Abstract
Deep coalbed methane (CBM) is widely distributed in China and is mainly commercially exploited in the Qinshui basin. The in situ stress and moisture content are key factors affecting the permeability of CH4-containing coal samples. Therefore, considering the coupled effects of compressing and infiltrating on the gas permeability of coal could be more accurate to reveal the CH4 gas seepage characteristics in CBM reservoirs. In this study, coal samples sourced from Tunlan coalmine were employed to conduct the triaxial loading and gas seepage tests. Several findings were concluded: (1) In this triaxial test, the effect of confining stress on the permeability of gas-containing coal samples is greater than that of axial stress. (2) The permeability versus gas pressure curve of coal presents a ‘V’ shape evolution trend, in which the minimum gas permeability was obtained at a gas pressure of 1.1MPa. (3) The gas permeability of coal samples decreased exponentially with increasing moisture content. Specifically, as the moisture content increasing from 0.18% to 3.15%, the gas permeability decreased by about 70%. These results are expected to provide a foundation for the efficient exploitation of CBM in Qinshui basin.
Highlights
Deep coalbed methane (CBM) is widely distributed in China and is mainly commercially exploited in the Qinshui basin
Understanding the permeability evolution of gas-containing coal is significant to both the extraction of CBM and the prevention of CH4 gas outburst disasters
The WYS-800 triaxial gas seepage apparatus was employed to investigate the evolution of gas permeability in the Tunlan coal samples under various stresses, moisture contents and gas pressures
Summary
Deep coalbed methane (CBM) is widely distributed in China and is mainly commercially exploited in the Qinshui basin. The in situ stress and moisture content are key factors affecting the permeability of CH4 -containing coal samples. Several findings were concluded: (1) In this triaxial test, the effect of confining stress on the permeability of gas-containing coal samples is greater than that of axial stress. (3) The gas permeability of coal samples decreased exponentially with increasing moisture content. The permeability of coal is influenced by many factors, such as in situ stress, moisture content, gas adsorption and loading/unloading conditions. The porosity of coal decreases with increasing buried depth, resulting in the low permeability of CBM reservoirs, affecting the effective extraction of CBM. The results indicated that the permeability of gas-containing coal decreases with the increase of axial stress and confining stress. When the pore pressure is greater than 1.9 MPa, the effective stress plays a major role in controlling the coal permeability
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