Wettability alteration of oil-wet sandstone surface by synergistic

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Wettability alteration of oil-wet sandstone surface by synergistic adsorption/desorption of cationic/nonionic surfactant mixtures Baofeng Hou, Ruixiu Jia, Meilong Fu, Yefei Wang, Yu Bai, and Youqing Huang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b03450 • Publication Date (Web): 02 Nov 2018 Downloaded from http://pubs.acs.org on November 3, 2018

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Wettability alteration of oil-wet sandstone surface by synergistic adsorption/desorption of cationic/nonionic surfactant mixtures Baofeng Houa,*, Ruixiu Jiab, Meilong Fua, Yefei Wangc, Yu Baic, Youqing Huanga aSchool

of Petroleum Engineering, Yangtze University, Wuhan 430100, China

bWuhan

campus, Yangtze University, Wuhan 430100, China

cSchool

of Petroleum Engineering, China University of Petroleum (East China),

Qingdao 266580, China

Abstract Various experimental methods including AFM, SEM, zeta potential measurement and contact angle measurement were used to analyze the mechanisms of wettability alteration of oil-wet sandstone surface by the cationic/nonionic surfactant mixture in this work. Due to the synergies between cationic surfactants and nonionic surfactants, head groups of CTAB and TX-100 interact with each other, making the cmc of the cationic/nonionic surfactant mixture lower compared to the single surfactant CTAB or TX-100. Ion pairs are produced by the carboxylic substances and the aggregates formed by CTAB and TX-100, which are irreversibly desorbed from the quartz surface and are solubilized into the mixed micelles formed by the CTAB/TX-100 mixture. The CTAB molecules are preadsorbed on the oil-wet sandstone surface by electrostatic attraction, acting as anchor particles, and the aggregates are formed by TX-100 and CTAB through hydrophobic interaction, thereby increasing the adsorption amount of CTAB on the oil-wet sandstone surface. The ability to form ion ∗ Corresponding

author. E-mail address: [email protected] (B. Hou).

ACS Paragon Plus Environment

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pairs for CTAB and the carboxylic substances in the presence of TX-100 and the solubilization ability of the mixed micelles are all enhanced, making the desorption capacity of ion pairs stronger. Thus, the CTAB/TX-100 mixture is more effective than the single surfactant CTAB in altering wettability of oil-wet sandstone surface toward a more water-wet condition. Keywords: Mechanisms; Wettability alteration; Cationic-nonionic surfactant mixtures; AFM; Synergistic effect

1. Introduction During the tertiary recovery, wetting inversion is achieved by surfactant-induced wettability alteration, resulting in higher oil recoveries

1-5.

Microcosmic mechanisms

of wettability alteration of oil-wet sandstone surface (OSS, The following “oil-wet sandstone surface” is abbreviated as “OSS” in this paper) induced by various surfactants remain to be further studied, especially the related research on the mixed surfactants. Many studies about wettability changes induced by surfactants have been investigated in recent years. Currently, the research of wettability change of water-wet surfaces has been carried out by most of the scholars

6, 7.

While some scholars have

made some assumptions for mechanisms of wettability alteration of OSS by various surfactants. Various macroscopic and microscopic methods have been used to investigate the microscopic mechanisms of wettability alteration of OSS in the past few years 8-11. The “ion-pair mechanism” and “adsorption mechanism” for wettability alteration of oil-wet carbonate surface induced by various surfactants were proposed


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by Standnes et al

12-14.

Microscopic methods were used to analyze and confirm the

mechanisms of wettability changes of oil-wet carbonate surface by Jarrahian et al 15. Various methods were also employed to study the microscopic mechanisms of wettability changes of OSS and the above hypothesis was confirmed by Hou et al 16. At present, most researches have been focused on the mechanism for wettability alteration of OSS induced by a single surfactant. However, there are only a few studies focusing on wettability alteration of OSS induced by the mixed surfactant system. For wettability alteration of OSS, the potential synergism of the Tween80/SDBS mixture was observed by Mandal et al.

17.

