Direct Observation of Fault-Zone Pore Pressure Evolution and Induced Slip from Stimulation of Enhanced Geothermal Reservoirs

Taeho Kim, Eric M. Dunham, Sireesh Dadi, Paul Segall, Aleksei Titov, & Shanna Chu

Submitted September 7, 2025, SCEC Contribution #14775, 2025 SCEC Annual Meeting Poster #TBD

Advancements in enhanced geothermal systems (EGS) through the use of multi-stage, plug-n-perf stimulation are rapidly improving the prospect of large-scale geothermal energy production. We present unique observations and models, of fault activation in an EGS at Project Cape, Utah (operated by Fervo Energy), where a downhole pressure gauge was likely located inside a fault damage zone. This rare dataset provides an unparalleled opportunity to probe fundamental earthquake physics, offering rare constraints on the coupled evolution of pore pressure, aseismic slip, and seismic rupture on a natural fault.

We focus on stimulation of three horizontal wells near a vertical monitoring well hosting the downhole pressure gauge. Fault orientation was identified by clustering the microseismicity catalog through density-based unsupervised learning. The initial shear to effective normal stress ratio on the fault is between 0.31 and 0.45; approximately 7 – 18 MPa pressure increase is required to reach criticality. Stimulation of the first well brought the fault to failure without triggering appreciable seismic slip.

The two largest observed pressure increases show qualitative differences. During stimulation of the first well, pressure changes are consistent with fluid leak-off and pressure diffusion away from a nearby hydraulic fracture into the low permeability formation. This model cannot explain the more rapid and larger pressure increase observed during stimulation of the two additional wells, which is more consistent with pressure transmission along a high-permeability fault damage zone hosting the pressure gauge.

Seismicity initiates near, but some distance away from, fracture–fault intersections. The lack of seismicity close to the intersections, combined with casing deformation where the fault intersects an adjacent well, implies aseismic slip where the pressure change was largest. Bottom hole treatment pressure suggests that pressure may have been large enough to open or dilate the fault. The observed heterogeneity of slip behavior along the fault raises fundamental questions about controls on seismic vs. aseismic slip. Possible explanations include an increase in nucleation size from low effective stress, heterogeneity of frictional properties, or heterogeneity of initial stress. We are developing earthquake sequence models, involving coupled slip and pressure diffusion through the fault zone, to explore these ideas.

Key Words
Induced Seismicity

Citation
Kim, T., Dunham, E. M., Dadi, S., Segall, P., Titov, A., & Chu, S. (2025, 09). Direct Observation of Fault-Zone Pore Pressure Evolution and Induced Slip from Stimulation of Enhanced Geothermal Reservoirs. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)