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Journal of Dispersion Science and Technology

ISSN: 0193-2691 (Print) 1532-2351 (Online) Journal homepage: http://www.tandfonline.com/loi/ldis20

The Wettability Alteration and the Effect of InitialRock Wettability on Oil Recovery in Surfactant-based Enhanced Oil Recovery Processes

Wan-Fen Pu, Cheng-Dong Yuan, Xiao-chao Wang, Lin Sun, Ruo-kun Zhao,Wen-jing Song & Xiao-feng Li

To cite this article: Wan-Fen Pu, Cheng-Dong Yuan, Xiao-chao Wang, Lin Sun, Ruo-kun Zhao,Wen-jing Song & Xiao-feng Li (2016) The Wettability Alteration and the Effect of Initial Rock

Wettability on Oil Recovery in Surfactant-based Enhanced Oil Recovery Processes, Journal of Dispersion Science and Technology, 37:4, 602-611, DOI: 10.1080/01932691.2015.1053144

To link to this article: http://dx.doi.org/10.1080/01932691.2015.1053144

Accepted author version posted online: 29 Jul 2015.

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The Wettability Alteration and the Effect of Initial RockWettability on Oil Recovery in Surfactant-basedEnhanced Oil Recovery Processes

Wan-Fen Pu,1,2 Cheng-Dong Yuan,1,2 Xiao-chao Wang,3 Lin Sun,1,2

Ruo-kun Zhao,4 Wen-jing Song,4 and Xiao-feng Li5

1State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu, China2School of Petroleum and Natural Gas Engineering, Southwest Petroleum University, Chengdu, China3CNOOC EnerTech-Drilling & Production Co., Tianjin, China4Gas Production Engineering Research Institute of PetroChina Southwest Oil-Gas Field Company,

Guanghan, China5China Petroleum & Chemical Corporation Sichuan Petroleum Branch, Chengdu, China

GRAPHICAL ABSTRACT

Wettablity alteration of rock surface is an important mechanism for surfactant-based enhancedoil recovery (EOR) processes. Two salt and temperature-tolerant surfactant formulationswere developed based on the conditions of high temperature (97–120C) and high salinity(20104 mg/L) reservoirs where a surfactant-based EOR process is attempted. Both the twosufactant formulations can achieve ultralow interfacial tension level (103 mN/m) with crudeoil after aging for 125 days at reservoir conditions. Wettability alteration of core slices inducedby the two surfactant formulations was evalutated by measuring contact angles. Core flooding

Received 7 May 2015; accepted 17 May 2015.Address correspondence to Cheng-Dong Yuan, School of Petroleum and Natural Gas Engineering, Southwest Petroleum

University, Chengdu, China. E-mail: [email protected] versions of one or more of the figures in the article can be found online at www.tandfonline.com/ldis.

Journal of Dispersion Science and Technology, 37:602–611, 2016

Copyright# Taylor & Francis Group, LLC

ISSN: 0193-2691 print=1532-2351 online

DOI: 10.1080/01932691.2015.1053144

602

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experiments were carried out to study the influence of initial rock wettabilities on oil recoveryin the crude oil/surfactant/formation water/rock system. The results indicated that the twoformulations could turn oil-wet core slices into water-wet at 90–120C and 20 104 mg/Lsalinity, while the water-wet core slices retained their hydrophilic nature. The core flooding experi-ments showed that the water-wet cores could yield higher oil recovery compared with the oil-wetcores in water flooding, surfactant, and subsequent water flooding process. The two surfactantformulations could successfully yield additional oil recovery in both oil-wet and water-wet cores.

Keywords Enhanced oil recovery, rock wettabiltiy, surfactant, wettability alteration

1. INTRODUCTION

An important aspect of any enhanced oil recovery (EOR)process is the effectiveness of process fluids in removing oilfrom the rock pores at the microscopic scale. This is aboutmicroscopic displacement efficiency which largely deter-mines the success or failure of a process.[1] Microscopic dis-placement efficiency is mainly affected by wettability,capillary force, distributions of oil and water in pore spaces,and relative permeability, etc.[2] These factors are alsorelated to each other. The relationships among these factorsare very complex in the crude oil=formation water=rock=

displacing fluid system. It is very important to quantifythe effect of each factor on oil recovery.For rock wettability, Jamaloei et al.[3] investigated the

influence of pore wettability on the microstructure of residualoil in surfactant-enhanced water flooding in heavy oil reser-voirs. Humphry et al.[4] reported the impact of wettabilityon residual oil saturation and capillary desaturation curves.Owens et al.[5] presented the effect of rock wettability onoil–water relative permeability relationships. Grattoni et al.[6]

studied the effects of wettability on gas and oil productionfrom water flood residual oil. However, rock wettability notonly affects relative permeability characteristics and the nat-ure of fluid saturations of a fluid=rock system, but also deter-

mines the value of capillary force which affects microscopicdisplacement efficiency. Therefore, it is necessary to deter-mine reservoir wettability and its ef fect on oil recovery.

