CO2 assisted steam flooding in late steam flooding in heavy oil reservoirs

To improve the oil recovery and economic efficiency in heavy oil reservoirs in late steam flooding, taking J6 Block of Xinjiang Oilfield as the research object, 3D physical modeling experiments of steam flooding, CO2-foam assisted steam flooding, and CO2 assisted steam flooding under different perforation conditions are conducted, and CO2-assisted steam flooding was proposed for reservoirs in the late stage of steam flooding. The experimental results show that after adjusting the perforation in late steam flooding, the CO2 assisted steam flooding formed a lateral expansion of the steam chamber in the middle and lower parts of the injection well and a development model for the production of overriding gravity oil drainage in the top chamber of the well; high temperature water, oil, and CO2 formed stable low-viscosity quasi-single-phase emulsified fluid; and CO2 acted as a thermal insulation in the steam chamber at the top, reducing the steam partial pressure inside the steam chamber, and effectively improving the heat efficiency of injected steam. Based on the three-dimensional experiments and the current situation of the J6 block in Xinjiang Oilfield, the CO2 assisted steam flooding for the J6 block was designed. The application showed that the CO2 assisted steam flooding made the oil vapor ratio increase from 0.12 to 0.16 by 34.0%, the oil recovery increase from 16.1% to 21.5%, and the final oil recovery goes up to 66.5% compared to pure steam flooding after perforation adjustment. © 2019, The Editorial Board of Petroleum Exploration and Development. All right reserved.