Heavy oil transportation as a solid-liquid dispersion

Abstract

Traditionally, heavy oil pipelines are designed to handle liquids with effective viscosity below 0.5 Pa s at the pump outlet, in order to minimize the frictional pressure gradient and obtain a pipeline size and economically optimum pumping requirements. Asphaltenes and resins are the components of crude oil which have the highest molecular weights and are, also, the more polar ones. It has been determined that the characteristics of the asphaltenes play an important role in the high viscosity of heavy oils of the Orinoco Oil Belt. This chapter presents an experimental investigation of the behaviour of a potential transport method for heavy oils based on precipitation and conditioning of asphaltenes, followed by an ulterior reincorpora-tion into the de-asphalted oil to obtain a solid-liquid dispersion (slurry) with a lower effective viscosity than the one of the original crude oil. The study comprises two steps: an analysis under static conditions to identify the rheological behaviour of the slurry for different solid contents, from 0 to 12 % (weight basis), and a fluid dynamic study to characterize the effectiveness of the solid–liquid dispersion method in a laminar flow regimen in a 1 inch horizontal pipeline, for mixture velocities between 0.2 and 2.3 m/s, corresponding to Reynolds Number values <1,400. A maximum effective viscosity of 0.15 Pa s @ 20◦C was measured 24 h after conducting the dynamic test, which implies a significant reduction compared to a typical viscosity range of 100–1,000 Pa s @20◦C for an original crude oil of similar API density and SARA composition. As expected, dispersion viscosity increases with time as asphaltenes are progressively reabsorbed into the de-asphalted oil as a colloidal suspension. The investigated transport method can be implemented together with a low pressure–low temperature de-asphalting process to improve transport properties of the heavy oils of Orinoco Oil Belt.