Broken, sliding rock can choke geothermal energy flow

Geothermal systems can provide reliable, abundant power by pumping water through cracks in hot rock underground. However, Los Alamos National Laboratory scientists found that when granite cracks develop from sideways pressure, water and heat do not always move through the rock easily.

High temperatures and fluid chemistry can create smooth-sided rock cracks that contribute less to water flow and heat extraction, the new study says. Because the walls are smoother, the cracks can sit closer together, leaving less space for fluid to move through and less surface area for fluid to absorb heat from.

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Why this matters: There has been a lack of research showing how shear fractures — cracks where the two sides of the rock slide past each other — change in geothermal conditions where heat, fluid flow, pressure and chemistry all interact at once.

• A shear fracture is a rock discontinuity (pre-existing fractures or faults) that can be activated, and hydroshearing is a potential stimulation method to enhance geothermal energy production.
• Now, models refined with this Los Alamos data can help engineers design more reliable, high-performing geothermal systems. 

What they did: Scientists measured how fracture permeability, aperture, strength, roughness and fluid chemistry evolve under realistic conditions using rock samples from the Utah Frontier Observatory for Research in Geothermal Energy (FORGE) site near Milford, Utah.

• Their findings capture complex fracture and flow changes, making models more accurate for FORGE and other granite-based projects for enhanced geothermal systems.

Funding: The U.S. Department of Energy (DOE) Basic Energy Sciences program, the DOE Office of Geothermal, and Los Alamos National Laboratory’s Laboratory Directed Research and Development program.

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LA-UR-26-23132