A salt-induced tackifying polymer for enhancing oil recovery in high salinity reservoirs: Synthesis, evaluation, and mechanism

Abstract

Polymer flooding is an effective method widely applied for enhancing oil recovery (EOR) by reducing the mobility ratio between the injected water and crude oil. However, traditional polymers encounter challenges in high salinity reservoirs due to their salt sensitivity. To overcome this challenge, we synthesized a zwitterion polymer (PAMNS) with salt-induced tackifying property through copolymerization of acrylamide and a zwitterion monomer, methylacrylamide propyl-N, N-dimethylbutylsulfonate (NS). NS monomer is obtained from the reaction between 1,4-butanesultone and dimethylamino propyl methylacrylamide. In this study, the rheological properties, salt responsiveness, and EOR efficiency of PAMNS were evaluated. Results demonstrate that PAMNS exhibits desirable salt-induced tackifying characteristics, with viscosity increasing up to 2.4 times as the NaCl concentration reaches a salinity of 30 x 104 mg L"'. Furthermore, high valence ions possess a much stronger effect on enhancing viscosity, manifested as Mg" > Са?! > Na". Molecular dynamics simulations (MD) and fluid dynamics experiment results demonstrate that PAMNS molecules exhibit a more stretched state and enhanced intermolecular associations in high-salinity environments. It is because of the salt-induced tackifying, PAMNS demonstrates superior performance in polymer flooding experiments under salinity ranges from 5 x 10 mg L! to 20 x 10 mgL |, leading to 10.38-19.83% higher EOR than traditional polymers. © 2023 Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-ne-nd/4.0/).

Headnote

Abstract

Polymer flooding is an effective method widely applied for enhancing oil recovery (EOR) by reducing the mobility ratio between the injected water and crude oil. However, traditional polymers encounter challenges in high salinity reservoirs due to their salt sensitivity. To overcome this challenge, we synthesized a zwitterion polymer (PAMNS) with salt-induced tackifying property through copolymerization of acrylamide and a zwitterion monomer, methylacrylamide propyl-N, N-dimethylbutylsulfonate (NS). NS monomer is obtained from the reaction between 1,4-butanesultone and dimethylamino propyl methylacrylamide. In this study, the rheological properties, salt responsiveness, and EOR efficiency of PAMNS were evaluated. Results demonstrate that PAMNS exhibits desirable salt-induced tackifying characteristics, with viscosity increasing up to 2.4 times as the NaCl concentration reaches a salinity of 30 x 104 mg L"'. Furthermore, high valence ions possess a much stronger effect on enhancing viscosity, manifested as Mg" > Са?! > Na". Molecular dynamics simulations (MD) and fluid dynamics experiment results demonstrate that PAMNS molecules exhibit a more stretched state and enhanced intermolecular associations in high-salinity environments. It is because of the salt-induced tackifying, PAMNS demonstrates superior performance in polymer flooding experiments under salinity ranges from 5 x 10 mg L! to 20 x 10 mgL |, leading to 10.38-19.83% higher EOR than traditional polymers. © 2023 Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-ne-nd/4.0/).

Keywords: High salinity reservoirs; Salt-induced tackifying polymer; Anti-polyelectrolyte behavior; Enhanced oil recovery

1. Introduction

Polymer flooding is a significant method for enhanced oil recovery (EOR), addressing challenges related to unfavorable mobility ratios and reservoir heterogeneities [1-4]. Laboratory experimental data and oil field application proved that the viscoelastic properties of polymers facilitate the extraction of residual oil from rock pores [5-8]. Partially hydrolyzed polyacrylamide (HPAM) is currently the most widely used. Although encouraging results have been obtained from field applications, HPAM exhibits evident salt sensitivity [9,10], leading to a sharp decrease in viscosity under high salinity concentrations. Notably, in oil reservoirs containing highvalent cations like Ca"? and Mg··, precipitation of ultra-high molecular weight polymer may occur [11-13]. Therefore, the high salinity reservoirs such as Tsiengui Oilfield (50 °C, 1010-3760 md, salinity of 28.6 x 10 mg L7'), Obangue Oilfield (51 °C, 500-1500 md, salinity of 20 x 10· mg L™"), and others (shown in Table $1) bring huge challenges to polymer flooding, especially in some reservoirs with salinities even over 20 x 10 mg L' [14-18]. Consequently, traditional HPAM fails to meet the requirements of high-salinity reservoir development, necessitating the exploration of alternative polymers.

