Fracture extension law of hydraulic fracture in coal with different structure

To find out the fracture extension law of coal hydraulic fracturing with different coal body structures can lay a foundation for reasonable well pattern deployment. Taking Shizhuang block of Qinshui basin as the research object, the fracture of coal core was observed, and four kinds of coal with fracture development degree were divided. Based on the theory of rock mass mechanics, the stress field calculation model of fracture tip and the judgment criterion of whether hydraulic fracture can pass through natural fracture in hydraulic fracturing process were established. According to the measured data of CBM wells, the reliability of theoretical analysis was verified, and the fracture extension law of hydraulic fracturing of coal with different coal body structures was obtained. The results show that the hydraulic fracture extension of two groups of natural fracture development is different before and after the induced stress is considered. With the increase of fracture length, the induced stress increases, and the hydraulic fracture extends from single direction to bidirectional direction. For a group of coal with natural fracture development, because the angle between the development direction of natural fracture and the direction of maximum principal stress is small, the extension direction of hydraulic fracture before and after considering induced stress is not obvious, and the overall extension tends to the natural fissure development direction. Hydraulic fractures always extend along the direction of maximum principal stress for granular occasional and powdery fractured coal. The research results provide a theoretical basis for the reasonable arrangement of the well network under different stress and fracture development in this area.