The mutual feedback mechanism between CO2 and multiphase fluids during CO2 injection into shale oil reservoirs

CO₂ injection can effectively promote the development and utilization of shale oil. The interaction between CO₂, shale oil and pore structure has attracted much attention as a key mechanism for oil resource exploitation. Therefore, we established a pore network model, injected shale oil and CO₂ successively into the model, and studied the occurrence state of miscible fluid at the nanoscale. This study takes the shale of Lucaogou Formation in Jimsar Sag of Junggar Basin as the research object. Nano-CT and scanning electron microscopy are used to observe the pore structure of shale layer by layer, and the pore structure is transformed into a molecular model layer by layer, and finally superimposed into a pore network molecular model. Through the analysis of crude oil group components and chromatography-mass spectrometry, the characteristics of crude oil components are identified and the corresponding molecular models are established. The occurrence state of shale oil in the pore network model is simulated by molecular dynamics. CO₂ is injected into the system to simulate the occurrence state of the miscible fluid. The fluid density in the system is analyzed, the interaction force between CO₂, shale oil and pore structure is calculated, and the capacity models of adsorbed oil, free oil and CO₂ storage are established. The reliability of the model is verified and applied by combining production data and experimental tests. This study plays a crucial role in advancing the understanding of CCUS (carbon capture, utilization, and storage) and the geological theory of shale oil and gas. It also has the potential to overcome the challenges and limitations in shale oil production technology, thus making significant contributions to this field.