We report an analysis of rising bubble experiments for ternary systems. We present experimental evidence that observations of changes in bubble appearance are primarily controlled by changes in interfacial tension (IFT) that occur as components transfer from the surrounding liquid to the rising bubble. We report experimental observations for an analog ternary system (brine/isopropanol/iso-octane) that confirm the influence of IFT on bubble appearance.
We also describe a simple diffusion model of composition changes during bubbles rise. A combination of experimental results and model calculations indicates that rising bubble experiments can be used to detect minimum miscibility pressure (or enrichment) for ternary vaporizing drives. Similar analysis shows, however, that falling drop experiments are more appropriate for ternary condensing displacements. Questions that remain to be resolved for systems with more than three components are outlined.
Slim tube displacements have long been used to measure minimum miscibility pressure (MMP) or minimum miscibility enrichment (MME) for displacements of an oil by a gas. An alternative method based on the appearance of the bubble of gas rising through the oil have been proposed more recently. The advantage of the rising bubble (RB) experiment is that it can performed more rapidly than slim tube experiments. Although several investigators have used RB experiments to measure MMP for model systems and crude oils, no quantitative analysis has been reported of the details of the composition changes that occur as a bubble rises. It has been assumed that the mechanisms of mass transfer involved in RB experiments are equivalent to those that arise in slim tube displacements. Christiansen and Haines stated: "We believe that the mass transfer process that occurs as the gas bubble rises through the oil in the glass tube is similar to the multiple-contact process described for gas displacements of oil in slim tube." They used an argument based on mixing of equilibrium gas with uncontacted oil in a ternary system to illustrate how bubble compositions could changes, an argument similar to that of Hutchinson and Braun for the development miscibility for a ternary vaporizing gas drive. In this paper, we examine in more detail the mass transfer involved in RB experiments, and we compare the resulting composition changes with those that occur during the development of miscibility in gas displacements.
We first report results of experiments with an analog ternary system. We then propose a simple diffusion model to describe the mechanisms of mass transfer and hence the development of miscibilty in the RB experiments. We then compare calculated results and experimental observations to demonstrate the relevance of the bubble appearance to the development of miscibility in gas displacements.
In interpretation of RB experiments, the "MMP is inferred from the pressure dependence of the behavior of the rising bubbles." The MMP or MME is determined from observations of changes in the shape and appearance of bubbles of the injected gas as they rise through the oil. The shape of a gas bubble rising through a quiescent liquid depends on the size of the bubble and the physical properties, which have been correlated by two dimensionless numbers: Reynolds number