Ethoxylated Oleyl Sulfonates as Model Compounds for Enhanced Oil Recovery

Precisely ethoxylated oleyl sulfonates were prepared and Precisely ethoxylated oleyl sulfonates were prepared and studied as model surfactant candidates for EOR. They were found to yield low interfacial tensions (IFT's), to give high solubilization parameters, and to have high electrolyte tolerance. Unfortunately, as a class of compounds they have a tendency to form liquid crystals (rather than microemulsions), which must be overcome by adding cosolvents, elevating temperatures, or restricting the maximally ethoxylated species. Introduction The indispensable primary requirement for any surfactant to be considered as a possible candidate in EOR processes is its ability to form systems with ultra low IFT's processes is its ability to form systems with ultra low IFT's between immiscible phases. To this requirement others must be added: minimal alcohol concentrations, good electrolyte tolerance (especially including multivalent cations such as Ca + + and Mg + +), and maximal values of solubilization parameters. Many ethoxylated species that satisfy the required tolerance to electrolyte have been studied in this laboratory; however, the species investigated have not given IFT's or solubilization parameters of as good quality as those found for many sulfonates. The commercially available species similar to the ones reported here have several disadvantages:(1)they exist only as sulfates, and these species hydrolyze at elevated temperatures;(2)there is a Gaussian distribution of ethylene oxide numbers (EON), which causes partitioning complications; and(3)there is less than perfect partitioning complications; and(3)there is less than perfect knowledge of the structure of the hydrophobic tail. The purpose of this study is to remove these three purpose of this study is to remove these three complications through the use of a monoisomeric ethoxylated sulfonate species, in particular 1-oleyl sulfonate with 1, 2, or 3 moles of ethylene oxide (EO) added between the oleyl and sulfonate groups. The species were chosen for two additional reasons. First, earlier results on alkylbenzene sulfonates indicated that straight-tailed hydrophobes maximized the solubilization parameter, and second, there is little information available on the effect of the benzene rings in the molecule on its EOR properties. In our paper a shorthand notation will be used properties. In our paper a shorthand notation will be used for the structure C8H17-CH=CH-C8H 16-(OCH2CH2), SO3Na, where n = 1, 2, 3. The molecules will simply be referred to as n=l, n=2, n=3. Experimental Procedure The synthesis of the surfactant species is described elsewhere, but a brief description is given in the appendix. The various alkanes (pure grade from Phillips Petroleum Co.), singly distilled water, NaCl (Baker's Petroleum Co.), singly distilled water, NaCl (Baker's CP), and alcohol cosolvents (sec-butanol [SB] and isopentanol [IP]), were Baker's pure grade. Surfactant formulations were equilibrated in sealed 5-cm [5-mL] disposable pipettes. The surfactant concentration in all studies was pipettes. The surfactant concentration in all studies was 0.025 M and the SB concentration usually Was held constant. The tubes were equilibrated daily by shaking; after the third day, the various phase volumes were found to no longer change with time. All the solubilization parameters reported here are for optimal systems (equal water and oil solubilized) and were calculated assuming that all the surfactant, but none of the alcohol, was in the middle phase. Furthermore, in this study the concentrations of phase. Furthermore, in this study the concentrations of surfactant, NaCl, CaC12, and alcohol are based on the initial aqueous-phase volume, and the WOR was always one. As found earlier, optimal formulations had minimal phase equilibrium times; this often was used to identify such systems preliminarily. Results and Discussion Effect of Temperature on Phase Behavior. Two standard methods previously have been used to examine the effect of temperature on phase behavior:studying its effect on optimal salinity andstudying its effect on optimal alkane carbon number (ACN). We have chosen to do the latter. The alcohol concentration chosen for this study was sufficiently high to destroy any liquid crystal or surfactant aggregations over the entire ACN/ temperature range studied. SPEJ P. 351