Study on directional hydraulic fracturing of prefabricated fissures in top coal

In order to improve the cavity and working surface operating environment of thick hard top coal，the top coal prefabricated fissure hydraulic fracturing technology was proposedThe basic principle of directional fracturing was studied and the stress models of borehole and fissures were analyzed then the cracking conditions，the propagation process and its morphology of fissures were obtainedThe RFPA2D-Flow percolation software was used to study the directional fracturing of top coal：In the initial stage of fracturing，the high stress concentration occurs at the tip of the fissures，a relief zone forms in the borehole and the both side of directional fissure and it gradually increases with water injection pressureMeanwhile，the high water pressure zone forms around drilling and directional cracks and it gradually increases with water injection pressureIn the early stage of fissures，the shear failure occurred in the coal body，and a large number of tensile damage occurred in the later stage of fracturingWhen the orientation crack angle α is between 0°~60°，cracks appear and extend，then change directionWhen the inclination angle α is 75°and 90°，the fissures extends along the maximum horizontal principal stress direction