A diver takes a water sample from seabed chamber. Image: Henrik Stahl, SAMS
An international team of scientists has this week published results from the first ever sub-sea carbon dioxide (CO₂) impact, detection and monitoring experiment relevant to Carbon Capture and Storage (CCS) in sub-seabed storage reservoirs.

This innovative study, which will be published in Nature Climate Change, was designed to understand how marine life on the seabed and in the water above might react to a real-life leakage, as well as determine methods for detection and monitoring of a small-scale CO₂ leak event. The research found that, for a leak of this scale, the environmental damage was limited; restricted to a small area and with a quick recovery of both the chemistry and biology.

The Quantifying and Monitoring Potential Ecosystem Impacts of Geological Carbon Storage (QICS) project was led by Plymouth Marine Laboratory's (PML) Jerry Blackford and funded by the Research Councils UK, the Natural Environment Research Council and the Scottish and Japanese Governments. A number of UK and Japanese institutes collaborated in the experimental controlled release of CO₂, undertaken in Ardmucknish Bay, near Oban, in Scotland in 2012. The experiment was co-ordinated by the Scottish Association for Marine Science (SAMS).

The international project included researchers from three SCCS partner institutes – British Geological Survey, Heriot-Watt University and the University of Edinburgh.

Around 4.2 tonnes of CO₂ (less than the annual CO₂ emission of a gas-heated UK home*) was injected over 37 days from a land-based lab via a borehole drilled through rock to the release site, 350 metres from the shore and 11 metres below the seabed. Scientists initially monitored how the CO₂ moved through the sediment and the 12 metres of water above. Over the following 12 months the impact on the chemistry and biology of the surrounding area was assessed using a combination of techniques, including chemical sensors, listening for bubbles and diver-mediated sampling.

A combination of chemical sensors and bubble acoustic techniques are shown to provide the optimal monitoring technology to detect leakage or give assurance of no leakage.

The impact of this simulated leak shows that the impact of escaped CO₂ on a similar scale would be limited. CO₂-induced chemical changes occurred towards the end of the CO₂ release but impacts, including changes to environmental chemistry, returned to background levels within 17 days of turning off the CO₂ release.

No biological effect was observed during the early stages of the release. At the end of the release period and early in the recovery period, there was a change in seabed-dwelling communities as well as the gene expression of microbes. These impacts were not catastrophic or long lasting and full recovery was seen within weeks.

Project leader Jerry Blackford, at PML, said:

These findings are contributing to the growing knowledge base necessary for optimal deployment of CCS as a climate change mitigation measure; in particular for the regulatory requirement for monitoring. The results show that small-scale leakage will not be catastrophic, although we do caution that impacts are likely to increase if a larger amount of CO₂ is released. Water movement in the area is also important; impacts are estimated to be less and recovery quicker in environments with stronger water mixing so that the CO₂ is dispersed more rapidly."

Dr Maxine Akhurst, of British Geological Survey, said:

BGS is very pleased to have contributed its established scientific research expertise to site selection, management of the high-resolution drilling of the release borehole, knowledge of natural submarine CO₂ flow, 3D modelling of the release site, and seismic survey and biogeochemical monitoring for the groundbreaking QICS project. BGS acquisition of data is ongoing to further understand the impact of CO₂ release. I would like to acknowledge the support given by the local people at Benderloch as being crucial to the success of the QICS project, and also advice given by regulatory, planning, government, environmental and industry stakeholders."

This study did not address the integrity of storage in reservoirs situated 1km or more below the sea floor, but addressed the "what if" scenario of leakage at the seabed. Leakage of CO₂ from storage reservoirs is thought to be unlikely.

Recommendations for CCS operators developing risk strategies include the following:

  • CCS site selection should be below dynamic bodies of water to promote dispersal of CO₂ in the unlikely event of leakage;
  • a comprehensive baseline study, encompassing sediment structure and content, sea water chemistry, biological community structure and ambient noise, is required to maximise monitoring efficiency;
  • a combination of chemical pH and bubble-listening sensors will maximise early leakage detection or, alternately, provide assurance that leakage is not occurring;

The partners involved in the project are Plymouth Marine Laboratory, Scottish Association for Marine Science, National Oceanography Centre, British Geological Survey, University of Southampton, University of Edinburgh, Heriot-Watt University, all UK; Research Institute of Innovative Technology for the Earth, Kyoto, International Institute for Carbon-Neutral Energy Research, Kyushu University, The General Environmental Technos Co, Central Research Institute of Electric Power Industry, University of Tokyo, National Institute of Advanced Industrial Science and Technology, all Japan.

* the typical annual energy use in a UK gas heated home equates to approximately 4.8 tonnes of CO₂ emissions (Ofgem 2010).

Download the project paper here

Jerry Blackford gives a short overview of project

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