A controlled CO2 gas release within the shallow sediments of the North Sea (STEMM-CCS) - monitoring and quantification

Carbon capture and storage (CCS) in sub-surface reservoirs or aquifers is one method for mitigating climate change. For CCS to be a widely adopted there needs to be confidence that if there is any leakage to the surface it can be detected and quantified.

We describe a unique experiment within the North Sea in which Carbon Dioxide tanks were placed on the seabed and a sub-surface pipe was used to release the CO₂ under the surface sediments. The pipe drill rig and the CO₂ storage tanks for deployment are bespoke and the drill rig is the first of a kind, designed for the experiment by Cellula Robotics of Canada. During the experiment we released increasing amounts of CO₂ (between 2 and 50 litres/minute, over an 11 day period) below the seabed to create a rising plume of dissolved CO2 which after reaching the seabed emitted a stream of CO₂ bubbles into the seawater. This release was monitored using AUV, ROV, landers and moorings with an aim to test all of the currently available, and developing technologies, to detect leakage from the seabed of the placed CO₂.

This presentation will describe the experiment completed in April and May 2019, and present some initial results, with a particular focus on passive and active acoustic monitoring of the CO₂ within the sub-surface and the water column.