Development of a combined geochemical-geophysical approach for quantification of regional submarine gas hydrate inventories

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The proposed project aims at developing a new approach to quantify the amount of gas hydrate (GH) in continental margin sediments by the complementary use of geochemical models and the implementation of the effective medium theory (EMT) for seismic modelling and inversion. Reflection seismics provides 2-D information on variations in P-wave interval velocities using migration velocity analysis (MVA), which will be inverted to determine in situ GH concentrations. In contrast, numerical models will provide reliable predictions of the formation potential of methane and GH when calibrated against geochemical data from ODP sites. Preliminary results show that the prediction of GH inventories by seismic methods is highly sensitive to the accurate determination of porosities. This may cause large uncertainties, which can be reduced by calibration against the numerical model. The basic strategy is to use the geochemical approach as constraint for basic parameterisations of the geophysical model in the vicinity of ODP sites. In turn, a well-calibrated geophysical model will then provide useful model inputs along seismic lines where no drilling data are available for geochemical modelling. This approach will yield solid information on regional variables (e.g. sediment thickness, heat flow, degradation constants), which can be used for empirical predictions of the GH inventory and distribution. In addition, selected key studies will be performed for high flux scenarios (e.g. mud volcanoes) to improve estimates of their proportional significance for the total GH inventory.