Mechanism of a novel ultrasonic promoting fracturing technology in stimulating permeability and gas extraction

Coalbed methane exploitation can optimize the energy composition, help to achieve carbon neutrality and carbon peak. As a key factor affecting the effect of coalbed methane production, fracturing fluid can greatly improve the micropore structure of the coal seam and the effect of gas desorption, and improve the efficiency of gas extraction. Due to the ordinary physical and chemical reaction rate between fracturing fluid and coal and the short effective extraction time, it is difficult to achieve an effective extraction effect. A novel ultrasonic promoting fracturing technology is proposed in this paper to increase gas production, that is, applying an ultrasonic field to the coal seam during the fracturing and extraction stage to enhance the fracturing effect, the desorption effect, and the integrity of the seepage channel. This technology uses the mechanical, cavitation, thermal and chemical effects of ultrasonic waves to strengthen the interaction effect of fracturing fluid and coal and gas extraction rate. In the ultrasonic–temperature–pressure multiple fields experiments, it is found that after the application of ultrasonic, the effect of the fracturing fluid was greatly improved, the diameter of the macropores was significantly increased, and a large number of new micropores were generated. Compared with the effect of only fracturing fluid, the pore volume, fractal dimension, and permeability of coal were increased by 14.1 %, 15.9 %, and 26.9 %, respectively. The experimental results prove the feasibility and effectiveness of the ultrasonic promoting fracturing technology.