Investigation of gas and gas hydrate accumulations along the continental margin of the Danube Delta (Romania and Bulgaria offshore) using seismic reflection data

Abstract

In 2012, a comprehensive study of the Danube River’s submarine channels continental slope was conducted, employing multi-beam bathymetry and over 2300 km of high-resolution two- dimensional seismic reflection data. The investigation aimed to delve into the area's morphology, potential for gas hydrate presence, and the correlation between stratigraphic units and gas hydrates. Three distinct zones, revealed Bottom Simulating Reflectors (BSRs) indicating the base of gas hydrate accumulations in the seismic data. These BSR areas exhibited Type-1 reflections, characterized by continuous cuts across layers. Notably, five discrete levels of BSRs were detected, suggesting a consistent gas composition across them. The multiple BSR formations are attributed to higher sedimentation rates relative to gas hydrate dissolution rates. Mass transport deposits (MTDs) within the gas hydrate stability zone (6 in total) were identified; their highly consolidated nature could account for the absence of gas hydrates within them. Additionally, one MTD displayed elevated heat flow measurements, indicating a higher geothermal gradient, likely due to its relatively high thermal conductivity. This disparity in thermal properties explains the deeper-than-expected BSR in this specific region, as it forms at a lower temperature equilibrium level due to efficient heat conduction.