Abstract
We report the first successful use of chemical sensors integrated on to an underwater vehicle to locate, map and estimate flux from a controlled sub-seabed CO2 release, analogous to a leak from a Carbon Capture and Storage (CCS) reservoir. This has global implications for the efficacy and cost of monitoring of offshore CCS sites and hence public and regulatory confidence as this tool for addressing climate change is considered and rolled out. A remotely operated vehicle (ROV) equipped with three different pH sensors was deployed to determine the spatial extent of the controlled release. The sensors each operated on a different principle (spectrophotometric, fluorescence, and electrochemical) and the strengths and weaknesses of each sensor are discussed. The sensor data demonstrated that evidence of the plume was limited to within 3 m of the seafloor, as predicted by previous modelling work. The data were then utilised to develop a model of the plume, to extend the spatial coverage of the data. This comparison of the three sensors and the insight into plume dynamics provided by the model would assist in the planning of future plume surveys to ensure the sensor and vehicle combination can resolve the plume of interest.
Highlights
Reduced greenhouse gas emissions alone are unlikely to be enough to reach the target of keeping global temperatures within 2 ◦C of prein dustrial levels, as is the aim of current policies set by the Paris agreement
In this paper we describe how an remotely operated vehicle (ROV) equipped with a suite of novel sensors was used to monitor a plume resulting from a controlled subseabed CO2 release as part of the European Union Horizon2020 proj ect titled Strategies for Environmental Monitoring of Marine Carbon Capture and Storage (STEMM-Carbon capture and storage (CCS))
Experiment overview The four-year STEMM-CCS project culminated in a six-week cruise in the North Sea in spring 2019 to carry out a controlled gas release, Table 1 Comparison of pH sensors on the ROV
Summary
Reduced greenhouse gas emissions alone are unlikely to be enough to reach the target of keeping global temperatures within 2 ◦C of prein dustrial levels, as is the aim of current policies set by the Paris agreement Previous studies have pointed to the benefit of using multiple vehi cles to collect data (German et al, 2012; Guerrero-Gonzalez et al, 2016) This has been suggested for CCS monitoring, using an AUV to monitor a large area and deploying an ROV to quantify the leak more accurately (Blackford et al, 2014; Dean et al, 2020). We develop a parameterised forward model based on the experimental results to expand the sparse spatial coverage of the survey data We demonstrate how such a model can be used during the planning phase to define the technical specifications of the autonomous vehicles and sensors required to conduct long-term monitoring of an offshore CCS project. This approach could be expanded to inform the design of plume monitoring programmes for other applications
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