Seismic expression of gas and gas hydrates across the western Black Sea |
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| Authors: | Irina Popescu Gilles Lericolais Nicolae Panin Marc De Batist Hervé Gillet |
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| Institution: | (1) Renard Centre of Marine Geology (RCMG), University of Ghent, Krijgslaan 281 S8, 9000 Ghent, Belgium;(2) IFREMER Brest, DRO/GM LES, B.P. 70, 29280 Plouzané, France;(3) GeoEcoMar Bucharest, Str. D. Onciul 23-25, Bucharest, 024053, Romania |
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| Abstract: | This study is a synthesis of gas-related features in recent sediments across the western Black Sea basin. The investigation
is based on an extensive seismic dataset, and integrates published information from previous local studies. Our data reveal
widespread occurrences of seismic facies indicating free gas in sediments and gas escape in the water column. The presence
of gas hydrates is inferred from bottom-simulating reflections (BSRs). The distribution of the gas facies shows (1) major
gas accumulations close to the seafloor in the coastal area and along the shelfbreak, (2) ubiquitous gas migration from the
deeper subsurface on the shelf and (3) gas hydrate occurrences on the lower slope (below 750 m water depth). The coastal and
shelfbreak shallow gas areas correspond to the highstand and lowstand depocentres, respectively. Gas in these areas most likely
results from in situ degradation of biogenic methane, probably with a contribution of deep gas in the shelfbreak accumulation.
On the western shelf, vertical gas migration appears to originate from a source of Eocene age or older and, in some cases,
it is clearly related to known deep oil and gas fields. Gas release at the seafloor is abundant at water depths shallower
than 725 m, which corresponds to the minimum theoretical depth for methane hydrate stability, but occurs only exceptionally
at water depths where hydrates can form. As such, gas entering the hydrate stability field appears to form hydrates, acting
as a buffer for gas migration towards the seafloor and subsequent escape. |
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