Experimental Study On Acoustic Emission Monitoring And Fracture Instability Characteristic During Hydraulic Fracturing In Coal

Hydraulic fracturing can wet and broken coal body, release elastic energy of coal body and transfer the stress concentration. In the coal mine, it has the function of reducing dust, preventing and controlling rock burst, releasing some gas in advance, weakening the hard roof and so on.Research methods including theoretical analysis, laboratory experiment, numerical analysis had been used to study on influence factors of hydraulic fracturing and its mechanism of initiation and crack propagation, Mainly include the following:(1) Homemade hydraulic fracturing three axis experiment system was used to hydraulic fracturing experiment of coal and rock mass under different confining pressure and different flow rate. Study the effect of stress state and water injection rate on the crack initiation mechanism, strain changes reflect borehole micro-deformation. AE source location monitors the dynamic evolution process of crack initiation, propagation and connection, which realizes effective and complete monitoring for hydraulic fracturing.(2) The borehole wall has tensile or compressive deformation and features zonal deformation. The compressive deformation has good recoverability, while the tensile deformation has a large residual deformation; as principle stress difference reduces, all kinds of interior flaw and weak structure of coal samples themselves play a leading role in crack growth. Consequently, crack propagation paths become more intricate and the number of cracks has also increased.(3) With the increase of flow rate, the greater the strain rate of hole wall, and the strain rate of the raw coal was obviously higher than that of proportioning coal; The cracking pressure of proportioning coal and raw coal has the general trend of increase, but did not increase gradually along with the increase of flow rate, appeared different degree of volatility,especially for raw coal, have larger fluctuation.(4) Carry out simulation analysis of the stress field and acoustic emission change law under different confining pressure and flow in the process of hydraulic fracturing experiment by using RFPA2D software, and the results obtained with hydraulic fracturing experimental results are basically identical; And analyzed the borehole layout and hydraulic cutting seal on the effect of hydraulic fracturing.