Research ArticleA Novel Method for Improving Water Injectivityin Tight Sandstone Reservoirs
Mohamad Yousef Alklih1 Bisweswar Ghosh1 and Emad Waleed Al-Shalabi2
1 Petroleum Engineering Department The Petroleum Institute PO Box 2533 Abu Dhabi UAE2Department of Petroleum amp Geosystems Engineering The University of Texas Austin Austin TX 78712 USA
Correspondence should be addressed to Mohamad Yousef Alklih moyalklihpiacae
Received 15 July 2014 Accepted 23 August 2014 Published 21 September 2014
Academic Editor Yunho Hwang
Copyright copy 2014 Mohamad Yousef Alklih et alThis is an open access article distributed under the Creative CommonsAttributionLicense which permits unrestricted use distribution and reproduction in anymedium provided the originalwork is properly cited
Applicability of electrokinetic effect in improving water injectivity in tight sandstone is studied DC potential and injection rateare varied for optimization and determination of their individual impact on clay discharge and movement The liberated clayswere characterized through size exclusion microfiltration and ICP-MS analysis Real time temperature and pH monitoring werealso informative Results showed that severalfold (up to 152) apparent increase of core permeability could be achieved Some ofthe experiments were more efficient in terms of dislodgement of clays and enhanced stimulation which is supported by producedbrines analysis with higher concentration of clay element The results also showed larger quantity of clays in the produced brinein the initial periods of water injection followed by stabilization of differential pressure and electrical current implying that thestimulation effect stops when the higher voltage gradient and flow rates are no more able to dislodge remaining clays Additionallyfluid temperature measurement showed an increasing trend with the injection time and direct proportionality with the appliedvoltage The basic theory behind this stimulation effect is predicted to be the colloidal movement of pore lining clays that results inwidening of pore throats andor opening new flow paths
1 Introduction
In general the three phases of petroleum recovery processesare primary secondary and tertiary oil recoveryThe primaryrecovery phase is mainly driven by the natural energy presentin the reservoir due to dissolved solution gas pressurepressure from the overlain gas cap or the pressure from anactive aquifer below the oil zone In most cases the naturaldriving mechanism is a relatively inefficient process andresults in a low overall oil recovery [1] The lack of sufficientand consistent natural driving energy is compensated by sup-plementingwith injection ofwater or gas (or a combination ofboth) which is the initiation of the secondary recovery phaseDue to several technoeconomic factors the most widespreadsecondary oil recovery process responsible formost of worldrsquosoil production is the waterflood recovery [2] Neverthelesswater injection may be associated with numerous hurdlesrelated to fluid incompatibility reservoir heterogeneity earlybreakthrough through thief zones permeability damage dueto suspended particles and clay swelling
Poor water injectivity is one of the problems oftenencountered especially in tight formations [3] This problemmay further aggravate when swelling type clays are presentdue to which pore throat blockage can occur [4] This situa-tion is often faced in clastic shaly sandstonesThe swelling andrelease of clay particles from pore walls and their subsequentredeposition downstream in smaller pore throats may inducesevere injectivity damage [5 6]
The current practice to enhance water injectivity in tightand clayey formation is centered around hydraulic fracturingandmatrix acidizing Unfortunately environmental concernsand difficulties to achieve the desired fracture length andorientation may discourage hydraulic fracturing [7] In mostcases matrix acidizing could be challenging to implement inclay rich sandstone formations due to the complex reactionsbetween hydrofluoric acid (HF) and the rock minerals (sili-cates feldspars and chlorites) and the damage thatmay occurby secondary precipitation particularly at high temperatures[8 9]
Hindawi Publishing CorporationJournal of Petroleum EngineeringVolume 2014 Article ID 864624 7 pageshttpdxdoiorg1011552014864624
2 Journal of Petroleum Engineering
+
+
+
+
+ +
+
+
+
+
+
+ +
+
+
+
++
+
+
+
+
+ +++++
++
++
+
++
++
+++++
+
+
+
+
+
+
+
+
+
+ + + + +
+ + + ++
+
++++
+++++
+++++
+++++
++++++
+++++
+
+
+
+
+
+
+ + + + + +
+ + + + + + +
minusminusminusminus
minus
minus
minus
minus
minus
minus
minus
minus
minus
minus
minus
minus
minus
minus
minus
minus
minus
minus
minusminusminus
minus
minus
minusminusminus
Swelling Particledisintegration
Figure 1 The mechanism of clay disintegration [19]
In view of the above we studied an alternative stim-ulation technology to improve water injectivity in tightand clay rich sandstone reservoir with the application ofelectrokinetic potential The application of electrokineticphenomena in improving oil recovery from heavy oil fieldwas first proposed and experimentally verified in 1960s byChilingar and his associates [10ndash12] In principle it involvespassage of direct current through an oil bearing formationresulting in complex electrokinetic transport phenomenainvolving electromigration electrophoresis electroosmosiselectrochemical reactions and Joule heating All of thesemechanisms contribute to improvement of fluid flow inporous media [12]
Electromigration is basically the gradual movement ofions that occurs between the anode and cathode Elec-trophoresis induces the separation andmovement of the neg-atively charged clay particles in the form of colloids or surfacechargedmicelles Electroosmosis is themovement of an ionicsolution (such as brine) in a porous media by the applicationof electrical potential [13] The electroosmosis flow is causedby Coulombrsquos force that is present in a mobile and electricallycharged solution The electrochemically enhanced reactionsoccur due to the interaction between the fluid host material(matrix) and the pore fluid These reactions are affectedby the changes in the electrical potential ionic strengthand pH of mobile fluid [14] Due to these electrokineticphenomena dislodgement and migration of clay may occuras colloids of submicron size which may directly stimulaterock permeability and increase effective porosity The mainmineralogical components of clay minerals are the phyllosil-icates Phyllosilicates are aluminum or magnesium silicateswith a certain degree of isomorphous substitution of theprincipal cations that can give a net electrical charge to thesolid The basic components which form the phyllosilicatesare silica (SiO
2) tetrahedral sheets and aluminum (Al) or
magnesium (Mg) oxides octahedral sheets Sheets can bestacked and arranged in different forms forming different
clay minerals The positive charges that are distributed onthe edges balance the negative charges that are distributedon the flat surfaces of the layers [15] When water is floodedinto the system the osmotic pressure differential of the watertends to pull the negatively charged ions along the surfaceof the layer Nevertheless the electrostatic charges that areassociated with the negative surface charges tend to holdagainst the osmotic pressure Eventually an electrical doublelayer is formed after a steady state is established between theosmotic pressure and the electrostatic pull [16] The doublelayer obviously consists of two layers One layer is fixed andcomposed of positive charges bonded to the negative surfacecharges forming a strong linear bond and the other layer ismobile composed of positive ions and some slackly bondedions Between these two layers there exists a slipping surfacewhich let the mobile layer move without disturbing the fixedlayer [17]This leads to migration of clay as colloidal particles(lt1 120583m size) upon introduction of the hydrodynamic flow(supported by electroosmotic flow) and eventually leadingto pore throat enlargement and permeability enhancementThis phenomenon is depicted schematically through Figure 1The electroosmotic flow rate is directly proportional toapplied potential gradient and zeta potential but inverselyproportional to ion concentration valence number andviscosity of the solution [18] Under electric potential thetotal flow rate (hydrodynamic and electroosmotic) througha porous media as proposed by Chilingar et al is given in [15]
119902119905=
119860119870Δ119875
120583119871
+
119860119870119890119864
120583119871
(1)
The first component of the right hand side of the equationis the hydrodynamic flow or the Darcy flow equation Thesecond component suggests that the increase in the flowrate due to the application of electrokinetic phenomena isdependent on the zeta potential dielectric constant andelectric field strength
Figure 2 Schematics of the flow setup under DC potential
The objective of this study is to improve injectivity of tightsandstone reservoir taking advantage of the electrokineticphenomena as described earlier This is achieved throughseveral coreflood studies in which positive DC potential isapplied on the injector side and the negative potential isapplied on the reference or production side of low permeablesandstone core plugs rich in clay minerals Two sets ofexperiments are conducted In the first set the DC potentialis varied and subsequently optimized during the waterinjection In the second set optimum potential is applied andkept constant and the injection rate is varied to determine thehydrodynamic flow effect on clay movement The liberatedclays are characterized through size exclusion microfiltrationand mineralogical analysis using ICP-MS technique TheJoule heating phenomena associated with electrokinetics arealso studied during the entire injection period
2 Methodology
Low permeability Berea sandstone core plugs of 910158401015840 in lengthand 1510158401015840 diameter were used as representative porous mediaAll plugs were subjected to porosity and N
2permeability
measurement Properties of the selected core plugs are givenin Table 1
An electrically nonconductive coreflooding setup is fabri-cated A schematic of the apparatus used for the corefloodingexperiments is given in Figure 2 In this set up we housedthe core plug in a rubber sleeve instead of a normal steelcore holder and confinement was applied using severaladjustable plumber rings Confinement pressurewas adjustedby tightening the rings A precession positive displacementpump was used to provide the hydrodynamic flow throughthe core Two filtration units with 3120583m and 1 120583mfilter paperswere connected on the production side of the core to collectparticles of different sizes produced with the produced brineTwo pressure transducers sensitive to 2 decimal places ofpsi with data logging system were connected as shown inFigure 2 One was installed across the core plug and the otheracross the filtration units to detect the anticipated pressurerise due to the accumulation of particles and blockage of filterpapers A stable DC power source with current and voltage
regulator was used to provide the required potential acrossthe core plug The whole flooding system was electricallyisolated to avoid current leakage and short circuit The core-flood experiments were conducted as single phase flow withnondamaging 4 ammonium chloride brine In additionarrangements were made to measure the temperature andpH of the effluent brine Finally quantification of producedclay was performed through the use of ICP-MS (inductivelycoupled plasma-mass spectroscopy) using Perkin ElmerSCIEX DRCe ICP-MS instrument
Prior to coreflooding all the core plugs were fully satu-rated with brine under vacuum followed by saturation under2000 psi pressure Absolute brine permeability was measuredat a constant flow rate of 02 ccmin Once the differentialflow pressure across the core plug is stabilized a premeditatedDC potential is applied and brine flow is continued Severalcorefloods were conducted in which the positive potentialwas applied on the injector side and the negative potential onthe reference or production side of the coreflood setup
The objective of the first set of corefloods is to optimizeDC potential gradient which was varied from 05Vcm to20Vcm at an increment of 05 V while brine flow ratewas kept constant at 02 ccmin All four corefloods werecontinued till a steady state was reached In the second set ofcorefloods the main objective is to optimize the flow rate Inthis set of four corefloods the DC potential was kept constantat 15 Vcm the optimized voltage was obtained from the firstset and the brine injection rates were varied from 03 ccminup to 06 ccmin at an increment of 01 ccmin A summaryof the above two sets of corefloods is presented in Table 2During the flow studies effluent temperature was measuredto investigate Joule heating effect on the porous media
3 Results and Analysis
Results of the first set of coreflood experiments (Table 2and Figure 3) show that the application of DC potentialhad significant impact on clay destabilization and resultingpermeability enhancement of the core and is dependent onthe applied potential gradient An apparent increase of corepermeability up to 325 could be seen by application of a
