A. M'Rabet¹, M.Hedi Acheche¹, F. Belkhadi¹, N. Gharieni¹
(1) Etap, 1002 Tunis, Tunisia

Abstract: Upper Jurassic-Mid Cretaceous Petroleum Systems in the south Gulf of Gabes Peri-Alpine Basin, Tunisia, North Africa

The Upper Jurassic to Mid-Cretaceous sandstones and carbonates are exploration targets in the South Gulf of Gabes Basin, a wide subsiding Mesozoic basin in southeastern Tunisia that resulted from Early Mesozoic rifting and having been affected by Mid-Late Cretaceous to Tertiary Alpine compressional stresses, with significant strike slip movements.

In the South Gulf of Gabes Basin, at least three fields (Ezzaouia, El Biban and Robbana) are producing oil, indicating the existence of active petroleum systems including proven clastic and carbonate reservoirs, good mature source rocks and a variety of trap types. Clastic reservoirs include the Upper Jurassic M'Rabtine and the Neocomian Meloussi sandstones. The pay zones, tens of meter thick, are represented by shallow marine fine grained sandy intervals exhibiting fair to excellent reservoir properties. The seals are provided by intraformational shales and anhydrites. Carbonate reservoirs correspond to the Cenomanian Zebbag bioclastic limestones and dolomites, having fair to good porosities and sealed by intra-Zebbag evaporites or Upper Cretaceous-Paleocene shales. Source rocks are the Callovian shales and the Aptian marls, in addition to organic-rich shale interbeds within the Late Liassic and Triassic organic-rich carbonates. Thermal modelling indicates that these source rocks have expelled most of their oil charge during Tertiary times; vertical migration from the generative areas being provided by deep seated faults.

Trap types especially include fault blocks, faulted anticlines and salt related structures. Most of these traps originated during Late Cretaceous compressional stresses. Reactivation that occurred during Tertiary tectonic events have not affected the trap integrity.

Large portions of the South Gulf of Gabes Basin remain under-explored including both awarded exploration concessions and open acreage areas.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana