ORIGINAL ARTICLE Experimental Study of Nanofluids Applied in EOR Processes Tereza Neuma de Castro Dantas 1 • Tamyris Thaise Costa de Souza 1 • Afonso Avelino Dantas Neto 1 • Maria Carlenise Paiva de Alencar Moura 1,2 • Eduardo Lins de Barros Neto 1 Received: 21 December 2016 / Accepted: 18 June 2017 Ó AOCS 2017 Abstract Nanoemulsions are small droplet-sized systems that have low surface tension and a small percentage of active material in their composition. In this study, low oil content nanoemulsion systems were developed for the use in enhanced oil recovery (EOR). The experiments were performed on a device capable of simulating petroleum reservoir conditions using sandstone rock cores. Nanoemulsions were obtained from a pre-selected microemulsion system composed of: RNX95 as surfactant, isopropyl alcohol as cosurfactant, kerosene as oil phase, and distilled water as aqueous phase. Different percentages of polyacrylamide were added to the systems obtained to evaluate the influence of viscosity in EOR results. The nanoemulsion droplet sizes ranged from 9.22 to 14.8 nm. Surface tension values were in the range of 33.6–39.7 dyn/ cm. A nanoemulsion system with 2.5 wt% surfactant was used in EOR assays. The oil recovery was directly pro- portional to polymer percentage in the nanoemulsion, ranging from 39.6 to 76.8%. The total oil in the place recovery ranged from 74.5 to 90%. Keywords Surfactant applications Á Non-ionic surfactants Á Interfacial science Á Surface activity Introduction Enhanced oil recovery (EOR), or tertiary oil recovery, is a method used to recover additional oil remaining in reser- voirs after primary and secondary recovery processes [1]. In the EOR technique, different types of surfactants alter interfacial properties and foam behaviors [2]. Polymers are also used in EOR to improve the water/oil mobility ratio by increasing the viscosity of the displacing fluid (water) [3]. The application of surfactant solutions and microemul- sions in EOR methods leads to increased oil recoveries [4–6]. The addition of polymer to these surfactant systems can create a very stable displacement front, increasing sweep efficiency. The use of surface active agents enhances oil recovery due to the following mechanisms: (1) production of very low interfacial tension ( \ 10 -3 mN/m) between oil and flooding solution; (2) spontaneous emulsification or microemulsification of the trapped oil; (3) alternation of the interfacial rheological properties at the oil–flooding solution interface; and (4) control of the wettability of the rock pores, optimizing oil displacement [7]. The microemulsion systems generally use high amounts of surfactants for this kind of application. However, the use of nanoemulsion systems presents an alternative for this application. Nanoemulsions, also referred to as miniemulsions or submicrometer emulsions, are transparent or translucent colloidal systems, with very small droplet size [8, 9]. Nanoemulsion droplets are kinetically stable against sedi- mentation or creaming. There are significant differences between nanoemulsions and microemulsions. The former are thermodynamically unstable systems and usually require energy input for their formation while the latter are thermodynamically stable and form spontaneously. The main advantage of nanoemulsions over microemulsions is & Tereza Neuma de Castro Dantas terezaneuma1011@yahoo.com.br 1 Department of Chemical Engineering, Federal University of Rio Grande do Norte, University Campus, Lagoa Nova, Natal, RN 59072-970, Brazil 2 Post-Graduate Program in Petroleum and Gas Engineering, Potiguar University, Natal, RN, Brazil 123 J Surfact Deterg DOI 10.1007/s11743-017-1992-2