Physical Simulation of Gas Injection Mechanism for High Dip Reservoir

Abstract

High dip angle reservoirs are affected by gravity, resulting in poor sweep performance at the middle and high parts during waterflooding development. Previous studies have proposed top gas injection development for this type of reservoir, which has provided direction for improving the development effect of such reservoirs. However, current research efforts have mainly focused on the analysis of gas injection effects, rather than delving deeper into the gas injection mechanism and its influencing factors. Furthermore, the research methods adopted thus far have been primarily theoretical and fail to take into account the typical characteristics of high dip reservoirs in actual oilfields. Using a similarity criterion, this study establishes a high-temperature and high-pressure physical simulation device with variable inclination to analyze the impact of gas injection under various water injection conditions on the development of high dip reservoirs. The results suggest that the earlier the injection of water and gas, the slower the overall increase in water cut, and the more distinct the oil wall effect after gas injection, leading to a higher ultimate recovery. In the experiments, earlier injection timing can increase the final recovery rate by 9.59%. In addition, a visualized physical simulation device with an adjustable inclination angle has been established to analyze the sweep performance of high dip reservoirs under various gas injection timings. It is concluded that energy supplement in the early stage of pressure decline in the reservoir resulted in a more uniform movement of the oil-water interface at the bottom and the oil-gas interface at the top, and reduced the probability of water and gas channeling. The overall displacement efficiency is found to be improved with this approach. Earlier injection timing increased sweep efficiency by 5.95% and recovery efficiency by 13.2%, respectively. The injection gas source determined in this study, which is associated gas, is beneficial for low carbon plan and exhibits satisfactory oil recovery. The development of high dip reservoirs through top gas injection in combination with bottom water injection can generate a synergistic effect, which significantly enhances sweep efficiency and ultimate oil recovery. This finding provides theoretical guidance for practical implementation in the field.