Varying the rate at which carbon dioxide (CO2) is injected into geological storage sites can enhance not just their efficiency but also their ability to store the greenhouse gas securely, according to a new study.
These findings will be invaluable to developers of carbon capture and storage (CCS) projects in the UK and abroad, where varying injection rates and interruptions are expected to occur over a project’s lifespan due to, for example, CO2 delivery rates from capture sites, pressure management and well maintenance.
The study by scientists at the University of Edinburgh suggests that, with every change or interruption to CO2 injection into a geological storage site:
- storage security would be enhanced because interruptions have the effect of increasing the amount of CO2 trapped within the pore spaces of the rock;
- the efficiency of storage is increased because trapped CO2 is less mobile than free flowing CO2 and so its migration within the reservoir is more contained;
- injection pressure would rise due to the increasingly trapped CO2 acting as a barrier to flow and this effect would need to be managed by storage site operators.
The researchers used rock samples to simulate the injection of CO2 and water into geological stores, creating numerical models which were then compared to a real-life, small-scale injection project at Otway in Australia.
As a CCS industry in the UK moves closer to reality, studies such as these illustrate just how the technology will work in practice and provide important data to guide development.
Dr Katriona Edlmann, Chancellor’s Fellow in Energy at the University of Edinburgh said: “It was great to see the commitment of the UK and Scottish governments at the turn of the year on the ambition to deploy CCS. With projects in the UK inching towards design studies, our findings can feed into that development. Naturally, greater efficiency brings cost reductions, and this will be welcome news for CCS project developers. We studied both in the lab and in the field to analyse what injection might look like at scale, specifically when injection rates and flow change over time. What we found was that security of storage is increased but so does pressure, and this will require suitable management.”
Gareth Johnson, Research Associate with SCCS and University of Edinburgh at the time of the study, said: “It was great to compare and validate our experimental and modelling studies against real-life injection studies at the Otway site in Australia. Climate change is a global problem and collaboration with international colleagues is really important to further CO2 storage, and we thank CO2CRC for providing the Otway data.”
SCCS Communications & Knowledge Exchange Executive
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 Read the paper Cyclic CO2 – H2O injection and residual trapping: Implications for CO2 injection efficiency and storage security by Katriona Edlmann, Sofi Hinchliffe, Niklas Heinemann, Gareth Johnson and Chris McDermott from the University of Edinburgh and Jonathan Ennis-King from CSIRO, Otway. Published in the International Journal of Greenhouse Gas Control, January 2019: https://www.sciencedirect.com/science/article/pii/S1750583618302226
 Carbon capture and storage – or CCS – is a set of technologies that tackles emissions of carbon dioxide (CO₂) at source to prevent increased atmospheric concentration of the gas, which causes climate change. It is being used at a number of sites across the world. The CCS process has three distinct parts: capture, transport and storage. Once captured, cleaned and compressed, the CO₂ is transported to a geological storage site to be permanently stored deep below ground.
 The UK needs to reduce its carbon emissions by at least 80% from 1990 levels by 2050. Carbon Capture and Storage (CCS) is a key means of achieving this at lowest cost and with added benefits for everyone. Scotland, with its unique access to secure and commercially ready CO₂ storage sites offshore, is extremely well placed within the UK to deliver this new industry. For example, the Acorn CCS Project based at St Fergus is making steady progress towards full design studies with support from research by The University of Edinburgh and other SCCS partner institutes: http://actacorn.eu/
 Scottish Carbon Capture & Storage (SCCS) is a research partnership of British Geological Survey, Heriot-Watt University, University of Aberdeen, the University of Edinburgh and the University of Strathclyde. Its researchers are engaged in high-level CCS research as well as joint projects with industry to support the development and commercialisation of CCS as a climate mitigation technology. www.sccs.org.uk