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Mechanism of active silica nanofluids based on interface-regulated effect during spontaneous imbibition

Mechanism of active silica nanofluids based on interface-regulated effect during spontaneous... The ultra-low permeability reservoir is regarded as an important energy source for oil and gas resource development and is attracting more and more attention. In this work, the active silica nanou fl ids were prepared by modie fi d active silica nanopar - ticles and surfactant BSSB-12. The dispersion stability tests showed that the hydraulic radius of nanofluids was 58.59 nm and the zeta potential was − 48.39 mV. The active nanofluids can simultaneously regulate liquid–liquid interface and solid–liquid interface. The nanofluids can reduce the oil/water interfacial tension (IFT) from 23.5 to 6.7 mN/m, and the oil/water/solid contact angle was altered from 42° to 145°. The spontaneous imbibition tests showed that the oil recovery of 0.1 wt% active nanofluids was 20.5% and 8.5% higher than that of 3 wt% NaCl solution and 0.1 wt% BSSB-12 solution. Finally, the effects of nanofluids on dynamic contact angle, dynamic interfacial tension and moduli were studied from the adsorption behavior of nanofluids at solid–liquid and liquid–liquid interface. The oil detaching and transporting are completed by synergistic effect of wettability alteration and interfacial tension reduction. The findings of this study can help in better understanding of active nanofluids for EOR in ultra-low permeability reservoirs. Keywords Active nanofluids · Regulate interface · Ultra-low permeability · Spontaneous imbibition 1 Introduction et al. 2016; Qiao et al. 2017; Peng et al. 2018; Zhang et al. 2019; Wang et al. 2019). It has become a decisive problem With the technology development of oil and gas exploration, restricting the development of ultra-low permeability oil and unconventional oil and gas resources have become a new gas resources. The key to developing ultra-low permeability global energy supply. The ultra-low permeability reservoirs oil and gas resources is increasing the utilization of matrix are important parts of unconventional oil and gas resources; reserves. there are great challenges in exploitation and utilization. Spontaneous imbibition is a process in which the wet- Compared with conventional reservoirs, ultra-low permea- ting phase in porous media displaces the non-wetting phase bility reservoirs have the characteristics of low porosity, low under the action of capillary force (Jamaloei et al. 2010; permeability, and poor connectivity (Zhao et al. 2014; Qu Meng et al. 2015; Foley et al. 2017; Jabbari et al. 2019). Spontaneous imbibition is an extremely important mech- anism for EOR in ultra-low permeability reservoirs. Sur- Edited by Yan-Hua Sun factants are commonly used as spontaneous imbibition * Ming-Wei Zhao agents, which can enhance oil recovery primarily through zhaomingwei@upc.edu.cn reducing interfacial tension (IFT) and altering wettability. * Cai-Li Dai Many studies of spontaneous imbibition of surfactants have daicl@upc.edu.cn been reported. Standnes (2004) studied the oil recovery rates of spontaneous imbibition for cationic surfactants C TAB by Key Laboratory of Unconventional Oil and Gas estimation of capillary diffusivity coefficients in oil-wet car - Development, Ministry of Education, School of Petroleum Engineering, China University of Petroleum (East China), bonates. Xie et al. (2005) pointed out that spontaneous imbi- Qingdao 266580, Shandong, China bition recovery rate was faster in nonionic surfactant solu- Shandong Key Laboratory of Oilfield Chemistry, School tions than in cationic surfactant solutions owing to the lower of Petroleum Engineering, China University of Petroleum interfacial tension. Saputra et al. (2016) provided the field (East China), Qingdao 266580, China Vol.:(0123456789) 1 3 884 Petroleum Science (2021) 18:883–894 data analysis and the numerical field-scale model evidences et al. (2019) developed a kind of nonionic surfactant by inte- that the addition of surfactant into an oil/water/rock system grating with hydrophilic silica nanoparticles for EOR. enhanced spontaneous imbibition oil recovery by reducing Our group has also done a lot of research on the spon- the IFT. Mirchi et al. (2017) measured the equilibrium IFT taneous imbibition of nanofluids. Most of previous studies and found the surfactant solution playing an important role focused on the low permeability (1–10 mD) reservoirs, and in local trapping of oil phase during spontaneous imbibition. the study of ultra-low permeability (0.1–1 mD) has not been Ali et al. (2020) proved ferro-nanoparticles accounted for further carried out. In this work, interface-regulated nanoflu- the effectiveness in reducing interfacial tension because of ids were prepared and showed excellent ability to enhance higher silicate sorption capacity. spontaneous imbibition recovery of ultra-low permeability In recent years, SiO, TiO , and other nanomaterials have cores. At present, the research on active nanofluids mainly 2 2 been used more and more in oilfields (Dai et al. 2015a, b; focused on the improvement of some specific properties of Ehtesabi et al. 2014, 2015; Li et al. 2017a, b; Olayiwola et al. pure surfactants by adding nanoparticles, and the mecha- 2019a, b, 2020a, b; Wang et al. 2018; Xu et al. 2020; Zhao nism of spontaneous imbibition was mainly explained by et al. 2020; Zhou et al. 2019). Due to nanoscale size and the synergistic effect of nanoparticles and surfactants on oil unique thermodynamic properties, nanofluids show great droplet detachment. However, the effects of nanoparticles potential in spontaneous imbibition EOR processes. Nano- and surfactants on the adsorption behavior at solid–liquid particles can enter porous media and effectively adsorb at and liquid–liquid interfaces are not clear. In addition, after the solid–liquid interface to alter wettability, thus improving oil droplets are detached from the formation surface, the the effect of spontaneous imbibition. There have been many migration of oil droplets by nanofluids in pore throats has investigations into the impact of nanofluids on wettability. also not been discussed in depth. Li et al. (Li et al. 2017a) presented that the silica-based In this work, the active nanofluids were prepared by non- nanofluid is a promising method to enhance oil recovery ionic surfactant BSSB-12 and modified silica nanoparticles. in water-wet sandstone reservoirs by altering the wettabil- The nanofluids can simultaneously regulate oil/water and ity to neutral-wet. Erfani et al. (2017) concluded that the oil/solid interface to reduce interfacial tension and alter wet- water-based nanofluid is better used in high permeability tability. It can improve the oil displacement in ultra-low per- sandstone rocks. Nowrouzi et al. (2019) investigated the meability reservoirs through synergistic effect of surfactant effects of concentration and size of TiO nanoparticles on and nanosilica. The nanofluids prepared in this study have wettability alteration and oil production during spontaneous some limitations. The average particle size of nanofluids imbibition. Wu et al. (2020) studied silica-based amphiphi- is among 50–60 nm. It may be not suitable for tight and lic Janus nanofluid with improved interfacial properties and shale reservoirs with much lower permeability. When the stable adsorption for EOR. Farad