TERTIARY STRUCTURING ANDHYDROCARBON POTENTIAL IN THE GULF OFHAMMAMET

摘要

The Gulf of Hammamet is characterized by a complex tectonic history during the Cretaceousrntime and mainly during the Tertiary time by more accentuated events. This complex tectonicrnhistory has developed throughout the area a variety of tertiary structural styles. Structuresrninclude compressional anticlines, tilted fault blocks and rollover anticlines. The tertiaryrnstructure, the more apparent, is due to the effects of convergence and/or translation betweenrnthe African and the European plates and rifting events in the central Mediterranean area.rnThe Pyrenean (Early Atlassic orogeny ) compression phase caused regional uplift and erosionrnin the Late Eocene and Oligocene , resulting in the inversion of normal faults and thernformation of the some structures . In the other hand, the Middle Miocene transgression led torncarbonate development (Ain Grab Fm.) over most the region. Regional subsidence allied torncontinued sea-level rise led to widespread shale deposition in the Late Langhian .rnThe Alpine Neogene compressive phase (Major Atlassic orogeny ) caused Upper Miocenernfolding and thrusting . The carbonates and evaporites , deposited during the Messinian , wererndeformed and eroded at the end of Miocene . Continued, NW-SE oriented, Alpine Neogenerncompression during the Early Pliocene led to regional inversion of the Miocene foredeep.rnMiocene sub-basins became highs while Miocene highs became basins. The Alpine Neogenernstress regime was modified by contemporaneous ENE-WSW orientated extension associatedrnwith rifting in the central Mediterranean. The result was the formation of a network of deeprnPliocene grabens filled with shales and sandstones.rnTertiary hydrocarbon accumulations discovered in the Gulf of Hammamet are mainlyrnassociated with Ketatna limestones , Ain Grab limestones and Birsa sandstones .rnThe Ketatna Formation (Oligocene-Aquitanian), largely developed in the East of the Gulf ofrnHammamet, corresponds to a reef- like carbonates deposits.rnThe Ain Grab Formation (Langhian), exhibits good petrophysical characteristics (15 to 30%rnof porosity and 150 md of Permeability). This reservoir consists in bioclastic limestonesrndeposited in a shallow marine environment.rnThe Birsa Formation (Lower Serravallian) presents a good porosity (10 to 33%) and isrnproducing Oil in some fields and in the Zelfa and Baraka discovery wells.rnThe Middle Miocene sansdtones remain the major target in the Gulf of Hammamet. Thernreservoir quality is by far the most attractive in the area. Most of the other targets rely onrnfracturing, diagenesis process and are deeper. The residual potential remain significant.rnThere are also other reservoirs related to the Tertiary time, such as, The Halk El Menzelrnfractured limestone , the Fortuna and Lower Beglia sandstones , all of which have eitherrntested hydrocarbons or at least given shows.