Mesozoic and Cenozoic Petroleum Systems of Tunisia, North Africa

By

 M. Hedi Acheche¹, Ramzi Ghenima¹, Moncef Saidi¹

(1) ETAP, Tunis, Tunisia

 The North Africa and Tunisia are best known for their Paleozoic petroleum systems and yet,the greatest production in Tunisia derives from Mesozoic and Cenozoic petroleum systems. Most of these petroleum systems originate from Albian-Turonian and Eocene widespread source rocks. Mesozoic and Cenozoic prospectivity extends over all the onshore and offshore areas, northern of the Ghadames Basin which represents the Paleozoic province. However, the Gulf of Gabes contributes the vast majority of the oil and gas reserves (e.g:Ashtart field; 1Bb of oil and Miskar field; 2TCFG). Stratigraphically, Mesozoic and Cenozoic reserves are spread over a wide range of reservoirs, predominantly carbonate, the most productive reservoirs lie in the Upper Cretaceous-Eocene levels. Jurassic and Lower Cretaceous petroleum systems apparently of limited extension, rely on Mid-Jurassic source rocks and probable Triassic organic rich intervals. Further potential petroleum systems are predicted in the unexplored Northern thrust belt area. Recent geochemical investigations have confirmed the potential of conventional Upper Cretaceous-Eocene source beds and have particularly revealed the presence of an overlooked mature Oligocene-Miocene source rock.

Success of exploration within Mesozoic and Cenozoic basins is controlled by several factors including maturity of source rocks, migration pathways, preservation, fracturing of reservoirs and early trap development. With the exception of the Gulf of Gabes, vast areas of Mesozoic and Cenozoic provinces remained underevaluated and still undrilled or lightly drilled. Moreover, drilling has generally focused on relatively shallow targets. Remaining potential appears to be still significant. Exploration needs to be driven by new technologies, new forms of analysis and new data in the mature areas. In the less mature basins and in frontier exploration areas, application of petroleum system approach would help to reduce exploration risks.