Molecular Simulation of Hydrogen-Shale Gas System Phase Behavior under Multiscale Conditions: A Molecular-Level Analysis of Hydrogen Storage in Shale Gas Reservoirs

摘要

To reduce carbon emissions, hydrogen (H_2) has been considered an important energy carrier, since its combustion only generates water. With the development of shale gas, depleted shale gas reservoirs might be good candidates for H_2 storage. However, the mechanism of H_2 storage in depleted shale gas reservoirs is not clearly understood. Therefore, in this work, we apply Monte Carlo simulation to analyze the compositional distribution and phase behavior of the H_2- shale gas (H_2-SG) system under multiscale (bulk + nanoscale) conditions. Our molecular simulation results show that compositional heterogeneity exists between the bulk region and the nanopores. The bulk fluid has a higher percentage of H_2 while more hydrocarbons are present in nanopores. For the fluids in nanopores, hydrocarbons are adsorbed near the boundary while H_2 molecules are freely distributed, which makes H_2 molecules more likely to be released to the bulk region. The compositional heterogeneity and hydrocarbon adsorption collectively lead to a high percentage of H_2 in the bulk fluid. Since the bulk fluid is produced during the extraction process, the high percentage of H_2 in the bulk fluid means a high purity of H_2 in the extracted fluid, which can be a positive factor for H_2 storage in shale gas reservoirs. An increase in the volume percentage of nanopores can increase the H_2 purity in the extracted fluid.