Influence of High-Molecular n-Alkane Associates on Rheological Behavior of the Crude Oil Residue

In this paper, we present the results of chemical and physical investigations of the crude oil residue of low-sulfur but high-paraffin-base crude oil produced from the Mangyshlak (Kazakhstan) reservoir. The object contains 14.6 wt % of resins and significant amounts of high-molecular alkanes. A non-Newtonian behavior of the system is preserved even at 70-90 degrees C. H-1 NMR data revealed divergence in temperature-dependent ratios corresponding to the low-viscous liquid petroleum products. The experimental results indicate the existence of associations of n-alkanes among themselves, as well as with resins and asphaltenes in the composition of the crude oil residue sample. In paraffin-base crude oil, the size of such associates (coacervates) is in the range of 100-300 nm. The associative behavior of medium- and long-chain n-alkanes is explained by their existence in transitional plastic (rotator) phases. As building blocks, associates of n-alkanes can be combined into worm-like structures due to adsorption of resins and asphaltenes on their surface and adhesion, thereby determining the non-Newtonian behavior and thixotropy of the system. Worm-like structures may be partially destructed under shear thinning (torn into shorter pieces) but can regenerate their structure over time. The optical and electron microscopy results justify the asphaltene aggregation model proposed by Balestrin and Loh. The formation of coacervates from asphaltene and concomitant molecules, which are surrounded by solvation shells of high-molecular alkanes, is evidenced. It is proposed that high-molecular n-alkane associates, as well as coacervates containing asphaltene and concomitant molecules, are compositional parts of many oil dispersed systems.

Automated summary

This paper presents the results of chemical and physical investigations of the crude oil residue obtained from the Mangyshlak reservoir in Kazakhstan. The study reveals the presence of associations between n-alkanes and between n-alkanes, resins, and asphaltenes in the crude oil residue sample. Additionally, the non-Newtonian behavior of the system at temperatures of 70-90 degrees C is observed.