Reservoir characterization is one of the most challenging subjects in Carbonate reservoirs. In this study Flow Zone Index, Winland and initial water saturation methods were used to classify rock typing in an Iranian oil field located in the south-eastern region. In addition, the predicted initial water saturation along with log and core data was used for capillary pressure estimation.
The studied field is a Cretaceous fractured oil bearing reservoir composed of tightly packed limestone characterized by high porosity but poor permeability with a thickness of 55-65 meters throughout the reservoir. The matrix permeabilities and porosity are in the range of 0.01-150 md and 5-40 percent respectively. The oil gravity is 21.5 degree API.
Conventional Core data were first used to define the rock types for the cored intervals in which nine district rock types were defined. Furthermore, the FZI (Flow Zone Index) log was also generated based on the permeability which was obtained from FMI (Full-bore Formation Micro Imager) and porosity logs of cored and un-cored intervals. In addition, SLMP (Stratigraphic Modified Lorenz) plots were generated for the purpose of identifying flow zone and barriers in each well. Also, Winland method was also used for the same purpose. The results of SLMP were consistent with Winland result and FZI. The Scanning Electro Microscopy Photomicrographs of the obtained rock type were studied and found to be consistent with the finding of this work.
Further, the available initial water saturations obtained from log data were classified in three groups and found to consistent with FZI and Winland methods. Based on the DRT (District Rock Type) obtained from the FZI method a correlation between initial water saturation from the log and DRT was developed for the purpose of initial water saturation prediction. The generated data was used for the capillary pressure and relative permeability estimation. The generated capillary pressure and relative permeability were consistent with available scale data and provided sufficient Pc curve for the uncored intervals.