Asphaltene precipitation is usually responsible for many flow assurance problems such as wettability changes and pore clogging in reservoirs, fouling in wellbore tubings and production surface facilities. This study develops a novel approach by using nanoemulsions (NE) for controlled delivery and release of asphaltene inhibitors (AI) to minimize asphaltene precipitation with reduced AI amount. LUMiSizer was utilised to study the effectiveness and performance of controlled release by three cases on asphaltene sedimentation: i) strong organic acids (dodecyl benzene sulfonic acid, DBSA), ii) nanoemulsions (blank NEs), and iii) nanoemulsions loaded with DBSA (DBSA NEs). The experiments suggested that the optimum inhibitor concentration for completely stabilizing asphaltene were 4 vol. % for DBSA. This amount of inhibitor can be significantly reduced by ~ 20 times by using the DBSA NEs, and the release time can be greatly extended. A mechanistic understanding of the controlled release effect is proposed based on interfacial properties and electron microscopic studies, which is related to the hydrophilicity of DBSA and the strong intermolecular interactions among all DBSA NE's components and the asphaltene molecules.

The decrease of aromaticity and the reduction in the aliphatic side chains of asphaltene are responsible for increased asphaltene stability.

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Nanoparticle-assisted enhanced oil recovery (Nano-EOR) has attracted intensive interest in the laboratory as a promising oil recovery technology. However, the nanoparticles’ stability and long-distance delivery of nanoparticles (NPs) in large-scale reservoirs are two main challenges. In this work, we developed a novel concept of in situ synthesizing NPs at the oil–water interface inside the reservoir for EOR instead of injecting presynthesized NPs from outside. The pore-scale flooding experiments show that EOR efficiencies for tertiary flooding were 6.3% without reaction (Case 3), 14.6% for slow reaction (Case 1), and 25.4% for relatively quick reaction (Case 4). Examination of the EOR mechanism shows that in situ produced SiO2 NPs in microchannels could alter the substrate wettability toward neutral wetting. Moreover, the produced NPs tended to assemble on the immiscible oil–water interface, forming a barrier toward interface deformation. As the reaction continued, excessive surface-modified NPs could also diffuse into aqueous brine and accumulate as a soft gel in the flowing path swept by brine. Collectively, these processes induced a “shut-off” effect and diverted displacing fluids to unswept areas, which consequently increased the sweep efficiency and improved the oil recovery efficiency. Auxiliary bulk-scale experiments also showed that the reaction-induced nanoparticle synthesis and assembly at an immiscible interface reduced the interfacial tension and generated an elastic oil–water interface.

The asphaltene aggregation and subsequent precipitation in nonpolar media may have a profound effect on plugging wellbores and production equipment. Continuing our work on controlled release of asphaltene inhibitor by using nanoemulsions (NEs), this work provides new evidence from optical measurement and reveals the release mechanisms kinetically. Multiple light scattering (Turbiscan) and dynamic light scattering (DLS) have been used to study "in situ" the effectiveness and performance of controlled release by three cases on asphaltene aggregation/precipitation: i) strong organic acids (dodecyl benzene sulfonic acid, DBSA), ii) nanoemulsions (blank NEs), and iii) nanoemulsions loaded with DBSA (DBSA NEs). The results suggested that the new approach reduced the amount of asphaltene inhibitor by ~ 20 times and achieved high asphaltene inhibition efficiency ~84 % with prolonged release time. A mechanistic understanding of the controlled release effect was proposed based the effect of DBSA NEs on the asphaltene particle morphology variation, which was related to the