Current research primarily focuses on the development of salt-tolerant polymers through salt-resistant functional group modification or viscosity compensation such as increasing molecular weight and using hydrophobic association [19,20]. These polymers have shown improved viscosity retention rates in high-salinity reservoirs [20]. Among them, the ultra-high molecular weight polymers increase initial viscosity [10], but do not intrinsically solve the problem of salt sensitivity, the viscosity still drops substantially under high salinity. The modified polymers introduce salt-resistant groups such as sulfonic acid, which possesses a thicker hydration layer than carboxylic acid [21-23], thereby weakening the shielding effect of salt ions on hydrophilic segments and improving viscosity retention in high salinity environments. Hydrophobicassociated polymers improve salt resistance by triggering hydrophobic interactions between interchain components. When salt is added, the polarity of the solvent is enhanced, reducing the damage to the copolymer network structure and thus reducing viscosity loss [24-30]. Current salt-resistant polymers aim to maintain acceptable viscosities during the displacement of high salinity reservoirs but still experience alarming viscosity reduction when encountering high salinity and fail to adequately address the problems in high salinity/ ultra-high salinity reservoirs.

Limited research has been focused on the utilization of salt during polymer flooding. However, recent studies have reported zwitterion monomers and their copolymers. Due to the electrostatic attraction between positive and negative charges between intra- and interchain, the zwitterionic polymers are in a state of incomplete in low salinity conditions. Once encountering high salinity, ions shield electrostatic interaction, resulting in a more stretching conformation of polymer, which shows the presence of anti-polyelectrolyte behavior [31-37]. Zwitterionic polymers can be roughly classified into two categories based on differences in their side chains. The first category is betaine-like monomers that carry both anionic and cationic groups in a branch chain [38-41]. The second category is the polyampholytic electrolyte type, which contains equal cationic and anionic monomers on the polymer chains [42-46]. Both categories mentioned above have approximately equivalent negative and positive charges, resulting in electrical neutrality. In the absence of salt, electrostatic attraction between cation and anion ions within monomers and intra- and interchain interactions can lead to a contracted conformation of polymer structure [47]. However, upon adding salt to the solution, ions penetrate the polymer solution and shield electrostatic interactions between monomers, and intra-/interchain charges, thereby inducing a more stretched configuration [48- 52]. That is to say, the hydrodynamic radius of the polymer chains increases under the existence of salt ions [53,54]. Thus, a conception has been thought that they have the potential to increase viscosity in high salinity environments and the application prospect of improving the recovery of high salinity reservoirs.

Since betaine-like zwitterionic polymers can adjust the performance by adjusting the carbon chain length between anion and cation [55,56], in this paper, we proposed a zwitterionic salt-induced tackifying polymer (PAMNS) by copolymerizing acrylamide and betaine-like type monomer. The salt-response and tackifying mechanism of PAMNS were investigated [57,58]. Rheology properties and EOR efficiency of PAMNS were compared with traditional polymer to verify capability in chemical flooding in high salinity/ultra-high salinity reservoirs. This study aims to shed light on the understanding of the properties of zwitterionic salt-induced tackifying polymers and their potential to enhance oil recovery from high salinity/ultra-high salinity reservoirs.

2. Experimental details

2.1. Synthesis and characterization of NS and PAMNS

To synthesize the salt-induced tackifying polymer (PAMNS), a zwitterionic monomer methacrylamide propyl-N, N-dimethylbutane sulfonate (NS) was synthesized. The synthesis mechanism is illustrated in Fig. 51 (a,b). Specifically, 13.62 в 1,4-Butanesultone (BS) and 17.03 g dimethylamino propyl methacrylamide (DMAPMA) were dissolved in 50 mL acetonitrile and then placed in a freeze dryer for 24 h. During the reaction, BS cleaved the C-O bond and bound to the terminal N in the DMAPMA molecular chain, resulting in the desired zwitterionic monomer containing -N" and -SO;z". The resulting product was a white powder. Next, 6.24 g NS and 13.59 g AM were dissolved in 30 mL deionized water (Fig. 51 (b) and Fig. 1 (a)). The pH value of the solution was adjusted to approximately 7 using standard solutions of NaOH and HCI. The polymerization solution was then purged with nitrogen for 20 min before being transferred to a flask and placed in a thermostatic water bath at 40 °C. Stirring was maintained at a continuous speed of 200-300 г min '. To this mixture, 0.025 в 2,2'-[azobis (1-methylethylidene)]bis [4,5dihydro-1H-imidazole dihydrochloride] (AIBI) was added, representing 0.05% of the total polymerization solution. The entire reaction process took approximately 10 h. After completion of the polymerization, the polymer colloid was then fully purified using excess absolute ethanol for 2-3 cycles until it became milky white and hardened. Finally, the polymerization products were dried in a vacuum oven at 40 °C for 12 h and then ground into powder for further use. The resulting white powder was the salt-induced tackifying polymer (PAMNS). It is essential to store them in a dry environment and avoid moisture.

