Molecular Dynamics Study of Transport and Storage of Methane in Kerogen

Abstract

Abstract Studying kerogen structure and its interactions with fluids is important for understanding the mechanisms involved in storage and production of hydrocarbons from shale. In this study, adsorption and transport of methane in a three dimensional type II kerogen model are studied using molecular dynamics simulations. Grand Canonical Monte Carlo (GCMC) simulations are used to simulate the adsorption of methane and NonEquilibrium Molecular Dynamics (NEMD) simulations are employed to simulate transport of methane in the kerogen model. The kerogen model prepared by Ungerer et al. (2014) is used in this study. In order to build a representative solid state model of kerogen, eight kerogen molecules are placed in a periodic cubic cell. Once the initial configuration of kerogen molecules is prepared, constant-temperature constant-volume (NVT) simulations and then constant-temperature constant-pressure (NPT) simulations are performed to obtain the final structure. For the final structure, density values are calculated and compared with the reported density range for kerogen density. Adsorption isotherm, self and transport diffusion coefficients of methane in the final kerogen structure are also calculated. Simulation results for the adsorption isotherm are fairly close to experimental results reported for a Haynesville shale sample. Computed values for self and transport diffusivities decrease as pressure increases and transport diffusion coefficients approach the self-diffusion coefficients.