Feasibility of CO₂ storage and enhanced gas recovery in depleted tight sandstone gas reservoirs within multi-stage fracturing horizontal wells

Injecting CO₂ when the gas reservoir of tight sandstone is depleted can achieve the dual purposes of greenhouse gas storage and enhanced gas recovery (CS-EGR). To evaluate the feasibility of CO₂ injection to enhance gas recovery and understand the production mechanism, a numerical simulation model of CS-EGR in multi-stage fracturing horizontal wells is established. The behavior of gas production and CO₂ sequestration is then analyzed through numerical simulation, and the impact of fracture parameters on production performance is examined. Simulation results show that the production rate increases significantly and a large amount of CO₂ is stored in the reservoir, proving the technical potential. However, hydraulic fractures accelerate CO₂ breakthrough, resulting in lower gas recovery and lower CO₂ storage than in gas reservoirs without fracturing. Increasing the length of hydraulic fractures can significantly increase CH₄ production, but CO₂ breakthrough will advance. Staggered and spaced perforation of hydraulic fractures in injection wells and production wells changes the fluid flow path, which can delay CO₂ breakthrough and benefit production efficiency. The fracture network of massive hydraulic fracturing has a positive effect on the CS-EGR. As a result, CH₄ production, gas recovery, and CO₂ storage increase with the increase in stimulated reservoir volume.