Flow characteristics of waxy crude oils: Application to pipeline design

Abstract

IntroductionThe presence of crystallized wax in crude oil and petroleum products converts a simple Newtonian fluid, whose viscosity is readily measured using such devices as glass capillary viscometers, into a very complex non-Newtonian fluid whose flow properties are very difficult to measure in a reliable and repeatable manner even in the most sophisticated viscometers. Many crude oils throughout the world contain significant quantities of wax, which will readily crystallize during the production, transportation and storage of the oil, resulting in an increase in viscosity by several orders of magnitude, oil gelation (the formation of a yield stress) and deposition on pipeline walls.In the past, research has been carried out primarily to solve the pipelining difficulties of specific crude oils using a range of laboratory viscometers (Perkins and Turner, 1971;Sifferman, 1979;Withers and Mowll, 1982). In some instances, complex and costly pilot-scale pipelines have been utilized (Ford et al., 1965, Wyllie and Jones, 1960;Thomson and Farrant, 1984). However, poor reproducibility of the flow property measurements of different laboratory viscometers and of laboratory and pilot plant data (Davenport and Somper, 1971) has left considerable uncertainty in the scale-up of viscometric data to operating pipelines at temperatures below the pour point of the oil even in the simplest case of steady-state flow.Many pipelines are maintained at temperatures well above the pour point to avoid the problem of handling a waxy crude oil, for example, by using reheating stations (Yan and Luo, 1987). Maintaining an elevated temperature, however is, not an economic alternative for many pipelines, such as the 0.3-m-dia., 1,100-km Jackson to Brisbane pipeline in southern Queensland, where a combination of blending and the use of flow improver (pour point depressant) additives has been applied successfully to maintain production through the winter months when ground temperatures can fall to 10°C-some 12°C below the pour point of the oil (Thomson and Farrant, 1984).Originating from consulting work carried out for the Australian oil industry, research has been carried out at the University of Melbourne to determine appropriate measurement techniques for waxy crude oils and to study the parameters affecting the rheology. The most significant parameter has been found to be the effect of the shear rate(s) applied during the cooling of the oil (termed the shear history). Although it has long been recognized that the shear and thermal history must be controlled to measure the flow properties of waxy crude oils (Ford et al., (1965), the role of the shear history in determining the flow properties and the consequent effect on pipeline design has not been fully appreciated.This article summarizes the measurement techniques needed AIChE JournalJune 1991 Vol. 37, No. 6 871 to obtain reproducible results in two commonly used rotational viscometer geometries: the concentric cylinder viscometer and the cone and plate viscometer. Discussed also are the ...

Structural and thermal behavior of comb‐like polymer having n‐octadecyl side chains

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Studies on the Influence of Polymeric Additives as Flow Improvers for Waxy Crude Oil

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