Scientists Study Safety of Sub-Seabed CO2 Storage

GEOMAR Helmholtz Centre for Ocean Research Kiel has coordinated the ECO2 (Carbon Capture and Storage (CCS)) research project from May 2011 to April 2015.

Funded by the European Union, the ECO2 project developed recommendations for the selection and monitoring of submarine storage sites as well as an approach to a sound environmental risk assessment (ERA).

27 partner institutions from nine European countries cooperated in the project to help adjust CCS regulations and to operate sub-seabed CO2-storage sites more safely.

Storage of carbon dioxide in the offshore seabed as part of a Carbon Capture and Storage (CCS) strategy is often discussed as a means to reduce the increase of carbon dioxide (CO2) in the atmosphere.

During expeditions to the Norwegian storage sites Sleipner and Snøhvit and to several natural CO2 seepage sites for example in the Aeolian Sea, the Barents Sea and the North Sea, ECO2 scientists identified possible pathways for CO2 leakages, monitored seep sites, traced the spread of CO2 in bottom waters and studied the responses of benthic animals and plants to CO2. Their results and conclusions are compiled in a guide for the selection and monitoring of storage sites that has now been presented to the European Union.

ECO2 developed a generic approach for estimating consequences, probability and risks associated with sub-seabed CO2 storage. For the approach, the environmental value of local organisms is evaluated according to for example the Natura 2000 network of nature protection areas or the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR). Also, the vulnerability of environmental resources and possible impacts on them as well as consequences and risks are assessed. The major new element of this approach is the “Propensity to Leak Factor” which has been established by ECO2. The factor combines a compact description of the storage complex and heuristic techniques accommodating for the large number of parameter uncertainties. “It is not possible to simulate all relevant geological features, processes and events with reservoir modelling software currently available”, Todd Flach, principal research engineer at Det Norske Veritas Germanischer Lloyd (DNVGL) explains. “We therefore found a way to realistically estimate how likely a storage complex is to leak.”

For site selection, ECO2 recommends to avoid geological structures that may serve as conduits for formation water and gas release, geological formations containing toxic compounds and low-energy hydrographic settings with sluggish currents and strongly stratified water column. Also, storage sites should be established distant to valuable natural resources or areas in which biota is already living at its tolerance limits.

Based on its extensive field programme, ECO2 advises that overburden, seabed, and water column should be monitored with 3D seismic techniques, high-resolution bathymetry or backscatter mapping of the seabed, hydro-acoustic imaging of gas accumulations and outlets, video and photo imaging, chemical detection of dissolved CO2 in ambient bottom waters. “Most of the monitoring technology is available or developed and will soon become state of the art,” Prof. Dr. Klaus Wallmann, coordinator of the ECO2 project, points out. According to the ECO2 consortium, additional targeted studies have to be conducted if formation water or gas seeps and if pockmarks with deep roots reaching into the storage formation occur at the seabed. “It is important to check emission rates of gases and fluids and make sure that seepage is not invigorated or pockmarks are re-activated by the storage operation,” says Wallmann.

“Geophysicists, geologists, biologists, geochemists, oceanographers, legal experts, social scientists and economists worked closely together to create a multi-layered assessment of sub-seabed CO2 storage,” Prof. Wallmann summarizes. “We hope that our results help to update and adjust existing CCS rules and to develop new regulations. The knowledge we have gained is also very useful for companies planning or realizing CCS. And it can help to substantiate the discussion about CCS.”

Image: GEOMAR