Flow Improvers for Heavy Crude Oil Transport in Pipe

Abstract

The transportation of heavy oil is challenging as the oil has high viscosity and heavy components like asphaltenes. By finding an effective flow improver the transporting could be less demanding and more cost effective. Asphaltene aggregation is suspected to have an effect on the viscosity of the crude oil as asphaltenes act as colloids in the crude oil, and aggregate together. Traditionally it is accepted that asphaltenes are stabilized by other polar components, resins. Resin has a polar and a non-polar part that disperses the asphaltenes in the crude oil, and the structure of resins seems to be important. The polarity of the asphaltenes is believed to be an important parameter for finding a solvent that could have a stabilizing effect as resins. Solvents with active molecules as alcohol and ketone might have the potential to reduce the viscosity of a heavy oil by interacting with the asphaltenes. To find a solvent to be used as a flow improver the solubility parameters of Hildebrand and Hansen has been looked into. Different solvents already tested by other have been looked into, and the solubility parameters between these have been compared. Hildebrand solubility parameters around 22 MPa0.5 seem to be a good start point for finding a chemical that can be used as a flow improver. In the experimental work three different crude oils have been tested by adding thirteen different types of solvents in various amounts. The solvents were added in small amounts (≤ 3 wt %) to study the solvent s effect to reduce the viscosity by dispersing the asphaltenes in the oil. The analyses used to detect the effect from the studied solvents are Karl Fischer titration, viscometer, rheometer, near infrared spectroscopy and nuclear magnetic resonance spectroscopy. The three different crude oils that have been tested can be characterized as relatively viscous, with viscosity values ranging from 345 to 4152 mPa s at the actual test temperatures. The glycols have an opposite effect, they increased the viscosity in all tested crude oils. Some of the added solvents, as 1-hexanol and 2-butanone, have reduced the viscosity of the crude oil. However, this seems to be rather a diluting effect than a clear effect of dispersing the asphaltenes and thereby reducing the viscosity. The commercial products used in the experimental work, one viscosity reduction chemical and three asphaltene dispersant chemicals, reduced the viscosity mainly because of dilution. Using a glycol, 1-hexanol or 2-butanone in small amounts (≤ 3 wt %) as flow improver are not preferred instead of additive a lighter petroleum product, as naphtha, to reduce the viscosity of the oil.