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Ostwald ripening of gas bubbles is a spontaneous mass transfer process that can impact the storage volume of trapped gas in the subsurface. In homogeneous porous media with identical pores, bubbles evolve toward an equilibrium state of equal pressure and volume. How the presence of two liquids impacts ripening of a bubble population is less known. We hypothesize that the equilibrium bubble sizes depend on the surrounding liquid configuration and oil/water capillary pressure. We investigate ripening of nitrogen bubbles in homogeneous porous media containing decane and water using a level set method that alternately simulates capillary-controlled displacement and mass transfer between bubbles to eradicate chemical-potential differences. We explore impacts of initial fluid distribution and oil/water capillary pressure on the bubble evolution. Ripening in three-phase scenarios in porous media stabilizes gas bubbles to sizes that depend on their surrounding liquids. Bubbles in oil decrease in size while bubbles in water increase in size with increasing oil/water capillary pressure. Bubbles in oil reach local equilibrium before the three-phase system stabilizes globally. A potential implication for field-scale gas storage is that the trapped gas fractions in oil and water vary with depth in the oil/water transition zone. • Level set approach to gas bubble ripening on three-phase fluid configurations in porous media. • Equilibrium bubble sizes in oil and water depend on oil/water capillary pressure and gas/liquid interfacial tensions. • Ripening of gas bubbles in three-phase fluid systems displays a different behaviour in porous media than in bulk liquids. • Oil/water capillary pressure impacts the equilibration time for three-phase ripening scenarios in porous media. [ABSTRACT FROM AUTHOR]

The role of interfacial coatings in gas transport dynamics in foam coarsening is often difficult to quantify. The complexity of foam coarsening measurements or gas transport measurements between bubbles requires assumptions about the liquid thin film thickness profile in order to explore the effects of interfacial coatings on gas transport. It should be possible to independently quantify the effects from changes in film thickness and interfacial permeability by using both atomic force microscopy and optical microscopy to obtain time snapshots of this dynamic process. Further, it is expected that the surfactant and polymer interfacial coatings will affect the mass transfer differently. We measure the mass transfer between the same nitrogen microbubbles pairs in an aqueous solution using two methods simultaneously. First, we quantify the bubble volume changes with time via microscopy and second, we use Atomic Force Microscopy to measure the film thickness and mass transfer resistances using a model for the gas transport. Modelling of the interface deformation, surface forces and mass transfer across the thin film agrees with independent measurements of changes in bubble size. We demonstrate that an anionic surfactant does not provide a barrier to mass transfer, but does enhance mass transfer above the critical micelle concentration. In contrast, a polymer monolayer at the interface does restrict mass transfer. [ABSTRACT FROM AUTHOR]

Abstract: A forced Ostwald ripening experiment is performed on a single foam bubble. The bubble size is followed as the system is wetted with a constant liquid flow rate delivered from one of the bubble Plateau borders. Obtained ripening velocities cannot be described with a model based on a constant film thickness assumption. Within these well-controlled experimental conditions, the film thickness is measured and found to depend on the imposed liquid flow rate. It is shown that the bubble growth rate is well predicted as the films thickness evolution is explicitly introduced in the ripening model. Finally, it is suggested that existing results for the coarsening of draining foams could be understood following the approach validated on the bubble scale. [Copyright &y& Elsevier]

A thermodynamic model in order to study a single-component system where droplets or bubbles are inside smooth crevices is presented. Liquid–vapor interface curvature radius can change its sign as the droplet or bubble volume change. The results suggest that there is always dispersed phase inside smooth crevices of microscopic dimensions, even in the expected single-phase region. Thus, the occurrence of an anti-ripening phenomenon is predicted from a microscopic point of view; meanwhile the occurrence of a ripening phenomenon is energetically favorable at a macroscopic scale. The relevance of these results on the heterogeneous nucleation process is analyzed. [Copyright &y& Elsevier]

A thermodynamic model to obtain the radius of bubbles or droplets in a single-component system for a given temperature, total volume, and phase distribution is developed. The general formulation of the model includes bubbles or droplets in the form of spheres, truncated spheres on a flat solid surface or inside conical walls. In these three geometries the liquid–vapor curvature radius is positive but in the case of conical walls it can be also negative. States with different dispersed-phase distributions are compared using the total free energy of the system. When the curvature radius is positive, it has a minimum nonvanishing value and the occurrence of the Ostwald ripening is energetically favorable. On the other hand, when the curvature radius is negative, it is energetically more favorable to find the dispersed phase even in the expected single-phase region, and the occurrence of an anti-ripening phenomenon. The PV isotherms obtained from the model and the applicability of the results to the nucleation process are discussed. [Copyright &y& Elsevier]