Reply by Andy Chadwick 22 July 2008

Hi Mark,

Another good list of links but I’d like to take issue with your last point re. injecting CO2 into deep sea basalts. As I understand it they are relying mostly on fractures to provided the connected porosity required for storage. If such fractures connect to the seabed (or to unconsolidated sediment on the seabed) then they would pose a significant containment risk. Injecting large amounts of CO2 into a fractured but otherwise low permeability medium such as basalt will require injection pressures considerably above hydrostatic. Such pressures could easily expel CO2 via the fractures, even though CO2 is denser than water at these conditions. It’s the active injection phase where high dynamic pressures are encountered that poses the problems. Longer term prospects are better with the potential for chemical fixing (including hydrates), though diffusive leakage may remain an issue.