Molecular Insights into Pressure-Driven Carbon Sequestration and Storage Efficiency in Complex Geological Nanopore...

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.