Interfacial tension heavy oils

C. I. Chiwetelu, V. Homof, G. H. Neale, and A. E. George. Use of mixed surfactants to improve the transient interfacial tension behaviour of heavy oil/alkaline systems. Can J Chem Eng, 72(3) 534-540, June 1994. 

Interfacial Tension of Heavy Oil—Aqueous Systems at Elevated Temperatures... 

Oil/water interfacial tensions were measured for a number of heavy crude oils at temperatures up to 200°C using the spinning drop technique. The influences of spinning rate, surfactant type and concentration, NaCI and CaCI2 concentrations, and temperature were studied. The heavy oil type and pH (in the presence of surfactant) had little effect on interfacial tensions. Instead, interfacial tensions depended strongly on the surfactant type, temperature, and NaCI and CaCL concentrations. Low interfacial tensions (<0.1 mN/m) were difficult to achieve at elevated temperatures. 

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. 

Densities were measured using a Paar DMA 60 meter equipped with DMA 512 and DMA 601 HP external cells. Values in the 50-150°C range were interpolated from measured data (3-5 points) values above 150°C were extrapolated and are less accurate. Interfacial tension measurements at the minimum density difference encountered (0.05 g/cm3) could be in error by as much as 10%, which is within the repeatability of measurements with heavy crude oil samples (see below). 

Figure 4 Effect of temperature on the interfacial tension of an Alberta heavy oil in produced water containing LTS-18 surfactant. Data are from three separate replicate experiments conducted under the same conditions.

In n-octane/aqueous systems at 27°C, TRS 10-80 has been shown to form a surfactant-rich third phase, or a thin film of liquid crystals (see Figure 1), with a sharp interfacial tension minimum of about 5x10 mN/m at 15 g/L NaCI concentration f131. Similarly, in this study the bitumen/aqueous tension behavior of TRS 10-80 and Sun Tech IV appeared not to be related to monolayer coverage at the interface (as in the case of Enordet C16 18) but rather was indicative of a surfactant-rich third phase between oil and water. The higher values for minimum interfacial tension observed for a heavy oil compared to a pure n-alkane were probably due to natural surfactants in the crude oil which somewhat hindered the formation of the surfactant-rich phase. This hypothesis needs to be tested, but the effect is not unlike that of the addition of SDS (which does not form liquid crystals) in partially solubilizing the third phase formed by TRS 10-80 or Aerosol OT at the alkane/brine interface Til.121. 

Effect of Temperature. In the absence of surfactant, interfacial tensions of the Athabasca 1 211. Karamay 1 51, and other heavy oils 1 321 show little or no dependence on temperature. For surfactant-containing systems, Figure 6 shows an example of the effect of temperature (50-200°C) on interfacial tensions for the Athabasca, Clearwater and Peace River bitumens in Sun Tech IV solutions containing 0 and 10 g/L NaCI. The interfacial tension behavior for the three bitumens was very similar. At a given temperature, the presence of brine caused a reduction in interfacial tension by one to two orders of magnitude. The tensions were seen to increase substantially with temperature. For the case of no added NaCI, the values approached those observed T211 in the absence of surfactant. 

Effect of pH. Interfacial tensions between heavy crude oils and alkaline solutions were measured at temperatures up to 180°C by Mehdizadeh and Handy T341. They observed that tensions increased with an increase in temperature. However, recovery efficiencies obtained at high temperatures were comparable to those obtained at lower temperatures, apparently because the ease of emulsification at high temperatures counteracted the increase in tens i on. 

For results where comparisons could be made, the interfacial tension behavior was practically independent of the type of heavy oil used. Interfacial tensions strongly depended on the surfactant type, temperature, and NaCI and CaCI2 concentrations. Changes in the structure of the amphiphile at the oil/water interface is affected by these variables and accounted for some of the experimental observations. 

Assuming a typical oil reservoir containing medium heavy crude oil and employing a reservoir flow rate of 0.26 m/day. The solution viscosity could be increased to 30 mPa s by adding about 1000 pg/rril (0.1%) partially hydrolyzed polyacrylamide polymer (at pH 8.5). The interfacial tension could be reduced to 0.1 mN/m by adding 1% sodium carbonate, which reacts with the crude oil to produce natural surfactant. The interfacial tension could be further reduced to 0.03 mN/m by adding 0.1% ethoxylated alcohol sulfate cosurfactant. 

FIGURE 12.8 Interfacial tensions of heavy oil/brine as a function of Na2C03 concentration at (different measurement times. Source Liu et al (2006b),... 

Song, J.-R, 1993. A study of the interfacial tension between a heavy oil and an alkaline solution with or without polymer. Petroleum Exploration and Development 20 (4), 81-86. 

In this paper we report first the spontaneous emulsification mechanisms in the petroleum sulfonate and caustic systems. This is followed by the kinetics of coalescence in alkaline systems for both the Thums Long Beach (heavy) crude oil and the Huntington Beach (less viscous) crude oil. Measurements of interfacial viscosity, interfacial tension, interfacial charge and micellar aggregate distributions are presented. Interrelationships between these properties and coalescence rates have been established. 

Interfacial Tension Behavior. Reduction in the residual oil saturation over and above that obtained by steam injection is desirable and, in many heavy oil reservoirs, essential to ensure efficient foam formation during application of steam-foam processes (13). The extent of heavy oil desaturation is, however, dependent on the reduction in interfacial tension between oil and water. Thus, foam-forming surfactants can improve their own cause by reducing interfacial tensions at steam temperature. 

Several micellar-polymer flooding models as applied to the EOR are discussed in [237]. It is noted that the co-solvent ordinarily used in this process considerably influences not only the microemulsion stabilisation, but also the removal of impurities in the pores of the medium. The idea of using an alkali in micellar-polymer flooding is discussed in [238] in detail. The alkali effect on the main oil components was studied aromatic hydrocarbons, saturated and unsaturated compounds, light and heavy resin compounds and asphaltenes. It is demonstrated that at pH 12 surfactants formed from resins allow to achieve an interfacial tension value close to zero. For asphaltenes, such results are achieved at pH 14. In the system alkali solution (concentration between 1300 to 9000 ppm)/crude oil at 1 1 volume ratio a zone of spontaneous emulsification appears, which is only possible at ultra-low interfacial tensions. 

Metallic sulfonates, such as sodium sulfonate, are often used as emulsifiers in both water-in-oil and oil-in-water emulsions. Other emulsifiers used include ethylene oxide condensation products and derivatives of polyhydroxy alcohols such as sorbitol and sulfosuccinates for water-in-oil emulsions. For oil-in-water emulsions, soaps of fatty acids, rosins, or naphthenic acids are often used as emulsifiers. In either application, the role of emulsifiers is to change the interfacial tension at the water and oil interface. In cases where emulsification with water is undesirable, demulsifiers are used. Frequently, the demulsifiers are heavy metal soaps, such as alkaline earth sulfonates. These surfactants function by lowering emulsion stability. 

Iranian Heavy crude oil/distilled water interfaces were aged for set intervals on the dilatational modulus apparatus. The interfacial length was initially set as 13.5 cm and amplitudes of area oscillation of 0.5 cm were used. The Wilhelmy plate (platinum, hydrophobic) was always aligned parallel to the oscillating barrier. The X-Y recorder was used to produce Lissajou figures of interfacial tension-interfacial Wilhelmy... 

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