Abstract
A gas hydrate reservoir, identified by the presence of the bottom simulating reflector, is located offshore of the Antarctic Peninsula. The analysis of geophysical dataset acquired during three geophysical cruises allowed us to characterize this reservoir. 2D velocity fields were obtained by using the output of the pre-stack depth migration iteratively. Gas hydrate amount was estimated by seismic velocity, using the modified Biot-Geerstma-Smit theory. The total volume of gas hydrate estimated, in an area of about 600 km2, is in a range of 16 × 109–20 × 109 m3. Assuming that 1 m3 of gas hydrate corresponds to 140 m3 of free gas in standard conditions, the reservoir could contain a total volume that ranges from 1.68 to 2.8 × 1012 m3 of free gas. The interpretation of the pre-stack depth migrated sections and the high resolution morpho-bathymetry image allowed us to define a structural model of the area. Two main fault systems, characterized by left transtensive and compressive movement, are recognized, which interact with a minor transtensive fault system. The regional geothermal gradient (about 37.5 °C/km), increasing close to a mud volcano likely due to fluid-upwelling, was estimated through the depth of the bottom simulating reflector by seismic data.
Highlights
Gas hydrates are solids composed by ice containing molecules of gas, usually methane, in the lattice which grow within the pore space of sediments [1]
Residual move-out is observed in the Common Image Gathers (CIGs); for this reason, residual move-out analysis is used to update the migration velocity [46]
A complex structural setting of the sedimentary prism and the gas hydrate reservoir was defined by the structural interpretation of the depth migrated seismic images
Summary
Gas hydrates are solids composed by ice containing molecules of gas, usually methane, in the lattice which grow within the pore space of sediments [1]. They are common in the upper hundred meters of sediments along both active and passive continental margins [2] and permafrost areas [3] and where high pressure, low temperature and adequate gas saturation fall within stability conditions [1]. The BSR is given by the result of strong acoustic contrast produced by the free gas accumulated at the base of the gas hydrate layer [4,5,6]. Some authors have pointed out how geological and environmental features can affect gas hydrate accumulation within marine sediments, even when stability conditions and adequate gas amounts are respected. The theory developed by Tinivella [26] was adopted to estimate gas hydrate amount, because no direct petro-physical parameters were available
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