As early as 1958, Bobek et al.[7] emphasized the signifi-cance of reservoir rock wettability and investigated the fac-tors which may alter rock wettability. In the past fewdecades, a great deal of the research efforts have focusedon the rock wettability. The related studies of rock wettabil-ity have been carried out in water flooding [8–10] and manyEOR processes: such as, wettability alteration induced bynanoparticles fluid for EOR processes.[11–15]

Wettability alteration as an important mechanism forsurfactant-based chemical flooding EOR process has also

attracted extensive attention. Ravi et al.[16] investigated theeffects of a new plant surfactant (extracted from mulberrytree leaves) on wettability alteration. Dehghan et al.[17]

reported the interfacial tension and wettability changephenomena during alkali–surf actant interactions with acidicheavy crude oil. Zhang et al.[18] studied wettability alterationby trimeric cationic surfactant at water-wet=oil-wet micamineral surfaces. Jarrahian et al.[19] did a mechanistic study

on wettability alteration of carbonate rocks by surfactants.Rostami Ravari et al.[20] investigated the wettabilityalteration of carbonates in combined surfactant-enhancedgravity drainage. Bera et al.[21] carried out the mechanisticstudy of wettability alteration of quartz surface induced bynonionic surfactants. Mohan et al.[22] studied wettabilityaltering by many surfactants in carbonate rocks. Salehiet al.[23] conducted mechanistic study of wettability alterationusing surfactants with applications in naturally fracturedreservoirs. Goudarzi et al.[24] indicated anionic the mixtureof surfactant and alkali can alter wettability from oil-wet tostrongly water-wet conditions for carbonates. However, mostof the scientific literatures have focused on mechanistic stu-dies on wettability alteration by surfactants and paid lessattention to the effect of initial rock wettability on oil recov-ery in surfactant flooding process. And these previous studiesmainly aimed at medium-low temperature and salinity reser-voirs. Reviewing the literatures in this field, there is littleresearch conducted on surfactant flooding EOR techniquesfor high temperature and high salinity reservoirs (e.g.,90–120C and 20 104mg=L salinity). Such high tempera-ture and salinity put forward higher requirements for surfac-tant achieving steady ultralow interfacial tension (IFT).

In this study, we attempt to improve the recovery by

surfactant-based EOR processes from water flooded reser-voirs with temperatures ranging from 97C to 120C and asalinity of 20 104 mg=L. Two low concentration andhighly effective surfactant formulations that could obtainultralow IFT at reservoir conditions were developed. Thisstudy focuses on a systematic investigation of the wettabil-ity alteration induced by surfactants and the effect of initialrock wettability on oil recovery. The effects of surfactantconcentration and temperature on wettability alterationwere evaluated by measuring contact angles. Initial water-wet and oil-wet cores were employed to carry out coreflooding experiments to investigate the effect of initial rockwettability on oil recovery in the crude oil=surfactant=

formation water=rock system.

2. EXPERIMENTAL SECTION

2.1. Materials

Sodium alpha-olefine sulfonates (AOS, RCH(OH)(CH2)n-SO3Na n¼C14–16) and amphocaroxymethylimidazoline (AI) were obtained from Jinan Bao Li Yuan

603WETTABILITY ALTERATION AND INITIAL ROCK WETTABILITY


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Chemical Co., Ltd (China) and Taiyuan FinechemChemical Co., Ltd (China), respectively. Sodium alcoholether sulfate (AES, C12H25NaO3S) and ethoxylated fattyalcohol carboxylate (AEC, R-(OCH2CH2)nOCH2COONa, R¼C16=C18, n¼ 9) were provided by GuangzhouHui He Chemical Co., Ltd, China. Crude oil, reservoirinjection water, and sandstone core were obtained from ablock (Tarim Basin, China). This block is a sandstonereservoir with a formation temperature of 97C. The proper-ties of reservoir injection water are shown in Table 1. Theviscosity and density of the crude oil are 2.88 mPa s and0.814 g=cm3 at reservoir condition, respectively. The satu-rated hydrocarbon composition was analyzed by the HP6890 Series gas chromatography (Agilent Technologies,Inc., USA), and the results are presented in Figure 1.

