Study on the Bottom-Hole Rock-Breaking Law of Electrohydraulic Shockwave

Electrohydraulic shockwave drilling (EHSD) technology can effectively break rocks in the laboratory. However, there are few studies on the effect of this technology on bottom-hole rock, which limits the practical application. It is of great significance to study the bottom-hole rock-breaking law by establishing a model. In this context, a model for calculating the stress wave in the bottom-hole rock under electrohydraulic shockwave was established based on the stress wave theory, and coaxial electrode, bottom-hole stress field, and rock surface crack were considered. Then, the distribution law of stress wave peak value was studied. Based on the key parameters of rocks obtained by experiments, the influence laws of electrical parameters, location parameters, and well depth on the stress wave peak value were further studied. The results showed that EHSD breaks the bottom-hole rock mainly through compression and shear stress. When there are internal boundaries such as surface cracks or bedding planes, tensile stress failure also occurs near these boundaries. With the increase of capacitance and voltage, the damage effect of EHSD increases. With the decrease of the distance between the electrode, rock, and crack, the maximum stress peak value increases. With the increase of well depth, the shear and compressive stress increases, but the effective tensile stress decreases as a whole. Finally, a confirmatory experiment was carried out on granite and limestone samples with coaxial electrodes. The results showed that there are special orthogonal tensile cracks and “bell mouth” shear cracks, which are consistent with the model calculation. The research can improve our understanding of how EHSD breaks bottom-hole rock during drilling, which can promote the application of this technology in auxiliary drilling.