4 Journal of Petroleum Engineering
Table 1 Petrophysical properties of core plugs
Core Length (cm) Diameter (cm) Porosity by He expansion () Pore volume (cc) Absolute permeability (mD) Exp1 2390 3783 1400 3776 1195 Set 12 2390 3809 1367 3740 1171 Set 13 2385 3789 1415 3830 1247 Set 14 2380 3816 1181 3243 1193 Set 15 2390 3792 1492 4043 933 Set 26 2395 3820 1134 3119 855 Set 27 2385 3791 1232 3338 698 Set 28 2390 3811 1388 3799 745 Set 2
Table 2 Summary of coreflood experiments and experimental results
Exp 1 05 Vcm at 02 ccmin 1195 1664 3925Exp 2 10 Vcm at 02 ccmin 1171 1993 7020Exp 3 15 Vcm at 02 ccmin 1247 2822 12630Exp 4 20Vcm at 02 ccmin 1193 5533 36379
Set 2Exp 5 03 ccmin at 15 Vcm 933 2189 13462Exp 6 04 ccmin at 15 Vcm 855 1994 13322Exp 7 05 ccmin at 15 Vcm 698 1759 15201Exp 8 06 ccmin at 15 Vcm 745 2530 23960
0
10
20
30
40
50
60
0 1 2 3 4 5 6
Perm
eabi
lity
(mD
)
Injected pore volume (cc)
WF05Vcm + WF10Vcm + WF15Vcm + WF
20Vcm + WF
Figure 3 Increase of core permeability on application of differentDC potential (DC voltage optimization)
potential gradient of 2Vcm however the sudden increaseof permeability after approximately 45 PV of brine indicatesdislodgment of large amount of clays and larger size particlesand possibly damaging the matrix itself It is obvious fromTable 3 that larger accumulation of mass on the filters (gt3 120583mand gt1 120583m) was observed in Experiment 4 which indicateslarge size particle production Thus 15 Vcm potential isconsidered as optimum in which slow and progressiveincrease of permeability is observed (126)
In the second set of experiments the optimized potential(15 Vcm) was applied and fluid flow rates were varied Itcould be seen from the coreflooding results (Table 2 and
Table 3 Mass of clay accumulations on size exclusion filters for allexperiments
Mass of accumulation on filtration unitsExperiments 3 120583 paper (g) 1 120583 paper (g)Set 1
Figure 4) that upon the application of a fixed voltage perme-ability increased from its base value as the hydrodynamic flowrate was increased An apparent increase of core permeabilityup to 240 could be observed by application of 06 ccminflow rate However the sudden increase of permeability afterapproximately 45 PV of brine implies dislodgement of largersize particles which was observed in the size exclusion filters(Table 3)Therefore 05 ccmin injection rate is considered asoptimum in terms of slow and gradual increase of permeabil-ity (152)
A comparison of the results from the two sets ofexperiments shows that the effect of DC potential is more
Figure 4 Permeability changes results from set 2 experiments(injection rate optimization)
001
010
100
1000
10000
100000
1 2 3 4 5 6
Elem
enta
l con
cent
ratio
n (p
pm)
Injected pore volume
AlMg
NaK
Figure 5 ICP-MS analysis results (15 Vcm and 05 ccmin)
pronounced than the effect of hydrodynamic potential ICP-MS analysis results of the effluents collected at each PVof brine injection (after application of DC potential) showmetal elements corresponding to clay minerals in abundantquantity (Figure 5) whereas the quantity of clay trapped inthe filter papers is much lessThis indirectly indicates that theclays producedwith effluents are smaller than 1micron in sizeand flow easily through the pore channels (Table 3) It is alsoevident from this plot that the concentration of the relevantclay elements is seen to be reduced drastically after 5 porevolumes of water injection when the stabilized conditions areachieved and no further clay production is noticed
Temperature measurements during the flow studiesshowed an increasing trend with the injection time anddirect proportionality with the applied voltages (Figure 6)Nevertheless the behavior of temperature changes is similaramong set 2 experiments upon which the same potentialgradient was applied for all the flow experiments (Figure 7)This is due to the fact that Joule heating is proportional to theapplied voltage gradient
pHmeasurements of the effluent samples (Figure 8) showinitial increase of pH followed by a stabilization period tillthe end of the flow indicating alkaline environment on
15
20
25
30
35
40
0 1 2 3 4 5 6Injected pore volume
WFWF + 05VcmWF + 10VcmWF + 15Vcm
WF + 20Vcm
Flow
tem
pera
ture
(deg
∘C)
Figure 6 Temperature change upon application of different DCpotential
202224262830323436
0 1 2 3 4 5 6Injected pore volume
WF03 ccmin + 15Vcm
04 ccmin + 15Vcm05 ccmin + 15Vcm06 ccmin + 15Vcm
Flow
tem
pera
ture
(deg
∘C)
Figure 7 Temperature change at different flow rates at 15 Vcm
application of DC potential Asmentioned earlier differentialpressure across the filters is measured on continuous basisto monitor plugging of filter papers this is represented byFigure 9 From this figure it is evident that there is noincrease in Δ119875 during the brine flow indicating no clay orfine production However after commencing electrokineticassisted flow the Δ119875 across the filters increased rapidly atthe initial period slowed down after about 05 PV of brineinjection and finally stabilized after 5 PV of injection
4 Discussion
Overall observation from the above results shows that waterinjection efficiency can be enhanced by application of DCpotential Table 2 illustrates this phenomenon depicting alinear correlation between applied voltage and permeabil-ity increase or core stimulation This phenomenon canbe explained only by the fact that clay disintegration andmigration in submicron sizes take place under the influenceof various electrokinetic mechanisms as discussed earlier Itis known that the structure of clay mineral is capable ofchanging the sign of their surface potential with a changein pH of the medium In an acidic medium the surface of
6 Journal of Petroleum Engineering
555
665
775
885
99510
0 1 2 3 4 5 6
pH
Injected pore volume
WF15Vcm + 05 ccmin
Figure 8 pHmeasurements at optimized conditions (15 Vcm and05 ccmin)
01020304050607080
0 1 2 3 4 5 6Injected pore volume
WF15Vcm + 05 ccmin
ΔP
acro
ss fi
lters
(psi)
Figure 9 Differential pressure change across filtration units(15 Vcm and 05 ccmin)
clay particles is seen to be heteropotential the basal surfacesgain a net negative potential and the edges gain a net positivepotential [20] whereas in the alkaline medium the basalsurface of the mineral and their edges bear the same negativepotential This is due to the fact that Al and Fe hydroxides(which make part of the crystalline structure of the clayminerals) show amphoteric properties and depending on thepH of the medium may have excess of negative or positivecharges [21]
In the single phase flow experiment with NH4Cl brine
the net flow of ions towards the producer cathode is NH4
+
and H+ Being a bulky ion NH4
+ will find it difficult topenetrate between two basal plates of clay matrix howeverthe tiny H+ ions would easily penetrate and concentrate onthe basal surface Thus the production and flow of H+ ionsfrom the anode (injector side) towards cathode (producerside) may have twofold impacts on the clay structures (1) itwould increase the electrostatic repulsion between layers dueto excess of positive charges between the layers and increasethe distance between them (2) it would introduce localchanges in the pHandmake the clay particles heteropotentialwhich in turn change the clay structures from a compactlayered structure to colloidal ldquohouse of cardsrdquo structure asshown in Figure 1 With the help of the hydrodynamic and
electroosmotic potential the submicron size colloidal parti-cles would easily flow through the micron size pore channelsincreasing pore throat sizes and enhance core permeabilityThis explanation is supported by the high content of metals(Na Al Mg and K) in the produced brine (ICP-MS analysisFigure 5) which are naturally present in the claysThe impactof DC potential on clay disintegration and migration is alsosupported by the fact that filter paper clogging and resultingpressure rise were observed only after the application of DCpotential and not during normal brine flooding
5 Conclusion
The study aimed to investigate an alternate method toimprove water injectivity in tight sandstone reservoir Thefindings of this study can be summarized as follows
(i) Application of DC potential enhances the permeabil-ity of tight clay rich sandstone rocks which furtherboosts water injection efficiency
(ii) Clay disintegration and mobilization are believedto be one of the main contributing mechanisms topermeability enhancement by electrokinetics in sand-stone rocks However the effect of the application ofDC potential on the mineralogy of clays yet needs tobe thoroughly investigated
(iii) Permeability enhancement increases as both appliedpotential gradient and hydrodynamic injection rateincrease
(iv) The application of carefully studied injection rate andpotential difference may facilitate the injectivity ofwater based on the rock characteristics
(v) Flow temperature measurements showed an increas-ing trend with the injection time and direct propor-tionality with applied voltages
(vi) pH of the effluent is seen to increase when the flowwas subjected under DC potential which may haveimpact on clay disintegration
Nomenclature
119860 Cross-sectional area of flow m2119864 Applied electrical potential V119870 Absolute permeability m2 or D119896119890 Intrinsic electroosmotic permeability Pasdotm2V119871 Length of core mΔ119901 Pressure difference Pa119872 Dynamic viscosity Pasdots
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors are grateful to the Petroleum EngineeringDepartment at The Petroleum Institute Abu Dhabi for
Journal of Petroleum Engineering 7
providing the laboratory facilities to conduct the laboratoryexperiments
References
[1] T Ahmed Reservoir Engineering Handbook Gulf ProfessionalPublishing 2nd edition 2001
[2] P Willhite Waterflooding SPE Textbook Series vol 3 Societyof Petroleum Engineers 1986
[3] S Pang and M Sharma ldquoA model for predicting injectivitydecline inwater-injectionwellsrdquo SPE Formation Evaluation vol3 no 12 pp 194ndash201 1997
[4] A Tchistiakov ldquoPhysio-chemical aspects of clay migrationand injectivity decrease of geothermal clastic reservoirsrdquo inProceedings of theWorld Geothermal Congress (WGC rsquo00) 2000
[5] M A Miniawi W A F Ahmed Y A Ahmed and A R SoufildquoIn situ gelled acid as a diverting system in water injection wellrdquoin Proceedings of the SPEIADCMiddle East Drilling TechnologyConference and Exhibition pp 333ndash337 October 2007
[6] X Yi ldquoWater injectivity decline caused by sand mobilizationsimulation and predictionrdquo in Proceedings of the SPE PermianBasin Oil and Gas Recovery Conference Paper SPE 70032 pp202ndash209 Midland Tex USA May 2001
[7] B Scarth andCVozniak ldquoProduction problems associatedwithoverstressed hydraulic fracture treatmentsrdquo Paper SPE 89-40-79 Presented atAnnual TechnicalMeeting BanffCanada 1989
[8] X Wang H Zou X Cheng et al ldquoA new approach for matrixacidizing of water injectors in low-permeability Sandstonefieldsrdquo Paper SPE 73780 Presented at International Symposiumand Exhibition on Formation Damage Control Lafayette LaUSA 2012
[9] H A Al-Anazi H A Nasr-El-Din M K Hashem and J AHopkins ldquoMatrix acidizing of water injectors in a sandstonefield in Saudi Arabia a case studyrdquo in Proceedings of theSPEAAPG Western Regional Meetings Paper SPE 62825 pp585ndash594 Long Beach Calif USA June 2000
[10] S A Amba G V Chilingar and C M Beeson ldquoApplication ofelectrokinetics phenomena in civil and petroleum engineeringrdquoThe New York Academy of Sciences vol 118 no 14 pp 585ndash6021965
[11] S A Amba G V Chilingar and C M Beeson ldquoUse of directelectrical current for increasing the flow rate of reservoir fluidsduring petroleum recoveryrdquo Journal of Canadian PetroleumTechnology vol 3 no 1 pp 8ndash14 1964
[12] G Chilingar and C Beeson ldquoUse of direct electrical current forincreasing the flow rate of oil and water in a porous mediumrdquoJournal of Canadian Petroleum Technology vol 4 no 1 pp 81ndash88 1965
[13] M R Haroun G V Chilingar S Pamukcu J K Wittle HA Belhaj and M N A Bloushi ldquoOptimizing electroosmoticflow potential for electrically enhanced oil recovery (EEOR)in carbonate rock formations of Abu Dhabi based on rockproperties and compositionrdquo in Proceedings of the InternationalPetroleum Technology Conference (IPTC rsquo09) Paper SPE 13812pp 2645ndash2659 Doha Qatar December 2009
[14] J K Wittle D G Hill and G V Chilingar ldquoDirect currentelectrical enhanced oil recovery in heavy-oil reservoirs toimprove recovery reducewater cut and reduceH2S productionwhile increasing API gravityrdquo in Proceedings of the SPEWesternRegional and Pacific Section AAPG Joint Meeting (SPE rsquo08) pp405ndash423 Bakersfield Calif USA April 2008
[15] G Chilingar A El-Nassir and R Steven ldquoEffect of directelectrical current on permeability of sandstone corerdquo Journal ofPetroleum Technology vol 22 no 7 pp 830ndash836 1970 PaperSPE 2332
[16] J E Killough and J A Gonzalez ldquoA fully-implicit model forelectrically enhanced oil recoveryrdquo in Proceedings of the 61stAnnual Technical Conference and Exhibition New Orleans LaUSA October 1986