et al. (2020) found that temperature is more than 90 °C and the salinity exceeds hydroxyl-functionalized silica-based nanofluids altered the 100,000 mg/L, the stability of nanofluids will become worse. wettability from intermediate-wet to stronger water-wet as The active silica nanofluids are also not suitable for reser - 2+ the concentration of nanoparticles increased. Eltoum et al. voir brine with high divalent ion contents, such as Ca and 2+ (2020) summarized and analyzed different kinds of nanopar - Mg . ticles on wettability alteration. Spontaneous imbibition is an important mechanism for EOR in low permeability reservoirs. The nanofluids of pure 2 Experimental nanoparticles have less effect of reducing IFT and are unsta- ble for long-term effectiveness, while for surfactant solu-2.1 Materials and apparatus tions, the effectiveness of spontaneous imbibition is limited due to too much loss of surfactants. As shown in Fig. 1, when Sodium hydroxide (NaOH), hydrochloric acid (HCl), ethyl combining nanoparticles and surfactants together, the inter-alcohol (C H OH), and N,N-dimethylformamide (DMF) 2 5 facial tension can be reduced and wettability can be altered. were provided by Xilong Chemical Co., Ltd., China. Silica This type of nanofluids (also called active nanofluids) has nanoparticles, vinyltriethoxysilane (VTES), 2-mercapto- higher oil displacement potential than pure surfactant solu- benzimidazole, and 2,2-dimethoxy-2-phenylacetophenone tions or pure nanofluids. Nwidee et al. (2017) studied that (DMPA) were purchased from Aladdin Reagent Co., Ltd., all these different surfactant–nanoparticle nanofluids (ZrO / China. Surfactant BSSB-12 (dodecyl sulfobetain) was CTAB, ZrO /TX-100, NiO/C TAB and NiO/TX-100) can from Shanghai Chuxing Chemical Co., Ltd., China. The 16 2 16 alter the wettability of oil-wet limestone during spontaneous simulated oil used in this study was a mixture of dehy- imbibition. Zhao et al. (2018) proved that the spontaneous drated crude oil obtained from Xinjiang Oilfield, and imbibition oil recovery of silica nanofluids was higher than kerosene with a volume ratio of 1:17. 3 wt% NaCl solu- that of TX-100 solution in the same concentration. Zhong tion was used as reservoir brine with a density of 1.02 g/ 1 3 Petroleum Science (2021) 18:883–894 885 Excellence in Excellence in reducing altering wettability interfacial tension SiO BSSB-12 Active nanofluids Regulate oil/water and oil/solid interface simultaneously Fig. 1 The effect of interface-regulated active silica nanofluids cm and a dynamic viscosity of 0.91 mPa s at 25 °C. The microscopy (SEM) images of core slices were obtained ultra-low permeability sandstone cores with gas perme- with an S-4800 field emission scanning electron micro- ability of about 0.2 mD and porosity of about 15% were scope (Hitachi, Ltd). purchased from Haian Oil Scientific Research Apparatus Co., Ltd., China. The morphology of modified silica nanoparticles was 2.2 Preparation of active nanofluids characterized with a JEM-2100 transmission electron microscope (TEM) (Japan Electronics Co., Ltd.). The The silica nanoparticles were modified following the particle size and zeta potential were measured by a Nano- previous study (Dai et al. 2017). The active nanof luid Brook Omni laser particle size analyzer (Brookhaven was prepared as follows: the modified silica nanopar- Instruments Co., Ltd). To determine the interfacial activ- ticles (0.2 g) and BSSB-12 (0.2 g) and distilled water ity, the interfacial tensions between oil and active nano- (199.6  g) were added into a beaker. NaOH solution fluids were measured at 60  °C and 6000 r/min with a (0.1 mol/L) was used to adjust the pH of the nanof lu- TX-500C spinning drop interfacial tensiometer (Bowing ids. The nanof luids were stirred with a magnetic stir- Industry Corporation). The contact angles were measured rer for 0.5 h and then put in an ultrasonicator for 2 h with a JC2000D2 contact angle measurement (Zhongchen until the dispersion was clear and transparent. Figure 2 Digital Technic Apparatus Corporation). The dynamic shows the preparation process of active nanof luids. The interface modulus and interfacial tension of active nano- parameters of ultra-low permeability cores are shown fluids were measured with a interfacial rheometer (TEC - in Table 1. LIS Interface Technology Co., Ltd). The scanning electron 1 3 886 Petroleum Science (2021) 18:883–894 NaOH Silica nanoparticle BSSB-12 Fig. 2 The preparation process of active nanofluids solution, and 0.1 wt% active nanofluids, respectively. The Table 1 The parameters of cores imbibition devices were placed in a constant-temperature Number Length, mm Diameter, mm Porosity, % Perme- bath at 60 °C, and the volume of oil separated from cores ability, was recorded at regular intervals. mD 1 33.24 25.16 14.55 0.25 2 32.51 25.15 13.32 0.26 2.4 The broken‑up behavior of oil droplets 3 33.22 25.07 14.42 0.23 A microfluidic device with 3-D pore throat structure was used to simulate the pore throats in the formation, and the diagram of the microfluidic device is shown in Fig.  3. 2.3 Spontaneous imbibition tests 0.1 wt% BSSB-12 solution and 0.1 wt% active silica nanofluids were used as continuous phase and n -hexane The cores with a diameter of 2.5 cm were cut into columns was as dispersed phase. At first, the microfluidic device with a length of 3 cm. After dried in a vacuum oven at was placed under an inverted microscope (Leica DMi8 110 °C for 24 h, the cores were taken out and weighted C). Then, the continuous phase was injected at a flow rate after cooling to room temperature. Then, these cores and of 0.1 mL/min, and the dispersed phase was injected at a the simulated oil were simultaneously evacuated for 12 h. flow rate of 0.005 mL/min. The structure of “cross” con- The experimental procedures for core saturation and vergence is used to generate oil droplets. The broken-up imbibition tests were the same as the previous study (Dai behavior of oil droplets was recorded with a Photron Fast- et al. 2017). After aging at 90 °C for 48 h, the weight of cam SA-Z high-speed camera. Finally, the average size of cores saturated with simulated oil was recorded. The cores oil droplets in the process of broken-up was calculated. were immersed in 3 wt% NaCl solution, 0.1 wt% BSSB-12 Continuous phase Dispersed phase Fig. 3 Schematic diagram of the microfluidic device 1 3 Petroleum Science (2021) 18:883–894 887 the simulated oil and active nanofluids of different silica nanoparticle and BSSB-12 concentrations were measured. The results are shown in Fig. 6a. When the concentration of active nanoparticles was 0.1 wt%, the interfacial tensions between the simulated oil and active nanofluids decreased with the increase in the concentration of BSSB-12. When the concentration of BSSB-12 was 0.1 wt%, the interfacial tensions rarely changed with the increase in the concentra- tion of silica nanoparticles. The minimum interfacial tension was 6.7 mN/m in the case of 0.1 wt% silica nanoparticles and 0.1 wt% BSSB-12. Based on the influence of differ - ent concentrations of silica nanoparticles and BSSB-12 on the oil–water interfacial tensions, it can be concluded that nanofluids can reduce interfacial tensions mainly through Fig. 4 TEM image of active nanofluids surfactant BSSB-12, and silica nanoparticles cannot greatly reduce the interfacial tension between the simulated oil and nanofluids. The effect of active nanofluids on reducing interfacial tension