Adaptive Global Upscaling for 3D Fractured Reservoirs

@inproceedings{VitelRM2007,
 abstract = { Most existing upscaling methods attempt to evaluate effective permeabilities of coarse-scale gridblocks, so that the upscaled model locally reproduces the steady-state single-phase flow behavior of the fine-scale grid, under a set of boundary conditions. When applied to fractured reservoirs, the dual-medium model of Warren and Root [1963] is usually used. However this model suffers several limitations. First it assumes the existence of a representative elementary volume (REV); yet no REV may exist for fractured systems, which are characterized by a wide variety of fracture sizes. Second, the fractured system is idealized and thus over-simplified. Third, the arbitrarily imposed local boundary conditions introduce bias in the resulting effective permeability. Finally, the evaluation of the matrix-to-fracture transfer function is a critical issue. The presented method overcomes all four limitations by using an adaptive unstructured methodology which aims at preserving the same pressure response on the coarse-scale model as the detailed geological model, at a set of selected points. The upscaling uses as input an accurate discretization of the fractured model based on a connectivity-list representation. A set of nodes is first selected in the fine model, to be preserved in the coarse model, in order to capture the key flow paths. The non-selected nodes are then iteratively decimated by applying electric simplifications until only the selected points remain, so that pressures are the same at the selected nodes between the fine and the coarse models. Finally, connections with lowest transmissibilities are decimated, converting a full system into a sparser one, and an optimization procedure updates the remaining connections so that the mass conservation equation is honored at each node. Flow simulation results obtained on upscaled models are in good accordance with those obtained before upscaling, with significant speedups, and show appreciable improvements compared to conventional structured local approaches. },
 author = { Vitel, Sarah },
 booktitle = { 27th gOcad Meeting },
 month = { "june" },
 publisher = { ASGA },
 title = { Adaptive Global Upscaling for 3D Fractured Reservoirs },
 year = { 2007 }
}