Enhancing Oil Recovery in Low Permeability Reservoirs through CO2 Miscible Flooding: Mechanisms and Dynamics

Understanding the dynamic characterization of the CO2 miscible flooding process in low permeability reservoirs and its mechanism for oil recovery enhancement is crucial for controlling CO2 miscible flooding sweep efficiency and further enhancing oil recovery. This study was conducted in a low permeability reservoir in Jilin, China, using both online nuclear magnetic resonance CO2 miscible flooding and long-core CO2 miscible flooding experiments. A refined dynamic characterization of the CO2 miscible flooding process from the macroscopic core scale to the microscopic pore scale was achieved through multiple spatial online nuclear magnetic resonance testing methods. Analysis of dynamic characteristics of physical parameters was based on long-core displacement experiments and gas chromatography. This study summarizes the influence mechanism of CO2 miscible flooding on enhanced oil recovery in low permeability reservoirs and demonstrates the feasibility of CO2 miscible flooding. The results indicated that (1) CO2 miscible flooding enables simultaneous oil recovery from micro-, meso-, and macropores, significantly improving displacement efficiency. (2) The recovery process unfolds in two stages: the initial CO2 miscible flooding stage before gas breakthrough and the subsequent CO2 miscible transport stage after gas breakthrough. (3) Both stages are instrumental in expanding the macroscopic swept range of CO2, thereby enhancing oil recovery. (4) The miscibility of CO2 with crude oil can affect the oil's composition. (5) The combined effect of miscible flooding and transport underpins the high displacement efficiency of CO2 miscible flooding. Emphasizing these critical aspects could enhance oil recovery from CO2 miscible flooding in field production.