In general, cationic

surfactants have better performance in altering the wettability of OSS compared to the nonionic surfactants and anionic surfactants

15.

Sandstone surface is negatively

charged when the pH value of aqueous phase is around 7, making the adsorption loss of cationic surfactants during the oilfield development very high. The addition of an appropriate amount of nonionic surfactants into the system can reduce the adsorption loss of the surfactants. One cationic/nonionic composite surfactant system was constructed and mechanisms of wettability alteration of OSS induced by the cationic/nonionic surfactant mixture were explored in this paper. There is less research on wettability alteration of OSS induced by the cationic/nonionic surfactant mixture and the research in this area is mainly focused on wettability change of water-wet surfaces

18-21.

The adsorption model of

cationic/nonionic surfactant mixture on the water-wet bentonite surface was obtained by Zhang et al

22.

The synergistic mechanism of wettability alteration of the solid


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surface induced by the cationic/nonionic surfactant mixture was also proposed by them and they concluded that TX-100 adsorption was promoted by the pre-adsorbed HDPB molecules acting as anchors. Zhou et al.18 found that the ability to change wettability for the surfactant mixture was greatly improved due to the synergistic effect

between

nonionic

surfactants

(n-dodecyl-β-d-maltoside)

and

cationic

surfactants (C12-C4-C12 gemini surfactant). While the related research about wettability alteration of OSS induced by the cationic/nonionic surfactant mixture has been conducted by only a few scholars in recent years. The coadsorption mechanism of the CTAB/NP-n mixture on polytetra fluoroethylene (PTFE) surface was investigated by Desai et al. and they concluded that the affinity of the CTAB/NP-n mixture toward the PTFE surface is enhanced by the presence of each other and the stronger hydrophobic interactions and the presence of mixed surfactant aggregates are proposed to be the main mechanism for the observed synergistic effect 23. In short, the research about the microscopic mechanism of wettability alteration of OSS by the cationic/nonionic surfactant mixture is still not deep enough and needs to be further studied. The main purpose of this article is to investigate the mechanisms of wettability alteration of OSS induced by the cationic/nonionic surfactant mixture. Various experimental methods including AFM, SEM, zeta potential measurement and contact angle measurement were utilized to analyze the above microscopic mechanism in this work. In addition, quartz plates, mica plates and quartz sands were employed to simulate sandstone surfaces. Thus, this paper can provide some theoretical guidance


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for the oilfield site.

2. Experimental 2.1. Materials 2.1.1. Solid materials The employed quartz plates (20 × 20 × 1.5 mm) and mica plates (10 × 10 × 0.2 mm) in this paper were all purchased from Xingtai Weiye Technology Co., Ltd. (Shenzhen, China). In addition, the used analytical-grade quartz sand was purchased from Aladdin Reagents Co., Ltd. (Shanghai, China). 2.1.2. Aging system The oil phase used in this work consists of crude oil and kerosene and the mass ratio of these two substances is 1:1. The oil phase utilized in this paper was obtained from Daqing oilfield, China. The density and viscosity of the oil phase measured at room temperature were 0.82 g/cm3 and 62.1 mPa·s, respectively. What’s more, the acid number of the used oil phase was 1.46 mg of KOH/g. 2.1.3. Reagents For the used reagents, n-heptane, MgCl2·6H2O, CaCl2 and NaCl are all analytically pure, which were purchased from Aladdin Reagents (Shanghai, China) Co., Ltd. Distilled water was used to prepare different surfactant solutions and ionic composition of the simulated formation water employed in the present work is shown in Table 1. 2.1.4. Surfactants The used surfactants CTAB and TX-100 were analytically pure and chemically pure,