IR spectra of PAMNS and NS were obtained by the Nicolet-10 infrared spectrometer (ThermoFisher, China) using D,0, or CDCl; as solvents. IR spectroscopy typically uses wavelength (A) or wavenumber (с) as the abscissa to indicate the position of the absorption peak, while transmittance (T%) or absorbance (A) is used as the ordinate to indicate the absorption intensity. The AV400 spectrometer (Bruker, Germany) was used to conduct 'H NMR spectroscopy on PAMNS and NS. Chemical shifts were expressed in ppm (6). The errors in the integration measurements were limited by the accuracy (approximately 5%).

2.2. Rheology and salt-induced experiments

Rheology measurements were conducted using a HAKKE RS600B rheometer to measure the viscosity of polymer solutions at variable shear and temperatures. The relationship between polymer viscosity and concentration was evaluated by measuring the viscosity of different concentrations (0.1 wt% - 0.6 wt%) at 25 °C and a shear rate of 7.34 s '. To further assess the properties of the polymer solutions, an illustration was provided using a concentration of 0.2 wt%. Considering that polymer solutions undergo high-rate shear during injection into the formation through the wellbore, it is important to validate the retention of high viscosity in the target reservoir. Therefore, the shear stability of the polymer solutions was studied at a shear rate of 100 $"! for 3600 в. Besides, the viscoelasticity of PAMNS and PAM solutions in deionized water and 10 x 10 salinity (Table S2) were examined using dynamic oscillatory testing within the linear viscoelastic range, and spanning angular frequency range of 0.1-16 Hz.

Additionally, to investigate the anti-polyelectrolyte effect of zwitterionic polymerization, we conducted molecular dynamic simulations (MD) and fluid dynamics experiments of PAMNS in deionized water and 10 x 10· salinity solvents. Among them, the fluid dynamics experiments used the method of dynamic light scattering (DLS). Furthermore, solutions of PAMNS and PAM were prepared using various concentrations of NaCl (0-30 x 10 mg L™"), CaCl, (0-5000 mg L™"), and MgCl, (0-5000 mg L"') brine. Due to the low calcium and magnesium content commonly found in oil reservoirs, only a concentration of 5000 mg L ' was considered for this experiment. All solutions were allowed to stand in the indoor environment for 24 h after configuration to ensure homogeneity. Subsequently, the viscosity of polymer solutions was measured at 25 °C, 7.34 s' to study the effects of different concentrations of Na", Ca"·, and Mg"? on the viscosity of the polymer solutions.

2.3. Core flooding experiments

The injection pressure of PAMNS and PAM with different salinities (5 x 10% mg Lİ, 10 x 10 mg LA, 15 x 10 mg L™", 20 x 10 mg L™") were measured, to study the sweep efficiency of polymer solutions. The core samples used in the flooding experiments were selected from outcrop cores of Changqing Oilfield, and the rock composition was sandstone. Based on the results depicted in Fig. S4, we have chosen to utilize polymer solution with a concentration of 0.15 wt% for conducting core flooding experiments. The core sample parameters used are shown in Table S3, and the core flooding setup is shown in Fig. S5.

Besides, core flooding experiments were performed to investigate PAMNS flooding performance in different salinity, from 5 x 10 mg L to 20 x 10 mg LA, compared with a traditional polymer (PAM). To simulate the real reservoir characteristics, the cores after saturated oil were placed in a 50 °C oven for 5-7 days. After waterflooding, which resulted in a water cut exceeding 98%, a polymer solution with a volume of 0.5 PV was injected; then, follow-up waterflooding and the final recovery measurements. The parameters of the core samples and flooding processes are shown in Table S4. From these eight experiments, we intended to investigate the pattern of enhanced recovery efficiency of new polymer (PAMNS) and PAM with salinity. The experimental oil is introduced in Supporting Information.

Then the T, spectra of the cores in the initial stage, after water flooding (D>O) after polymer flooding (0.15 wt% PAMNS/PAM solution), and the follow-up waterflooding (D,0) under 25 x 10 mg LÂ salinity at 50 °C were measured, respectively. Besides, nuclear magnetic resonance imaging was also employed to investigate the EOR efficiency of PAMNS and PAM solutions. The parameters of the core samples used were summarized in Table S5. The pore distribution of the cores was obtained through a mercury intrusion experiment, shown in Fig. S6. By the nuclear magnetic resonance (NMR) method, to study the utilization of large/small porous oil driven by different polymer solutions in ultra-high salinity reservoirs. The polymer solution segment was also plugged in at 0.5 PV.

