Time To See if Fracturing for Steam Pays Off

Abstract

Two test sites in the southwest US have successfully fractured geothermal injection wells in hot, dry hard-rock formations. Now it is time to find out if they can create really hot water by pumping cold water through the fractures in that hot rock into a second well. Both Fervo Energy and Utah FORGE test sites are using fracturing and reported hopeful signs at the recent SPE Hydraulic Fracturing Technology Conference and Exhibition (HFTC). But there are some fundamental differences in the goals of the organizations behind those test sites. Fervo is a startup with an aggressive timeline for commercial geothermal development that uses widely applied methods developed to produce oil and gas from extremely tight rock. FORGE is a research site managed by the University of Utah and funded by the US Department of Energy (DOE). Its goals are to help launch geothermal in hot, dry rocks by trying a number of approaches, as well as promoting the development and testing of tools needed in extremely hot formations. So far, both sites have shown it is possible to fracture the hard rock in granitic or metamorphosed formations. It appears they both created the long, simple fractures needed for high-volume flows. During a panel discussion at the opening session of HFTC, Jack Norbeck, Fervo’s co-founder, and chief technology officer, played up the connections between fracturing for oil production and geothermal. “There’s a lot of similarities about what we’re trying to do and what y’all do every day. Probably the biggest difference is that we try to actually achieve frac hits,” he said. Fervo’s testing is further along, with the second well of its pair of horizontal wells drilled, which FORGE will be doing later this spring. While drilling, they collected proppant from the first well, which will be the injector, indicating a fracture connecting the pair. Fervo’s modeling suggests they created a fracture network with the surface area needed to heat the 40,000–60,000 B/D of steam needed per well, which is in line with FORGE’s well capacity, Norbeck said. High-volume flows matter because the high upfront cost of building a hot-rock injection geothermal system limits the number of wells they can build per power plant. “We were able to show that the stimulator reservoir volumes that we generated in this project were sufficient for economic production,” Norbeck said. As with fracturing for oil production, creating a large volume of fractured surface area is a prerequisite. But they still need to show they can produce enough water at a high enough temperature over a long period of time.