Molecular simulation and modelisation of methane/ethane mixtures adsorption onto a microporous molecular model of kerogen under typical reservoir conditions

Abstract

The prediction of mixture adsorption is a challenging task in gas industry when dealing with shales for both resources prospect or production forecast. In this work, we used molecular simulation and models to study the adsorption of methane/ethane mixtures onto a mature kerogen model under typical reservoir conditions (338K, up to 20MPa). Using Molecular Dynamics, we first generated microporous structures of kerogen, representative of field samples. Monte Carlo simulations in the Grand Canonical ensemble were used to produce pure compound and mixture adsorption isotherms on these adsorbent structures. The ability to predict simulation results of the Ideal Adsorbed Solution model and a modified statistical mechanical derivation of the Extended Langmuir model have been studied at low pressures (up to 1MPa) where species are supposed ideal and at higher pressures (up to 20MPa) where species non-ideality is partially introduced in the models. At low pressures, the adsorption isotherms predicted by the two models are in good agreement with the results from molecular simulation, independently of the confinement. At higher pressures, this agreement is only valid for the less confined structures and worsened as the micropore size decreases.