Effect of igneous intrusions and normal faults on coalbed methane storage and migration in coal seams near the outcrop

Abstract

Faults and igneous intrusions simultaneously encountered in a coal seam can significantly affect the gas emission, i.e., by changing the storage (sorption) and migration properties. Knowledge of the mechanism about their effect will help the gas extraction or methane control in underground coal mines. Fifty samples were collected from five different roadways, where the sequence is truncated by 3.61-m-thick igneous intrusion, in the Tashan coal mine in Datong, China. Coal rank was changed from sub-bituminous coal or high volatile bituminous coal to anthracite, low or medium volatile bituminous coal. Enrichment of coal pores and thus higher specific surface area led to an increase of measured Langmuir volume (from 18.14–21.71 and 22.37–24.81 to 26.43–27.35 and 31.43–34.85 m3/t in Panels I and II, respectively). As a result, the measured gas contents in Panel I lie between 0.3 and 0.5 m3/t which were lower than those in Panel II (with values between 0.7 and 1.9 m3/t). However, faults serve as conduits for gas flow in Tashan coal mine. The gas content lies between 0.72 and 0.98 m3/t near the faults and between 1.04 and 1.89 m3/t far away from the faults in Panel II.