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Regional 3D basin and Petroleum System Modeling Study of the Murzuq Basin, Libya

Abstract

A 3D basin and petroleum system modeling study of the Murzuq basin was performed at regional scale. Despite of the abundance of well and seismic data, little information was found to constrain the dynamics of the basin and their associated fluids. Temperature and vitrinite were calibrated from a selection of key wells. AFTA data and fluid inclusions were used to better constrain the past history of the thermal regime. Seven erosion phases were also taken into account since they play a crucial role in the petroleum system history (reservoir and trap shape, source rock deposition, maturity and hydrocarbon migration).

The patchy distribution of the thin but very rich Silurian hot shale, with initial TOC that can exceed 20%, has always been considered as a major exploration risk. By reconstructing the sea-level rise and the paleo-topography that resulted from the Late Ordovician glaciation of Gondwana we could delineate the paleo-depressions where the organic matter may have been better preserved. The overpressure generated during kerogen cracking is the principal driving mechanism for moving hydrocarbon downward and inside the Mamuniyat (upper Ordovician) and Hawaz (middle Ordovician) formations. Three source rock areas with fair to excellent generative potential were identified. The most prolific is located in the North.

From these expulsion pods hydrocarbon migrated laterally inside the permeable layers following gravity driven mechanism. The expulsion stopped at the Austrian uplift (end of Early Cretaceous) except in the South-East of the studied area where it continued until the Tertiary Alpine uplift.

The Austrian event tilted the basin and caused the shift of its depocenter from North to South. Until Early Cretaceous, the depocenter was at the North of the basin, today it sits at the South of it. We note that the largest discoveries are located along the hinge line of this basin tilt. This could be explained by a favorable location for hydrocarbon charge. These structures were first charged by hydrocarbons coming from the North and after the Austrian event, they might have also been charged from the South.