Study on the superposition effect of stress waves in coal body induced by high voltage pulse discharge fracturing in water

In order to improve the extraction efficiency of coalbed methane in low permeability coal seams, fracturing and permeability enhancement methods are often used. High voltage pulse discharge fracturing in water, as a new fracturing method, has achieved more prominent results than before. This paper focuses on exploring the superposition effect of stress waves passing through primary cracks with different filling media and inclination angles when high voltage pulse discharge are used to crack coal in water, and analyzing the cracking effects in different situations. By preparing specimens and conducting similar simulation tests in the laboratory, it aims to investigate the effect of stress wave superposition on enhancing permeability and fracturing when the filling media are air, water, and lime. Simultaneously establish a numerical model and use PFC2D discrete element simulation software to establish the stress wave superposition effect of three different inclination cracks perpendicular to the maximum principal stress, perpendicular to the minimum principal stress, and at a 45° angle to the maximum principal stress. Research has show that under the same stress conditions, the ability of stress waves to penetrate and cause cracks in different filling media under high voltage pulse discharge is as follows water>lime>air. The ability to hinder the generation and propagation of cracks air>water>lime. Stress wave superposition effect air>lime>water. The effect of different inclination angles of primary cracks on fracturing and permeability enhancement that the fine cracks near the primary cracks show a trend of first increasing, then decreasing, and gradually stabilizing with the increase of peak stress wave pressure. This has a positive effect on improving the permeability of coal seams and effectively extracting coalbed methane.