Varied CO2 injection rates could boost efficiency and security of geological storage sites

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, reports Scottish Carbon Capture & Storage (SCCS). 

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.