Influence of silica nanoparticles on heavy oil microrheology via time-domain NMR T2 and diffusion probes

Abstract

The objective of the present work is to determine the effect of silica nanoparticles on the microrheological properties of heavy and extra-heavy crude oils using time-domain nuclear magnetic resonance (TD-NMR) methods. Three heavy crude oils with different asphaltene contents were studied. The oils steady-state rheograms were collected as a function temperature and nanoparticles concentration. Transverse relaxation time (T2) and diffusion coefficient measurements were used as probes of the crude oils microrheological responses. A clear inverse correlation between either the log-mean T2 (T2,LM) or the diffusion coefficient and the rheometric oil viscosity in the presence of nanoparticles was found. Results further show the likely existence of an optimal concentration of nanoparticles in the vicinity of 1000 mg/L. The maximum viscosity reduction of roughly 35–45% was observed for the three heavy crude oils. The heavy oil refractive index decreases after the oil was placed in contact with nanoparticles, confirming adsorption of polar material on nanoparticles. T2 and the diffusion coefficient increase in the apparent region of optimal concentration of nanoparticles and decrease at higher concentration. The improved NMR responses, which reflect the enhanced translational and rotational motion of restricted hydrogen-bearing oil molecules/aggregates proves that microrheological changes occur as oil polar molecules aggregates break down due to the adsorption of asphaltenes. Finally, a multivariate statistical analysis evidences which parameter has the greatest influence on the system response. It is the first time, to the best of our knowledge, that these characterization tools have been used in heavy crude oils in the presence of nanoparticles.