| As a typical representative of high gas mining area in China,Huaibei mining area generally has the characteristics of loose coal seam and low permeability,and direct extraction is restricted.Therefore,a systematic study on the ground drilling well extraction mining dynamic unloading gas technology is beneficial to the efficient and economic extraction of unloading gas.In this paper,we take the 1071 working face of Yangliu coal mine in Huabei mining area as the research object,and combine theoretical analysis,numerical simulation and engineering practice to study the response of ground drilling wells in mining areas to overburden movement under the influence of mining movement and the research of anti-breakage technology.The formation characteristics of the "three zones" of the overburden were analysed,and the maximum height of the overburden fall zone at workface 1071 was calculated to be about 11.3m and the maximum height of the fracture zone was about 41 m according to the empirical formula.UDEC software was used to simulate the development of overburden fissures and the horizontal and vertical displacements of different measurement points with the advance of the working face.It was concluded that the relative displacement of the overburden movement is more intense near the open cut than in the middle of the mining area.Therefore,it was considered that the best extraction effect would be achieved by drilling the surface holes within the fissure circle,at a distance of about 60 m from the open cut.FLAC3D software was used to simulate and analyse the variation of the stress uniformity coefficient K at three different locations on the inclination of the ground borehole as the working face was pushed through different distances,and to analyse the spatial and temporal evolution mechanism of stress and strain at three different locations on the inclination of the ground borehole during the coal seam mining process.The comparison leads to the conclusion that the closer the surface drilling well is to the centre of the quarry,the more severe the radial and axial compression is,and considering that the surrounding location of the mining area is a circular fracture zone,where the extraction effect is more effective,the surface drilling well should be considered to be placed in the fracture circle about 10 m from the centre of the quarry.In addition,the damage response mechanism of surface drilling to overburden movement under shear,compression and tension conditions was simulated using the relative movement of the double layer of rock.The main damage mode of surface drilling is shear destabilisation,and the greater the relative slip of adjacent rock layers,the more severe the shear damage to surface drilling.Combining the evolutionary characteristics of off-bed fractures and vertical fractures in the coal seam group mining site and the "O" circle theory,the location of the surface drilling well is optimised from two aspects.In the vertical direction,the final vertical height of the surface drilling hole is set in the gas-rich area;in the horizontal direction,the hole is placed in the "O" circle around the quarry,near the return airway,for better gas production and longer extraction life.In conjunction with the current surface drilling structure,the design of the unloading CBM casing column can be referred to the petroleum system casing design theory;and recommendations are given in terms of drilling construction techniques and well completion enhancement.It also provides a reference for the method of surface drilling to extract unloading gas from coal bed groups.Figure 21 Table 10 Reference 96... |
PDF Full Text Request