The Hydraulic Fracturing Parameters Optimization Of Underground Borehole In Sijiazhuang Coalmine

The hydraulic fracturing technique as an important antireflection technique hasbeen widely used in the development of CBM. Taking the hydraulic fracturingtechnique underground, could extract the borehole spacing and improve the gasextraction concentrations. The purpose is to achieve the safe and efficient exploitationof coal. However, the ground hydraulic fracturing equipment, construction site and soon is different from the underground. So it is localized and blindfold to useindiscriminately the CBM well fracturing technique the underground. Therefore,according to the unique characteristics of the coal seam and construction site conditionsunderground, developed to match the underground borehole hydraulic fracturingparameters optimization theory system is a pressing problem.According to the geological strength factor (GSI) and the coal structure features,derived a quantitative characterization method of the coal structure which based on theGSI. With this method, combined with the geological evolution history of Si Jiazhuangmine, divided the No.15coal seam quantitatively in the coal structure. Classify thefracturing technique which is applicable in the different GSI coal. The boreholes alongthe coal seam and the borehole across the coal seam are adoptted to the GSI>45tofracture. The pseudo-reservoir boreholes are adoptted to the GSI <45to fracture. Usingthe theoretical analysis and laboratory studies, combined with the fracturing test, hasoptimized the fracturing borehole parameters (distance, inclination and azimuth). Obtainthat the optimal distance of the fracturing hole is2times of the fracture’s half length.The best inclination is elevation. The best azimuth of the borehole is as vertical as withthe orientation of the maximum principal stress and the original fracture. Compare withthe borehole’s forming, the sealing technique’s complexity degree, the economy andother aspects, to analysis the advantages and disadvantages of the cement sealingprocess and the packer sealing process. Obtain that the boreholes along the coal seamshould adopt a special cement mortar sealing, the borehole across the coal seam and thepseudo-reservoir borehole should adopt the packer sealing. Numerical simulating by theANSYS software, combined with theoretical analysis, studied the sealing depth of thetunnel place and the roadway’s two sides. Found that the best sealing depth for thetunnelling place is10-15m. The best sealing depth for the roadway’s two sides is14-20 m. Basing on the Hoek-Brown rupture criteria, combined with GSI to establish thecalculated model of the coal’s tensile strength, fracture pressure, extending pressure andthe pumping pressure. Comparatively analysis the filter loss performance, reservoirdamage and sand carrying capacity properties of three commonly used fracturing fluids(activity water, linear plastic fluid and gel fracturing fluid). Studied that optimize theactivity water is the best fracturing fluid for the underground borehole hydraulicfracturing in Si Jiazhuang coalmine. By modifying the KGD model, established thecomputational geometry model of the fracture for the underground borehole hydraulicfracturing in coal seams. Optimized a pumping injection program of liquid injectiondisplacement and total liquid which is apply to fracture in different GSI coal for SiJiazhuang coalmine.Based on the optimization model and theory, fractured testing in the15201returnair roadway by using the borehole along the coal seam, testing in the north limb beltroadway and the15203alternate interior tail roadway. The test results are close to thetheory. The verification of underground borehole hydraulic fracturing parametersoptimization theory and model are reasonable and feasible.