Taking the efficient exploitation of coalbed methane resources as the object in the soft coal strata, experiments on the formation of crack system were investigated by fracturing large-size coal-rock combination specimens. The results shows that due to the differences in mechanical properties and characteristics between coals and sandy mudstone, In the process of hydraulic fracturing from the hard sandy mudstone into the coal mass, the complex fracture system was formed on the coal-rock combination. The penetration, diversion or offset occur at the interface between the coal and the rock under the influence of the interfacial cohesive force. The diversion or offset leading to the fracture patterns complex, which will improve the fracture system.


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