can be explained by Fig. 6b. When the concentra- tion of BSSB-12 is low, pure silica nanoparticles and silica nanoparticles coated with BSSB-12 coexist in active nano- fluids. There exists a competitive adsorption of BSSB-12 between the surface of nanoparticles and the oil/water inter- face, which makes less BSSB-12 adsorption on the oil/water interface. Thus, the effect of reducing interfacial tension is poor. When the concentration of BSSB-12 is high, there are sufficient silica nanoparticles coated with BSSB-12. The adsorption amount on the surface of an oil droplet is enough to reduce the interfacial tension greatly. Therefore, the active nanofluids with a high concentration of BSSB-12 10 100 1000 have a stronger ability to reduce the interfacial tension than Particle size, nm the nanofluids with a low concentration of BSSB-12. Fig. 5 The particle size distribution of active nanofluids 3.3 Wettability alteration 3 Results and discussion To investigate the effect of silica nanoparticles and BSSB- 12 on solid–liquid interface, the equilibrium contact angles 3.1 Characterization of active nanofluids between the simulated oil and active nanofluids were meas- ured. The paraffin-coated oil-wet glass slices were aging in The TEM image of active nanoparticles is shown in Fig. 4. active nanofluids, and the final stable oil/water/solid three- The active nanoparticles were approximately spherical. phase contact angles were recorded as the equilibrium con- The particle size of the modified silica nanoparticles was tact angles. The equilibrium contact angles of silica nano- about 30 nm. As shown in Fig. 5, the particle size distribu- particles and BSSB-12 with different concentrations are tion of active nanofluids was 10–110 nm and the average shown in Fig. 7a. When the concentration of active nanopar- hydraulic radius was 58.59 nm. The zeta potential of active ticles was 0.1 wt%, the equilibrium contact angles increased nanofluids was − 48.39 mV, indicating the excellent stabil- with the increase in the concentration of BSSB-12 and the ity. Active nanoparticles are not easy to aggregate and can variation in wettability was 47°. When the concentration be stable for a long time. of BSSB-12 was 0.1 wt%, the equilibrium contact angles increased with the increase in the concentration of active 3.2 Oil–water interfacial tension nanoparticles and the variation in wettability was 75°. The pure active nanoparticles or BSSB-12 cannot achieve much To investigate the effect of silica nanoparticles and BSSB- stronger ability to alter wettability than 0.1 wt% active nano- 12 on interfacial tensions, the interfacial tensions between fluids. The ability to alter wettability was achieved by the 1 3 Transmittance, % 888 Petroleum Science (2021) 18:883–894 synergistic action of active nanoparticles and BSSB-12, in surface of oil droplets. It was difficult for active nanopar - which the active nanoparticles played a stronger role than ticles to approach the oil/water/solid three-phase contact- BSSB-12 at this point. ing area, and the alteration of wettability mainly depended The effect of active nanofluids on altering wettability can on the action of BSSB-12. This resulted in the poor effect be revealed by Fig. 7b. When the concentration of active of altering wettability. The wettability alteration caused by nanoparticles was low and the BSSB-12 concentration was high concentration of active nanoparticles is consistent with high, BSSB-12 formed a double-layer adsorption on the the mechanism of structural disjoining pressure proposed by (a) BSSB-12 Active silica nanoparticles 0 0.02 0.04 0.06 0.08 0.10 Concentration, % (b) Water Water Oil Oil Low concentration of BSSB-12 Water Water Oil Oil High concentration of BSSB-12 Fig. 6 The interfacial tension of different concentrations of active silica nanoparticles (the concentration of BSSB-12 was 0.1 wt%) and BSSB- 12 (the concentration of silica nanoparticles was 0.1 wt%) (a) and adsorption diagram of active nanofluids on simulated oil and water phases (b) 1 3 Interfacial tension, mN/m Petroleum Science (2021) 18:883–894 889 Wasan and Nikolov (2003), Wasan et al. (2011), Kondiparty solution, 0.1 wt% active nanofluids, and simulated oil were et al. (2012), and Liu et al. (2012). When sufficient nanopar - studied. The dynamic contact angles of three solutions ticles were present, the Brownian motion of nanoparticles are shown in Fig.  10. In the initial state, all the contact caused the structural disjoining pressure in the oil/water/ angles in the three solutions were less than 90° due to the solid three-phase contact area and the wettability was altered oil-wet treatment of the surface of glass slices. The con- to strongly water-wet. Hence, the active silica nanoparticles tact angles were invariably less than 90° in 3 wt% NaCl have a stronger ability to alter wettability than BSSB-12. solution and 0.1 wt% BSSB-12 solution, reflecting poor ability to alter wettability. The change of contact angles in 3.4 Spontaneous imbibition active nanofluids was significantly faster than that in the pure surfactant solution and brine. In active nanofluids, the The oil dischargement effect of 3  wt% NaCl solution, contact angle reached the equilibrium state after 10 h, and 0.1 wt% BSSB-12 solution and 0.1 wt% active nanofluids the final contact angle was 145°. The nanofluids altered was investigated by static spontaneous imbibition tests. The the wettability of the glass slice surface from oil-wet to oil recovery versus time during spontaneous imbibition is water-wet. The combination of the surfactant BSSB-12 shown in Fig. 8. In the initial 3 days, the oil recovery of three and silica nanoparticles significantly improved the ability liquids increased rapidly with time and the active nanofluids of detaching oil droplets from the solid surface. performed the highest oil dischargement effect among the three liquids. After 4 days, the oil recovery of the active 3.5.2 Oil transportation through pore throats nanofluids increased continuously, while that of 3 wt% NaCl solution and BSSB-12 solution did not change much. The The dynamic interfacial moduli between the simulated oil final oil recovery of the active nanofluids was 26.5%; the and different fluids are shown in Fig.  11a. The interfacial oil recovery of BSSB-12 solution and 3 wt% NaCl solution moduli between the simulated oil and active nanofluids was 17% and 6%, respectively. According to the evaluation increased with time, and the stable moduli were 6 mN/m experiment of oil dischargement during spontaneous imbibi- after 2500 s. The interfacial moduli of brine and the BSSB- tion, the oil recovery of active nanofluids is higher than that 12 solution were unchanged with time, and the values of of pure surfactant solution and brine, which can be ascribed interfacial moduli were 1.2 mN/m and 0.6 mN/m, respec- to the synergistic effect of active silica nanoparticles and tively. Compared with brine and the pure surfactant solution, BSSB-12. the interfacial moduli between active silica nanofluids and the simulated oil clearly increased. The results showed that 3.5 T he mechanism of active nanofluids a stronger interfacial film was formed due to the adsorption during spontaneous imbibition of active silica nanoparticles and BSSB-12 at the oil–water interface. Meanwhile, the interfacial tensions decreased with 3.5.1 Oil detachment from solid surface time (Fig. 11b). The interfacial tension between the simu- lated oil and the