Increased resolution in reservoir characterization is driving the need for efficient and accurate upscaling techniques for reservoir simulation, on which reservoir performance prediction relies. Unfortunately, the existing averaging methods (i.e., harmonic, arithmetic, power law, geometric, or a combination of harmonic and arithmetic methods) are only applicable under the circumstances of perfectly layered or perfectly random heterogeneity distributions, which are rarely seen in realistic reservoir descriptions. This paper presents a new averaging method that improves these upscaling averaging methods for realistic reservoirs and can substitute for the orders-of-magnitude slower direct-simulation methods, such as pressure-solver techniques. The new averaging method first calculates the upper and lower bounds of the effective properties based on the nature of geology and then employs a new correlation, scaling, and rotation technique to estimate the effective properties for the upscaled grid. The approach not only preserves the accuracy of the time-consuming simulation methods but also retains the speed of the traditional averaging methods.
Five real sandstone and carbonate reservoir geologic models (three of which are multimillion-cell models) from Africa, North America, and South America were employed as benchmarks and working data sets to develop and validate the new technique. The technique has the advantage of handling the more irregular geometries [i.e., pinchouts, faults, and flexible simulation grids such as the Perpendicular Bisection (PEBI) grid].