Nanofluids in recent years have shown great potential as a chemical enhanced oil recovery (EOR) technology, thanks to their excellent performance in altering interfacial properties. However, because of the great challenge in preparing stable systems suitable for an elevated temperature and a high salinity environment, expanding the application of nanofluids has been greatly restrained. In this work, a novel nanofluid was prepared by integrating positively charged amino-terminated silica nanoparticles (SiNP-NH 2 ) with negatively charged anionic surfactant (Soloterra 964) via electrostatic force. The resulted nanofluid could be stored at relatively high salinity (15 wt % NaCl solution) and high temperature (65 °C) for more than 30 days without aggregation. Successful coating of the surfactant on target SiNPs was verified by Fourier transform infrared spectrometry and the surface charge and size distribution. In addition, the potential of the nanofluid in recovering oil was investigated by analyzing the nanofluid/Bakken oil interfacial tension and the variation trend of the oil contact angle when brine was replaced by nanofluids. Experimental results showed that the water−oil interfacial tension of the Bakken crude oil decreased by 99.85% and the contact angle increased by 237.8% compared to the original value of 13.78 mN/m and 43.4°, respectively, indicating strong oil displacement efficiency and obvious wetting transition from oil-wet toward water-wet. Spontaneous imbibition tests conducted on Berea rocks showed that the nanofluid yielded a high oil recovery rate of 46.61%, compared to that of 11.30, 16.58, and 22.89% for brine, pure SiNP-NH 2 , and pure surfactant (Soloterra 964), respectively. In addition, when core flooding was applied, a total of 60.88% of the original oil in place could be recovered and an additional oil recovery of 17.23% was achieved in the chemical flooding stage. Moreover, a possible mechanism of the EOR using the nanofluid was proposed. Overall, the developed nanofluid is a promising new material for EOR.

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Nonionic surfactants are nonvolatile and benign chemicals widely used in the oil and gas industry. However, their huge loss especially under high temperature and high salinity conditions has limited their large-scale applications; thus, various additives were introduced to prepare compounded systems. This paper mainly focuses on nonionic surfactant−silica nanoparticle augmented systems. Herein, an extensive series of adsorption tests related to the adsorption of surfactant on nanoparticles and surfactant adsorption behavior change with the presence of nanoparticles was conducted, together with their combined effects on interfacial properties and their potentials in boosting oil production, trying to systematically evaluate their synergistic interactions and reveal the underlying functional mechanisms. Experimental results showed that surfactant adsorption was generally reduced with the addition of nanoparticles, and the efficiency largely depended on the adsorbents and nanoparticle size. In addition, the properties of nanofluids differ at varying surfactant/nanoparticle concentration ratios because of diverse surfactant adsorption structures, and smaller particles turned out to be better surfactant carriers. In the spontaneous imbibition tests, positive cooperative effects by integrating nanoparticles with surfactant were highlighted, where the nanoparticles efficiently improved the surfactant performance and a considerable amount of additional oil was recovered. Acknowledging the interactions and combined effects of nonionic surfactants and hydrophilic silica nanoparticles may shed light on the development and improvement of potential nanofluids for industrial practices.

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The production of sands in oil well production has long been a crucial and thorny issue, but many related technologies are either costly or ineffective. This study introduced a new aggregating reagent, pentaerythritol phosphate melamine salt (PPMS for short), for controlling this problem. PPMS was the reaction product of pentaerythritol, phosphoric acid, and melamine, and there was an amine and a phosphate ester (both are positively charged) in its chemical structure. It could effectively change the ζ potentials of solid particles and help them aggregate through hydrogen bonds and electrostatic interactions, thereby aggregated particles could settle down at the bottom of the pore holes without severe formation permeability damage, which plays a remarkable role in eliminating the co-production of formation particles with oil. PPMS exhibited an excellent performance when the concentration was 0.8 wt % under 60 °C at a neutral environment, at which PPMS (positively charged) not only can highly condense the double layer electric field but also can better react with clay particles (negatively charged) through adsorption and charge neutralization; thus the negative charge of clay surface could decrease to the minimum (almost 0 mV). At the same time, PPMS might have the potential to enhance oil recovery.