In order to explore the evolution law of stress and strain in the process of hydraulic fracturing, a hollow inclusions stress-strain gauge was used for monitoring. The results show that the influence range of high-pressure water spreads to the monitoring borehole at 47m after 2 hours of hydraulic fracturing, and its influence on the stress-strain monitoring point reaches the maximum, and the strain tends to be stable in the later stage. After 6 days of hydraulic fracturing, the strain returns to a stable state without any change, but it is still larger than the state before hydraulic fracturing. During hydraulic fracturing, the increment of principal stress increases, but the amplitude is different. Hydraulic fracturing mainly affects the increment of vertical stress, which is related to the stress-strain monitoring point and the space location of the hydraulic fracturing borehole. After hydraulic fracturing, the stress increment decreases gradually and tends to return to the original stable state due to the gradual pressure relief of fracturing fluid, but it is still larger than the state without hydraulic fracturing. Hydraulic fracturing has little effect on the azimuth and dip angle of coal and rock mass. The stress-strain law can provide reference for the exploration of the coal seam permeability increasing mechanism of hydraulic fracturing.
In soft coal bedding drilling hard into the problem of hole, based on the drilling of coal in the process of motion, from two aspects to improve the traditional drilling technology, selection of high power, large torque drill and selecting reasonable parameters of drilling tools and better way of powder, formed a “high power drill, shallow blade spiral drill pipe, wind pressure in the wind” of the construction process. The field application test was carried out in Xinxin Coal Mine of Yunnan Province, and the test results show that the average monthly footage of drilling rig is 8000 m/rig•month. The average depth is 137m, the primary pore formation rate reaches 90%. Compared with the original drilling technology, the new technology increases the average hole depth by 12%∼70%, the drilling efficiency by 30%∼46%, the extraction concentration by more than one time, and the single hole extraction amount by 33.6%. The drilling technology of soft outburst coal seam has improved the drilling efficiency and realized the full coverage of gas drainage in working face, which is worthy of reference and reference in soft coal seam mine.
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