Drilling deeper into supercritical geothermal; game-changer or science experiment?

Sunday, 1 December 2024

New Zealand could become the first country to unleash a powerful new form of energy, Marit Brommer, executive director of the German-based International Geothermal Association, believes.

Resources Minister Shane Jones announced last month that the Government had earmarked $60 million for GNS Science to drill the first of three exploratory wells deep into the volcanic zone near Taupō.

The target would be pockets of water, trapped at a depth of about 5 kilometres, that are believed to be heated and pressurised into a “supercritical state” by magma deeper underground.

The hope is such water could be extracted to generate electricity in larger volumes than is yielded by conventional geothermal resources, which already provide about 20% of the country’s power.

Technology Minister Judith Collins says developing and proving the drilling and engineering systems for extracting supercritical geothermal resources would be a big challenge, but “globally ground-breaking”.

GNS estimates supercritical geothermal could in practice generate about 2 gigawatts of electricity by 2050, or enough to meet about 20% of the country’s current electricity needs, roughly doubling the output from existing geothermal plants.

What’s ‘supercritical’ water?

Deep underground when heated by the magma to a temperature above 373 degrees C and pressurised above 220 bar, water enters enters a “fourth” state where it behaves differently to water, steam or ice.

GNS Science geoscientist Isabelle Chambefort says it is hard state to describe, but supercritical water behaves a bit like a gas and a bit like a fluid.

“You don’t have a boundary any more between the two phases.”

The important thing from a practical perspective, though, is that supercritical water holds three times as much energy for its mass as water that is just below the supercritical state, she says.

“It's less dense and it has more energy capacity. Its entropy drastically increases.”

So a large volume of supercritical water could provide a lot of geothermal power.

Is it currently used as an energy source?

Not exactly.

Some thermal power stations heat water all the way up to a supercritical state above 600 degrees, rather than just into steam, to drive turbines to more efficiently produce electricity, Chambefort says.

“We've been investing for the last five years in an experimental supercritical geochemistry lab where we are able to simulate that and go up to 700 degrees, so it's not like we are going into a new magical realm.”

Supercritical water has also been intercepted before in the Earth’s crust in Iceland, the United States, Italy and Japan, she says.

But commercially exploiting water that is already naturally heated and pressurised into a supercritical state – rain water trapped underground – would be new.

The ‘million dollar question’, is why it hasn’t been done before, Brommer says.

“Part of it is because there were easier-to-access geothermal reservoirs.”

Times are also different now, with climate change, she says.

“’Supercritical’ may cost more and maybe it is a little bit more daunting when it comes down to these higher temperatures, but the yields could be 10 times higher.”

Why the central North Island?

Brommer says most of the world’s accessible underground reserves of supercritical water exist near plate boundaries, such as the Taupo volcanic zone, where magma rises close to the surface.

“There are many places where we see tectonic boundaries either colliding, or subsiding where the crust is relatively thin.”

But she describes New Zealand as almost like “a living lab“.

Chambefort says it’s “really gifted” with its high temperature geological setting.

She won’t reveal the exact location of GNS Science’s first proposed exploratory well, but indicates it will be in the area of an existing, producing geothermal field.

When is this happening?

GNS will need to adapt an existing resource consent to drill, Chambefort says.

“If it's a year, I will be amazed; 18 months to two years is probably more realistic.”

Then, if the first well is a success, two more exploratory wells would be drilled.

The second would be a bit deeper “to understand the permeability of the crust and how supercritical water moves above magma” and the third would focus more on what was required for extraction.

“So it is a long game,” she says.

Has anyone drilled to 5km before?

Yes. Chambefort notes that wouldn’t be the deepest well in the world, by any means.

That title goes to the 12.3km deep Kola Superdeep research borehole in Siberia, and companies have also drilled deeper than 5km for oil and gas.

“The challenge is not the drilling, it is designing a well that will sustain those conditions,” she says.

One risk is that GNS drills a well and “then realises we don't have those fluids, which is a possibility, because we have never been there”.

Measuring how seismic waves travel through the crust and its electrical conductivity should reduce that risk though.

“We know water is circulating, because we see the water heat up and come back up at the surface, so it's a matter of identifying where it's flowing.”

Is it safe?

Chambefort believes there is negligible risk from the drilling itself.

