The Effect of Asphaltenes on the Gelation of Waxy Oils

Abstract

The phase stability of crude oil is dependent on a multitude of factors, including temperature, pressure, and component fractions, especially long chain paraffin and polar asphaltene fractions. Paraffins precipitate out of the crude oil during pipeline transportation due to solubility limits, and form paraffin-oil gel deposits on the pipe walls. The presence of asphaltenes in crude oil is postulated to affect the formation of these paraffin gels. To quantify this effect, a controlled stress rheometer was used to study the gelation temperature and the yield stress of a model paraffinoil system. It was observed that the addition of asphaltenes in small proportions (∼0.1 wt %) resulted in a significant decrease both in the gelation temperature and the yield stress of the model system, indicating that the presence of asphaltenes hinders the gelation mechanism. Addition of higher amounts of asphaltenes resulted in macroscopic phase separation: a deposit consisting of asphaltenes and paraffins separated out of the liquid. The effects of operating conditions and the asphaltene polarity on the gelation process were also studied. Polarized light microscopy and nuclear magnetic resonance spectroscopy were used to obtain insights into the rheometric results.

A regular, hydrophobically modified polyampholyte as novel pour point depressant

“…The appearance of platelike paraffin aggregates is probably due to the adsorption of paraffin molecules on the surface of asphaltenes and resins. 41 It was observed for a model paraffin-oil system that the presence of asphaltenes in small proportions (ϳ0.1 wt %) hinders the paraffin gelation, 40 whereas the presence of higher amounts of asphaltenes resulted in macroscopic phase separation: a deposit consisting of asphaltenes and paraffins separated out of the liquid. Since the Akshabulak crude oil contains 0.58 wt % of asphaltenes, it is likely that asphaltene-paraffin complexes are responsible for formation of big aggregates after the heat treatment.…”

On the Influence of Micro- and Macro-Cristalline Paraffins on the Physical and Rheological Properties of Crude Oil and Organic Solvents

“…According to an in-house developed analytical procedure, the thermal memory of all fluid systems under investigation was previously eliminated by pre-heating the DSC sample containing crucible ≅ 353 K (1 h time lapse). Statistical evidences show this procedure helps increasing the repeatability of WAT results [14,15]. Following this heating stage, both the sample containing and the reference (hollow) crucibles of the µ-DSC apparatus are submitted to a controlled cooling process.…”

Review of studies on asphaltene - wax interaction and the effect thereof on crystalilization

“…Some have confirmed that the presence of asphaltenes decreases pour point (Venkatesan et al, 2003), others report that they increase pour point (García & Carbognani, 2001) and yet others say that they have no effect (Yang & Kilpatrick, 2005). García and Carbognani (2001), evaluated the effect of asphaltenes in solution and flocculated asphaltenes on the interaction with wax, for which they took asphaltenes with different aromaticity and stability: from operationally unstable crude oil, stable crude oil and deposit crude oil.…”

“…In the meantime, the dispersed asphaltenes act as connectors between the wax crystals, accelerating the gelling of the crude oil and increasing gel strain. Venkatesan et al (2003) studied the effect of asphaltene polarity on the rheological properties of waxes. Three fractions extracted from the crude oil of the Zuata field in Venezuela were added to a synthetic oil with previously dissolved waxes at 5% w/w.…”