Coated Iron Oxide Nanoparticles as Asphaltene Inhibitors for Pore Plugging Control during Miscible Displacement in Microfluidic Glass Porous Media: A Pore-Level Study

Asphaltene deposition in petroleum reservoirs leads to severe damage. To address this issue, an asphaltene inhibitor was synthesized by grafting oleate groups onto Fe3O4 nanoparticles. Pore-level observations of the inhibitor performance were made during miscible displacement of a model oil and a dead oil sample by n-hexane in glass porous media monitored by a high-resolution camera. The pore/throat size and geometry of the porous medium as well as the n-C6 injection rate were adjusted to have different patterns of asphaltene deposition. The optimum dose of the inhibitor was determined by a conventional asphaltene dispersant test (ADT). The particle size, structural properties, and coating level of the grafting ligands of the nanoparticles were well-characterized. The coating of mostly chemisorbed oleate groups on the crystalline Fe3O4 nanoparticles (average size of 5.7 nm) is confirmed. It is found that the coated nanoparticles interact with the asphaltene to form asphaltene–nanoparticle complexes, stable enough even at the harsh conditions of the ADTs. The optimum dose of the inhibitor is found to be 200 ppm, with ADT efficiencies of 84.6 and 94.3% for the model oil and dead oil samples, respectively. In addition, during the dynamic displacement of the model oil, the deposit volume of the asphaltene is diminished by 56 and 78% in the presence of 100 and 200 ppm of the inhibitor, respectively. In the absence of the inhibitor, the asphaltene deposit appears as pore-bridging, pore-filling, and pore-throat-plugging patterns, especially during molecular-diffusion-dominated flow via the transverse dispersion mechanism. No complete pore throat plugging and pore filling are observed in the presence of the optimum dose of the inhibitor. Asphaltenes interact with the coated nanoparticles; thereby, their aggregation and growth are controlled. Therefore, the asphaltene flocculates are small enough to be stable in the liquid phase and move in the pores/throats even under diffusion-dominated flow. This prevents the pore throat plugging and, thus, severe asphaltene damage.