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

Yang Yang,Wang Wang,Zhang Zhang,Luo Luo,Lin Lin,Li Li,Chen Chen,Fan Fan

doi:10.3390/app9163421

Yang Yang, Wang Wang + Show 6 more

Open Access

https://doi.org/10.3390/app9163421

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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.

Highlights

Coalbed methane (CBM) is one kind of natural gas found in a coal reservoir [1]
CH4 and H2 O adsorptions on graphene were tested in order to validate our computational methods, as well as to provide a baseline for the binding affinity to CH4 and H2 O
The results suggest that PBE+density-functional theory (DFT)-D can achieve accuracy equivalent to that produced by m11-L, which is a meta-generalized gradient approximation (GGA) functional and computational more expensive [27]

Summary

Introduction

Coalbed methane (CBM) is one kind of natural gas found in a coal reservoir [1]. It is generally presumed that gas holding capacity and permeability are two important factors which characterize a CBM reservoir. The former factor determines the gas capacity of the reservoir, while the latter one suggests the easiness of gas extraction [1]. CBM is often found with other components, including water and carbon dioxide, in the coal reservoir. A study on the adsorption and diffusion behaviors of methane on coal, especially in the presence of water, can generate a better understanding of CBM reservoirs and provide insights on the development of the exploration technologies

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