Application Of Hydraulic Fracturing In Low Permeability Coal Seam In Uncovering Coal At Cross-hole

Coal and gas outburst has always been chief offender which affects normal duration, and threatens the safety of workers, but coal and gas outburst is mostly happened in the uncovering coal in crosscut. Panyi East Mine coal uncovering 13-1, by the relevant information and technical means, predict gas pressure of uncovering coal is about 6Mpa, gas content is about 15 m3, with high risk, so adopt hydraulic fracturing hydro-fracture technology to keep uncovering coal in crosscut safely.To achieve a normal schedule and safe exposing coal seam 13-1, this paper firstly analyzes hydraulic fracturing characteristics,then use RFPA-Flow simulation software to make numerical simulation, finally practiced in PanYi East mine according to fore principle of parameter choice of hydraulic fracturing test parameter.According to the research of hydraulic fracturing relief anti-reflection, find it easy to form plastic zone around the pressure hole, and the radius of plastic zone is proportional to the borehole diameter. Starting-crack is decided by water pressure and rock stress, that is coal seam burst when tangential stress is bigger than tensile strength of coal seam. The location of fracture initiation is concerned with side stress coefficient λ,when λ> 1, initiation point is in the middle;when X=1, initiation direction is random;when X<1, initiation point is on two sides of the borehole.By RFPA-Flow numerical simulation, find fracture pressure of coal seams is concerned with borehole diameter, the larger borehole diameter, the lower the pressure required for crack initiation. Simulation results seam initiation pressure is about 33MPa.Field test shows:After taking hydraulic fracturing process, the average gas extraction concentration was 63.2% and the average extraction purity is 0.235m3/min, single borehole extraction purity is 0.0610m3/min.The average gas drainage concentration is 1.2 times as pre-fracture,average single borehole extraction purity is 3.5 times as pre-fracture. By measuring the moisture content of coal seam and gas content and, finds that the scope of hydraulic fracturing come up to as far as 50m.Through preliminary theoretical analysis and results of numerical simulation, hydraulic fracturing test is successfully implemented in Panyi east mine,achieves the safe purposes. This has some significance for subsequent hydraulic fracturing operations.