Enhanced Geothermal Systems Explained: Fervo and the Tech Behind Deep Drilling Geothermal
In early October, enhanced geothermal company Fervo Energy began producing 33 MW of energy from its first large-scale geothermal project at Cape Station, Utah selling that to Shell Energy.
Fervo’s project will come online in phases, with Phase One made up of three 33 MW so-called “GeoBlocks.” The next two of those GeoBlocks will come online by the end of the year. An additional 400 MW is should come online in 2028.
This is different than conventional geothermal wells that rely on underground reservoirs of hot water. Those are typically located near areas of tectonic activity, along the planet’s so-called “ring of fire.”
One needs not heat, water, and permeability in the rock, so new water can enter the system, heat up, and generate additional steam. The world’s largest such complex is the Geysers in California. It once generated 1,875 MW of energy, but too many wells were drilled into it, overharvesting the available steam. The project was partially resuscitated by injecting treated wastewater, so that it now yields about 900 MW.
By contrast, the new geothermal technologies are either advanced or enhanced. Both involve drilling miles down into hot - and often very hard – dry rock, such as granite, deploying horizontal drilling and fracking technology.
Advanced geothermal involves the creation of a networked horizontal closed loop of underground pipes, with the surface area of the pipe exposed to the hot rock.
These networks are difficult to construct. The most advanced is Eavor’s project in Germany, connecting two wells almost five miles deep. The original goal was to connect 12 lateral pairs of pipes, each pair about four miles in length, but drilling difficulties resulted in connection of only six of the lateral wells.
Enhanced geothermal differs in that it utilizes fracking technology both for the drilling and the reservoir creation. It doesn’t use a closed loop system – water can circulate directly through the rock.
Fervo’s technology is truly astonishing, with wells drilled three to four miles deep, with the bits then steered to move horizontally for about a mile through rock at 400-450 degrees F.
A pair of wells are drilled, with one vertical/horizontal wells serving as the injection well, and the other as the production well.
Solid steel pipe is positioned into the horizontal borehole by lowering individual threaded 30-40 foot sections of pipe and moving them through the elbow of the hole, with its wide turning radius. They are then screwed together into a single string, and cemented in place.
Next is multistage hydraulic fracturing, where mechanical plugs isolate sections of the injection well, after which perforating guns detonate small explosive charges that blast a series of small holes through the pipe and the cement into the granite. Then the hydraulic fracking process uses high pressure water to similar to that used for shale and oil fracking. A temporary plug is installed and process is repeated on the next section.
That activity forces open existing micro-fissures in the granite creating channels that both create large surface areas to heat the water, and link the injection well to the production well.
Fervo then pumps degraded water (saline water, run-off, water unsuitable for agriculture) into the injection well, allowing it to circulate through the fissures in the rock. It gains heat as it travels to the production well.
Once brought to the surface, this hot water transfers its heat to a secondary working fluid in a closed system, vaporizing that fluid. That creates pressure and spins a turbine. The geothermal brine goes back down the injection well for re-use.
Fervo is the U.S. leader at the moment, with Cape Station looking at potential expansion up to 2,000 MW. It also has another project slated for Nevada to serve Google through a special Clean Transition Tariff contract with utility NV Energy, at $107/MWh. That gives you some idea of the economic and data center willingness to pay.
Fervo has company. There are about a dozen companies located just in the Houston area alone, with other contracts frequently being announced. Sage Geosystems has a 150 MW PPA with Meta, and is partnering with established geothermal company Ormat. XGS Energy announced a deal for a 150 MW project with Meta in New Mexico.
So, geothermal companies may become a big deal. However, there’s much hotter rock in the western U.S. – a result of the continent’s tectonic past. Areas in the west show suitable rock and temps at 1.5 to 3 miles down. In the eastern U.S. one must go 5 to 8 miles down, increasing costs and risks of failure.