Water-hydrocarbon interfacial tension

Water invariably occurs with petroleum deposits. Thus, a knowledge of the properties of this connate, or interstitial, or formation water is important to petroleum engineers. In this chapter, we examine the composition of oilfield water water density, compressibility, formation volume factor and viscosity solubility of hydrocarbons in water and solubility of water in both liquid and gaseous hydrocarbons and, finally, water-hydrocarbon interfacial tension. An unusual process called hydrate formation in which water and natural gas combine to form a solid at temperatures above the freezing point of water is discussed in Chapter 17. 

Using this expression for water—hydrocarbons interfacial tension (y h) die dispersive surface energy component of water may be found. As basic components for hydrocarbons should be zero, the dispersive component is the surface tension of the hydrocarbon. Measuring yu, Yw> and YwH die only unknown is y which turns to be... 

However, Greiner and co-workers [60,80] found fluorinated surfactants of the type H(CF2CF2) CH20(CH2CH20) ,H and their sulfates to lower interfacial tension between hydrocarbons and water and function as effective emulsifiers. The sulfates lowered water-nonane interfacial tension between water and nonane to 5 mN/m. 

Different oils (mainly hydrocarbons or silicone oils) and their mixtures with hydrophobic solid particles are widely used for destruction of undesirable foam. For a long time, the entry, E, spreading, S, and bridging, B, coefficients (which can be calculated from the oil-water, oil-air, and water-air interfacial tensions) were used to evaluate the activity of such oil-based antifoams (AFs). However, recent studies showed that there was no correlation between the magnitudes of E, S, and B and the antifoam activity—the only requirement for having an active AF, in this aspect, is to have positive E and B. Instead, it was shown that the so-called entry barrier, which characterizes the ease of entry of pre-emulsified oil drops in the solution smface, was of crucial importance an easy entry (low entry barrier) corresponded to an active AF and vice versa. We developed a new method, the film trapping technique (FTT), which allows one for the first time to measme directly the critical capillary pressure, P , which induces the entry of micrometer-sized oil drops, identical to those in real AFs. This chapter describes the main results obtained so far by the FTT with various systems. 

IHP) (the Helmholtz condenser formula is used in connection with it), located at the surface of the layer of Stem adsorbed ions, and an outer Helmholtz plane (OHP), located on the plane of centers of the next layer of ions marking the beginning of the diffuse layer. These planes, marked IHP and OHP in Fig. V-3 are merely planes of average electrical property the actual local potentials, if they could be measured, must vary wildly between locations where there is an adsorbed ion and places where only water resides on the surface. For liquid surfaces, discussed in Section V-7C, the interface will not be smooth due to thermal waves (Section IV-3). Sweeney and co-workers applied gradient theory (see Chapter III) to model the electric double layer and interfacial tension of a hydrocarbon-aqueous electrolyte interface [27]. 

Sulfonates for Enhanced Oil Recovery. The use of hydrocarbon sulfonates for reducing the capillary forces in porous media containing cmde oil and water phases was known as far back as 1927—1931 (164,165). Interfacial tensions between 10 and 10 N/m or less were estabUshed as necessary for the mobilization and recovery of cmde oil (166—169). 

These are molecules which contain both hydrophilic and hydrophobic units (usually one or several hydrocarbon chains), such that they love and hate water at the same time. Familiar examples are lipids and alcohols. The effect of amphiphiles on interfaces between water and nonpolar phases can be quite dramatic. For example, tiny additions of good amphiphiles reduce the interfacial tension by several orders of magnitude. Amphiphiles are thus very efficient in promoting the dispersion of organic fluids in water and vice versa. Added in larger amounts, they associate into a variety of structures, filhng the material with internal interfaces which shield the oil molecules—or in the absence of oil the hydrophobic parts of the amphiphiles—from the water [3]. Some of the possible structures are depicted in Fig. 1. A very rich phase... 

Water-in-oil macroemulsions have been proposed as a method for producing viscous drive fluids that can maintain effective mobility control while displacing moderately viscous oils. For example, the use of water-in-oil and oil-in-water macroemulsions have been evaluated as drive fluids to improve oil recovery of viscous oils. Such emulsions have been created by addition of sodium hydroxide to acidic crude oils from Canada and Venezuela. In this study, the emulsions were stabilized by soap films created by saponification of acidic hydrocarbon components in the crude oil by sodium hydroxide. These soap films reduced the oil/water interfacial tension, acting as surfactants to stabilize the water-in-oil emulsion. It is well known, therefore, that the stability of such emulsions substantially depends on the use of sodium hydroxide (i.e., caustic) for producing a soap film to reduce the oil/water interfacial tension. 

Isaacs and Smolek [211 observed that low tensions obtained for an Athabasca bitumen/brine-suIfonate surfactant system were likely associated with the formation of a surfactant-rich film lying between the oil and water, which can be hindered by an increase in temperature. Babu et al. [221 obtained little effect of temperature on interfacial tensions however, values of about 0.02 mN/m were obtained for a light crude (39°API), and were about an order of magnitude lower than those observed for a heavy crude (14°API) with the same aqueous surfactant formulations. For pure hydrocarbon phases and ambient conditions, it is well established that the interfacial tension behavior is dependent on the oleic phase [15.231 In general, interfacial tension values of crude oiI-containing systems are considerably higher than the equivalent values observed with pure hydrocarbons. 

