Modeling Heavily Faulted Reservoirs

Abstract

The gap between a geological reservoir model and its numerical simulation model increased rapidly in the last decade. Due to 3D seismic and other highly sophisticated techniques the geological model can now account for normal and reverse slanted faults, high permeability channels, discontinuities, etc. down to a resolution of 10x10x1 feet. The reservoir can be represented by 100 million grid points and include accurate positioning of 3D faults and other surfaces. In a simulation grid the faults are conventionally represented by the Cartesian, corner point or curvilinear grid block boundaries. In this way only few faults can be handled and even then, they are inaccurately modeled. It is therefore not possible to model a heavily faulted reservoir with conventional methods.The paper presents a new concept and a fully developed solution to this problem. The fundamental difference between this method and all previous ones is that the faults are regarded as inner boundaries and the flow equation will not be used to calculate the fluid transfer through these surfaces but instead it will be handled by boundary conditions. The concept allows the automatic alignment of the grid in a heavily faulted reservoir. The location of the grid points is not changed and only the shape of grid blocks along the fault traces is modified. The method is applicable for Cartesian as well as kPEBI (perpendicular bisection grid with full permeability tensor) grids. The mathematical basis of the gridding and the fault construction methods were already published1,2,3. This paper presents the implementation in industrially used simulator(s) and shows the advantages of the new method. The practical applicability is demonstrated by 2 case studies. The first one is the 2000 km2 Aderklaa conglomerate containing several oil and gas fields. The second is a slanted well traversing several reverse faults.