Varying the rate at which carbon dioxide (CO2) is injected into geological storage sites can enhance not just the sites efficiency but also its ability to store the greenhouse gas securely, according to a new study.

A new study by scientists at the University of Edinburgh, one of the founding partners of the Scottish Carbon Capture & Storage (SCCS) research partnership, 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 findings 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.”

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