A Multi-Scale Modeling of CH₄ and H₂O Adsorption on Coal Molecules and the Water Blocking Effect in Coalbed Methane Extraction

Abstract

Coalbed methane (CBM) is of great economic value. However, at the same time, CBM is facing a multitude of technological challenges. The water blocking effect (WBE) is one of the physical effects that controls the production of CBM. To alleviation WBE, it is necessary to study its mechanisms at the molecular level. In this study, we used a combined first-principles calculation and molecular simulation approach to investigate the adsorption and diffusion of both methane and water in coal. The results suggest that water does not compete with methane in the adsorption on coal surfaces, yet the presence of water significantly slows down the diffusion of methane within the micropores of coal. This work not only explains the fundamental mechanisms of the WBE but also provides a simulation framework for building strategies to alleviate WBE.

Keywords

• coalbed methane (CBM)
• density functional theory (DFT)
• adsorption
• molecular dynamics
• water blocking effect (WBE)