Reservoir Rock Typing in a Giant Carbonate

Abstract

Abstract Lithofacies classifications are a purely geological grouping of reservoir rocks, which have similar 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 types scheme within ZADCO. We discuss criteria used to define reservoir rock types in the current scheme and its limitations. The objective of the proposed rock type scheme is to address shortcomings identified with the current one in use and is based on the following criteria: Each Rock Type can be characterized by similar depositional and diagenetic environment■Each rock type has a typical and unique set of Pore Throat Size Distribution curves.■Each rock type has similar set of Capillary Pressure/Relative Permeability curves at a given wettability.■Porosity/Permeability overlap is minimal between different rock types.■Rock types can be predicted with satisfactory accuracy using logs in uncored wells.■Spatial 3D distribution of the rock types is predictable within a well-defined geological framework.