BELHAIZA, A., and A. BEN GACHA, ETAP, Tunis, Tunisia

Abstract: Upper Cretaceous Abiod Fractured Limestone Reservoir In The Gulf Of Hammamet- North East Offshore Tunisia

The Gulf of Hammnarnet is a Mesozoic and Cenozoic province. The oldest penetrated rocks are Jurassic platform carbonates and locally Triassic dolomites and evaporites.

During the Campanian-Early Maastrichtian, after the intra-Santonian tectonic instability and associated local uplifts and submarine erosion, the Gulf of Hammamet remained under deep marine conditions leading to the deposition of a chalky wackestone 300 to 500 in thick in the western part, suggesting local active subsidence. It is possible that parts of this thick  Abiod section were derived from adjacent slope areas as debris flow deposits. The thickness decreases progressively towards the east, eroded in the central part and is about 100 m thick in the eastern part.

Local tectonic movements may have created fault bounded depocenters separated by relatively rigid zones in the southern part. The sloping margins of these depocenters may have been the sites of slumping and gravity flow sediment deposition. Post-Cretaceous tectonism has created sets of orthogonal fractures partially filled with a mosaic of sparite and microsparite. It is worth noting that in high structures, most of the fractures remained open and form an effective porosity system. On seismic, Paleocene (El Haria) shales are seen to onlap NE-SW trending Abiod paleohighs in the southern part of the Gulf of Hammamet. In the central and northern areas, younger unconformity suggests uplifting of a N-S trending zone. This led to the formation of structural and stratigraphic traps which may have been sourced by the Albian shale. The latter entered the oil window in Tortonian (10-8 my), generated oil in late Tortonian-Early Pleistocene, (8-5 my), moved to condensate during the Messinian-Early Pleistocene and generated gas from Pleistocene to recent time. The Lower Turonian source rock reached the oil window in the early Messinian (6.25 my) and has generated oil since the late Pliocene.

The main seal of the upper Abiod reservoir is the Upper Maastrichtian-Paleocene (El Haria) shale. 

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England