Dynamics of CO2 release from below the seafloor, mixing and environmental impacts - Dynamics of CO2 release from below the seafloor, mixing and environmental impacts - Biannual report VISTA 2008

Project director: Alendal, Guttorm

Post-doc/ scholar: Enstad, Lars Inge

Project duration: 01.01.07 – 31.12.08

Technical contact person in Statoil: Ståle, Johnsen

Division head: Ståle, Johnsen

Project number: 6152

Object:

The main object of the project is to establish fundamental understanding about mechanism for release of CO₂ rich fluid through the seabed. In order to do so an appropriate model for flow in porous media will be combined with a General Ocean Circulation Model. To develop and test the dynamical models, selected natural occurrences of CO₂ releases at the ocean floor will be studied. Gas seepage through the sea floor is a diverse phenomenon which is observed both in volcanic areas and in hydrocarbon rich areas. The choice of which leakage type to use as comparison depends both on suitability of the seepage in regard to the project goals and the availability of measurements. Once selection has been done the porous media model can be designed to fit to the type of geology and driving forces in areas of interest. An in-house droplet/bubble model will be connected to the General Ocean Circulation Model which already is capable of modelling the transport and spreading of CO₂ as a dissolved active tracer. The modelling tool will then be applied to a selected and well monitored seepage location.

Status:

During the first two months of 2008 the newly coupled droplet/bubble and MITgcm was debugged and further developed. It now includes both mass transfer and momentum transfer from the droplet/bubbles to the surrounding fluids. Some preliminary results for slow seepages in simple flow geometry has been produced.

For three months during spring 2008 Lars Inge visited Klaus Wallmann’s group at IFM-GEOMAR in Kiel. He benefited from the high competence level in this group regarding natural leakages of gases at the seabottom. During these months he worked closely with members of the group to improve rise velocity predictions of CO2 and CH4 droplets or bubbles. This resulted in a suggestion of a new drag parametrization for such droplet/bubbles which had a good agreement with newly performed experiments at IFM-GEOMAR. This new parametrization will improve the droplet/bubble model which is to be used in the further studies. He also obtained information of the cruise performed in March-April, monitoring and studying a CO2 leakage location outside Japan by members of IFM-GEOMAR. A contact has been initiated to see if data from this cruise can be used as comparison with the model.

Publications:

“Dissolution of a CO2 lake, modeled using an advanced vertical turbulence mixing scheme”, Enstad, L.I., Rygg, K., Haugan, P. M. and Alendal, G., J Greenhouse Gas Control, In Press

“A new drag parametrization of CH₄ and CO₂ droplets or bubbles with or without hydrate cover”, In preparation

«Comparison of properties of methane and carbon dioxide in seawater with relevance for dissolution and

spreading from a leakage point», Enstad L. I., Haugan P. M. & Alendal G., to be resubmitted

Previous publications:

«Dissolution from a CO₂ lake», Enstad, L. I., Haugan, P. M. & Alendal G., Geochimica et Cosmochimica Acta 71 (15): A257-A257 Suppl. S, AUG 2007

«Natural seabed seeps, preparations for numerical studies», Enstad, L. I. , BCCS Technical Report Series,

NO-22