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

To reduce carbon emissions, hydrogen (H2) 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.

Automated summary

In this study, Monte Carlo simulation is used to analyze the compositional distribution and phase behavior of the H-2-shale gas (H-2-SG) system. The results indicate the presence of compositional heterogeneity and adsorption of hydrocarbons in the nanopores. The adsorption of hydrocarbons near the boundary leads to a higher percentage of H-2 in the bulk fluid, which implies a high purity of H-2 in the extracted fluid. Increasing the volume percentage of nanopores can further enhance the H-2 purity in the extracted fluid.