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respectively. These surfactants were obtained from Aladdin Reagents Co., Ltd. (Shanghai, China). Concentrations of the employed surfactants were all fixed at 0.25 wt% during the SEM and AFM determinations. In addition, the mass ratio of CTAB to TX-100 is 1:2 in the surfactant mixture (CTAB/TX-100). Molecular structures of the surfactants utilized in the present paper are shown in Fig. 1. 2.2. Methods 2.2.1. Solid surface treatment Certain methods were used to obtain the aged solid materials 24. The aged quartz sand and quartz (mica) plates were then treated with various surfactants for the following measurements 16. 2.2.2. Surface tension (SFT) measurement SFT values of different solutions were determined at ambient temperature in this study 1. The determined SFT values are shown in Fig. 2. 2.2.3. Atomic force microscopy (AFM) determination Topographic images of the clean and aged mica surfaces treated with various surfactants were obtained by the atomic force microscope scanning 16. 2.2.4. Scanning electron microscope (SEM) determination Micromorphology of the clean and the treated quartz sand surfaces was determined using the SU8200 Hitachi cold field emission scanning electron microscope in this paper 25, 26. 2.2.5. Zeta potential measurement Different quartz particle suspensions were prepared for the zeta potential


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measurement at ambient temperature. Malvern Zetasizer (Nano-ZSE, UK) was utilized to determine the zeta potential of quartz particles in this paper 16. 2.2.6. Contact angle measurement Sessile drop method was employed to determine contact angles at room temperature in this work 27. Contact angles mentioned in this paper refer to the water phase contact angle after achieving dynamic balance.

3. Results and discussion Various macro- and micro-analysis methods were utilized to explore the mechanisms for wettability alteration of OSS induced by the CTAB/TX-100 mixture in the present work. In addition, the differences between single surfactants and mixed surfactants in the behavior of changing wettability were also investigated. 3.1. Surface tension measurement In order to determine the cmcs of different surfactants, surface tension measurements were carried out in this paper. Effect of surfactant concentration on the surface tension is shown in Fig. 2. From Fig. 2 one can see that the surface tension values gradually decrease and then tend to be stable with the increase of the surfactant mass fraction. The critical micelle concentrations of the CTAB/TX-100 mixture, the single surfactants CTAB and TX-100 are 0.0035 wt%, 0.0075 wt% and 0.028 wt%, respectively. Due to the synergies between the cationic surfactants and nonionic surfactants, hydrophilic head groups of the two surfactants in the mixture interact with each other. Thus, electrostatic repulsion between the cationic head groups of CTAB weakens, making the cmc of the CTAB/TX-100 mixture lower compared to the single


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surfactant CTAB or TX-100. 3.2. Atomic force microscopy (AFM) Mean roughness (MR) of solid surface can be measured by AFM, which can be used to describe the micro-roughness of rock surface and to analyze the mechanisms of wettability alteration of rock surface induced by various fluids 16, 28, 29. Topographic images and MR of the studied surfaces were obtained by AFM in this paper. Fig. 3 shows the two-dimensional (2D) and three-dimensional (3D) microtopography pictures of different samples. Different colors are used to show the height difference of the mica surface in Figs. 3 and 4. Section analysis was utilized to measure the roughness of the microscopic surface in this paper. Fig. 3(a) shows the topographic images of the fresh mica surface and MR of the fresh surface is 0.30 nm. The fresh mica surface aged by the oil phase is shown in Fig. 3(b) and MR of the aged mica surface is 41.60 nm. Asphaltenes in the oil phase are adsorbed on the mica surface, increasing the MR of the solid surface (Fig. 3(b), 3D image). Microscopic images of the aged mica surfaces treated with various surfactants are shown in Fig. 4. Concentrations of the used surfactants were fixed at 0.25 wt% (> cmc) in this part. MR of the aged surface treated with the cationic surfactant CTAB is 0.75 nm. As can be seen from the comparison of Fig. 3(b) and Fig. 4(a), due to the desorption of the formed ion pairs from the rock surface, the adsorbed solid particles significantly reduce for the aged surface after being treated with CTAB (Fig. 4(a)). From the 3D image in Fig. 4(b) one can see that the aged mica surface becomes much smoother after the treatment of TX-100. Due to the adsorption of TX-100 molecules


