Tailoring Water-Gas Ratios to Saturation Distribution for Improved Oil Recovery in Low-Permeability Reservoirs

Water-gas alternation technology (WAG) is considered to be one of the methods that can effectively improve the effect of the CO₂ flooding in heterogeneous reservoirs. The proportion of WAG and the timing of WAG adjustment are key factors affecting the oil displacement effect. This article analyzes the influence of adjusting the WAG ratio on the oil recovery effect of heterogeneous rock cores at different gas flooding stages based on gas flooding experiments. Second, the influence of WAG ratio changes on the recovery rate of displacement experiments under different saturation distributions was studied through numerical simulation. Finally, the oilfield model currently in production was used to optimize the WAG ratio adjustment of the reservoir recovery as a constraint condition. Moreover, the correlation between the fluid distribution of the reservoir and the timing of WAG adjustment was verified. The displacement experiment shows that adjusting the WAG ratio has a significant impact on the displacement effect of crude oil under the same heterogeneous conditions. After adjusting the WAG ratio from 1:2 to 2:1 at 0.5 HCPV and 1 HCPV, the final RF showed significant changes. There is an optimal timing for adjusting the WAG ratio under the same heterogeneity. If the WAG ratio is increased earlier, it will lead to a decrease in the CO₂ injection volume and reduce the effectiveness of CO₂ flooding. If the WAG ratio is increased later, it will lead to the formation of gas channeling channels and affect the effect of adjusting the WAG ratio on flooding.