ECO₂ partners from National Oceanography Centre (Southampton, UK) convened a special session entitled “Fluid Conduits and Biogeochemical Impacts of Sub-Seabed Carbon Storage (CCS) Leakage” at the AGU 2013 Fall Meeting (9^th – 13^th Dec) in San Francisco, USA. A journalist from Nature listened to the talks and interviewed several ECO₂ partners during the subsequent poster session. The consortium highly appreciates the coverage by Nature (the article). It should, however, be noted that the report was produced by a journalist and was not previewed by ECO₂ scientists. The headline and first paragraphs are written in a rather alarmist style to attract the attention of a broad audience. The members of the ECO₂ consortium would have preferred the unspectacular but more precise scientific code and would like to make the following points in order to avoid confusion among the readership:

1. Despite extensive surveys, the ECO₂ project has not found any indication that CO₂ has leaked from Sleipner in its 17 years of operation.
2. The Hugin fracture is located 25 km north of the Sleipner injection site and it is extremely unlikely that CO₂ will ever come closer than a few kilometres of it, and therefore it is considered that the probability of a CO₂ leak through this structure is negligible.
3. ECO₂ is currently evaluating the propensity to leak from Sleipner taking into account all seabed and overburden macroscopic features in the area. This work is still on-going, and at the present time, we don`t know how likely or unlikely it is that leakage may occur in the future.
4. The available data strongly suggest that, if leakage did occur, leakage rates and impacts would be minimal, and the overall net emissions reductions benefit of the CO₂ storage project would still be very positive.
5. ECO₂ project public perception studies have found no evidence that offshore storage will always be preferable to onshore storage; publics understand that environmental systems are complex and do not want reassurance that a site will never leak but want to know that all provisions have been taken to minimize the risk.

An overview on our current knowledge and the scientific work performed by ECO₂ can be found in the abstract summarizing the introductory talk of the AGU session (add link to abstract).

Abstract:

Sub-seabed CO₂ Storage: Impact on Marine Ecosystems (ECO₂)

by Klaus Wallmann and the ECO₂ consortium

The European collaborative project ECO₂ sets out to assess the environmental risks associated with storage of CO₂ below the seabed (http://www.eco2-project.eu). It includes 28 partners from 7 European nations assessing the likelihood of leakage and impact of leakage on marine ecosystems. ECO₂ studies the sedimentary cover and the overlying water column at active CO₂ storage sites (Sleipner, Snøhvit) to look for any leakage pathways through the overburden and locate any seep sites at the seabed. High-resolution seismic data have been interpreted to feature a large number of vertical pipes and chimney structure cutting through parts of the sedimentary overburden at both storage sites. Formation waters are released through a 3 km long fracture 25 km north to the Sleipner platform while both natural gas and formation water are seeping through three abandoned wells located in the Sleipner area, as through many other old wells in the North Sea. The currently available data indicate that gases and fluids seeping at the seabed in the vicinity of the storage complex originate from the shallow overburden while CO₂ stored at Sleipner and Snøhvit is fully retained in the storage formation. However, the observed geological features pose a number of important questions that are currently addressed by ECO₂ via field work, data evaluation and numerical modelling: Are there any high permeability pathways for gas and fluid flow cutting through the overburden and linking the storage formation to the seep sites discovered at the seabed? Are seepage rates amplified by the ongoing storage operation at Sleipner? May CO₂ stored at Sleipner and elsewhere ultimately leak through the overburden via seismic pipe and chimney structures, fractures and abandoned wells? CO₂ release at the seabed was studied at three natural seep sites (Salt Dome Juist, Jan Mayen vent fields, Panarea) and via deliberate CO₂ release experiments conducted in the vicinity of the Sleipner storage complex. The field work confirmed previous modelling results predicting that CO₂ gas bubbles and droplets are rapidly and completely dissolved in ambient bottom waters. The efficient dissolution inhibits CO₂ release into the atmosphere and produces a significant pH drop in ambient bottom waters. A high degree of temporal and spatial variability was observed in, both, CO₂ emission rates and bottom water pH values. The response of different biota to bottom water and pore water acidification was studied at natural seep sites and in shore-based mesocosm experiments. The ongoing biological studies revealed that a limited number of species which are highly abundant at natural CO₂ seeps are resilient to elevated pCO₂. Other more sensitive species are trying to avoid and escape CO₂ affected areas. Harmful effects of CO₂ include alterations in early ontogeny of echinoderms, a phenomenon overlooked in previous studies. The field campaigns in 2012 and 2013 included 16 marine expeditions to offshore storage and seepage sites with a total ship time of 220 days. The large data sets assembled over the first project phase will be further evaluated by the ECO₂ consortium to provide a comprehensive environmental risk assessment for the Sleipner storage site, to improve monitoring strategies, and to develop guidelines for the environmentally safe operation of sub-seabed storage sites.