Insights Into Upscaling Using 3D Streamlines

Abstract

Summary Large, multimillion-cell geological models are frequently constructed in an effort to "capture" the vertical heterogeneity measured by well logs and the areal heterogeneity inferred by the depositional environments. These criteria often result in fine-scale models at a resolution of 0.1 to 0.3 m vertically and 30 to 100 m areally, resulting in reservoir models on the order of 107 grid cells. Recourse is made to upscaling to obtain coarsened but computationally efficient flow-simulation models. The coarsened models commonly result in no more than 1 to 5% of the original grid size, underscoring the need for judicious upscaling. Of greater importance is demonstrating, for the chosen grid dimensions, that the upscaled representation is both reasonable and optimal in the sense that a significantly better template would be difficult to obtain. We consider two nonuniformly coarsened models to demonstrate the issues involved and show that the use of 3D streamline methods offers insightful alternatives to decoupled analysis for both the scaleup template design and the pre- and post-diagnostics. We confine ourselves to property-upscaling methods that use local grid information as opposed to estimating upscaled properties based on some global measure. For this class of problems, we demonstrate that the diagnostic phases are necessarily separate from the upgridding and upscaling processes.