The EGS Collab Project: Outcomes and Lessons Learned from Hydraulic Fracture Stimulations in Crystalline Rock at 1.25 and 1.5 Km Depth: Article No. 103178

Tim Kneafsey, Pat Dobson, Doug Blankenship, Paul Schwering, Mark White, Joseph Morris, Lianjie Huang, Tim Johnson, Jeff Burghardt, Earl Mattson, Ghanashyam Neupane, Chris Strickland, Hunter Knox, Vince Vermuel, Jonathan Ajo-Franklin, Pengcheng Fu, William Roggenthen, Tom Doe, Martin Schoenball, Chet HoppVeronica Tribaldos, Mathew Ingraham, Yves Guglielmi, Craig Ulrich, Todd Wood, Luke Frash, Tatiana Pyatina, George Vandine, Megan Smith, Roland Horne, Mark McClure, Ankush Singh, Jon Weers, Michelle Robertson

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Abstract

With the goal of better understanding stimulation in crystalline rock for improving enhanced geothermal systems (EGS), the EGS Collab Project performed a series of stimulations and flow tests at 1.25 and 1.5 km depths. The tests were performed in two well-instrumented testbeds in the Sanford Underground Research Facility in Lead, South Dakota, United States. The testbed for Experiment 1 at 1.5 km depth contained two open wells for injection and production and six instrumented monitoring wells surrounding the targeted stimulation zone. Four multi-step stimulation tests targeting hydraulic fracturing and nearly year-long ambient temperature and chilled water flow tests were performed in Experiment 1. The testbed for Experiments 2 and 3 was at 1.25 km depth and contained five open wells in an outwardly fanning five-spot pattern and two fans of well-instrumented monitoring wells surrounding the targeted stimulation zone. Experiment 2 targeted shear stimulation, and Experiment 3 targeted low-flow, high-flow, and oscillating pressure stimulation strategies. Hydraulic fracturing was successful in Experiments 1 and 3 in generating a connected system wherein injected water could be collected. However, the resulting flow was distributed dynamically, and not entirely collected at the anticipated production well. Thermal breakthrough was not observed in the production well, but that could have been masked by the Joule-Thomson effect. Shear stimulation in Experiment 2 did not occur - despite attempting to pressurize the fractures most likely to shear - because of the inability to inject water into a mostly-healed fracture, and the low shear-to-normal stress ratio. The EGS Collab experiments are described to provide a background for lessons learned on topics including induced seismicity, the correlation between seismicity and permeability, distributed and dynamic flow systems, thermoelastic and pressure effects, shear stimulation, local geology, thermal breakthrough, monitoring stimulation, grouting boreholes, modeling, and system management.
Original languageAmerican English
Number of pages26
JournalGeothermics
Volume126
DOIs
StatePublished - 2025

NREL Publication Number

  • NREL/JA-6A20-92437

Keywords

  • coupled process modeling
  • crystalline rock
  • EGS Collab
  • enhanced geothermal systems
  • experimental
  • field test
  • flow test
  • Sanford Underground Research Facility
  • stimulation

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