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China Surfactant Detergent & Cosmetics ›› 2023, Vol. 53 ›› Issue (6): 617-624.doi: 10.3969/j.issn.2097-2806.2023.06.002

• Basic research • Previous Articles     Next Articles

Effect of CO2 on physical properties of produced oil and water in Changqing and emulsion stabilization mechanism

Wang Huazheng1,2,Zhang Liang1,2,*(),Kang Xin3,Kang Wanli1,2,Li Zhe1,2,Yang Hongbin1,2   

  1. 1. Key Laboratory of Unconventional Oil & Gas Development (China University of Petroleum (East China)), Ministry of Education, Qingdao, Shandong 266580, China
    2. School of Petroleum Engineering in China University of Petroleum (East China), Qingdao, Shandong 266580, China
    3. Chengdu Branch of Daqing Oilfield Exploration and Development Research Institute, Chengdu, Sichuan 610000, China
  • Received:2022-09-27 Revised:2023-05-29 Online:2023-06-22 Published:2023-06-25
  • Contact: *E-mail: zhangliangkb@163.com.

Abstract:

Carbon dioxide (CO2) flooding has become an important means to improve the recovery efficiency of low-permeability oil fields, with the advantages including wide range of application, low production cost and high oil-washing efficiency. However, due to the special physical and chemical properties of CO2, the stability of corresponding produced liquid is significantly enhanced compared with that of conventional water flooding, which brings many difficulties to the treatment of produced liquid. By means of optical microscope, dynamic light scattering, rheology and other methods, the effects of CO2 treatment on the physical properties of Changqing crude oil and produced water under different pressures and the stability of the water-in-oil (W/O) emulsion were studied, and the factors affecting the emulsification and stability of the produced liquid from CO2 flooding were studied. The results showed that, with the increase of CO2 pressure, the mass concentrations of Ca2+and Mg2+ ions in produced water for CO2 flooding were decreased, while the overall content of CO32- and HCO3- ions was increased, and the pH value of the water phase was slightly decreased, changing from weak alkalinity to weak acidity. CO2 treatment led to the decrease of light components and the increase of heavy components (such as resins and asphaltenes) in crude oil, and the enhancement of crude oil polarity. The abnormal temperature and wax precipitation point of the crude oil after CO2 treatment were both increased, and the viscosity of the crude oil was increased. After CO2 treatment, the droplet size of W/O emulsion became smaller, and its homogeneity was enhanced. The particle size changed from 2.14 μm to 0.61 μm. As the viscosity of the emulsion was increased and the resins, asphaltenes and the particles in water adsorbed on the oil-water interface to form a film, the strength of the interfacial film was improved and the stability of the emulsion was thus enhanced. The clarification of emulsion stabilization mechanism could provide theoretical guidance and technical support for treatment process to the produced liquid from CO2 flooding.

Key words: CO2 flooding, emulsion, stability, physical properties of crude oil, rheology

CLC Number: 

  • O648.23