Foams surfactant solutions

Reservoir-foam applications may involve slug injection, in which foaming surfactant solution is injected into the gas stream at the well-head over a period of a few hours, semi-continuous injection, in which surfactant solution is injected at intervals over a period of a day or so, and continuous injection, in which surfactant solution is injected continuously for months or even years. Recently, much attention has been paid to near-well applications of foams [345,726-728],... 

Plotting the same foam stability data versus lamella number (39) shows that for these four oils, the same variation of foam breakage frequency with lamella number is observed. Thus, even though for a given foaming surfactant solution the foam does not have the same stability in the presence of each oil, the stability is still well predicted by the surface properties, as reflected in the lamella number (equations 4 and 5). Also, using the surface properties allows the effects of the dodecane to be... 

A review on field applications of steam foams is given in [261]. It is shown that experiments on injection of aqueous steam foam surfactant solutions, conducted earlier gave a relatively low increase in oil recovery, but remained profitable nevertheless. To achieve better results, the reservoir structure must be taken into consideration for the choice of an optimum foam injection regime. 

These surfactant sticks (often referred to under a variety of common and trade-marked names such as soap sticks ) can be dropped manually or with automatic stick launchers. The gas-releasing capability from so-equipped sticks are not very large this feature is intended for use in stimulating completely dead wells. Alternatively, one can continuously inject foaming surfactant solution through tubing in the annulus. This consumes more surfactant but can lead to a more consistent unloading of the water with less pressure fluctuation. The surfactants that have been used are mostly anionic or anionic/non-ionic blends [53, 60]. 

Montufar, E. B., Traykova, T., C. Gil, I. H., Almirall, A., Aguirre, A., Engel, E., Planell, J. A. Ginehra, M. P. (2009) Foamed surfactant solution as a template for selfsetting injectable hydroxyapatite scaffolds for bone regeneration. Acta Biomaterialia. 

Antifoams additives are usually surface-active compounds weakly soluble in the foaming surfactant solution. They are derived from various natural fats and oils, petroleum derivatives, or silicone oils. Our goal is not to enter into the details of all the types of antifoam agent but to point out those most often used in various applications. Many review articles exist on this subject [41-43]. 

The ability of the additive to lower the critical micelle concentration (CMQ of the foaming surfactant solution. 

Fig. XIV-16. A photomicrograph of a two-dimensional foam of a commercial ethox-ylated alcohol nonionic surfactant solution containing emulsified octane in which the oil drops have drained from the foam films into the Plateau borders. (From Ref. 234.)...

Lignosulfonate has been reported to increase foam stabihty and function as a sacrificial adsorption agent (175). Addition of sodium carbonate or sodium bicarbonate to the surfactant solution reduces surfactant adsorption by increasing the aqueous-phase pH (176). 

Phenomena at Liquid Interfaces. The area of contact between two phases is called the interface three phases can have only aline of contact, and only a point of mutual contact is possible between four or more phases. Combinations of phases encountered in surfactant systems are L—G, L—L—G, L—S—G, L—S—S—G, L—L, L—L—L, L—S—S, L—L—S—S—G, L—S, L—L—S, and L—L—S—G, where G = gas, L = liquid, and S = solid. An example of an L—L—S—G system is an aqueous surfactant solution containing an emulsified oil, suspended soHd, and entrained air (see Emulsions Foams). This embodies several conditions common to practical surfactant systems. First, because the surface area of a phase iacreases as particle size decreases, the emulsion, suspension, and entrained gas each have large areas of contact with the surfactant solution. Next, because iaterfaces can only exist between two phases, analysis of phenomena ia the L—L—S—G system breaks down iato a series of analyses, ie, surfactant solution to the emulsion, soHd, and gas. It is also apparent that the surfactant must be stabilizing the system by preventing contact between the emulsified oil and dispersed soHd. FiaaHy, the dispersed phases are ia equiUbrium with each other through their common equiUbrium with the surfactant solution. 

AH these mechanisms except high bulk viscosity require a stabilizer in the surface layers of foam films. Accordingly, most theories of antifoaming are based on the replacement or modification of these surface-active stabilizers. This requires defoamers to be yet more surface active most antifoam oils have surface tensions in the 20 to 30 mN/m range whereas most organic surfactant solutions and other aqueous foaming media have surface tensions between 30 and 50 mN/m(= dyn/cm). This is illustrated in Table 3. 

There are many laboratory methods for testing the relative merits of one defoamer against another. It is a simple matter to measure foam height as a function of time to compare the performance of various foam surfactants and defoamers. Unfortunately, this simplicity has led to a wide variety of methods and conditions used with no standard procedure that would make the measurement of foaminess as characteristic of a solution as its surface tension or viscosity. It has been suggested that the time an average bubble remains entrapped ia the foam is such a quantity (49), but very few workers ia the defoamer iadustry have adopted this proposal. Ia practice, a wide variety of methods are used that geaerally fall iato oae of five maia categories ... 

