Effect of Microstructural Flexibility on Methane Flow in Kerogen Matrix by Molecular Dynamics Simulations

We investigate the flow of methane in a kerogen matrix with microstructural flexibilities at various pressures. The matrix is constructed by compressing a collection of 60 type II kerogen macromolecules. In the past, simulations of methane flow in kerogen matrices have been performed assuming rigid molecular structures. We extend the simulations from rigid molecules to flexible molecules. The gas flow simulations are performed based on the boundary-driven method. We introduce a limited number of virtual “nails” to keep the flexible kerogen matrix in place. It is demonstrated that the flexibility of the kerogen microstructure has a significant effect on gas diffusion, which is the primary transport mechanism in kerogen that contains micropores. The adsorption in flexible kerogen is higher than in rigid kerogen. Adsorption in flexible kerogen matrix may narrow the main flow path and reduce gas flow in the confined environment under subsurface conditions. On the other hand, the occasional opening of pore throats in the flexible kerogen matrix can provide additional flux. We find that the transport of methane in flexible kerogen is less than that in rigid kerogen due to changes in pore shape, despite the additional transport from pore opening in the flexible kerogen matrix