Incorporation of Sub-Resolution Porosity into Two-Phase Flow Models with
a Multiscale Pore Network
Abstract
Porous materials, such as carbonate rocks, frequently have pore sizes
which span many orders of magnitude. This is a challenge for models that
rely on an image of the pore space, since much of the pore space may be
unresolved. There is a trade off between image size and resolution. For
most carbonates, to have an image sufficiently large to be
representative of the pore structure, many fine details cannot be
captured. In this work, sub-resolution porosity in X-ray images is
characterized using differential imaging which quantifies the difference
between a dry scan and 30 wt\% KI brine saturated rock
images. Once characterized, we develop a robust workflow to incorporate
the sub-resolution pore space into network model using Darcy-type
elements called micro-links. Each grain voxel with sub-resolution
porosity is assigned to the two nearest resolved pores using an
automatic dilation algorithm. By including these micro-links with
empirical models in flow modeling, we simulate single-phase and
multiphase flow. By fine-tuning the micro-link empirical models, we
achieve effective permeability, formation factor, and drainage capillary
pressure predictions that align with experimental results. We then show
that our model can successfully predict steady-state relative
permeability measurements on a water-wet Estaillades carbonate sample
within the uncertainty of the experiments and modeling. Our approach of
incorporating sub-resolution porosity in two-phase flow modeling using
image-based multiscale pore network techniques can capture complex pore
structures and accurately predict flow behavior in porous materials with
a wide range of pore size.