Microcosmic oil displacement mechanism of CO2/water alternation in ultra-low permeability reservoirs
Low-permeability fault reservoirs in northern Jiangsu Basin are characterized by small,fragmented,deep,thin,and low-permeability formations,posing challenges in selecting efficient methods to enhance oil recovery after short-term elastic development.The Water Alternating Gas(WAG)method,with its ability to suppress water and gas channeling,has been successfully applied in low-permeability reservoirs by combining the advantages of water and CO2 flooding,but its microscale oil displacement mechanism and practical effects still need further research and evaluation.In this study,taking the ZD oilfield in northern Jianngsu Basin as the research object,a pore-scale microscopic numerical simulation method based on the three-dimensional numerical model of ultra-low permeability natural core was used to investigate the dynamic evolution of gas-water interfaces during CO2/water alternating flooding and to elucidate the microscopic mechanism of improved oil recovery in low-permeability reservoirs with WAG.The results showed that the WAG method resulted in larger swept areas and less residual oil volume.CO2 flooding exhibited better flowability and ability to overcome viscosity effects,while water flooding demonstrated enhanced oil displacement efficiency through imbibition and plugging.Therefore,WAG can effectively stimulate low-permeability reservoirs and synergistically enhance oil recovery by improving reservoir sweep and displacement efficiency.The findings of this study have important theoretical significance and practical field value for guiding the selection and implementation of oil recovery techniques in low-permeability reservoirs.
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