Anna Lichtschlag at the National Oceanography Center Southampton was awarded funding in the UKCCSRC’s Flexible Funding 2021 Call to look at “Sensor Enabled Seabed Landing AUV nodes for improved offshore Carbon Capture and Storage (CCS) monitoring”.
Within Europe, much of the geological capacity for storing CO2 lies in reservoirs that are located deep below the seafloor, such as depleted oil and gas reservoirs. These offshore storage reservoirs might play an important role in CCS as they are large and the infrastructure for transport and storage often already exists. Although these reservoirs are likely to safely contain the CO2 over geological times, national and international regulations require that these offshore storage complexes are monitored to assure that no CO2 escapes into the seawater or the atmosphere.
Currently, one of the most efficient ways to monitor these offshore storage complexes is with sensors that either measure the CO2 directly in the seawater above the complex or related parameters such as pH (as the water becomes more acidic when CO2 dissolves). These sensors can either be mounted on autonomous underwater vehicles (AUVs) that survey the area or on stationary platforms, deployed on the seafloor. Both of these approaches have some limitations, e.g. they are either very costly or only cover a small area.
In our UKCCSRC funded project, we assessed the possibility of a new approach that would combine the advantages of both monitoring platforms, i.e. novel seabed-landing AUVs (so called ‘Flying Nodes’) that are developed by Autonomous Robotics Ltd. (ARL). In particular, we tested if we can integrate the long-term deployable Lab-on-Chip chemical pH sensors, developed at the National Oceanography Centre Southampton, on these seabed-landing AUVs and how these sensor-enabled Flying Nodes then could be used to monitor potential CO2 leakage.
For this, we first designed a specification and tested how NOC’s pH sensors can be electronically and mechanically integrated into a Flying Node, and also established how the pH sensor and the Flying Node software can be integrated. This was followed by a first successful communication test between the two technologies. We concluded that the integration will be possible and ascertained that the Flying Node has the required capacity to fly properly whilst carrying all components of the sensor. As a next step, we used the commercial Comsol Mulitphysics software to identify the requirements of a potential deployment of the sensors-equipped Flying Nodes. Assuming a typical North Sea scenario, our model results showed that, for a small CO2 leakage rates (below 500 kg/d), the monitoring should occur as close as possible to the seafloor as this increases the detectable area of the plume (i.e. ca 100 m longer at 0.5 m height compared to 3 m height). The CO2-enriched plumes in the modelled setting are long (hundreds of metres), but thin and close to the seafloor, suggesting that a monitoring pattern of transverse sampling across the potential plume location, some tens of metres downstream of the likeliest release sites, would be the most successful strategy.
As part of this project we closely worked together with Autonomous Robotics Ltd. (ARL) who develop the Flying Nodes and we are very grateful for their contributions and the productive discussions during this project.