active nanofluids decreased from 7 mN/m The surface morphologies of ultra-low permeability core to 3.5 mN/m. The active nanofluids can reduce the inter - surface before and after adsorption of 0.1 wt% active nano- facial tensions due to the strong adsorption of active silica u fl ids were observed with an S-4800 e fi ld emission scanning nanoparticles at the oil–water interface to transport the oil electron microscope (Hitachi, Ltd.), as shown in Fig. 9. As droplets. Figure 12 shows the average size of broken-up oil shown in Fig. 9a, the cross section of the ultra-low perme- droplets in the BSSB-12 solution and active silica nanoflu- ability core was rough at 20,000 times magnification. Fig- ids. The average size of oil droplets decreased with time, ure 9b shows the cross section after the adsorption of active and the oil droplets were broken up completely after 2 s. The nanofluids at the same time magnification. The nanoparticle size of broken-up oil droplets in the BSSB-12 solution was adsorption layer has been formed on the cross section after larger than that in active silica nanofluids. The average size soaked by nanofluids. The nanoparticles were nearly spheri- of broken-up oil droplets in active silica nanofluids after 2 cal, and their particle sizes were about 50 nm, in agreement s was 17.96 μm, and it was easier to transport oil droplets well with the TEM results. The SEM results showed that with the help of active silica nanoparticles. active nanofluids could enter the pore throats of the ultra- The transportation of oil in core pores and throats is cos low permeability core and formed effective adsorption in the mainly affected by capillary force P = 2 and addi- pores, which provided the potential condition for nanofluids ∕ ∕ tional resistance of Jamin effect P = 2(1 R − 1 R ) . 1 2 altering the surface property of pores. For oil-wet rocks, the capillary force is the resistance for To further investigate oil detachment effect of active EOR during spontaneous imbibition and the reduction in nanofluids from the solid surface, the dynamic contact the interfacial tension will reduce the resistance to angles between 3 wt% NaCl solution, 0.1 wt% BSSB-12 1 3 890 Petroleum Science (2021) 18:883–894 (a) BSSB-12 Active silica nanoparticles 0 0.02 0.04 0.06 0.08 0.10 Concentration, % (b) Water Water Solid Solid Low concentration of active silica nanoparticles Water Water Solid Solid High concentration of active silica nanoparticles Fig. 7 The equilibrium contact angles of different concentrations of active silica nanoparticles (the concentration of BSSB-12 was 0.1 wt%) and BSSB-12 (the concentration of silica nanoparticles was 0.1 wt%) (a) and adsorption diagram of active nanofluids on the oil/water/solid three- phase contacting area (b) transporting oil droplets in core pores. At the same time, make the size of oil droplets smaller because the oil drop- when the oil droplets pass through the pore throats, a lets are emulsified and broken-up, so the oil droplets are resistance effect will be produced due to the deformation more likely to pass through the pore throats. Consequently, of oil droplets—Jamin effect. The reduction in oil–water the oil droplets can pass through the small pore holes and interfacial tension resulted in a decrease in resistance throats with less resistance. caused by the Jamin effect. The active silica nanofluids 1 3 Contact angle, degree Petroleum Science (2021) 18:883–894 891 3 wt% NaCl solution 3 wt % NaCl solution 0.1 wt% BSSB-12 solution 0.1 wt % BSSB-12 solution 0.1 wt% active silica nanofluids 0.1 wt % active nanofluids 02468 10 12 14 0246 8101214 Time, h Time, d Fig. 10 The dynamic contact angles in 3 wt% NaCl solution, 0.1 wt% Fig. 8 The oil recovery of 3  wt% NaCl solution, 0.1  wt% BSSB-12 BSSB-12 solution, 0.1 wt% active nanofluids solution, and 0.1 wt% active nanofluids shown in Fig.  13. The BSSB-12 solution has less effect There are numerous studies showing that when the pore on changing wettability, so the oil recovery during spon- wall is hydrophilic, it is favorable for spontaneous imbi- taneous imbibition is worse than the active nanofluids. bition. According to the experimental results of contact The active nanofluids can change the wettability to water- angles, the active nanofluids can change the wettability of wet due to the structural disjoining pressure between the solid surface from oil-wet to water-wet, thus changing the simulated oil and the pore wall generated by active silica capillary force from resistance to motivation and enhanc- nanoparticles. The oil displacement efficiency of ultra-low ing oil recovery. In the process of detaching an oil drop, permeability cores is obviously improved by the synergis- the adhesion work (W = (1 + cos )) decreased through tic effect of active silica nanoparticles and BSSB-12. reducing the interfacial tension and altering the wettabil- ity. The mechanism figure of spontaneous imbibition is Fig. 9 The SEM images of core samples before (a) and after (b) adsorption of 0.1 wt% active nanofluids 1 3 Oil recovery, % Contact angle, degree 892 Petroleum Science (2021) 18:883–894 8 30 (a) (b) 3 wt% NaCl solution 3 wt% NaCl solution 0.1 wt% BSSB-12 solution 0.1 wt% BSSB-12 solution 0.1 wt% active silica nanofluids 0.1 wt% active silica nanofluids 4 15 0 0 0 500 1000 1500 2000 2500 3000 3500 4000 0 500 1000 1500 2000 2500 3000 3500 4000 Time, s Time, s Fig. 11 The dynamic interfacial moduli (a) and interfacial tensions (b) of 3  wt% NaCl solution, 0.1  wt% BSSB-12 solution, 0.1  wt% active nanofluids 0.1 wt% BSSB-12 solution 0.1 wt% active silica nanofluids 4 Conclusions 0 s 1. The active nanofluids have good dispersion stability and 0.5 s excellent oil dischargement effect after surfactant BSSB- 1.0 s 12 adsorbed onto the surface of active silica nanoparti- 1.5 s 2.0 s cles. 2. BSSB-12 and active nanoparticles had their respective advantages in regulating liquid–liquid interface and solid–liquid interface to reduce interfacial tension and alter wettability. 3. When applied to EOR, the spontaneous imbibition 0 0.5 1.0 1.5 2.0 recovery of active nanofluids could reach 26.5%. Time, s 4. The mechanism for EOR was presented by the process of Fig. 12 The average size of broken-up oil droplets in the BSSB-12 detaching oil droplets with the help of active nanofluids. solution and active silica nanofluids Silica nanoparticle BSSB-12 solution BSSB-12 Active nanofluids Fig. 13 The mechanism image of spontaneous imbibition 1 3 Average size of oil droplets, μm Interfacial module, mN/m Interfacial tension, mN/m Petroleum Science (2021) 18:883–894 893 Acknowledgements This work was financially supported by National Water Resour. 2017;107:405–20. https: //doi.org/10.1016/j.advwa Natural Science Foundation of China (52074333, 51874337); Taishan tres.2017.04.012. Scholar Foundation of Shandong Province (tspd20161004); and Fun- Jabbari Y, Tsotsas E, Kirsch C, Kharaghani A. Determination of the damental Research Funds for the Central Universities (19CX07001A). moisture transport coefficient from pore network simulations of spontaneous imbibition in capillary porous media. Chem Eng Sci. 2019;207:600–10. https ://doi.org/10.1016/j.ces.2019.07.002. Compliance with ethical standards Jamaloei B, Asghari K, Kharrat R, Ahmadloo F. Pore-scale two-phase filtration in imbibition process through porous media at high- and Conflict of interest The authors declare that they have no known com- low-interfacial tension flow conditions. J Pet Sci Eng. 2010;72(3– peting financial interests or personal relationships that could have ap- 4):251–69. https ://doi.org/10.1016/j.petro l.2010.03.026. peared to influence the work reported in this paper. Kondiparty K, Nikolov A, Wasan D, Liu K. Dynamic spread- ing of nanofluids on solids. Part I: experimental. Langmuir. 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Mechanism of active silica nanofluids based on interface-regulated effect during spontaneous imbibition

