Towards improved understanding of spontaneous imbibition into dry porous media using pore-scale direct numerical simulations

TL;DR

This study uses pore-scale direct numerical simulations to analyze water imbibition in dry porous media, revealing detailed mechanisms that can enhance traditional predictive models for natural and industrial processes.

Contribution

It provides a detailed pore-scale analysis of imbibition dynamics using direct numerical simulations, addressing limitations of existing macro-scale and simplified pore-scale models.

Findings

Differences between converging and diverging geometries are characterized.

Dynamic pressure and meniscus reconfiguration during pore-filling are analyzed.

Impact of inertia, pore size, and pore geometry on imbibition and capillary barriers is quantified.

Abstract

Traditional approaches to mathematically describe spontaneous imbibition are usually based on either macro-scale models, such as Richards equation, or simplified pore-scale models, such as the bundle of capillary tubes (BCTM) or pore-network modeling (PNM). It is well known that such models cannot provide full microscopic details of the multiphase flow processes and that many pore-scale mechanisms still lack proper mathematical descriptions. To improve the predictive capabilities of traditional models, a fundamental understanding of pore-scale dynamics is needed. The focus of this paper is obtaining detailed insight and consistent explanation of particular processes during capillary-controlled water imbibition into dry porous media. We use two-dimensional model geometries and perform fully dynamic volume-of-fluid based direct numerical simulations of air-water multiphase flow at the pore-scale, to study processes that generally are not considered in traditional models. More specifically, we investigate differences between converging and diverging geometries, dynamic pressure and meniscus reconfiguration during pore-filling events, and the influence of inertia and pore size on imbibition dynamics and the occurrence of capillary barriers. Furthermore, we perform a detailed comparison between non-interacting and interacting BCTM and study the impact of the narrow contractions on imbibition dynamics and the trapping of the non-wetting phase. Obtained knowledge can be used to improve predictive models, which are broadly relevant considering the importance of spontaneous imbibition in many different natural and industrial processes.