Investigation of gas pressure and temperature effects on the permeability and steady-state time of chinese anthracite coal: An experimental study

Abstract

Understanding permeability evolution in coal is critical for the prediction of coalbed methane (CBM) production and prevention of mine gas disasters. The primary objective of this study is to investigate the influences of gas pressure and temperature on the permeability and steady-state time of a Chinese anthracite coal. Using a self-developed coal and rock steady-state permeability testing system, the permeabilities of Chinese anthracite coal samples with CH4, CO2 and helium were measured under various gas pressures and temperatures. Meanwhile, the relationships between the steady-state time and gas pressure and temperature were examined. The results indicate that the changes of methane and carbon dioxide permeability with respect to gas pressure do not always monotonically increase or decrease. A tendency of an initial decrease, and subsequent increase is observed. For a seepage system, the time required to achieve a steady state increases nonlinearly with the increment of gas pressure, which indicates the typical characteristics of the Langmuir model. If other conditions are held constant, the time required to reach a steady state is longer for higher confining pressures. Carbon dioxide takes longer to reach the steady state than methane. The relationship between permeability and temperature is relatively complicated. Temperature affects the permeability by influencing the thermodynamic expansion of coal, gas molecular dynamics and adsorption/desorption. The actual permeability depends on the influence of the leading factor. We believe that this research will have a substantial guiding significance for field CO2-ECBM and the prevention of mine gas disasters.