Carbonate Reservoir Heterogeneity Prediction Using Genetic Inversion Approach in Northeast Libya

Abstract In literature, the conventional reservoirs, calcite and dolomite-rich limestone rocks are readily fractured (brittle) compared to limestone with high clay rich contents (ductile) which has low reservoir quality. This example could be seen across 3D survey of Antelat Concession 41. The Antelat carbonate reservoir is highly heterogeneous, stratified and cemented over a short distance, this member contains significant amount of hydrocarbon in concession but could not be produced. To understand the problem of well productivity and the geological complexity of carbonate reservoirs in the lower Eocene succession a detailed quantitative interpretations and litho-facies analysis have been conducted in order to identify possible porous part of Antelat limestone reservoir and non-porous cap rock of lower Eocene and provide a recommendation for exploitation of Antelat reservoir. The understanding of rigidity g, and incompressibility Z, offers better attribute sets into lithology and reservoir facies discrimination (porous, tight and shaly limestones & dolomites) in the studied area. By using genetic inversion seismic attributes, acoustic impedance, Lambda, Mu, Young/Bulk modulus and Poisson's ratio, it was possible to characterize and discriminate carbonate reservoirs interval of Eocene formations. Based on genetic inversion attributes, it shows that Antelat limestone formation comprises of argillaceous with a high percentage of mud materials in Concession 41. From the results of attribute analysis, it could be concluded that Antelat formation possibly acts as both source and reservoir rocks due to heterogeneous lime-mudstone cement within reservoir member. This means its own oil/gas was generated locally and accumulated within the reservoir but lack permeability to expel it. Based on a study of Antelat reservoir heterogeneity, we recommended to perform extensive geo-mechanical studies to better understand the cap-rock and sealing effect of lower Eocene shale, the stress magnitude, orientation of faults and fractures reservoir integrity of Antelat member. We also recommended to perform hydraulic fractur stimulation to enhance the permeability prior to production of this reservoir and appraise Antelat reservoir by drilling horizontal wells to increase production. The genetic inversion method is robust, fast, and easy to use. It produces good-quality results that should be verified case by case for its added value. The genetic inversion workflow was applied successfully on a 3D seismic across Concession 41, where the inversion results were used to predict carbonate reservoir heterogeneity and identifying possible porous part of Antelat limestone reservoir and non-porous cap rock of lower Eocene