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THE APTIAN SERIES IN THE KASSERINE - EL KEF AREA (TAJEROUINE PERMIT): SEDIMENTARY CHARACTERS AND PETROLEUM POTENTIAL

NEGRA Mohamed Hédi, Nigel Wilson, Con Xydis, ZAGRANI Mohamed Faouzi, SKANJI Ahmed , JABALLAH Jalel, Bejaoui Jihéne, Chihaoui Sadri, Gharieni Nawfel, 2010

Tunisian Petroleum Exploration and production Conference, 1, 32, 35, Octobre 2010

Résumé

In the Tajerouine Permit, Aptian series well crop out in several sectors. The Jebel Bou

El Hanèche, located in Central-Western Tunisia, about 10km to the ENE of Kalaa Khasba city, could be considered as one of the best outcrops of Aptian series. Within the Northern flank of the Jebel Bou El Hanèche anticline, Aptian series are expressed by well individualised massively to bedded carbonates frequently crossed by NW-SE to NE-SW fractures. The Aptian series reaching a total thickness of 500m are mainly constituted of fractured bioclastic carbonates rich in orbitolinids, bivalves and oyster fragments. Sandstones which are obviously less common than carbonates (only 10m in total thickness) are included within a decametric unit (40m in thickness) in which sandstones are interbedded with silty shales and carbonates. Sandstones which show low-angle cross-beddings are formed of fine-grained and well sorted quartz material. Laterally, toward the North, such as in Jebel Ben Rhazouane and in Oued Djoumane, sandstones which appear more common, constitute clearly thicker units. In Oued Djoumane, for example, siliciclastic deposits (1300m in total thickness), include frequent sandstone units which could reach more than 100m in thickness. In terms of reservoir aspects, in addition to fracturing which is common and affecting all types of carbonates and sandstones, the bioclastic carbonates of Jebel Bou El Hanèche exhibit frequent plurimetric to larger "karsts". In fact, these "karsts" are the expression of dolomitisation processes transforming initial fine-grained bioclastic limestones into obviously porous and permeable coarse-grained dolosparitic material, showing intercrystal and vuggy pores. Similar pore types and "karstification" features were also identified in the Douleb field in which they have contributed to the improvement of the reservoir quality (Ouahchi et al., 1998; Troudi et al., 2010).