Molecular simulation on the effect of formation depth on methane adsorption by clay minerals

Shale gas is an unconventional natural gas with large reserves. Recently, its production has increased rapidly, significantly impacting the international gas market and global energy landscape. In addition to organic matter and quartz, clay minerals constitute the majority of shale, and their production activities are effectively guided by evaluating their shale gas adsorption capabilities. To explore shale gas reserves and model their distribution, the variation in shale gas content with formation depth should be investigated. Currently, experimental methods are used to evaluate the effect of formation depth on shale gas adsorption, the data are substituted into a theoretical model, and the resulting mathematical model is used to estimate the variation in methane adsorption with formation depth, considering only temperature and pressure. However, the experimental method is flawed, and the true adsorption content cannot be obtained. The absolute methane adsorption amount was calculated using molecular dynamics and the grand-canonical Monte Carlo method for the corresponding temperature and pressure conditions. The supercritical Dubinin–Radushkevich (SDR) equation was fitted, yielding a temperature-dependent equation for the SDR parameter. Shale gas adsorption can be predicted using the developed mathematical model based on formation depth and temperature–pressure gradient.