Petroleum sulfonate (PS) salt surfactants that are insoluble in high-salinity water were encapsulated into 10–60 nm oil swollen micelles dispersed by a cocamidopropyl hydroxysultaine zwitterionic cosurfactant to form a highly stable nanofluid at elevated salinity (∼56 000 mg/L) and temperature (∼100 °C). The resulting “Nano-Surfactant (NS)” fluid enables an economic, efficient, and environmentally friendly enhanced oil recovery (EOR) capable of targeted delivery of PS salt surfactantsone of the most abundant and inexpensive industrial surfactants, yet cannot be used in most EOR operations because of its insolubility in high-salinity waterto residual oil without the need of massive amounts of surfactants. The NS formulations presented here can be easily prepared in the field by a simple one-pot, one-step procedure at ambient temperatures and with a minimal energy input. This article reports the preparation method of the NS and results, demonstrating their long-term colloidal and chemical stability at 100 °C, reduction of crude oil–high-salinity water interfacial tension (IFT) by 3 orders of magnitude (from ∼10 to 0.008 mN/m), and improved mobilization of the trapped crude oil from the carbonate rock. Results point out the potential of NS formulations in enhancing oil mobilization under a variety of reservoir conditions. The NS platform described here can be utilized to encapsulate and deliver a variety of other chemical treatments, not only in oil recovery applications but also in others such as remediation of nonaqueous phase liquid-contaminated groundwater aquifers, well-drilling operations, and wellbore stimulation.

This paper describes a nanoparticle-based approach for stabilizing the low-cost petroleum sulfonate surfactants in high salinity and temperature water to enable their utility in EOR applications in typical carbonate reservoirs. The paper presents and discusses experimental results on the phase behavior of three of such NanoSurfactant formulations and their interfacial tensions (IFT) with crude oil, in order to evaluate their ability to mobilize oil during EOR operations. The three NanoSurfactant formulations were prepared through a one-step nano-emulsification process involving high salinity water, 5 wt% petroleum sulfonate solution and a low-dose of three different 4 wt% co-surfactant solutions. The resulting formulations had a 0.2 wt% of total active ingredients. One of the three formulations was persistently stable, colloidally and chemically, in high salinity water (~ 56,000 ppm) at high temperature (100 °C) for more than six months, while the other two showed signs of instability after about four months. Interfacial tensions between crude oil and NanoSurfactant solutions, measured using a spinning drop interfacial tensiometer at 90 °C, was in the 10−2 to 10−3 mN/m range and substantially lower than that with high salinity water alone or solutions of corresponding co-surfactants of similar concentrations. Phase behavior, investigated by monitoring the clarity and UV absorbance changes in a system of crude oil atop of the NanoSurfactant formulation at 100 °C without mechanical mixing, showed enhanced formation of homogeneous oil-in-water emulsions at 100 °C without the aid of any mixing. Our results demonstrate the ability of NanoSurfactants to mobilize oil under typical carbonate reservoir conditions. Their colloidal nature gives them advantages over conventional micellar surfactants by allowing them to migrate deeper in the reservoir due to size exclusion and chromatographic effects. The simple method utilized in making NanoSurfactants opens the door for better utilization of numerous low-cost, yet salinity- and temperature-intolerant chemicals in typical carbonate oil reservoir applications.

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A new class of surfactants for enhanced oil recovery (EOR) applications has been developed in the form of petroleum sulfonate salt nanoparticle dispersions in seawater. These NanoSuractants (NS) are 10- to 60-nm particles of the seawater-insoluble petroleum sulfonate salts, one of the most abundant and inexpensive industrial surfactants, that are resiliently stable in seawater at elevated temperatures via a special class of co-surfactants. They can be easily prepared in the field by mixing with seawater at ambient temperature and injected into the reservoir with seawater without any additional infrastructure. The colloidal nature and extremely small size of the NanoSurfactans particles allow them to migrate and deliver petroleum sulfonates to remaining and residual oil deep in the reservoir without the need of large quantities in order to compensate for losses by adsorption onto the rock surfaces and diffusion into water-filled small pores. This paper reports on the results of few tests conducted to evaluate the performance of NanoSurfactant formulations under reservoir conditions. Results showed consistent colloidal and chemical stability of the NanoSurfactant formulations for over six months at 100°C. They reduced the seawater-crude oil interfacial tension (IFT) by two to three orders of magnitude or formed oil-in-water emulsions at 100 °C without any mechanical mixing. Transmission electron miscroscopy (TEM) images revealed mostly round particle in the submicron range (10- to 60-nm). Finally, core-flood test at reservoir conditions using bottom-hole live oil samples indicated an additional oil recovery of about 7% of OOIP beyond several pore-volumes flooding with seawater by injecting 0.4 pore-volume of the NanoSurfactant at 0.2 wt% concentration.

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