Characteristics and Influence Factors of Natural Desorption in Coal Bodies from Fukang Mining Area, Xinjiang, China

Abstract

Coal body desorption characteristics are one of the key factors that influence the development of coalbed methane (CBM). In this study, 91 coal core samples from 11 CBM wells in the Fukang mining area were collected from Xinjiang, China, and the coal quality, high-pressure mercury compression, gas content, and natural desorption characteristics measurements were launched. With the detailed analyses of the differences in cumulative desorption volume, desorption ratio, and on-site average desorption rate for the coal samples with different body structures and macrolithotypes, the influence of the maximum reflectance of vitrinite, microscopic coal rock composition, and coal quality and pore characteristics on CBM desorption characteristics were discussed. The results showed that the cumulative desorption volume, desorption ratio, and desorption rate of cataclastic structure-bright coal are higher than those of primary structure-semibright coal. With the increase of R O,max and vitrinite content, the adsorption capacity of coal increases, and the increased methane concentration difference during desorption leads to an increase in cumulative desorption volume and on-site average desorption rate. The higher contents of moisture and ash yield would occupy the adsorption sites and hinder gas diffusion, which would decrease the desorption of coalbed methane. The greater porosity/pore volume ratio of medium and large pores can enhance the connectivity of pores, which increases the desorption ratio and the average desorption rate, while the higher micropore porosity/pore volume ratio can increase the gas adsorption space and the cumulative desorption volume. The pore characteristics have the most significant effect on the cumulative desorption volume and desorption ratio. The results of the study can help guide coal mine gas management and CBM development from middle-and low-rank coal reservoirs in Xinjiang.