Varied CO2 Injection Rates can Boost CO2 Storage Effectiveness

arying the rate at which carbon dioxide 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 from the University of Edinburgh.

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.

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 is published in the International Journal of Greenhouse Gas Control, January 2019.

The University of Edinburgh is one of the founding partners of the Scottish Carbon Capture & Storage (SCCS) research partnership.