[17] S Pamukcu ldquoElectrochemical transport and transformationsrdquoin Chapter 2 in Electrochemical Remediation Technologiesfor Polluted Soils Sediments and Groundwater Reddy andCamaselle Eds pp 29ndash65 John Wiley amp Sons New York NYUSA 2009
[18] D H Gray and J K Mitchell ldquoFundamental aspects of electro-osmosis in soilsrdquo Journal of the Soil Mechanics and FoundationsDivision vol 93 no 6 pp 209ndash236 1967
[19] B Ghosh E W Al Shalabi and M Haroun ldquoThe effect of DCelectrical potential on enhancing sandstone reservoir perme-ability and oil recoveryrdquo Petroleum Science and Technology vol30 no 20 pp 2148ndash2159 2012
[20] V Sokolov ldquoModels of clay soil microstructuresrdquo InzhenernayaGeologiya no 6 pp 32ndash42 1991
[21] V I Osipov V N Sokolov and V V Eremeev Clay Seals of Oiland Gas Deposits Balkema RotterdamThe Netherlands 2004
Figure 1 The mechanism of clay disintegration [19]
In view of the above we studied an alternative stim-ulation technology to improve water injectivity in tightand clay rich sandstone reservoir with the application ofelectrokinetic potential The application of electrokineticphenomena in improving oil recovery from heavy oil fieldwas first proposed and experimentally verified in 1960s byChilingar and his associates [10ndash12] In principle it involvespassage of direct current through an oil bearing formationresulting in complex electrokinetic transport phenomenainvolving electromigration electrophoresis electroosmosiselectrochemical reactions and Joule heating All of thesemechanisms contribute to improvement of fluid flow inporous media [12]
Electromigration is basically the gradual movement ofions that occurs between the anode and cathode Elec-trophoresis induces the separation andmovement of the neg-atively charged clay particles in the form of colloids or surfacechargedmicelles Electroosmosis is themovement of an ionicsolution (such as brine) in a porous media by the applicationof electrical potential [13] The electroosmosis flow is causedby Coulombrsquos force that is present in a mobile and electricallycharged solution The electrochemically enhanced reactionsoccur due to the interaction between the fluid host material(matrix) and the pore fluid These reactions are affectedby the changes in the electrical potential ionic strengthand pH of mobile fluid [14] Due to these electrokineticphenomena dislodgement and migration of clay may occuras colloids of submicron size which may directly stimulaterock permeability and increase effective porosity The mainmineralogical components of clay minerals are the phyllosil-icates Phyllosilicates are aluminum or magnesium silicateswith a certain degree of isomorphous substitution of theprincipal cations that can give a net electrical charge to thesolid The basic components which form the phyllosilicatesare silica (SiO
2) tetrahedral sheets and aluminum (Al) or
magnesium (Mg) oxides octahedral sheets Sheets can bestacked and arranged in different forms forming different
clay minerals The positive charges that are distributed onthe edges balance the negative charges that are distributedon the flat surfaces of the layers [15] When water is floodedinto the system the osmotic pressure differential of the watertends to pull the negatively charged ions along the surfaceof the layer Nevertheless the electrostatic charges that areassociated with the negative surface charges tend to holdagainst the osmotic pressure Eventually an electrical doublelayer is formed after a steady state is established between theosmotic pressure and the electrostatic pull [16] The doublelayer obviously consists of two layers One layer is fixed andcomposed of positive charges bonded to the negative surfacecharges forming a strong linear bond and the other layer ismobile composed of positive ions and some slackly bondedions Between these two layers there exists a slipping surfacewhich let the mobile layer move without disturbing the fixedlayer [17]This leads to migration of clay as colloidal particles(lt1 120583m size) upon introduction of the hydrodynamic flow(supported by electroosmotic flow) and eventually leadingto pore throat enlargement and permeability enhancementThis phenomenon is depicted schematically through Figure 1The electroosmotic flow rate is directly proportional toapplied potential gradient and zeta potential but inverselyproportional to ion concentration valence number andviscosity of the solution [18] Under electric potential thetotal flow rate (hydrodynamic and electroosmotic) througha porous media as proposed by Chilingar et al is given in [15]
119902119905=
119860119870Δ119875
120583119871
+
119860119870119890119864
120583119871
(1)
The first component of the right hand side of the equationis the hydrodynamic flow or the Darcy flow equation Thesecond component suggests that the increase in the flowrate due to the application of electrokinetic phenomena isdependent on the zeta potential dielectric constant andelectric field strength
Figure 2 Schematics of the flow setup under DC potential
The objective of this study is to improve injectivity of tightsandstone reservoir taking advantage of the electrokineticphenomena as described earlier This is achieved throughseveral coreflood studies in which positive DC potential isapplied on the injector side and the negative potential isapplied on the reference or production side of low permeablesandstone core plugs rich in clay minerals Two sets ofexperiments are conducted In the first set the DC potentialis varied and subsequently optimized during the waterinjection In the second set optimum potential is applied andkept constant and the injection rate is varied to determine thehydrodynamic flow effect on clay movement The liberatedclays are characterized through size exclusion microfiltrationand mineralogical analysis using ICP-MS technique TheJoule heating phenomena associated with electrokinetics arealso studied during the entire injection period
2 Methodology
Low permeability Berea sandstone core plugs of 910158401015840 in lengthand 1510158401015840 diameter were used as representative porous mediaAll plugs were subjected to porosity and N
2permeability
measurement Properties of the selected core plugs are givenin Table 1
An electrically nonconductive coreflooding setup is fabri-cated A schematic of the apparatus used for the corefloodingexperiments is given in Figure 2 In this set up we housedthe core plug in a rubber sleeve instead of a normal steelcore holder and confinement was applied using severaladjustable plumber rings Confinement pressurewas adjustedby tightening the rings A precession positive displacementpump was used to provide the hydrodynamic flow throughthe core Two filtration units with 3120583m and 1 120583mfilter paperswere connected on the production side of the core to collectparticles of different sizes produced with the produced brineTwo pressure transducers sensitive to 2 decimal places ofpsi with data logging system were connected as shown inFigure 2 One was installed across the core plug and the otheracross the filtration units to detect the anticipated pressurerise due to the accumulation of particles and blockage of filterpapers A stable DC power source with current and voltage
regulator was used to provide the required potential acrossthe core plug The whole flooding system was electricallyisolated to avoid current leakage and short circuit The core-flood experiments were conducted as single phase flow withnondamaging 4 ammonium chloride brine In additionarrangements were made to measure the temperature andpH of the effluent brine Finally quantification of producedclay was performed through the use of ICP-MS (inductivelycoupled plasma-mass spectroscopy) using Perkin ElmerSCIEX DRCe ICP-MS instrument
Prior to coreflooding all the core plugs were fully satu-rated with brine under vacuum followed by saturation under2000 psi pressure Absolute brine permeability was measuredat a constant flow rate of 02 ccmin Once the differentialflow pressure across the core plug is stabilized a premeditatedDC potential is applied and brine flow is continued Severalcorefloods were conducted in which the positive potentialwas applied on the injector side and the negative potential onthe reference or production side of the coreflood setup
The objective of the first set of corefloods is to optimizeDC potential gradient which was varied from 05Vcm to20Vcm at an increment of 05 V while brine flow ratewas kept constant at 02 ccmin All four corefloods werecontinued till a steady state was reached In the second set ofcorefloods the main objective is to optimize the flow rate Inthis set of four corefloods the DC potential was kept constantat 15 Vcm the optimized voltage was obtained from the firstset and the brine injection rates were varied from 03 ccminup to 06 ccmin at an increment of 01 ccmin A summaryof the above two sets of corefloods is presented in Table 2During the flow studies effluent temperature was measuredto investigate Joule heating effect on the porous media
3 Results and Analysis
Results of the first set of coreflood experiments (Table 2and Figure 3) show that the application of DC potentialhad significant impact on clay destabilization and resultingpermeability enhancement of the core and is dependent onthe applied potential gradient An apparent increase of corepermeability up to 325 could be seen by application of a
4 Journal of Petroleum Engineering
Table 1 Petrophysical properties of core plugs
Core Length (cm) Diameter (cm) Porosity by He expansion () Pore volume (cc) Absolute permeability (mD) Exp1 2390 3783 1400 3776 1195 Set 12 2390 3809 1367 3740 1171 Set 13 2385 3789 1415 3830 1247 Set 14 2380 3816 1181 3243 1193 Set 15 2390 3792 1492 4043 933 Set 26 2395 3820 1134 3119 855 Set 27 2385 3791 1232 3338 698 Set 28 2390 3811 1388 3799 745 Set 2
Table 2 Summary of coreflood experiments and experimental results
Exp 1 05 Vcm at 02 ccmin 1195 1664 3925Exp 2 10 Vcm at 02 ccmin 1171 1993 7020Exp 3 15 Vcm at 02 ccmin 1247 2822 12630Exp 4 20Vcm at 02 ccmin 1193 5533 36379
Set 2Exp 5 03 ccmin at 15 Vcm 933 2189 13462Exp 6 04 ccmin at 15 Vcm 855 1994 13322Exp 7 05 ccmin at 15 Vcm 698 1759 15201Exp 8 06 ccmin at 15 Vcm 745 2530 23960
0
10
20
30
40
50
60
0 1 2 3 4 5 6
Perm
eabi
lity
(mD
)
Injected pore volume (cc)
WF05Vcm + WF10Vcm + WF15Vcm + WF
20Vcm + WF
Figure 3 Increase of core permeability on application of differentDC potential (DC voltage optimization)
potential gradient of 2Vcm however the sudden increaseof permeability after approximately 45 PV of brine indicatesdislodgment of large amount of clays and larger size particlesand possibly damaging the matrix itself It is obvious fromTable 3 that larger accumulation of mass on the filters (gt3 120583mand gt1 120583m) was observed in Experiment 4 which indicateslarge size particle production Thus 15 Vcm potential isconsidered as optimum in which slow and progressiveincrease of permeability is observed (126)
In the second set of experiments the optimized potential(15 Vcm) was applied and fluid flow rates were varied Itcould be seen from the coreflooding results (Table 2 and
Table 3 Mass of clay accumulations on size exclusion filters for allexperiments
Mass of accumulation on filtration unitsExperiments 3 120583 paper (g) 1 120583 paper (g)Set 1
Figure 4) that upon the application of a fixed voltage perme-ability increased from its base value as the hydrodynamic flowrate was increased An apparent increase of core permeabilityup to 240 could be observed by application of 06 ccminflow rate However the sudden increase of permeability afterapproximately 45 PV of brine implies dislodgement of largersize particles which was observed in the size exclusion filters(Table 3)Therefore 05 ccmin injection rate is considered asoptimum in terms of slow and gradual increase of permeabil-ity (152)
A comparison of the results from the two sets ofexperiments shows that the effect of DC potential is more
Figure 4 Permeability changes results from set 2 experiments(injection rate optimization)
001
010
100
1000
10000
100000
1 2 3 4 5 6
Elem
enta
l con
cent
ratio
n (p
pm)
Injected pore volume
AlMg
NaK
Figure 5 ICP-MS analysis results (15 Vcm and 05 ccmin)
pronounced than the effect of hydrodynamic potential ICP-MS analysis results of the effluents collected at each PVof brine injection (after application of DC potential) showmetal elements corresponding to clay minerals in abundantquantity (Figure 5) whereas the quantity of clay trapped inthe filter papers is much lessThis indirectly indicates that theclays producedwith effluents are smaller than 1micron in sizeand flow easily through the pore channels (Table 3) It is alsoevident from this plot that the concentration of the relevantclay elements is seen to be reduced drastically after 5 porevolumes of water injection when the stabilized conditions areachieved and no further clay production is noticed
Temperature measurements during the flow studiesshowed an increasing trend with the injection time anddirect proportionality with the applied voltages (Figure 6)Nevertheless the behavior of temperature changes is similaramong set 2 experiments upon which the same potentialgradient was applied for all the flow experiments (Figure 7)This is due to the fact that Joule heating is proportional to theapplied voltage gradient
