Microscopic Visualization Experiment of High Temperature and High Pressure CO2-C2H6/DME Displacement in Tight Reservoirs

Abstract The tight reservoir exhibits pronounced heterogeneity and possesses complex physical properties, thereby constraining crude oil exploitation. Water and CO2 injection for enhanced oil recovery encounter challenges related to low sweep efficiency and viscous fingering, resulting in suboptimal recovery effectiveness. In recent years, there has been growing attention towards the synergistic advantages of oil displacement through the injection of fluids such as CO2, hydrocarbon gases, and chemical additives. This paper presents the design of a microscopic visualization experimental system specifically tailored for studying high-temperature and high-pressure composite fluid displacement in actual tight oil reservoir conditions. Based on the pore throat characteristics inside the core, a visual micro-nano scale pore throat model was created to simulate the flow of composite fluid in micro-nano channels under high temperature and high pressure conditions. The research findings indicate that adding dimethyl ether and ethane to composite gases enhances their solubility and expansion in crude oil. Comparing the occurrence characteristics of residual oil after CO2 injection development reveals that injecting a composite gas (CO2- C2H6-DME) leads to a notable reduction in residual oil in the form of Clustered and oil Porous. The experimental results show that the final recovery rate of composite gas flooding can reach 92.8%, which is 46.7% higher than pure CO2. This paper presents, for the first time, the synergistic enhanced oil recovery (EOR) technology of injecting a composite gas mixture (CO2, C2H6, DME) into tight reservoirs. This study employs microscopic visualization techniques to assess the variation in residual oil characteristics and the enhancement of recovery in crude oils driven by different gases.