Influence of asphaltene aggregation and pressure on crudeoil emulsion stability

Abstract

Water-in-crude oil emulsions stabilised by various surface-active components are one of the major problems in relation to petroleum production. This thesis presents results from high-pressure separation experiments on "live" crude oil and model oil emulsions, as well as studies of interactions between various indigenous stabilising materials in crude oil. A high-pressure separation rig was used to study the influence of gas and gas bubbles on the separation of water-in-crude oil emulsions. The results were interpreted as a flotation effect from rising gas bubbles, which led to increased separation efficiency. The separation properties of a "live" crude oil were compared to crude oil samples recombined with various gases. The results showed that water-in-oil emulsions produced from the "live" crude oil samples, generally separated faster and more complete, than emulsions based on recombined samples of the same crude oil.

Adsorption of asphaltenes and resins onto a hydrophilic surface from solutions with varying aromatic/aliphatic character was investigated by a quarts crystal microbalance. The results showed that asphaltenes adsorbed to a larger degree than the resins. The resins were unable to desorb pre-adsorbed asphaltenes from the surface, and neither did they adsorb onto the asphaltene-coated surface. In solutions of both of resins and asphaltenes the two constituents associated in bulk liquid and adsorbed to the surface in the form of mixed aggregates. Near infrared spectroscopy and pulsed field gradient spin echo nuclear magnetic resonance were used to study asphaltene aggregation and the influence of various amphiphiles on the asphaltene aggregate size. The results showed interactions between the asphaltenes and various chemicals, which were proposed to be due to acid-base interactions. Among the chemicals used were various naphthenic acids. Synthesised monodisperse acids gave a reduction of size of the asphaltene aggregates, whereas polydisperse naphthenic acids seemed to affect the state of the asphaltenes only to a minor extent. The effect of the naphthenic acids on the asphaltenes appeared however, to depend on the asphaltene type. Other amphiphiles such as amines and alcohols, showed a varying effect on the dispersion of the asphaltenes into smaller aggregates. Furthermore, measurements of diffusion coefficients upon increased concentration of asphaltenes, implied that the asphaltenes began to self-associate at concentrations above 0.1 wt-% in toluene-d8.