Strategies for detection and monitoring of CO2 leakage in sub-seabed CCS

Carbon dioxide (CO2) capture and storage (CCS) in sub-seabed geological formations is currently being studied as a potential option to mitigate the accumulation of anthropogenic CO2 in the atmosphere. For the verification of CO2 storage integrity in the sub-seafloor, developments of the techniques to detect and monitor CO2 leaked from the seafloor is vital. Seafloor-based acoustic tomography is a technique that can be used to detect emissions of liquid CO2 droplets or gas CO2 bubbles from the seafloor. An in-situ pH/pCO(2) sensor can provide rapid and high-precision measurements in seawater, and is therefore able to detect pH and pCO(2) changes caused by the leaked CO2. An autonomous underwater vehicle (AUV) installed with the pH/pCO(2) sensor provides an automated observation technology that can detect and monitor CO2 leakage from the seafloor. By towing a multi-layer monitoring system consisting of a number of pH/pCO(2) sensors and transponders, the dispersed area of leaked CO2 overlying a CCS site can also be identified. The seafloor-mounted automatic elevator consists of a buoy equipped with pH/pCO(2) and depth sensors, collecting intermittently a CTD-like data as it ascends and descends. Hence, CO2 leakage from the seafloor is detected and monitored as follows. Step 1: detect the CO2 leakage by the seafloor-based acoustic tomography. Step 2: map the distribution of the leakage points using the pH/pCO(2) sensor installed on the AUV. Step 3: monitor the impacted area using a remotely operated underwater vehicle or the automatic elevator or by towing the multi-layer monitoring system. (C) 2013 The Authors. Published by Elsevier Ltd.