Insight into the Tectonics of the Kaboudia Area and Related Petroleum Systems, Eastern Tunisian Offshore (Tunisia)

Abstract

The Kaboudia permit belongs to the Pelagian domain that has experienced extensional tectonics in the framework of the Tethys oceanic opening since Triassic. As the rest of the Northern African Mesozoic basins, peritethyan basins underwent a syn-rift opening during Late Triassic- Jurassic with coeval magmatic intrusions. This extensional period extended until Lower Cretaceous within the Tunisian basins. After Austrian uplift and erosional event, the former tectonic subsidence and extension was followed by a post-rift phase, which is marked by the deposition of a thick shale series of Fahdene during Albian-Cenomanian period. The Late Cretaceous to Eocene represents tectonically a quiet period that was characterized by the deposition of condensed sections and compressional periods such as, Santonian and Priabonian phases. Horst and grabens tectonics associated to a transtension occurred during Upper Miocene along the NW-SE extensional faults that are related to the Opening of the Tyrrhenian Sea and subsequent movement of Sicily with regard to Africa in the framework of the Ionian subduction. The Kaboudia permit conceals already oil accumulations within the Serdj and Allam Cretaceous carbonate reservoirs that are sourced from Lower Fahdene (Vraconian) source rock. After lab data, only few samples of such shale have shown a certain potential. However, Delta Log R method and seismic interpretation show source indications within the paleo-troughs around Mahdia structure and Kuriat furrow (near Taboulba). On the other hand, lab data shows also few samples from Allam and Serdj Aptian shale with higher TOC’s and residual potential S2. In terms of petroleum system working, the Mouelha could charge Allam limestone reservoir in a perdescensum. However, the reservoir below might be charged only when the latter is comprised within the same structural closure of the structure (trap). In addition, the Serdj reservoir could be charged downward by Allam and Mouelha shale within the kitchen zones. The postmortem analysis of exploration results at Kaboudia and the surrounding blocks, revels that the main risk regarding the petroleum system is the source rock potential, its extension and at a lesser degree the seal capacity.