Exploration and practice of stress-strain evolution law of hydraulic fracturing in coal mine

Abstract

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.