Experimental Study On Optimal Co2 Flooding Pressure Before And After Fracturing In Heavy Oil Reservoirs

Low-permeability heavy oil reservoirs have the characteristics of low reservoir permeability, high crude oil viscosity, and poor flow coefficient. In the conventional single gas injection development process, the mechanism of dissolved gas flooding and miscible flooding can reduce the seepage resistance of porous media to a certain extent. However, the low permeability properties of the reservoir often limit the ultimate recovery. In this paper, from the perspective of reservoir reconstruction, tight sandstone reservoir cores are selected for gas flooding experimental evaluation before and after fracturing. Four groups of gas injection pressure values of 16.3 MPa, 18.0 MPa, 20.0 MPa, and 22.0 MPa are set to evaluate the porosity and permeability, variation, recovery factor and recovery degree under different gas injection PV numbers before and after fracturing. The experimental results show that there is an obvious start-up pressure gradient in the process of gas injection and flooding of heavy oil in tight sandstones before fracturing. The recovery rates of gas injection after fracturing are higher than before fracturing. After increasing the injection pressure, the recovery rate tends to decrease. As the corresponding gas injection pressure is 24 MPa, the recovery factor per unit gas injection PV is the highest. The experimental research in this paper shows that in the process of gas injection development in low-permeability heavy oil reservoirs, on the basis of reservoir reconstruction, an appropriate increase in gas injection pressure value can achieve a higher recovery degree.