Detecting sea floor carbon dioxide anomalies

Detecting sea floor carbon dioxide anomalies

Sam Soffes / Unsplash 

​PML scientists are highlighting a new way of detecting carbon dioxide (CO2) anomalies on the sea floor, and how this can help to monitor Carbon Dioxide Capture and Storage (CCS).

CCS is one strategy which could help to control greenhouse gas emissions that contribute to climate change and ocean acidification. CO2, captured from sources – such as fossil fuel-burning power plants or industry - is relocated beneath the ocean floor in suitable geological formations. There it is permanently stored, well away from the planet’s atmosphere. Storage beneath the sea floor is not without challenges, however, and the integrity of the geological storage sites must be demonstrated to ensure confidence that no CO2 will leak into the atmosphere.

To be confident that leaks are not occurring potential leakage needs to be detected accurately and promptly. Storage monitoring uses seismic techniques to produce images of geologically stored CO2, which is an expensive method. Instead, a chemical way of checking for emissions at the sea floor could be more suitable. But this process in itself is complex, and what to measure remains open to debate. CO2 levels in seawater are naturally variable and increases in CO2 could be a result of other factors, such as rivers, circulation patterns, changes in temperature, biological activity and ocean acidification.

A group of PML scientists have developed an effective strategy for assuring the absence of leaks by first characterising natural variability of CO2 in their North Sea study area using sophisticated computer models of the marine system. They have shown that by taking measurements of seawater acidity (pH) several times an hour, they can be certain that changes as small as 0.01pH unit (representing a tiny amount of additional CO2) would indicate an anomaly – or possible leak - rather than natural variability. As a result monitoring strategies can be recommended that will give assurance that stored CO2 is secure, and in the very unlikely event of leakage, enable rapid detection and management.

Detecting anomalies – and potential CO2 leaks - in this way is cost-effective, practical and highly sensitive. Thus PML’s modelling expertise will contribute to an increase in confidence for carbon capture and storage.

“Climate change remains an existential crisis, and it is important that society invests in a range of methods of reducing CO2 emissions, including renewable energy, energy efficiency and techniques like CCS,” said Jerry Blackford, Head of Science for Marine Ecosystems Models and Predictions at PML. “Our work demonstrates that we could monitor the integrity of subsea CO2 storage with confidence, as well as develop bespoke monitoring strategies for subsea CCS storage around the globe.”
 

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