Initiation pressure calculation model and judgment criterion for hydraulic fracturing of inclined coal seam

As for the problem of ambiguous mechanism of crack initiation in inclined coal seam, it leads to a blind increase in water pressure or water injection rate to enhance the coal seam permeability during hydraulic fracturing in underground coal mines. In this paper, the stress state around the fracturing boreholes is analyzed using the in-situ stress coordinate conversion, then a model is established using the maximum tension stress (MTS) theory to calculate the initiation parameters of the borehole rocks. The influences of in-situ stress and coal seam inclination on the hydraulic fracturing initiation pressure and locations in underground coal mines are investigated using the model. The field test is conducted at Tonghua coal mine of Chongqing Songzao Coal and Electricity Co. Ltd. The results show that: according to the stress state in fracturing area, the crack initiation pressure increases along with the increasing coal inclination. With the increase in the coal inclination, initiation location moves to the strike direction. The results in field test are consistent with the calculated result which is that initiation pressure increases along with increasing coal inclination. It verfies the feasibility of the calculation model.