Science in the subsurface
On the quest to achieve net zero, Mike Stephenson reports on the role for subsurface research laboratories in geoscience
Recent research suggests that the effects of climate change are already tangible, making the requirement for net zero – the balance between the emission and removal of greenhouse gases to and from the atmosphere – more pressing than ever.
Geo-energy technologies in the subsurface, such as aquifer thermal energy storage, geothermal, compressed air energy storage and carbon dioxide storage, will be part of the solution. To make these technologies count, geoscientists need to test their ideas beyond laboratory-scale research and modelling and show that they work at full scale. Test sites for subsurface net zero technology are therefore essential. To consider how we can improve investment in test sites and identify gaps in capability in existing sites, the virtual conference ‘The role of subsurface research labs in delivering net zero’ was convened by the Geological Society of London in February 2021.
In geological decarbonisation technologies, the main questions surround our ability to characterise rocks geochemically and geomechanically, as well as to understand fluid flow. Yet, our knowledge of these processes beyond the laboratory scale is limited. We need to know how fractures and faulting, stratigraphy, permeability, porosity and shear strength influence the direct implementation of technology, and we need to understand these characteristics at realistic scales, from the micrometre to the kilometre scale. This is why test sites are so important.
In the disposal of radioactive waste, for example, we must test models and laboratory-derived results. Nuclear energy will contribute to low-carbon power production in the future, but nuclear power plants come with radioactive waste. In the UK, it is likely that by 2100, we will have 2.6 million tonnes of high-level radioactive waste that will need to be safely managed, probably within a geological disposal facility. Such facilities use engineered materials and structures, including concrete, metals and clays, as well as the surrounding geological environment as containment barriers. To safely and effectively contain waste, we need to understand the processes and timescales for the self-sealing of fractures in clay rocks, as well as the fate of repository-generated gases.
The fate of gases was investigated at the large-scale gas injection test (LASGIT) project at the Äspö Hard Rock Laboratory in Sweden. Test outputs have already confirmed early laboratory results on gas migration behaviour relating to dilatational pathways in bentonite and their impact on stress and pore-water pressures, helping to build the safety case (presentations by Fiona McEvoy, British Geological Survey; Jonathan Turner, Radioactive Waste Management).
The Glasgow UK Geoenergy Observatory was established in 2020 to investigate the use of coal mine water as a sustainable source of heat and to characterise the hydrogeology of flooded, abandoned coal mine workings. Many cities and towns in Britain are located on disused coalfields, and could provide a significant potential customer base for renewable heat energy schemes using abandoned coal mines. Information from the Glasgow Observatory will help us to understand the connectivity, flow and heterogeneity of the mine water system, as well as its response to small-scale heat and flow cycling, and will greatly improve the evidence base for coal mine geothermal and heat storage (Alison Monaghan, British Geological Survey).
To make these technologies count, geoscientists need to test their ideas beyond laboratory-scale research and modelling
Regulation and social acceptance
In addition to providing data that aid implementation, geo-energy test sites may provide the scientific basis for regulation, in particular by helping to establish the balance between regulation that encourages the growth of new technology, while protecting the environment, property and people.
For example, Matthias Raab (CO2CRC Limited) and Peter Cook (University of Melbourne) described how developers at the Otway International Test Centre, located at a depleted natural gas field in Australia, worked with regulators to examine liability associated with long-term storage of sequestered CO2 by researching the interactions between minerals and injected CO2, and how this affects the long-term fate of CO2 in the subsurface. Similarly, Alwyn Hart (Environment Agency, UK) and Mark Ireland (Newcastle University, UK) discussed how research at observatories like the Glasgow UK Geoenergy Observatory could aid the regulation of low-temperature geothermal energy (ground source heat) by providing insights on how quickly heat is replenished, as well as the environmental impacts.
Test sites can also help to ‘socialise’ geo-energy among the public. The success of geo-energy technologies relies heavily on public acceptance and support – as potential adopters, hosts, consumers and proponents (Jennifer Dickie, University of Stirling). Again, the Otway site is a good example. Developers worked closely with local communities to achieve community acceptance and even a local sense of pride in the research being done at the facility.
During our discussions, two areas were singled out as potential gaps in our armoury of test facilities. The first concerns the realisation that for some subsurface technologies to be viable (such as low-temperature aquifer geothermal and heat/cool storage), they must operate in densely populated urban areas because low-grade heat will not be retained if transported far. So, low-cost, high-resolution, unobtrusive seismic and other monitoring will have to be developed for seismically noisy urban environments. How do we carry out monitoring and exploration in densely populated areas with sensitive or sceptical human populations? Do we need test sites that concentrate on subsurface monitoring, perhaps for several different kinds of technology?
The second gap concerns the need for test facilities to look at faults. If we want to use basins for geo-energy technology, we likely need to know much more about how faults reactivate and how they affect fluid flow. Faults are the locus for seismic events and can both allow and prevent fluid flow, meaning the occurrence of faults adds an element of risk. Do we therefore need a dedicated fault observatory, perhaps one that involves boreholes penetrating fault planes, allowing access to the rocks on the foot wall and hanging wall, where perturbations can be applied and changes measured and assessed?
We are acutely aware that in many ways our colleagues in astronomy, physics and engineering are well ahead of geoscience in using big infrastructure to solve big problems – like CERN or the Jodrell Bank Observatory do, for example. There is so much to gain by geoscientists coming together to tackle geoscience problems with big kit, but we need to encourage investment.
We can start by making alliances between similar test sites to encourage shared facilities and risk. We can then build best practice, joint strategies, data interoperability and international collaboration.
The virtual conference attracted attendees from across the world. It opened with a truly world-spanning talk on the value of test sites, delivered simultaneously by Sue Hovorka (The University of Texas at Austin) in Texas, USA and Linda Stalker (CSIRO) in Perth, Australia. To accommodate those calling in from East Asia, as well as North America, the talks were held between 10am and 3pm GMT.
The presentations covered aspects of carbon capture and storage, the UK Geoenergy Observatories project, international geothermal, heat storage, and radioactive waste test sites, the regulatory and policy needs for test sites, as well as the importance of public dialogue on geo-energy.
By Mike Stephenson
Mike is Executive Chief Scientist, decarbonisation and resource management, at the British Geological Survey.