Evolution of Discharge Behavior and Fracture Development During Repeated Electrohydraulic Pulse Fracturing

ABSTRACT: Enhanced geothermal systems (EGS), including super-hot geothermal concepts, offer strong potential as a clean and sustainable energy resource. A major challenge in EGS development, however, is creating and maintaining fracture networks with sufficient permeability and surface area for efficient heat extraction. Hydraulic fracturing is widely used for this purpose, but requires large volumes of water and raises environmental concerns. As a result, pulsed-power electrical stimulation has recently been proposed as an alternative reservoir stimulation technique. Despite its promise, key mechanisms remain poorly understood, including fracture propagation and evoluation, evolution of borehole-fluid electrical properties, and changes in electrical response during repeated pulsing. In this study, we address these gaps through a series of controlled laboratory experiments. Waterfilled boreholes were subjected to microsecond-scale electrical pulses while varying the pulse frequency and the number of pulses applied between measurements. Fluid conductivity and electrode gap resistance were measured before and after pulsing to quantify how the plasma formation changes the electrical behavior of the system. Fracture evolution was evaluated by comparing fracture development at different stages within individual tests and across test series. The results show that borehole-fluid conductivity remains largely unchanged, while electrode-gap resistance decreases with repeated pulsing. At the same time, peak current increases and exhibits a plateau behavior after several pulses within a single test, but decreases to a low value if the borehole fluid is exchanged. Higher peak currents are associated with greater fracture extent, indicating enhanced shock-wave generation.