Flow assurance in a model crude oil: a structural and rheometric study.
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Date
2008-04
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Publisher
Australian Nuclear Science and Technology Organisation
Abstract
This report investigates how the technique of small angle neutron scattering (SANS) helps elucidate the phenomenon of wax deposition in a petroleum crude oil. Specifically, we report SANS data, supplemented by results from dynamic light scattering (DLS), obtained from a synthetic petroleum crude oil: a mixture of commercial paraffin wax dissolved in an octane/cyclohexane solvent. The system is a gel below the cloud point. The onset and growth of this waxy gel, and changes in its nanostructure, are recorded here as a function of temperature over the range 10 ≤ T/°C ≤ 65. SANS indicates that the wax has a definite characteristic length of about 100 Å (10 nm) which can be observed at temperatures as high as 57°C, but DLS indicates that the wax also contains very large structures - of the order of a micrometer - over the temperature range 30° - 50°C. The structural studies are supplemented by corresponding sets of viscosity and stress data taken from the gelling wax when subjected to an applied shear. We observe that the stress will increase as the temperature falls - i.e. as the system gels - but, in general, will then reach a maximum and tend to decline. The wax results are compared with those from an equivalent system consisting of a major component of the wax: n-docosane, C22. Significant differences between the behavior of the wax and the pure component in the solvents are noted. The SANS patterns to 20°C from docosane do not give any indication of the nanoscale structure observed from the wax; the DLS patterns for docosane indicate that a solidification occurs over a very narrow temperature range between 10°C and 12°C, accompanied by a dramatic slowing of the dynamics; the large scale structure seen in the wax mixtures is not evident; and the rheological behavior of the two systems is markedly different. The paper also compares and contrasts the rheological behavior of the wax gel with that observed from defined system, gelled colloidal silica. Strong similarities are apparent.
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Keywords
Small angle scattering, Waxes, Deposition, Petroleum, Flow rate, Gels
Citation
Drabarek, E., Muzny, C., Bryant, G., Hanley, H. J. M. (2008). Flow assurance in a model crude oil: a structural and rheometric study. (ANSTO/E-766). Lucas Heights, NSW: Australian Nuclear Science and Technology Organisation.