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The Impact of the Messinian Salinity Crisis on the Petroleum System of the Eastern Mediterranean: A Critical Assessment Using 2-D-Petroleum System Modelling

Abstract

In the Eastern Mediterranean, the Messinian Salinity Crisis (MSC) was associated with removal of c. 1000 m of water and deposition of up to 2000 m of evaporites. As a result of this geologically instantaneous event, subsurface pressures and temperatures were strongly perturbed, which is expected to have a potentially significant impact on the petroleum systems in several ways. We undertake 2D petroleum system modelling (using PetroModTM) of a cross-section from the Levant Basin to examine the range of possible phase- and seal-related scenarios that may have occurred during the MSC. Our initial results show that the drawdown has an instantaneous effect on pressure whereas it has a transient effect on temperature. An overall decrease in pressure is likely to have caused the formation of gas caps above saturated oil accumulations, and existing gas accumulations to have reacted to the pressure reduction by expanding. A prerequisite for these volume and density changes within any individual hydrocarbon accumulation is a certain initial (pre-Messinian) composition, which defines the PVT diagram, in conjunction with a certain depth, which defines the pressure and temperature changes the individual accumulation was exposed to during the MSC. We suggest that this critical composition results from a mixture of thermogenic oil and biogenic gas. Any volume increase within existing structures which were initially filled to spill (trap-limited) would have caused displacement of oil from these closures and remigration to other traps located further updip. Accumulations which have been seal-limited prior to the MSC are assumed to have experienced a seal failure, as the rapid buoyancy increase triggered by the volume changes could not be accommodated by capillary leakage only. This is supported by pockmarks observed at the base of the Messinian salt. In addition, water load removal is expected to have created a geologically instantaneous pressure build-up with associated regional fracturing. We suggest that successful exploration should integrate the different scenarios of the Messinian drawdown impact in the risking analysis. Expected consequences are the transformation of the saturated oil fields into gas fields, catastrophic seal failure and loss of hydrocarbon and redistribution of hydrocarbon accumulation because of remigration. These controlling factors will be addressed in details in the presented paper.