Reducing the risk of finding a working petroleum system using SAR imaging, sea surface slick sampling, and geophysical seafloor characterization: An example from the eastern Black Sea basin, offshore Georgia

Abstract

As new plays emerge in deepwater settings, sea surface slicks are often overlooked as a source of geochemical information to help define potential petroleum systems. To demonstrate how sea surface hydrocarbon slicks can be used, a case study is presented from the eastern Black Sea in the Rioni Basin, offshore Republic of Georgia. There source rocks of Oligo-Miocene age (Maikop) are suspected of charging upper Miocene deepwater channel-levee sands in fold and thrust system traps. To reduce exploration risk, direct evidence of hydrocarbon generation and migration was sought using sea surface slicks observed there. To provide confirmation of charge, a collection of diverse data was used. First, synthetic aperture radar satellite images were utilized to verify the presence of large recurring sea surface slicks over prospective structures. These slicks were then sampled for later analysis during the acquisition of 3-D seismic data. To verify that the slicks were related to the subsurface expulsion, seafloor bathymetric and amplitude data were extracted from the 3-D seismic volume and used to identify potential seafloor features consistent with hydrocarbon seepage. Some of these seafloor features were found to be coincident with the apparent sea surface origins of the slicks. Seismic imaging was also used to demonstrate potential migration pathways which may link suspected deep subsurface traps and the seafloor. And finally, geochemical analysis showed that the compositional characteristics of the slicks’ hydrocarbons were similar to known Maikop sourced oils in the region. This combination of data provided a high level of confidence that the seismically imaged traps in offshore Republic of Georgia are charged, suggesting a working petroleum system was present. What it cannot tell us is how much petroleum may be in these structures. That question can only be answered by the drill bit.