Microscopic Oil Displacement Mechanism of CO2 in Low- Permeability Heterogeneous Glutenite Reservoirs in the Junggar Basin

Carbon dioxide (CO2) flooding is a promising method for developing low-permeability heterogeneous glutenite reservoirs (LPHGRs) featured with low natural energy. Herein, the focus of this work was to study the microscopic oil displacement mechanism of CO2 in LPHGRs. First, the micropore structure and mineral composition of LPHGRs were analyzed, and the effect of CO2 on low-permeability reservoirs was then studied. Also, the mechanism of CO2 displacement in low-permeability reservoirs on a pore scale was analyzed using nuclear magnetic resonance technology in different dimensions. The experimental results showed that the mineral composition of the rock mainly included quartz, feldspar, and clay minerals. The core pores were poorly developed and highly heterogeneous. The clay and other mineral particles produced by the dissolution reaction of rocks and minerals migrated and deposited with formation fluid to damage the reservoir. On the contrary, it also improved the pore structure, increased pore space, and increased reservoir permeability. The miscible interaction between CO2 and crude oil formed a stable displacement front, which enabled crude oil to be well displaced from the macropores and medium pores. However, this interaction generated negligible effects on the small pores. The experimental results provided important indicators for CO2 development in LPHGRs.