Methane Adsorption Characteristics and Adsorbed Gas Content of Low-Rank Coal in China

Abstract

Coalbed methane (CBM) reserve of low-rank coal (Ro,max < 0.65), occupying a proportion of more than 40% of the total CBM reserve of China, is 14.7 × 1012 m3. The exploration degree, particularly in situ gas content estimation of low-rank CBM reservoirs in China, is extremely low. Meanwhile, adsorption characteristics of low-rank coal reservoirs have not been revealed comprehensively. In this study, methane isothermal adsorption experiments of 30 low-rank coal samples collected from typical low-rank coal-bearing basins and coalfields in China were performed under different temperatures and moisture-equilibrated conditions. The results showed that the Langmuir volume, which was found to be relatively low when the inertinite content was above 50% and relatively high when the vitrinite content was above 50%, was positively correlated with the maximum vitrinite reflectance and generally decreased with the increase of the equilibrium moisture content. The adsorbed gas content decreased as the temperature increa...