M.Hedi Acheche¹, A M'Rabet¹, H. Ghariani¹, A. Ouahchi¹, H. Troudi¹, D. Kebaier¹
(1) Etap, 1002 Tunis, Tunisia

Abstract: Rejuvenated Triassic TAGI play in Southern Tunisia, Ghadames Basin, North Africa

The Middle Triassic TAGI sandstones remain the most important exploration target in the Tunisian part of the Ghadames Basin. Since the El Borma giant field discovery in the early sixties, only satellite fields have been discovered. Recent major discoveries made immediately to the west in the Algerian part revitilized the play, also many thanks to new geologic concepts and new exploration technical improvements including basin modelling and seismic imaging parameters.

Unconformably overlying various Paleozoic terms, the Triassic TAGI is represented by repeated sequences of sandstones and shales. Reservoirs, best developed in the basal sequences of the Formation, are capped by extensive Upper Triassic salt and evaporites. The Upper Devonian and basal Silurian shales have been established as the main source rocks for Paleozoic and Triassic reservoirs. Thermal modelling at basin scale indicates that maturity of these source rocks and associated generation and expulsion vary in time and space. In addition to vertical migration, the basal Triassic sands over the Hercynian unconformity have played an active role as a carrier through a NW-SE long distance migration. Over the last two decades, the exploration has been driven by 2D seismic surveys of limited resolution and a poor quality severely affected by statics. Common traps are subtle anticlines and their detection may be beyond the resolution of static corrections. New seismic acquisition and processing parameters greatly enhanced subsurface imaging with reliable data on faults and associated traps. Faults seem to be critical factor for trapping mechanism and many clearly defined structures are fault block traps.

Future oil and gas discoveries in southern Tunisia are expected from large to medium size fault blocks, in addition to channel fill traps and to the more classical anticline traps.

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