2.2. Surfactant Formulation Preparation

Two surfactant formulations, AOSþAEC and AESþAI, were prepared with reservoir injection water. The massconcentration ratio of AOS to AEC and AES to AI are 1:3

and 1:1, respectively. Each surfactant formulation was pre-pared at different concentration (0.05%, 0.1%, 0.2%, 0.3%).The determination of the two surfactant formulations wasbased on a large number of evaluation experiments wherethe capabilities of reducing IFT of 12 surfactants belongingto 5 different types of surfactants and their compoundedformulations were investigated. The whole evaluationprocess is not the purpose of this paper and will not beillustrated in detail here. Two surfactant formulations(0.05%AOS þ0.15%AEC and 0.05%AES þ0.05%AI)obained stable ultra-low IFT of 5.78 103 mN=m and7.83103 mN=m, respectively, with crude oil after agingfor 125 days at 120C and 20 104 mg=L salinity.

2.3. Core Slices Preparation

A series of core slices were used as the solid substrates todetermine the wettability behavior with the surfactant for-mulation. Thin core slices were cut from reservoir coresand were polished smooth. Core slices were immersed indiluted hydrochloric acid for 12 hours and then werewashed with deionized water. The wash was continued untilthe pH of flushing fluid was neutral, and they were dried inan oven thermostat at 80C for 24 hours. The contact anglesof the washed core slices obtained after all these treatments

are about 28, which is considered as water-wet. Some coreslices were submerged in simethicone to alter wettabilitiesfrom water-wet to oil-wet. These core slices successfullybecame hydrophobic after the surface treatment aging for5 weeks (approx.) at approx.100C in simethicone. Themeasured contact angles are about 138.

2.4. Contact Angle Determination

Both water-wet and oil-wet core slices were loaded intoheat-resistant plastic bottles filled with surfactant formula-tions. These core slices were immersed in the surfactantformulation AOSþAEC orAESþAI at different tempera-tures (60C, 90C, 120C) aging for different time (3 hours– 15 days). Then the core slices were taken out at the planedtime. The contact angle was measured directly on a contact

angle measuring instrument (HARKE-SPCA) at ambientconditions (25C and 1 atm). The formulation consisted of a core slice as solid substrate, crude oil as oleic-phase, andreservoir injection water as aqueous-phase. Treiber et al.[25]

defined the aqueous contact angle in a three-phase system(water, oil, and rock surface) as shown in Table 2. The sche-matic diagram of contact angle measuring is shown inFigure 2. Procedures were as follows: (1) The measuringunit filled with injection water was placed in the middle of objective table. The core slice was loaded into one placewhere is two-thirds of the measuring unit height from thebottom of the measuring unit. (2) Open figure analyzing

FIG. 1. Saturated hydrocarbon composition of crude oil.

TABLE 1Properties of reservoir injection water

Salinity(mg=L)

Ion content (mg=L)

pHDensity(g=cm3)KþþNaþ Ca2þ Mg2þ Cl SO4

2 HCO3 I Br

204672.24 67430.31 10279.6 1200.74 125501.51 150 88.17 6 60 5.4 1.144

604 W.-F. PU ET AL.


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software. Adjust the height of the objective table and thelocation of the measuring unit to make video image be ina proper measuring region. (3) Oil drop was hung belowthe lower surface of the core slice through a syringe needle.The contact angle was analyzed using the figure analyzingsoftware when the oil drop was stable.

2.5. Core Flooding Experiment

2.5.1. Core Preparation

The initial wettability of cores was determined by bothAmott method and contact angle method at ambient con-ditions. The Amott–Harvey wettability index (Iw) are ran-ging from þ0.5 toþ 0.7, and contact angle are rangingfrom 29 to 35, which are considered as water-wet. Toalter the wettabilities, the cores were soaked in simethiconeat approx.100C for 5 weeks (approx.). The cores wettabil-ities were successfully altered from water-wet to oil-wet.The measured Iw of cores after treatment were in the rangeof 0.4 to 0.3, and contact angle were ranging from 129

to 133, which are considered as oil-wet. Core sample with

its dimensions is shown in Figure 3.

2.5.2. Experimental Procedures

Rocks with different initial wettabilities (oil-wet andwater-wet) were chosen for the flooding experiments.Figure 4 shows the schematic diagram of the experimentalapparatus. Procedures were as follows:

1. All core samples were dried at 80C for 12 hours andthe dry weight was measured. Each core sample was

vacuumized for 12 hours and saturated with reservoirinjection water. Then the wet weight was measured.Pore volume (PV) and porosity were calculated basedon the weight difference before and after the core wassaturated.