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10.1007/s12182-020-00537-8
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Abstract

The ultra-low permeability reservoir is regarded as an important energy source for oil and gas resource development and is attracting more and more attention. In this work, the active silica nanou fl ids were prepared by modie fi d active silica nanopar - ticles and surfactant BSSB-12. The dispersion stability tests showed that the hydraulic radius of nanofluids was 58.59 nm and the zeta potential was − 48.39 mV. The active nanofluids can simultaneously regulate liquid–liquid interface and solid–liquid interface. The nanofluids can reduce the oil/water interfacial tension (IFT) from 23.5 to 6.7 mN/m, and the oil/water/solid contact angle was altered from 42° to 145°. The spontaneous imbibition tests showed that the oil recovery of 0.1 wt% active nanofluids was 20.5% and 8.5% higher than that of 3 wt% NaCl solution and 0.1 wt% BSSB-12 solution. Finally, the effects of nanofluids on dynamic contact angle, dynamic interfacial tension and moduli were studied from the adsorption behavior of nanofluids at solid–liquid and liquid–liquid interface. The oil detaching and transporting are completed by synergistic effect of wettability alteration and interfacial tension reduction. The findings of this study can help in better understanding of active nanofluids for EOR in ultra-low permeability reservoirs. Keywords Active nanofluids · Regulate interface · Ultra-low permeability · Spontaneous imbibition 1 Introduction et al. 2016; Qiao et al. 2017; Peng et al. 2018; Zhang et al. 2019; Wang et al. 2019). It has become a decisive problem With the technology development of oil and gas exploration, restricting the development of ultra-low permeability oil and unconventional oil and gas resources have become a new gas resources. The key to developing ultra-low permeability global energy supply. The ultra-low permeability reservoirs oil and gas resources is increasing the utilization of matrix are important parts of unconventional oil and gas resources; reserves. there are great challenges in exploitation and utilization. Spontaneous imbibition is a process in which the wet- Compared with conventional reservoirs, ultra-low permea- ting phase in porous media displaces the non-wetting phase bility reservoirs have the characteristics of low porosity, low under the action of capillary force (Jamaloei et al. 2010; permeability, and poor connectivity (Zhao et al. 2014; Qu Meng et al. 2015; Foley et al. 2017; Jabbari et al. 2019). Spontaneous imbibition is an extremely important mech- anism for EOR in ultra-low permeability reservoirs. Sur- Edited by Yan-Hua Sun factants are commonly used as spontaneous imbibition * Ming-Wei Zhao agents, which can enhance oil recovery primarily through zhaomingwei@upc.edu.cn reducing interfacial tension (IFT) and altering wettability. * Cai-Li Dai Many studies of spontaneous imbibition of surfactants have daicl@upc.edu.cn been reported. Standnes (2004) studied the oil recovery rates of spontaneous imbibition for cationic surfactants C TAB by Key Laboratory of Unconventional Oil and Gas estimation of capillary diffusivity coefficients in oil-wet car - Development, Ministry of Education, School of Petroleum Engineering, China University of Petroleum (East China), bonates. Xie et al. (2005) pointed out that spontaneous imbi- Qingdao 266580, Shandong, China bition recovery rate was faster in nonionic surfactant solu- Shandong Key Laboratory of Oilfield Chemistry, School tions than in cationic surfactant solutions owing to the lower of Petroleum Engineering, China University of Petroleum interfacial tension. Saputra et al. (2016) provided the field (East China), Qingdao 266580, China Vol.:(0123456789) 1 3 884 Petroleum Science (2021) 18:883–894 data analysis and the numerical field-scale model evidences et al. (2019) developed a kind of nonionic surfactant by inte- that the addition of surfactant into an oil/water/rock system grating with hydrophilic silica nanoparticles for EOR. enhanced spontaneous imbibition oil recovery by reducing Our group has also done a lot of research on the spon- the IFT. Mirchi et al. (2017) measured the equilibrium IFT taneous imbibition of nanofluids. Most of previous studies and found the surfactant solution playing an important role focused on the low permeability (1–10 mD) reservoirs, and in local trapping of oil phase during spontaneous imbibition. the study of ultra-low permeability (0.1–1 mD) has not been Ali et al. (2020) proved ferro-nanoparticles accounted for further carried out. In this work, interface-regulated nanoflu- the effectiveness in reducing interfacial tension because of ids were prepared and showed excellent ability to enhance higher silicate sorption capacity. spontaneous imbibition recovery of ultra-low permeability In recent years, SiO, TiO , and other nanomaterials have cores. At present, the research on active nanofluids mainly 2 2 been used more and more in oilfields (Dai et al. 2015a, b; focused on the improvement of some specific properties of Ehtesabi et al. 2014, 2015; Li et al. 2017a, b; Olayiwola et al. pure surfactants by adding nanoparticles, and the mecha- 2019a, b, 2020a, b; Wang et al. 2018; Xu et al. 2020; Zhao nism of spontaneous imbibition was mainly explained by et al. 2020; Zhou et al. 2019). Due to nanoscale size and the synergistic effect of nanoparticles and surfactants on oil unique thermodynamic properties, nanofluids show great droplet detachment. However, the effects of nanoparticles potential in spontaneous imbibition EOR processes. Nano- and surfactants on the adsorption behavior at solid–liquid particles can enter porous media and effectively adsorb at and liquid–liquid interfaces are not clear. In addition, after the solid–liquid interface to alter wettability, thus improving oil droplets are detached from the formation surface, the the effect of spontaneous imbibition. There have been many migration of oil droplets by nanofluids in pore throats has investigations into the impact of nanofluids on wettability. also not been discussed in depth. Li et al. (Li et al. 2017a) presented that the silica-based In this work, the active nanofluids were prepared by non- nanofluid is a promising method to enhance oil recovery ionic surfactant BSSB-12 and modified silica nanoparticles. in water-wet sandstone reservoirs by altering the wettabil- The nanofluids can simultaneously regulate oil/water and ity to neutral-wet. Erfani et al. (2017) concluded that the oil/solid interface to reduce interfacial tension and alter wet- water-based nanofluid is better used in high permeability tability. It can improve the oil displacement in ultra-low per- sandstone rocks. Nowrouzi et al. (2019) investigated the meability reservoirs through synergistic effect of surfactant effects of concentration and size of TiO nanoparticles on and nanosilica. The nanofluids prepared in this study have