Experimental geochemistry lab unlocks new knowledge for supercritical geothermal

The recent acquisition of new experimental reactor equipment has extended the lab’s capabilities, so that we can now replicate the high pressures and temperatures found in geothermal reservoirs up to 7km below the surface.

The facility now has four high temperature and pressure reactors, designed to study chemical reactions between water-based fluids and rocks at depth. The new equipment can operate at temperatures up to 700ºC and 300 atmospheres to simulate extreme conditions found in the deepest geothermal environments in the world. Three hundred atmospheres is 300 times the pressure you would feel at sea level.

The new equipment is already contributing significantly to supercritical research.

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Why is geothermal the key to a carbon neutral future?

Geothermal is a natural energy source that can be used to generate electricity.

Geothermal systems are found in areas where there are lots of volcanoes.

In Aotearoa, New Zealand, most geothermal fields

are found in the Taupō volcanic zone in the central North Island.

In this volcanic zone, CO2 is emitted naturally, let's look at this process.

Magma in the earth's crust heats water held in natural reservoirs.

As the water heats, CO2 from the magma dissolves into the water.

When hot water rises, CO2 is released from the water.

Gas then escapes through hot pools,

natural vents called fumaroles, or steam that escapes through the soil.

Gas that includes CO2.

So how can geothermal energy be carbon neutral? Let's examine how geothermal power plants work.

Water and steam are piped up from the geothermal reservoir under the ground.

Steam rotates the turbines.

A generator produces electricity, and then the water is injected back into the reservoir.

This helps maintain pressure in the system.

When the water turns into steam, so do the gases,

and at a geothermal power plant, even though the water is re-injected into the system, it may not

include all the CO2. Some CO2 is released into the atmosphere. Scientists in the geothermal industry,

including at GNS science are developing techniques to stop these gases escaping.

It involves re-dissolving the CO2 in water then re-injecting it back into the reservoir.

Doing this helps maintain the geothermal system,

while keeping the CO2 underground where it can't damage the environment.

Geothermal scientists are working towards a carbon neutral future.

Geothermal energy will give New Zealand energy security and help New Zealand

reach its goals of 100% renewable energy, and net zero carbon emissions by 2050.

Supercritical geothermal is uncharted territory. The reservoirs are more than 5km deep, and the fluid temperatures are above 400ºC – with the potential to produce many times more energy than conventional geothermal wells.

With increasing demand for low-emissions electricity, harnessing the potential of supercritical geothermal could play a key role in a carbon neutral future. While several countries are working towards this goal, no-one has yet managed to successfully harness these super deep resources.

At supercritical temperatures and pressures, fluid becomes a different beast and behaves more like a gas. It transfers energy much more efficiently than conventional fluids in lower temperature geothermal systems, but extreme pressures and corrosiveness encountered in these deeper environments can overwhelm conventional well and power station technologies.

Lead Scientist in the Experimental Geochemistry Laboratory, Dr Bruce Mountain, says the specialist equipment unlocks new knowledge about the chemical and physical reactions that occur in geothermal reservoirs.

“Understanding the complex chemical processes occurring at supercritical conditions is crucial to their successful and sustainable development."

Bruce Mountain

Lead Scientist - Experimental Geochemistry Lab (Wairakei)

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Our lab can reproduce these conditions and provide critical data to contribute to their understanding

Bruce Mountain Lead Scientist in the Experimental Geochemistry Laboratory GNS Science

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John Burnell Geothermal Modeller

John is a numerical modeller who has over 30 years experience working on a wide range of energy related projects. His main focus is geothermal reservoir modelling, undertaking both research and consulting. He has developed models of geothermal systems throughout the world, for both consenting purposes and resource planning. He has worked on models of: Ngawha, Wairakei, Rotokawa, Rotorua, Tauhara, Kawerau, Mokai, (New Zealand), Mt Apo, Bacman (Philippines), Kakkonda, Uenotai, Sumikawa (Japan), and Luiese (Papua New Guinea). He has long-standing involvement in the resource consent process in New Zealand, both developing models to assess environmental impacts and appearing as an expert witness at consent hearings. He is able to develop new software for solving modelling problems, and is the developer of a commercially available Tough2 pre-processor. John is currently the NZ convener of the IPGT Reservoir Modelling Group, and has served on the NZ Geothermal Association Board. In addition to geothermal modelling, John has worked on models of gas reservoirs, heat exchangers, heat transfer in reformer furnaces, casting furnaces, heater design, heat transfer in coolstores, biofilm growth and electroosmotic flow

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