Abstract

AbstractAt the pore scale, slow invasion of a wetting fluid in porous materials is often modeled with quasi‐static approximations which only consider capillary forces in the form of simple pore‐filling rules. The appropriateness of this approximation, often applied in pore network models, is contested in the literature, reflecting the difficulty of predicting imbibition relative permeability with these models. However, validation by sole comparison to continuum‐scale experiments is prone to induce model overfitting. It has therefore remained unclear whether difficulties generalizing the model performance are caused by errors in the predicted filling sequence or by subsequent calculations. Here, we address this by examining whether such a model can predict the pore‐scale fluid distributions underlying the behavior at the continuum scale. To this end, we compare the fluid arrangement evolution measured in fast synchrotron micro‐CT experiments on two rock types to quasi‐static simulations which implement capillary‐dominated pore filling and snap‐off, including a sophisticated model for cooperative pore filling. The results indicate that such pore network models can, in principle, predict fluid distributions accurately enough to estimate upscaled flow properties of strongly wetted rocks at low capillary numbers.

Highlights

  • Imbibition is the process where a wetting fluid replaces a nonwetting fluid in a porous medium

  • The results indicate that such pore network models can, in principle, predict fluid distributions accurately enough to estimate upscaled flow properties of strongly wetted rocks at low capillary numbers

  • We showed how Pore network models (PNMs) predictions can be mapped to fluid distributions measured with micro-CT to facilitate direct pore-by-pore comparisons in rock samples (Bultreys et al, 2018)

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Summary

Introduction

Imbibition is the process where a wetting fluid replaces a nonwetting fluid in a porous medium. While Navier-Stokes solvers are becoming mature enough to perform useful numerical experiments on domains tens of pores across over relatively short time scales (Alpak et al, 2018; Ferrari & Lunati, 2013; McClure et al, 2018; Shams et al, 2018), it remains desirable to define a more conceptual model which describes the emergence of structures at the scale of fluid clusters for upscaling (Hilfer et al, 2015) This is important to upscale multiphase flow properties, especially in heterogeneous porous media where representative elementary volume considerations may be crucial

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