Effects of bedding on hydraulic fracturing in coalbed methane reservoirs

Abstract

Bedding is a special structure of coal, which has notable effects on the mechanical parameters of coal and on the hydraulic fracture propagating in coalbed methane reservoirs. To study the effects of bedding on anisotropic characteristics of coal fracture toughness, three-point bending tests have been carried out on raw coal specimens. The results indicate that fracture toughness and failure modes of the specimens both have strong anisotropy due to bedding. A geological geomechanical model of a coalbed methane (CBM) reservoir is built taking into account the effect of bedding to study the hydraulic fracture propagation and the influence of bedding on the fracture network. The hydraulic fracture initiates at the end of the perforation and tends to bifurcate and swerve at the bedding to produce induced fractures. Ultimately, these fractures form a complicated fracture network. The fracture toughness of bedding has great influence on hydraulic fracture geometry. The fracture is likely to bifurcate and swerve at the bedding to form multiple secondary fractures with larger bedding fracture toughness.