Systematic Rock Typing in an Iranian Oil Reservoir

The degree of success in many production activities and secondary recovery processes depends on the accuracy of the models used in the reservoir description. Reservoir rock typing is one of the most essential parts of proper reservoir characterization. The goal in optimum rock typing is to overcome the extreme heterogeneity of the reservoir. This is to decrease the effects of heterogeneity for normalizing/averaging capillary pressure curves and estimation of permeability. Rock typing and hydraulic flow unit identification are elaborated to integrate both geological and petroleum engineering data. Flow unit is defined as a group of reservoir rocks with similar properties that affects fluid flow. Geological/petrophysical characterization incorporated the analysis of the complex variations in pore and pore throat geometry that control initial and residual fluid distribution. An undersaturated oil field reservoir in southwest of the Zagros belt in Iran was considered in this study. Asmari formation in this reservoir compromised of two main Carbonate and Sandstone bodies. Four lithotypes of Shale, Limestone, Dolomite, and Sandstone have been determined from geological and petrophysical studies. In this study, conventional porosity and permeability, mercury injection, capillary pressure, relative permeability and mineralogical data were used to characterize the reservoir pore systems into rock types having similar flow and storage capacity. Water Saturation, all of which is considered immobile, was found to be dependent on rock type, with pore throat being the dominant control on the flow characteristics of the reservoirs. Also, a different flow unit definition of FZI/RQI concept was applied on this field. Good consistency was observed between lithotypes and rock types to compromise the views of both geologists and reservoir engineers.