How do you store CO2?
North Sea aquifers and empty oil and gas reservoirs could help decarbonisation.
The North Sea could help the UK decarbonise — thanks to empty oil and gas reservoirs and saline aquifers.
Governments all over the globe are seeking to implement large scale carbon capture and storage (CCS) to reduce the amount of carbon dioxide (CO2) that is released into the atmosphere. CCS captures CO2 from sources including factories and power plants, or removes it directly from the air. Then the greenhouse gas is stored on a permanent basis — often in empty oil and gas reservoirs.
According to the International Energy Agency (IEA), if we are to limit temperature rises to 2 degrees Celsius, then we need to store 100 billion tonnes of CO2 globally by 2060.
Obviously, global capacity for CCUS must accelerate rapidly very soon, but where can we store all this extra CO2 — and what will happen to it when we do.
Where and how can we store CO2?
Many of the CCS projects that are already underway work are designed around injecting highly pressurised CO2 into porous underground rock formations, including former natural gas or oil reservoirs, coal beds that can no longer be mined, or saline aquifers — deep geological formations contain deposits of very salty water in the rock’s pores and are most commonly found under the ocean, including the North Sea and the area off the US Gulf Coast.
When the CO2 has been captured using proven CCS technology as a gas, it is transformed into ‘supercritical CO2’, which behaves more like a liquid. This is piped to the storage location and injected into rocks deep below the surface of the earth’s surface.
What happens to CO2 once it has been stored?
Usually after CO2 has been injected into rocks as part of a process known as geological sequestration , it moves up through the reservoir until it meets a layer of impermeable rock through which it cannot pass. This then acts as a ‘lid’ from which the CO2 is unable to escape.
Eventually, CO2 stored this way will begin to form chemical reactions with the elements in the minerals surrounding it — creating solid chalky minerals through a process called ‘mineral storage’.
The CO2 is unable to escape
Sometimes, for example when CO2 is stored in saline aquifers, it can slowly dissolve in the salty water — known as ‘dissolution storage’. Here, rather than rising, the dissolved CO2 slowly falls to the lowest part of aquifer.
These natural processes will be at work wherever CO2 is stored. And research points towards only minimal possibilities of it leaking out. A study in the journal Nature estimates that over 98% of injected CO2 will remain stored for over 10,000 years.
Reaching scale
Carbon storage is already reality in in Texas, Wyoming, Oklahoma and Illinois in the US, and projects are underway in the United Arab Emirates, Australia, Algeria and Canada. But it is still far from reaching the scale needed to combat climate change.
Yet there is huge potential around the world. Researchers from Imperial College London and E4tec published a reportthat details an estimated 70 billion tonnes of storage capacity in the UK alone, while the US could provide an estimated 10 trillion tonnes more.
The UK’s Drax power station could soon be using some of that storage capacity, through the bioenergy carbon capture and storage projects (BECCS). BECCS could enable Drax to become the first negative-emissions power station in the world.