pHmeasurements of the effluent samples (Figure 8) showinitial increase of pH followed by a stabilization period tillthe end of the flow indicating alkaline environment on
15
20
25
30
35
40
0 1 2 3 4 5 6Injected pore volume
WFWF + 05VcmWF + 10VcmWF + 15Vcm
WF + 20Vcm
Flow
tem
pera
ture
(deg
∘C)
Figure 6 Temperature change upon application of different DCpotential
202224262830323436
0 1 2 3 4 5 6Injected pore volume
WF03 ccmin + 15Vcm
04 ccmin + 15Vcm05 ccmin + 15Vcm06 ccmin + 15Vcm
Flow
tem
pera
ture
(deg
∘C)
Figure 7 Temperature change at different flow rates at 15 Vcm
application of DC potential Asmentioned earlier differentialpressure across the filters is measured on continuous basisto monitor plugging of filter papers this is represented byFigure 9 From this figure it is evident that there is noincrease in Δ119875 during the brine flow indicating no clay orfine production However after commencing electrokineticassisted flow the Δ119875 across the filters increased rapidly atthe initial period slowed down after about 05 PV of brineinjection and finally stabilized after 5 PV of injection
4 Discussion
Overall observation from the above results shows that waterinjection efficiency can be enhanced by application of DCpotential Table 2 illustrates this phenomenon depicting alinear correlation between applied voltage and permeabil-ity increase or core stimulation This phenomenon canbe explained only by the fact that clay disintegration andmigration in submicron sizes take place under the influenceof various electrokinetic mechanisms as discussed earlier Itis known that the structure of clay mineral is capable ofchanging the sign of their surface potential with a changein pH of the medium In an acidic medium the surface of
6 Journal of Petroleum Engineering
555
665
775
885
99510
0 1 2 3 4 5 6
pH
Injected pore volume
WF15Vcm + 05 ccmin
Figure 8 pHmeasurements at optimized conditions (15 Vcm and05 ccmin)
01020304050607080
0 1 2 3 4 5 6Injected pore volume
WF15Vcm + 05 ccmin
ΔP
acro
ss fi
lters
(psi)
Figure 9 Differential pressure change across filtration units(15 Vcm and 05 ccmin)
clay particles is seen to be heteropotential the basal surfacesgain a net negative potential and the edges gain a net positivepotential [20] whereas in the alkaline medium the basalsurface of the mineral and their edges bear the same negativepotential This is due to the fact that Al and Fe hydroxides(which make part of the crystalline structure of the clayminerals) show amphoteric properties and depending on thepH of the medium may have excess of negative or positivecharges [21]
In the single phase flow experiment with NH4Cl brine
the net flow of ions towards the producer cathode is NH4
+
and H+ Being a bulky ion NH4
+ will find it difficult topenetrate between two basal plates of clay matrix howeverthe tiny H+ ions would easily penetrate and concentrate onthe basal surface Thus the production and flow of H+ ionsfrom the anode (injector side) towards cathode (producerside) may have twofold impacts on the clay structures (1) itwould increase the electrostatic repulsion between layers dueto excess of positive charges between the layers and increasethe distance between them (2) it would introduce localchanges in the pHandmake the clay particles heteropotentialwhich in turn change the clay structures from a compactlayered structure to colloidal ldquohouse of cardsrdquo structure asshown in Figure 1 With the help of the hydrodynamic and
electroosmotic potential the submicron size colloidal parti-cles would easily flow through the micron size pore channelsincreasing pore throat sizes and enhance core permeabilityThis explanation is supported by the high content of metals(Na Al Mg and K) in the produced brine (ICP-MS analysisFigure 5) which are naturally present in the claysThe impactof DC potential on clay disintegration and migration is alsosupported by the fact that filter paper clogging and resultingpressure rise were observed only after the application of DCpotential and not during normal brine flooding
5 Conclusion
The study aimed to investigate an alternate method toimprove water injectivity in tight sandstone reservoir Thefindings of this study can be summarized as follows
(i) Application of DC potential enhances the permeabil-ity of tight clay rich sandstone rocks which furtherboosts water injection efficiency
(ii) Clay disintegration and mobilization are believedto be one of the main contributing mechanisms topermeability enhancement by electrokinetics in sand-stone rocks However the effect of the application ofDC potential on the mineralogy of clays yet needs tobe thoroughly investigated
(iii) Permeability enhancement increases as both appliedpotential gradient and hydrodynamic injection rateincrease
(iv) The application of carefully studied injection rate andpotential difference may facilitate the injectivity ofwater based on the rock characteristics
(v) Flow temperature measurements showed an increas-ing trend with the injection time and direct propor-tionality with applied voltages
(vi) pH of the effluent is seen to increase when the flowwas subjected under DC potential which may haveimpact on clay disintegration
Nomenclature
119860 Cross-sectional area of flow m2119864 Applied electrical potential V119870 Absolute permeability m2 or D119896119890 Intrinsic electroosmotic permeability Pasdotm2V119871 Length of core mΔ119901 Pressure difference Pa119872 Dynamic viscosity Pasdots
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors are grateful to the Petroleum EngineeringDepartment at The Petroleum Institute Abu Dhabi for
Journal of Petroleum Engineering 7
providing the laboratory facilities to conduct the laboratoryexperiments
References
[1] T Ahmed Reservoir Engineering Handbook Gulf ProfessionalPublishing 2nd edition 2001
[2] P Willhite Waterflooding SPE Textbook Series vol 3 Societyof Petroleum Engineers 1986
[3] S Pang and M Sharma ldquoA model for predicting injectivitydecline inwater-injectionwellsrdquo SPE Formation Evaluation vol3 no 12 pp 194ndash201 1997
[4] A Tchistiakov ldquoPhysio-chemical aspects of clay migrationand injectivity decrease of geothermal clastic reservoirsrdquo inProceedings of theWorld Geothermal Congress (WGC rsquo00) 2000
[5] M A Miniawi W A F Ahmed Y A Ahmed and A R SoufildquoIn situ gelled acid as a diverting system in water injection wellrdquoin Proceedings of the SPEIADCMiddle East Drilling TechnologyConference and Exhibition pp 333ndash337 October 2007
[6] X Yi ldquoWater injectivity decline caused by sand mobilizationsimulation and predictionrdquo in Proceedings of the SPE PermianBasin Oil and Gas Recovery Conference Paper SPE 70032 pp202ndash209 Midland Tex USA May 2001
[7] B Scarth andCVozniak ldquoProduction problems associatedwithoverstressed hydraulic fracture treatmentsrdquo Paper SPE 89-40-79 Presented atAnnual TechnicalMeeting BanffCanada 1989
[8] X Wang H Zou X Cheng et al ldquoA new approach for matrixacidizing of water injectors in low-permeability Sandstonefieldsrdquo Paper SPE 73780 Presented at International Symposiumand Exhibition on Formation Damage Control Lafayette LaUSA 2012
[9] H A Al-Anazi H A Nasr-El-Din M K Hashem and J AHopkins ldquoMatrix acidizing of water injectors in a sandstonefield in Saudi Arabia a case studyrdquo in Proceedings of theSPEAAPG Western Regional Meetings Paper SPE 62825 pp585ndash594 Long Beach Calif USA June 2000
[10] S A Amba G V Chilingar and C M Beeson ldquoApplication ofelectrokinetics phenomena in civil and petroleum engineeringrdquoThe New York Academy of Sciences vol 118 no 14 pp 585ndash6021965
[11] S A Amba G V Chilingar and C M Beeson ldquoUse of directelectrical current for increasing the flow rate of reservoir fluidsduring petroleum recoveryrdquo Journal of Canadian PetroleumTechnology vol 3 no 1 pp 8ndash14 1964
[12] G Chilingar and C Beeson ldquoUse of direct electrical current forincreasing the flow rate of oil and water in a porous mediumrdquoJournal of Canadian Petroleum Technology vol 4 no 1 pp 81ndash88 1965
[13] M R Haroun G V Chilingar S Pamukcu J K Wittle HA Belhaj and M N A Bloushi ldquoOptimizing electroosmoticflow potential for electrically enhanced oil recovery (EEOR)in carbonate rock formations of Abu Dhabi based on rockproperties and compositionrdquo in Proceedings of the InternationalPetroleum Technology Conference (IPTC rsquo09) Paper SPE 13812pp 2645ndash2659 Doha Qatar December 2009
[14] J K Wittle D G Hill and G V Chilingar ldquoDirect currentelectrical enhanced oil recovery in heavy-oil reservoirs toimprove recovery reducewater cut and reduceH2S productionwhile increasing API gravityrdquo in Proceedings of the SPEWesternRegional and Pacific Section AAPG Joint Meeting (SPE rsquo08) pp405ndash423 Bakersfield Calif USA April 2008
[15] G Chilingar A El-Nassir and R Steven ldquoEffect of directelectrical current on permeability of sandstone corerdquo Journal ofPetroleum Technology vol 22 no 7 pp 830ndash836 1970 PaperSPE 2332
[16] J E Killough and J A Gonzalez ldquoA fully-implicit model forelectrically enhanced oil recoveryrdquo in Proceedings of the 61stAnnual Technical Conference and Exhibition New Orleans LaUSA October 1986
[17] S Pamukcu ldquoElectrochemical transport and transformationsrdquoin Chapter 2 in Electrochemical Remediation Technologiesfor Polluted Soils Sediments and Groundwater Reddy andCamaselle Eds pp 29ndash65 John Wiley amp Sons New York NYUSA 2009
[18] D H Gray and J K Mitchell ldquoFundamental aspects of electro-osmosis in soilsrdquo Journal of the Soil Mechanics and FoundationsDivision vol 93 no 6 pp 209ndash236 1967
[19] B Ghosh E W Al Shalabi and M Haroun ldquoThe effect of DCelectrical potential on enhancing sandstone reservoir perme-ability and oil recoveryrdquo Petroleum Science and Technology vol30 no 20 pp 2148ndash2159 2012
[20] V Sokolov ldquoModels of clay soil microstructuresrdquo InzhenernayaGeologiya no 6 pp 32ndash42 1991
[21] V I Osipov V N Sokolov and V V Eremeev Clay Seals of Oiland Gas Deposits Balkema RotterdamThe Netherlands 2004
Figure 2 Schematics of the flow setup under DC potential
The objective of this study is to improve injectivity of tightsandstone reservoir taking advantage of the electrokineticphenomena as described earlier This is achieved throughseveral coreflood studies in which positive DC potential isapplied on the injector side and the negative potential isapplied on the reference or production side of low permeablesandstone core plugs rich in clay minerals Two sets ofexperiments are conducted In the first set the DC potentialis varied and subsequently optimized during the waterinjection In the second set optimum potential is applied andkept constant and the injection rate is varied to determine thehydrodynamic flow effect on clay movement The liberatedclays are characterized through size exclusion microfiltrationand mineralogical analysis using ICP-MS technique TheJoule heating phenomena associated with electrokinetics arealso studied during the entire injection period
2 Methodology
Low permeability Berea sandstone core plugs of 910158401015840 in lengthand 1510158401015840 diameter were used as representative porous mediaAll plugs were subjected to porosity and N
2permeability
measurement Properties of the selected core plugs are givenin Table 1
An electrically nonconductive coreflooding setup is fabri-cated A schematic of the apparatus used for the corefloodingexperiments is given in Figure 2 In this set up we housedthe core plug in a rubber sleeve instead of a normal steelcore holder and confinement was applied using severaladjustable plumber rings Confinement pressurewas adjustedby tightening the rings A precession positive displacementpump was used to provide the hydrodynamic flow throughthe core Two filtration units with 3120583m and 1 120583mfilter paperswere connected on the production side of the core to collectparticles of different sizes produced with the produced brineTwo pressure transducers sensitive to 2 decimal places ofpsi with data logging system were connected as shown inFigure 2 One was installed across the core plug and the otheracross the filtration units to detect the anticipated pressurerise due to the accumulation of particles and blockage of filterpapers A stable DC power source with current and voltage
regulator was used to provide the required potential acrossthe core plug The whole flooding system was electricallyisolated to avoid current leakage and short circuit The core-flood experiments were conducted as single phase flow withnondamaging 4 ammonium chloride brine In additionarrangements were made to measure the temperature andpH of the effluent brine Finally quantification of producedclay was performed through the use of ICP-MS (inductivelycoupled plasma-mass spectroscopy) using Perkin ElmerSCIEX DRCe ICP-MS instrument
