![](images/Logos/Science.jpg)
Catching Fire
Past efforts to coax geothermal
energy from hot, dry rock deep underground have faltered.
But new techniques could crack the problem
Milford, Utah—The day started inauspiciously for John McLennan,
as he tried to break the curse haunting a 45-year quest to coax
abundant energy from deep within Earth.
First came news of an overnight accident
that left one researcher recuperating in a hotel with a sore back.
Then reports trickled in that seismic sensors dangling inside holes
bored deep into the Escalante Desert here were malfunctioning. Repairs
were delayed by gale-force winds that whipped the sagebrush-covered
hills and buffeted a drilling rig that rose 50 meters from the desert
like a misplaced lighthouse. Workers were already a day behind
schedule, and each day burned an additional $350,000.
Finally, shortly before sunset, McLennan,
a geomechanics engineer at the University of Utah, was ready to take a
critical step in advancing a $218 million project, 4 years in the
making, known as FORGE (Frontier Observatory for Research in
Geothermal Energy). If successful, FORGE will help show how to
transform dry, intensely hot rock found belowground all over the world
into a major renewable source of electricity—and achieve a technical
triumph where many others, over many years, have failed.
Gusts no longer rocked the trailer where
McLennan, eyes baggy with fatigue and wearing the same brown sweater
as the day before, faced five computer screens. The trailer’s door
opened and a co-worker—a giant of a man wearing a white hard
hat—looked in. “You ready for me to go?”
“Yeah,” McLennan replied. “We’re ready.”
With that, powerful pumps nearby sprang
to life and began pushing thousands of liters of water down a hole
drilled 3 kilometers into the hard granite below.
The
concept of using Earth’s internal heat to generate electricity
is attractively simple. Temperatures in the planet’s core approach
those found at the surface of the Sun, and the heat leaks outward. In
places this geothermal energy emerges at Earth’s surface as molten
lava, steaming vents, and hot springs. More often, however, it remains
trapped in deep sediments and rock.
There’s plenty of it. By one recent
estimate, more than 5000 gigawatts of electricity could be extracted
from heat in rock beneath the United States alone. That’s nearly five
times the total currently generated by all U.S. power plants.
Geothermal energy is also attractive because it doesn’t burn fossil
fuels, isn’t imported, and can run around the clock, unlike solar
panels and wind turbines.
![](images/images_07_19_2022/pic5.jpg)
In Utah,
researchers are testing new ways to use hot, dry basement rock to
produce energy.Eric
Larson/Flash Point SLC
Tapping that heat, however, has proved
difficult. Some nations—notably volcanically active Iceland—siphon hot
groundwater to heat buildings and generate electricity. In most
places, however, the rock lacks the water or the cracks needed to
easily move heat to the surface. For decades engineers have sought to
coax heat from this hard, dry basement rock, which can reach
temperatures of more than 250°C. But those efforts have largely
failed, often at huge expense—and sometimes after causing damaging
earthquakes. As a result, geothermal energy provides just 0.33% of the
world’s electricity, little changed from 1990, according to the
International Energy Agency.
In recent years, new hope for this
renewable energy source has come from an unlikely source: new
technologies developed by the oil and gas industry. The same methods
that have boosted fossil fuel production in the United States, such as
targeted drilling and fracking—artificially fracturing deep rock with
high pressure fluids—can, it’s hoped, be put to work to efficiently
and safely extract energy from hot, dry rock. Government agencies and
private companies are pouring hundreds of millions of dollars into the
approach, called enhanced geothermal systems (EGS), though it, too,
has had setbacks. Now, FORGE, situated on a remote patch of land in
southwestern Utah, has become a closely watched effort to demonstrate
and fine-tune EGS technologies—and finally break the losing streak.
“Geothermal isn’t going to work if we
can’t make this [EGS] work,” says geologist Joseph Moore of the
University of Utah, who leads FORGE. “That’s really the bottom line.”
For
McLennan, FORGE brings a sense of déjà vu. In 1983, when he was
an engineer at an oilfield company, he worked with scientists from the
Department of Energy’s (DOE’s) Los Alamos National Laboratory on a
pioneering attempt to exploit hot, dry rock in New Mexico’s Jemez
Mountains. The scientists had hoped to create what amounted to
artificial hot springs, by injecting water into deep fractures and
then channeling the heated water back to the surface via a nearby exit
well. But much of the injected water never resurfaced; researchers
later concluded that they had misread the underlying geology, and the
water disappeared into undetected cracks.
“It was a disappointment,” McLennan
recalls. And it was one of many.
