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

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Annual report VISTA 2008

Project title "Dynamics of CO2 release from below the seafloor, mixing and environmental impacts"

Project director: Alendal, Guttorm, University of Bergen

Post-doc/ scholar: Enstad, Lars Inge

Project duration: 01.01.07 – 31.12.08

Technical contact person in Statoil: Last name, First name

Division head: Johnsen, Ståle

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 and subsequent dissolution and spreading. In order to do so an appropriate model for flow in porous media should be combined with a General Ocean Circulation Model (OGCM). By coupling the OGCM to droplet/bubble models the transfer and subsequent transport of the dynamically active tracer can be simulated. To develop and test the dynamical models selected natural occurrences of CO₂ releases at the ocean floor will be studied. Gas seepage through the seafloor is a diverse phenomenon which is observed both in volcanic areas (CO₂ release) and in hydrocarbon rich areas (CH₄ release). An important factor in the project will therefore be to identify which type of release which will be most suitable to investigate to fulfil the project goals. Once this has been established the porous media model can be designed to fit to the type of geology and driving forces in areas of interest. The modelling tool will then be applied to a selected and well monitored seepage location.

Status:

During spring 2008 the PostDoc candidate visited IFM-GEOMAR in Kiel for three months. This institution was involved in a cruise outside Japan where there is leakage of liquid CO₂ at 1600 meters depth. The result from the cruise is currently beeing analyzed. Contact has been made regarding the possibility to use data from this cruise to compare with model output. Also recently compiled experiments on the fate of rising CO₂ droplets was made available. A simplified formulation of drag coefficient of CO₂ and CH₄ droplets and bubbles was suggested based on this collaboration. Based on this improved parametrization the bubble/droplet model has been developed further. Progress has also been made in regard to implementation and verification of the coupling of the OGCM and the droplet/bubble model. Modified solubility parameterization in the model shows good agreement with data from in situ experiments. Since the model has not yet been coupled with porous media solver the flux at the bottom is assumed constant. By using a very simplified Darcy equation temporal variation due to tides could be included.

Publications:

«Natural seabed seeps, preparations for numerical studies», Enstad, L. I. , BCCS Technical Report Series, NO-22

“Dissolution of CO₂ from a CO₂ lake modeled using advanced vertical turbulence mixing scheme”, L. I. Enstad, K. Rygg, P. M. Haugan, G. Alendal, Greenhouse Gas Control, 2008

«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

“Terminal velocities of pure and hydrate coated CO₂ droplets and CH₄ bubbles rising in a simulated oceanic environment”, Lars Inge Enstad, Nikolaus Bigalke, to be submitted