wettability alteration and oil production during spontaneous some limitations. The average particle size of nanofluids imbibition. Wu et al. (2020) studied silica-based amphiphi- is among 50–60 nm. It may be not suitable for tight and lic Janus nanofluid with improved interfacial properties and shale reservoirs with much lower permeability. When the stable adsorption for EOR. Farad et al. (2020) found that temperature is more than 90 °C and the salinity exceeds hydroxyl-functionalized silica-based nanofluids altered the 100,000 mg/L, the stability of nanofluids will become worse. wettability from intermediate-wet to stronger water-wet as The active silica nanofluids are also not suitable for reser - 2+ the concentration of nanoparticles increased. Eltoum et al. voir brine with high divalent ion contents, such as Ca and 2+ (2020) summarized and analyzed different kinds of nanopar - Mg . ticles on wettability alteration. Spontaneous imbibition is an important mechanism for EOR in low permeability reservoirs. The nanofluids of pure 2 Experimental nanoparticles have less effect of reducing IFT and are unsta- ble for long-term effectiveness, while for surfactant solu-2.1 Materials and apparatus tions, the effectiveness of spontaneous imbibition is limited due to too much loss of surfactants. As shown in Fig. 1, when Sodium hydroxide (NaOH), hydrochloric acid (HCl), ethyl combining nanoparticles and surfactants together, the inter-alcohol (C H OH), and N,N-dimethylformamide (DMF) 2 5 facial tension can be reduced and wettability can be altered. were provided by Xilong Chemical Co., Ltd., China. Silica This type of nanofluids (also called active nanofluids) has nanoparticles, vinyltriethoxysilane (VTES), 2-mercapto- higher oil displacement potential than pure surfactant solu- benzimidazole, and 2,2-dimethoxy-2-phenylacetophenone tions or pure nanofluids. Nwidee et al. (2017) studied that (DMPA) were purchased from Aladdin Reagent Co., Ltd., all these different surfactant–nanoparticle nanofluids (ZrO / China. Surfactant BSSB-12 (dodecyl sulfobetain) was CTAB, ZrO /TX-100, NiO/C TAB and NiO/TX-100) can from Shanghai Chuxing Chemical Co., Ltd., China. The 16 2 16 alter the wettability of oil-wet limestone during spontaneous simulated oil used in this study was a mixture of dehy- imbibition. Zhao et al. (2018) proved that the spontaneous drated crude oil obtained from Xinjiang Oilfield, and imbibition oil recovery of silica nanofluids was higher than kerosene with a volume ratio of 1:17. 3 wt% NaCl solu- that of TX-100 solution in the same concentration. Zhong tion was used as reservoir brine with a density of 1.02 g/ 1 3 Petroleum Science (2021) 18:883–894 885 Excellence in Excellence in reducing altering wettability interfacial tension SiO BSSB-12 Active nanofluids Regulate oil/water and oil/solid interface simultaneously Fig. 1 The effect of interface-regulated active silica nanofluids cm and a dynamic viscosity of 0.91 mPa s at 25 °C. The microscopy (SEM) images of core slices were obtained ultra-low permeability sandstone cores with gas perme- with an S-4800 field emission scanning electron micro- ability of about 0.2 mD and porosity of about 15% were scope (Hitachi, Ltd). purchased from Haian Oil Scientific Research Apparatus Co., Ltd., China. The morphology of modified silica nanoparticles was 2.2 Preparation of active nanofluids characterized with a JEM-2100 transmission electron microscope (TEM) (Japan Electronics Co., Ltd.). The The silica nanoparticles were modified following the particle size and zeta potential were measured by a Nano- previous study (Dai et al. 2017). The active nanof luid Brook Omni laser particle size analyzer (Brookhaven was prepared as follows: the modified silica nanopar- Instruments Co., Ltd). To determine the interfacial activ- ticles (0.2 g) and BSSB-12 (0.2 g) and distilled water ity, the interfacial tensions between oil and active nano- (199.6  g) were added into a beaker. NaOH solution fluids were measured at 60  °C and 6000 r/min with a (0.1 mol/L) was used to adjust the pH of the nanof lu- TX-500C spinning drop interfacial tensiometer (Bowing ids. The nanof luids were stirred with a magnetic stir- Industry Corporation). The contact angles were measured rer for 0.5 h and then put in an ultrasonicator for 2 h with a JC2000D2 contact angle measurement (Zhongchen until the dispersion was clear and transparent. Figure 2 Digital Technic Apparatus Corporation). The dynamic shows the preparation process of active nanof luids. The interface modulus and interfacial tension of active nano- parameters of ultra-low permeability cores are shown fluids were measured with a interfacial rheometer (TEC - in Table 1. LIS Interface Technology Co., Ltd). The scanning electron 1 3 886 Petroleum Science (2021) 18:883–894 NaOH Silica nanoparticle BSSB-12 Fig. 2 The preparation process of active nanofluids solution, and 0.1 wt% active nanofluids, respectively. The Table 1 The parameters of cores imbibition devices were placed in a constant-temperature Number Length, mm Diameter, mm Porosity, % Perme- bath at 60 °C, and the volume of oil separated from cores ability, was recorded at regular intervals. mD 1 33.24 25.16 14.55 0.25 2 32.51 25.15 13.32 0.26 2.4 The broken‑up behavior of oil droplets 3 33.22 25.07 14.42 0.23 A microfluidic device with 3-D pore throat structure was used to simulate the pore throats in the formation, and the diagram of the microfluidic device is shown in Fig.  3. 2.3 Spontaneous imbibition tests 0.1 wt% BSSB-12 solution and 0.1 wt% active silica nanofluids were used as continuous phase and n -hexane The cores with a diameter of 2.5 cm were cut into columns was as dispersed phase. At first, the microfluidic device with a length of 3 cm. After dried in a vacuum oven at was placed under an inverted microscope (Leica DMi8 110 °C for 24 h, the cores were taken out and weighted C). Then, the continuous phase was injected at a flow rate after cooling to room temperature. Then, these cores and of 0.1 mL/min, and the dispersed phase was injected at a the simulated oil were simultaneously evacuated for 12 h. flow rate of 0.005 mL/min. The structure of “cross” con- The experimental procedures for core saturation and vergence is used to generate oil droplets. The broken-up imbibition tests were the same as the previous study (Dai behavior of oil droplets was recorded with a Photron Fast- et al. 2017). After aging at 90 °C for 48 h, the weight of cam SA-Z high-speed camera. Finally, the average size of cores saturated with simulated oil was recorded. The cores oil droplets in the process of broken-up was calculated. were immersed in 3 wt% NaCl solution, 0.1 wt% BSSB-12 Continuous phase Dispersed phase Fig. 3 Schematic diagram of the microfluidic device 1 3 Petroleum Science (2021) 18:883–894 887 the simulated oil and active nanofluids of different silica nanoparticle and BSSB-12 concentrations were measured. The results are shown in Fig. 6a. When the concentration of active nanoparticles was 0.1 wt%, the interfacial tensions between the simulated oil and active nanofluids decreased with the increase in the concentration of BSSB-12. When the concentration of BSSB-12 was 0.1 wt%, the interfacial tensions rarely changed with the increase in the concentra- tion of silica nanoparticles. The minimum interfacial tension was 6.7 mN/m in the case of 0.1 wt% silica nanoparticles and 0.1 wt% BSSB-12. Based on the influence of differ - ent concentrations of silica