Further information on transport and storage security.
Transport security focuses around the possibility of a leak. Pinhole leaks could be the result of corrosion (particularly caused by impurities in the flow of CO2), while pipeline fractures could result from external puncture. Apart from the fact that escape of CO2 nullifies the effects of capturing it in the first place, the gas poses a much more immediate risk to local populations.
Since it is denser than air it is likely to collect in low lying areas, suffocating anything and anyone caught under the cloud. Having said this, significant uncertainty exists regarding both the behaviour of pipes upon fracture, and the likely movement of the gas upon release.
As with transport, storage security focuses on ensuring that captured and stored CO2 cannot escape. The two main components of the storage solution are the storage area itself and the trapping mechanism for securing the CO2; the trapping mechanism used will be closely related to the storage area selected. Structural trapping involves the utilisation of an impermeable rock layer above the storage reservoir and when combined with a porous and permeable rock reservoir provides good CO2 storage.
Other trapping mechanisms are residual trapping, where water surrounds pockets of CO2; solubility trapping, where CO2 is dissolved in pore water, and mineral trapping where CO2 is converted to mineral form.
Depleted oil and gas reservoirs provide the most obvious storage areas, since they have been proven to be effective at holding gas and liquids. Saline aquifers also have potential, although more research is needed in this case, particularly regarding an appropriate trapping mechanism.