3. Results and discussions

3.1. Structural characterizations

According to the experimental steps depicted in Fig. | (a), we synthesized the zwitterionic monomer (NS) and polymer (PAMNS), and then their structures were characterized by IR spectra (Fig. 1 (b)) and 'H NMR spectroscopy (Fig. 1 (с)). Fig. 1 (b) shows that the -SO; symmetric and asymmetric vibrations absorption peaks at 1034.15 em"! and 1170.88 cm ', respectively; the -C-S vibration peak at 604.94 cm ', confirming that NS was obtained through the polymerization of BS and DMAPMA. Moreover, the absence of a C=C peak in the IR spectra of PAMNS confirms its formation via the polymerization of AM and NS. Additionally, Fig. 1 (с) displays that the peaks at 6 1.96 and ö 3.26 correspond to the two -CH,- peaks resulting from the opening of 1,4-butanesultone (BS) and coincide with dimethylamino propyl methacrylamide (ОМАРМА); the peaks at 6 2.87 and 6 1.84 represent the first and second -CH>- linked to sulfonic acid after the opening of 1,4-butanesultone, respectively; while 6 2.99 is the -CH; linked to the quaternary ammonium cation. Furthermore, in the 'H NMR spectra of PAMNS, the peaks 6 0.99 and 6 1.38 are the -CH; and -CH>- on the polymer skeleton, notably, there is still no C=C peak in the 'H NMR spectra of PAMNS. Overall, the consistent results obtained from Fig. 1 (b,c) indicate that the synthesized compound aligns well with the expected chemical structure of NS and PAMNS, as represented in Fig. 1 (a) and Fig. 51.

3.2. Rheology and salt-induced tackifying properties

As depicted in Fig. 2 (a), PAMNS possesses a superior viscosity enhancement capacity than polymer PAM with higher molecular weight (1000 W), and the critical association concentration (CAC) of PAMNS is approximately 3000 mg L !, while that of PAM is circa 3250 mg L-'. This difference is attributed to the additional intermolecular electrostatic force and hydrophobic force of PAMNS, whereas PAM mainly possesses van der Waals force and hydrogen bonds [44]. Thus, with increasing concentration, PAMNS exhibits a more complex network structure and a faster increase in viscosity. Furthermore, PAMNS demonstrates exceptional anti-shearing performance as shown in Fig. 2 (b). For traditional polymers, their viscosity relies on the entanglement of long-chain molecules, while high shear rates will lead to breakage of the molecular chain and a reduction in polymer viscosity. In contrast, the viscosity of PAMNS strongly depends on the molecular interaction, which is reversible, and can reduce the extent of structural damage under high shear rates. Consequently, the three-dimensional structure of PAMNS can withstand long-term shear without disintegrating easily, resulting in superior anti-shearing performance compared to regular polymers like PAM. Thus, when using PAMNS for chemical flooding, it is capable of maintaining the viscosity in the reservoirs during the treatment.

According to Fig. 2 (c,d), the viscosity and elastic modulus of PAMNS were found to be slightly lower than those of PAM in deionized water environments. Nevertheless, as salinity increased to 10 x 10 mg L™", the viscosity and elastic modulus of PAMNS improved significantly while those of PAM drastically decreased. It is widely recognized that high salinity environments cause the molecular chains of PAM to curl, disrupting the network structure and resulting in a notable reduction in both viscosity and elasticity. However, the molecular dynamic simulations (Fig. 3 (a,b,c)) revealed distinct behaviors of PAMNS compared to PAM. The simulations depicted in Fig. 3 (d,e) demonstrated that in 10 x 10 mg L™" brine, the distances between -N· and -SO47 increased, leading to an expansion in the radius of gyration of PAMNS molecules. Moreover, Fig. 3 (f) indicated a decrease in the solvent-accessible surface area of PAMNS molecules in high-salinity environments, suggesting an enhanced hydrophobicity. Besides, Fig. 3 (g) illustrated the presence of an associative peak for PAMNS, representing larger sizes in 10 x 10 mg L' brine. These observations (Fig. 3 (f,g)) suggest a weakening of intra-chain interactions and an enhancement of inter-chain interactions in PAMNS molecules at high salinity environments. Overall, under high salinity conditions, the molecular chains of PAMNS adopt a stretched state and intertwine with each other, leading to an increase in viscosity and elasticity.

