Reservoir Rock Types of Kharaib reservoirs have been defined as an interval of rock within which the geological and petrophysical properties that effect fluid flow are consistent and predictable. Lithofacies classifications are a purely geological grouping of reservoir rocks, which have similar lithology, texture, grain size, sorting etc. Each lithofacies indicates a certain depositional environment with a distribution trend and dimension. Petrophysical groups are classified by Porosity, Permeability, Capillary Pressure and Pore throat size distribution.
A Rock Type combines both these classifications by linking petrophysical properties and lithofacies as part of the reservoir rock type definition. It has been previously shown that the static rock types are not always representative of multi-phase flow behavior in the reservoir. In this paper, we will present evolution of the rock type scheme within ZADCO. We discuss criteria used to define reservoir rock types in the current unified scheme. The objective of the proposed rock type scheme is to address shortcomings identified with the previous one in use and is based on the following criteria: a) each Rock Type can be characterized by similar depositional environment and diagenetic process; b) Porosity/Permeability overlap is minimal between different rock types; c) each rock type has a typical and unique set of Pore Throat Size Distribution; and d) each rock type has similar set of Capillary Pressure/Relative Permeability curves at a given wettability.
The recognized Reservoir Rock Types have been assigned to reservoir layers were built within a framework based on sequence stratigraphic concepts to ensure that the spatial 3D distribution of each rock types is predictable within a well-defined geological framework and finally to be used in history matching simulation models.