Mesoscopic law of stress and fracture evolution of coal seams hydraulic fracturing

Hydraulic fracturing is a technology to increase coal seam permeability, and its stress evolution characteristics and the judgment of fracture morphology and propagation range are particularly important. In this paper, based on directional fracturing, a fluid-structure coupling model of hydraulic fracturing is established by using the discrete element numerical method. The effects of fracturing flow, Poisson’s ratio, natural fracture density on stress evolution and fracture evolution, and their mesoscopic laws are investigated by means of the stress path and crack hot spot diagram. The results show that the stress evolution direction and the final stress path curve shape are obviously different at different fracturing rates. The stress ratio near the crack increases gradually at a low fracturing rate, but increases first and then decreases at a high fracturing rate. The larger the Poisson’s ratio, the smaller the fracture radius, but its influence on fracture initiation time and fracture propagation morphology is not obvious. The development of natural fractures plays a key role in the propagation of hydraulic fractures, and the direction of fracture propagation is more random in coal seams with high natural fracture development, and the direction of stress evolution is reversed. The stress evolution characteristics of different regions can reflect the propagation state of fractures in the fracturing process, the propagation range of the hydraulic fracture network can be determined by monitoring the triaxial stress of several fixed positions near the fracture zone.