--> ABSTRACT: Middle Miocene Transtensional Regime: Effects and Impacts on the Distribution of the Miocene Petroleum Systems in the Northeastern Offshore Tunisia, by Abderrahman Ouahchi, Fraj Hammouda, and Mohamed Hedi Acheche; #90906(2001)

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Abderrahman Ouahchi1, Fraj Hammouda1, Mohamed Hedi Acheche1

(1) ETAP, 1002 Tunis, Tunisia

ABSTRACT: Middle Miocene Transtensional Regime: Effects and Impacts on the Distribution of the Miocene Petroleum Systems in the Northeastern Offshore Tunisia

The Middle Miocene Oum Douil sandstones are a major target in Northeastern offshore Tunisia (Gulf of Hammamet) and host most of the oil and gas discoveries in this area. These facies are deposited following the drowning of the Ain Grab carbonate platform in the Middle Miocene due to NNW-SSE transtensional faults. Recurrent movements along border faults provided the necessary displacement for accumulation of clastic sediments. Pull-a-part basins generated during this event, became the site of the Birsa-Zelfa sandstones sedimentation. These areas were uplifted and inverted during the late Alpine phase giving arise to the actual " rombo horst " or push up structures largely widespread in the Gulf of Hammamet. The so called Birsa and Zelfa sandstones are the principal pay intervals. Reservoirs, best developed in the edge of the Birsa/Zelfa pull a part basin are capped by Middle Miocene intraformational shales. Two major source rocks are identified in the area. The Albian Fahdene shales and the Lower Eocene Bou Dabbous limestones.The thermal modelling narrowed the contribution to the Albian source rocks. The main episodes of petroleum generation and migration took place during the late Miocene-Pliocene times. The main paths are the deep faults. Most of the oil and gas in Miocene reservoirs are trapped in fault blocks against major faults. These traps are created during the late Alpine orogenic phase prior to the expulsion from the main source rock of the area. The sealing of the faults is a critical factor for trapping mechanism. Sealing property is proved by the numerous discoveries in fault related traps, however, few structures are underfilled. The remaining potential is still significant. The prospective areas are situated at the edge of the grabens where reservoir development and charge are the most favourable.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado