Heterogeneity of the fine-scale models will result in full tensor effects for the upscaled models, especially in reservoirs with channels or fractures. A flow-based upscaling approach integrating multiple flow scenarios is developed to effectively capture the full-tensor effects when upscaling from fine-scale discrete fracture models. The new approach is proposed to deliver computationally affordable simulation models under precision comparable to the high-resolution models.

The approach starts with several sets of flow-based single scenario upscaling procedures. A fine-scale discrete fracture model is built up as the reference model for all the successive procedures and comparisons. Then several flow cases (referred as scenarios) are determined according to the target simulation conditions. A global upscaling technique under multipoint flux approximation scheme is introduced to each flow scenario. An integrated output least squares method, which aims to minimize the total bias of simulation results of all the flow scenarios, is adopted to obtain the optimal transmissibility connection list of the coarse-scale models.

We design and implement several examples including two synthetic conceptual cases and a real field case. In each case, comparisons are provided for the simulation results of the proposed approach and previous upscaling approaches based on two point flux approximation schemes. The coarse-scale models upscaled by different methods are based on the same fine-scale (reference) model in each case. The results of the upscaled models are also compared to the reference model. The numerical results show that the new approach generates coarse-scale models which are closer to the fine-scale model. Although under certain conditions, traditional upscaling methods can achieve equivalent results, it is proven that the new approach is more robust when applied to more general flow scenarios. It can be noted that it may take a bit more time for the numerical simulation of coarse-scale models upscaled by the new method, due to the introduction of the non-neighbor connections. When compared to the fine- scale model, however, the improvement of computational efficiency is still pretty significant. The last case is a real field case with about 500,000 fine-scale grids and 10,000 coarse-scale grids, which demonstrates the ability of the new approach to be applied in the industry.

The novelty of the proposed approach is the optimization technique integrating multiple scenarios to generate a high precision coarse-scale model under multipoint flux approximation scheme. The new method effectively capture the anisotropic features of the coarse-scale models, which is a challenge for flow-based upscaling procedures because a single flow simulation is usually inadequate to obtain full tensor information of the upscaled models.

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