Foam Stability in the Presence of Oil

Among the many available defoamers, crude oil has been used to prevent the formation of foams or destroy foams already generated in a variety of industrial processes [99-101]. Crude oil can also destabilize foams applied in petroleum reservoirs, that is, foams in porous media [66, 102-106] (see Section 11.2.2). Although crude oils tend to act as defoamers, foams actually exhibit a wide range of sensitivities to the presence of oils, and some foams are very resistant to oil [66, 107, 108]. Many system variables influence the oil tolerance of a given foam, and many attempts have been made to correlate foam—oil sensitivity with physical parameters [67, 105-110]. These have met with mixed success [65, 111, 112]. 

A major difficulty is the proper selection of foam-forming surfactants for the challenging environments involved in petroleum reservoir applications, since many characteristics are thought to be necessary for performance, including good tolerance of the foam to interaction with crude oil in porous media [66, 102]. Here, the physical situation is even more complex than for bulk foams due to influences of pore structure, wettability and oil saturation. For both bulk foams and foams in porous media, oil-sensitive foams are usually less stable as increasing amounts of emulsified oil are contacted (bulk tests) or in the presence 

There are several mechanisms by which bulk foams can be destabilized by oils, and more than one mechanism may be involved in any given situation. 

Oil droplet size is thought to be quite important to the effectiveness of crude oils at destabilizing foams, with smaller droplets being the more effective [44,114,330,342]. A number of microvisual and core-flood studies suggest that the emulsification/ imbibition of oil into foam can be a very important factor [44,114,328,330,339,342]. 

The thin liquid films bounded by gas on one side and by oil on the other, denoted air/water/oil are referred to as pseudoemulsion films [301], They are important because the pseudoemulsion film can be metastable in a dynamic system even when the thermodynamic entering coefficient is greater than zero. Several groups [301,331,342] have interpreted foam destabilization by oils in terms of pseudoemulsion film stabilities [114]. This is done based on disjoining pressures in the films, which may be measured experimentally [330] or calculated from electrostatic and dispersion forces [331], The pseudoemulsion model has been applied to both bulk foams and to foams flowing in porous media. 

In summary, many foams are completely unstable in the presence of oil, many others are moderately unstable in the presence of oil, and some foams are very stable in the presence of oil. Much is known about the factors contributing to foam-oil sensitivity, but attempts at correlation with independent physical parameters have met with mixed success. 

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Foam stability in the presence of oil can be described from thermodynamics in terms of the spreading and entering coefficients S and E respectively. These coefficients are defined as follows ... 

The interactions between foams and emulsified oil drops are discussed in the second part of this chapter. In the presence of emulsified oil, the mechanisms of foam stability are more complex than without oil. The mechanism of foam stability in the presence of oil drops is shown to be determined by the stability of the pseudoemulsion film. When the pseudoemulsion film is stable, the oil drops enhance the foam stability when the film is unstable, the oil acts as an antifoam (defoamer). In... 

As has been shown in the previous section, the stability of foam, emulsion and pseudoemulsion films manifest stratification phenomena, curvature phenomena and M arangoni phenomena. We will first discuss the microstructure of the thinning films due to micellar interactions, which we have observed through stratification phenomena. We will then discuss the observed behavior of the pseudoemulsion films with curvature and finally the role of Marangoni effects in the stabilization of the foam structure in the presence of oil. 

The interactions between an oil phase and foam lamellae are extremely complex. Foam destabilization in the presence of oil may not be a simple matter of oil droplets spreading upon foam film surfaces but may often involve the migration of emulsified oil droplets from the foam film lamellae into the Plateau borders where critical factors, such as the magnitude of the Marangoni effect in the pseudoemulsion film, the pseudoemulsion film tension, the droplet size and number of droplets may all contribute to destabilizing or stabilizing the three phase foam structure. 

In contrast, Figure 25 shows frames with the C16AOS solution. The oil drops drain from the films into the Plateau borders without entering or spreading, and the foam does not break. This observation was also in accordance with the observation that the typical oil configuration on the surface of C16AOS solution (Figure 23) was stable (thick or thin) pseudoemulsion film. These experiments clearly showed that the foam stability in the presence of emulsified oil is controlled by the stability of the pseudoemulsion film. 

If the pseudoemulsion film is stable, the larger drops formed from the unstable emulsion get trapped faster in the Plateau borders and stabilize the foam. On the other hand, if the pseudoemulsion film is unstable, the larger drops can bridge easier and break the foam lamellae faster (Figure 36). Thus, the unstable emulsion film also plays an important role in foam stability in the presence of emulsified oil. 

