Stress Variation Characteristics Of Cross-Seam Borehole And Its Effect On Gas Drainage

Coal and gas outburst is an urgent problem to be solved in coal mine safety production, coal and gas outburst accidents often occur in the process of outburst coal seam. In our country, the condition of mining protection layer is less, and the gas is gradually becoming the main technical means to prevent coal and gas outburst accident. At the same time, for low permeability and high gas coal seam, conventional pre-pumping method is not effective. The breakthrough point of improving the effect of coal seam gas pre-pumping lies in the layout parameters and methods of drilling holes. At present, in solving the problem of low permeability coal seam, the main problem is to use the combination of hydraulic drilling and common drilling to achieve the purpose of unloading pressure and increasing the permeability of coal seam. Therefore, it is helpful to the optimization design of drilling hole to study the variation characteristic around the borehole. There is great significance to the overall planning of mine production, ease the pressure of mining and promote coal and gas mining.In this paper, use the physical experiment and numerical simulation, theoretical analysis and industrial test method, to carry out relationship of the hole diameter, hole inclination, pre-extraction time, extraction pressure of sterss distribution around the borehole and drainage influence radius, in order to optimize the location for drilling combes. The main research results are as follows:(1)Study on the hole diameter, angle, initial stress, strength of coal seam stress variation of borehole surrounding. The hole diameter increase caused by coal seam internal dumping pressure range increases, and stress concentration zone will transfer to deep coal seam; at the same position, the strength of small coal unloading pressure high degree, coal seam in the stress concentration zone of stress value and the initial stress compared to the increase in the degree; initial stress value is greater, vertical direction of drilling pressure relief range was larger, relief degree is higher and higher, however, in the horizontal direction stress concentration degree will be greater.(2)Study on relationship the hole diameter, obliquity, pre-drainage time, drainage with negative pressure and drainage influence radius. Borehole inclination would increase borehole gas drainage radius decreases first and then increases, in the angle of 75 degrees, 90 degrees to minimum; with the increase of the hole diameter, drillingdrainage radius of influence also increases, however, the rate of increase decrease and eventually constant; drainage radius and pre-extraction time and extraction of negative pressure relationship showed a similar trend; slotting borehole radius is about 4-5 times that of ordinary drilling and slotting borehole pressure relief effect and the slotted disc has a direct relationship.(3)To determine the reasonable layout of regional coal roadway and the bottom roadway, the theoretical analysis of the spatial position relation of coal roadway and roadway bottom. From the wear layer dip angle of hole, stress distribution of bottom drainage roadway and vertical distance and horizontal distance between the relations of research, the results show: coal roadway and bottom drainage roadway over the distance should be greater than 17m; horizon of bottom drainage roadway can affect its position determined, inclined coal seam on the bottom pumping lane position choice of the smaller impact, established calculation model of borehole length.These research results have important theoretical and practical significance for optimizing borehole layout and improve the drilling parameters.