Rheology, particle size distribution, and asphaltene deposition of viscous asphaltic crude oil-in-water emulsions for pipeline transportation

The rheology of an asphaltic heavy crude oil-in-water emulsions stabilized by an anionic (RN) and a nonionic (TEP) surfactants individually or in a mixture has been studied. The investigated crude oil has a non-Newtonian, time dependent, shear thickening, rheopectic behavior with a relatively high yield stress. The relatively high yield stress of this crude oil is attributed to the presence of a relatively high asphaltene and resins content. The viscosity of the crude oil decreases when it is emulsified with synthetic formation water in the form of an oil-in-water type of emulsion using a nonionic or an anionic surfactant. It has been found that, the maximum oil content required for forming an oil-in-water emulsion of acceptable viscosity is the 60% oil-containing emulsion. However, the 70% oil-containing emulsion is not an oil-in-water type of emulsion but it is rather a complicated mixture of oil-in-water-in-oil type of emulsion. The presence of the anionic and the nonionic surfactants together has a synergistic effect in decreasing the total surfactant concentration required to stabilize the emulsion and to form low viscosity emulsion. It has been emphasized that the nonionic surfactant has a positive contribution in forming emulsions with low viscosity. Meanwhile, the anionic surfactant contributes in stabilizing the emulsion at lower concentrations. Flocculation point measurements showed that the added surfactants caused no sign of asphaltene deposition. This implies that it is safe to use the investigated surfactants in forming oil-in-water emulsion for viscous asphaltic crude oils without any fear of asphaltene deposition.