nanoparticles and BSSB-12 on the oil–water interfacial tensions, it can be concluded that nanofluids can reduce interfacial tensions mainly through Fig. 4 TEM image of active nanofluids surfactant BSSB-12, and silica nanoparticles cannot greatly reduce the interfacial tension between the simulated oil and nanofluids. The effect of active nanofluids on reducing interfacial tension can be explained by Fig. 6b. When the concentra- tion of BSSB-12 is low, pure silica nanoparticles and silica nanoparticles coated with BSSB-12 coexist in active nano- fluids. There exists a competitive adsorption of BSSB-12 between the surface of nanoparticles and the oil/water inter- face, which makes less BSSB-12 adsorption on the oil/water interface. Thus, the effect of reducing interfacial tension is poor. When the concentration of BSSB-12 is high, there are sufficient silica nanoparticles coated with BSSB-12. The adsorption amount on the surface of an oil droplet is enough to reduce the interfacial tension greatly. Therefore, the active nanofluids with a high concentration of BSSB-12 10 100 1000 have a stronger ability to reduce the interfacial tension than Particle size, nm the nanofluids with a low concentration of BSSB-12. Fig. 5 The particle size distribution of active nanofluids 3.3 Wettability alteration 3 Results and discussion To investigate the effect of silica nanoparticles and BSSB- 12 on solid–liquid interface, the equilibrium contact angles 3.1 Characterization of active nanofluids between the simulated oil and active nanofluids were meas- ured. The paraffin-coated oil-wet glass slices were aging in The TEM image of active nanoparticles is shown in Fig. 4. active nanofluids, and the final stable oil/water/solid three- The active nanoparticles were approximately spherical. phase contact angles were recorded as the equilibrium con- The particle size of the modified silica nanoparticles was tact angles. The equilibrium contact angles of silica nano- about 30 nm. As shown in Fig. 5, the particle size distribu- particles and BSSB-12 with different concentrations are tion of active nanofluids was 10–110 nm and the average shown in Fig. 7a. When the concentration of active nanopar- hydraulic radius was 58.59 nm. The zeta potential of active ticles was 0.1 wt%, the equilibrium contact angles increased nanofluids was − 48.39 mV, indicating the excellent stabil- with the increase in the concentration of BSSB-12 and the ity. Active nanoparticles are not easy to aggregate and can variation in wettability was 47°. When the concentration be stable for a long time. of BSSB-12 was 0.1 wt%, the equilibrium contact angles increased with the increase in the concentration of active 3.2 Oil–water interfacial tension nanoparticles and the variation in wettability was 75°. The pure active nanoparticles or BSSB-12 cannot achieve much To investigate the effect of silica nanoparticles and BSSB- stronger ability to alter wettability than 0.1 wt% active nano- 12 on interfacial tensions, the interfacial tensions between fluids. The ability to alter wettability was achieved by the 1 3 Transmittance, % 888 Petroleum Science (2021) 18:883–894 synergistic action of active nanoparticles and BSSB-12, in surface of oil droplets. It was difficult for active nanopar - which the active nanoparticles played a stronger role than ticles to approach the oil/water/solid three-phase contact- BSSB-12 at this point. ing area, and the alteration of wettability mainly depended The effect of active nanofluids on altering wettability can on the action of BSSB-12. This resulted in the poor effect be revealed by Fig. 7b. When the concentration of active of altering wettability. The wettability alteration caused by nanoparticles was low and the BSSB-12 concentration was high concentration of active nanoparticles is consistent with high, BSSB-12 formed a double-layer adsorption on the the mechanism of structural disjoining pressure proposed by (a) BSSB-12 Active silica nanoparticles 0 0.02 0.04 0.06 0.08 0.10 Concentration, % (b) Water Water Oil Oil Low concentration of BSSB-12 Water Water Oil Oil High concentration of BSSB-12 Fig. 6 The interfacial tension of different concentrations of active silica nanoparticles (the concentration of BSSB-12 was 0.1 wt%) and BSSB- 12 (the concentration of silica nanoparticles was 0.1 wt%) (a) and adsorption diagram of active nanofluids on simulated oil and water phases (b) 1 3 Interfacial tension, mN/m Petroleum Science (2021) 18:883–894 889 Wasan and Nikolov (2003), Wasan et al. (2011), Kondiparty solution, 0.1 wt% active nanofluids, and simulated oil were et al. (2012), and Liu et al. (2012). When sufficient nanopar - studied. The dynamic contact angles of three solutions ticles were present, the Brownian motion of nanoparticles are shown in Fig.  10. In the initial state, all the contact caused the structural disjoining pressure in the oil/water/ angles in the three solutions were less than 90° due to the solid three-phase contact area and the wettability was altered oil-wet treatment of the surface of glass slices. The con- to strongly water-wet. Hence, the active silica nanoparticles tact angles were invariably less than 90° in 3 wt% NaCl have a stronger ability to alter wettability than BSSB-12. solution and 0.1 wt% BSSB-12 solution, reflecting poor ability to alter wettability. The change of contact angles in 3.4 Spontaneous imbibition active nanofluids was significantly faster than that in the pure surfactant solution and brine. In active nanofluids, the The oil dischargement effect of 3  wt% NaCl solution, contact angle reached the equilibrium state after 10 h, and 0.1 wt% BSSB-12 solution and 0.1 wt% active nanofluids the final contact angle was 145°. The nanofluids altered was investigated by static spontaneous imbibition tests. The the wettability of the glass slice surface from oil-wet to oil recovery versus time during spontaneous imbibition is water-wet. The combination of the surfactant BSSB-12 shown in Fig. 8. In the initial 3 days, the oil recovery of three and silica nanoparticles significantly improved the ability liquids increased rapidly with time and the active nanofluids of detaching oil droplets from the solid surface. performed the highest oil dischargement effect among the three liquids. After 4 days, the oil recovery of the active 3.5.2 Oil transportation through pore throats nanofluids increased continuously, while that of 3 wt% NaCl solution and BSSB-12 solution did not change much. The The dynamic interfacial moduli between the simulated oil final oil recovery of the active nanofluids was 26.5%; the and different fluids are shown in Fig.  11a. The interfacial oil recovery of BSSB-12 solution and 3 wt% NaCl solution moduli between the simulated oil and active nanofluids was 17% and 6%, respectively. According to the evaluation increased with time, and the stable moduli were 6 mN/m experiment of oil dischargement during spontaneous imbibi- after 2500 s. The interfacial moduli of brine and the BSSB- tion, the oil recovery of active nanofluids is higher than that 12 solution were unchanged with time, and the values of of pure surfactant solution and brine, which can be ascribed interfacial moduli were 1.2 mN/m and 0.6 mN/m, respec- to the synergistic effect of active silica nanoparticles and tively. Compared with brine and the pure surfactant solution, BSSB-12. the interfacial moduli between active silica nanofluids and the simulated oil clearly increased. The results