What is CO2 capture and storage?

The CO2 released from producing or burning fossil fuels can be captured and kept out of the atmosphere for thousands of years by storing it away in various forms. This wins the world valuable time to develop and deploy large-scale alternative sources of energy.

CO2 capture

There are various ways to capture CO2 from fossil fuels. The higher pressure and higher purity the CO2 captured, the easier and more cost effective it is to store it.

Pre-combustion capture. The CO2 can be removed in advance by reforming the fossil fuel into hydrogen. This is, for example, what our coal gasification technology does with coal and what the proposed CCS project in mid-Norway does with natural gas.
Oxygen combustion with capture. The fuel can be burnt in pure oxygen and the highly concentrated CO2 flue gas captured
Post-combustion capture. The fuel can be burnt normally, in air, and the diluted CO2 scrubbed out of the flue gas.

CO2 storage

Once captured, there are various ways to store (or sequester) the CO2:

Geological sequestration involves the injection of CO2 into underground geological formations, like aquifers or depleted oil or gas reservoirs. If injected into the latter, the CO2 can be used to recover more oil or gas from the reservoir. This is called CO2 enhanced recovery.

The technology required for geological sequestration is proven and in common use in the oil and gas industry for enhanced oil recovery: enough storage capacity has been identified, spread around the world to store significant amounts of global CO2 emissions over the next century and; research has shown that CO2 can be securely stored for thousands of years or longer. Further research and field trials are underway to further clarify and manage the risks involved.
Biological sequestration uses the natural absorption of CO2 by plants to remove CO2 from the atmosphere and store it away in trees and crops. This creates biological ‘carbon sinks’. Activities like changing how land is used (including aforestation and reforestation), or turning CO2 into algae that can then be used as a renewable energy source all reduce for a time the amount of CO2 in the atmosphere. Taking such measures can indirectly compensate for (or ‘offset’) the CO2 emissions from producing or using fossil fuel. We recognise that biological sequestration could play a role in our portfolio of activities to manage CO2 emissions.
Surface mineralisation involves fixing CO2 chemically into inorganic carbonates that can be used for building materials and other long life goods. Shell is active in the development of technologies in this field.
Ocean sequestration involves injecting high purity CO2 into the deep part of the oceans where it can remain in liquid state at low temperature and under high pressure. This technology is still in its infancy. Considerable further development is required, including dealing with potential risks to the deep ocean ecosystem and understanding how long the CO2 is likely to stay stored away.

→ Shell Sustainability Report 2006

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