![](images/images_07_19_2022/pic1.jpg)
Geomechanics
engineer John McLennan is part of the FORGE team.Eric
Larson/Flash Point SLC
Much the same thing happened decades
later to a $144 million geothermal plant in Australia’s arid Cooper
Basin. Water pumped into the wells flowed into a previously unknown
fault, and the project shut down in 2016, after just 5 years.
In some places, EGS projects had more
dramatic failures, as high-pressure water injected for fracking caused
existing faults to slip, setting off earthquakes. In 2006, engineers
shuttered a project beneath Basel, Switzerland, after earthquakes
caused minor damage. Eleven years later, a magnitude 5.5 quake struck
Pohang, South Korea, killing one person, injuring dozens, and causing
more than $75 million in damage. It was traced to a new, nearby EGS
project where, despite a series of tremors, operators had injected
fluid at high pressures near a previously unknown natural fault.
The high cost of drilling into hot, dry
rock is also a challenge. Equipment designed for the softer, cooler
sedimentary rock often found in oil fields falters in the extremes of
hot, hard metamorphic rocks such as granite.
Today, just three EGS power plants—all
near the border of France and Germany—produce electricity. In total,
they generate less than 11 megawatts, enough to power about 9000
homes.
EGS “always has been fraught with
technological challenges,” says Jamie Beard, an attorney and executive
director of the new nonprofit Project InnerSpace, which is seeking
donations to help geothermal startups. And “EGS in its pure form like
FORGE is hard,” she adds.
Even as EGS projects have struggled,
however, new techniques have emerged from the oil and gas industry.
Engineers learned to drill horizontally instead of just vertically.
Today they can create wells that can resemble rollercoaster routes,
curving and doubling back on themselves. Sophisticated steering
systems allow drillers to target their fracking to release oil and gas
from veins of rock as narrow as 5 meters. The advances have prompted
investors and governments to take a fresh look at EGS.
Plumbing the earth
Scientists are trying to extract the
abundant heat trapped belowground in places where hot water doesn’t
flow through the bedrock. Their goal: to create artificial systems
that act like hot springs, commonly known as enhanced geothermal
systems (EGS).
![](images/images_07_19_2022/pic3.jpg)
![](images/images_07_19_2022/pic4.jpg)
1 In EGS, a cold
fluid such as water is injected into wells deep enough to reach
hot, dry rock, often kilometers down.
2 Water is heated as
it flows into cracks in the rock. In EGS, high-pressure fluids
are used to create new fractures or enlarge existing ones, a
technique much like the fracking used in the oil and gas
industry.
3 Hot water is pumped
to the surface via exit wells drilled not far from the injection
well. The water turns to steam as the pressure drops closer to
the surface.
4 The steam is
directed to turbines that generate electricity. Most of the
water is reused and continues the cycle.
5 EGS-like techniques
can also be used to create water that’s not hot enough to
efficiently generate electricity. But the artificial hot springs
can be used to warm homes and commercial buildings, and drive a
variety of industrial processes.
C. Bickel/Science
In the United States, more than two dozen
geothermal companies have emerged since 2020, Beard says; that’s more
startups than she counts in the previous decade. In Germany, the
Helmholtz Association of German Research Centers announced in June it
is putting €35 million into a new underground laboratory dedicated to
geothermal research in deep crystalline rock, including EGS. And DOE
in April announced plans to spend $84 million on four EGS pilot
projects. They’ll be placed in different geological settings in the
United States to study the best ways to extract heat from different
types of rock.
Those plants will build on the results of
FORGE, which DOE launched in 2014 with a competition to create a
laboratory for honing EGS tools. In 2018, DOE announced the University
of Utah and partners had won the funding to build the facility near
the small railroad town of Milford, Utah, where Earth’s feverish
interior creeps close to the surface.
The
Milford Valley’s veneer of vegetation is so thin that much of
its geologic history is exposed like an open book. Moore has spent
more than 40 years reading that tome. Earlier this year, he stood next
to a low cliff of silica that runs north to south along the top of a
small hill. “This is a fundamental boundary,” he declared.
The wall divides what are, for the
purposes of geothermal energy, two different worlds. To the east, the
ground quickly rises to the flanks of the Mineral Mountains, rounded
peaks speckled with granite outcroppings and juniper trees. A
flat-topped mountain devoid of granite marks the top of a long-dead
volcano, one of nine that testify to the heat still trapped beneath
the ground in this region.
