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Numerical Modeling of Hydraulic Fracturing in Super-Hot EGS
Nicolas CARDENAS ACEVEDO, Kiseok KIM, Wencheng JIN
[Texas A&M University, USA]
The development of Super-Hot Enhanced Geothermal Systems (SHEGS) presents a transformative opportunity to access vast, untapped geothermal energy resources. However, the extreme conditions of super-hot geothermal reservoirs pose significant technical challenges. One critical question is whether hydraulic fracturing can reliably create a fracture network that connects injection and production wells for effective heat extraction. While recent successes in stimulation and circulation tests at the Utah FORGE site and Fervo Energy’s Cape Project affirm this possibility for conventional EGS, laboratory experiments indicate that under ultra-high temperatures, cloud-like fracture networks tend to form in granite due to the low viscosity of injected fluids. We hypothesize that injecting high-viscosity fluid can promote the formation of connected fractures in super-hot geothermal reservoirs. To test this, we developed fully coupled hydro-mechanical numerical models based on the parallel, open-source MOOSE (Multiphysics Object-Oriented Simulation Environment) framework and spring-lattice XSite software. The MOOSE model employs the discontinuous Galerkin method and the PPR potential-based cohesive zone model to simulate fracture propagation, incorporating a traction-separation law that captures the brittle-to-ductile transition relevant to SHEGS conditions. Fluid flow is modeled using the cubic law for fractures and Darcy’s law for the surrounding rock matrix. The XSite model utilizes the synthesized rock mass concept and is capable of simulating arbitrary fracture paths upon fluid injection. Using these models, we conduct a parametric study, varying the injection rate and temperature—hence, the viscosity—of the injected fluid at both single- and multi-cluster scales. Results show that injecting cooler, high-viscosity water can indeed induce hydraulic fractures under SHEGS conditions. However, the resulting fracture geometries differ markedly from those observed in conventional EGS due to ductile fracture propagation.
Topic: Enhanced Geothermal Systems