In the presence of decane and a decane-toluene mixture, C16 HAS gives more stable foams than C16 AS. However, such is not the case for the corresponding C18 compounds. In the presence of the decane-toluene mixture, C18 AS and C18 HAS produce foams of approximately equal stability. In the presence of decane, C18 HAS produces a more stable foam than C18 AS. The reason for the differences in behavior between the C16 and C18 compounds is not understood. However, the cause may be related to the hydrophobe carbon number and the oil phase polarity. 

In a system obtained from 1% NaDoS solution + 1.75% NaCI + kerosene (at W/O ratio 1 1) the increase in the concentration of pentanol and at SAD not much less than zero, a maximum in the stability of the O/W emulsion is observed. At SAD = 0, there is a sharp decrease in stability while at SAD > 0, the stability of W/O emulsion increases. Similarly changes the volume and stability of the foam (Fig. 7.19). In the presence of kerosene the foam volume and stability fall down to zero at SAD > 0. In the presence of oil the foam volume and stability reach a minimum at SAD = 0, then increase at SAD > 0. Similar decrease in foam stability with the increase in SAD is observed when the salt concentration in the following systems is raised NaDoS + alcohol + a complex foaming agent (Coatex + isooctane W/O =... 

An early attempt to correlate the physical properties of surfactant solutions and their foams with oil recoveries was performed by Deming in 1964 (50). Deming concluded that high foaming ability favored high displacement efficiency, but that high foam stability were not required for high displacement efficiency. Bernard and Holm found that oil substantially decreased the abilities of most surfactants to reduce aqueous permeabilities, but that some surfactants remained effective even in the presence of oil (52,53). 

Examination of the data summarized in Table I indicated that, at a constant number of carbon atoms in the hydrophobe, foam stability generally increased as the number of ethylene oxide groups was increased. The effect of a change in EO level on foam volume in the presence of a hydrocarbon phase was generally greater at lower EO levels (Figure 2). For some oils such as west Texas stock tank oil, the foam volume reached a maximum at ca 20-30 moles EO per mole AE and then decreased. 

Oil Configurations in Foams. In the presence of oil, the mechanisms of foam stability are more complex than without oil. Solubilized oil decreases the stability by accelerating the stepwise foam film thinning, as shown in the previous section. The effect of emulsified oil on foams is closely connected with the configuration of oil relative to the aqueous and gas phases. This configuration can be, in most cases, one of the following (Figure 22) ... 

This chapter will focus on the stability of foams flowing in porous media when in the presence of crude oil. Many laboratory investigations of foam-flooding have been carried out in the absence of oil, but comparatively few have been carried out in the presence of oil. For a field application, where the residual oil saturation may vary from as low as 0 to as high as 40% depending on the recovery method applied, any effect of the oil on foam stability becomes a crucial matter. The discussion in Chapter 2 showed how important the volume fraction of oil present can be to bulk foam stability. A recent field-scale simulation study of the effect of oil sensitivity on steam-foam flood performance concluded that the magnitude of the residual oil saturation was a very significant factor for the success of a full-scale steam-foam process (14). 

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... 

It was shown that in the presence of oil-soluble surfactants, stable foams are formed at a certain water content in diesel fuel, and maximum stability is achieved at a relatively low aqueous phase concentration (1% - 2%) corresponding to the transition of the solubilised solution to an inverted emulsion [265] with increasing viscosity of the surfactant solutions in the diesel fuel, the foam stability increases substantially. These ideas can be used when considering foam formation in other petroleum products containing small amounts of water and natural surfactants. 

Examples of industrial relevance for the first two phase combinations are the adsorption of pollutants from waste air or water onto activated carbon. Combinations three and four are relevant, for example, related to foam formation and stabilization in the presence of surfactants on water/air interfaces or at the interface of two immiscible liquids (e.g., oil and water). This book deals mainly with the case most typical for preparative chromatographic separations, that is, the exploitation of solid surfaces, liquid mobile phases, and dissolved feed mixtures. The following definitions are made The solid onto which adsorption occurs is defined as the adsorbent. The adsorbed molecule is defined in its free state as the adsorptive and in its adsorbed state as the adsorpt. There are typically different solutes, which are often called components (for example, A and B, Figure 2.1). 

The results in Table 22 for a series of one atmosphere 75 °C foaming experiments indicate the effect of hydrophobe carbon number. The foam stability of C18 AS is greater than that of C16 AS in the absence of an oil phase, in the presence of decane, and in the presence of the decane-toluene mixture. The foam stability of C18 HAS is greater than that of C16 HAS in the absence of an oil phase. In the presence of decane and in the presence of the decane-toluene mixture, the foam stability of the C18 HAS is, if anything, slightly less than that of C16 HAS. This may have been the result of partitioning effects. 

