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Description
The occurrence and transport mechanisms of methane (CH4) and ethane (C2H6) in organic nanopores are crucial for the efficient development of shale gas reservoirs. While prior studies have examined the adsorption and recovery behaviors of light hydrocarbons (e.g., CH4, C2H6, C3H8) in kerogen nanopores, most analyses have focused on equilibrium states, with limited attention to dynamic production processes. Moreover, existing work has predominantly relied on single slit-shaped nanopore models, overlooking the role of interconnected pore structures. In this work, we therefore construct a model of two interconnected slit-shaped kerogen nanopores with different apertures (2 nm and 4 nm) to investigate the adsorption and extraction of CH4 and C2H6 using coupled grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. Results show that C2H6 exhibits stronger adsorption affinity than CH4, with smaller pores favoring higher adsorption selectivity. During pressure depletion, the transport partition ratio of CH4 from the dead-end pore to the channel and from the channel to the fracture region greatly exceeds the pore size ratio (~19/32 vs ~4). For C2H6, the transport ratio from dead-end pore to channel is comparable to the pore size ratio (~5.6 vs ~4), whereas from channel to fracture it is significantly higher (~19 vs ~4). During CO2 soaking, nearly all gas components are recovered through the larger pore toward the fracture region. CH4 and C2H6 in the smaller nanopore channel follow a more complex path: from channel to dead-end pore, then to the larger pore, and finally to fractures. The flow partition ratio of CO2 from the fracture into nanochannels matches the pore size ratio. However, CO2 entering the smaller nanopore tends to remain in the channel and does not migrate further into the dead-end pore, meaning the CO2 in dead‑end pores originates mainly from the larger channel. After equilibrium, CH4 shows decreases in both adsorbed and bulk phases, while the adsorbed phase of C2H6 is enhanced. During CO2 soaking, CO2 injection mobilizes mainly the adsorbed hydrocarbons, with little effect on the bulk phase, leading to higher displacement efficiency in smaller pores where adsorbed gas predominates. This work advances the understanding of gas recovery behavior from a dynamic and structurally heterogeneous perspective, providing theoretical insights and simulation‑based guidance for the efficient development of shale gas reservoirs.
| Country | China |
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