Prior to coreflooding all the core plugs were fully satu-rated with brine under vacuum followed by saturation under2000 psi pressure Absolute brine permeability was measuredat a constant flow rate of 02 ccmin Once the differentialflow pressure across the core plug is stabilized a premeditatedDC potential is applied and brine flow is continued Severalcorefloods were conducted in which the positive potentialwas applied on the injector side and the negative potential onthe reference or production side of the coreflood setup
The objective of the first set of corefloods is to optimizeDC potential gradient which was varied from 05Vcm to20Vcm at an increment of 05 V while brine flow ratewas kept constant at 02 ccmin All four corefloods werecontinued till a steady state was reached In the second set ofcorefloods the main objective is to optimize the flow rate Inthis set of four corefloods the DC potential was kept constantat 15 Vcm the optimized voltage was obtained from the firstset and the brine injection rates were varied from 03 ccminup to 06 ccmin at an increment of 01 ccmin A summaryof the above two sets of corefloods is presented in Table 2During the flow studies effluent temperature was measuredto investigate Joule heating effect on the porous media
3 Results and Analysis
Results of the first set of coreflood experiments (Table 2and Figure 3) show that the application of DC potentialhad significant impact on clay destabilization and resultingpermeability enhancement of the core and is dependent onthe applied potential gradient An apparent increase of corepermeability up to 325 could be seen by application of a
4 Journal of Petroleum Engineering
Table 1 Petrophysical properties of core plugs
Core Length (cm) Diameter (cm) Porosity by He expansion () Pore volume (cc) Absolute permeability (mD) Exp1 2390 3783 1400 3776 1195 Set 12 2390 3809 1367 3740 1171 Set 13 2385 3789 1415 3830 1247 Set 14 2380 3816 1181 3243 1193 Set 15 2390 3792 1492 4043 933 Set 26 2395 3820 1134 3119 855 Set 27 2385 3791 1232 3338 698 Set 28 2390 3811 1388 3799 745 Set 2
Table 2 Summary of coreflood experiments and experimental results
Exp 1 05 Vcm at 02 ccmin 1195 1664 3925Exp 2 10 Vcm at 02 ccmin 1171 1993 7020Exp 3 15 Vcm at 02 ccmin 1247 2822 12630Exp 4 20Vcm at 02 ccmin 1193 5533 36379
Set 2Exp 5 03 ccmin at 15 Vcm 933 2189 13462Exp 6 04 ccmin at 15 Vcm 855 1994 13322Exp 7 05 ccmin at 15 Vcm 698 1759 15201Exp 8 06 ccmin at 15 Vcm 745 2530 23960
0
10
20
30
40
50
60
0 1 2 3 4 5 6
Perm
eabi
lity
(mD
)
Injected pore volume (cc)
WF05Vcm + WF10Vcm + WF15Vcm + WF
20Vcm + WF
Figure 3 Increase of core permeability on application of differentDC potential (DC voltage optimization)
potential gradient of 2Vcm however the sudden increaseof permeability after approximately 45 PV of brine indicatesdislodgment of large amount of clays and larger size particlesand possibly damaging the matrix itself It is obvious fromTable 3 that larger accumulation of mass on the filters (gt3 120583mand gt1 120583m) was observed in Experiment 4 which indicateslarge size particle production Thus 15 Vcm potential isconsidered as optimum in which slow and progressiveincrease of permeability is observed (126)
In the second set of experiments the optimized potential(15 Vcm) was applied and fluid flow rates were varied Itcould be seen from the coreflooding results (Table 2 and
Table 3 Mass of clay accumulations on size exclusion filters for allexperiments
Mass of accumulation on filtration unitsExperiments 3 120583 paper (g) 1 120583 paper (g)Set 1
Figure 4) that upon the application of a fixed voltage perme-ability increased from its base value as the hydrodynamic flowrate was increased An apparent increase of core permeabilityup to 240 could be observed by application of 06 ccminflow rate However the sudden increase of permeability afterapproximately 45 PV of brine implies dislodgement of largersize particles which was observed in the size exclusion filters(Table 3)Therefore 05 ccmin injection rate is considered asoptimum in terms of slow and gradual increase of permeabil-ity (152)
A comparison of the results from the two sets ofexperiments shows that the effect of DC potential is more
Figure 4 Permeability changes results from set 2 experiments(injection rate optimization)
001
010
100
1000
10000
100000
1 2 3 4 5 6
Elem
enta
l con
cent
ratio
n (p
pm)
Injected pore volume
AlMg
NaK
Figure 5 ICP-MS analysis results (15 Vcm and 05 ccmin)
pronounced than the effect of hydrodynamic potential ICP-MS analysis results of the effluents collected at each PVof brine injection (after application of DC potential) showmetal elements corresponding to clay minerals in abundantquantity (Figure 5) whereas the quantity of clay trapped inthe filter papers is much lessThis indirectly indicates that theclays producedwith effluents are smaller than 1micron in sizeand flow easily through the pore channels (Table 3) It is alsoevident from this plot that the concentration of the relevantclay elements is seen to be reduced drastically after 5 porevolumes of water injection when the stabilized conditions areachieved and no further clay production is noticed
Temperature measurements during the flow studiesshowed an increasing trend with the injection time anddirect proportionality with the applied voltages (Figure 6)Nevertheless the behavior of temperature changes is similaramong set 2 experiments upon which the same potentialgradient was applied for all the flow experiments (Figure 7)This is due to the fact that Joule heating is proportional to theapplied voltage gradient
pHmeasurements of the effluent samples (Figure 8) showinitial increase of pH followed by a stabilization period tillthe end of the flow indicating alkaline environment on
15
20
25
30
35
40
0 1 2 3 4 5 6Injected pore volume
WFWF + 05VcmWF + 10VcmWF + 15Vcm
WF + 20Vcm
Flow
tem
pera
ture
(deg
∘C)
Figure 6 Temperature change upon application of different DCpotential
202224262830323436
0 1 2 3 4 5 6Injected pore volume
WF03 ccmin + 15Vcm
04 ccmin + 15Vcm05 ccmin + 15Vcm06 ccmin + 15Vcm
Flow
tem
pera
ture
(deg
∘C)
Figure 7 Temperature change at different flow rates at 15 Vcm
application of DC potential Asmentioned earlier differentialpressure across the filters is measured on continuous basisto monitor plugging of filter papers this is represented byFigure 9 From this figure it is evident that there is noincrease in Δ119875 during the brine flow indicating no clay orfine production However after commencing electrokineticassisted flow the Δ119875 across the filters increased rapidly atthe initial period slowed down after about 05 PV of brineinjection and finally stabilized after 5 PV of injection
4 Discussion
Overall observation from the above results shows that waterinjection efficiency can be enhanced by application of DCpotential Table 2 illustrates this phenomenon depicting alinear correlation between applied voltage and permeabil-ity increase or core stimulation This phenomenon canbe explained only by the fact that clay disintegration andmigration in submicron sizes take place under the influenceof various electrokinetic mechanisms as discussed earlier Itis known that the structure of clay mineral is capable ofchanging the sign of their surface potential with a changein pH of the medium In an acidic medium the surface of
6 Journal of Petroleum Engineering
555
665
775
885
99510
0 1 2 3 4 5 6
pH
Injected pore volume
WF15Vcm + 05 ccmin
Figure 8 pHmeasurements at optimized conditions (15 Vcm and05 ccmin)
01020304050607080
0 1 2 3 4 5 6Injected pore volume
WF15Vcm + 05 ccmin
ΔP
acro
ss fi
lters
(psi)
Figure 9 Differential pressure change across filtration units(15 Vcm and 05 ccmin)
clay particles is seen to be heteropotential the basal surfacesgain a net negative potential and the edges gain a net positivepotential [20] whereas in the alkaline medium the basalsurface of the mineral and their edges bear the same negativepotential This is due to the fact that Al and Fe hydroxides(which make part of the crystalline structure of the clayminerals) show amphoteric properties and depending on thepH of the medium may have excess of negative or positivecharges [21]
In the single phase flow experiment with NH4Cl brine
the net flow of ions towards the producer cathode is NH4
+
and H+ Being a bulky ion NH4
+ will find it difficult topenetrate between two basal plates of clay matrix howeverthe tiny H+ ions would easily penetrate and concentrate onthe basal surface Thus the production and flow of H+ ionsfrom the anode (injector side) towards cathode (producerside) may have twofold impacts on the clay structures (1) itwould increase the electrostatic repulsion between layers dueto excess of positive charges between the layers and increasethe distance between them (2) it would introduce localchanges in the pHandmake the clay particles heteropotentialwhich in turn change the clay structures from a compactlayered structure to colloidal ldquohouse of cardsrdquo structure asshown in Figure 1 With the help of the hydrodynamic and
electroosmotic potential the submicron size colloidal parti-cles would easily flow through the micron size pore channelsincreasing pore throat sizes and enhance core permeabilityThis explanation is supported by the high content of metals(Na Al Mg and K) in the produced brine (ICP-MS analysisFigure 5) which are naturally present in the claysThe impactof DC potential on clay disintegration and migration is alsosupported by the fact that filter paper clogging and resultingpressure rise were observed only after the application of DCpotential and not during normal brine flooding
5 Conclusion
The study aimed to investigate an alternate method toimprove water injectivity in tight sandstone reservoir Thefindings of this study can be summarized as follows
(i) Application of DC potential enhances the permeabil-ity of tight clay rich sandstone rocks which furtherboosts water injection efficiency
(ii) Clay disintegration and mobilization are believedto be one of the main contributing mechanisms topermeability enhancement by electrokinetics in sand-stone rocks However the effect of the application ofDC potential on the mineralogy of clays yet needs tobe thoroughly investigated
(iii) Permeability enhancement increases as both appliedpotential gradient and hydrodynamic injection rateincrease
(iv) The application of carefully studied injection rate andpotential difference may facilitate the injectivity ofwater based on the rock characteristics
(v) Flow temperature measurements showed an increas-ing trend with the injection time and direct propor-tionality with applied voltages
(vi) pH of the effluent is seen to increase when the flowwas subjected under DC potential which may haveimpact on clay disintegration
Nomenclature
119860 Cross-sectional area of flow m2119864 Applied electrical potential V119870 Absolute permeability m2 or D119896119890 Intrinsic electroosmotic permeability Pasdotm2V119871 Length of core mΔ119901 Pressure difference Pa119872 Dynamic viscosity Pasdots
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors are grateful to the Petroleum EngineeringDepartment at The Petroleum Institute Abu Dhabi for
Journal of Petroleum Engineering 7
providing the laboratory facilities to conduct the laboratoryexperiments
References
[1] T Ahmed Reservoir Engineering Handbook Gulf ProfessionalPublishing 2nd edition 2001
[2] P Willhite Waterflooding SPE Textbook Series vol 3 Societyof Petroleum Engineers 1986
[3] S Pang and M Sharma ldquoA model for predicting injectivitydecline inwater-injectionwellsrdquo SPE Formation Evaluation vol3 no 12 pp 194ndash201 1997
[4] A Tchistiakov ldquoPhysio-chemical aspects of clay migrationand injectivity decrease of geothermal clastic reservoirsrdquo inProceedings of theWorld Geothermal Congress (WGC rsquo00) 2000
[5] M A Miniawi W A F Ahmed Y A Ahmed and A R SoufildquoIn situ gelled acid as a diverting system in water injection wellrdquoin Proceedings of the SPEIADCMiddle East Drilling TechnologyConference and Exhibition pp 333ndash337 October 2007
[6] X Yi ldquoWater injectivity decline caused by sand mobilizationsimulation and predictionrdquo in Proceedings of the SPE PermianBasin Oil and Gas Recovery Conference Paper SPE 70032 pp202ndash209 Midland Tex USA May 2001
[7] B Scarth andCVozniak ldquoProduction problems associatedwithoverstressed hydraulic fracture treatmentsrdquo Paper SPE 89-40-79 Presented atAnnual TechnicalMeeting BanffCanada 1989
[8] X Wang H Zou X Cheng et al ldquoA new approach for matrixacidizing of water injectors in low-permeability Sandstonefieldsrdquo Paper SPE 73780 Presented at International Symposiumand Exhibition on Formation Damage Control Lafayette LaUSA 2012
[9] H A Al-Anazi H A Nasr-El-Din M K Hashem and J AHopkins ldquoMatrix acidizing of water injectors in a sandstonefield in Saudi Arabia a case studyrdquo in Proceedings of theSPEAAPG Western Regional Meetings Paper SPE 62825 pp585ndash594 Long Beach Calif USA June 2000
[10] S A Amba G V Chilingar and C M Beeson ldquoApplication ofelectrokinetics phenomena in civil and petroleum engineeringrdquoThe New York Academy of Sciences vol 118 no 14 pp 585ndash6021965
[11] S A Amba G V Chilingar and C M Beeson ldquoUse of directelectrical current for increasing the flow rate of reservoir fluidsduring petroleum recoveryrdquo Journal of Canadian PetroleumTechnology vol 3 no 1 pp 8ndash14 1964