2. All equipments were connected as shown in Figure 4.The single-phase liquid (formation water) waterpermeability was tested.

3. The core holder was placed in an oven thermostat (set in100C). An annular pressure was put on to the coreholder, and crude oil was injected into the core at a

constant rate of 1.0 ml=min. The oil injection did notstop until there was no water produced in the outletand the pressure difference was stable. Irreducible watersaturation and initial oil saturation were establishedaccording to the water yield. The core holder was settledfor 3 days.

4. The reservoir injection water was injected into cores at aconstant rate of 2.0 ml=min for water flooding. Thewater flooding was stopped when water cut was at

TABLE 2The evaluation index of rock wettability[25]

Wettability Wettability index Contact angle ()

Strong oil-wet 1–0.7 153–180Oil-wet 0.7–0.3 117–153Weak oil-wet 0.3–0.1 99–117

Intermediate wet 0.1–0.1 81–99Weak water-wet 0.1–0.3 63–81Water-wet 0.3–0.7 27–63Strong water-wet 0.7–1 0–27

FIG. 2. The schematic diagram of contact angle measuring.

FIG. 3. Core sample with its dimensions.



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70%. Meanwhile, accumulative oil production wasrecorded. The water flooding recovery was calculated.

5. A 0.3 PV surfactant formulation (0.05% AOS þ0.15%AEC or 0.05% AES þ0.05% AI) was injected for surfac-tant flooding. Then, the subsequent water flooding wasconducted. The water injection was stopped when watercut was at 98%. The accumulative oil production wasrecorded. The water flooding recovery was calculated.The surfactant and subsequent water flooding recoverywas calculated.

3. RESULTS AND DISCUSSION

3.1. Wettability Alteration of Core Slices by AOSþAECSurfactant Formulations

3.1.1. The Effect of the Concentration of AOS þAEC

Surfactant formulations with different concentrations(0.05%, 0.1%, 0.2%, 0.3%) were evaluated at 100C. Theresults are shown in Table 3. All initial water-wet core sliceskept their hydrophilic nature after being immersed in thesedifferent concentration AOSþAEC formulations. Thehydrophilic groups in AOSþAEC formulation were anionand nonionic. There is an electrostatic repulsion between

anionic surfactant molecule and core slice surface with anegative charge. Therefore, the anionic surfactant mole-cules could only absorb the quartz plate surface in smallamounts with the hydrophilic group toward the solutionthrough a Van der Waals force and a hydrophobic interac-tion force. Thus, the core slices still retain hydrophilic.However, the contact angles of the water-wet core slicesoverall increased with aging time and concentration. This

is because the anionic surfactant molecules would aggregatein core slices’ surface and form hemi-micelle or micellesadsorption with increasing aging time and concentration.[26]

This leads to the wettability alteration from stronglywater-wet to weak water-wet.

However, for the initial oil-wet core slices, wettabilityreversal occurred in 1 day after being immersed in differentconcentration AOSþAEC formulations. The higher the con-centration, the quicker the core slices changed from oil-wet towater-wet. This is because micelles were formed in the higherconcentration AOSþAEC solution. The micelles had a goodsolubilization capacity to simethicone on the core slices’surface. The simethicone was washed out of core slices, whichrecovers the hydrophilic nature of core slices.[27]

FIG. 4. Schematic diagram of the water flooding and surfactant flooding experiments.

TABLE 3The effect of the concentration of AOSþAEC on the

wettability of core slices

Concentration (%)

Contact angle ()

3hours

1day

6days

10days

15days

Initialwater-wetcore slices

0.05 – 37.7 46.6 41.9 27.90.10 – 23.4 28.0 46.2 50.60.20 – 38.2 33.5 55.0 54.90.30 – 32.8 46.3 51.5 57.3

Initial oil-wetcore slices

0.05 1 28.9 41.6 25.9 36.5 23.60.10 1 25.3 40.7 44.3 36.4 38.80.20 1 14.5 40.9 29.3 37.2 24.90.30 98.8 36.7 50.4 27.2 27.8

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3.1.2. The Effect of Temperature on Wettability for

