Carbon Capture and geological Storage

Carbon Capture and Storage (CCS) is internationally considered as an important option to strongly reduce the emission of CO₂ to likely more stringent post-Kyoto targets. The technique consists of three basic steps:

1. capturing CO₂ at large and stationary point sources,
2. transporting the CO₂ from a source to a sink, and
3. injecting the CO₂ in suited geological reservoirs or sinks.

The technique is briefly explained in these 9 slides.

Nevertheless, carbon sequestration is still in a test phase. Model projects include an ocean sequestration field experiment in Norway and a Statoil project in the Sleipner field where CO₂ is pumped into a saline aquifer. In May 2006, an installation to capture CO₂ in the flue gases of the Esbjerg coal-fired power station in Denmark (Castor project) was inaugurated. This project aims to achieve capture and geological storage of 30% of the CO₂ emissions of European large industrial facilities. Here, post-combustion capture is tested, where separation of CO₂ (only a few to 20% of the total gas) from the flue gas is essential.

CCS is often referred to as the necessary technical fix, because it allows to continue using fossil fuels. CCS is therefore generally regarded as a transition option during the first half of the 21^st century, that can help bridging the time gap posed by the urgent need to act against climate change and the time needed to fully develop and implement renewable energy.


Public perception on carbon capture and geological storage

A study reported by Gough and Shackley (2003) shows that:

• storage of CO₂ underground will probably be accepted if also other options like energy efficiency and renewable energy are applied
• acceptance of new technology will mainly be influenced by the media and by the trust level in key institutions

Questions mainly rise on the subject of safety and security of carbon storage:

• geochemically: corrosion of the reservoir rock matrix, mineral precipitation, dehydration or dissolution of components of the cap rock, dissolution of CO₂ into the pore fluid
• with respect to pore fluid pressure: fracturing of the cap rock, opening of former migration paths, CO₂ transport through cap rock due to high gas pressure
• concerning well: CO₂ escape via poorly sealed former wells or failure in injection well, CO₂ escape due to corrosion of cement or steel in wells
• other issues: presence of unidentified migration paths, CO₂ escape via spill point at the base of the closed structure, displacement of highly saline brines from storage location