Geothermal energy systems extract heat from deep underground by circulating water through networks of rock fractures. These systems depend on keeping those fractures open and connected under changing pressure and stress conditions. Understanding how fractures form and grow—especially in rock with complex microstructures—is key to improving geothermal energy production. The research described here is part of a collaborative project at the Sanford Underground Research Facility, which offers a rare opportunity to study these processes in a real-world, deep underground setting.

Rock samples taken from the site were deformed under controlled conditions that simulate the high pressures and fluid conditions found at depth. Although the samples responded similarly at first, they fractured at different stress levels depending on the water pressure. Higher water pressure made the cracking process more stable and gradual. Electrical resistivity measurements showed clear changes as the rock began to fracture, offering a way to detect early signs of failure. Following the experiments, high-resolution 3D imaging was used to examine the shape and connectivity of the resulting cracks.