Imbibition in Disordered Media

The physics of liquids in porous media gives rise to many interesting phenomena, including imbibition where a viscous fluid displaces a less viscous one. Here we discuss the theoretical and experimental progress made in recent years in this field. The emphasis is on an interfacial description, akin to the focus of a statistical physics approach. Coarse-grained equations of motion have been recently presented in the literature. These contain terms that take into account the pertinent features of imbibition: non-locality and the quenched noise that arises from the random environment, fluctuations of the fluid flow and capillary forces. The theoretical progress has highlighted the presence of intrinsic length-scales that invalidate scale invariance often assumed to be present in kinetic roughening processes such as that of a two-phase boundary in liquid penetration. Another important fact is that the macroscopic fluid flow, the kinetic roughening properties, and the effective noise in the problem are all coupled. Many possible deviations from simple scaling behaviour exist, and we outline the experimental evidence. Finally, prospects for further work, both theoretical and experimental, are discussed.Comment: Review article, to appear in Advances in Physics, 53 pages LaTe

The impact of tides on the capillary transition zone

The capillary transition zone, also known as the capillary fringe, is a zone where water saturations decrease with height above the water table/oil–water contact as a result of capillary action. In some oil reservoirs, this zone may contain a significant proportion of the oil in place. In groundwater assessments, the capillary fringe can profoundly affect contaminant transport. In this study, we investigated the influence of a tidally induced, semi-diurnal, change in water table depth on the water saturation distribution in the capillary fringe/transition zone. The investigation used a mixture of laboratory experiments, in which the change in saturation with depth was monitored over a period of 90 days, and numerical simulation. We show that tidal changes in water table depth can significantly alter the vertical water saturation profile from what would be predicted using capillary–gravity equilibrium and the drainage or imbibition capillary pressure curves

Modelling of hydraulic fracturing process by coupled discrete element and fluid dynamic methods

A three-dimensional model is presented and used to reproduce the laboratory hydraulic fracturing test performed on a thick-walled hollow cylinder limestone sample. This work aims to investigate the implications of the fluid flow on the behaviour of the micro-structure of the rock sample, including the material strength, its elastic constants and the initialisation and propagation of fractures. The replication of the laboratory test conditions has been performed based on the coupled Discrete Element Method (DEM) and Computational Fluid Dynamics scheme. The numerical results are in good agreement with the experimental data, both qualitatively and quantitatively. The developed model closely validates the overall behaviour of the laboratory sample, providing a realistic overview of the cracking propagation towards total collapse as well as complying with Lame’s theory for thick-walled cylinders. This research aims to provide some insight into designing an accurate DEM model of a fracturing rock that can be used to predict its geo-mechanical behaviour during Enhanced Oil Recovery applications