[12] G Chilingar and C Beeson ldquoUse of direct electrical current forincreasing the flow rate of oil and water in a porous mediumrdquoJournal of Canadian Petroleum Technology vol 4 no 1 pp 81ndash88 1965
[13] M R Haroun G V Chilingar S Pamukcu J K Wittle HA Belhaj and M N A Bloushi ldquoOptimizing electroosmoticflow potential for electrically enhanced oil recovery (EEOR)in carbonate rock formations of Abu Dhabi based on rockproperties and compositionrdquo in Proceedings of the InternationalPetroleum Technology Conference (IPTC rsquo09) Paper SPE 13812pp 2645ndash2659 Doha Qatar December 2009
[14] J K Wittle D G Hill and G V Chilingar ldquoDirect currentelectrical enhanced oil recovery in heavy-oil reservoirs toimprove recovery reducewater cut and reduceH2S productionwhile increasing API gravityrdquo in Proceedings of the SPEWesternRegional and Pacific Section AAPG Joint Meeting (SPE rsquo08) pp405ndash423 Bakersfield Calif USA April 2008
[15] G Chilingar A El-Nassir and R Steven ldquoEffect of directelectrical current on permeability of sandstone corerdquo Journal ofPetroleum Technology vol 22 no 7 pp 830ndash836 1970 PaperSPE 2332
[16] J E Killough and J A Gonzalez ldquoA fully-implicit model forelectrically enhanced oil recoveryrdquo in Proceedings of the 61stAnnual Technical Conference and Exhibition New Orleans LaUSA October 1986
[17] S Pamukcu ldquoElectrochemical transport and transformationsrdquoin Chapter 2 in Electrochemical Remediation Technologiesfor Polluted Soils Sediments and Groundwater Reddy andCamaselle Eds pp 29ndash65 John Wiley amp Sons New York NYUSA 2009
[18] D H Gray and J K Mitchell ldquoFundamental aspects of electro-osmosis in soilsrdquo Journal of the Soil Mechanics and FoundationsDivision vol 93 no 6 pp 209ndash236 1967
[19] B Ghosh E W Al Shalabi and M Haroun ldquoThe effect of DCelectrical potential on enhancing sandstone reservoir perme-ability and oil recoveryrdquo Petroleum Science and Technology vol30 no 20 pp 2148ndash2159 2012
[20] V Sokolov ldquoModels of clay soil microstructuresrdquo InzhenernayaGeologiya no 6 pp 32ndash42 1991
[21] V I Osipov V N Sokolov and V V Eremeev Clay Seals of Oiland Gas Deposits Balkema RotterdamThe Netherlands 2004
Exp 1 05 Vcm at 02 ccmin 1195 1664 3925Exp 2 10 Vcm at 02 ccmin 1171 1993 7020Exp 3 15 Vcm at 02 ccmin 1247 2822 12630Exp 4 20Vcm at 02 ccmin 1193 5533 36379
Set 2Exp 5 03 ccmin at 15 Vcm 933 2189 13462Exp 6 04 ccmin at 15 Vcm 855 1994 13322Exp 7 05 ccmin at 15 Vcm 698 1759 15201Exp 8 06 ccmin at 15 Vcm 745 2530 23960
0
10
20
30
40
50
60
0 1 2 3 4 5 6
Perm
eabi
lity
(mD
)
Injected pore volume (cc)
WF05Vcm + WF10Vcm + WF15Vcm + WF
20Vcm + WF
Figure 3 Increase of core permeability on application of differentDC potential (DC voltage optimization)
potential gradient of 2Vcm however the sudden increaseof permeability after approximately 45 PV of brine indicatesdislodgment of large amount of clays and larger size particlesand possibly damaging the matrix itself It is obvious fromTable 3 that larger accumulation of mass on the filters (gt3 120583mand gt1 120583m) was observed in Experiment 4 which indicateslarge size particle production Thus 15 Vcm potential isconsidered as optimum in which slow and progressiveincrease of permeability is observed (126)
In the second set of experiments the optimized potential(15 Vcm) was applied and fluid flow rates were varied Itcould be seen from the coreflooding results (Table 2 and
Table 3 Mass of clay accumulations on size exclusion filters for allexperiments
Mass of accumulation on filtration unitsExperiments 3 120583 paper (g) 1 120583 paper (g)Set 1
Figure 4) that upon the application of a fixed voltage perme-ability increased from its base value as the hydrodynamic flowrate was increased An apparent increase of core permeabilityup to 240 could be observed by application of 06 ccminflow rate However the sudden increase of permeability afterapproximately 45 PV of brine implies dislodgement of largersize particles which was observed in the size exclusion filters(Table 3)Therefore 05 ccmin injection rate is considered asoptimum in terms of slow and gradual increase of permeabil-ity (152)
A comparison of the results from the two sets ofexperiments shows that the effect of DC potential is more
Figure 4 Permeability changes results from set 2 experiments(injection rate optimization)
001
010
100
1000
10000
100000
1 2 3 4 5 6
Elem
enta
l con
cent
ratio
n (p
pm)
Injected pore volume
AlMg
NaK
Figure 5 ICP-MS analysis results (15 Vcm and 05 ccmin)
pronounced than the effect of hydrodynamic potential ICP-MS analysis results of the effluents collected at each PVof brine injection (after application of DC potential) showmetal elements corresponding to clay minerals in abundantquantity (Figure 5) whereas the quantity of clay trapped inthe filter papers is much lessThis indirectly indicates that theclays producedwith effluents are smaller than 1micron in sizeand flow easily through the pore channels (Table 3) It is alsoevident from this plot that the concentration of the relevantclay elements is seen to be reduced drastically after 5 porevolumes of water injection when the stabilized conditions areachieved and no further clay production is noticed
Temperature measurements during the flow studiesshowed an increasing trend with the injection time anddirect proportionality with the applied voltages (Figure 6)Nevertheless the behavior of temperature changes is similaramong set 2 experiments upon which the same potentialgradient was applied for all the flow experiments (Figure 7)This is due to the fact that Joule heating is proportional to theapplied voltage gradient
pHmeasurements of the effluent samples (Figure 8) showinitial increase of pH followed by a stabilization period tillthe end of the flow indicating alkaline environment on
15
20
25
30
35
40
0 1 2 3 4 5 6Injected pore volume
WFWF + 05VcmWF + 10VcmWF + 15Vcm
WF + 20Vcm
Flow
tem
pera
ture
(deg
∘C)
Figure 6 Temperature change upon application of different DCpotential
202224262830323436
0 1 2 3 4 5 6Injected pore volume
WF03 ccmin + 15Vcm
04 ccmin + 15Vcm05 ccmin + 15Vcm06 ccmin + 15Vcm
Flow
tem
pera
ture
(deg
∘C)
Figure 7 Temperature change at different flow rates at 15 Vcm
application of DC potential Asmentioned earlier differentialpressure across the filters is measured on continuous basisto monitor plugging of filter papers this is represented byFigure 9 From this figure it is evident that there is noincrease in Δ119875 during the brine flow indicating no clay orfine production However after commencing electrokineticassisted flow the Δ119875 across the filters increased rapidly atthe initial period slowed down after about 05 PV of brineinjection and finally stabilized after 5 PV of injection
4 Discussion
Overall observation from the above results shows that waterinjection efficiency can be enhanced by application of DCpotential Table 2 illustrates this phenomenon depicting alinear correlation between applied voltage and permeabil-ity increase or core stimulation This phenomenon canbe explained only by the fact that clay disintegration andmigration in submicron sizes take place under the influenceof various electrokinetic mechanisms as discussed earlier Itis known that the structure of clay mineral is capable ofchanging the sign of their surface potential with a changein pH of the medium In an acidic medium the surface of
6 Journal of Petroleum Engineering
555
665
775
885
99510
0 1 2 3 4 5 6
pH
Injected pore volume
WF15Vcm + 05 ccmin
Figure 8 pHmeasurements at optimized conditions (15 Vcm and05 ccmin)
01020304050607080
0 1 2 3 4 5 6Injected pore volume
WF15Vcm + 05 ccmin
ΔP
acro
ss fi
lters
(psi)
Figure 9 Differential pressure change across filtration units(15 Vcm and 05 ccmin)
clay particles is seen to be heteropotential the basal surfacesgain a net negative potential and the edges gain a net positivepotential [20] whereas in the alkaline medium the basalsurface of the mineral and their edges bear the same negativepotential This is due to the fact that Al and Fe hydroxides(which make part of the crystalline structure of the clayminerals) show amphoteric properties and depending on thepH of the medium may have excess of negative or positivecharges [21]
In the single phase flow experiment with NH4Cl brine
the net flow of ions towards the producer cathode is NH4
+
and H+ Being a bulky ion NH4
+ will find it difficult topenetrate between two basal plates of clay matrix howeverthe tiny H+ ions would easily penetrate and concentrate onthe basal surface Thus the production and flow of H+ ionsfrom the anode (injector side) towards cathode (producerside) may have twofold impacts on the clay structures (1) itwould increase the electrostatic repulsion between layers dueto excess of positive charges between the layers and increasethe distance between them (2) it would introduce localchanges in the pHandmake the clay particles heteropotentialwhich in turn change the clay structures from a compactlayered structure to colloidal ldquohouse of cardsrdquo structure asshown in Figure 1 With the help of the hydrodynamic and
electroosmotic potential the submicron size colloidal parti-cles would easily flow through the micron size pore channelsincreasing pore throat sizes and enhance core permeabilityThis explanation is supported by the high content of metals(Na Al Mg and K) in the produced brine (ICP-MS analysisFigure 5) which are naturally present in the claysThe impactof DC potential on clay disintegration and migration is alsosupported by the fact that filter paper clogging and resultingpressure rise were observed only after the application of DCpotential and not during normal brine flooding
5 Conclusion
The study aimed to investigate an alternate method toimprove water injectivity in tight sandstone reservoir Thefindings of this study can be summarized as follows
(i) Application of DC potential enhances the permeabil-ity of tight clay rich sandstone rocks which furtherboosts water injection efficiency
(ii) Clay disintegration and mobilization are believedto be one of the main contributing mechanisms topermeability enhancement by electrokinetics in sand-stone rocks However the effect of the application ofDC potential on the mineralogy of clays yet needs tobe thoroughly investigated
(iii) Permeability enhancement increases as both appliedpotential gradient and hydrodynamic injection rateincrease
(iv) The application of carefully studied injection rate andpotential difference may facilitate the injectivity ofwater based on the rock characteristics
(v) Flow temperature measurements showed an increas-ing trend with the injection time and direct propor-tionality with applied voltages
(vi) pH of the effluent is seen to increase when the flowwas subjected under DC potential which may haveimpact on clay disintegration
Nomenclature
119860 Cross-sectional area of flow m2119864 Applied electrical potential V119870 Absolute permeability m2 or D119896119890 Intrinsic electroosmotic permeability Pasdotm2V119871 Length of core mΔ119901 Pressure difference Pa119872 Dynamic viscosity Pasdots
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors are grateful to the Petroleum EngineeringDepartment at The Petroleum Institute Abu Dhabi for
Journal of Petroleum Engineering 7
providing the laboratory facilities to conduct the laboratoryexperiments
References
[1] T Ahmed Reservoir Engineering Handbook Gulf ProfessionalPublishing 2nd edition 2001
[2] P Willhite Waterflooding SPE Textbook Series vol 3 Societyof Petroleum Engineers 1986
[3] S Pang and M Sharma ldquoA model for predicting injectivitydecline inwater-injectionwellsrdquo SPE Formation Evaluation vol3 no 12 pp 194ndash201 1997
[4] A Tchistiakov ldquoPhysio-chemical aspects of clay migrationand injectivity decrease of geothermal clastic reservoirsrdquo inProceedings of theWorld Geothermal Congress (WGC rsquo00) 2000
[5] M A Miniawi W A F Ahmed Y A Ahmed and A R SoufildquoIn situ gelled acid as a diverting system in water injection wellrdquoin Proceedings of the SPEIADCMiddle East Drilling TechnologyConference and Exhibition pp 333ndash337 October 2007
[6] X Yi ldquoWater injectivity decline caused by sand mobilizationsimulation and predictionrdquo in Proceedings of the SPE PermianBasin Oil and Gas Recovery Conference Paper SPE 70032 pp202ndash209 Midland Tex USA May 2001
[7] B Scarth andCVozniak ldquoProduction problems associatedwithoverstressed hydraulic fracture treatmentsrdquo Paper SPE 89-40-79 Presented atAnnual TechnicalMeeting BanffCanada 1989
[8] X Wang H Zou X Cheng et al ldquoA new approach for matrixacidizing of water injectors in low-permeability Sandstonefieldsrdquo Paper SPE 73780 Presented at International Symposiumand Exhibition on Formation Damage Control Lafayette LaUSA 2012
[9] H A Al-Anazi H A Nasr-El-Din M K Hashem and J AHopkins ldquoMatrix acidizing of water injectors in a sandstonefield in Saudi Arabia a case studyrdquo in Proceedings of theSPEAAPG Western Regional Meetings Paper SPE 62825 pp585ndash594 Long Beach Calif USA June 2000
[10] S A Amba G V Chilingar and C M Beeson ldquoApplication ofelectrokinetics phenomena in civil and petroleum engineeringrdquoThe New York Academy of Sciences vol 118 no 14 pp 585ndash6021965
