Building the Messinian Salt Layer in the East Mediterranean Basins
The main challenge in imaging the pre-Messinian section in the East Mediterranean is the Messinian salt section. The distribution of salt in the two major basins; the Herodotus and the Levant, is interrupted primarily by detrital deposits from the Nile Delta. At the basin margins the salt body geometry changes from a horizontal bedding in a compressive regime, to a more diapiric system closer to the cone of the Nile Delta. Away from the diapiric region, in both the Levant and Herodotus basins, the salt layer shows complex intra-salt reflectivity. Despite this complexity, a constant salt velocity layer flattens the structure of the base of salt (BOS) in areas at the Levant basin. While in regions offshore Cyprus, where the BOS shows clear salt velocity variations, a variable salt velocity was imbedded. Well logs showed that the intra-salt reflectivity takes the form of thin clay beds with much lower velocities than salt. We approached the variable salt velocity modeling by comparing the variation of the gather flatness at BOS (gamma field) with the RMS amplitude map extracted in the salt section. This showed that the salt has a lower average velocity where there was significant intra-salt reflectivity. The salt layer was split into clean and dirty regions, where the clean salt velocity that flattened the gathers was 4350 m/s, and the dirty salt velocities varied depending on the salt thickness. This yielded a velocity model that both flattened the base-salt reflector and improved the flatness of the intra-salt events. In offshore west Egypt, the salt layer is completely intruded by an inflow of the Miocene turbidites lying just below the salt layer. The modeling of this complex intercalated shales/salt is required but considered to be a challenging task for the interpreter. The effect of inserting those complex shale flow inside the salt layer has restored the structure integrity of the pre-Messinian as well as the amplitude information. The seismic interval velocities are compared across the different salt layers in both major basins as well as a detailed deeper carbonate velocity study at the Eratosthenes Sea Mount. This work shows the salt layer model building strategies for three locations across the Eastern Mediterranean, including offshore Egypt, Cyprus and Lebanon and summarizes the velocity distributions in the Messinian and the pre-Messinian sections.
AAPG Datapages/Search and Discovery Article #90355 © 2019 AAPG Africa Region, The Eastern Mediterranean Mega-Basin: New Data, New Ideas and New Opportunities, Alexandra, Egypt, September 6-7, 2019