Upscaling of the
geological model is an important stage in a reservoir simulation work-flow that
introduces error due to averaging of sub-grid heterogeneity and numerical
diffusion. Upscaling errors are generally more severe in compositional flow
simulation than in black oil modeling due to the inherent equilibrium
assumption that increases numerical diffusion significantly. When coarse grid
blocks involve high and low permeability channels or layers, current
single-porosity upscaling techniques are very sensitive to the level of
upscaling and generally fail in representing the fine scale response adequately.
In this work, the
effect of heterogeneity on displacement efficiency in coarse-scale modeling is
studied and a dual-porosity upscaling approach is proposed that significantly
reduces the upscaling error due to averaging of heterogeneity. Pore space is divided,
based on flow contribution, into two distinct continua and a dual-porosity
dual-permeability model is used for coarse-scale flow simulation. A streamline
index (SI), defined as the ratio of streamline density to time-of-flight, is
used for division of storage into primary pore volume that covers the high flow
pathways in the porous system and secondary pore volume that acts mainly as
source/sink and feed into major flow pathways. Global single-phase upscaling is
applied to calculate inter-continuum and inter-block transmissibility.
technique is used to simulate miscible and immiscible displacements on 3D models.
Displacement calculations are performed on the original fine grid and on a
uniform coarse grid with single-porosity (classical approach) and dual-porosity
upscaling. Several simulation results demonstrate the superiority of the
proposed approach in effectively capturing the sub-grid heterogeneity effects
on multi-phase flow. The sensitivity of the proposed upscaling technique is then
investigated for settings where gravity forces are significant. We show that
the proposed technique is accurate at high upscaling ratios and that it is
significantly less sensitive to the upscaling level relative to single-porosity
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