| Based on the theoretical analysis, numerical simulation and field test, this text studied the technology of hydraulic fracturing in Pansan mine. The experiment of hydraulic fracturing was did in13-lcoal seam of1791(3) bottom lane. The results show that after hydraulic fracturing measures, the permeability coefficient of coal seam and extraction rate were improved, the internal gas flow was strengthened, and the danger of outburst in coal seam was reduced.Combined with the basic knowledge of fracture mechanics, the location of crack borehole was analyzed and the rules of cracks extension were studied from the aspects of crack initiation and extension. Thus the effect of hydraulic fracturing improve permeability was discussed. It is concluded that the calculation formula of hydraulic fracturing crack initiation pressure is.Using the simulation software RFPA established the calculation model simulation, to simulate the hydraulic fracturing process in different depth coal seam. It is concluded that crack initiation pressure increases with depth of coal seam; From the stress diagram arrived at the conclusion that hydraulic fracturing process can be divided into three stages, namely stress accumulation stage, stage of stable crack extension and crack instability of extension stage; By analyzing the fracturing path, when the maximum principal stress parallel to the coal seam, the fracture took place in transverse direction of coal seam, and when the maximum stress is perpendicular to the coal seam, the fracture was mainly in vertical direction of coal seam.In the13-1coal seam field experiments of hydraulic fracturing, the fracturing process and the investigation plan before and after fracturing were designed in detail. After hydraulic fracturing, the effective radius of extraction in13-1coal seam is about12m, and gas permeability coefficient is0.173m2/(MPa2·d), which is86.5times of the original permeability coefficient. In addition, the gas extraction concentration and extraction quantity improved obviously, the average extraction concentration is78.3%, the scalar average is0.91m3/min, puckering extraction from scalar is0.0396m3/min. Accordingly, the average extraction concentration after fracturing is1.7times that of before fracturing, and the single-hole average extraction from scalar is3.5times before fracturing.Combining with the actual measured, the study of hydraulic fracturing for pressure relief and permeability improvement in13-1coal seam of Pansan mine verify the accuracy of the theoretical analysis results and the numerical simulation results. |
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