The Late Cenomanian-Coniacian Gattar and Aleg reservoirs in Sidi Bouzid area, Central Tunisia: Logging, diagenesis and reservoir implications

At the Sidi Bouzid area located in Central Tunisia, Cenomanian-Turonian reservoir rocks are well outcropping, especially in the Jebel el Kébar and Meloussi areas. The present work confirms that these carbonate intervals constitute the lateral equivalent of the Early-Middle Turonian Biréno and Late Turonian-Coniacian Douleb reservoir Members which are included within the pelagic marls of the Turonian-Early Campanian Aleg Formation. In addition to the Late Cenomanian-Early Turonian Gattar dolomites, the Biréno and Douleb fractured carbonates constitute, in this area, good reservoirs and thus potential targets in subsurface since they produce oil to the East in Sfax area or in the Gulf of Gabès. Detailed sedimentological, petrographic and petrophysical studies carried out from several sections surveyed at Jebel el Kébar and Jebel Meloussi have focused on the vertical stacking of the carbonate series, thickness, geometry, composition and pore types within the main Cenomanian-Turonian reservoir layers. However, at a North-South transect, these reservoir layers are characterized by frequent and rapid changes in facies and thickness from Jebel el Kébar to Jebel Meloussi and within the Jebel el Kébar itself. These lateral changes appear in close relation with the particular paleogeographic setting which could be governed by several processes such as sea level changes and, especially, contemporaneous tectonic activities. The latter have strongly influenced the reservoir thickness and properties. Furthermore, this study focuses on the origin of fluids controlling the main diagenetic processes (e.g., dolomitization and dissolution) and on the pore type, volume and their interconnection. These latter could be a part of the reservoir aspect characterization. Moreover, attention will also be paid to the spatio-temporal distribution of the Cenomanian-Turonian carbonate Members which would be served as an analog for reservoirs in the Sidi Bouzid area (Central Tunisia) and elsewhere (e.g., African Tethyan margin, North America, and Middle East).