Structural interpretation of waxy crude oil gels

Ruben F.G. Visintin¹, Romano Lapasin², Paolo D'Antona³ and Thomas P. Lockhart¹

¹ EniTecnologie SpA, Via Maritano 26, 20097 San Donato Milanese (MI), Italy.

² Universita degli Studi di Trieste, Piazzale Europa 1, 34127 Trieste (TS), Italy

³ Eni Div. E&P, Via Emilia 1, 20097 San Donato Milanese (MI), Italy.

The phase separation of paraffinic crystals from crude oil constitutes a major operating issue for the petroleum industry because their aggregation generates an extended network structure which leads to severe flow assurance problems. The starting point to understand these phenomena is the observation that crude oil gels display features common to those of gels formed from dispersions of weakly attractive colloidal particles.

In this work we have develop a quantitative interpretation of their internal structure by means of fractal geometry and the comparison between three waxy oil gels (by two crude and one model oil) and other colloidal particle gels. It has been possible to estimate the fractal dimension in the gelation regime and a parameter () which defines the balance between the magnitude of intra and inter-floc links. This approach has allowed us to formulate a mechanism of waxy crude oil gel formation which is fully consistent with experimental observations.

An important result is the finding that the fractal formed flocs are more rigid than the interfloc links: it is the strength of the interfloc links that determines the elasticity of the gel. Crude oil gels, in fact, behave like an elastic solid until the interfloc links can bear the stress application: after a critical value of deformation these links are damaged and the mechanical properties will degrade smoothly, due to the minor degree of connectivity of the dispersion of (unlocked) aggregates.