Study on the influence of different bedding dip angle and spacing conditions on propagation law of hydraulic fractures in deep coal seams

Deep coal seams often have low permeability and high in-situ stress, and the expansion process of hydraulic fractures in deep coal seams is more complex. To investigate the influence of bedding dip-spacing on the hydraulic fracturing of deep coal seams, a finite element model covering various bedding dips (0^\circ , 20^\circ , 40^\circ , 60^\circ , 80^\circ ) and spacing (4 m, 6 m, 8 m) of coal rock hydraulic fracturing fracture propagation is established based on the second-order nominal stress criterion of zero-thickness Cohesive element. The hydraulic fracturing effects of coal rock under different bedding dip-spacing conditions were characterized by the hydraulic fracture morphology, the maximum fracture width, fracture length, and bedding dip-spacing ratio, and validated in the ZS67 well of Zhengzhuang Block of Qinshui Basin. The study shows that: when the bedding dip is 40°, the fracture network morphology is the most complex; when the bedding spacing is 6 m, the number of fracture branches reaches its maximum value; when the bedding dip is 40° and the bedding spacing is 6 m, the hydraulic fracture area reaches 0.27 m², showing the best expansion characteristics, forming a multi-layered and multi-directional fracture network structure. Under this condition, the fracture extends 19.57 m along the bedding plane, with 14 branches, the maximum fracture width of 5.63 mm, and the fracture length of 48.47 m, with the bedding dip-spacing ratio of 7.15. The optimization of 40° and 6 m bedding combination scheme significantly enhances the permeability of the fracturing fluid through Zhengzhuang Block ZS67 well.