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on the aged mica surface, MR of the aged mica surface treated with the nonionic surfactant TX-100 is reduced to 3.5 nm (Fig. 4(b)). Compared with the mica surface treated with CTAB (Fig. 4(a)), MR of the aged surface treated with the CTAB/TX-100 mixture is only 0.45 nm (Fig. 4(c)). In addition, the aged mica surface treated with the CTAB/TX-100 mixture is smoother than that treated with CTAB. Compared to the aged surface treated with CTAB, there are fewer adsorbed solid particles on the aged mica surface treated with the CTAB/TX-100 mixture (Fig. 4(c)). Through the above phenomenon, one conclusion can be drawn that the desorption capacity of ion pairs for the CTAB/TX-100 mixture is stronger than that for CTAB. In the surfactant mixture, there is a good synergistic effect between the molecules of CTAB and TX-100. The pre-adsorbed CTAB molecules acting as anchors are adsorbed on OSS and the aggregates are formed by the pre-adsorbed CTAB molecules and TX-100 through hydrophobic interactions, thereby increasing the adsorption amount of CTAB on OSS. The formation of mixed micelles is promoted by the presence of TX-100. What’s more, the ability to form the ion pairs for CTAB and the carboxylic substances in the presence of TX-100 is enhanced, making the desorption capacity of the ion pairs stronger. 3.3. Scanning electron microscope (SEM) To further analyze and validate the mechanisms of wettability alteration of OSS induced by the CTAB/TX-100 mixture, SEM scanning was carried out in this work. Fig. 5 shows the microscopic morphology of different sandstone surfaces. From Fig. 5(a) and Fig. 5(b) one can see that compared to the clean sandstone surface,


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asphaltenes of the oil phase are adsorbed on the quartz surface by polar interactions and ion-binding, etc. for the aged quartz surface

30, 31.

asphaltene has anionic groups (carboxylates) in it

8,12,13,15.

Moreover, the adsorbed While the microscopic

morphology of OSS remains substantially unchanged after the treatment of formation water (Fig. 5(c)). Thus, the formation water has little effect on the wettability of OSS. Figs. 5(d), (e), and (f) show the microscopic morphology of the aged sandstone surfaces treated with CTAB, TX-100, and the CTAB/TX-100 mixture, respectively. There are still many asphaltenes on the quartz surface after the treatment of TX-100 (Fig. 5(e)). Due to the desorption of the formed ion pairs from the rock surface, the adsorbed asphaltene particles are significantly reduced after the treatment of CTAB and the CTAB/TX-100 mixture (Figs. 5(d), (f)), rendering the quartz surfaces present water-wet state. In addition, the quartz surface in Fig. 5(f) is cleaner than that in Fig. 5(d). Due to the presence of TX-100, the ability to form the ion pairs for the CTAB/TX-100 mixture is stronger than that for the single surfactant CTAB. The mixed micelles formed by the CTAB/TX-100 mixture also have stronger solubilization ability, making the ion pair's desorption ability stronger and the solid surface cleaner. Thus, the synergy between CTAB and TX-100 is indirectly confirmed by the SEM determination 32. The results of SEM scanning are consistent with the AFM measurements. 3.4. Zeta potential determination Zeta potential of the aged quartz particles after being soaked in various solutions for 24 h is shown in Fig. 6. From Fig. 6 one can see that the zeta potential of the aged


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particle without being treated with the surfactants is -4.00 mV. For the surfactants CTAB and the surfactant mixture, zeta potential values of the aged quartz powders first increase and then decrease, eventually tend to reach equilibrium with increasing the surfactants mass fraction (Fig. 6). After being treated with the TX-100 solution, zeta potential values of the aged quartz particles first decrease slightly and then tend to achieve balance with the increase of the TX-100 concentration. When the surfactant mass fraction is lower than cmc, the zeta potential value of the solid particle treated with the CTAB/TX-100 mixture is higher than that treated with CTAB at the same concentration. However, the balanced value of the zeta potential for the CTAB/TX-100 mixture is lower than that for CTAB. Fig. 7 shows the schematic diagrams of wettability change of OSS induced by various surfactants. In Figs. 7(a), (b) and (c), both the “Low concentration” and “Moderate concentration” are below cmc, while the “High concentration” is above cmc. Under the low mass fraction conditions (cmc), ion pairs formed by CTAB and the carboxylic substances are irreversibly desorbed from the quartz surface and are solubilized into the micelles formed by the CTAB molecules, rendering the zeta potential of the quartz surface treated with CTAB decrease from 21.1 mV to 14.1 mV

16.

