Browsing by Author "Schoenball, Martin"

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    The EGS Collab project: Outcomes and lessons learned from hydraulic fracture stimulations in crystalline rock at 1.25 and 1.5 km depth
    (Elsevier, 2025) Kneafsey, Tim; Dobson, Pat; Blankenship, Doug; Schwering, Paul; White, Mark; Morris, Joseph P.; Huang, Lianjie; Johnson, Tim; Burghardt, Jeff; Mattson, Earl; Neupane, Ghanashyam; Strickland, Chris; Knox, Hunter; Vermuel, Vince; Ajo-Franklin, Jonathan; Fu, Pengcheng; Roggenthen, William; Doe, Tom; Schoenball, Martin; Hopp, Chet; Tribaldos, Verónica Rodríguez; Ingraham, Mathew; Guglielmi, Yves; Ulrich, Craig; Wood, Todd; Frash, Luke; Pyatina, Tatiana; Vandine, George; Smith, Megan; Horne, Roland; McClure, Mark; Singh, Ankush; Weers, Jon; Robertson, Michelle
    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.
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    Source mechanism of kHz microseismic events recorded in multiple boreholes at the first EGS Collab testbed
    (Elsevier, 2024) Qin, Yan; Li, Jiaxuan; Huang, Lianjie; Schoenball, Martin; Ajo-Franklin, Jonathan; Blankenship, Douglas; Kneafsey, Timothy J.; EGS Collab Team
    Continuous microseismic monitoring using three-component (3C) accelerometers deployed in multiple boreholes allows for tracking the detailed evaluation of mesoscale (∼10 m scale) fracture growth during the fracture stimulation experiments at the first Enhanced Geothermal Systems (EGS) Collab testbed. Building on a well-constrained microseismic event catalog, we invert for moment tensor of the events to better understand the fracture geometry and stress orientations. However, it is challenging because of the unknown orientation of 3C accelerometers and low signal-to-noise-ratio nature of high-frequency (several kHz) monitoring. To address these challenges, we first perform the hodogram analysis on the continuous active-source seismic monitoring (CASSM) data to determine the orientations of the 18 3C accelerometers. We then apply the principal component analysis (PCA) to the observed microseismic waveforms to improve the signal-to-noise ratios. We perform a grid search for the full moment tensor by fitting the PCA-denoised waveforms at a frequency range of 5 to 8 kHz. The moment tensor results show both the creation of hydraulic fractures and the reactivation of natural fractures during the hydraulic stimulations. Our stress inversion based on the inverted moment tensors reveals the alteration of stress regime caused by hydraulic fracture stimulations.