Enhanced Gas Recovery Coupled with CO2 Sequestration in Tight Sandstone Reservoirs with Different Pore-Throat Structures

Driven by concerns over carbon neutrality, enhancing gas recovery coupled with CO2 sequestration (CO2-EGR) has emerged as a prominent research topic worldwide. Tight sandstone gas reservoirs are characterized by a low primary recovery rate, and the adsorbed CH4 within the reservoir is challenging to recover via conventional pressure decay. In this study, we first classified tight sandstone reservoirs based on their pore-throat structural characteristics. Subsequently, we conducted gas isothermal adsorption experiments, relative permeability experiments, and stress sensitivity experiments. Utilizing the physical experiment date, 12 gas reservoir-scale numerical models were constructed to study the effects of CO2 injection timing, interlayer permeability, reservoir rhythm, and permeability heterogeneity on CH4 recovery and CO2 sequestration. The results show that when the interlayer is impermeable, the ultimate CH4 recovery rate of CO2-EGR was only 2.46% higher than that of the pressure decay. However, CO2-EGR achieved a CO2 storage volume of up to 0.2997 × 108 m3. The timing of CO2 injection exhibited a significant effect on CH4 recovery and CO2 storage. For a development period of 30 years, the optimal CO2 injection window is between the 5th and 15th years. Higher interlayer permeability corresponds to higher cumulative CH4 production and CO2 storage volume, as well as delayed CO2 breakthrough. Reservoir rhythm exerted a very weak effect on the CO2-EGR in tight sandstone reservoirs. Notably, reservoirs with lower permeability heterogeneity consistently exhibited a lower CO2 storage volume, regardless of interlayer permeability.