Research on CO2 injection for water control and enhanced nature gas recovery in heterogeneous carbonate reservoirs

Abstract

During the development of edge-water driven carbonate gas reservoirs, the impact of the heterogeneity of carbonate rocks on water invasion in production wells remains unclear. This study utilizes parallel core experimental models and heterogeneous reservoir numerical simulation models to investigate the water invasion in heterogeneous carbonate rocks and the potential of using CO₂ injection as a water control solution after water flooding in production wells. Based on this, it explores the influence of factors such as injection pressure, permeability ratio, and injection location on water control effectiveness. The study focuses on the impact of various sensitivity parameters of CO₂ injection on edge water production and natural gas increment, and elucidates the mechanism of these sensitivity parameters on water control and production efficiency in heterogeneous formations. The results show that: 1) Due to the larger seepage channels, high-permeability cores experience a greater increase in the degree of water invasion compared to low-permeability cores, resulting in a shorter water-free gas production period; 2) After CO₂ injection, CO₂ can mobilize more water-locked gas in high-permeability cores, achieving better water control and production enhancement effects; 3) When the core pressure recovery from CO₂ injection increases from 60% to 100%, the recovery increases from 9.56% to 35.42%, and the cumulative water reduction increases from 3 ml to 10 ml. This pushes the edge water further back, slows down the flow of edge water in the core in the form of slugs, and extends the time before water invasion; 4) When the permeability ratio of the core is changed, the higher the permeability of the parallel core combination, the higher the production of water-locked gas, the better the water control effect, with a maximum recovery increment of 53.13% and a maximum cumulative water reduction of 15 ml; 5) Near-water end wells, being closer to the edge water, achieve better water control and production enhancement effects after CO₂ injection compared to far-water end wells. These findings are crucial for optimizing the recovery rate of edge-water gas reservoirs and provide guidance for the application of CO₂ injection for water control and CO₂ sequestration in carbonate gas reservoirs.