Applying upscaling techniques is an undeniable demand in reservoir simulation, considering the difference between level of details in a geological model and level of details that can be handled by reservoir simulators. Upscaling reservoir model involves first constructing a coarse grid by employing gridding algorithms and then computing average properties for coarse grid blocks. Although various techniques have been proposed for each of these steps, one has to be aware of strengths and weaknesses of each technique before attempting to apply them. In this paper, we focus on different gridding methods and evaluate their performances. Three main grid generation techniques are considered: permeability-based (PB), flow-based (FB), and vorticity-based (VB) gridding. We apply all three methods to some 2D heterogeneous models and simulate two-phase flow on the constructed grids. Then we compare their obtained global and local results. Fluid cuts at producer is employed as global performance indicator and saturation distribution error as local indicator. We show that FB and VB gridding, which are dynamic methods, are superior to PB gridding, which is a static method. Based on this analysis, we then concentrate on FB and VB griddings and investigate their performances in greater details. While FB gridding uses fluid velocity as grid blocks density indicator, VB gridding combines velocity and permeability variation in gridding according to its definition and takes advantages of both. Therefore, although performance of FB and VB griddings are comparable in many cases, VB has benefit of producing coarse grid blocks with more uniform permeability and fluid properties distribution. This in turn yields more accurate global and local results and reduces application of sophisticated upscaling techniques and full-tensor permeability upscaling.

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