Linxing-Shenfu Gangue Interaction Coal Seam Hydraulic Fracture Cross-Layer Expansion Mechanism

The deep coal reservoir in Linxing-Shenfu block of Ordos Basin is an important part of China’s coalbed methane resources. In the process of reservoir reconstruction, the artificial fracture morphology of coal seam with gangue interaction is significantly different, which affects the efficient development of coalbed methane resources in this area. In this paper, the surface outcrop of Linxing-Shenfu block is selected, and three kinds of interaction modes between gangue and coal seam are set up, including single-component coal rock sample, coal rock sample with different thicknesses of gangue layer and coal rock sample with different numbers of gangue. Through true triaxial physical simulation and three-dimensional discrete element numerical simulation, the law of artificial fracture initiation and propagation in multi-gangue interaction coal seam is analyzed in depth, and the hydraulic fracture initiation and propagation mode under different interaction modes of gangue layer in Linxing-Shenfu deep coal reservoir was clarified. The research shows that the initiation of artificial fractures in a single coal seam is affected by geological-engineering factors. The maximum principal stress dominates the direction of fracture propagation, and the stress difference controls the fracture morphology. When the stress difference is 2 MPa, the fracture morphology is complex, which is easy to connect to the weak surface of coal and rock cleat, and the fracture morphology of the stress difference is mainly a single main fracture. After the thickness of the gangue layer is increased from 2 to 5 cm, it is difficult for the artificial fracture to penetrate the layer vertically after the fracture initiation, and the effective transformation area of the reservoir is limited. The more the number of gangue layers, the greater the hydraulic energy consumption in the process of fracture propagation, and the more difficult the fracture propagation.