Water-fluid interfaces

This property is useful in helping to define the interface between fluids. The intercept between the gas and oil gradients indicates the gas-oil contact (GOG), while the intercept between the oil and water gradients indicates the free water level (FWL) which is related to the oil water contact (OWC) via the transition zone, as described in Section 5.9. 

Miller, R., Fainerman, V.B., Makievski, A.V., Kragel, J., Grigoriev, D.O., Kazakov, V.N., Sinyachenko, O.V. (2000a). Dynamics of protein and mixed protein + surfactant adsorption layers at the water-fluid interface. Advances in Colloid and Interface Science, 86, 39-82. 

Formation of hydrate nuclei (from aqueous liquid) occurs as heterogeneous nudeation, usually at an interface (either fluid + solid, gas + liquid, or liquid + liquid). When both a nonaqueous liquid and vapor are present with water, hydrates form at the liquid-liquid interface. 

V. B. Fainerman, E. H. Lucassen-Reynders and R. Miller, Description of the adsorption behaviour of proteins at water/fluid interfaces in the framework of a two-dimensional solution model, Adv. Colloid Interface Sci. 106, 237-259 (2003). 

Double layers at water-fluid interfaces form spontaneously. The driving force is chemical in the sense of non-electrostatic. Electrostatic interactions oppose double layer formation. The situation is the same as for all double layers in dispersed systems (sec. II.3.1). 

B.V. Derjaguin (= Deryagin). N.V. Churaev, Properties of Water Layers Adjacent to Interfaces, in Fluid Interfacial Phenomena, C.A. Croxton, Ed., Wiley (1986) Ch. 15, p. 663. 

Zhang TC, Bishop PL. Experimental-determination of the dissolved-oxygen boundary-layer and mass-transfer resistance near the fluid-biofilm interface. Water Sci Technol 1994 30 47-58. 

In paper [11] we developed the two-phase flow model coupled with the dynamics of two bacterial populations. One of them represents bacteria living in water, while the second one is the neuston - a thin biofllm situated at the interfaces between water and gas. We also developed the mathematical model of chemotaxis in two-phase fluid, which is the main mechanism of neuston formation bacteria living in water feel the presence of nutriments concentrated in the injected gas and move to the direction of the interfaces water-gas without crossing them. We have shown that the chemotaxis law should satisfy some specific conditions to ensure the neuston formation. In particular, the bacteria diffusion is shown to be a regularizing mechanism which ensures mathematically the existence of regular solutions. 

To summarise the results obtained for the theoretical background, it was shown that essentially the same model can be used to describe the adsorption of ionic surfactants at the water/air, water/alkane vapor and water/liquid alkane interfaces. For the water/air interface we use the set of Eqs. (l)-(4), for the water/vapor interface Eqs. (7)-(9), and for the water/bulk oil interface Eqs. (7), (9) and (10). In the following sections the theoretical models are used to fit experimental surface and interfacial tension data obtained in studies of CnTABs at the three mentioned different water/fluid interfaces. 

Using surface and interfacial tension data for some members of the homologous series of cationic surfactants we want to demonstrate to suitability of the thermodynamic approach of competitive adsorption for the formation of adsorption layers at different water/fluid interfaces, including those to alkane vapor and liquid alkane. We will restrict ourselves here to hexane as the oil or vapor phase. The particular effects of the alkane chain length have been discussed for example in [9]. For oils different from alkanes less systematic data exist, however, a specific impact of the molecular structure can be expected and the molecular characteristics might be rather different from those we obtained for alkanes. 

Surface tension arises at a fluid to fluid interface as a result of the unequal attraction between molecules of the same fluid and the adjacent fluid. For example, the molecules of water in a water droplet surrounded by air have a larger attraction to each other than to the adjacent air molecules. The imbalance of forces creates an inward pull which causes the droplet to become spherical, as the droplet minimises its surface area. A surface tension exists at the interface of the water and air, and a pressure differential exists between the water phase and the air. The pressure on the water side is greater due to the net inward forces... 

Finally, it is worth remembering the sequence of events which occur during hydrocarbon accumulation. Initially, the pores in the structure are filled with water. As oil migrates into the structure, it displaces water downwards, and starts with the larger pore throats where lower pressures are required to curve the oil-water interface sufficiently for oil to enter the pore throats. As the process of accumulation continues the pressure difference between the oil and water phases increases above the free water level because of the density difference between the two fluids. As this happens the narrower pore throats begin to fill with oil and the smallest pore throats are the last to be filled. 

When the radial flow of fluid towards the wellbore comes under the localised influence of the well, the shape of the interface between two fluids may be altered. The following diagrams show the phenomena of coning and cuspingoi water, as water is displacing oil towards the well. 

In the context of the structural perturbations at fluid-solid interfaces, it is interesting to investigate the viscosity of thin liquid films. Eaily work on thin-film viscosity by Deijaguin and co-workers used a blow off technique to cause a liquid film to thin. This work showed elevated viscosities for some materials [98] and thin film viscosities lower than the bulk for others [99, 100]. Some controversial issues were raised particularly regarding surface roughness and contact angles in the experiments [101-103]. Entirely different types of data on clays caused Low [104] to conclude that the viscosity of interlayer water in clays is greater than that of bulk water. 

An interesting question that arises is what happens when a thick adsorbed film (such as reported at for various liquids on glass [144] and for water on pyrolytic carbon [135]) is layered over with bulk liquid. That is, if the solid is immersed in the liquid adsorbate, is the same distinct and relatively thick interfacial film still present, forming some kind of discontinuity or interface with bulk liquid, or is there now a smooth gradation in properties from the surface to the bulk region This type of question seems not to have been studied, although the answer should be of importance in fluid flow problems and in formulating better models for adsorption phenomena from solution (see Section XI-1). 

If the drill string becomes differentially stuck, mechanical methods or spotting fluids can be appHed, or the hydrostatic pressure can be reduced (147). In general, penetration of water- or oil-based spotting fluids into the interface between the filter cake and the pipe accompanied by dehydration and cracking results in reduction of differential pressure across the drill string (147,148). Spotting fluids are usually positioned in the open hole to completely cover the problem area. 

Work in the area of simultaneous heat and mass transfer has centered on the solution of equations such as 1—18 for cases where the stmcture and properties of a soHd phase must also be considered, as in drying (qv) or adsorption (qv), or where a chemical reaction takes place. Drying simulation (45—47) and drying of foods (48,49) have been particularly active subjects. In the adsorption area the separation of multicomponent fluid mixtures is influenced by comparative rates of diffusion and by interface temperatures (50,51). In the area of reactor studies there has been much interest in monolithic and honeycomb catalytic reactions (52,53) (see Exhaust control, industrial). Eor these kinds of appHcations psychrometric charts for systems other than air—water would be useful. The constmction of such has been considered (54). 

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