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Quantifying the Impact of the Messinian Salinity Crisis on the Eastern Mediterranean Petroleum Systems

Abdulaziz N. Al-Balushi, Alastair J. Fraser, Philip A. Allen, and Chris Jackson

The Eastern Mediterranean has become the focus for increased oil and gas exploration following significant discoveries in the pre-Messinian succession offshore Egypt and the Levant margin. An important event known as the “Messinian Salinity Crisis (MSC)” at c. 5 Ma played a major role in shaping the present day distribution of oil and gas in the region.

During the MSC the Mediterranean Sea witnessed a dramatic fall in sea level and rapid deposition of evaporites as a result of the closure of the Gibraltar Straits, which isolated the Mediterranean Sea from the Atlantic Ocean. The geologically instantaneous unloading of water and subsequent deposition of evaporites may have had a major impact on the pre-existing petroleum accumulations. Firstly, the uplift caused by isostatic rebound of the lithosphere due to water unloading would be associated with a significant pressure release, causing saturated oil fields to become two phase, with the associated gas expansion leading to either seal failure or remigration of oil via structural spill points. Secondly, uplift, if accompanied by erosion, may also be associated with a decrease in subsurface temperatures. As a result of this, biodegradation could have been active and might have resulted in transformation of hydrocarbons to a lower quality heavy crude and dry biogenic gas.

In this study, we used several regional deep 2D seismic datasets with a recording length of 12 sec TWT and up to 20 sec TWT for some lines. Based on seismic observations presented in this study, we estimate that the magnitude of the sea-level drawdown associated with the MSC was at least 2400 m. This figure was then used in a flexural backstripping analysis to test the isostatic response of the lithosphere. Our models indicate that the flexural isostatic uplift due to the removal of water associated with the MSC affected both the basin centre and at the basin margin. Initial results show that the basin margin may have experienced up to 1 km of uplift over a width of 130-230 km, depending on the flexural rigidity of the lithosphere.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013