Gehrmann, Romina

Henke, T.

Hensen, Christian

Marquardt, Mathias

Mueller, C.

Wallmann, Klaus

English

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Geophysical Research Abstracts,Vol. 11, EGU2009-10180, 2009EGU General Assembly 2009© Author(s) 20092D–Gas hydrate inventories offshore Costa RicaM. Marquardt (1), T. Henke (2), C. Hensen (1), C. Mueller (2), R. Gehrmann (1), and K. Wallmann (1)(1) Leibniz-Institute of Marine Sciences, IFM-GEOMAR, Kiel, Germany (chensen@ifm-geomar.de), (2) Federal Institute forGeosciences and Natural Resources, BGR, Hannover, GermanyMarine gas hydrate inventories have been estimated along 2 seismic lines across the Pacific continental marginoffshore Costa Rica. A complementary approach has been developed using geochemical reactive-transportmodels and geophysical rock physics modelling to quantify regional GH inventories. In detail, a geochemicaltransport-reaction model has been applied to predict sub-seafloor gas hydrate distributions under varying envi-ronmental conditions and constrained by field data derived from various DSDP and ODP drill sites. Based onthese results, a simplified transfer-function has been derived that enables the calculation of gas hydrate by 3 easilyaccessible parameters: the gas hydrate stability field, the sedimentation rate, and the sub-seafloor penetrationof seawater sulphate. Independently, in situ gas hydrate concentrations have been determined by inversion ofP-wave velocities from multichannel seismic data. The geophysical approach uses the Migration Velocity Analysis(MVA) for determination of in-situ P-wave velocities. The gas hydrate concentrations are then derived from theseseismic velocities using a petrophysical model based on an effective medium theory (EMT) and e.g. lithologicalparameters from local drill sites. In addition, the interpretation of the post-stack seismic sections has been used toderive regional variations of the thermal gradient (using the depth of the BSR) and the overall sediment thickness.Applying the transfer function results in GH concentrations ranging from 0 to 100 g CH4 per cm2 seafloor. Thehighest amounts of GH are expected at mid-slope depths, where optimal conditions with respect to organic matterinput, sediment thickness and stability conditions are met. Integration of the GH bearing sediments along the pro-file and subsequent extrapolation to 1 km of continental margin length yield a GH potential of 18.7 Tg CH4 per km.

2D-gas hydrate inventories offshore Costa Rica

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