Experimental study on CO 2 flooding characteristics in low-permeability fractured reservoirs

ABSTRACTCO2 flooding in oil reservoir is a complex process, which includes fluid flow in fractured sandstone and interaction of CO2 and displaced oil. In order to thoroughly understand the CO2 flooding characteristics in low-permeability fractured reservoirs, a series of CO2 flooding experiments were conducted based on the multi-field coupling experimental system. Considering the difference of the fractured cores, pore cores and pore-fracture model, the effect of fracture, injection pressure, CO2 phase, and heterogeneity of horizontal composite on the CO2 flooding were analyzed. The results show that the oil recovery of fractured core was 46.96%, 7.13% higher than that of pore core, and there was no relatively stable gas-oil ratio (GOR) stage. For the pore-fracture model, the final recovery of two models increased from 49.45% to 45.86% at 2 MPa to 78.83% and 77.35% at 8 MPa, and the pore core was the main contributor to enhance oil recovery. The supercritical CO2 (sc-CO2) enhanced the oil recovery in post-gas breakthrough state, which accounted for final recovery 65.02%. Compared with the vertical layered heterogeneity, the horizontal composite heterogeneity had less influence on the final oil recovery, with differences of below 2%, and the highest CO2 utilization rate was occurred at the permeability model of Low-High-Low. The work provides insight on oil recovery improvement of CO2 flooding in low-permeability fractured reservoirs.KEYWORDS: Low-permeability fractured sandstoneCO2 floodingpore-fracture modeloil recoverygas-oil ratio AcknowledgementsThe authors want to acknowledge the great help of the State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mines, Huainan, Anhui, China.Disclosure statementNo potential conflict of interest was reported by the authors.Author contributionTong Zhang: Conceptualization, writing – review and editing, funding acquisition, supervision. Guoliang Zhou: Conceptualization, formal analysis, investigation, writing – original draft. Ming Tang: writing – original draft. Jun Wu: writing – review and editing. Xin Yang: writing – review and editing Ming Zhu: writing – reviewing. Zhizheng Xie: validation. The manuscript was written through the contributions of all authors. All authors have read and agreed to the published version of the manuscript.Additional informationFundingThis work was supported by Excellent Youth Project of Anhui Province (2022AH030086), China; Natural Science Research Project of University in Anhui (KJ2021ZD0050), China; National Key Research and Development Plan Project (2022XBZD-09); Institute of Energy, Hefei Comprehensive National Science Center (Grant No.21KZS216), China; Collaborative Innovation Project of Colleges and Universities of Anhui Province (Grant No. GXXT-2021- 019), China; the National Youth Science Foundation (Grant no. 51904011), China; the Open Fund of State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mines (Grant No. SKLMRDPC19ZZ05), China; Open Fund of National Local Joint Engineering Research Center for Safe and Accurate Coal Mining (EC2021002).Notes on contributorsTong ZhangTong Zhang, male, born in 1990, Associate professor, mainly engaged in the coal and co-associated resource exploitation.Guoliang ZhouGuoliang Zhou, male, born in 1999, Master candidate, mainly engaged in the CO2 enhanced oil recovery technology.Ming TangMing Tang, male, born in 1997, PhD candidate, mainly engaged in the CO2 enhanced oil recovery and carbon capture and storage.Jun WuJun Wu, male, born in 1999, Master candidate, mainly engaged in the prevention and control of coal mine water disasters.Xin YangXin Yang, male, born in 1997, PhD candidate, mainly engaged in uranium mining extractionMing ZhuMing Zhu, female, born in 1999, Master candidate, mainly engaged in the CO2 enhanced oil recovery technology.Zhizheng XieZhizheng Xie, male, born in 1999, Master candidate, mainly engaged in the hydraulic fracturing technology.