When the surfactant concentration is higher

than cmc, the zeta potential value of the quartz surface treated with TX-100 tends to be stable, indicating that saturated adsorption is achieved on the aged quartz surface for TX-100. After reaching the critical micelle concentration, the zeta potential value of the quartz surface decreases from 33.2 mV to 10.0 mV for the CTAB/TX-100 mixture. The desorbed ion pairs are produced by the carboxylic substances and the aggregates formed by CTAB and TX-100. The balanced zeta potential value of the aged quartz particle treated with CTAB is 14.1 mV, while the balanced zeta potential value is 10 mV for the CTAB/TX-100 mixture, indicating that there are fewer CTAB molecules remaining on the surface treated with the CTAB/TX-100 mixture than that


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treated with CTAB alone. In summary, the synergistic mechanisms for wettability alteration of OSS by the CTAB/TX-100 mixture are confirmed by the above measurements including AFM determination, SEM scanning and zeta potential measurement. 3.5. Contact angle measurements If the synergistic mechanism is responsible for the wettability change of OSS induced by the CTAB/TX-100 mixture, the ability of altering wettability toward a water-wet surface for the CTAB/TX-100 mixture should be stronger than that for CTAB. To further confirm the proposed mechanism, contact angle determination was conducted at ambient temperature. Fig. 8 shows the contact angles of oil droplets on the quartz surfaces treated with the studied surfactants at various concentrations and Fig. 9 shows the balanced contact angles of oil drops for various systems at ambient temperature. The initial contact angle of oil drop on the OSS without being treated with surfactants is 134 degrees (Fig. 9(a)). From Fig. 8 one can see that as the surfactant concentrations increase, the contact angles gradually decrease and eventually achieve balance for the three surfactant systems. The balanced contact angle using TX-100 is 108 degrees (Fig. 9(c)). While the balanced contact angles using CTAB and the CTAB/TX-100 mixture are as low as 57 and 43 degrees, respectively (Figs. 9(b), (d)). Obviously, the CTAB/TX-100 mixture is more effective than the single surfactant CTAB in altering the wettability of OSS. Experimental results of contact angle determination are consistent with the conclusions of the above several measurements. Thus, the synergistic mechanism of wettability change of OSS


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induced by the CTAB/TX-100 mixture is nicely revealed in this study.

4. Conclusions Various experimental methods were used to analyze the mechanisms for wettability change of OSS caused by the CTAB/TX-100 mixture in the present study. The obtained conclusions are as follows: Due to the synergies between cationic surfactants and nonionic surfactants, head groups of CTAB and TX-100 interact with each other, making the cmc of the cationic/nonionic surfactant mixture lower compared to the single surfactant CTAB or TX-100. Owing to the synergistic effect between CTAB and TX-100, the CTAB molecules are preadsorbed on the oil-wet quartz surface by electrostatic attraction, acting as anchor particles, and the aggregates are formed by TX-100 and CTAB through hydrophobic interaction, thereby increasing the adsorption amount of the CTAB molecules on the OSS. The ion pairs are produced by the carboxylic substances and the aggregates formed by CTAB and TX-100, which are irreversibly desorbed from the quartz surface and are solubilized into the mixed micelles formed by the CTAB/TX-100 mixture. The ability to form ion pairs for CTAB and carboxylic substances in the presence of TX-100 is enhanced, making the desorption capacity of ion pairs stronger. Thus, the CTAB/TX-100 mixture is more effective than the single surfactant CTAB in changing the wettability of OSS toward a more water-wet condition.

