Optimization design of the system for rock fragmentation by high-voltage pulsed discharge

Aiming to address the lack of a quantitative analysis in the design of the system for rock fragmentation by high-voltage pulsed discharge (RHPD), an optimization design method for the RHPD system based on medium breakdown characteristics and stress impulse constraints is proposed, and a multi-physical parameter coupling mathematical model based on numerical calculation and circuit simulation is constructed. Considering the drilling condition with a 3 1/2 in. wellbore diameter, the optimal energy parameter of the RHPD system with an 88.9 mm claw-shaped discharge electrode is obtained based on the optimization design model. The optimal energy parameter of the system and the corresponding equivalent capacitance, equivalent charging voltage of the system are 58.75 J, 2.966 nF, and 199.03 kV, respectively. Using these optimal parameters, a RHPD system with a coaxial Marx generator as the topological structure is developed. The rock fragmentation performance of the system is tested in a transformer oil-granite medium. After 180 min, a drilling effect is observed on the granite surface, with a hole diameter of 92.66 mm and a depth of 35.70 mm. The energy consumption per unit volume for fragmentation of the developed system is approximately 967 J/cm³, and the rate of penetration at a 10 Hz pulse discharge frequency is approximately 0.3 m/h. This research provides theoretical guidance for the parameter optimization and structural design of the RHPD system.