As illustrated by Fig. 4, in contrast to PAM, the PAMNS showed a remarkable salt-induced tackifying property. Specifically, as depicted in Fig. 4 (a), when the NaCl content increased from 0 to 30 x 10· mg L7', the viscosity of the PAMNS solution increased by 2.4 times, while the viscosity retention rate of the PAM solution was only 33%, which resulted in a significant difference in viscosity between the two polymers, reaching up to 84.66 cp. To further investigate the impact of ion types on polymer viscosity, different ions (Nat, Са", Mg"·) were added to the polymer solutions. The results are presented in Fig. 4 (b,c,d). As the concentration of sodium chloride increased from 0 to 5000 mg L™", the viscosity of the PAMNS solution increased by 1.23 times, while the PAM viscosity retention rate is of 39.13%, with a resulting viscosity difference between the two of 35.48 cp. Once calcium chloride was added, the viscosity of the PAMNS solution increased by 1.56 times, the PAM viscosity retention rate was only 20.17%, viscosity difference between the two reached 59.08 cp. Similarly, when magnesium chloride was added, the PAMNS solution increased by 1.61 times, the PAM viscosity retention rate decreased to 19.47%, and the viscosity difference between the two was 61.59 cp. The results suggest that divalent cations have a more substantial impact on the viscosity of polymers compared to monovalent cations, as evidenced by the rapid decrease in PAM viscosity in divalent cation solutions, and the viscosity of PAMNS increases more in divalent cations solutions. This trend can be attributed to the stronger screen effect of high-valence, causing a more stretched state of the molecular chains compared to low-valence salt ions. Consequently, as the valence number of salt ions increases, the PAMNS exhibits stronger salt-induced tackifying performance due to its capability to form networks with other molecules through its extended chains. In addition, it is evident from Fig. 4 (e,f) that different types of salts exert varying degrees of influence on polymer viscosity, with Mg"? > Ca"? > Na".

The underlying mechanism responsible for this saltinduced tackifying property is the anti-polyelectrolyte effect of zwitterion polymer. Specifically, as shown in Fig. 4 (g), due to the carbon chains between the NS section, these branch chains fold up together in deionized water, leading to relatively low viscosity. When salt ions are added, the electrostatic interaction between positive and negative charges on NS is shielded, as a result, the branch chains of the polymer stretch out and hydrophobic associations occur. This phenomenon leads to a rapid increase in the viscosity of the PAMNS solution, which is consistent with the observations in Fig. 2 (c,d) and Fig. 3 (d,e,f,g).

3.3. Core flooding results

The eguilibrium pressure differential between the core inlet and outlet during polymer flooding was used as a preliminary evaluation for sweep efficiency [55,56]. Fig. 5 (a,b,c,d) illustrates the injection pressure variations at the inlet end by PAMNS and PAM under different salinity conditions. Analysis of Fig. 5 (a,b,c,d) indicates that the inlet pressure underwent a rapid initial increase, followed by a gradual stabilization until reaching equilibrium. Across the salinities ranging from 5 x 10· mg L to 20 x 10· mg L' (Table S2) tested, the equilibrium pressure of PAMNS flooding was consistently higher than that of PAM, with the differences between them being 0.06 MPa, 0.144 MPa, 0.24 MPa, and 0.31 MPa respectively. Furthermore, Fig. 5 (e) shows the pressure differences between the inlet and outlet under different salinity. Specifically, the pressure differences measured were 0.679 МРа-0.699 MPa for PAM and 0.739 МРа-0.999 MPa for PAMNS, with increasing salinity. Higher pressure differences occurred in PAMNS flooding but no significant change for PAM. This demonstrates that the synthesized polymer has a superior ability to thicken injection water, which can more effectively control oil-water mobility ratios, leading to better utilization of crude oil and ultimately improving recovery efficiency in high salinity/ultra-high salinity reservoirs.

