Incorporation of Sub-Resolution Porosity Into Two-Phase Flow Models With a Multiscale Pore Network for Complex Microporous Rocks

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. 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% potassium iodide brine saturated images. Once characterized, we develop a robust workflow to incorporate the sub-resolution pore space into a network model using Darcy-type elements called microlinks. Each grain voxel with sub-resolution porosity is assigned to the two nearest resolved pores using an automatic dilation algorithm. By including these microlinks with empirical models in flow modeling, we simulate single-phase and multiphase flow. By fine-tuning the microlink empirical models, we match permeability, formation factor (the ratio of the resistivity of a rock filled with brine to the resistivity of that brine), and drainage capillary pressure to 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. A dilation-based algorithm adds sub-resolution porosity, quantified by differential imaging, as microlinks to an extracted pore network Empirical models are used to characterize the flow properties of microlinks The tuned multiscale network, using permeability, formation factor, and capillary pressure, matches experimental relative permeability