Study of the fracturing behaviour of an electrohydraulic shock wave in sandstone under static pressure

Abstract

To understand the application of electrohydraulic shock waves (EHS) in deep rock formations, the fracturing behaviour of repetitive EHS under a static pressure environment is studied in this paper. The static pressure environment of sandstone is simulated and a load model of the transmission wave of EHS at the liquid–rock interface is proposed. Analysis of the spatial distribution, dense zone and fracture zone of microcracks shows that static pressure has a significant inhibitory effect on the formation, distribution and growth of microcracks under repetitive EHS. Compared with normal pressure, cracks in a static pressure environment are mainly concentrated around the well hole, the microcracks are denser and the extension length is shorter. At the same time, the degree of damage is established to evaluate the overall cumulative damage to the sandstone. The coupling relationship between degree of damage, static pressure, discharge energy and discharge times is fitted. The fitting model shows a behaviour of continuous decelerating growth of microcracks, which can be divided into two phases, an initial growth phase and a slow-growth phase. The increase in static pressure mainly suppresses the initial growth phase, and the discharge energy needs to be increased to promote the initial degree of damage and the rate of accumulation of microcracks in the slow-growth phase. The rate of accumulation of microcracks in the slow-growth phase can be controlled through multi-level adjustment of the discharge energy. This paper provides guidance and simulation methods for rock fracturing applications of EHS in static pressure environments.