Research On Hydraulic Fracturing Pretreatment Technology Of Hard Rock Fault In Coal Mining Face

When the coal mining face exposes the hard rock fault,it causes the production problems such as serious loss of the shearer pick,slow advance speed of the working face and poor coal quality.In the existing technology,loose blasting method,carbon dioxide blasting method and static fracturing technology are usually used to deal with hard rock faults,so that the working face can pass through the hard rock faults smoothly.However,there are the following problems in this kind of treatment of hard rock faults :1)The shock wave generated by blasting may affect the high-precision electronic components required by the intelligent working face and the strict control of modern mine pyrotechnics.The blasting method does not have applicability;2)The use of CO2 fracturing blasting technology is cumbersome and inefficient;3)The static fracturing technology needs to drill dense boreholes and increase the construction process.The prolonged reaction of static fracturing cartridges or slurry impedes the effective production of a working face.A green and effective way to preprocess hard rock faults is urgently required,due to the inadequacies of the technologies mentioned above.In this thesis,double-hole hydraulic fracturing technology is proposed to pretreat hard rock faults.According to the working conditions of 2112 working face,theoretical analysis,laboratory experiments,numerical simulation and other research methods are used to systematically study the hydraulic fracturing to improve the rock breaking efficiency of shearer,and expand the application of hard rock faults in coal mining face.The main results are as follows:(1)The basic rock mechanical properties of hard rock faults exposed in 2112 working face were tested,and the production problems of working face caused by hard rock faults were analyzed.The hydraulic fracturing technology is used to measure the ground stress in the hard rock fault area of the working face,which provides data support for the laboratory experiment and numerical simulation of hydraulic fracturing.(2)The transparent gelatin material was used to replace the traditional rock as a similar simulation experiment material,and the self-developed experimental device was used to study the initiation and propagation of non-directional hydraulic fracturing fractures under three-dimensional conditions.The influence of principal stress difference and preset borehole dip angle on the propagation law of hydraulic fractures is studied.The results show that hydraulic fractures and radial fractures may occur simultaneously in non-directional hydraulic fracturing.Axial fractures and radial fractures have tendency to expand to the maximum horizontal low stress direction under the action of stress difference.The larger the principal stress difference is,the smaller the fracture deflection is,and the radial fracture growth rate is slow,mainly in the axial direction.Radial hydraulic fractures are more likely to occur when the borehole is inclined than when it is perpendicular to the maximum principal stress.(3)The seepage software RFPA 2D is used to simulate the fracture propagation law of double-hole hydraulic fracturing.The effects of hole spacing and lateral pressure coefficient on the propagation and intersection of double-hole hydraulic fractures are studied.The results show that the larger the hole spacing is,the hydraulic pressure required for the intersection of hydraulic fractures between two holes and the number of tensile fractures at the intersection of fractures will increase,forming a complex fracture network structure.There is obvious stress concentration at the tip of each hydraulic fracture.The larger the lateral pressure ratio,the boreholes on both sides tend to fracture and intersect from the horizontal direction.(4)Based on gelatin hydraulic fracturing experiment and numerical simulation results,the main hydraulic fracturing parameters such as water injection fracturing,hole spacing and effective length of single-sealed capsule are determined,and the matching fracturing equipment is selected and optimized.Two fracturing schemes were set up and the field industrial test of hydraulic fracturing was carried out on the 2112 working face.The results show that the shearer can pass through the hard rock fault after hydraulic fracturing pretreatment.There are 60 figures,17 tables and 71 references in this thesis.