Experimental Study on the Rock Breaking Effect of Stepped Cyclic Electro-Hydraulic Shockwaves: The Influence of Liquid Conductivity and Electrode-Rock Spacing

Stepped cyclic electro-hydraulic shockwave drilling technology (S-EHSD) utilizes cyclic alternating shockwave loads to break rocks more quickly. In recent years, S-EHSD is considered a potential new technology that can effectively improve the drilling speed of oil and gas wells. Therefore, it is necessary to study the impact of key influencing factors on the rock-breaking effect. In this study, rock-breaking experiments were conducted under different liquid conductivity and electrode-rock spacing, which are the two main factors that affect the rock-breaking effect. The results showed that: (1) With the increase of liquid conductivity, the impact time required for rock breaking first increases and then decreases. When the liquid conductivity is 4 mS/cm, the electrical energy leakage and breakdown speed reach the optimal balance. At this time, the impact times required for rock breaking are the smallest, and the internal damage growth rate and mechanical strength degradation rate are also the fastest. (2) As the electrode-rock spacing increases, the impact times required for rock breaking gradually increase, and the diameter of the crush pits area on the rock sample top face also gradually increases. The ultrasonic testing data showed that as the electrode-rock spacing decreases, the attenuation of P-wave amplitude and dynamic mechanical parameters increases exponentially, which is consistent with the attenuation law of shockwave peak value in liquid media. Overall, this study deeply revealed the influence of liquid conductivity and electrode-rock spacing on rock breaking effect, which provides a basis for the field application of this technology and can improve our understanding of the application effect of this technology in actual drilling.