[11] S A Amba G V Chilingar and C M Beeson ldquoUse of directelectrical current for increasing the flow rate of reservoir fluidsduring petroleum recoveryrdquo Journal of Canadian PetroleumTechnology vol 3 no 1 pp 8ndash14 1964
[12] G Chilingar and C Beeson ldquoUse of direct electrical current forincreasing the flow rate of oil and water in a porous mediumrdquoJournal of Canadian Petroleum Technology vol 4 no 1 pp 81ndash88 1965
[13] M R Haroun G V Chilingar S Pamukcu J K Wittle HA Belhaj and M N A Bloushi ldquoOptimizing electroosmoticflow potential for electrically enhanced oil recovery (EEOR)in carbonate rock formations of Abu Dhabi based on rockproperties and compositionrdquo in Proceedings of the InternationalPetroleum Technology Conference (IPTC rsquo09) Paper SPE 13812pp 2645ndash2659 Doha Qatar December 2009
[14] J K Wittle D G Hill and G V Chilingar ldquoDirect currentelectrical enhanced oil recovery in heavy-oil reservoirs toimprove recovery reducewater cut and reduceH2S productionwhile increasing API gravityrdquo in Proceedings of the SPEWesternRegional and Pacific Section AAPG Joint Meeting (SPE rsquo08) pp405ndash423 Bakersfield Calif USA April 2008
[15] G Chilingar A El-Nassir and R Steven ldquoEffect of directelectrical current on permeability of sandstone corerdquo Journal ofPetroleum Technology vol 22 no 7 pp 830ndash836 1970 PaperSPE 2332
[16] J E Killough and J A Gonzalez ldquoA fully-implicit model forelectrically enhanced oil recoveryrdquo in Proceedings of the 61stAnnual Technical Conference and Exhibition New Orleans LaUSA October 1986
[17] S Pamukcu ldquoElectrochemical transport and transformationsrdquoin Chapter 2 in Electrochemical Remediation Technologiesfor Polluted Soils Sediments and Groundwater Reddy andCamaselle Eds pp 29ndash65 John Wiley amp Sons New York NYUSA 2009
[18] D H Gray and J K Mitchell ldquoFundamental aspects of electro-osmosis in soilsrdquo Journal of the Soil Mechanics and FoundationsDivision vol 93 no 6 pp 209ndash236 1967
[19] B Ghosh E W Al Shalabi and M Haroun ldquoThe effect of DCelectrical potential on enhancing sandstone reservoir perme-ability and oil recoveryrdquo Petroleum Science and Technology vol30 no 20 pp 2148ndash2159 2012
[20] V Sokolov ldquoModels of clay soil microstructuresrdquo InzhenernayaGeologiya no 6 pp 32ndash42 1991
[21] V I Osipov V N Sokolov and V V Eremeev Clay Seals of Oiland Gas Deposits Balkema RotterdamThe Netherlands 2004
Figure 4 Permeability changes results from set 2 experiments(injection rate optimization)
001
010
100
1000
10000
100000
1 2 3 4 5 6
Elem
enta
l con
cent
ratio
n (p
pm)
Injected pore volume
AlMg
NaK
Figure 5 ICP-MS analysis results (15 Vcm and 05 ccmin)
pronounced than the effect of hydrodynamic potential ICP-MS analysis results of the effluents collected at each PVof brine injection (after application of DC potential) showmetal elements corresponding to clay minerals in abundantquantity (Figure 5) whereas the quantity of clay trapped inthe filter papers is much lessThis indirectly indicates that theclays producedwith effluents are smaller than 1micron in sizeand flow easily through the pore channels (Table 3) It is alsoevident from this plot that the concentration of the relevantclay elements is seen to be reduced drastically after 5 porevolumes of water injection when the stabilized conditions areachieved and no further clay production is noticed
Temperature measurements during the flow studiesshowed an increasing trend with the injection time anddirect proportionality with the applied voltages (Figure 6)Nevertheless the behavior of temperature changes is similaramong set 2 experiments upon which the same potentialgradient was applied for all the flow experiments (Figure 7)This is due to the fact that Joule heating is proportional to theapplied voltage gradient
pHmeasurements of the effluent samples (Figure 8) showinitial increase of pH followed by a stabilization period tillthe end of the flow indicating alkaline environment on
15
20
25
30
35
40
0 1 2 3 4 5 6Injected pore volume
WFWF + 05VcmWF + 10VcmWF + 15Vcm
WF + 20Vcm
Flow
tem
pera
ture
(deg
∘C)
Figure 6 Temperature change upon application of different DCpotential
202224262830323436
0 1 2 3 4 5 6Injected pore volume
WF03 ccmin + 15Vcm
04 ccmin + 15Vcm05 ccmin + 15Vcm06 ccmin + 15Vcm
Flow
tem
pera
ture
(deg
∘C)
Figure 7 Temperature change at different flow rates at 15 Vcm
application of DC potential Asmentioned earlier differentialpressure across the filters is measured on continuous basisto monitor plugging of filter papers this is represented byFigure 9 From this figure it is evident that there is noincrease in Δ119875 during the brine flow indicating no clay orfine production However after commencing electrokineticassisted flow the Δ119875 across the filters increased rapidly atthe initial period slowed down after about 05 PV of brineinjection and finally stabilized after 5 PV of injection
4 Discussion
Overall observation from the above results shows that waterinjection efficiency can be enhanced by application of DCpotential Table 2 illustrates this phenomenon depicting alinear correlation between applied voltage and permeabil-ity increase or core stimulation This phenomenon canbe explained only by the fact that clay disintegration andmigration in submicron sizes take place under the influenceof various electrokinetic mechanisms as discussed earlier Itis known that the structure of clay mineral is capable ofchanging the sign of their surface potential with a changein pH of the medium In an acidic medium the surface of
6 Journal of Petroleum Engineering
555
665
775
885
99510
0 1 2 3 4 5 6
pH
Injected pore volume
WF15Vcm + 05 ccmin
Figure 8 pHmeasurements at optimized conditions (15 Vcm and05 ccmin)
01020304050607080
0 1 2 3 4 5 6Injected pore volume
WF15Vcm + 05 ccmin
ΔP
acro
ss fi
lters
(psi)
Figure 9 Differential pressure change across filtration units(15 Vcm and 05 ccmin)
clay particles is seen to be heteropotential the basal surfacesgain a net negative potential and the edges gain a net positivepotential [20] whereas in the alkaline medium the basalsurface of the mineral and their edges bear the same negativepotential This is due to the fact that Al and Fe hydroxides(which make part of the crystalline structure of the clayminerals) show amphoteric properties and depending on thepH of the medium may have excess of negative or positivecharges [21]
In the single phase flow experiment with NH4Cl brine
the net flow of ions towards the producer cathode is NH4
+
and H+ Being a bulky ion NH4
+ will find it difficult topenetrate between two basal plates of clay matrix howeverthe tiny H+ ions would easily penetrate and concentrate onthe basal surface Thus the production and flow of H+ ionsfrom the anode (injector side) towards cathode (producerside) may have twofold impacts on the clay structures (1) itwould increase the electrostatic repulsion between layers dueto excess of positive charges between the layers and increasethe distance between them (2) it would introduce localchanges in the pHandmake the clay particles heteropotentialwhich in turn change the clay structures from a compactlayered structure to colloidal ldquohouse of cardsrdquo structure asshown in Figure 1 With the help of the hydrodynamic and
electroosmotic potential the submicron size colloidal parti-cles would easily flow through the micron size pore channelsincreasing pore throat sizes and enhance core permeabilityThis explanation is supported by the high content of metals(Na Al Mg and K) in the produced brine (ICP-MS analysisFigure 5) which are naturally present in the claysThe impactof DC potential on clay disintegration and migration is alsosupported by the fact that filter paper clogging and resultingpressure rise were observed only after the application of DCpotential and not during normal brine flooding
5 Conclusion
The study aimed to investigate an alternate method toimprove water injectivity in tight sandstone reservoir Thefindings of this study can be summarized as follows
(i) Application of DC potential enhances the permeabil-ity of tight clay rich sandstone rocks which furtherboosts water injection efficiency
(ii) Clay disintegration and mobilization are believedto be one of the main contributing mechanisms topermeability enhancement by electrokinetics in sand-stone rocks However the effect of the application ofDC potential on the mineralogy of clays yet needs tobe thoroughly investigated
(iii) Permeability enhancement increases as both appliedpotential gradient and hydrodynamic injection rateincrease
(iv) The application of carefully studied injection rate andpotential difference may facilitate the injectivity ofwater based on the rock characteristics
(v) Flow temperature measurements showed an increas-ing trend with the injection time and direct propor-tionality with applied voltages
(vi) pH of the effluent is seen to increase when the flowwas subjected under DC potential which may haveimpact on clay disintegration
Nomenclature
119860 Cross-sectional area of flow m2119864 Applied electrical potential V119870 Absolute permeability m2 or D119896119890 Intrinsic electroosmotic permeability Pasdotm2V119871 Length of core mΔ119901 Pressure difference Pa119872 Dynamic viscosity Pasdots
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors are grateful to the Petroleum EngineeringDepartment at The Petroleum Institute Abu Dhabi for
Journal of Petroleum Engineering 7
providing the laboratory facilities to conduct the laboratoryexperiments
References
[1] T Ahmed Reservoir Engineering Handbook Gulf ProfessionalPublishing 2nd edition 2001
[2] P Willhite Waterflooding SPE Textbook Series vol 3 Societyof Petroleum Engineers 1986
[3] S Pang and M Sharma ldquoA model for predicting injectivitydecline inwater-injectionwellsrdquo SPE Formation Evaluation vol3 no 12 pp 194ndash201 1997
[4] A Tchistiakov ldquoPhysio-chemical aspects of clay migrationand injectivity decrease of geothermal clastic reservoirsrdquo inProceedings of theWorld Geothermal Congress (WGC rsquo00) 2000
[5] M A Miniawi W A F Ahmed Y A Ahmed and A R SoufildquoIn situ gelled acid as a diverting system in water injection wellrdquoin Proceedings of the SPEIADCMiddle East Drilling TechnologyConference and Exhibition pp 333ndash337 October 2007
[6] X Yi ldquoWater injectivity decline caused by sand mobilizationsimulation and predictionrdquo in Proceedings of the SPE PermianBasin Oil and Gas Recovery Conference Paper SPE 70032 pp202ndash209 Midland Tex USA May 2001
[7] B Scarth andCVozniak ldquoProduction problems associatedwithoverstressed hydraulic fracture treatmentsrdquo Paper SPE 89-40-79 Presented atAnnual TechnicalMeeting BanffCanada 1989
[8] X Wang H Zou X Cheng et al ldquoA new approach for matrixacidizing of water injectors in low-permeability Sandstonefieldsrdquo Paper SPE 73780 Presented at International Symposiumand Exhibition on Formation Damage Control Lafayette LaUSA 2012
[9] H A Al-Anazi H A Nasr-El-Din M K Hashem and J AHopkins ldquoMatrix acidizing of water injectors in a sandstonefield in Saudi Arabia a case studyrdquo in Proceedings of theSPEAAPG Western Regional Meetings Paper SPE 62825 pp585ndash594 Long Beach Calif USA June 2000
[10] S A Amba G V Chilingar and C M Beeson ldquoApplication ofelectrokinetics phenomena in civil and petroleum engineeringrdquoThe New York Academy of Sciences vol 118 no 14 pp 585ndash6021965
[11] S A Amba G V Chilingar and C M Beeson ldquoUse of directelectrical current for increasing the flow rate of reservoir fluidsduring petroleum recoveryrdquo Journal of Canadian PetroleumTechnology vol 3 no 1 pp 8ndash14 1964
[12] G Chilingar and C Beeson ldquoUse of direct electrical current forincreasing the flow rate of oil and water in a porous mediumrdquoJournal of Canadian Petroleum Technology vol 4 no 1 pp 81ndash88 1965
[13] M R Haroun G V Chilingar S Pamukcu J K Wittle HA Belhaj and M N A Bloushi ldquoOptimizing electroosmoticflow potential for electrically enhanced oil recovery (EEOR)in carbonate rock formations of Abu Dhabi based on rockproperties and compositionrdquo in Proceedings of the InternationalPetroleum Technology Conference (IPTC rsquo09) Paper SPE 13812pp 2645ndash2659 Doha Qatar December 2009
[14] J K Wittle D G Hill and G V Chilingar ldquoDirect currentelectrical enhanced oil recovery in heavy-oil reservoirs toimprove recovery reducewater cut and reduceH2S productionwhile increasing API gravityrdquo in Proceedings of the SPEWesternRegional and Pacific Section AAPG Joint Meeting (SPE rsquo08) pp405ndash423 Bakersfield Calif USA April 2008
[15] G Chilingar A El-Nassir and R Steven ldquoEffect of directelectrical current on permeability of sandstone corerdquo Journal ofPetroleum Technology vol 22 no 7 pp 830ndash836 1970 PaperSPE 2332
[16] J E Killough and J A Gonzalez ldquoA fully-implicit model forelectrically enhanced oil recoveryrdquo in Proceedings of the 61stAnnual Technical Conference and Exhibition New Orleans LaUSA October 1986
[17] S Pamukcu ldquoElectrochemical transport and transformationsrdquoin Chapter 2 in Electrochemical Remediation Technologiesfor Polluted Soils Sediments and Groundwater Reddy andCamaselle Eds pp 29ndash65 John Wiley amp Sons New York NYUSA 2009
