REV Grid Technique for Reservoir Upscaling

Lasseter et al. (Lasseter, T. J., Waggoner, J. R., Lake, L. W. (1986). Reservoir Heterogeneities and Their Influence on Ultimate Recovery. Reservior Characterization, Orlando, Florida: Academic Press Inc., 545.) proposed that scale-up of properties should be done from the scale of a representative elementary volume (REV), a volume for which the measured property does not change with an increase in scale over a given limit of scale. The notion of REV has been a quite argued concept owing to its definition is not unequivocal, and it did not address how to obtain it in real system, some people even argue if REV really exists. Qi et al. (Qi, D., Wong, P. M., Liu, K. (2001). An improved global upscaling approach for reservoir simulation. Petroleum Science and Technology 19(7-8):779-795.) based on REV concept, proposed the new idea of REVG (representative elemental volume grid). This article further developed this idea, and based on it, proposed the REV grid upscaling technique. This new technique uses an algorithm, which is a combination of two-procedure-upgridding with reverse stepwise approach, it is a field-oriented 3D model. The new method concentrates on constructing a unique coarse grid, referred to as pseudo-REVG, which could best describe the heterogeneity of the original model at given scale. Mathematically, the variance of properties in REVG is the smallest within each block, and largest between the blocks. The proposed method is applied to two case studies, one of them is a 3D multiphase real reservoir, and the flow simulation results show that the consistency of the reservoir behavior before and after upscaling with REV grid technique is excellent. It is much better than that of the conventional upscaling methods.