A scrub-dotted plain near the town of Milford in southwestern Utah, USA, may provide a glimpse of geothermal power’s future. At a site about 16 km north of the town, the Utah Frontier Observatory for Research in Geothermal Energy (FORGE), a project funded by the US Department of Energy (DOE), has been drilling wells that are up to 3350 m deep to test whether techniques borrowed from the oil and gas industry, such as hydraulic fracturing, or fracking, can unlock new sources of geothermal energy (
Fig. 1) [
1]. Nearby, the startup Fervo Energy, based in Houston, TX, USA, is capitalizing on many of these methods to build a 400 MW geothermal power plant that is expected to begin generating in 2026 [
2].
Advances in drilling technology made in recent years mean that “everywhere in the world has geothermal potential. You just need to drill deep enough,” said Taylor Mattie, director of technology at Project InnerSpace, a nonprofit that promotes geothermal power development. And researchers are now hoping to push the limits of drilling to tap even hotter strata. The startup Quaise Energy, headquartered in Cambridge, MA, USA, aims to enlist gyrotrons, devices used in nuclear fusion research, to generate millimeter wave electromagnetic radiation that can vaporize rock [
3]. The company claims that the technology could deliver up to ten times more energy than conventional geothermal steam by boring down as far as 20 km, almost twice as deep as any well ever drilled [
3], [
4].
Geothermal today provides about of 0.4% of electrical power in the United States and about 0.3% globally [
3], [
5]. But DOE projects that emerging technologies could boost geothermal power generation in the United States from less than 4 GW today to more than 90 GW by 2050 [
6]. Obstacles remain—some of the drilling approaches are unproven, costs of power are higher than for other renewables, and the possibility the projects will trigger earthquakes remains a concern [
7]. Still, the technology to produce a dramatic increase in geothermal energy “is at our fingertips,” said Mattie.
Geothermal checks many of the boxes for a clean energy source. It is renewable and, depending on the type of generation plant, produces little or essentially no CO
2 [
8]. Because geothermal plants require about one-eighth as much land as solar facilities and about one-third as much as wind farms, construction is usually less environmentally destructive [
9]. And unlike solar and wind, geothermal can provide constant power because its output does not fluctuate with weather conditions or time of day [
9].
Despite these upsides, geothermal development has remained what one writer called “the also-ran of renewable energy” [
10]. To produce enough steam to generate power, a geothermal reservoir needs “a heat source, a source of water, and permeability” to allow water to percolate through the rock and heat up, said Joseph Moore, professor of civil and environmental engineering at the University of Utah in Salt Lake City, UT, USA, and the principal investigator of Utah FORGE. These requirements have restricted traditional geothermal power plants to areas that naturally have all three features. Iceland (
Fig. 2), for example, takes advantage of its plentiful geothermal activity to generate 25% of its electricity [
11]. In the United States, Nevada obtains 10% of its power from geothermal sources, while California obtains 5% [
12]. In contrast, 43 of the 50 US states currently have no utility-scale geothermal plants [
12].
More than 50 years ago, researchers began trying to overcome this limitation by creating geothermal reservoirs, termed enhanced geothermal systems (EGS) [
13]. The procedure involves injecting water under pressure into the rock to induce fractures [
13]. So far, however, only a handful of EGS plants are operating commercially, and they produce little electricity [
14]. “People have made EGS work, but they have not done it at scale and made much money from it,” said Roland Horne, professor of Earth sciences at Stanford University in Stanford, CA, USA.
By honing the techniques of fracking and horizontal drilling to squeeze more oil and natural gas from shale deposits, the oil and gas industry has unintentionally come to geothermal’s rescue [
15], [
16], Horizontal drilling can reach rock formations that were hard to access with traditional vertical drilling [
17]. Fracking involves injecting fluids deep into rock formations to produce cracks through which oil and gas can travel to a collection well [
15]. Neither technique was new, but improvements have made them more useful [
18].
Utah FORGE has demonstrated that these approaches can work for geothermal power projects. Moore said that FORGE’s first success was showing the value of polycrystalline diamond compact (PDC) drill bits, which are standard in oil and gas drilling because they are so durable [
19]. Since the bits do not need to be changed as frequently as the roller-cone bits made of steel and tungsten that are usually deployed in geothermal drilling, wells can be completed faster. Drilling accounts for about half of the cost of a geothermal project, but with the PDC bits, “we can save 30% or more on the cost of drilling,” said Moore.
Another advance that Utah FORGE has made, Moore said, is to case geothermal wells, lining them with steel pipe. Although the step is standard for oil and gas wells, previous EGS projects skipped it because it increases costs, he said. Once the well is cased, the Utah FORGE researchers perform a procedure known in the oil and gas industry as plug and perf, which involves setting off small underground charges that punch holes in a portion of the casing. They can then pump in high-pressure water, which flows through the holes in the casing into the surrounding rock, expanding existing cracks and creating new ones. “That would be hard to do without casing the well,” said Moore.