Acknowledgements


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This paper was supported by National Natural Science Foundation of China (Youth Fund) (51704036). We also thank all the authors and the relevant experts for their hard work.

Nomenclature wt% =weight % SFT =surface tension (mN/m) cmc = critical micelle concentration OSS = oil-wet sandstone surface MR = mean roughness

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sugar-based surfactants with other surfactants at solid/liquid interfaces: II. Adsorption of n-dodecyl-β-d-maltoside with a cationic surfactant and a nonionic ethoxylated surfactant on solids. J. Colloid Interface Sci. 2006, 302(1), 25-31. (22)Zhang, Y.; Zhao, Y.; Zhu, Y.; Wu, H.; Wang, H.; Lu, W., Adsorption of mixed cationic-nonionic surfactant and its effect on bentonite structure. J. Environ. Sci. 2012, 24(8), 1525-1532. (23)Desai, T. R.; Dixit, S. G., Coadsorption of cationic-nonionic surfactant mixtures on polytetra fluoroethylene (PTFE) surface. J. Colloid Interface Sci. 1996, 179(2), 544-551. (24)Hou, B.; Wang, Y.; Huang, Y., Study of spontaneous imbibition of water by oil-wet sandstone cores using different surfactants. J. Dispersion Sci. Technol. 2015, 36(9), 1264-1273. (25)Polson, E. J.; Buckman, J. O.; Bowen, D. G.; Todd, A. C.; Gow, M. M.; Cuthbert, S. J., An environmental-scanning-electron-microscope investigation into the effect of biofilm on the wettability of quartz. SPE J. 2010, 15(1), 223-227. (26)Combes, R.; Robin, M.; Blavier, G.; Aıdan, M.; Degreve, F., Visualization of imbibition in porous media by environmental scanning electron microscopy: application to reservoir rocks. J. Pet. Sci. Eng. 1998, 20(3-4), 133-139. (27)Hou, B.; Wang, Y.; Huang, Y., Mechanism and influencing factors of wettability alteration of water-wet sandstone surface by CTAB. J. Dispersion Sci. Technol. 2015, 36(11), 1587-1594. (28)Seiedi, O.; Rahbar, M.; Nabipour, M.; Emadi, M. A.; Ghatee, M. H.; Ayatollahi,


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S., Atomic force microscopy (AFM) investigation on the surfactant wettability alteration mechanism of aged mica mineral surfaces. Energy Fuels 2010, 25(1), 183-188. (29)Zargari, S.; Ostvar, S.; Niazi, A.; Ayatollahi, S., Atomic force microscopy and wettability study of the alteration of mica and sandstone by a biosurfactant-producing bacterium Bacillus thermodenitrificans. J. Adv. Microsc. Res. 2010, 5(2), 143-148. (30)Morrow, N. R.; Lim, H. T.; Ward, J. S., Effect of crude-oil-induced wettability changes on oil recovery. SPE Form. Eval. 1986, 1(1), 89-103. (31)Buckley, J.; Liu, Y.; Monsterleet, S., Mechanisms of wetting alteration by crude oils. SPE J. 1998, 3(1), 54-61. (32) Zhao, G.; You, Q.; Tao, J.P.; Gu, C.L.; Aziza, H.; Ma, L.P.; Dai, C.L. Preparation and application of a novel phenolic resin dispersed particle gel for in-depth profile control in low permeability reservoirs. J. Petrol. Sci. Eng. 2018, 161, 703-714.


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Table Captions Table 1 Ion components of the used formation water Description: The formation water is the base fluid for various solutions.


