The Calculation Model of Initiation Pressure During Hydraulic FracturingProcess of Perforated Coal Seams

摘要

There are lots of cleats, fractures and many other structure weak planes in coal seams, which make the bulletholes and cleats intersecting. During the hydraulic fracturing process in coal seams, fractures will initiate at coal rockbody of borehole wall, and cleats or fractures are different from conventional reservoirs. Thus a new model for initiationpressure calculation during coal seams fracturing should be established. Based on the rock mechanics and elasticitymechanics, and also on network distribution characteristics of coal seam cleats and the space position relationshipsbetween the intersected bullet holes and cleats, stress distribution around the bullet holes and at the cleats wall werededucted. The model was established in tensile failure condition. The calculated initiation fracture pressure of Well HX-3was 10.71MPa. The pressure obtained from bottom hole pressure gauge was 11.24MPa. The relative error was 4.72%.The model could be applied for initiation pressure calculation during hydraulic fracturing process in coal seams. Thefractures would initiate at the cleats during fracturing.