Table S7 presents the oil recovery results under varying salinity levels, water flooding resulted in oil recoveries ranging from 40.5% to 43.03%, while polymer flooding with PAMNS and PAM resulted in significantly higher oil recoveries ranging from 53.59% to 75.54%. Notably, PAMNS demonstrated consistently higher EORs than PAM, with a maximum EOR difference of 19.83%. The recovery curves in Fig. 6 (a,b,c,d) indicate that at varying salinity levels, the final recovery of injecting 0.5 РУ PAMNS solution was higher by 10.38%, 14.48%, 17.97%, and 19.83% compared to PAM solution for salinities of 5 x 10% mg Lİ, 10 x 10% mg LA, 15 x 10· mg L7', and 20 x 10 mg LA, respectively. The contrast in EOR between PAMNS and PAM grew with increasing salinity. Furthermore, Fig. 6 (e) shows that with increasing salinity levels from 5 x 10% mg L to 20 x 10° mg L7', the EOR of PAMNS flooding alone, the cumulative sum of PAMNS flooding, and follow-up waterflooding all demonstrated an increase. However, the EOR for only PAM flooding, the sum of PAM and follow-up waterflooding remained almost unchanged, which is consistent with the findings in Fig. 5. Overall, PAMNS yielded superior EOR results in high salinity/ultra-high salinity reservoirs due to its improved viscosity and viscoelasticity in such environments, as confirmed by Fig. 2 (c,d) and Fig. 4.

3.4. Enhance recovery mechanism

The pore distribution of the core sample was shown in Fig. S6, revealing that the majority of pores in both samples are distributed within the range of 5-20 um due to their shared batch origin. Subsequently, Fig. 7 (a,b) displays four T, spectra curves representing different stages: before core flooding, after water flooding, after polymer flooding, and after follow-up waterflooding. Each curve represents the oil distribution at the corresponding stage of the cores. Fig. 7 (c,d) illustrates nuclear magnetic resonance (NMR) imaging at two stages: before core flooding (left) and after follow-up waterflooding (right). The yellow color indicates the presence of crude oil, which aligns with the T, results obtained from NMR experiments. The results show that the PAMNS solution exhibits superior utilization of small pores at a salinity of 25 x 10 mg L7'. Based on the aforementioned observations, the synthesized salt-induced tackifying polymer has excellent performance in EOR in high salinity reservoirs (Fig. 2, Fig. S3, Fig. S4, Figs. 4, Fig. 5, and Fig. 6). The EOR mechanism of PAMNS, based on its properties illustrated in Fig. 2 (c,d), Figs. 3 and 4, is depicted in Fig. 7 (e,f). As shown in Fig. 7 (e), the polymer solution prepared by low salinity water is injected into the wellbore. Before encountering the high salinity water in the reservoir, the electrostatic attraction causes the polymer chains to adopt a contracted conformation, leading to low viscosity and easy injection. However, upon encountering the high salinity water, the molecular structure of PAMNS, as depicted in Fig. 7 (1), leads to increased viscosity and elasticity. This in turn, enlarges the sweep area and enhances the ability to mobilize oil within small pores, ultimately improving the fingering phenomenon associated with traditional polymers and resulting in enhanced oil recovery. Consequently, the synthesized salt-induced tackifying polymer holds promising prospects for improving oil recovery in highsalinity/ultra-high-salinity reservoirs.

4. Conclusions

In summary, the zwitterion monomer (NS) can be obtained by dissolving BS and DMAPMA in acetonitrile. Subsequently, the polymerization process at 40 °C using AM, NS, and 0.05% AIBI as an initiator enables the synthesis of the salt-induced tackifying polymer (PAMNS). The synthesized polymer exhibits excellent rheological properties, with its viscoelasticity improving as salinity increases. Through molecular dynamics simulations (MD) and fluid dynamics experiments, it has been observed that in a high salinity environment, the distance between -N· and -$Оу as well as the hydrophobic force of PAMNS both increase resulting in an expansion in the radius of gyration and stronger intermolecular associations. Additionally, the viscosity of PAMNS solution increases by 2.4 times at a NaCl salinity of 30 x 10 mg L™', exhibiting stronger responsiveness to high-valent ions, with the order of manifestation being Mg"? > Са?! > Nat. This study further highlights that PAMNS outperforms traditional polymers, leading to a 10.38-19.83% higher БОК across salinity ranges from 5 x 10· mg LA to 20 x 10· mg LA. Overall, these findings underscore the significant potential of PAMNS as an effective oil displacement agent in high-salinity/ultra-highsalinity reservoirs.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The financial support of the National Natural Science Foundation of China (No. 52120105007), and the National Key Research and Development Program of China (2019Y FA0708700) are gratefully acknowledged.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.gee.2023.10.006.

Sidebar

Received 29 June 2023; revised 2 October 2023; accepted 27 October 2023 Available online 7 November 2023

References

References

[1] Z. Li, D. N Espinoza, T. B Matthew, SPE J. 28 (2023) 289-300.

[2] L. He, Е. Lin, X. Li, H. Sui, Z. Xu, Chem. Soc. Rev. 44 (2015) 54465494.

