AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
The Upper Cretaceous and Eocene Source Rocks in the Sfax Offshore Permit – Gulf of Gabes - Tunisia, Pelagian Basin, North Africa: Source Rock Characterization, Petroleum Generation, Charge History and Prediction of Migration Pathways
(1) Atlas Petroleum EXploration Worldwide, Ltd, Tunis, Tunisia.
(2) StratoChem Services, Cairo, Egypt.
(3) Platte River Associates, Inc, Boulder, CO.
(4) Atlas Petroleum EXploration Worldwide, Ltd, Houston, TX.
Several petroleum systems have been established in the northern part of Gulf of Gabes-Pelagian Basin extending Offshore Tunisia and Libya. They are driven by two major source rocks, the Bahloul and Bou Dabbous Formations.
The late Cenomanian - early Turonian Bahloul Formation is a laminated black limestone with Type II kerogen and good generation capacity although often only thinly developed. The Bahloul is established to be the source rock for the immediately overlying and therefore ideally positioned Upper Cretaceous reservoirs.
The Ypresian Bou Dabbous source rock comprises a series of marls and limestones which consist of Type II amorphous material with excellent oil-prone and associated wet gas potential. This system is prolific and accounts for the majority of fields in the Pelagian Basin in both Tunisia and Libya. Oil expelled from Bou Dabbous source rock migrated up-dip along intra-formational pathways and was hosted in the lateral equivalent nummulite banks of the Ypresian El Garia reservoir.
An extensive 3D basin modeling study carried out in the Sfax Offshore Permit indicates that the Bou Dabbous is currently in the mid-late mature stage in the southeastern part of the Sfax Offshore Permit. Hydrocarbon expulsion commenced about 10 my ago.
In the western part of the Sfax Offshore Permit the Bahloul is currently in the early mature stage; while it is in the late mature and mainly gas generation stage in the eastern part of the permit. Hydrocarbon expulsion has occurred earlier in the eastern and north-eastern part of the permit (40 my ago). As such, the timing of trap formation is more critical than in the western part which makes the Upper Cretaceous reservoirs more prospective in terms of charge. Comparison with known fields and accumulations suggests that the NW-SE fault trend dominating the area is not sealing.
The basin modeling study revealed that the traps charged from Bahloul source rock are located in the NNW and SSE on either side of the so-called Kerkennah Arch, a NE-SW trending high formed during the Late Cretaceous. Most of the traps interpreted to be charged from the Ypresian Bou Dabbous source rock are located in the eastern part of the permit and further east within the Gabes-Tripolitaine Basin.