シェール複雑地質ナノポア構造における圧力駆動炭素隔離と貯蔵効率の分子論的洞察

Injection of CO₂ into unconventional gas reservoirs and desorption of residual CH₄ to enhance gas recovery currently are currently hot topics of research worldwide. In order to quantitatively determine the CO₂ sequestration capacity and CH₄ displacement efficiency during the carbon sequestration process, it is necessary to investigate the adsorption, desorption, flow, and displacement behaviors of CO₂ and CH₄ at the microscopic level. Thus, this work employs the molecular dynamics (MD) simulation method to assess the influence of CO₂ displacement pressure on CH₄/CO₂ competitive adsorption and flow characteristics, CO₂ sequestration, and storage efficiency. The novelty of this work is that a MD kerogen model of complex geological pore structure of shale is built and implemented to calculate the CH₄ displacement efficiency, CO₂ storage efficiency, and selectivity coefficient of CH₄ and CO₂ driven by pressure gradient. The key results of this study demonstrate that as CO₂ molecules are injected into pores, the sequestration rate of CO₂ in pores gradually decreases until it stabilizes. When the number of CH₄ molecules in pores reaches a minimum value, the displacement stage is completed. Then, the CO₂ and CH₄ molecules in the pores are in a competitive adsorption state. Meanwhile, as the CO₂ displacement pressure increases, the displacement efficiency gradually increases, while the storage efficiency first rises to reach its maximum value and then decreases. Hence, the CO₂ displacement pressure plays a key role in achieving the optimal CO₂ storage efficiency and CH₄ displacement efficiency, ultimately contributing to the application of pressure-driven carbon sequestration in complex geological pore structures of shale.