Evolution characteristics and mechanism of coal fracture under resonance excitation based on computed tomography scanning

The resonance of coal reservoir induced by external excitation is a kind of environment-friendly stimulation technology. In this work, an experimental system was established to carry out the coal resonance fracturing experiments, and the change trend of fracture structure was investigated by computed tomography scanning. The results showed that under the excitation of vibration within the resonance frequency band range, the coal fracture will gradually expand to failure. There are three forms of coal fracture expansion under the condition of resonant, which are the formation of slip zones in coal, the formation of fracture at phase interface and the formation of ‘void’. When the excitation frequency is constant, the natural frequency of coal decreases gradually with the expansion of fractures, resulting in the vibration frequency gradually deviating from the natural frequency of coal, and the fracture propagation behaviour of vibrating coal gradually changes from divergence to convergence.