REPORTETH Zurich researchers working at NAGRA’s Grimsel rocklaboratory have retreated deep inside the mountain.
By fracturing solid rock, they are hoping to re-examine
the feasibility of geothermal power plants based on
petrothermal technology.
TEXT Peter Rüegg

IMAGE Daniel Winkler

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It’s an icy-cold early December day atthe Grimsel Test Site, nestled at thefoot of the dam that holds back theRäterichsbodensee reservoir. Water
has frozen into bizarrely shaped icestreams on the huge slabs of rock. We
take one last glimpse out of the window
before the VW minibus plunges into
a tunnel leading into the mountainbeneath the dam wall.
After driving a good kilometre, theminibus stops next to a niche in therock. Bicycles are propped against thewall to the right of a greenish-blue steel
door. An illuminated sign spells out“Welcome to the NAGRA Rock Laboratory”, marking the entrance to theresearch facility’s centre of operations.
It’s not as cold here: deep inside theJuchlistock mountain, with 450 metresof solid granite over our heads, thetemperature stays at a steady 13 degrees. Engineering geologist Florian
Amann covers the last few hundred
metres to the laboratory on foot, advancing further down the tunnel thatwas carved out by the energy supply
company Kraftwerke Oberhasli AG
when it built the hydroelectric power
plant.
Amann swings open a metal doorand heads down a concrete staircasethat leads to a large cavern. A researcher is crouched on the floor staring
transfixed at his laptop, which ispropped up in front of him on a chair.
One of his colleagues in bright yellow
work trousers is monitoring a dozenpressure sensors, and a tangle of green
hoses is lashed to a rack on the wall. Nodaylight enters the cavern, and apartfrom the murmurs of the scientists
there’s not a sound to be heard.
This underground cavern is thesetting for a one-of-a-kind experimentthat aims to pave the way for deep geothermal energy in Switzerland: theIn-situ Stimulation and Circulation experiment, known for short as ISC.

Project manager Florian Amann. One turn is all it takes to adjust
the water pressure in a borehole.

The scientists working on this experiment are hoping to discover how to
crack solid rock in order to create andmaintain an efficient heat exchanger –a key component in producing electricity in geothermal power plants (seepage 41).

“Once we start theexperiment nobody will
be able to walk arounddown here.”
Florian Amann

To fracture solid rock, researchers“stimulate” it by pumping water into
boreholes under high pressure. This
causes the rock to rupture, after whichwater can be heated up by pumping it
through the resulting system of cracks.
The researchers hope to discoverwhether this system of cracks can be
maintained over a longer period oftime and whether the water circulation
is sufficient to make operation of theheat exchanger economically viable.

The experiment is also designed toshow which method of fracturing rockis the most practical. Rock can be fractured in two different ways, and thescientists here are using both. The first
method is hydraulic fracturing, where
the scientists steadily increase thewater pressure in a borehole until thesolid rock cracks. The second method
is hydraulic shearing, where the geoengineers apply targeted increases inwater pressure to existing cracks in therock. That causes the crack walls to dislocate, making the cracks bigger.

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The rockcrackers

REPORT

Political pressure
The scientists are particularly keen tofind ways of minimising the numberand intensity of earthquakes that occur
during stimulation. This issue was oneof the key reasons behind the failure of
the deep geothermal energy projects
in Basel and St. Gallen. At both sites,
local inhabitants felt the earthquakesthat were triggered when the bedrock
was pressurised. Both projects wereterminated, marking a setback for geothermal energy.
“Current experience of petrothermal systems amassed around theworld indicates that there is a way

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REPORT

Two years of preparation
Amann and his team have spent twoyears carefully preparing every last aspect of the experiment. Everything has

to be in place the day he finally presses
the “red button”: “We only get one
shot at cracking the rock,” says the engineering geologist, noting that therock can’t be patched up again once it’s
been fractured. “If something goeswrong, we would have to develop awhole new fresh body of rock, andwe simply don’t have the time or themoney for that.”
To prepare the experiment, the researchers conducted a detailed analysis of the rock at the test site to familiarise themselves with every last centimetre of the rocky mass. That puts
them in a position to compare the condition of the rock before and after thewater is injected.
They also drilled 15 boreholes into
the rock ranging from 18 to 50 metres
deep and up to 15 centimetres in diam-eter and equipped these with highlysensitive measuring instruments.
The researchers need three of theboreholes to conduct strain and temperature measurements, four for seismic measurements, and four for pressure and strain monitoring. They needto capture every last detail of any
dislocation, deformation or change ofpressure in the rock. Highly sensitive
micro seismometers are also positioned outside the boreholes to record
any vibrations that occur before, during and after the water stimulation.
Amann leaves the cavern andenters a circular tunnel drilled by a tunnel boring machine. Cables run along
the walls and water from the rock trickles along the floor. After 30 metres, hestops in front of an inconspicuous littlebox mounted on the rocky floor ofISC-EXPERIMENTThe ISC experiment falls
under the remit of the Swiss
Competence Center for
Energy Research – Supplyof Electricity (SCCER-SoE).
It involves six professors fromETH Zurich and one fromthe University of Neuchâtel.
The experiment is led
by Florian Amann fromSCCER-SoE. The ISC experiment is funded by the Swiss
National Science Foundation,
the Swiss Federal Office ofEnergy and industrial partnersincluding Shell and EKZ.
→ www.sccer-soe.ch/research/geo-energy

Team member Reza Jalali carefully feeds a fibre-optic cable into a borehole.

