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ABSTRACT
By adjusting the composition of injection water, including ionic type and strength, the goal of enhance oil recovery rate can be achieved. However, there is no clear understanding of which factor, ionic type or strength, has a greater impact. In this paper, based on the formation water of the offshore G oilfield, various brines with different ionic strengths and types were prepared. By measuring the zeta potential of rock powder and oil droplets, three-phase contact angle, interfacial tension between oil and water, emulsification properties of brines, and film strength of oil-water interface, the variation rules of the core wettability and emulsification performance of brine were systematically analyzed when the ionic strength and ionic type were changed. The experimental results showed that ionic strength has a greater impact than that of ionic type. For the oil-water-solid (rock) system of the G oilfield, an ionic strength of 82 mM/kg is the threshold for low salinity effect. Reducing ionic strength resulted in an increase in the hydrophilicity of rock and the ability of water flooding to emulsify oil droplets, which contribute to the improvement of oil displacement efficiency. Theoretically, water flooding to enhance oil recovery can be achieved by only reducing the ionic strength. This understanding was verified by dual polarization interferometry (DPI) experiments and low-field nuclear magnetic resonance experiments, which showed that reducing the salinity of the injection water from 42,000 mg/L (ionic strength of 820 mM/kg) to 4200 mg/L (ionic strength of 82 mM/kg) enhanced the oil recovery by 7.9%.
Abbreviations list
| DPI | = | Dual polarization interferometry; |
| EOR | = | Enhanced oil recovery; |
| LSWF | = | Low salinity water flooding; |
| NMR | = | Nuclear magnetic resonance; |
| W | = | Adhesion work; |
| σ | = | Interfacial tension |
Disclosure statement
No potential conflict of interest was reported by the author(s).
Author contributions
Investigation, writing-original draft preparation, B.C., N.Z., C.W.; Conceptualization, funding acquisition, supervision, L.Z., F.Y.; Writing-review and editing, X.W.; Data analyzing, Y.S., X.W., G.L., X.L. All authors have read and agreed to the published version of the manuscript.
Data availability statement
The data presented in this study are available on request from the corresponding author.
Additional information
Funding
Notes on contributors
Bin Chen
Dr. Bin Chen mainly engages in the R&D and production of oilfield chemicals, leading and participating in over 30 national-level projects and key enterprise projects.
Lin Zhao
Lin Zhao primarily focuses on the research and application of oilfield chemistry and polymer composites, having led or participated in more than 30 national key projects, provincial and ministerial key projects, and horizontal collaboration projects with oilfield enterprises and institutions.
Ning Zhang
Dr. Ning Zhang is mainly involved in the implementation of water injection in offshore oilfields, having led or participated in 12 national key projects and key enterprise projects.
Chengsheng Wang
Dr. Chengsheng Wang, Chief Engineer, primarily works on enhancing oil recovery technologies and their application in offshore oilfields, having led or participated in 20 national key projects and key enterprise projects.
Xiujun Wang
Dr. Xiujun Wang, Director, mainly focuses on the design and application of oilfield chemicals, having led or participated in 15 national and key enterprise projects.
Yanhui Su
Dr. Yanhui Su, primarily engages in the research and application of water injection technology in offshore oilfields, having led or participated in 10 national key projects and key enterprise projects.
Xiaoyan Wu
Dr. Xiaoyan Wu, Senior Engineer, mainly works on enhancing oil recovery technologies and their application in offshore oilfields, having led or participated in 10 national key projects and key enterprise projects.
Guanjun Liu
Dr. Guanjun Liu, Senior Engineer, is mainly involved in enhancing oil recovery technologies and their application in offshore oilfields, having led or participated in 3 national key projects and key enterprise projects.
Fei Yi
Dr. Fei Yi primarily focuses on enhancing oil recovery technologies and their application in offshore oilfields, having led or participated in more than 30 national key projects and key enterprise projects.