Prediction of the wax content of the incipient wax-oil gel in a pipeline: An application of the controlled-stress rheometer

Abstract

High molecular weight paraffins are known to form gels of complex morphology at low temperatures due to the low solubility of these compounds in aromatic or naphthene-base oil solvents. The characteristics of these gels are strong functions of the shear and thermal histories of these samples. A model system of wax and oil was used to understand the gelation process of these mixtures. A significant depression in the gel point of a wax-oil sample was observed by either decreasing the cooling rate or increasing the steady shear stress. The wax-oil sample separates into two layers of different characteristics, a gel-like layer and a liquid-like layer, when sheared with a controlled-stress rheometer at high steady shear stresses and low cooling rates. The phase diagram of the model wax-oil system, obtained using a controlled-stress rheometer, was verified by analyzing the wax content of the incipient gel deposits formed on the wall of a flow loop. Based on the rheological measurements, a law has been suggested for the prediction of the wax content of the gel deposit on the laboratory flow loop walls. The wax content of the incipient gel formed on the wall of a field subsea pipeline was predicted to be much higher than that for the flow loop at similar operating conditions. This variation in the gel deposit characteristics is due to the significant differences in the cooling histories in the two cases.

Causes of Floccules Formation in Hydro-Treated Lubricating Base Oil

“…Singh et al (1999) pointed out the question of the threedimensional structure of the network in gels and of the type of interactions between crystals. They discussed the changes of the morphology of the crystals under different rates of cooling.…”

Tailored Polymer Additives for Wax (Paraffin) Crystal Control

“…The waxes form stacked lamellar crystals with sizes of hundreds of micrometers and an overall morphology resembling a "house-of-cards" (Abdallah et al, 2000) that readily entrains liquid oil, primarily through surface tension, and effectively forms an organic gel. The occurrence and deposition of such large wax crystals cause a reduction of the ease of flow of crude oils and a loss of fluidity and filterability of middle distillates (Venkatesan et al, 2005;Singh et al, 1999). Wax deposition affects the storage tanks and conduits (Fig.3).…”

Estudo Sobre a Influência Da Contração Do Petróleo Ao Gelificar No Reinício Do Escoamento

“…O petróleo é uma mistura complexa de hidrocarbonetos (alcanos, aromá-ticos, naftenos, resinas e asfaltenos) (21). Um petróleo é definido como parafí-nico quando possui alta concentração de alcanos de alto peso molecular, com número de carbono que podem variar de 5 até mais de 100 (1).…”

“…A solubilidade das parafinas de alto peso molecular cai rapidamente com a redução da temperatura. Portanto, estas moléculas começam a formar cristais estáveis a baixas temperaturas (21).…”

“…As parafinas de alto peso molecular são responsáveis por grandes problemas no transporte e processamento de petróleo (21).…”