2D profile-based physical simulation and gravity stabilization mechanism of water-to-gas flooding in high-dip-angle reservoirs

In high-dip-angle reservoirs, the strong intra- and inter-layer heterogeneity combined with pressure propagation between injection and production wells renders top gas injection-assisted gravity drainage prone to trigger instability of the gas-liquid interface. Maintaining the stability of the gas-liquid interface is crucial to enhancing oil recovery from these reservoirs. Focusing on the X oil reservoir, we construct a 2D profile-based physical model with high dip angles. By combining saturation monitoring techniques, we systematically simulate the displacement process of water-to-gas flooding. Based on the analysis of the dimensionless gravity number and capillary number, as well as the visualized gas saturation profiles from 2D physical simulation, we explore the microscopic mechanical mechanisms behind top gas injection-assisted gravity drainage and elucidate the stability mechanisms of the gas-liquid interface. Based on the residual oil distribution after water and gas flooding, we determine the conditions required for stable gas flooding. The results indicate that increasing the formation dip and the injection-production ratio (IPR) can enhance gravitational differentiation and compress the pressure drop funnel, thereby extending the stability period of the gas-liquid interface. The gas flooding process can be divided into three stages: the initial, effective, and gas breakthrough stages. The first two stages are primarily subjected to gravitational differentiation, which drives the upward migration of the gas phase and helps maintain the interface stability. In contrast, the breakthrough stage is governed by viscous forces, which accelerate the fingering expansion and promote the formation of preferential seepage pathways.