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Figure Captions Fig. 1 Molecular structure of surfactants used in this article Description: The cationic surfactant CTAB and the nonionic surfactant TX-100 were employed in this article (Fig.1). Fig. 2 Surface tension of the surfactant systems at different concentrations Description: Critical micelle concentrations of different surfactant systems can be analyzed from Fig.2. Fig. 3 Height images of different surfaces determined by AFM Description: The effect of crude oil on the roughness of mica surface can be seen from this figure. Fig. 4 Height images of aged mica surfaces treated with various surfactants Description: The effect of various surfactants on the roughness of oil-wet mica surface can be seen from this figure. Fig. 5 Microscopic morphology of sandstone surfaces determined by SEM Description: The effect of the CTAB/TX-100 mixture on the wettability of OSS can be seen from this figure. Fig. 6 Zeta potential of various systems at different concentrations Description: The effect of the CTAB/TX-100 mixture on the chargeability of OSS can be seen from this figure. Fig. 7 Mechanism diagram of wettability alteration induced by various surfactants


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Description: Fig. 7 can help the readers understand the synergy between CTAB and TX-100. Fig. 8 Contact angles of oil droplets on the quartz surfaces treated with the studied surfactants at various concentrations Description: The synergistic mechanism of wettability alteration of OSS induced by the CTAB/TX-100 mixture is indirectly revealed. Fig. 9 Balanced contact angles of oil drops for different systems at room temperature Description: This figure can visually demonstrate the ability of different systems to change the wettability of OSS.


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Graphical Abstract Schematic diagram of wettability alteration induced by the CTAB/TX-100 mixture Low concentration

Moderate concentration

Carboxylic substances

CTAB

High concentration

TX-100

Under the low mass fraction conditions (< cmc), due to the synergistic effect between CTAB and TX-100, the molecules of CTAB are preadsorbed on the oil-wet quartz surface by electrostatic attraction, acting as anchor particles, and aggregates are formed by TX-100 and CTAB through hydrophobic interaction, thereby increasing the adsorption amount of the CTAB molecules on the oil-wet quartz surface. When the surfactant mass fraction exceeds the critical micelle concentration (> cmc), The desorbed ion pairs are produced by the carboxylic substances and the aggregates formed by CTAB and TX-100. The CTAB/TX-100 mixed surfactants have better desorption capacity for carboxylic substances than the single cationic surfactant CTAB. Thus, the CTAB/TX-100 mixture is more effective than CTAB in wettability alteration of oil-wet rock surface.


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Tables Table 1 component

concentration, (mg/L)

Na+

6910.5

Ca2+

420.6

Mg2+

226.2

Cl-

12520.7


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Figures Fig. 1 N

(a) CTAB

O n=9-10 (b) TX-100


OH n

. Br -

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Fig. 2 80

CTAB/TX-100 mixture CTAB TX-100

70

Surface tension, mN/m

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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60

50

40

30 0.00

0.05

0.10

0.15

0.20

Surfactant concentration, wt%


0.25

0.30

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Fig. 3

(a) Fresh mica surface

（b）Aged mica surface


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Fig. 4

(a) Aged mica surface treated with CTAB

(b) Aged mica surface treated with TX-100

(c) Aged mica surface treated with CTAB/TX-100 mixture


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Fig. 5

(a) Clean surface

(b) Oil-wet surface

(c) Oil-wet surface treated with formation water

(d) Oil-wet surface treated with CTAB

(e) Oil-wet surface treated with TX-100

(f) Oil-wet surface treated with CTAB/TX-100


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Fig. 6 40

CTAB TX-100 CTAB/TX-100 mixture

30

Zeta potential, mV

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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20

10

0

-10 0.00

0.02

0.04

0.06

0.08



0.10

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Fig. 7 Low concentration


CTAB

High concentration

Carboxylic substances (a) CTAB

Low concentration


TX-100

High concentration

Carboxylic substances

(b) TX-100 Low concentration

CTAB


Carboxylic substances (c) CTAB/TX-100 mixture


High concentration

TX-100

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Fig. 8 140

CTAB/TX-100 mixture CTAB TX-100

120

100

Contact angle, °

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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80

60

40

20 0.00

0.05

0.10

0.15

0.20



0.25

0.30

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Fig. 9

(a) Aged quartz plate: 134°

(b) Treated with CTAB: 57°

(c) Treated with TX-100: 108°

(d) Treated with CTAB/TX-100: 43°


Wettability alteration of oil-wet sandstone surface by synergistic

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