Carbonate reservoirs are extremely challenging for reservoir modeling and flow simulation due to their high heterogeneity and the complexity of controls on the porosity and permeability. The porosity and permeability may be connected or weakly connected, which can cause difficulties in coarse grid design and upscaling of flow. We report on the application of a recently developed "Diffuse Source" upscaling approach here applied to the upscaling of a high resolution 3D carbonate reservoir model.

A high-resolution 3D geological model of the Amellago carbonate outcrop was utilized for analysis. This model, which has similar stratigraphy, structure and diagenetic controls as Middle East reservoirs, has proven to be a challenge for existing layer upgridding and flow-based upscaling approaches. We utilize flow-based "Diffuse Source" upscaling to obtain the intercell transmissibility and well indices, as this approach has improved localization and resolution compared to steady state calculations, and also allows us to distinguish between well connected and weakly connected sub-volumes.

We report on the performance of the statistical layer upgridding approaches used to design the flow simulation grid from the underlying 3D geologic model, and the impact of the choice of the heterogeneity measure (velocity error, time of flight error, or a combination of the two). We benchmarked the Diffuse Source against several methods available in the literature. Finally, we demonstrate the utility of a recently developed method for flow diagnostics that allows us to test the quality of the coarse simulation models relative to the fine-scale geologic model. All of the upscaled models are tested using commercial finite difference simulation and are compared to the upscaling approaches available within commercial flow simulation and geologic modeling applications.

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