Effect of sorption-induced deformation on methane flow in kerogen slit pores

Shale gas production relies on the movement of methane through nanopores which are characterized by extra-low permeability in shale formations. However, there is a lack of understanding on methane transport in realistic organic nanopores, especially in relation to sorption-induced swelling. Here, using Monte Carlo and molecular dynamics simulations, the effect of kerogen deformation on gas transport is investigated by comparing the flow rate differences in slit pores with rigid (non-deformable) and flexible (deformable) kerogen matrices, constructed from 27 type II-D kerogen units. Simulation results show that sorption-induced swelling reduces methane mass flux significantly in large slit pores (20-40 & ANGS;) as pressure increases. By incorporating kerogen deformation into a diffusive-viscous gas flow model, it is concluded that the observed mass flux decrease is likely attributed to the narrowing pore size which mainly suppresses the viscous flux component. Further calculations suggest that kerogen swelling may decrease the apparent permeability of the slit pore by up to ~40% within pore pressure of 50 MPa. Additional findings show that diffusion can enhance the maximum gas velocity in the slit pores threefold compared with the Hagen-Poiseuille equation when pore pressure is ~2 MPa, and the diffusion and the viscous flow dominate the total mass flux when Kn > 10 and Kn < 0.1, respectively.

Automated summary

This study investigates the effect of kerogen deformation on methane transport through simulation, and finds that sorption-induced swelling significantly reduces methane mass flux. Additionally, the study also shows that the influence of diffusion and viscous flow changes with different pressures.