AOS þAEC Formulation

The initial water-wet and oil-wet core slices were treatedwith 0.05%AOS þ0.15%AEC formulation at different tem-peratures (60C, 90C, 120C). The results are shown inTable 4. For water-wet core slices, in each temperature,the contact angles increased with aging time at first. Com-

pared with 60

C and 90

C, this increased trend was aheadat 120C where the contact angle increased to 58.3 afterthe core slice was immersed for 1 day. The primary causeis that the higher temperature (120C) enhanced the thermalmotion of surfactant molecules, which accelerates theadsorption of surfactant molecules on the surface of coreslices. However, the contact angles decreased with theincreasing of aging time. This can be attributed to twoaspects. On the one hand, the adsorption is an exothermicprocess.[28] Long duration in high temperature is detrimentalto the adsorption process. On the other hand, the solubilityof ionic surfactant in water is increased, which causes thedecrease of adsorption capacity as the ability of surfactant

molecules to absorb on the solid surface is reduced.For oil-wet core slices, wettability reversal occurred in

each temperature. And, it was easier for wettability reversalat higher temperatures. After aging for 3 hours, the coreslices at 60C and 90C still retained oil-wet, but the coreslice at 120C was changed to intermediate wet. At a relativelow temperature, there is a strong hydrogen bonds actionbetween simethicone molecules and core slices. It is moredifficult to strip simethicone molecules from the surface of core slices. When temperature is increased to higher tem-perature (120C), the hydrogen bonds are weakened evenbroken. In addition, the activity of surfactant formulationis enhanced. Consequently, it is easier to strip simethicone

molecules from core slices, and the core slices restored theirhydrophilic nature. These core slices after becoming water-wet were continued to be immersed in the surfactantsolution. The contact angle variation exhibited the sametrend with that of the initial water-wet core slices.

3.2. Wettability Alteration of Core Slices by AOSþAECSurfactant Formulations

3.2.1. The Effect of the Concentration of AES þAI

Surfactant formulations with different concentrations(0.05%, 0.1%, 0.2%, 0.3%) were evaluated at 100C. Theresults are shown in Table 5. For initial water-wet core slices,the results are consistent with AOSþAEC formulation. All

core slices kept their initial water-wet state after the treatmentof different concentration AESþAI formulations. SurfactantAI is an ampholytic surfactant with cationic groups. Thehydrophilic groups of surfactant AI have both anionic andcationic groups. The hydrophilic groups of surfactant AIhave both anionic and cationic groups, which means thereexists anion and kation in the surfactant solution. The hydro-philic groups of the surfactant AI molecules absorb on thenegatively charged core slices’ surfaces. However, there iselectrostatic repulsion between the anionic groups of hydro-philic groups and negative charge in the surface of core slices,which reduces the interaction point between core slice’s sur-face and hydrophilic groups of surfactant AI molecules.

Thus, the other surfactant molecules can insert the absorbedlayer through the hydrophilic groups’ interaction withabsorbed surfactant AI molecules. Consequently, the anal-ogous single absorbed layer structure with hydrophilic groupsfacing outward was formed.[27] Therefore, the core slices’ sur-face still retained their hydrophilic character with only a slightfluctuation of the contact angle. For initial oil-wet core slices,AESþAI formulation could make wettability reversal occuras AOSþAEC did. Also, the higher the concentration of AESþAI formulation, the faster the core slices changed fromoil-wet to water-wet.

3.2.2. The Effect of Temperature on Wettability for

AES þAI FormulationThe initial water-wet and oil-wet core slices were treated

in 0.05% AES þ0.05% AI formulation at different tempera-tures (60C, 90C, 120C). The results are shown in Table 6.

TABLE 4The effect of temperature on the wettability in AOSþAEC

system

Aging

time

Initial water-wet Initial oil-wet

60C 90C 120C 60C 90C 120C

3 hours

C o n t a c t a n g l e

– – – 126.2 115.5 88.31 day 22.1 27.5 58.3 26.2 26. 8 38.43 days 24.6 39.4 44.8 34.1 37.7 52.56 days 47.5 41.6 30.5 42.6 45.1 29.710 days 44.6 39.8 33.0 43.2 37.0 31.715 days 38.5 40.6 31.5 37.7 37.1 33.9

TABLE 5The effect of the concentration of AES þAI on the

wettability of core slices

Concentration (%)

Contact angle ()

3hours

1day

6days

10days

15days

Initialwater-wetcore slices

0.05 – 21.9 29.8 24.4 22.70.10 – 23.2 30.7 27.2 23.00.20 – 27.1 28.0 25.3 32.00.30 – 26.4 43.1 36.3 38.4

Initial oil-wetcore slices

0.05 119.0 48.1 28.1 27.8 22.00.10 103.5 39.4 26.5 32.2 32.30.20 71.1 41.8 35.3 45.0 29.60.30 82.7 27.3 41.3 32.3 30.3



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For both the initial water-wet and oil-wet core slices, thecontact angles have the same change trend in AESþAIformulation with that of AOSþAEC formulation.

