A new technique for evaluating coarse grids based on flow thresholding

摘要

Current upgridding techniques usually require the scale-up factor to be known a priori and,in practice,the scale-up factor is selected rather subjectively.The main consideration is that the scale-up factor should be large enough for practical use and not so large that the results are likely to be very inaccurate.A more objective approach to selecting the scale-up factor is desirable.This paper proposes a novel approach to determine a more appropriate scale-up factor for a coarse model.The new approach is based on an analysis of the flows in the fine-scale model.The regions that make a significant contribution to the flow are identified using a thresholding technique.A range of scale-up factors is tested and high flow regions are identified in each case.The percentage overlap(denoted by R_o)of the high flow regions in the coarse and fine grids is then calculated.The value of R_o can be used as a predictor of the accuracy of upscaling and the appropriate coarse grid size can thus be evaluated.When the upscaling is performed using a global method,there is litde extra computational cost.This method is suitable for use in multi-phase flow simulations of 3D heterogeneous reservoir models.The technique is demonstrated using a simulation of a waterflood in a highly heterogeneous 2D model.