Enhanced Gas Recovery Coupled with CO<sub>2</sub> Sequestration in Tight Sandstone Reservoirs with Different Pore-Throat Structures
Jiangtao Hu, Shenglai Yang, Kun Yang, Hui Deng, Mengyu Wang, Jiajun Li, Xinyuan Gao
Abstract
Driven by concerns over carbon neutrality, enhancing gas recovery coupled with CO 2 sequestration (CO 2 -EGR) has emerged as a prominent research topic worldwide. Tight sandstone gas reservoirs are characterized by a low primary recovery rate, and the adsorbed CH 4 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 CO 2 injection timing, interlayer permeability, reservoir rhythm, and permeability heterogeneity on CH 4 recovery and CO 2 sequestration. The results show that when the interlayer is impermeable, the ultimate CH 4 recovery rate of CO 2 -EGR was only 2.46% higher than that of the pressure decay. However, CO 2 -EGR achieved a CO 2 storage volume of up to 0.2997 × 10 8 m 3 . The timing of CO 2 injection exhibited a significant effect on CH 4 recovery and CO 2 storage. For a development period of 30 years, the optimal CO 2 injection window is between the 5th and 15th years. Higher interlayer permeability corresponds to higher cumulative CH 4 production and CO 2 storage volume, as well as delayed CO 2 breakthrough. Reservoir rhythm exerted a very weak effect on the CO 2 -EGR in tight sandstone reservoirs. Notably, reservoirs with lower permeability heterogeneity consistently exhibited a lower CO 2 storage volume, regardless of interlayer permeability.