The Effect of Ethoxylated Sulfonates on Salt Tolerance and Optimal Salinity of Surfactant Formulations for Tertiary Oil Recovery

The addition of an ethoxylated sulfonate (EOR-200) and its effect on the salt tolerance and optimal salinity of formulations containing a petroleum sulfonate (TRS 10-410 or Petrostep-465) petroleum sulfonate (TRS 10-410 or Petrostep-465) and an alcohol was investigated. When salt concentration increases, the mixed surfactant formulations undergo the following changes: isotropic, birefringent, phase separation. The salt concentration required for phase separation increased with the fraction of the ethoxylated sulfonate in the formulation. When mixed surfactant formulations were equilibrated with an equal volume of oil (decane or hexadecane) a middle-phase microemulsion formed in a specific salinity range. The optimal salinity increased with the fraction of the ethoxylated sulfonate in the mixed surfactant formulations. At optimal salinity as high as 32-percent NaCl, these surfactant formulations exhibited ultra-low interfacial tension (10-2 to 10-3 dynes/cm). These formulations also showed that an increase in the solubilization parameter decreases the interfacial tension. parameter decreases the interfacial tension Introduction The potential use of petroleum sulfonates for tertiary oil recovery has been discussed and several patents have been issued during the past two decades. The solubilization, phase behavior and interfacial tension of petroleum sulfonates have been studied. Petroleum sulfonates are known to exhibit relatively low salt tolerance and a low value of optimal salinity (1- to 2-percent NACl). Dauben and Froning studied the effect of Amoco Wellaid 320 (ethoxylated alcohol) on a surfactant formulation that was primarily a petroleum sulfonate. They observed that surfactant formulations prepared using ethoxylated alcohols as cosurfactants exhibited improved temperature stability and were less sensitive to salts, compared with formulations prepared with isopropanol as a cosurfactant. Several prepared with isopropanol as a cosurfactant. Several patents were issued on the possible use of patents were issued on the possible use of ethoxylated alcohols and ethoxylated sulfonates in oil recovery formulations. This study reports the effect of blending an ethoxylated sulfonate (EOR-200) with a petroleum sulfonate (TRS 10-410 or Petrostep-465) on various properties of the mixed surfactant formulations (for properties of the mixed surfactant formulations (for examples, salt tolerance, optimal salinity, interfacial tension, and solubilization). MATERIALS AND METHODS Petroleum sulfonates TRS 10-410 and Petrostep-465 were supplied by Witco Chemicals and Stepan Petrostep-465 were supplied by Witco Chemicals and Stepan Chemicals, respectively. Ethoxylated sulfonate EOR-200 was supplied by Ethyl Corp. Paraffinic oils (n-hexadecane and n-decane) as well as 99-percent pure isobutanol and n-pentanol were purchased from Chemicals Samples Co. All purchased from Chemicals Samples Co. All surfactants were used as received. The average equivalent weight of TRS 10-410 and Petrostep-465 was 420 and 465, respectively, and the activity of surfactants was approximately 60 percent (as reported by the manufacturers). The molecular weight of EOR-200 was given as 523 by Ethyl and the sample contained 25.3 weight percent active solid surfactant. Aqueous solutions composed of Petrostep-465 (5 percent) and n-pentanol (2 percent) were prepared on the basis of weight. Aqueous surfactant solutions were equilibrated with the same volume of n-decane. Optimal salinity values were obtained using the approach described by Healy and Reed. The effect of EOR-200 on the properties of mixed surfactant formulations was studied by gradually replacing Petrostep-465 with EOR-200 and keeping the total surfactant concentration constant at 5 weight percent. Another surfactant formulation studied was composed of TRS 10-410 (5 percent) and IBA (3 percent). Optimal salinity was determined using percent). Optimal salinity was determined using n-hexadecane. TRS 10-410 was replaced gradually by EOR-200, keeping the total surfactant concentration constant at 5 weight percent. The systems studied are tabulated in Table 1. SPEJ P. 167