The world is in an era of energy transition – shifting from a reliance on fossil fuels to a future powered by sustainable energy sources including solar, wind and hydropower.
A key reason is the urgent need to combat climate change and reduce greenhouse gas emissions, but with big change also come significant challenges.
Scaling up renewable energy sources that are consistent and reliable and which can meet ever-greater demand requires significant technological innovation, economic investment and no little time.
In addition, there are key industries – such as iron, steel and cement production – that require high-temperature heat that is much harder to generate via renewables.
To solve some of these problems during this period of transition, engineers are proposing the increased use of the earth itself to help generate clean energy and store unwanted emissions to better protect our environment and combat climate change.
Geoenergy and geostorage are ways experts believe we can make a smoother transition on the path to Net Zero.
UNSW Professor Christoph Arns, a geophysics expert from the School of Mineral and Energy Resources Engineering, says both are likely to prove vital in moving the global community towards a cleaner, greener energy future.
"Geoenergy and geostorage is a key part of the transition to a cleaner future," Prof. Arns says.
"We can't just switch off oil and gas overnight and there are certain industries, such as cement production, that generate huge amounts of CO2 and we haven't yet found an easy way of eliminating those emissions.
"That's why I believe current renewables such as solar, wind and hydrogen will not be able to meet the increasing demand for energy in the short-to-medium term and emission offsets are required.
"In terms of renewables, to scale up to completely replace all fossil fuels would require a huge amount of landmass which is in potential competition with other land use, including agricultural. That would need to be carefully managed.
"Geostorage and geoenergy are actually some of the cornerstones of the pathway to Net Zero according to the Intergovernmental Panel on Climate Change (IPCC) which is part of the United Nations."
Some analysts believe more than 15% of greenhouse gas emissions could be eliminated by 2050 via the implementation of geostorage solutions and geothermal energy production.
So what exactly is geostorage and geoenergy? And how can they help us achieve our Net Zero goals in the next 20 to 30 years?
Here, Prof. Arns helps explain everything you ever wanted to know.
What is geostorage?
Geostorage is the process by which material is stored underground.
In the case of CO2, the reason is to stop the greenhouse gas from being in the atmosphere where it can cause climate change and instead permanently store it in the ground.
This geological carbon storage can be done in a number of different ways.
One option is a deep saline aquifer, whereby CO2 is injected into porous rock formations filled with brine, trapping the carbon dioxide by both a physical and chemical process.
Another option is to utilise depleted oil and gas reservoirs and repressurise them with CO2. The benefit of this process is that the reservoirs have already been well studied and analysed by engineers and are known to be naturally capable of storing fluids and gases – as they originally did.
CO2 can also be stored in existing coal seams, usually those that are not suitable for mining. The coal absorbs the CO2, but also releases methane which can then be captured and utilised as a fuel for heating or as a feedstock in chemical industries.
What are the challenges with geostorage?
Finding suitable places and geological formations to store CO2 is not a straightforward task and requires skilled engineers.
The existence of an impermeable cap rock, which helps to prevent the CO2 from escaping, is often vital to identify.
In the case of deep saline aquifers, the geological properties need to be accurately measured and analysed to ensure the CO2 will not leak and subsequently potentially contaminate the groundwater.
Injecting CO2 into a saline aquifer also increases the pressure within the formation. This pressure needs to be monitored and/or controlled to prevent fracture of the cap rock, but also to ensure that seismic activity – in the form of earthquakes – is not induced.
How feasible is the geostorage of CO2?
Countries like Canada, USA and Norway are already storing a significant amount of CO2 underground.
For example, the Alberta Carbon Trunk Line in Canada – the world's largest carbon capture and storage project – compresses and stores up to 14.6 million tonnes of CO2 per year by injecting it into depleted oil reservoirs.
However, analysis suggests that 90% of storage capacity comes from deep saline aquifers, potentially being able to store up to 10,000 gigatons of CO2.
And some industry experts are predicting the carbon capture, use and storage (CCUS) market will be worth $US4 trillion by 2050.
What is geoenergy?
Geoenergy is the utilisation of energy from beneath the Earth's surface to generate electricity or provide heating.
Oil and gas are actually themselves a form of geoenergy, but in a Net Zero future engineers are planning to increase the use of the intrinsic heat within the ground – that is, geothermal energy – to help reduce greenhouse gas emissions.
Certain geothermal sources are well known, such as those associated with volcanoes where high-temperature magma heats surrounding rocks and water, creating accessible geothermal reservoirs.
Otherwise, a process known as enhanced geothermal system (EGS) involves fracturing hot rocks underground to increase permeability and extract heat.
Another form of geothermal energy comes via a closed loop system which involves burying pipes containing fluid in the ground and exchanging heat with the earth. This geothermal heat pump is most often used to heat and cool buildings.
Certain types of rocks are best suited for geothermal energy production. For example, granite, basalt, sandstone and limestone are often found in geologically active areas where geothermal energy potential is highest.
What are the challenges of geoenergy?
Drilling into the ground, especially at depths sometimes required to find suitable rock formations, can be extremely costly.
In addition, geothermal resources are geographically limited, most often found in specific areas like volcanic regions or tectonic plate boundaries. This means geothermal energy may not be readily available in certain parts of the world.
Drilling deep into the earth is technically challenging and requires skilled engineers to deal with the problems.
Environmental risks also need to be carefully analysed and managed properly. The development of geothermal energy sources can lead to land subsidence, seismic activity and have impacts on local water resources.
How feasible is geoenergy in helping achieve Net Zero?
Geothermal energy is a sustainable, low-carbon energy source which can provide continuous, baseload power. Unlike solar or wind, it is not dependent on weather conditions, making it a reliable component of a balanced energy mix.
Technical advancements in enhanced geothermal systems have the potential to unlock resources in locations which are currently less favourable.
Geoscience Australia has previously estimated that the amount of heat in rocks less than 5km deep but over 150°C in temperature in the Australian continent is enough to make energy resource practically limitless – but the key is being able to extract that heat at an economic cost that is not prohibitive.
Overall, direct use of geothermal energy and geothermal power plants emit significantly less CO2 compared with fossil fuels.
But substantial investment in research, development, and infrastructure – as well as an increase in skilled engineers – is needed to make geoenergy a more prominent part of the global energy portfolio.
Key Facts:
A UNSW geophysics expert explains what geoenergy and geostorage are, and why they are likely to be crucial on the journey to a cleaner future.
