Petrophysics and sedimentology of the Turonian-Coniacian Bireno and Douleb reservoir analogues in north-central Tunisia
Résumé
The study of Turonian-Coniacian reservoir analogues well outcropping in the Jebel Serj-Bargou area (northern-central Tunisia), using a multidisciplinary approach, has led to establish a detailed layering within these heterogeneous multi-layers reservoir rocks. Some of the selected layers show a relatively high reservoir potential. The used approach which could be used as a guide for further studies on subsurface petroleum systems, is based on sedimentological and petrophysical techniques using varied physical parameters. The conducted analysis consist mainly of measurements of the grain density, P-wave velocities, thermal conductivity and porosity. This study contributes to the understanding of heterogeneities of pore types resulting in different petrophysical signatures of Cretaceous carbonates Bireno and Douleb equivalent Members. The data provide a better insight into possible variations in reservoir quality and have led to encouraging results showing that the lower part of the Coniacian Douleb carbonates constitute the best layers in terms of reservoir potential. Detailed Petrographical and petrophysical analysis of the studied Turonian-Coniacian series revealed that porosity is influenced by the facies type, fracturing and diagenesis. In terms of reservoir properties, the highest values of helium porosity and permeability were measured in the lower part of the Coniacian Douleb equivalent Member which consists of fractured micritic limestones. These units are mainly affected by dissolution and matrix dolomitization that create significant secondary intercrystalline and intracrystalline porosities, whereas compaction and cementation are rather destructive of the reservoir potential. The investigated analysis were compared, on a regional scale, with time and facies equivalent from the Albanian area. Comparison at various settings allows to constrain the depositional and diagenetic controls on the petrophysical properties and reservoir quality.