Colloidal liquid aphrons (CLAs), obtained by diluting a polyaphron phase, are postulated to consist of a solvent droplet encapsulated in a thin aqueous film ( soapy-shell ), a structure that is stabilized by the presence of a mixture of nonionic and ionic surfactants [57]. Since Sebba s original reports on biliquid foams [58] and subsequently minute oil droplets encapsulated in a water film [59], these structures have been investigated for use in predispersed solvent extraction (PDSE) processes. Because of a favorable partition coefficient for nonpolar solutes between the oil core of the CLA and a dilute aqueous solution, aphrons have been successfully applied to the extraction of antibiotics [60] and organic pollutants such as dichlorobenzene [61] and 3,4-dichloroaniline [62]. 

Results are presented of studies of the oxidation of cable insulation consisting of a solid PE skin and PE foam in contact with a copper conductor. Measurements were made of the stability of PE containing stabilisers and metal deactivators in the presence of blowing agents and hydrocarbon oils, and interactions between stabilisers and blowing agents were analysed. 

Foams stabilized with proteins, such as egg white, can be quite sensitive to the presence of oil (fat) droplets (see also Section 5.6.7). Just as is the case with foam sensitivity to oil in other industries, the presence of even small amounts of oil (0.03 mass % in foods [814]) can destabilize a foam. Oils such as lipids are thought to interfere with foaming by displacing proteins from the air-aqueous interface. One approach to improving the foam stability involves combining acidic proteins, such as whey or serum albumin, with basic proteins [814]. 

Early researchers turned to foamability or foaminess" measurements to screen surfactants for flow experiments (51). In one variation of this test, a long, vertical glass cylinder with a frit at the bottom was filled with the test solution, and gas was forced through the frit. The height of foam formed in the column was then measured, or, the foam was collected and the amount of liquid in the foam determined (51). In his screening of some 200 materials, Raza measured interfacial tensions of aqueous solutions with respect to air and to oil, and the foamability and foam stability in the absence and presence of oil. The latter experiment consisted simply of shaking the solution in a test tube and measuring the volume of foam at various times (60). 

To confirm the marked effect of the electrolyte concentration upon the pseudoemuIsion film stability we increased the NaCl concentration to 3 wt % and used DI to investigate the configuration of Salem crude oil droplets in the presence of C AOS surfactant (since this surfactant yields the most stable foam). 

In Figure 12 the process of collapse versus time for the three surfactant solutions and two oil phases is presented. From these results we conclude that C. A0S in the presence of n-octane and n-dodecane and Enordet AE 1215-30 in the presence of n-dodecane are low stability foams. Higher stability foams are formed by C. AOS in the presence of n-dodecane and Enordet AE 1215-30 in the presence of n-octane. 

Procedures of these 40 C (104 F) experiments are described in the Experimental Section. Tests were performed at a representative west Texas formation temperature using a typical west Texas stock tank oil and a synthetic brine having a composition typical of west Texas injection waters. Results are summarized in Table III. The ratio of foam volume after 30 minutes at 40 C to that after 1 minute was used as an indication of foam stability. The surfactants which produced the greatest initial (1.0 minute) foam volumes also exhibited the greatest foam stability over the thirty minute test period. Because test temperature and salinity were different than used in earlier experiments, results in the presence of west Texas stock tank oil cannot be compared to results described above. However, trends in foam stability were consistent with those described above. Average stability of the foams produced by the AEGS and AES surfactant classes was greater than that of the AE foams. 

A fundamental concern in CO2 foam applications is how far foams can be transported at reservoir temperatures and salinities in the presence of crude oil. Oils that spread at gas/brine interfaces are known to have severe debilitating effects on foam stability. Another concern is that surfactants may retard oil droplet coalescence and therefore reduce tertiary oil reconnection and mobilization efficiency. 

Spherical beads that can be expanded into foam under the influence of heat or steam are produced directly by suspension polymerization in the presence of blowing agent. The term suspension polymerization describes a process in which water-insoluble monomers are dispersed as liquid droplets with suspension stabilizer and vigorous stirring to produce polymer particles as a dispersed solid phase. Initiators used in suspension polymerization are oil-soluble. The polymerization takes place within the monomer droplets. The kinetic mechanism of the suspension process is considered to be a free radical, water-cooled microbulk polymerization [1]. 

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