Aleksey N. Rozhkov

Foam in porous media: thermodynamic and hydrodynamic peculiarities

Abstract Thermodynamic and hydrodynamic properties of foams in porous media are examined from a unified point of view. We show that interactions between foam films (lamellae) and wetting films covering the pore walls play an important role in treating experimental data and constructing a general theory of foam residence and motion through porous media. Mechanisms of in situ bubble generation, foam patterning, and rheological peculiarities of foams in pores are discussed in detail. In particular, we clarify the difference between foam lamellae and liquid lenses, focusing on intermolecular forces in thin foam and wetting films. A consistent description of conditions of mechanical equilibrium of curved lamellae, including dynamic effects, is presented for the first time. This microlevel approach enables us to describe the dependence of the capillary pressure in the Plateau border on the current state of the pair ‘wetting film–foam lamella’. We review a theory of foam patterning under a load. Two driving forces are invoked to explain specific interactions between the solid skeleton and foams. The binding forces caused by bubble compressibility and the pinning forces due to capillarity determine a specific ordering of lamellae in porous media. The microscopic bubble train model predicts asymptotic expressions for the start-up-yield pressure drop. We consider key problems that underlay the understanding of physical mechanisms of anomalous foam resistance. Different micromechanical models of foam friction are thoroughly discussed. Brethertons (1961) theory of the forced, steady fluid–fluid displacement is reviewed in application to bubble transport through pore channels. The origins of disagreement of the theory and experiment are discussed. The Bretherton theory is augmented based on a new sailboat model, which accounts for thermodynamic coupling of foam lamellae and wetting films. Special attention is paid to studies of stick-slip motion of lamellae and bubbles in pores of varying diameter. Finally, we discuss macroscale models and analyze topical problems of foam behavior in porous media, including reservoirs, granular, and fibrous materials.

Spontaneous absorption of viscous and viscoelastic fluids by capillaries and porous substrates

We have developed a new technique to monitor spontaneous adsorption of fluids by porous substrates. The method is based on an optical electronic measuring system providing millisecond resolution. The method capabilities are demonstrated with the example of the absorption of millimeter-size droplets of water and aqueous solutions of polyethylene oxide and polyacrylamide by capillaries. It is shown that polymer additives even in a small amount reduce significantly the rate of adsorption. We have introduced a generalized Lucas-Washburn equation to account for the fluid elasticity. This equation is shown to explain the observed kinetics quantitatively without invoking adjustable parameters. We have derived a modified Bosanquet equation for the initial velocity of penetration, which accounts for the fluid elasticity. This simple formula gives a reasonable estimate of the rate of absorption of small droplets. We report visualization experiments on absorption of water and polymer solutions by sugar cubes as an example of porous substrates. Although the kinetics of droplet adsorption by porous substrates is similar to the kinetics of droplet adsorption by capillaries, the interpretation of experimental data is more complex and requires a plausible hydrodynamic model for lateral spreading in pores.

About transformation of the deep-water methane bubbles into hydrate powder and hydrate foam

During the Russian Academy of Sciences “MIRI na Baikale, 2008–2010” expedition, deep-water experiments with the bubbles of methane seeping from the bottom at depths 405, 860 and 1400 meters were carried out. These depths correspond to gas hydrate stability zone. Bubbles were caught by the trap which was looked like an inverted glass. It was found that the behavior of bubbles in a trap depends on the depth. At depth of 405 meters formation of hydrates was not observed. Having got to a trap at the depth of 860 meters, bubbles became covered by solid hydrate envelope, kept the initial form, and after a time period collapsed in a number of hydrate fragments which showed all properties of a granular matter. No visible changes in the hydrate granular matter were observed in the course of lifting it to a depth of 380 meters. Shallower, the decomposition of the hydrate granular matter into methane gas was observed. In the experiments at depth of 1400 meters the caught bubbles, becoming covered by hydrate envelope formed solid hydrate foam in the trap. At lifting this foam structure was deformed slightly but simultaneously a free gas left the foam and filled the trap. The volume of free gas in the trap at lifting varied according to the Boyle-Mariotte law.

Heat and mass transfer effects during displacement of deepwater methane hydrate to the surface of Lake Baikal

The present paper focuses on heat and mass exchange processes in methane hydrate fragments during in situ displacement from the gas hydrate stability zone (GHSZ) to the water surface of Lake Baikal. After being extracted from the methane hydrate deposit at the lakebed, hydrate fragments were placed into a container with transparent walls and a bottom grid. There were no changes in the hydrate fragments during ascent within the GHSZ. The water temperature in the container remained the same as that of the ambient water (~3.5 °С). However, as soon as the container crossed the upper border of the GHSZ, first signs of hydrate decomposition and transformation into free methane gas were observed. The gas filled the container and displaced water from it. At 300 m depth, the upper and lower thermometers in the container simultaneously recorded noticeable decreases of temperature. The temperature in the upper part of the container decreased to –0.25 °С at about 200 m depth, after which the temperature remained constant until the water surface was reached. The temperature at the bottom of the container reached –0.25 °С at about 100 m depth, after which it did not vary during further ascent. These observed effects could be explained by the formation of a gas phase in the container and an ice layer on the hydrate surface caused by heat consumption during hydrate decomposition (self-preservation effect). However, steady-state simulations suggest that the forming ice layer is too thin to sustain the hydrate internal pressure required to protect the hydrate from decomposition. Thus, the mechanism of self-preservation remains unclear.

Physical mechanisms of foam flow in porous media

Publisher Summary This chapter focuses on the physical mechanisms that govern foam flow in porous media. The motion of foams through porous media is a problem in physicochemical hydrodynamics. The basic mechanisms of foam transport reviewed contain some, but certainly not all, of the relevant physics of foam flow in porous media. Foam flow in porous media is a multifaceted process in which, on one hand, foam texture strongly governs foam rheology, and on the other, foam texture is in turn regulated by the porous medium through the capillary pressure. The chapter analyzes main features of this process with examples of foam motion in model pore channels. The modem theories of the foam lamella transport in pore channels of varying cross-section and the models of the weak foam flow are also discussed. Careful analyses of the flow on the scale of individual pores or channels are useful in exposing effects of various physical parameters on foam motion and in identifying flow-induced patterns. In addition, the basic physical mechanisms of foam microhydrodynamics underlie a variety of technological processes in oil recovery, groundwater/soil remediation, and textile manufacturing.