Effect of Oil Type on Solubilization by Amphiphiles
- M. Bourrel (Elf-Aquitaine) | F. Verzaro (Elf-Aquitaine) | C. Chambu (Elf-Aquitaine)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- February 1987
- Document Type
- Journal Paper
- 41 - 53
- 1987. Society of Petroleum Engineers
- 5.5.2 Core Analysis, 5.3.2 Multiphase Flow, 4.1.2 Separation and Treating, 4.6.3 Gas to liquids, 5.2.1 Phase Behavior and PVT Measurements, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 4.1.5 Processing Equipment, 5.7.2 Recovery Factors, 2.5.2 Fracturing Materials (Fluids, Proppant)
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Summary. Systems optimized for micellar flooding are not all equivalent in terms of solubilization, interfacial tensions (IFT's), and oil recovery efficiency. The basic conditions that promote high solubilization into microemulsions, a property correlated to the values of IFT'S, were established in a previous paper. Changes in oil type, for example, have to be compensated for by adjustment of the lipophile of the surfactant; however, this is not always sufficient to guarantee a high solubilization.
The purpose of this paper is to investigate the influence on solubilization of the relationship between the oil type to be solubilized and the surfactant lipophile. We found that this relationship is a determining factor for solubilization at a given temperature and salinity. For example, we observed that for the alkane series, solubilization is not affected by the alkane carbon number (ACN), provided that the compensation be achieved by adjustment of the surfactant lipophile length. For other oils or mixture of oils, like crudes, however, this is not necessarily the case; the solubilization may be found to be more or less different from that of alkanes, depending on the structure of the surfactant lipophile.
A particularly interesting case of oil mixtures is mixtures of hydrocarbons and methane (under pressure), because this gas is often dissolved in substantial amounts in live crudes. The incidence of the presence of methane is shown to be a function of the amount of gas presence of methane is shown to be a function of the amount of gas dissolved and of the nature of the dissolving hydrocarbon. An interpretation of the results is proposed, based on the oil/lipophile, oil/oil, and lipophile/lipophile interaction energies, which are involved in Winsor's R-theory.
The design of the micellar or microemulsion slug for surfactant flooding requires careful attention to attain the low IFT's essential for mobilizing the residual oil trapped in the reservoir. Ultralow IFT's have been shown to occur when a surfactant-rich phase-called middle phase-is in equilibrium with both excess oil and water phases. 2 The IFT values were found to correlate to the amount of oil and water solubilized in the middle phase: the higher the solubilization, the lower the tensions. It is then convenient to compare various systems through their solubilizing power. For meaning comparison, however, a reference state has to be chosen, generally the three-phase system in the middle phase of which equal volumes of oil and water have been solubilized. Such systems are commonly said to be "at optimum" and can be obtained by scanning any formulation variable.
Comparison of optimized systems through their solubilizing power will reveal that they are not all equivalent. This raises the problem of finding the best surfactants from the solubilization and IFT standpoints. A corollary question is whether a meaningful comparison of surfactants, though taken at optimum, can be achieved, whatever the composition of the system. This question has been addressed in a previous paper, which showed that a key factor was the level of the interaction energies of the surfactant with oil and water. At optimum, the compensation for the change in a formulation variable that has affected one side of the water/oil interface (where the surfactant is adsorbed) has to be carried out on the same side so as not to decrease the solubilization. For example, a shortening of the surfactant tail compensated for by an increase in salinity entails a decrease in solubilization. In the same way, an augmentation in the hydrophobicity of the oil-e.g., through its ACN-decreases the solubilization if the compensation is achieved through an increase in salinity. On the other hand, a variation of normal ACN can be compensated for by adjustment of the surfactant tail length at constant salinity without serious damage to solubilization.
Regarding the effect of oil on solubilization, however, some difficulties have appeared in some cases when hydrocarbons different from the normal alkane series were used, even though the compensation had been carried out through the surfactant tail length. The purpose of this paper is to investigate in detail the relationship between paper is to investigate in detail the relationship between the surfactant lipophile and the oil to be solubilized.
The results obtained when the oil change is compensated for by adjustment of the surfactant tail length will be presented first. Compensation by changing the surfactant hydrophile will be discussed next.
Oils of various natures and molecular weights will be used, as well as mixtures. The effect of the presence of dissolved methane in the oil will be seen as an interesting particular case of mixture.
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