shown in Figure 5. The higher value of H-factor is corresponding to the lower recovery factor,and the e�ect of fracture in higher H value is muchmore profound.

5.1. Comparison between experimental resultsand the model

For two cases of the micro-models, the comparisonsbetween experimental results and the model have beendone.

Case 1: The micro-model with fracture length of 6 cm(LFD = 0:5) and orientation of 0�. For this case, the H

Table 1. Physical and hydraulic properties that are usedin Eq. (8).

Property ValueM 2.5n 1sid or siw 0�d or �w, (cp) @ 21�C 0.9776�o or �n�C10, (cp) @ 21�C 0.8998

Figure 5. Representative graph of Eq. (8) for di�erent Hvalues.

Figure 6. Comparison between experimental data andthe model for Case 1.

value was 2.295 and the breakthrough time occurred at0.469 injected pore volume. For this case, the recoveryfactor versus injected pore volume is shown in Figure 6.The doted points and solid line were attained fromexperimental data and the model, respectively. InFigure 6, the e�ect of fracture on recovery factor isvisible in the experimental data and the approachedmodel.

Case 2: The micro-model with fracture length of 8 cm(LFD = 0:667) and orientation of 45�. For this case, theH value was 1.685 and the breakthrough time occurredat 0.557 injected pore volume. For this case, therecovery factor versus injected pore volume is shownin Figure 7.

Figure 7. Comparison between experimental data andthe model for Case 2.

E. Kamari/Scientia Iranica, Transactions C: Chemistry and ... 22 (2015) 2373{2378 2377

In general, when a fracture exists in porous media,the main part of injected uid passes through thefracture, and consequently, the displaced uid will betrapped to some extent. As a result, recovery factor ofa fractured porous media is much lower than that ofthe homogeneous porous media.

6. Conclusions

The obtained results show that longer fracture inline drive micro-models causes lower recovery factor.Also, increasing the angle of fracture orientation, withrespect to the mean ow direction of displacing uid,leads to increment of oil recovery factor. In addition, inmodels with only one fracture, after breakthrough time,the e�ect of fracture is noticeable and the recoveryfactor will be decreased due to the displaced uidbeing trapped. As well, the proposed model is in goodagreement with the obtained experimental data.

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Biography

Ehsan Kamari holds a BS degree from the PetroleumUniversity of Technology and MS and PhD degreesfrom Sharif University of Technology, all in Reser-voir Engineering. His academic experience includesresearch on experimental and simulation studies of dif-ferent EOR processes, micro-model experiments, andproperties of petroleum uids. He has authored/co-authored more than 20 technical papers, which havebeen presented and/or published in international con-ferences and journals. He is a member of SPE. He isnow a project manager in Department of PetroleumEngineering, Research Institute of Petroleum Industry(RIPI). He has served as the Manager of GraduateStudents and several research projects.