Research On Coal Softening And Hydraulic Fracturing’s Expanding Under Facturing Fluid

Coal seam hydraulic crack softening technologies, is through the fracturing and softening action ways, and to the purpose of the top-coal is weakening in advance,is a coal mine safety guarantee of mining technology. Based on Xiao honggou water injection softening as project background, in view of Xiao honggou B1+2coal seam,using theoretical analysis and experimental research, numerical simulation and field test of research methods, We obtained the following conclusions:We conducted a hydrophilic test of Biand B2, according to the results of the coal sample water test and the coal sample fracture statistics, we determine Bi coal samples more broken compared to the B2samples,and the pores are mostly open cracks, indicating that the B1coalkind of coal than the B2sample is easy to soften; According to different fracturing fluid hydrophilic test, combined with softening criterion, we determine the softening properties of the fracturing fluid (the second> fourth>first> third).After immersion of the fracturing fluid saturated coal samples for uniaxial compression tests and ultrasonic tests, test results show that compared with the natural state, except the coal sample specimen, the specimen fracturing fluid under the action of mechanical parameters are subject to varying degreesweakening of the fracturing fluid,it has a softening effect of the coal sample, but to soften the effect, Based on the test result, we give the damage evolution variables and two constitutive model under fracturing fluidUsing F-RFPA software simulation of fracturing fluid under the action of water pressure on hole crack, that was based on matrix mechanics parameters attenuation model and matrix heterogeneity the model.Because of the pressure of fracturing fluid effect of coal and the natural state of coal physical parameters and homogeneous degree coefficient assignment is different, compared with the natural state, under the action of external force, coal under fracturing fluid, is easier to crack initiation and propagation of cracks, crack surface is rough, bifurcated crack forming time is short, amount is more also, and eventually formed the main crack and vertical included angle is bigger, moreover, energy can release much slower, i.e. injury is a gradual process.B1+2coal seam top-coal caving is evaluated, we know that top-coal caving is poor; Proceed with coal seam strength, mining depth, we reveal mechanism of the fracturing fluid to raise the top coal caving.Research results in steep hard top coal caving mining, the results show that it can increase top coal caving and the recovery rate.