The Diagenesis of the Upper Oligocene and Mio-Pliocene Sandstones and its Relevance to Hydrocarbon Exploration in the East Anatolia Basin, Turkey

Upper Oligocene (Komurlu, Penek, and Gumusali) and Mio-Pliocene (Zirnak and Aras) formations contain sandstones that are petroleum reservoirs in thc East Anatolia basin. Deltaic and fluvial sandstones are the dominant facies in the basin. Petrology, depositional and diagenetic history, and reservoir quality of the Upper Oligocene and Mio-Pliocene sandstones are defined in this paper. Reservoir quality is primarily the result of burial diagenesis. Dominant textural modifications are the destruction of primary porosity by precipitation of authigenic minerals, primarily smectite-illite, feldspar overgrowths, illite, and quartz overgrowths, and porosity enhancement by dissolution of framework feldspar and calcite, to a lesser extent quartz and lithic fragments. As much as 30 % of the total porosity probably was caused by the dissolution processes, largely by meteoric water introduced during Upper Oligocene and Miocene uplifts. Average porosities of the Oligocene and Mio-Pliocene sandstones range fiom 10 to 16% in the study area.