Oligomers of perfluorohexyl-ethene fulfilled these expectations in all preclinical studies, in vitro tests as well in animal tests. A radical polymerisation, followed by ultra-purification steps, created a crystal clear gel-like substance. The behaviours of the mixture of dimeric, trimeric and tetrameric star-shaped species with an inner core of hydrocarbon bonds and an outer layer of perfluoro-alkyl chains could be adjusted by the ratio of the dimeric, trimeric and tetrameric species, using a thin layer distillation. In dependence on this ratio, the viscosity could be adjusted in the range between 90 mPas and 1700 mPas, the specific density between 1.60 g/ml and 1.66 g/ml and the interfacial tension against water between... 

Doe PH, Wade WH, Schechter RS (1977) Alkyl benzene sulfonates for producing low interfacial tensions between hydrocarbons and water. J Colloid Interface Sci 59 525-531... 

During the past few years, the determination of the interfacial properties of binary mixtures of surfactants has been an area in which there has been considerable activity on the part of a number of investigators, both in industry and in academia. The Interest in this area stems from the fact that mixtures of two different types of surfactants often have interfacial properties that are better than those of the individual surfactants by themselves. For example, mixtures of two different surface-active components sometimes reduce the interfacial tension at the hydrocarbon/water interface to values far lower than that obtained with the individual surfactants, and certain mixtures of surfactants are better foaming agents than the individual components. For the purpose of this discussion we define synergism as existing in a system when a given property of the mixture can reach a more desirable value than that attainable by either surface-active component of the mixture by itself. 

EXAMPLE 6.5 Estimation of Interfacial Tensions Using the Girifalco-Good-Fowkes Equation. The following are the interfacial tensions for the various two-phase surfaces formed by n-octane (O), water (W), and mercury (Hg) for n-octane-water, y = 50.8 mJ m 2 for n-octane-mercury, y = 375 mJ m 2 and for water-mercury, y = 426 mJ m 2. Assuming that only London forces operate between molecules of the hydrocarbon, use Equation (100) to estimate y d for water and mercury. Do the values thus obtained make sense Take y values from Table 6.1 for the interfaces with air of these liquids. 

The definition of interfacial tension given in Chapter 8 also applies to water-hydrocarbon systems. 

Interfacial Tension of Water-Hydrocarbon Gas — Interfa-cial Tension of Water-Hydrocarbon Liquid Exercises 467... 

One interfacial tension (upper left) is considered located between water and the polar parts (unfilled circles) of the surfactant (upper right) and one (middle left) between the nonpolar part (filled circles) of the surfactant and the hydrocarbon (middle right). The different convexities of the O/W interface giving normal micelles, a surfactant phase or an inverse micelle are formally referred to different ratios of these interfacial tensions (bottom of figure) at a plane interface. 

Shinoda rationalized the results in terms of a divided total interfacial tension one between the polar parts of the surfactants and the water (yw/p), and one between the hydrocarbon and the nonpolar part of the surfactant (7o/n) similar reasonings have been used by Prince (34, 35) and Robbins (36) (Figure 4). Essentially the theory states that at low temperatures the interfacial tensions at a plane interface... 

To give some sense of the extent to which surfactants can lower surface and interfacial tension, many hydrocarbon surfactants, at high concentrations (above the critical micelle concentration see Section 3.5.3), can lower the surface tension of water at 20 °C from 72.8 mN/m to about 28 mN/m. Polysiloxane surfactants can reduce it further, to about 20 mN/m, and perfluoroalkyl surfactants can reduce it still further, to about 15 mN/m. Similarly, hydrocarbon surfactants can reduce the interfacial tension of water-mineral oil from about 40 down to about 3 mN/m. 

Adsorption can be measured by direct or indirect methods. Direct methods include surface microtome method [46], foam generation method [47] and radio-labelled surfactant adsorption method [48]. These direct methods have several disadvantages. Hence, the amount of surfactant adsorbed per unit area of interface (T) at surface saturation is mostly determined by indirect methods namely surface and interfacial tension measurements along with the application of Gibbs adsorption equations (see Section 2.2.3 and Figure 2.1). Surfactant structure, presence of electrolyte, nature of non-polar liquid and temperature significantly affect the T value. The T values and the area occupied per surfactant molecule at water-air and water-hydrocarbon interfaces for several anionic, cationic, non-ionic and amphoteric surfactants can be found in Chapter 2 of [2]. 

At the liquid-liquid interface between a hydrocarbon oil and water under mixing, the molecules encounter unbalanced attraction forces, pull inwardly, and contract as other molecules leave the interface for the interior of the bulk liquid. As a result, spherical droplets are formed. Customarily, the boundaries between a liquid and gas and between two liquids are the surface and the interface, respectively. The interfacial tension (or interfacial free energy) is defined as the work required to increase the interfacial area of one liquid phase over the other liquid phase isothermally and reversibly. Moving molecules away from the bulk to the surface or interfacial surface requires work (i.e., an increase in free energy). Water molecules and hydrocarbon oil molecules at the interface are attracted to the bulk water phase as a result of water-water interaction forces (i.e., van der Waals dispersion y and hydrogen bonding y ), to the bulk oil phase due to the oil-oil dispersion forces, y 1, and to the oil-water phase by oil-water interactions, y )W (i.e., dispersion forces). As mentioned in Chapter 3, the oil-water dispersion interactions are related to the geometric mean of the water-water and oil-oil dispersion interactions. The interfacial tension is written as ... 

Surfactants increase the apparent solubility of the contaminant in water and thus water becomes more effective in the removal of nonaqueous phase liquids (NAPLS). Surfactants also reduce the interfacial tension between the water and the NAPL, thus NAPL mobility increases. However, cationic surfactants increase the capacity of soil to sorb hydrophobic organic chemicals such as polyaromatic hydrocarbons (PAHs). 

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