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.

et al. "Nail" and "comb" eff ects of cholesterol modifi ed NIPAm oligomers on cancer targeting liposomes

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This article reports on a novel simple method for transforming the high-salinity-incompatible petroleum sulfonates into a persistently stable oil-swollen micelles, referred to here as nanosurfactant. We present and discuss the effect of three different nanosurfactant formulations on the interfacial tension (IFT) between high-salinity water and crude oil, their phase behavior, and the effect of their dilution on IFT to assess their ability to reduce mobilize oil after injection into high-salinity and temperature reservoirs. The three nanosurfactant formulations were prepared in high-salinity water following a direct-mixing procedure in which solutions in fresh water of 5 wt% petroleum sulfonate in mineral oil and three 4 wt% zwitterionic co-surfactants were mixed with high-salinity water at room temperature to give a combined concentration of all active ingredients of 0.2 wt%. The IFT between crude oil and different nanosurfactant formulations was measured using a spinning drop interfacial tensiometer at 90°C. IFT was measured every 5 minutes while the oil drop was spinning at ~4000 rpm. The phase behavior was investigated by monitoring the turbidity and UV absorbance changes in a system of crude oil atop of the nanosurfactant formulation over time at 100°C without any mechanical mixing. The particle size of the three nanosurfactant formulations is in the range of 40 to 80 nm, depending on the co-surfactant used. All formulations were persistently stable, colloidally, and chemically under high-salinity (~56,000 ppm) and temperature (100°C) for more than four months. All formulations showed substantial reduction in IFT with crude oil compared to high-salinity water alone. Dilution with high-salinity water up to five times further reduced the IFT, suggesting improved performance after injection into the reservoir. This behavior was consistent with the observed gradual decrease in surface tension of the nanosurfactant formulation as its concentration decreases toward the CMC value. Phase behavior experiments showed enhanced formation of homogeneous micelles at 100°C without the aid of any mixing. Our results demonstrate the ability of nanosurfactants to solubilize oil under typical carbonate reservoir conditions. Their colloidal nature allows them to migrate deeper in the reservoir compared to conventional surfactants due to size exclusion and chromatographic effects. Nanosurfactants are novel oil-swollen micelles of the inexpensive and abundant petroleum sulfonate salts that are efficient in reducing IFT under typical carbonate reservoir conditions. The formulation method can be extended to other surfactants and chemical treatments that are incompatible with high-salinity water at high temperatures. Their nanoparticle character and colloidal behavior suggest their ability to migrate and penetrate deep in the reservoir. Nanosurfactants can therefore help overcome some of the most critical drawbacks in conventional chemical EOR technologies.

The oil mobilization in tertiary mode using chemicals has been shown to be a promising approach. In such technique, surfactants with or without polymers, designed for specific reservoir conditions, are added into water during water flooding to further drive remaining oil out of the porous structure of the reservoir rock into production wells. The success of the method depends on the cost of the chemicals used and the amount of the additional incremental oil mobilization achieved beyond water flooding. Thus, utilizing reservoir-compatible and inexpensive surfactants is a key. Petroleum sulfonates are some of the most abundant and inexpensive surfactants that can be made available at the scale required for efficient oil mobilization operations. However, petroleum sulfonates lack solubility in harsh reservoir conditions which makes them rather inapplicable for reservoirs with high salt content (e.g. > 50,000 ppm) and high temperature (e.g. 100 °C). We have successfully developed a simple, one-step nano-encapsulation technique to transform petroleum sulfonates into nano-sized multi-emulsion droplets in high salinity injection water featuring long-term stability at high temperatures. To further improve the economics and sustainability of such NanoSurfactants (NS), we developed a continuous and cost-effective synthesis process of petroleum sulfonates, directly from crude oil. The in-house-produced sulfonates were then formulated into a NS solution in high salinity injection water utilizing our encapsulation method. Results showed that petroleum sulfonates were successfully synthesized as seen from NMR analysis. The formulated NS was persistently stable at reservoir conditions, altered the wettability of the oil-wet rock as verified by contact angle measurements, and triggered crude oil release from the rock by spontaneous imbibition. This work provides a solution to produce petroleum sulfonates and formulate NS on-site for use in cost-efficient oil mobilization operations in high salinity and high temperature reservoirs.