Abstract

Enhanced geothermal systems (EGS) have emerged as a key technology for harnessing high-temperature energy from hot dry rock (HDR) at depths of ~3–10 km. Rapid progress in horizontal drilling and multi-stage hydraulic fracturing has enabled creation of large stimulated reservoir volumes, yet major challenges remain — fracture-flow short-circuiting, limited ability to characterize permeability evolution during stimulation, and injection-induced seismicity.

We illustrate and address some of these challenges through coupled thermo-hydro-mechanical (THM) simulations of a partially bridging multi-stage hydraulic-fracture well design that mitigates short-circuiting and delays thermal breakthrough relative to conventional fully bridging designs (Yu et al., 2021a). Building on this framework, we quantify permeability evolution and evaluate induced seismicity driven by long-term thermo-poroelastic stressing during production (Yu et al., 2023). By separating thermoelastic, poroelastic, and combined thermo-poroelastic contributions, we show that thermoelastic stressing dominates stress redistribution and seismicity rate in the stimulated reservoir, while poroelastic effects tend to stabilize and delay failure by moderating stress changes.

During shear stimulation, microearthquakes (MEQs) carry information about hydraulic rock properties, particularly permeability. We develop a mechanistic scaling that links seismic moment as diagnostic of incremental permeability creation during shear stimulation, and validate the relationship using laboratory fault-reactivation experiments with absolute constraints on seismic moment, demonstrating proportionality between permeability change and seismic moment (Yu et al., 2026). This MEQ–permeability linkage is applied to field data from the 2021 Gonghe EGS stimulations to infer the evolving 3D permeability distribution by estimating source parameters (e.g., source radius and stress drop) from raw waveforms. The resulting workflow enables near-real-time reservoir state estimation to support operational decision-making during stimulation.

Bio

Dr. Pengliang Yu is a postdoctoral researcher at the EMS Energy Institute and the G3 Center in the Department of Energy and Mineral Engineering at The Pennsylvania State University. He received his Ph.D. in 2022 from the Geothermal Institute, University of Auckland, New Zealand. His research advances safe and efficient subsurface energy engineering, with an emphasis on enhanced geothermal systems, integrating theoretical analysis, coupled thermal–hydro–mechanical (THM) modeling, machine learning, and laboratory experimentation. Dr. Yu received the 2025 ARMA Rock Mechanics Research Award and the 2024 Penn State EMS Postdoctoral Excellence in Research Award.

Research/Related Papers

Yu, P., Dempsey, D., & Archer, R. (2021). A three-dimensional coupled thermo-hydro-mechanical numerical model with partially bridging multi-stage contact fractures in horizontal-well enhanced geothermal system. International Journal of Rock Mechanics and Mining Sciences, 143, 104787.

Yu, P., Dempsey, D., Archer, R., Marone, C., Elsworth, D. (2023) Numerical Modeling of Permeability Enhancement and Induced Seismicity during EGS Operation using a Partially Bridging Multi-Stage Hydraulic Fracture design. World Geothermal Congress 2023 https://worldgeothermal.org/pdf/IGAstandard/WGC/2023/360.pdf

Yu, P., Eijsink, A., Wang, J., Marone, C., & Elsworth, D. (2026). Seismicity diagnostic of permeability creation from centimeter to subkilometer scales in crystalline rock during shear stimulation. Science Advances, 12(2), eady5201.