Characterization of the strain response of the borehole wall in coal rock fractured by high pressure gas

In order to explore the relationship between cracks and strains in the process of high-pressure gas fracturing, high-pressure gas fracturing tests with five impact angles (0°, 30°, 45°, 60° and 90°) were carried out using a true triaxial test system, and the fracture morphology of the coal rock body, air pressure curve and the strain response of the borehole wall in the process of air fracturing were investigated. The results show that: (1) with the increase of angle, the fracture morphology of coal rock body shows the distribution characteristics of complex and then single; (2) the air pressure curve in the fracturing process shows four stages of air pressure rise, steep air pressure drop, pressure aggregation, and stable pressure release; (3) the results of the monitoring of the borehole strain show that the data of the borehole strain mainly consists of tensile strain, and there are two obvious peaks in the curves. (4) When the impact angle is 45, and the specimen is easy to sprout complex cracks inside. network, the fracturing effect is the best. The conclusion has certain guiding significance for the effect of pressure relief and penetration enhancement in high-pressure coal rock fracturing project.