Chlebicki and Slipko [127] determined the foam ability of sodium propoxyl-ated alcohol sulfates by the Ross-Miles method. These substances are low-foaming surfactants the greatest foam height was observed for dodecyl and tetradecyl chains. As expected, as the number of polyoxypropylene units on the same alcohol chain increases, foam height decreases. The maximum foam height obtained was 225 mm for a 2 g/L solution of sodium tetradecyl (1 PrO) sulfate. 

The mechanisms that affect heat transfer in single-phase and two-phase aqueous surfactant solutions is a conjugate problem involving the heater and liquid properties (viscosity, thermal conductivity, heat capacity, surface tension). Besides the effects of heater geometry, its surface characteristics, and wall heat flux level, the bulk concentration of surfactant and its chemistry (ionic nature and molecular weight), surface wetting, surfactant adsorption and desorption, and foaming should be considered. 

Additive of surfactant leads to enhancement of heat transfer compared to water boiling in the same gap size however, this effect decreases with decreasing channel size. For the same gap size CHF in surfactant solutions is significantly lower than that in water. At high values of heat flux some foaming patches began to occur this process increased with decrease in gap size and led to decrease in CHF, Hetsroni et al. (2007). 

Periodically injecting simultaneously or alternately a noncondensable gas and a foaming composition solution containing alkalis, surfactants and polymers to form combined foam or periodically injecting the gas and the foam previously formed from the solution... 

A foam can be generated by using an inert gas and a fluorocarbon surfactant solution in admixture with an amphoteric or anionic hydrocarbon surfactant solution. A relatively small amount of the fluorocarbon surfactant is operative when mixed with the hydrocarbon surfactant and foamed. The foam has better stability than a foam made with hydrocarbon surfactant alone when in contact with oil [1491]. 

Foam generated in porous media consists of a gas (or a liquid) dispersed in a second interconnected wetting liquid phase, usually an aqueous surfactant solution (1). Figure 1 shows a micrograph of foam flowing in a two-dimensional etched-glass porous medium micromodel (replicated from a Kuparuk sandstone, Prudhoe Bay, Alaska (2)). Observe that the dispersion microstructure is not that of bulk foam. Rather discontinuous... 

For the wet case, the foam enters and achieves steady state after several pore volumes. A mobility reduction compared to water of about 90% ensues. However, for the dry case, there is about a one pore-volume time lag before the pressure responds. During this time, visual observations into the micromodel indicate a catas-tropic collapse of the foam at the inlet face. The liquid surfactant solution released upon collapse imbibes into the smaller pores of the medium. Once the water saturation rises to slightly above connate (ca 30%), foam enters and eventually achieves the same mobility as that injected into the wet medium. 

Figure 1. Micrograph of foam in a 1.1 pm, two dimensional etched-glass micromodel of a Kuparuk sandstone. Bright areas reflect the solid matrix while grey areas correspond to wetting aqueous surfactant solution next to the pore walls. Pore throats are about 30 to 70 /xm in size. Gas bubbles separated by lamellae (dark lines) are seen as the nonwetting "foam" phase.

Figure 2. Transient pressure drop across the porous-medium micromodel of Figure 1 for foam pregenerated in an identical upstream medium. The foam frontal advance rate is 186 m/d. In the wet case, foam advanced into the downstream micromodel which was completely saturated with aqueous surfactant solution. In the dry case, the downstream micromodel contained only air.

High pressure equipment has been designed to measure foam mobilities in porous rocks. Simultaneous flow of dense C02 and surfactant solution was established in core samples. The experimental condition of dense CO2 was above critical pressure but below critical temperature. Steady-state CC -foam mobility measurements were carried out with three core samples. Rock Creek sandstone was initially used to measure CO2-foam mobility. Thereafter, extensive further studies have been made with Baker dolomite and Berea sandstone to study the effect of rock permeability. 

In this section the laboratory measurements of CC -foam mobility are presented along with the description of the experimental procedure, the apparatus, and the evaluation of the mobility. The mobility results are shown in the order of the effects of surfactant concentration, CC -foam fraction, and rock permeability. The preparation of the surfactant solution is briefly mentioned in the Effect of Surfactant Concentrations section. A zwitteronic surfactant Varion CAS (ZS) from Sherex (23) and an anionic surfactant Enordet X2001 (AEGS) from Shell were used for this experimental study. 

Figure 3. Typical plot of data output from the rig, showing values of the weight of effluent from the capillary test unit as a function of time, during an experiment. The portion of the curve from B - C shows the efflux of surfactant solution from the foam generator which precedes gas break-through. Portion C -D< shows the efflux of foam of increasing quality. At times larger than D only "dry gas, without liquid phase, emerges.

Although silicone oils by themselves or hydrophobic particles (e.g., specially treated silica) are effective antifoams, combinations of silicone oils with hydrophobic silica particles are most effective and commonly used. The mechanism of film destruction has been studied with the use of surface and interfacial tensions, measurements, contact angles, oil-spreading rates, and globule-entering characteristics for PDMS-based antifoams in a variety of surfactant solutions.490 A very recent study of the effect of surfactant composition and structure on foam-control performance has been reported.380 The science and technology of silicone antifoams have recently been reviewed.491... 

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