“I know there has been a comment from a minister saying that we're going to drill into magma; that is absolutely not what we’re trying to do.”

While trying to avoid that, it has happened before in Iceland and not released a volcano, she says.

“You generally lose your drill bit, but there is not much potential to create an environmental impact.”

Nor is it the same as ‘fracking’, which involves trying to fracture rocks to release hydrocarbons, she says.

“We are hoping to find fluid flowing through natural fractures, which are everywhere in New Zealand.”

What about the economics?

The target is to produce power at a cost of no more than 10 cents a kilowatt-hour, Chambefort says.

That would put it broadly it line with solar and onshore wind energy, and position it as a lower cost alternative to offshore wind, she says.

But, of course, if supercritical geothermal was “a sure thing” then the Government wouldn’t need to be funding an exploration well through a regional development grant – a power company would be drilling instead.

Brommer says there will be “some rules of thumb”.

“But we're all waiting for the first wells to understand the challenges. And in order to cost the challenges, you have to do it, right?”

Former Mercury Energy chief executive Vince Hawksworth struck a cautious note describing the potential of supercritical geothermal to Parliament’s Transport and Infrastructure select committee in February.

Mercury had been building some relationships with start-ups in the sector, but he said it still had questions over whether it would be possible to commercialise it in a socially responsible way that took into account the more volcanic nature of the central North Island.

“If you think about the US, they have massive oil gas infrastructure that drives drilling costs down and they also have much higher electricity prices.

“We still have a lot of resources in New Zealand that are easily accessible, whether that's solar, wind, or geothermal. There's still a lot of opportunity in what we might call the more traditional geothermal space,” he said then.

Geothermal provides baseload power, which is good, right?

Yes, to a degree, power that is always flowing is more useful than renewable energy from wind and solar – at least in New Zealand’s case where power demand peaks in winter mornings and evenings.

It should perhaps be remembered the country’s current power-market challenge is to ensure there is enough ‘easily turn-on and turn-offable’ energy (to borrow a phrase from an old UK gas advert) at a reasonable price just to meet those peaks and substitute for hydro during dry winters.

Former Genesis Energy chief executive Marc England explained that was one reason why nuclear energy – a different form of more expensive baseload generation – didn’t really stack up here.

Ring-fencing some geothermal power just for peak demand was an idea being explored by the Ministry of Business, Innovation and Employment under the former government, but it might be economically challenging to keep a supercritical geothermal well just sitting in reserve.

But that’s not to say it wouldn’t be a useful addition to the energy mix, especially as totally electricity demand grows.

Any other reasons to drill?

Maybe.

Chambefort says GNS isn’t trying to just drill a well for science.

“It's really an exploration to identify resources that will make a difference for New Zealand.

“I think, in this environment, it's really important to show science is not just for dreamers and people in in lab coats.”

That said, Brommer says there is likely to be a lot of interest overseas in GNS’ learnings.

Those could potentially help other countries switch away from fossil fuels, benefiting everyone on the planet, including Kiwis.

“It is going to be tested, explored and evaluated here in New Zealand, maybe as a ‘first’. But the idea, of course, is that this is ‘a global play’ and that could help leverage multiple countries towards a supercritical approach.”

Chambefort said GNS is still working out what the framework would be for allowing people overseas to make use of intellectual property that GNS generates as a result of its exploratory wells.

Less altruistically, the knowledge it gains could help New Zealand geothermal businesses sell their services and expertise to the world.

Christchurch-founded subsurface software firm Seequent, which employed just one person in 2004 and was bought for a whopping $1.05 billion in 2021, announced at a conference in Auckland last month that it had secured a new partnership with the International Geothermal Association.

Seequent’s software, which is used to model and assess underground conditions, already supports more than half of the world’s geothermal electricity production.

Its energy market director, Jeremy O’Brien, says New Zealand has been a pioneer in the geothermal industry, and supercritical geothermal is just the next stage.

“The learnings we will get out of this will not only impact, hopefully, the physical production of more energy, but all the technological downstream benefits.”

The geothermal industry is already one of the “unsung heroes” among New Zealand exporters, spawning companies such as Seequent that have been decarbonising power production around the world, he says.

“The combination of whatever we learn from this drilling, with the existing expertise that New Zealand has; that export capability will only get stronger.”