Asphaltene Inhibitor Preparation via Simultaneous Synthesis and Coating of Fe3O4 Nanoparticles: Performance Evaluation by a Dispersant Test and Interfacial Rheology Analysis

During oil production, asphaltene nanoaggregates self-associate and can precipitate out from the oil phase, especially light crudes, followed by deposition on rock, tubing, and surface facilities. Metal oxide nanoparticles can provide highly dense surface groups with a high tendency for strong interactions with asphaltene. Therefore, the coating of the nanoparticles by carbon-containing chains with appropriate functional groups can provide a nanostructured asphaltene inhibitor. The inhibitor-asphaltene interactions control the adsorption tendency of the asphaltene-inhibitor complexes to the oil–water interface, thus affecting both the dynamics of adsorption and the equilibrium interfacial tension (IFT). In this work, simultaneous synthesis and coating of iron oxide nanoparticles by oleic acid were done via an interface-assisted phase-transfer method. The crystalline structure and particle size of the nanoparticles as well as the coating level considering the oleic acid-nanoparticle interactions were characterized well. A conventional asphaltene dispersant test (ADT) on a crude oil sample was performed to assess the inhibitor-asphaltene interactions and thus stability. It is found that even a small dose (250–1000 ppm) of the as-synthesized Fe3O4 nanoparticles (average size 5.7 nm), coated mostly with chemisorbed oleate groups, can stabilize the asphaltene even under the harsh conditions of the ADT tests. In addition, for the treated oil–water interface, an increase in the equilibrium IFT with the inhibitor dosage as well as variations in the dynamic IFT during the interfacial area extension/contraction are introduced as a new approach for a better understanding of the stabilization mechanism and evaluation of the performance of the synthesized inhibitor. The IFT measurements along with interfacial elasticity analysis illustrate the level of self-association and linkage of the asphaltene, which is an important indicator of the precipitation process. Therefore, IFT and interfacial elasticity analysis can provide quantitative information about the optimum inhibitor dosage with a descriptive mechanism as a novel complementary method to the conventional ADT test.