Methane Desorption Characteristics of Coal at Different Water Injection Pressures Based on Pore Size Distribution Law

Dong Zhao,Zengchao Feng,Tao Gao,Yulin Ma

doi:10.3390/en11092345

Abstract

Methane desorption characteristics of coal under definite water pressure comprises a complex two-phase flow process. A series of mercury intrusion porosimetry (MIP) and desorption experiments at different water injection pressures are reported in this study. Three lumpy coal samples were used in desorption experiments at three different water injection pressures and at natural desorption for comparison. Samples comprising two ranks of coal were used for MIP measurements including the distribution of porosity and pore sizes. The results of this study enable the establishment of a new model that encompasses a critical theoretical pore size that is most effective for water injection into coalbeds and that can be related to water injection pressure, the length of residual water, and gas adsorption capacity. Data show that the use of different water injection pressures leads to different gas desorption capacities as well as variable time effects and degree of gas desorption. Critical pore size is therefore proposed as a new parameter that can be employed to describe high pressure water effects in the context of gas desorption and can be calculated using pore size and the volume distribution law, as well as via the moisture ratio that remains after experiments and the permanent desorption percentage.

Highlights

Coalbed methane (CBM) is a significant natural energy resource that is increasingly playing a key role in the development of clean new energy in China
Methane desorption from coal at various conditions is affected by numerous factors—including gas content from underground boreholes, coalbed permeability, initial gas desorption properties, and coal strength—all variables that can be measured in the laboratory as well as in situ at the coal field [6,7,8,9]
Two ranks of coal samples were used in this study in a series of desorption experiments at different water injection pressures combined with mercury intrusion porosimetry (MIP) measurements to study the relationship between desorption law and pore size distributions

Summary

Introduction

Coalbed methane (CBM) is a significant natural energy resource that is increasingly playing a key role in the development of clean new energy in China. A range of studies have assessed how high-pressure water injection into a coalbed will influence the desorption capacity of CH4 because of residual moisture [5,11,12,13] This process can improve coalbed permeability gas output is influenced by high pressures as moisture content increases [14,15]. Additional technologies, including carbon dioxide enhanced coalbed methane (CO2-ECBM) and coalbed heating, can be utilized for CBM exploitation [16,17]; all these methods improve gas production and break original adsorption and desorption equilibrium states to create very large discrepancies between experimental processes and engineering practice [18]

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Discussion

Conclusion