Design and use of a laboratory rig for the study of the chemical‐physical effects on aquatic environments of potential seepage from CO 2 storage sites

In sub‐seabed storage, CO 2 is injected under the seafloor in geological structures that are able to trap and retain it. Even if the overall procedure is considered safe, the effects of potential seepage must be addressed in order to develop a reliable risk assessment of the process. This study focuses on the effects of CO 2 seepage on the chemistry of sediments and on the overlying water column in shallow‐water environments. To study these effects, an experimental rig was designed, fabricated, and tested. The main unit of the rig is a transparent Plexiglas vertical cylindrical vessel that can be filled with sediment in the bottom section and water in the upper part. CO 2 is injected as gas from the bottom through nozzles fed by a CO 2 cylinder. Sensors are used to monitor the variation of the main physical and chemical properties of water and sediments. Gas, water, and sediment samples can be collected for further analysis. The results highlight a fast response of the system to the injected CO 2 with a sharp reduction of the pH values of the interstitial water inside the sediments; once the injection stops, a recovery toward the initial values is recorded. The water above the sediment is also affected by the presence of CO 2 ; in this case the gas‐water interaction is controlled by the water movements induced by the rising bubble column. © 2012 Society of Chemical Industry and John Wiley & Sons, Ltd