Characteristics of Coalbed Methane Reservoirs in Faer Coalfield, Western Guizhou

Abstract

Based on analysis of the geological background and gas content data in Faer coalfield, we discuss the occurrence characteristics of coalbed methane (CBM) and its distribution along the stratigraphic sequence and in coal seams. We analyze the methane adsorption isotherm experiments, reservoir deformations and mercury intrusion porosimetry (MIP), and further discuss the reservoir physical properties. The results show that gas content and gas content gradient of CBM fluctuate with stratigraphic sequence that is mainly caused by the difference in absorption capacity of each coal seam and distributions of CBM reservoir pressure systems. The relatively low gas content gradients of those coal seams buried below 500 m depth result from the dissipation of CBM into the surrounding rocks of thin and unstable Nos. 28 to 34 coal seams and the lateral migration of CBM along the strata in high-elevation area. The Yangmeishu syncline and topography are the main controlling factors that affect the current distribution pattern of CBM content, which is higher in the north than in the south and has a northeastern trend. The theoretical gas saturation is generally lower than 60%, combined with well-developed brittle fractures and macropores, formed by structural deformation. The exploration prospects for CBM in Faer coalfield is good.