Rheological Behavior and Structural Interpretation of Waxy Crude Oil Gels

Abstract

A waxy crude oil which gels below a threshold temperature has been investigated under static and dynamic conditions, using a combination of rheological methods, optical microscopy, and DSC. Particular attention is given in this work to the influence of the mechanical history on gel strength and to describing the time-dependent rheological behavior. The gels display a strong dependence of the yield stress and moduli on the shear history, cooling rate, and stress loading rate. Of particular interest is the partial recovery of the gel structure after application of small stress or strain (much smaller than the critical values needed for flow onset) during cooling, which can be used to reduce the ultimate strength of the crude oil gel formed below the pour point. A second focus of this study is to further develop the physical interpretation of the mechanism by which wax crystallization produces gelation. Gelation of the waxy crude oil studied is suggested to be the result of the association between wax crystals, which produces an extended network structure, and it is shown that the system displays features common to attractive colloidal gels, for one of which, fumed silica (Aerosil 200) in paraffin oil, rheological data are reported. The colloidal gel model provides a simple and economical basis for explaining the response of the gelled oil to various mechanical perturbations and constitutes a fruitful basis from which to develop technologies for controlling the gelation phenomenon, as suggested by the rheological results reported.

Evaluation of Nigerian Waxy Crude Oil Using Rheological Models

“…The presence of long-chain saturated alkanes in crude oil can lead to relentless problems associated with wax precipitation and deposition in petroleum transport pipelines and processing equipment 3 . Furthermore, the presence of solid waxes in oil systems may affect the prediction and evaluation of the flow properties.…”

“…In general, Crude oils contain not only n-paraffins but also considerable amounts of isoparaffins and cyclic compounds. It is found that n-paraffin dissolved in organic solvents display a sharp transition in gel strength at the pour point, whereas by addition of isoparaffins, the buildup in gel strength as a function of temperature is much more gradual, because increasing isoparaffin fraction facilitates the formation of amorphous wax solids 3 .…”

Physical Properties of Water–oil Mixtures Involving Waxing

“…While studying the impact of water on the gelation and rheology of waxy crudes, Visintin et al [15] report that although the effect of dispersed water on crude oil rheology had been well characterised, little attention has been given to the study of the potential impact of emulsified water on crude oil gelation. Their study shows that the presence of water can enhance greatly the formation of gel, the pour point temperature and its yield strength.…”

Synthesis and characterization of organogel from poly(acrylic acid) with cellulose acetate

“…An example of formation of an undesired thermoreversible network is the occurrence of wax crystallization in crude oil [7].…”