The researchers start with the bottom section of the well, and after they have perforated the casing and pumped in water, they plug that section—hence the term “plug and perf”—and repeat the procedure on each section of the well above the plug. The difference between this approach and fracking in the oil and gas industry is what happens to the water, said Moore. Water is a waste product for oil and gas operations that must be disposed of—it is often injected deep into the ground at different locations, although this practice has led to earthquakes [
20]. Geothermal projects can reuse the water, reinjecting it into the ground to heat up again. This recycling cuts the amount of water that projects require and reduces the risk of seismic activity, said Moore.
Utah FORGE has made important contributions to the understanding of how to develop geothermal systems, said Mattie, who has no connection to the project. But it is not attempting to produce electricity, let alone turn a profit. That is what a pack of companies that includes Fervo, Sage Geosystems of Houston, TX, USA, and GreenFire Energy of Walnut Creek, CA, USA, is trying to do. Fervo is the farthest along. Since late 2023, the company has been delivering 3.5 MW of electricity for Google data centers in Nevada [
21]. It has also signed a contract to provide 360 MW from its plant under construction near Milford to Southern California Edison, the power supplier for much of southern California, including parts of the Los Angeles area [
22].
Fervo has taken advantage of plug and perf and horizontal drilling to tap into geothermal reservoirs, said Horne. He serves on the advisory board of the company, which two of his former students founded, but said he is not directly involved in its operations. As the injected water infiltrates fissures underground, it warms. The larger the surface area of rock the water contacts, the hotter it becomes. Combining horizontal drilling with plug and perf at multiple levels in the well increases the amount of rock surface the water encounters, Horne said. In turn, that boosts the odds that the water will absorb enough heat for power generation. In a 2023 preprint, Fervo reported that it had drilled two horizontal wells at a Nevada test site and then pumped cold water into one. The water emerged from the other well at temperatures of up to 169 °C, warm enough to generate 3.5 MW of electricity [
23]. A geothermal plant at this site is the one supplying power to Nevada’s grid. The company also said that it has cut drilling time by 70% [
24]. That improvement could help reduce the high upfront cost of geothermal power, which is one of its downsides [
8].
An unorthodox strategy for drilling up to 20 km deep could also help cut geothermal’s costs, some experts say. The benefits of deep wells are substantial. “The deeper you can drill, the higher the temperatures you can get,” said Horne. And higher temperatures translate into increased power production. If wells go down deep enough, they could reach supercritical water, which is above 374 °C at pressures of 220 atm (1 atm = 101 325 Pa) [
25]. Plants using supercritical water can be more efficient and produce relatively more power than facilities using cooler water [
10]. Moreover, this water is hot enough to drive turbines in existing coal, natural gas, and nuclear plants, theoretically allowing these plants to switch to a renewable energy source. “If you can get to 15 km, you could locate geothermal plants almost anywhere in the world and access water that can be heated to supercritical,” said Paul Woskov, a senior research engineer at the Massachusetts Institute of Technology’s Plasma Science and Fusion Center in Cambridge, MA, USA.
However, no one has ever drilled deeper than 12.2 km [
26]. Moore noted that at temperatures above 200 °C, conventional drilling equipment begins to break down and the electronics for monitoring well status begin to fail. These temperatures occur at relatively shallow depths around the world, he said. At Utah FORGE, for example, temperatures can exceed 225 °C once wells reach 3350 m.
In 2008, Woskov came up with the idea to use a gyrotron that generates millimeter waves, which fall between 30 and 300 GHz on the electromagnetic spectrum, to vaporize rocks even at temperatures that are too high for conventional drilling equipment [
3]. The device would remain on the surface and transmit the waves through a tube known as a wave guide that would be inserted into the well.
Drilling in this way could provide other benefits besides being able to operate in high-temperature rock. For instance, because the waves melt the sides of the bore hole, they will create a casing for the well, Woskov said. And if the technology could be adapted to allow reuse of existing fossil fuel and nuclear facilities, “our geothermal plants are already 75% built,” said Woskov. Quaise Energy has taken over development of the technology and plans to use a prototype portable gyrotron system to start drilling its first test wells in late 2024 [
3].
“Anything that can allow us to drill faster, cheaper, and deeper is useful,” said Moore. But he and other researchers are waiting for a demonstration that the gyroton technology can integrate with standard drilling equipment and penetrate to those depths. “Show me that it works,” said Jefferson Tester, professor of sustainable energy systems at Cornell University in Ithaca, NY, USA.
Technical and economic barriers could hold back further development of EGS projects, said Moore. The cost of geothermal projects must come down to be competitive with other renewable sources and fossil fuels, he said. The possibility of earthquakes is another worry, said Horne. Earthquakes triggered by previous drilling “were sufficiently large to upset a bunch of people and kill a couple of projects,” he said. However, researchers are studying steps to reduce the risk, such as carefully monitoring seismic activity and siting projects away from faults.
Still, experts think that companies and researchers will overcome the obstacles, allowing geothermal to meet a greater share of energy needs. The United States will not be obtaining 50% or even 30% of its power from geothermal sources in the next 20 to 30 years, said Horne. But a figure like 6% “seems reasonable,” he said.
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