Seismic characterization of multiple BSRs in the Eastern Black Sea Basin

Abstract:

The base of the present-day gas hydrate stability field is generally inferred in seismic data from the presence of a single reflector known as a bottom-simulating-reflector (BSR). However, up to three or more BSRs at different depths have been observed along some active and passive continental margins. The deeper BSRs are often interpreted either as remnants of an older BSR that no longer marks the hydrate stability limit following temperature, eustatic, tectonic, and/or sedimentation changes perturbing the hydrate equilibrium system, or as marking stability limits for different hydrate-forming gas compositions or different overpressured zones. Nevertheless, their origin and formation mechanisms are yet not fully understood. The Black Sea basin allows investigation of the formation mechanisms and dynamics of multiple BSRs, as these have previously been discovered in the western part of the basin, but not in other parts of the basin. This study presents new seismic evidence for the occurrence of multiple BSRs within the folded and thrusted sediments located on the NE margin of the Eastern Black Sea Basin (EBSB), based on long-offset seismic reflection data acquired in 2011 by Geology Without Limits and ION GXT. Our aim is to use these seismic reflection data to define a high resolution, 2D velocity model within the multiple BSRs area by applying a travel-time tomography to the first refracted arrival picked along downward-continued shot and receiver gathers, as well as to selected reflecting boundaries. This velocity model will then be used to infer hydrate distribution and saturation in sediments, changes in sediment physical properties and the presence of potential overpressured zones. This information can provide insights into the physical parameters characterizing multiple BSRs, and thus, into the mechanisms responsible for their generation in the EBSB.