Study on CO2 Flooding Effect of Heterogeneous Reservoir Under Different Well Pattern

Both Well pattern and reservoir heterogeneity are important factors affecting the effectiveness of CO2 flooding development, and blind well placement in inhomogeneous reservoirs can seriously limit the efficient development of CO2 flooding. In this paper, the effects of square and triangular well pattern with different degrees of inhomogeneity on the flowline field and residual oil distribution field are investigated using numerical simulations, and their effects on the drive effectiveness are evaluated comprehensively by sweep efficiency, miscibility degree, production gas oil ratio and recovery degree. The results show that the heterogeneity of the reservoir changes the intensity of the streamline in the process of CO2 flooding, the presence of the main river channel causes the injected CO2 in the low-permeability zone to preferentially accumulate and break through to the high-permeability zone, and the oil displacement efficiency in the sweep region of the main river channel decreases compared to that of the homogeneous reservoir. The use of different well patterns for CO2 drive will result in different sweep characteristics and residual oil distribution. Compared with the diamond-shaped inverted nine-spot well pattern, the straight-line row well pattern is more likely to spread to the center of the area and the surrounding crude oil, and still maintains a high sweep efficiency in heterogeneous reservoirs. Compared with the homogeneous reservoir, the recovery rate of the high-grade poor reservoir increases by 3.1%, while the recovery rate of the diamond-shaped inverted nine-spot well pattern decreases by 11.95%. The recovery rate of the staggered well pattern in the high-grade poor reservoir is 31.58% lower than that of the homogeneous reservoir, and the sweep efficiency was reduced by 26.49% compared to homogeneous reservoirs when the CO2 injection reached 2.0 HCPV. The research results have certain guiding significance for the deployment of CO2 flooding well pattern in heterogeneous reservoirs.