Research And Application Of Hydraulic Fracturing Control Technology For Hard Roof In Xiaojiawa Coal Mine

In view of the fact that the mining face of Xiaojiawa Coal Mine is covered with hard roof slab,and the working face has long-term hidden dangers such as too long overhanging distance at the end and severe rock pressure in the goaf roadway,this thesis has carried out the research and application of hydraulic fracturing control technology of hard roof in Xiaojiawa Coal Mine through comprehensive research methods such as field investigation,laboratory test,theoretical calculation,numerical simulation,and industrial test.In this thesis,the process of hydraulic fracturing is theoretically analyzed,and the theoretical initial fracturing pressure is determined under the condition of homogeneous,continuous and no fracture;RFPA is used to simulate and analyze the process of hydraulic fracturing crack propagation of coal and rock mass,and determine the hydraulic fracturing radius;3DEC numerical simulation software was used to simulate the hanging length of the hard roof plate and the characteristics of the stope rock pressure appearance of the 110805 working face and the law of the stope rock pressure appearance before and after the top cutting of the 211304 working face;Industrial tests of directional hydraulic fracturing,shallow hole hydraulic fracturing and deep hole cyclic fracturing were carried out on site.The main conclusions of the study are as follows:(1)Through theoretical calculation and numerical simulation,it can be concluded that under homogeneous,continuous,and fissure free conditions,the theoretical initial fracturing pressure of the roof fracturing layers of the 8#and 13#coal seams is between 22.87 and 25.97 MPa,and the hydraulic fracturing macroscopic fracture length is 4.5 m.Under hydraulic fracturing,sandstone strata exhibit a nearly linear distribution after fracturing;When a coal seam cracks,the cracks exhibit a linear diffusion distribution characteristic.(2)Through the simulation of the roof collapse characteristics of the 110805working face,it is found that the stress concentration peak at the suspended roof length from 16m to complete collapse decreases from 20MPa to less than 10MPa,and the stress at the hinge point decreases from 38MPa to 18MPa;When the cantilever of the lateral roof of the working face is too long,the cantilever is subjected to the load of the overlying strata,and the coal pillar is squeezed,resulting in severe deformation of the roadway along the goaf.With the decrease of cantilever length,the fracture roof forms a lap structure at the edge of the coal pillar,which reduces the load of the coal pillar and slows down the deformation of the roadway along the goaf.(3)Through the simulation of different suspended roof distances in 211304working face,it can be concluded that under the conditions of natural collapse and roof cutting pressure relief,the critical points of vertical stress distribution on the left side of the coal pillar are 4m and 2m,respectively,and the roof cutting pressure relief effectively reduces the distribution range of tensile stress zone;The displacement after roof cutting and pressure relief is obviously greater than that under natural collapse;At the side of the goaf roadway,the displacement of the coal pillar side is reduced from 213 mm to 128 mm under the roof cutting pressure relief,which greatly reduces the extrusion pressure and horizontal deformation of the coal pillar side;The vertical stress distribution at 25m above the natural collapse is similar to that at 35m above the roof cutting pressure relief.The bearing layer is transferred upward for about 10m,and the roof cutting can make the roof bearing stress distribution more balanced.(4)Through industrial experiments,the use of hydraulic fracturing technology resulted in timely collapse of the top plate at the end,and the suspended ceiling area was controlled at 2×3m~2;The deformation of the goaf roadway has been significantly reduced,with the maximum displacement of the top and bottom plates being about543mm and the maximum displacement of the two sides being 446mm,greatly alleviating the degree of rock pressure manifestation in the goaf roadway.At the same time,three construction techniques,directional hydraulic fracturing,shallow hole single fracturing technology,and deep hole cyclic fracturing,were compared and analyzed.The results showed that deep hole cyclic fracturing can improve construction efficiency and be more conducive to the implementation of subsequent hydraulic fracturing work.