supercritical advantage

Growing New Zealand: powering our economy with Earth energy.

Supercritical geothermal fluids (>5 km, >400°C) offer ten times more energy than geothermal fluids found at current depths (~3.5 km) and reservoir temperatures (<350°C).

supercritical advantage

Renewable earth energy is instrumental to achieving New Zealand’s low-carbon aspirations

Supercritical geothermal fluids (>5 km, >400°C) are expected to offer more energy than geothermal fluids found at current depths (~3.5 km) and reservoir temperatures (<350°C). To utilise these in a sustainable way, a greatly enhanced scientific understanding is needed to realise the potential of supercritical resources, and offer industry-ready solutions.

A bunch of geologists walking over geothermal rock
Geologists hiking through geothermal terrain in Tongariro National Park, located in the central zone of the North Island of New Zealand. Photo Credit: Melissa Climo
New Zealand seeks a zero-carbon future. Geothermal energy is always available, regardless of weather or climate, and is a low-carbon alternative to fossil fuels.

Supercritical resources are supercharged geothermal systems.

Earth energy is renewable heat, created when the planet formed. Groundwater percolates downwards towards the heat source and becomes heated to high temperatures before buoyancy returns these fluids to shallower levels, or even the surface. In the upper few kilometres of crust, faults and fractures in the rock act as natural channels.

Geothermal resources are underground stores of the Earth’s heat.

Permeable rock formations store some of the rising fluids, forming geothermal reservoirs of heat. Drilling into these reservoirs is a renewable, reliable and secure source of energy. At around 2.5 km deep, a geothermal well can produce water and steam at about 300°C, resulting in about 5 megawatts of electricity generation – enough to power over 3,000 homes, or to run a large-scale timber drying kiln.

For over sixty years, the Earth’s energy has powered New Zealand.

Our position along the Pacific – Australian tectonic plate boundary means high temperature fluids run through natural pathways close to the surface, which makes accessing the fluid and their heat an economically viable option – unlike many places around the world. Geothermal energy supplies over 17% of the nation’s electricity, as well as heat for domestic, commercial and industrial applications – from timber drying and milk processing to greenhouses and bathing.

Simple conceptual model of a geothermal system.
Simple conceptual model of a geothermal system.
The next generation of geothermal energy use will tap into temperatures and pressures higher than any we’ve used before – a significantly greater energy resources for the future.

Supercritical resources are supercharged geothermal systems.

Supercritical conditions occur near the brittle–ductile transition zone in the Earth’s crust, where cooler brittle rock overlays hotter plastic rock, and superhot fluids circulate. Above 374°C and 221 bars of pressure, water transforms into a supercritical fluid, where distinct liquid and gas phases don't exist. These fluids have a higher heat content and lower density than liquid water, so have the potential to generate much more energy than the same volume of a conventional geothermal fluid.

Innovative research is underway to realise the potential of abundant renewable geothermal energy.

International projects aim to harness the power of the Earth’s supercritical heat. Innovative drilling and well completion techniques are needed to deal with extreme temperatures and aggressive fluid chemistry.

We have begun our search for New Zealand’s supercritical earth energy resources

Supercritical water at 400°C contains five times as much energy as water at 200°C.

Supercritical resources offer a near-limitless energy supply that will fundamentally transform New Zealand’s energy sector. This future includes a decarbonised electricity system with vastly improved environmental performance.

Supercritical  provides for new investment opportunities. Economic development will be supported through commercial applications of supercritical geothermal resources for material processing, industrial scale forestry, dairy and other industrial uses.

Simplified phase diagram showing the state (liquid, vapour, solid) of pure water as a function of pressure and temperature at different depths in the Taupo Volcanic Zone (New Zealand).
The central North Island has a high natural heat flux due to it’s tectonic setting, so unlike many other countries, we don't have to drill to 10 km to reach temperatures above 400°C.

New Zealand’s supercritical fluids are likely to be found at depths greater than 4 km.

Conventional geothermal wells in New Zealand tend to be 1.5 km – 3 km deep. We are searching for supercritical conditions at 4 km – 6 km depth, where magmatic heat encounters permeable rocks, allowing hot fluids to pass through relatively easily.

This research programme is addressing the unknowns.

The tools usually used to probe beneath the Earth’s surface depths have not been calibrated for rocks at extreme temperatures and pressures. We don’t know the geology nor how the rocks and fluids interact under supercritical conditions. The drilling, piping and electronic materials were never designed to handle the temperatures nor corrosive chemistry of supercritical fluids.

It is essential to define the heat transfer mechanisms from magma to surface, and understand the behaviour of magma bodies, their high temperature envelop, and the integrating fluid and heat transfer at these supercritical conditions. Then to translate this science into real world application and thinking. The Geothermal: The Next Generation research programme aims to do just that.

Read more about our Projects

an engineer performs maintenance on equipment at the Ngatamariki power plant