In the centre of the North Sea is an iconic carbon capture and storage (CCS) project, which has been storing carbon dioxide stripped from natural gas production since 1996. The Sleipner CO₂ storage project was the first of its kind in the world, and Norwegian operator Statoil has so far captured and stored around 14 million tonnes of the greenhouse gas, driven by the commercial imperative to avoid offshore carbon taxes combined with the ambition to behave in a more sustainable way.
|Image: Alligator film/BUG - Statoil|
Using seismic data, the researchers tracked CO₂ behaviour after injection into the Utsira formation – the project’s saline aquifer storage site. Using a novel method of percolation-flow modelling, they have established that the subsurface imaging of CO₂ plumes (the observed migration of CO₂ after injection) can be mass-balanced to the CO₂ injected; that there is no leakage detectable using seismic techniques; and that residual saturation together with multiple thick seal rock layers act to retain the CO₂.
The researchers propose a novel mechanism to explain the shape of the CO₂ plume – namely, that the mudrock barriers within the Utsira reservoir must be fractured to allow the very rapid vertical ascent of the plume. Furthermore, they speculate that the fracturing was caused by rapid pore fluid pressure change during the deglaciation of the UK-Scandinavian ice sheet about 12,000 years ago. The research concludes that the Sleipner site, which serves as an exemplar for saline formation storage projects worldwide, shows no evidence of unplanned leakage of either CO₂ or methane.
Correspondence by SCCS experts is also published today in Nature (read the letter here), which counters a news article that appeared in the science journal in December. This had claimed that the discovery of seabed fractures in the North Sea may place doubt on the viability of large-scale CO₂ storage projects, such as Sleipner. The correspondence by SCCS summarises a working paper published in January, where the authors expressed concern that this was the latest in a series of unsubstantiated claims, based on data from the European Commission’s €10-million ECO₂ research project, which have not been adequately supported by peer-reviewed published information. Read the full paper here.
The SCCS authors state: “It is now important to provide an alternative perspective, based on published information, that geological storage of CO₂ by deep injection for CCS is both sufficiently secure, and knowable in its environmental impacts. Furthermore, research has shown that there is good support from many parts of the public, although qualified, for CCS as an essential part of a response to the threat of global climate change and ocean acidification.”