showed that 3.5 T he mechanism of active nanofluids a stronger interfacial film was formed due to the adsorption during spontaneous imbibition of active silica nanoparticles and BSSB-12 at the oil–water interface. Meanwhile, the interfacial tensions decreased with 3.5.1 Oil detachment from solid surface time (Fig. 11b). The interfacial tension between the simu- lated oil and the active nanofluids decreased from 7 mN/m The surface morphologies of ultra-low permeability core to 3.5 mN/m. The active nanofluids can reduce the inter - surface before and after adsorption of 0.1 wt% active nano- facial tensions due to the strong adsorption of active silica u fl ids were observed with an S-4800 e fi ld emission scanning nanoparticles at the oil–water interface to transport the oil electron microscope (Hitachi, Ltd.), as shown in Fig. 9. As droplets. Figure 12 shows the average size of broken-up oil shown in Fig. 9a, the cross section of the ultra-low perme- droplets in the BSSB-12 solution and active silica nanoflu- ability core was rough at 20,000 times magnification. Fig- ids. The average size of oil droplets decreased with time, ure 9b shows the cross section after the adsorption of active and the oil droplets were broken up completely after 2 s. The nanofluids at the same time magnification. The nanoparticle size of broken-up oil droplets in the BSSB-12 solution was adsorption layer has been formed on the cross section after larger than that in active silica nanofluids. The average size soaked by nanofluids. The nanoparticles were nearly spheri- of broken-up oil droplets in active silica nanofluids after 2 cal, and their particle sizes were about 50 nm, in agreement s was 17.96 μm, and it was easier to transport oil droplets well with the TEM results. The SEM results showed that with the help of active silica nanoparticles. active nanofluids could enter the pore throats of the ultra- The transportation of oil in core pores and throats is cos low permeability core and formed effective adsorption in the mainly affected by capillary force P = 2 and addi- pores, which provided the potential condition for nanofluids ∕ ∕ tional resistance of Jamin effect P = 2(1 R − 1 R ) . 1 2 altering the surface property of pores. For oil-wet rocks, the capillary force is the resistance for To further investigate oil detachment effect of active EOR during spontaneous imbibition and the reduction in nanofluids from the solid surface, the dynamic contact the interfacial tension will reduce the resistance to angles between 3 wt% NaCl solution, 0.1 wt% BSSB-12 1 3 890 Petroleum Science (2021) 18:883–894 (a) BSSB-12 Active silica nanoparticles 0 0.02 0.04 0.06 0.08 0.10 Concentration, % (b) Water Water Solid Solid Low concentration of active silica nanoparticles Water Water Solid Solid High concentration of active silica nanoparticles Fig. 7 The equilibrium contact angles of different concentrations of active silica nanoparticles (the concentration of BSSB-12 was 0.1 wt%) and BSSB-12 (the concentration of silica nanoparticles was 0.1 wt%) (a) and adsorption diagram of active nanofluids on the oil/water/solid three- phase contacting area (b) transporting oil droplets in core pores. At the same time, make the size of oil droplets smaller because the oil drop- when the oil droplets pass through the pore throats, a lets are emulsified and broken-up, so the oil droplets are resistance effect will be produced due to the deformation more likely to pass through the pore throats. Consequently, of oil droplets—Jamin effect. The reduction in oil–water the oil droplets can pass through the small pore holes and interfacial tension resulted in a decrease in resistance throats with less resistance. caused by the Jamin effect. The active silica nanofluids 1 3 Contact angle, degree Petroleum Science (2021) 18:883–894 891 3 wt% NaCl solution 3 wt % NaCl solution 0.1 wt% BSSB-12 solution 0.1 wt % BSSB-12 solution 0.1 wt% active silica nanofluids 0.1 wt % active nanofluids 02468 10 12 14 0246 8101214 Time, h Time, d Fig. 10 The dynamic contact angles in 3 wt% NaCl solution, 0.1 wt% Fig. 8 The oil recovery of 3  wt% NaCl solution, 0.1  wt% BSSB-12 BSSB-12 solution, 0.1 wt% active nanofluids solution, and 0.1 wt% active nanofluids shown in Fig.  13. The BSSB-12 solution has less effect There are numerous studies showing that when the pore on changing wettability, so the oil recovery during spon- wall is hydrophilic, it is favorable for spontaneous imbi- taneous imbibition is worse than the active nanofluids. bition. According to the experimental results of contact The active nanofluids can change the wettability to water- angles, the active nanofluids can change the wettability of wet due to the structural disjoining pressure between the solid surface from oil-wet to water-wet, thus changing the simulated oil and the pore wall generated by active silica capillary force from resistance to motivation and enhanc- nanoparticles. The oil displacement efficiency of ultra-low ing oil recovery. In the process of detaching an oil drop, permeability cores is obviously improved by the synergis- the adhesion work (W = (1 + cos )) decreased through tic effect of active silica nanoparticles and BSSB-12. reducing the interfacial tension and altering the wettabil- ity. The mechanism figure of spontaneous imbibition is Fig. 9 The SEM images of core samples before (a) and after (b) adsorption of 0.1 wt% active nanofluids 1 3 Oil recovery, % Contact angle, degree 892 Petroleum Science (2021) 18:883–894 8 30 (a) (b) 3 wt% NaCl solution 3 wt% NaCl solution 0.1 wt% BSSB-12 solution 0.1 wt% BSSB-12 solution 0.1 wt% active silica nanofluids 0.1 wt% active silica nanofluids 4 15 0 0 0 500 1000 1500 2000 2500 3000 3500 4000 0 500 1000 1500 2000 2500 3000 3500 4000 Time, s Time, s Fig. 11 The dynamic interfacial moduli (a) and interfacial tensions (b) of 3  wt% NaCl solution, 0.1  wt% BSSB-12 solution, 0.1  wt% active nanofluids 0.1 wt% BSSB-12 solution 0.1 wt% active silica nanofluids 4 Conclusions 0 s 1. The active nanofluids have good dispersion stability and 0.5 s excellent oil dischargement effect after surfactant BSSB- 1.0 s 12 adsorbed onto the surface of active silica nanoparti- 1.5 s 2.0 s cles. 2. BSSB-12 and active nanoparticles had their respective advantages in regulating liquid–liquid interface and solid–liquid interface to reduce interfacial tension and alter wettability. 3. When applied to EOR, the spontaneous imbibition 0 0.5 1.0 1.5 2.0 recovery of active nanofluids could reach 26.5%. Time, s 4. The mechanism for EOR was presented by the process of Fig. 12 The average size of broken-up oil droplets in the BSSB-12 detaching oil droplets with the help of active nanofluids. solution and active silica nanofluids Silica nanoparticle BSSB-12 solution BSSB-12 Active nanofluids Fig. 13 The mechanism image of spontaneous imbibition 1 3 Average size of oil droplets, μm Interfacial module, mN/m Interfacial tension, mN/m Petroleum Science (2021) 18:883–894 893 Acknowledgements This work was financially supported by National Water Resour. 2017;107:405–20. https: //doi.org/10.1016/j.advwa Natural Science Foundation of China (52074333, 51874337); Taishan tres.2017.04.012. 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Journal

Petroleum Science – Springer Journals

Published: Jan 4, 2021

Keywords: Active nanofluids; Regulate interface; Ultra-low permeability; Spontaneous imbibition

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