Laboratory study of fracture permeability of mineral-filled coal from Fanzhuang Block, southern Qinshui Basin, China

Abstract

Coalbed methane (CBM) has achieved commercial production in China over the past decade. However, its single well production rate is relatively low. This is mainly due to the low coal permeability, which is a critical property for gas production. Fanzhuang block, southern Qinshui Basin, is a main CBM production area in China. The coals have mineral fillings in the cleat system and the mineral fillings have significant impact on coal permeability, thus the production rate. In this work, methane permeabilities on two selected samples from the Fanzhuang block were measured from high gas pressure to low gas pressure, simulating the gas production process. CT scans were performed on the two samples and two sets of fracture systems were observed. One set of fractures was filled with minerals, while another set of fractures was open. Therefore, the impact of minerals filling on permeability and fracture compressibility is complex. Moreover, the strong swelling strain anisotropy and low Poisson's ratio are also speculated to be closely related to the mineral fillings in the fracture system. • The permeability evolutions of mineral filled coal fracture samples are studied. • The measurement procedure has a significant impact on permeability results. • Mineral fillings in the facture have complex impact on coal permeability. • Swelling anisotropy and mechanical properties are also highly impacted by mineral fillings.