*Wintershall Libya, Zat Al-Imad Complex, Tower No. 2, Floor 12(Exploration), PO Box 469 and 905 , Tripoli, GSPLAJ Libya.
robert.gruenwald@wintershall.tlmail.com
The main phase of rifting the Sirt Basin (Libya) had ceased by the mid-Cretaceous but later Alpine-related tectonic pulses in the late Eocene resulted in northward tilting of the basin. In the Maragh Trough (SE Sirt basin), a regional unconformity consequently separates Eocene carbonates from the overlying Oligocene succession. The unconformity marks a change from Eocene fully-marine sedimentation to more mixed, shallow-marine type deposition in the Oligocene. A regional transgression re-established fully marine conditions in the Miocene.
Deeply-buried (Triassic) source rocks in the Maragh Trough reached peak oil generation during the Oligocene. Two potential reservoir intervals have been identified: upper Eocene rudstones of the Augila Formation, and unconformably-overlying sandstones of the Lower Oligocene Arida Formation. Mid-Oligocene shales provide a regional seal
Facies distributions and reservoir properties are related to rift-related structural highs. Despite the absence of a nearby source kitchen, Upper Eocene carbonates have been found to be oil-bearing in the Maragh Trough at wells D1- and F1-96. This indicates that hydrocarbons have migrated along graben-bounding faults from deeply-buried source rocks to platform and sub-platform areas. Traps are of combined structural and stratigraphic type.