[3]M. Cheng, J. Jiang, J. Wang, J. Fan, ACS Sustain. Chem. Eng. 7 (2019) 8195-8205.

[4] A. Nabiyan, J.B. Max, EH. Schacher, Chem. Soc. Rev. 51 (2022) 995- 1044.

[5] Е. Liu, W.F. Pu, D.J. Du, J. Ind. Eng. Chem. 46 (2017) 80-90.

[6] Y. Zhang, X. Tong, L. Yu, L. Meng, P. Guo, S. Xue, Green Energy Environ. 4 (2019) 424-431.

[7] S. Rajesh, У. Thiévenaz, A. Sauret, Soft Matter 18 (2022) 3147-3156.

[8] A. Das, С. Chauhan, A. Verma, P. Каша, К. Ojha, J. Petrol. Sci. Eng. 167 (2018) 559-567.

[9] H. Gong, H. Zhang, L. Xu, K. Li, L. Yu, Y. Li, M. Dong, RSC Adv. 7 (2017) 39564-39575.

[10] М. Concilio, V.P. Beyer, С.К. Becer, Polym. Chem. 13 (2022) 64236474.

[11] W.F. Pu, В. Liu, В. Li, EY. Jin, О. Peng, S. Lin, D.J. Du, ES. Yao, RSC Adv. 5 (2015) 88002-88013.

[12] L. Li, X. Li, S. Zhang, H. Yan, X. Qiao, H. He, T. Zhu, B. Tang, Green Energy Environ. 7 (2022) 840-853.

[13] T.S. Muzata, J.P. L, $. Bose, Phys. Chem. Chem. Phys. 22 (2022) 20167- 20188.

[14] D. Kawale, E. Marques, Pacelli L.J. Zitha, T.K. Michiel, R.R. William, E.B. Pouyan, Soft Matter 13 (2017) 765-775.

[15] EM. Mohamed, H. Eirik, A.A. Safwat, A.H. Ibnelwaleed, A.K. Malcolm, Green Chem. 24 (2022) 7171-7183.

[16] К. Durgesh, В. Gelmer, $. Shaurya, L.J. Zitha Pacelli, Т.К. Michiel, R.R. William, E.B. Pouyan, Soft Matter 13 (2017) 8745-8755.

[17] J. Zhang, $. Xu, H. Jin, С. Liu, Chem. Commun. 56 (2020) 1093010933.

[18] Е. Hu, Nelson L.C. Leung, B.Z. Tang, Chem. Soc. Rev. 43 (2014) 4494- 4562.

[19] A. Chu, M. Yang, J. Chen, J. Zhao, J. Fang, Z. Yang, H. Li, Green Energy Environ. 9 (2024) 1698-1710.

[20] Q. Li, J. Chen, L. Fan, X. Kong, Y. Lu, Green Energy Environ. 1 (2016) 18-42.

[21] В. Li, Y. Liu, X. Zhang, P. He, H. Zhou, Green Energy Environ. 4 (2019) 3-19.

[22] C. Hu, J.H. Park, N.Y. Kang, X. Zhang, Y.J. Lee, S.W. Jeong, Y.M. Lee, J. Mater. Chem. A 11 (2023) 2031-2041.

[23] J. Li, H. Zhu, X. Wang, D.R. MacFarlane, M. Armand, M. Forsyth, J. Mater. Chem. A 3 (2015) 19989-19995.

[24] H. Zhang, M. Zhu, W. Zhao, S. Li, G. Feng, Green Energy Environ. 3 (2018) 120-128.

[25] X. Li, LC. Bourg, Atmos. Chem. Phys. 23 (2023) 2525-2556.

[26] F. Candau, S. Biggs, A. Hill, J. Selb. Prog. Org. Coat. 24 (1994) 11-19.

[27] M. Mamusa, P. Tempesti, A. Bartolini, E. Carretti, A.F. Ghobadi, J. Smets, Y.G. Aouad, P. Baglioni, Nanoscale 11 (2019) 6635-6643.

[28] Z. Hu, G. Chen, J. Mater. Chem. A 2 (2014) 13593-13601.

[29] У.Е. Korolovych, A. Erwin, A. Stryutsky, H. Lee, W.T. Heller, V.V. Shevchenko, L.A. Bulavin, V.V. Tsukruk, Macromolecules 51 (2018) 4923-4937.

[30] K.T. Huang, K. Ishihara, C.J. Huang, Biomacromolecules 20 (2019) 3524-3534.