Between the cliff and the mountains,
abundant hot groundwater flows close to the surface. A squat, brown
building tucked into the foothills holds a 38-megawatt conventional
geothermal power plant whose wells tap into that water. Just beyond,
the steaming vent of a hot spring emerges next to the rock-walled
ruins of a crudely built “resort” from the late 1800s. It catered to
miners from the nearby Horn mine, once declared the world’s richest
silver deposit. At Moore’s feet sat opal gemstones formed about 1600
years ago when hot springs saturated with silica spilled to the
surface, leaving behind rocks candy-striped in yellow, red, and white.
West of what is known as the Opal Mound
fault, the groundwater is blocked by an underground wall of solid
granite that reaches temperatures of 235°C—truly hot, dry rock.
FORGE’s drilling rig perches above that granite, its metal skeleton
dwarfing the trucks and one-story buildings clustered around it.
Starting in 2020, crews used a similar
rig to drill an injection well. The completed shaft, 22 centimeters in
diameter, extends for 3.3 kilometers. The well includes features that
are standard in fracking operations but still cutting edge in EGS. For
example, FORGE’s shaft dives into the target granite at an angle that
is close to horizontal—chosen to intersect with natural stresses in
the rock in a way that would enable engineers to amplify tiny existing
fractures.
At its deepest point, the shaft pierces
rock that is 1.7 billion years old. Conventional metal drill bits
struggled to cut through this stone, and the younger granite above,
advancing just 3 meters per hour and frequently disintegrating. That
prompted a switch to tougher drills tipped with synthetic diamonds—a
first for geothermal drilling in granite. The bits sliced through the
rock 10 times faster, and are “definitely a breakthrough,” says Peter
Meier, an engineer and CEO of the Swiss geothermal company Geo Energie
Suisse, who visited FORGE earlier this year to help with seismic
monitoring. “This is already a very big result of the project.”
![](images/images_07_19_2022/pic6.jpg)
In Utah’s
Milford Valley, a 50-meter-tall drilling rig marks where scientists
are working to extract geothermal heat from deep in the rock below.
Water is pumped through the rig into a well drilled 3.3 kilometers
down into hot, dry granite.Eric
Larson/Flash Point SLC
The FORGE well is lined with a steel
casing that’s standard in oil fracking. Such linings make it easier to
use specially designed gaskets to seal off sections of pipe in which
operators detonate small explosives, shattering the pipe and exposing
the surrounding rock. That helps FORGE fracture rock bit by
bit—another novelty in EGS.
That piecemeal approach could help EGS
projects avoid fracking in seismically sensitive areas that could
trigger nearby faults, says William Ellsworth, a Stanford University
geophysicist who has studied drilling-induced tremors, including the
Pohang quakes. But he cautions that spotting problem faults in hard
basement rock is “an exceedingly difficult imaging problem.”
At FORGE, moreover, the granite’s high
heat has crumbled the gaskets typically used in cooler oil and gas
wells. It’s also fried seismic sensors essential to tracking the
fracking operation. So, the team has been testing special
high-temperature gaskets and new monitoring tools, including fiber
optic cables able to withstand the heat while detecting tiny
vibrations in the earth.
Universities, government labs, and
companies are currently developing other technologies they hope to
test at FORGE. One is a small device, resembling a motorized
skateboard, that would drive deep into the well to open and shut
“windows” in the steel casing that expose nearby rock for fracking,
another technique for targeting specific regions of rock. Such “tool
development … is absolutely critical” to moving EGS into the
mainstream, Moore says.
On 16
April, McLennan and the FORGE team were ready for one of their
first big tests: seeing whether they could pump enough water into the
deepest part of the well, under enough pressure, to enlarge tiny
cracks or create new ones in pockets of granite.
The equipment malfunctions and high winds
had initially thrown the schedule into disarray. But by late in the
day, McLennan was perched in front of his computer screens, like an
air traffic controller ready to guide a plane in for a landing.
Voices crackled over radios. Beside him,
Kevin England, a veteran petroleum engineer, issued short bursts of
commands.
Outside, a full Moon rose over a row of
water tanks, each nearly as big as a school bus. The roar of motors
filled the air as powerful truck-mounted pumps moved water to the well
through a spaghetti of pipes.
![](images/images_07_19_2022/pic7.jpg)
At FORGE, a
vast network of pipes helps move water around the drilling site.Eric
Larson/Flash Point SLC
On McLennan’s screen, numbers began to
climb, tracking the water flooding into the hole, where the pressure
would hit the last 60 meters of rock, left exposed without a steel
shell. The engineers hoped that would allow them to create a focused,
dense cloud of fractures, like an acupuncturist inserting needles into
a specific nerve.
