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Reservoir heterogeneity of Ordovician sandstone reservoir (Bedinan Formation, SE Turkey): Diagenetic and sedimentological approachs

The sandstone-bearing reservoir levels (Bedinan Formation) in the Diyarbakir Basin, SE Turkey show strong heterogeneity in porosity, permeability and capillary pressure, which influences oil production rates of the studied 6 wells and beclouds the prediction of hydrocarbon reserves. Therefore, comprehensive understanding of the sandstone reservoir characteristics has been necessitated to optimize its ultimate hydrocarbon recovery, maximize its lifetime and to make more accurate performance predictions for the use in economic risk assessment. In this study, integrated analysis of paleogeography, depositional characteristics, petrographic features, provenance, pore structure, reservoir heterogeneity rating, diagenetic stage and its possible impacts on reservoir quality were examined by employing thin section analysis, sedimentary structure analysis, petrophysical interpretations, geostatistic methods, X-ray diffraction (XRD) and non-destructive X-ray computed tomography. It is concluded that the Upper Ordovician sands were laid down under shallow marine conditions (lower shoreface to upper shoreface) in an ice-distal glaciomarine environment and have been subjected to a complex history of diagenesis. The sandstone succession was sourced from plutonic rocks and derived from a stable craton. The presence of detrital and diagenetic rooted clay-coating minerals (illite, kaolinite, illite/smectite mixed clay layer) together with cementation by quartz overgrowth and carbonate concretions in the matrix of the sandstone layers are the main factors deteriorating the reservoir quality by plugging pore throats and decrease production rates and oil recovery. However, the type of clay-coating minerals and the amount of those are the key factors modifying reservoir architecture in comparison with the cementing materials. Besides that the integration of illitization of kaolinite and smectite in mesodiagenetic stage, the presence of minerals such as quartz, feldspar and illite altering the pore spaces from oil-wet to water-wet and compaction induced micropores are culprits in causing high water saturation in the sandstones even in the zone above oil-water contact.