Test Shows Fracturing Can Also Create Underground Water Heating Systems

Abstract

Fervo Energy has shown that fracturing can be used to build a geothermal heating system in hot, hard rock. During a 37-day test at its Project Red test site, the Houston company produced as much as 63 L/s (998 gal/min) of water heated to 336°F. By pumping water from an injection well through fractured hot rock to a producing well, it heated enough water to generate up to 3.5 MW of power, according to a company release. In a world where demand is commonly measured in gigawatts, that’s not much, but it is more than double the highest flow rate from tests going back decades. And unlike those earlier tests, the company has a clear path to heating higher volumes and lowering the cost. “I think this is just a big moment for both our company, but also the industry at large, to finally have this proof point where we can deliver commercial levels of permeability and flow rates for these wells,” said Jack Norbeck, co-founder and chief technical officer for Fervo. The idea of injecting water through hot rock has been around for decades as a way to create enhanced geothermal systems (EGS), but this is the first time someone has achieved this level of flow and is moving next to create a group of geothermal wells for commercial generation. Fervo has taken methods developed to extract oil and gas from ultratight rock and shown they can be used to do something quite different. “Overall, there’s nothing really surprising here—they used a pretty standard shale frac design and observed pretty similar performance from what you would see in a shale play. Or at least, what you’d expect if you used a shale well as a long-term water injector and circulated fluid over to a neighboring production well,” said Mark McClure, chief executive of ResFrac, a reservoir modeling and consulting firm, in a blog post. This fracturing-based option poses a challenge to EGS researchers who live in countries where completions using oil industry fracturing techniques are not an option. “The EGS community has conventionally been focused on ‘stimulating natural fractures,’ and this has led them to use fracture designs that would be considered suboptimal, from the perspective of oil and gas field experience,” McClure said. What Fervo has done is show that fracturing can be used to get past a barrier blocking EGS development using current fracturing technology. “The breakthrough is that someone actually had the guts and organization to go out and do it,” McClure said. Those at Fervo, though, have little time to celebrate the milestone as they focus on improving those methods to economically produce geothermal energy. “In successfully completing this project, we have demonstrated that no major technical barriers exist to deploying horizontal EGS in similar meta-sedimentary or igneous formations to temperatures of approximately 400°F,” according to a Fervo paper. That feat was recognized by a leader at the FORGE test site, which is also doing EGS research and development with substantial financial support from the US Department of Energy.