Exploring the Limitations of Fracture Caging in NextGen Enhanced Geothermal Systems

Fracture caging limits hydraulic fracture growth and the activation of faults during high-rate high-pressure fluid injection using pre-drilled boundary wells around the injection well. If successful, this approach could offer a means to limit injection induced seismic magnitudes by preventing the activation of large faults outside of the cage. This concept has many possible applications, but the most relevant should be geothermal energy where caging could enable safe and economic energy production. In this study we explore the validity of caging using experiments and models to identify the well design, flow rate, economic, and engineering limits for deploying caging successfully in the field. Our work shows that the two primary mechanisms for failure of a cage can be attributed to poor well-fracture connectivity due to poor well placement in uncertain stress fields or due to undersized production wells. Ultimately, we find that (1) fracture caging combined with (2) limited entry injection wells, (3) high-temperature directional drilling, and (4) sustained high-pressure high-rate injection could unlock vast reserves of geothermal energy, all without requiring major new technological advancements.