Laboratory simulations and field-study of CO2 seepage in aquatic environments

Sub-seabed represents a valid storage solution for anthropogenic carbon dioxide (CO)2 and it is the preferred target for carbon dioxide capture and storage (CCS) projects in several countries, including the UK and Japan, which do not have large onshore storage capacity. Moreover off-shore storage is now also being considered by other countries, including the USA specifically in the East Coast and Gulf of Mexico regions, for its larger storage potential and reduced interaction with human infrastructures as compared to inland areas.

Storing large volumes of CO2 requires extreme attention to avoid any negative impact on the delicate marine environment and therefore, reliable seepage detection and monitoring techniques are mandatory.

In this paper, a small-scale laboratory experiment aimed at studying the interaction between CO2, sediments and water is described and compared with outcomes from the study of a submarine natural area where CO2 is emitted from the seafloor in shallow-water.

The main findings are that the presence of even small levels of CO2 can be easily detected by the drop in pH in the presence of carbonate minerals with high buffering potential. In the natural emissions gas exchange between the rising bubbles and the surrounding water was observed. This is an important control factor in the diffusion of CO2. The emission points and the dimension of the bubbles showed a correlation with the granulometry of the sediments covering the seafloor. Comparable similar behaviours were observed in the laboratory experiment.