Experimental and Theoretical Study of Viscosity Reduction in Heavy Crude Oils by Addition of Nanoparticles

Abstract

Heavy and extra-heavy oils generally exhibit high viscosity, which is detrimental to their production, transport, and refining. The oil and gas industry has thoroughly investigated the use of chemical agents to improve the mobility of this type of low-quality crude oil at the surface as well as reservoir conditions for many years. In this sense, the main objective of this paper is to provide unexpected experimental evidence of heavy oil and extra-heavy crude oils viscosity reduction resulting from the presence of nanoparticles (NPs) of different chemical natures (SiO 2 , Fe 3 O 4 , and Al 2 O 3 ), particle size, surface acidity, and concentration at low-volume fractions. The viscosity of the enhanced fluids was measured using a rotational rheometer at shear rates varying between 1 and 75 s −1 . Upon addition of nanoparticles, viscosity reduction was observed in all cases evaluated. However, the maximum viscosity reduction of roughly 52% was obtained at a concentration of 1000 mg/L with 7 nm SiO 2 nanoparticles at shear rates below 10 s −1 , contrary to expectations from Einstein's viscosity theory in particulate systems. A mathematical model based on a modification to Pal and Rhodes Model for the viscosity of suspensions is proposed in this work. The said model that relates the concentration of nanoparticles to the fluid mixture viscosity was validated successfully using experimental data, as evidenced by RSME% values lower than 10%. The importance of our findings lies in the lack of previous experimental and theoretical data in the open literature showing heavy crude oil viscosity reduction in the presence of nanoparticles.

A New Model for Describing the Rheological Behavior of Heavy and Extra Heavy Crude Oils in the Presence of Nanoparticles

“…There are models independent of the shear rate, for example, wax-oil gels, which is instead dependent on the strain [38][39][40]. Our previous model [33] describes well the experimental data previously obtained but is dependent on the shear rate at which the viscosity is measured. For this reason, the proposed new model mainly seeks to explain the nanoparticles-induced viscosity reduction process phenomenologically for the entire shear rate range at which the viscosity is measured.…”

“…Our approach was validated using the experimental rheological results varying the SiO 2 nanoparticles concentration [33]. Therefore, it is possible to obtain a mathematical approach that matches what is obtained in the laboratory for a fixed shear rate (…”

“…These particles, at a determined concentration according to the characteristics of the crude oil, have the capacity to produce proven structural changes in yield stress and viscosity changes. By means of steady-state rheology measurements of light crudes and de-asphalted oil in the presence of nanoparticles, viscosity increases were obtained [31,33]. This result suggests that viscosity reduction is produced precisely by the interaction with asphaltenes.…”

“…It has previously been shown that the presence of SiO 2 nanoparticles has the ability to lower the viscosity of heavy crude [11,[31][32][33]. Said viscosity reduction is produced due to the interaction between the nanoparticles and the heavy hydrocarbons present in the crude oil (asphaltenes and resins).…”

“…Likewise, the first mathematical approximation to understanding the phenomenon was developed through the mathematical modification of the viscosity model in suspensions previously proposed by Pal and Rhodes [33]. They proposed a non-Newtonian shear model based on Einstein´s theory, which has been applied to explain the behavior of the viscosity of several crude oils and de-asphalted oils (DAO) varying their content of asphaltenes by their addition.…”