Pore structure and gas adsorption characteristics in stress-loaded shale on molecular simulation

Abstract

Since stress from overlying strata is one of the primary factors influencing pore structure and gas content in shale reservoirs, understanding its role is crucial for developing shale gas fields. In this study, Molecular Mechanics and Molecular Dynamics methods were employed to investigate the intrinsic relationship between pore structure, energy, and adsorption performance of the organic matter matrix under different stress conditions. The results show that the pore structure of the organic matrix can be categorized into three stages with the variation of external stress, with 0.2 and 0.8 GPa as the boundaries. The effect of external stress significantly impacts the methane adsorption capacity in the organic matrix. Changes in stress not only result in a reduction of adsorption space but also an increase in adsorption sites. These two factors have opposite effects on CH4 adsorption in the model. That is, the negative impact of the reduction in adsorption space outweighs the positive impact of the increase in adsorption sites, resulting in a decrease in the adsorption capacity. At 0.8 and 1 GPa, the maximum CH4 adsorption capacity was reduced by 70 % and 58 %, respectively. This study provides an important reference for understanding the pore structure of the organic matrix and the adsorption characteristics of CH4 in shale gas reservoirs.