3.3. The Effect of Initial Rock Wettability on OilRecovery

The core flooding experimental results from several coresare summarized in Table 7 and Figures 5–7. The initialwater saturation (Swi) of oil-wet core was smaller than thatof water-wet core. These results are consistent with Craig[29]

and Hendraningrat et al.[2]. In water-wet cores, water fills

the small pores and forms a thin water film on rock surfaces.Hence, water saturation is relatively high. However, in

oil-wet cores, water is found as discrete droplets in the cen-ter of larger pores, and oil is found in the small pores as thinoil films on rock surfaces. Water saturation will typically bemuch lower than in water-wet cores. The oil recovery duringthe water flooding process indicated that initial wettabilityaffects water flooding behavior. Water-wet cores have ahigher oil recovery than oil-wet cores. This is mainlybecause capillary force is driving force in water-wet poresduring water flooding. However, capillary force is resistancein oil-wet pores.

For the two surfactant formulations, after 0.3 PV formu-lation was injected, additional oil recovery was successfullyobtained in both oil-wet and water-wet cores due to the sur-

factant flooding and subsequent water flooding recoveryprocesses. Similar to the trend in the water flooding process,for both two surfactant formulations, water-wet cores have

TABLE 6The effect of temperature on the wettability in AES þAI

system

Agingtime

Initial water-wet Initial oil-wet

60C 90C 120C 60C 90C 120C

3 hours

C o n t a c t

a n g l e ( ) – – – 115.3 95.9 83.41 day 25.2 27.3 24.0 28.2 24.7 47.9

6 days 23.7 25.4 37.2 32.0 23.8 52.210 days 26.3 34.4 44.1 30.8 32.6 44.115 days 21.2 22.1 41.4 27.2 20.9 36.9

TABLE 7Petrophysical properties of cores and the results of core

physical simulation experiment

Core no. ww1 ow1 ww2 ow2

Diameter (cm) 3.74 3.76 3.75 3.74Length (cm) 6.98 7.04 7.02 7.00Wettability Water-wet Oil-wet Water-wet Oil-wetPorosity (%) 32.03 35.48 32.96 35.23Permeability

(103mm2)38.17 38.03 39.13 36.52

Initial oilsaturation (%)

72.99 78.27 74.06 81.63

Initial watersaturation (%)

27.01 21.73 25.94 18.37

Water floodingrecovery (%)

36.48 31.57 35.47 30.25

Surfactantsystem

0.05% AOSþ0.15%AEC

0.05% AESþ0.05% AI

Surfactant andsubsequentwater floodingrecovery (%)

24.06 19.86 21.42 15.25

Total recovery(%)

60.54 51.43 56.89 45.50

Residual oilsaturation (%)

28.80 38.01 31.93 44.49

FIG. 5. Oil recovery versus injected PV profile during WF, SF, andSWF processes in cores with different wettabilities for AOSþAECsystem.

FIG. 6. Oil recovery versus injected PV profile during WF, SF, andSWF processes in cores with different wettabilities for AES þAI system.

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a higher additional oil recovery than oil-wet cores as shownin Figure 7. To water-wet cores, the additional oil recoveriesof 24.06% and 21.42% were achieved for AOS þAEC andAESþAI formulation, respectively. The oil-wet cores

yielded the additional oil recovery of 19.86% and 15.25%for AOSþAEC and AESþAI formulation, respectively.This indicated that the two surfactant formulations couldgreatly improve oil recovery. The improving oil recoverymechanism of the surfactant formulations was mainlyattributed to the reducing IFT effect. Whether the residualoil after water flooding would flow again depends on therelative values of the driving force and the resistance. Atthe initiation of a typical water flooding, the displacedphase (oil phase) is initially at a relatively high saturation.The phase is essentially in continuous contact throughoutthe porous medium. For water-wet cores, at this situation,the capillary force is the driving force. However, experience

indicates that once the oil phase is trapped, it is more diffi-cult to mobilize it due to the Jamin effect where the pressurerequired to force a trapped oil phase through a capillarysystem, such as a porous rock, can be quite high. [1] Thephenomenon can be described most easily by analyzing atrapped oil droplet in a preferentially water-wet unequaldiameter pores, as shown in Figure 8. Assuming the press-ure within the oil drop is constant from one end of the drop

to the other. The additional capillary force, p, can beexpressed by (assuming h1¼ h2)

[30]:

p2 p1 ¼ p ¼ 2rowcos h 1

r2

1

r1

½1

Because r1> r2, then p2>p1 and a pressure drop(additional capillary force) exists in the direction frompoint 2 to 1. Hence, an extra driving force that will haveto exceed the additional pressure drop is required to forcethe oil drop through the narrower part of the capillaryconstriction.

