Dynamics of CO2 release from below the seafloor, mixing and environmental impacts - Biannual report VISTA 2009

Biannual report VISTA 2009

Dynamics of CO2 release from below the seafloor, mixing and environmental impact

Project director: Alendal, Guttorm, UoB

Post-doc/ scholar: Enstad, Lars Inge

Project duration: 01.04.2009 – 31.03.2011

Technical contact person in Statoil: Last name, First name

Division head: Mostad, Helle Britt

Project number: 6152

Object:

The main objective of this project is to clarify how CO₂ enters oceanic waters and subsequently dissolve and spread in the water column. This is to be done by comparing model data with existing data from observed natural analogues. Such natural analogues are until now only observed at the seafloor in volcanic areas where temperature and salinity gradients are high. To serve as a natural analogue the geological conditions are also quite different from what one would expect to find in an area with a potential to be used as a geological storage site for CO₂. Another known and observed form of gas leakage at the seafloor are hydrocarbons, mainly CH₄, seeping out in areas with pockmarks. These are found in hydrocarbon rich areas where the geological conditions are more similar to what one would expect to find at a storage site. Unfortunately the chemical properties of CH₄ is quite different from that of CO₂ in seawater. To be able to use natural occurrences of gas seepage as analogues it is important to identify the most suitable seepage sites and to use the appropriate model tools.

Status:

During the first part of the first two year period of this project a literature survey were performed to map and identify different types of gas seepage at the seafloor and a technical report was written based on this. Since the most frequently observed gas leaking from the seafloor is CH₄ the chemical properties of CH₄ was investigated and relevant properties were implemented in a library. The first two year period also included a visit to Klaus Wallmann’s research group in Kiel. During this visit the possibility to improve the drag parametrization of CO₂ and CH₄ droplets and bubbles both with and without hydrate coating using experimental data open up. A manuscript from this collaboration is currently under preparation. The contact with the German group also opens the possibility to use their data from a cruise outside Japan to one of the best known CO₂ seepages to compare with model results. A single droplet/bubble model has been coupled with the MIT general circulation model to make a model tool for numerical simulation of such a gas seep available. In the start of the new project period Gregor Rehder and Nikolaus Bigalke from the German group visited Bergen to elaborate further on the drag parametrization and present data from the cruise.

Publications:

Conferences:

TCCS-4, Trondheim, October 2007, “Comparison of methane and carbon dioxide behavior in seawater: Lessons relevant to CO₂ leakage”, Oral presentation

Ocean in a high CO₂ world, Monaco, October 2008, “A numerical study of transport and spreading of gases from gas-seepage through the seafloor”, Poster presentation

GHGT9, Washington, November 2008, “A numerical study of transport and spreading from natural gas-seepage analogues through the seafloor”, Poster presentation

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