(615g) Modeling Adsorption Equilibrium in Flexible Kerogen Pores Using Hybrid Molecular Dynamics/Monte Carlo

Shale gas reservoirs are sedimentary rocks which are being explored for natural gas production. Kerogen, an insoluble organic part of shale, is both a source and reservoir of hydrocarbons, and exhibits an amorphous structure depending on the level of maturity. It is critical to understand the hydrocarbon adsorption in hierarchical porous network found in kerogen and the effect of adsorption induced deformation on the kerogen structure. This knowledge is crucial for predicting the storage capacities of oil and gas, as well as enhancing hydrocarbon recovery.

To begin, we create three-dimensional molecular models of microporous kerogen matrix of type II-A with the same density as a typical experimental sample. Using the kerogen matrix, we also create mesoporous slit pores of different sizes.¹ To incorporate the effect of adsorption stress exerted by the gas molecules on kerogen matrix, we use the hybrid molecular dynamics/Monte Carlo approach. This involves multiple iterations of grand canonical Monte Carlo simulations and molecular dynamics in NPT ensemble until the convergence in the number of particles and unit cell volume is achieved. We study adsorption of CH₄, CO₂, and octane in flexible kerogen matrix and slit pores. Contribution of adsorption and deformation is measured in the microporous kerogen matrix and mesoporous slit pores. Through our hybrid approach, we aim to gain a deep understanding of deformation of kerogen upon hydrocarbon adsorption, which holds significant implications for advancing techniques for hydrocarbon recovery from shale reservoirs.

This work is supported by the NSF CBET grant 1834339 and ExxonMobil.

1. Parashar, S; Ravikovitch P.I.; Neimark, A.V. Molecular Modeling and Adsorption Characterization of Micro-Mesoporous Kerogen Nanostructures. Energy & Fuels. 2022.