If r1 r2, then Equation (1) can be written as following:

p2 p1 ¼ p ¼ 2rowcos h=r2 ½2

For example, r2¼ 1 mm, row¼ 5 mN=m, then the drivingforce that pushes the oil drop through the narrower partmust exceed 104 Pa. Further, assuming the average length

of these unequal diameter pores is 50 mm, and there is onedrop in each pore. If we want to mobilize every oil drop,the needed pressure gradient should be calculated asfollows:

ðp2 p1Þ=L ¼ 104N=m2 50 106m

¼ 2 108N=m

½3

Obviously, there are no such reservoirs that can give such ahigh pressure gradient. That is, only reducing the requiredpressure gradient could the oil drop hopefully be mobilizedagain. The ultralow IFT is expected at this situation. This iswhy the two ultralow IFT surfactant formulations have the

capability to greatly enhance oil recovery.For oil-wet cores, the capillary force is always a resist-

ance in water flooding process. The concept of capillarynumber (Nca) was introduced to quantitatively analyzehow the residual oil could be remobilized again. The Ncahas been proven to be reasonably successful. The capillarynumber was defined as the ratio of viscous force to capil-lary force as in Equation (4).[1]

Nca ¼ vmwrowcos h

½4

where v is interstitial velocity, mw is the viscosity of displa-

cing phase, and row is the IFT between the displaced anddisplacing phases. It has been verified that the bigger theNca, the higher the oil recovery. Therefore, we can see thatreducing row is still the effective method which is easier toachieve.

The initial oil-wet cores after flooding were taken outand cut into thin core slices using the method mentionedin Sec. 2.3. The core wettabilities were checked. Table 8

FIG. 7. Water flooding recovery, surfactant, and subsequent waterflooding recovery for different initial wettability.

FIG. 8. A oil drop is trapped in a preferentially water-wet unequaldiameter pore. Adapted from reference [30].


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shows the results of wettability check. We also observedthat both two surfactant formulations changed the wett-ability from oil-wet to water-wet (from 129.57 to 37.72

for AOSþAEC formulation, from 132.41 to 34.46 forAESþAI formulation) during the flooding process. Thismeans that the two surfactant formulations have an excel-lent improvement effect on the oil-wet core wettability,which facilitates for the mobilization of trapped oil.

4. CONCLUSION

1. The two ultrolow IFT surfactant formulations AOSþAEC and AESþAI can make the wettability of theinitial oil-wet cores slices changed from oil-wet towater-wet at 90–120C and 20 104 mg=L salinity.The higher the temperature, the quicker the wettabilityreversal occurred. The initial water-wet cores still retaintheir hydrophilic nature.

2. Surfactant concentration has an effect on wettabilityreversal of the initial oil-wet cores. The higher theconcentration, the quicker the core slices changed from

oil-wet to water-wet.3. The Swi of oil-wet cores was smaller than in water-wet

cores due to the different existing state of water in theporous media. The initial rock wettability affects thewater flooding process. Water-wet cores have a higheroil recovery than oil-wet cores during the water floodingprocess as the capillary force is resistance in oil-wetpores and the driving force in water-wet pores.

4. The initial rock wettability also has an influence on thesurfactant flooding and subsequent water floodingrecovery processes. Similar to the trend in the waterflooding process, water-wet cores have a higheradditional oil recovery than oil-wet cores. Likewise, the

ultralow IFT surfactant formulations can make theinitial oil-wet cores change their wettability to water-wetduring flooding process.

5. The two ultralow IFT surfactant formulations success-fully yielded additional oil recovery in both oil-wet andwater-wet cores. The results indicated that the two sur-factant formulations have a great potential for improv-ing oil recovery, and low concentration surfactant

flooding under the ultralow IFT is a promising EORtechnique for high temperature and high salinity oilreservoirs.

FUNDING

This research is partially supported by technology inno-vation talent project (2014-070), Sichuan province.

REFERENCES

[1] Green, D.W. and Willhite, G.P. (1998) Enhanced Oil Recovery;Richardson, Texas: Henry L. Doherty Memorial Fund of

AIME, Society of Petroleum Engineers.

[2] Hendraningrat, L. and Torsæter, O. (2014) Energy Fuels,28(10): 6228–6241.

[3] Jamaloei, B.Y., Kharrat, R., Asghari, K., and Torabi, F.(2011) J. Pet. Sci. Eng., 77(1): 121–134.