A red line crawled across the screen,
marking the gradual rise in water pressure. Eventually, the line
wavered, bouncing around a pressure of about 28 megapascals, more than
250 times the atmospheric pressure. The flutter was good news: It
probably meant the rock was giving way. “We’re getting some action,”
McLennan announced. “This is nice.”
Over the next half hour, the signals
continued to be encouraging. For the first time in days, McLennan
appeared at ease. “This is beautiful,” he said. “It fractures, it
stops, then it propagates again.”
![](images/images_07_19_2022/pic8.jpg)
Joseph Moore, a University of Utah geologist, manages research at the
Department of Energy’s Frontier Observatory for Research in Geothermal
Energy.
Eric Larson/Flash Point SLC
It was hard to know exactly what was
happening nearly 3 kilometers below. But Jim Rutledge, a seismologist
at a nearby screen, was gathering clues. Clusters of black dots
appeared on a grid, marking tiny earthquakes detected by sensors in a
monitoring well half a kilometer away. The tiny tremors were no cause
for alarm—just a sign that the fracking was going as planned. “We have
a big cloud,” Rutledge said.
At 77 minutes in, the volume of water
pouring down the well had grown to 50 barrels per minute—an
aspirational target some had predicted the team wouldn’t reach because
of the unyielding rock.
“Let’s go to 60,” Moore pushed.
But McLennan urged caution: “Let’s stick
to the plan.” An hour later, the pumps went quiet.
Moore
and McLennan were buoyant the day after the April test: They
had pulled off their first successful frack. Now, the FORGE team is
sifting through the mountains of data collected during that test as
well as two subsequent fracks at locations higher up in the same well.
What they learn will shape their next steps.
A 3D map of the tiny seismic events
triggered during the tests, for example, will help them decide where
to drill a second well. If all goes as planned, in 2023 they will pump
water down the first hole and then see what, if anything, flows back
up the second.
Others are watching FORGE closely for
lessons. Meier is leading plans for an EGS project in Switzerland. He
hopes FORGE’s technique of executing smaller, segmented fracks will
point the way to reducing the risk that EGS will cause damaging
earthquakes, like those that shut down his company’s previous work in
Basel.
Others are eager to see whether FORGE can
identify ways to make EGS more commercially attractive by solving
problems that today scare off would-be investors, including
time-consuming drilling, broken equipment, and prolonged uncertainty
over whether a well can produce hot water.
“That’s where we’re focusing all of our
time and energy—taking away the risk from the [geothermal energy]
community,” says Lauren Boyd, acting director of DOE’s Geothermal
Technologies Office.
Others, however, see more immediate
commercial promise in other strategies. Call them EGS 2.0. Beard, for
example, argues for targeting softer, slightly cooler rocks at
shallower depths, familiar territory for oil drilling. The approach
would still rely on engineered hot springs and possibly fracking. But
the formations are easier to work in, Beard says, and drillers have
gained expertise from boring tens of thousands of wells into such
geology.
Sage Geosystems is one company pursuing
that strategy. Founded in 2020 by scientists and executives from the
oil giant Shell, the Houston-based company aims to drill and frack a
single well in sedimentary rock and use a set of concentric pipes to
pump cool fluids into the rock and draw out hot ones. Instead of
water, the firm might use liquid carbon dioxide, because it has a
lower boiling point. The resulting steam would drive turbines
specially designed to operate with carbon dioxide.
One longtime EGS proponent is trying a
different, less technically challenging approach. Chemical engineer
Jeff Tester of Cornell University helped run the Los Alamos work in
the 1970s and was the lead author of a 2006 DOE report touting EGS.
Now, he’s overseeing a program that this summer started to drill a
test well in sedimentary rock on the Cornell University campus in New
York state. Although rock temperatures could top out at just 100°C,
that would be enough to produce hot water to heat all the university’s
buildings, Tester says. And these lower temperatures are found in rock
in many more places. “It doesn’t have to be high temperature,” he
says. “That’s the beautiful feature of using [cooler rock] directly
for heating.”
Around
the FORGE site, researchers believe the hot, dry rock just a
few kilometers below holds enough heat to power a city the size of
Salt Lake City. Given its mission as a testbed, however, the facility
might never produce enough power to light a single bulb.
That doesn’t trouble Moore. “The purpose
of things like this is not to solve all the problems,” Moore said the
day after the first frack, as he stood on a dirt road a short distance
from the drill rig. Instead, he said, FORGE’s goal is to see whether
it can “take [EGS] to the point where the private sector can see its
viability.”
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