Zusammenfassung
Cavities and fractures can significantly affect the flow paths of carbonate reservoirs and should
be accurately accounted for during flow simulation. Herein, our goal is to compute the effective
permeability of rock samples based on high-resolution 3D CT-scans containing millions of voxels.
To this end, we need a flow model that properly accounts for the effects of Darcy flow in the porous
material and Stokes flow in the void volumes on all relevant scales. The presence of different length
scales and large contrasts in the petrophysical parameters leads to highly ill-conditioned linear sys-
tems that make such a flow model very difficult to solve, even on large-scale parallel computers. To
identify simplifications that render the problem computationally tractable, we analyze the relative
importance of the Stokes and Darcy terms for a wide variety of parameter ranges on an idealized 2D
model. We find that a system with a through-going free flow region surrounded by a low permeable
matrix can be accurately modeled by ignoring the Darcy matrix and simulating only the Stokes flow.
Using the obtained insight, we are able to compute the effective permeability of a specific model
from a CT-scan that contains more than eight million voxels.
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