[4] Humphry, K.J., Suijkerbuijk, B.M.J.M., van der Linde,H.A., Pieterse, S.G.J., and Masalmeh, S.K. (2013) InProceedings of the Annual Symposium of the Society of Core

Analysts, Paper 2013–025.[5] Owens, W.W. and Archer, D. (1971) J. Pet. Technol., 23(07):873–878.

[6] Grattoni, C.A. and Dawe, R.A. (2003) J. Pet. Sci. Eng.,39(3): 297–308.

[7] Bobek, J.E., Mattax, C.C., and Denekas, M.O. (1957)Presented at 32nd Annual Fall Meeting of Society of Petroleum Engineers, Dallas, Texas, October 6–9, PaperSPE-895-G.

[8] Jadhunandan, P.P. and Morrow, N.R. (1995) SPE. Reserv.Eng., 10(1): 40–46.

[9] Morrow, N.R. (1990) J. Pet. Technol., 42(12): 1476–1484.[10] Karabakal, U. and Bagci, S. (2004) Energy Fuels, 18(2):

438–449.

[11] Dwarakanath, V., Jackson, R.E., and Pope, G.A. (2002)Environ. Sci. Technol., 36(2): 227–231.

[12] Mousavi, M.A., Hassanajili, S., and Rahimpour, M.R.(2013) Appl. Surf. Sci., 273: 205–214.

[13] Maghzi, A., Mohammadi, S., Ghazanfari, M.H., Kharrat,R., and Masihi, M. (2012) Exp. Therm. Fluid. Sci., 40:168–176.

[14] Roustaei, A., Saffarzadeh, S., and Mohammadi, M. (2013)Egyptian J. Pet., 22(3): 427–433.

[15] Karimi, A., Fakhroueian, Z., Bahramian, A., Pour Khiabani,N., Darabad, J.B., Azin, R., and Arya, S. (2012) EnergyFuels, 26(2): 1028–1036.

[16] Ravi, S.G., Shadizadeh, S.R., and Moghaddasi, J. (2015) Pet.Sci. Technol., 33(3): 257–264.

[17] Dehghan, A.A., Masihi M. and Ayatollahi, S. (2015) EnergyFuels, 29(2): 649–658.

[18] Zhang, R., Qin, N., Peng, L., Tang, K., and Ye, Z. (2012)Appl. Surf. Sci., 258(20): 7943–7949.

[19] Jarrahian, K., Seiedi, O., Sheykhan, M., Sefti, M.V., andAyatollahi, S. (2012) Colloids Surf. A: Physicochem. Eng.Aspects, 410: 1–10.

[20] Rostami Ravari, R., Strand, S., and Austad, T. (2011)Energy Fuels, 25(5): 2083–2088.

TABLE 8The contact angles of the initial oil-wet core slices before

and after surfactant flooding

Coreno. Surfactant system

Contact angles ()

Beforeflooding

Afterflooding

ow1 0.05% A OS þ0.15% AEC 129.57 37.72ow2 0.05% A ES þ0.05% AI 132.41 34.46

610 W.-F. PU ET AL.


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[21] Bera, A., Ojha, K., Kumar, T., and Mandal, A. (2012)Energy Fuels, 26(6): 3634–3643.

[22] Mohan, K., Gupta, R., and Mohanty, K.K. (2011) EnergyFuels, 25(9): 3966–3973.

[23] Salehi, M., Johnson, S.J., and Liang, J. (2008) Langmuir,24(24): 14099–14107.

[24] Goudarzi, A., Delshad, M., Mohanty, K.K., andSepehrnoori, K. (2015) J. Pet. Sci. Eng., 125: 136–145.

[25] Mao, W., Yu, B.J., and Hou, X.L. (2007) Petrol. Geol. Eng.,21(5): 90–92.

[26] Singh, P.K., Adler, J.J., Rabinovich, Y.I., and Moudgil,B.M. (2001) Langmuir, 17(2): 468–473.

[27] Seethepalli, A., Adibhatla, B., and Mohanty, K.K. (2004)Presented at SPE=DOE Symposium on Improved OilRecovery, Tulsa, Oklahoma April 17–21, Paper SPE89423.

[28] Jiang, Q.Z. (2006) Surfactant Science and Application. ChinaPetrochemical Press, Beijing. (in Chinese)

[29] Craig, F.F. (1993) The Reservoir Engineering Aspectsof Waterflooding; Richardson, Texas: Henry L.

Doherty Memorial Fund of AIME, Society of PetroleumEngineers.

[30] Ye, Z.B. (2000) Enhanced Oil Recovery. Petroleum IndustryPress, Beijing. (in Chinese)


the wettability alteration and the effect of initial rock wettability on oil recovery in surfactant...

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