[31] М.7. Li, J.H. Li, X.S. Shao, J. Miao, J.B. Wang, Q.Q. Zhang, Х.Р. Xu, J. Membr. Sci. 405-406 (2012) 141-148.

[32] Y. Chang, Y. Shih, C. Lai, H. Kung, S. Jiang, Adv. Funct. Mater. 23 (2013) 1100-1110.

[33] M. Sun, L. Yang, P. Jose, L. Wang, J. Zweit. J. Mater. Chem. B 1 (2013) 6137-6146.

[34] S. Xiao, У. Zhang, М. Shen, Е. Chen, P. Fan, М. Zhong, В. Ren, J. Yang, J. Zheng, Langmuir 34 (2018) 97-105.

[35] B. Liang, E. Jia, X. Yuan, G. Zhang, Z. Su, Chem. Eng. J. 401 (2020) 126114.

[36] D. Li, Q. Wei, С. Wu, X. Zhang, О. Xue, T. Zheng, М. Cao, Adv. Colloid Interface. 278 (2020) 102141.

[37] R. Iwata, P. Suk-In, V.P. Hoven, A. Takahara, K. Akiyoshi, Y. Iwasaki, Biomacromolecules 5 (2004) 2308-2314.

[38] Y. Liu, J. Wu, H. Liang, Z. Jin, L. Sheng, X. Hu, N. Zhu, K. Guo, Green Energy Environ. 6 (2021) 578-584.

[39] M. Kobayashi, Y. Terayama, M. Kikuchi, A. Takahara, Soft Matter 9 (2013) 5138-5148.

[40] R. Zhang, S. Ma, Q. Wei, Q. Ye, B. Yu, V.D.G. Jasper, F. Zhou, Macromolecules 48 (2015) 6186-6196.

[41] К. Quintana, М. Gosa, D. Jañczewski, E. Kutnyanszky, G.J. Vancso, Langmuir 29 (2013) 10859-10867.

[42] S. Xiao, B. Ren, L. Huang, M. Shen, Y. Zhang, M. Zhong, J. Yang, J. Zheng, Curr. Opin. Chem. Eng. 19 (2018) 86-93.

[43] C.M. Heil, A. Jayaraman. Soft Matter 18 (2022) 8175-8187.

[44] A.B. Asha, Y. Chen, R. Narain, Chem. Soc. Rev. 50 (2021) 11668-11683.

[45] N.N. Nguyen, A.V. Nguyen, L.X. Dang, Fuel 197 (2017) 488-496.

[46] Y. Liu, D. Zhang, B. Ren, X. Gong, L. Xu, Z.Q. Feng, Y. Chang, Y. He, J. Zheng, J. Mater. Chem. B 8 (2020) 3814-3828.

[47] X. Li, LC. Bourg, Environ. Sci. Technol. 57 (2023) 13092-13103.

[48] PS. Liu, С. Qiang, X. Liu, В. Yuan, S.C. Lin, Biomacromolecules 10 (2009) 2809-2816.

[49] G. Li, H. Xue, С. Gao, Е. Zhang, $. Jiang, Macromolecules 43 (2010) 14-16.

[50] G. Poulladofonou, K. Neumann, Polym. Chem. 13 (2022) 4416-4420.

[51] T. Du, B. Li, X. Wang, B. Yu, X. Pei, W.T.S. Huck, F. Zhou, Angew. Chem., Int. Ed. 55 (2016) 4260-4264.

[52] Y.Y. Yuan, C.Q. Mao, X.J. Du, J.Z. Du, Е. Wang, J. Wang. Adv. Mater. 24 (2012) 5476-5480.

[53] J. Zheng, M. Li, Y. Yao, X. Zhang, L. Wang, J. Mater. Chem. A 5 (2017) 13730-13739.

[54] P. Hemstrôm, M. Szumski, К. Irgum, Anal. Chem. 78 (2006) 7098-7103.

[55] M. Kobayashi, Y. Terayama, N. Hosaka, M. Kaido, A. Suzuki, N. Yamada, N. Torikai, K. Ishihara, A. Takahara, Soft Matter 3 (2007) 740-746.

[56] P. Mary, D.D. Bendejacq, M.P. Labeau, P. Dupuis, J. Phys. Chem. B 111 (2007) 7767-7777.

[57] Q. Wang, 7. Meng, J. Li, $. Peng, 7. Xiang, Green Energy Environ. 7 (2022) 948-956.

[58] S. Hou, Y. Sun, X. Jiang, P. Zhang, Green Energy Environ. 5 (2020) 484- 491.