Experiment on influence of gas on hydraulic fracture process of coal

The experiments under different gas pressures and constant injection rate were carried on,with the self-developed coal hydraulic fracture experimental system,to obtain the resistivity response curves and fracture morphology of coal samples. Based on the test results,the influence of gas on hydraulic fracture process was analyzed. The results showed that the fracture morphology of coal samples tends to be complicated. Number of fracture is much less and wider for coal samples without gas compared with that in the gas-borne coal. Meanwhile,the generated new fractures become less with the increase of gas pressure and the raw fractures are motivated gradually. Gas pressure makes the initial pressure increase. And the resistivity curves show two shapes. Resistivity curve tends to increase if the gas pressure is low and tends to decrease if the gas pressure is high. Based on the test results,the gas may has two actions in the process of hydraulic fracture of coal. First of all,the gas pressure increases the fracture resistivity and thus the initial pressure of coal. And the second one is that the gas induces the water flow into the raw cracks and thus motivates the raw fracture.