[18] D H Gray and J K Mitchell ldquoFundamental aspects of electro-osmosis in soilsrdquo Journal of the Soil Mechanics and FoundationsDivision vol 93 no 6 pp 209ndash236 1967
[19] B Ghosh E W Al Shalabi and M Haroun ldquoThe effect of DCelectrical potential on enhancing sandstone reservoir perme-ability and oil recoveryrdquo Petroleum Science and Technology vol30 no 20 pp 2148ndash2159 2012
[20] V Sokolov ldquoModels of clay soil microstructuresrdquo InzhenernayaGeologiya no 6 pp 32ndash42 1991
[21] V I Osipov V N Sokolov and V V Eremeev Clay Seals of Oiland Gas Deposits Balkema RotterdamThe Netherlands 2004
Figure 8 pHmeasurements at optimized conditions (15 Vcm and05 ccmin)
01020304050607080
0 1 2 3 4 5 6Injected pore volume
WF15Vcm + 05 ccmin
ΔP
acro
ss fi
lters
(psi)
Figure 9 Differential pressure change across filtration units(15 Vcm and 05 ccmin)
clay particles is seen to be heteropotential the basal surfacesgain a net negative potential and the edges gain a net positivepotential [20] whereas in the alkaline medium the basalsurface of the mineral and their edges bear the same negativepotential This is due to the fact that Al and Fe hydroxides(which make part of the crystalline structure of the clayminerals) show amphoteric properties and depending on thepH of the medium may have excess of negative or positivecharges [21]
In the single phase flow experiment with NH4Cl brine
the net flow of ions towards the producer cathode is NH4
+
and H+ Being a bulky ion NH4
+ will find it difficult topenetrate between two basal plates of clay matrix howeverthe tiny H+ ions would easily penetrate and concentrate onthe basal surface Thus the production and flow of H+ ionsfrom the anode (injector side) towards cathode (producerside) may have twofold impacts on the clay structures (1) itwould increase the electrostatic repulsion between layers dueto excess of positive charges between the layers and increasethe distance between them (2) it would introduce localchanges in the pHandmake the clay particles heteropotentialwhich in turn change the clay structures from a compactlayered structure to colloidal ldquohouse of cardsrdquo structure asshown in Figure 1 With the help of the hydrodynamic and
electroosmotic potential the submicron size colloidal parti-cles would easily flow through the micron size pore channelsincreasing pore throat sizes and enhance core permeabilityThis explanation is supported by the high content of metals(Na Al Mg and K) in the produced brine (ICP-MS analysisFigure 5) which are naturally present in the claysThe impactof DC potential on clay disintegration and migration is alsosupported by the fact that filter paper clogging and resultingpressure rise were observed only after the application of DCpotential and not during normal brine flooding
5 Conclusion
The study aimed to investigate an alternate method toimprove water injectivity in tight sandstone reservoir Thefindings of this study can be summarized as follows
(i) Application of DC potential enhances the permeabil-ity of tight clay rich sandstone rocks which furtherboosts water injection efficiency
(ii) Clay disintegration and mobilization are believedto be one of the main contributing mechanisms topermeability enhancement by electrokinetics in sand-stone rocks However the effect of the application ofDC potential on the mineralogy of clays yet needs tobe thoroughly investigated
(iii) Permeability enhancement increases as both appliedpotential gradient and hydrodynamic injection rateincrease
(iv) The application of carefully studied injection rate andpotential difference may facilitate the injectivity ofwater based on the rock characteristics
(v) Flow temperature measurements showed an increas-ing trend with the injection time and direct propor-tionality with applied voltages
(vi) pH of the effluent is seen to increase when the flowwas subjected under DC potential which may haveimpact on clay disintegration
Nomenclature
119860 Cross-sectional area of flow m2119864 Applied electrical potential V119870 Absolute permeability m2 or D119896119890 Intrinsic electroosmotic permeability Pasdotm2V119871 Length of core mΔ119901 Pressure difference Pa119872 Dynamic viscosity Pasdots
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors are grateful to the Petroleum EngineeringDepartment at The Petroleum Institute Abu Dhabi for
Journal of Petroleum Engineering 7
providing the laboratory facilities to conduct the laboratoryexperiments
References
[1] T Ahmed Reservoir Engineering Handbook Gulf ProfessionalPublishing 2nd edition 2001
[2] P Willhite Waterflooding SPE Textbook Series vol 3 Societyof Petroleum Engineers 1986
[3] S Pang and M Sharma ldquoA model for predicting injectivitydecline inwater-injectionwellsrdquo SPE Formation Evaluation vol3 no 12 pp 194ndash201 1997
[4] A Tchistiakov ldquoPhysio-chemical aspects of clay migrationand injectivity decrease of geothermal clastic reservoirsrdquo inProceedings of theWorld Geothermal Congress (WGC rsquo00) 2000
[5] M A Miniawi W A F Ahmed Y A Ahmed and A R SoufildquoIn situ gelled acid as a diverting system in water injection wellrdquoin Proceedings of the SPEIADCMiddle East Drilling TechnologyConference and Exhibition pp 333ndash337 October 2007
[6] X Yi ldquoWater injectivity decline caused by sand mobilizationsimulation and predictionrdquo in Proceedings of the SPE PermianBasin Oil and Gas Recovery Conference Paper SPE 70032 pp202ndash209 Midland Tex USA May 2001
[7] B Scarth andCVozniak ldquoProduction problems associatedwithoverstressed hydraulic fracture treatmentsrdquo Paper SPE 89-40-79 Presented atAnnual TechnicalMeeting BanffCanada 1989
[8] X Wang H Zou X Cheng et al ldquoA new approach for matrixacidizing of water injectors in low-permeability Sandstonefieldsrdquo Paper SPE 73780 Presented at International Symposiumand Exhibition on Formation Damage Control Lafayette LaUSA 2012
[9] H A Al-Anazi H A Nasr-El-Din M K Hashem and J AHopkins ldquoMatrix acidizing of water injectors in a sandstonefield in Saudi Arabia a case studyrdquo in Proceedings of theSPEAAPG Western Regional Meetings Paper SPE 62825 pp585ndash594 Long Beach Calif USA June 2000
[10] S A Amba G V Chilingar and C M Beeson ldquoApplication ofelectrokinetics phenomena in civil and petroleum engineeringrdquoThe New York Academy of Sciences vol 118 no 14 pp 585ndash6021965
[11] S A Amba G V Chilingar and C M Beeson ldquoUse of directelectrical current for increasing the flow rate of reservoir fluidsduring petroleum recoveryrdquo Journal of Canadian PetroleumTechnology vol 3 no 1 pp 8ndash14 1964
[12] G Chilingar and C Beeson ldquoUse of direct electrical current forincreasing the flow rate of oil and water in a porous mediumrdquoJournal of Canadian Petroleum Technology vol 4 no 1 pp 81ndash88 1965
[13] M R Haroun G V Chilingar S Pamukcu J K Wittle HA Belhaj and M N A Bloushi ldquoOptimizing electroosmoticflow potential for electrically enhanced oil recovery (EEOR)in carbonate rock formations of Abu Dhabi based on rockproperties and compositionrdquo in Proceedings of the InternationalPetroleum Technology Conference (IPTC rsquo09) Paper SPE 13812pp 2645ndash2659 Doha Qatar December 2009
[14] J K Wittle D G Hill and G V Chilingar ldquoDirect currentelectrical enhanced oil recovery in heavy-oil reservoirs toimprove recovery reducewater cut and reduceH2S productionwhile increasing API gravityrdquo in Proceedings of the SPEWesternRegional and Pacific Section AAPG Joint Meeting (SPE rsquo08) pp405ndash423 Bakersfield Calif USA April 2008
[15] G Chilingar A El-Nassir and R Steven ldquoEffect of directelectrical current on permeability of sandstone corerdquo Journal ofPetroleum Technology vol 22 no 7 pp 830ndash836 1970 PaperSPE 2332
[16] J E Killough and J A Gonzalez ldquoA fully-implicit model forelectrically enhanced oil recoveryrdquo in Proceedings of the 61stAnnual Technical Conference and Exhibition New Orleans LaUSA October 1986
[17] S Pamukcu ldquoElectrochemical transport and transformationsrdquoin Chapter 2 in Electrochemical Remediation Technologiesfor Polluted Soils Sediments and Groundwater Reddy andCamaselle Eds pp 29ndash65 John Wiley amp Sons New York NYUSA 2009
[18] D H Gray and J K Mitchell ldquoFundamental aspects of electro-osmosis in soilsrdquo Journal of the Soil Mechanics and FoundationsDivision vol 93 no 6 pp 209ndash236 1967
[19] B Ghosh E W Al Shalabi and M Haroun ldquoThe effect of DCelectrical potential on enhancing sandstone reservoir perme-ability and oil recoveryrdquo Petroleum Science and Technology vol30 no 20 pp 2148ndash2159 2012
[20] V Sokolov ldquoModels of clay soil microstructuresrdquo InzhenernayaGeologiya no 6 pp 32ndash42 1991
[21] V I Osipov V N Sokolov and V V Eremeev Clay Seals of Oiland Gas Deposits Balkema RotterdamThe Netherlands 2004
providing the laboratory facilities to conduct the laboratoryexperiments
References
[1] T Ahmed Reservoir Engineering Handbook Gulf ProfessionalPublishing 2nd edition 2001
[2] P Willhite Waterflooding SPE Textbook Series vol 3 Societyof Petroleum Engineers 1986
[3] S Pang and M Sharma ldquoA model for predicting injectivitydecline inwater-injectionwellsrdquo SPE Formation Evaluation vol3 no 12 pp 194ndash201 1997
[4] A Tchistiakov ldquoPhysio-chemical aspects of clay migrationand injectivity decrease of geothermal clastic reservoirsrdquo inProceedings of theWorld Geothermal Congress (WGC rsquo00) 2000
[5] M A Miniawi W A F Ahmed Y A Ahmed and A R SoufildquoIn situ gelled acid as a diverting system in water injection wellrdquoin Proceedings of the SPEIADCMiddle East Drilling TechnologyConference and Exhibition pp 333ndash337 October 2007
[6] X Yi ldquoWater injectivity decline caused by sand mobilizationsimulation and predictionrdquo in Proceedings of the SPE PermianBasin Oil and Gas Recovery Conference Paper SPE 70032 pp202ndash209 Midland Tex USA May 2001
[7] B Scarth andCVozniak ldquoProduction problems associatedwithoverstressed hydraulic fracture treatmentsrdquo Paper SPE 89-40-79 Presented atAnnual TechnicalMeeting BanffCanada 1989
[8] X Wang H Zou X Cheng et al ldquoA new approach for matrixacidizing of water injectors in low-permeability Sandstonefieldsrdquo Paper SPE 73780 Presented at International Symposiumand Exhibition on Formation Damage Control Lafayette LaUSA 2012
[9] H A Al-Anazi H A Nasr-El-Din M K Hashem and J AHopkins ldquoMatrix acidizing of water injectors in a sandstonefield in Saudi Arabia a case studyrdquo in Proceedings of theSPEAAPG Western Regional Meetings Paper SPE 62825 pp585ndash594 Long Beach Calif USA June 2000
[10] S A Amba G V Chilingar and C M Beeson ldquoApplication ofelectrokinetics phenomena in civil and petroleum engineeringrdquoThe New York Academy of Sciences vol 118 no 14 pp 585ndash6021965
[11] S A Amba G V Chilingar and C M Beeson ldquoUse of directelectrical current for increasing the flow rate of reservoir fluidsduring petroleum recoveryrdquo Journal of Canadian PetroleumTechnology vol 3 no 1 pp 8ndash14 1964
[12] G Chilingar and C Beeson ldquoUse of direct electrical current forincreasing the flow rate of oil and water in a porous mediumrdquoJournal of Canadian Petroleum Technology vol 4 no 1 pp 81ndash88 1965
[13] M R Haroun G V Chilingar S Pamukcu J K Wittle HA Belhaj and M N A Bloushi ldquoOptimizing electroosmoticflow potential for electrically enhanced oil recovery (EEOR)in carbonate rock formations of Abu Dhabi based on rockproperties and compositionrdquo in Proceedings of the InternationalPetroleum Technology Conference (IPTC rsquo09) Paper SPE 13812pp 2645ndash2659 Doha Qatar December 2009
[14] J K Wittle D G Hill and G V Chilingar ldquoDirect currentelectrical enhanced oil recovery in heavy-oil reservoirs toimprove recovery reducewater cut and reduceH2S productionwhile increasing API gravityrdquo in Proceedings of the SPEWesternRegional and Pacific Section AAPG Joint Meeting (SPE rsquo08) pp405ndash423 Bakersfield Calif USA April 2008
[15] G Chilingar A El-Nassir and R Steven ldquoEffect of directelectrical current on permeability of sandstone corerdquo Journal ofPetroleum Technology vol 22 no 7 pp 830ndash836 1970 PaperSPE 2332
[16] J E Killough and J A Gonzalez ldquoA fully-implicit model forelectrically enhanced oil recoveryrdquo in Proceedings of the 61stAnnual Technical Conference and Exhibition New Orleans LaUSA October 1986
[17] S Pamukcu ldquoElectrochemical transport and transformationsrdquoin Chapter 2 in Electrochemical Remediation Technologiesfor Polluted Soils Sediments and Groundwater Reddy andCamaselle Eds pp 29ndash65 John Wiley amp Sons New York NYUSA 2009
[18] D H Gray and J K Mitchell ldquoFundamental aspects of electro-osmosis in soilsrdquo Journal of the Soil Mechanics and FoundationsDivision vol 93 no 6 pp 209ndash236 1967
[19] B Ghosh E W Al Shalabi and M Haroun ldquoThe effect of DCelectrical potential on enhancing sandstone reservoir perme-ability and oil recoveryrdquo Petroleum Science and Technology vol30 no 20 pp 2148ndash2159 2012
[20] V Sokolov ldquoModels of clay soil microstructuresrdquo InzhenernayaGeologiya no 6 pp 32ndash42 1991
[21] V I Osipov V N Sokolov and V V Eremeev Clay Seals of Oiland Gas Deposits Balkema RotterdamThe Netherlands 2004
