Sleipner, a reference for saline aquifer storage - Questions to Noalwenn Sallée, IFPEN Project Manager

Located in the North Sea, in Norwegian waters, the Sleipner site is the main pilot in the geological storage of CO₂ in saline aquifers. Each year since 1996, the Statoil company has stored a million tons of CO₂ resulting from treatment of the natural gas produced at the gas field there. The CO₂ is buried at a depth of over 800 m under the seabed.

Questions to...   Noalwenn Sallée, Methodology of CO2 storage site monitoring Project Manager

What is IFP Energies nouvelles doing in terms of monitoring at the Sleipner site ?

N. S.: Sleipner is one of the injection pilots being studied as part of the European CO₂ ReMoVe project. IFP Energies nouvelles has been involved in the monitoring of the site since 2008. In 2010, our researchers developed an innovative new methodology making it possible to assess CO₂ saturation on the basis of the reservoir's seismic response. Seismic monitoring makes it possible to identify the presence of CO₂ at significant depths and to monitor its migration in the underground environment using imaging techniques. We have already conducted a study that enabled us to verify that the CO₂ remained trapped within the storage structure, under the principal cap rock.

We have also compared two seismic surveys conducted at the Sleipner site: the first in 1994, before injection of CO₂, and the second in 2006 after injection. Comparison of these data provided us with a 3D image of the distribution of CO₂ within the aquifer and enabled us to quantify it. This will contribute to the development of a model to predict the evolution of CO₂ in a complex geological medium. Finally, in 2010, we applied a methodology developed by IFP Energies nouvelles at the Sleipner site, making it possible to evaluate CO₂ saturation on the basis of the storage site's seismic response.

How important is this last result?

N. S.: It is a major step forward. Until now, seismic methods could only be used to determine whether or not there was any CO₂ present in the geological formation of the storage site. Additional methods were required to quantify it.

Now, however, thanks to our methodology, we can link the variation in seismic response with CO₂ saturation and thereby accurately determine in what quantities it is present and how it is distributed. It will be possible to implement this method at other sites with the same characteristics as Sleipner. But we are also working on adapting it to more complex sites, where pressure effects can be triggered by injection. This will be of interest to both storage site operators and geophysical contractors.

Use of seismic data to determine CO₂ quantities and distribution in the underground environment - (c) IFP Energies nouvelles