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the tunnel. He stoops down to briefly
check that it’s intact. “This is a tiltmeter,” he explains, “which measures
the inclination of the granite tunnel
floor to detect any deformation causedby changes in the rock.” The tiltmetercan even detect the tiny inclination ofthe floor that occurs when somebody
walks past the sensor. “Once we start
the experiment nobody will be able towalk around down here,” emphasises
the project manager, “as this would
distort the readings and we would haveto remove that interference from thedata afterwards.”
Real-time modelling
Data is central to this experiment, andso is data management. Seismic monitoring alone generates terabytes ofdata. The researchers have continuous
access to this data from ETH Zurich
thanks to the cavern’s direct internetconnection.
“A lot of computing power comes
into play during stimulation,” says
Amann. The data is transmitted in realtime to enable a simulation to instantly
predict the next few minutes of the experiment.
Analysing all the data will take
two to three years. “We’re producing
enough data for generations of doctoral students,” notes the project manager. A full overview of the ISC experiment is not due to be completed until
2020, though industrial partners won’t
have to wait that long for the key findings. “Industry is very interested in ourresults. We’ll be providing them withvaluable data from an early stage,”
Amann says.
Nonetheless, the researchers (andthe electricity industry) are still verymuch at the start of a long journey. TheISC experiment is “only” a pilot project and is on a much smaller scale thana “proper” geothermal power plant.
So why bother with this kind of ex-

Underground shop talk:Florian Amann (left) chats to rocklab director Ingo Blechschmidt.

periment? “The method we’re using tocrack the rock can’t be tested in a borehole that’s 5,000 metres deep,” says
Amann. As well as the prohibitive costs
this would entail, it would also be virtually impossible to equip such a deep
geothermal borehole with this type ofsophisticated measuring equipment.
That’s why the researchers have to reproduce this kind of system on a small
scale and then use a computer model toscale it up. “The work we’re doing here
is a key part of minimising and perhaps
even eliminating the risks posed by thistechnology,” Amann adds.
Convinced of its feasibility
Time underground passes at a sluggish
pace. The fluorescent lights cast a
steady glow that gives no clue as to howmuch of the day has already passed.
Occasionally the sound of an enginepenetrates as far as the cavern. The
men’s stomachs start to rumble. It’s
midday, time to get a bite to eat withthe other researchers back at the rocklaboratory’s centre of operations.
Amann heads up the stairs, followed by his colleagues. He opens thegreenish-blue steel door, enters thedimly lit main tunnel and makes hisway back to the main offices on foot.

Originally the researchers had wanted
to fracture the rock in early December,but problems with the delivery of certain measuring instruments upset theirplans. Amann doesn’t see that as a badomen, though. He is confident that theexperiment will generate valuable data
and mark an important step forward
for deep geothermal energy.
His faith in this method of power
generation is equally unshakeable:“I’m convinced that geothermal power
plants will meet some of our energy
needs in the future. And what we’re doing here will provide the basis for
Switzerland to exploit this low-CO2
energy source.”

DEEP GEOTHERMAL ENERGY
Temperatures at depths of 4,000
to 6,000 metres lie between 150
and 200 degrees Celsius. Thisgeothermal energy can be used togenerate electricity. Hydrothermalsystems (e.g. St. Gallen) work bytapping into aquifers. The hot water
is piped to the surface and used to
produce electricity. Deep hot-wateraquifers are hard to find, however,and they are rare in Switzerland.
That’s why a more realistic option
for this particular country isto exploit petrothermal systems(e.g. Basel). That involves drilling
down into the 200-degree-Celsius
crystalline bedrock. Injecting
water under high pressure createsa system of cracks through which
the water circulates. This makes
the water hotter, so it can beused to drive turbines and generate
electricity once it returns to thesurface. ETH Zurich launcheda research initiative in the area ofgeothermal energy four years
ago, supported by funding from theWerner Siemens Foundation.

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to do this without causing detectableearthquakes,” says Amann, “and that’s
what we want to achieve, too.” The
researchers have also been spurred onby recent political events: in its Energy
Strategy 2050, the Swiss FederalCouncil included the goal of using
geothermal power plants to generate
7 percent of Switzerland’s energy requirements, amounting to 4.4 terawatt
hours, or one and a half times the output of the Beznau I nuclear power
plant. To achieve this goal, a total of
25 geothermal power plants, each generating 20 megawatts, will need to becommissioned over the next 30 years.

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