Abstract
Rheological measurements are essential in transporting crude oil, especially for waxy crude oil. Several rheological measurements have been conducted to determine various rheological properties of waxy crude oil including the viscosity, yield strength, wax appearance temperature (WAT), wax disappearance temperature (WDT), storage modulus and loss modulus, amongst others, by using controlled stress rheometers. However, a procedure to determine the correct parameters for rheological measurements is still unavailable in the literature. The paper aims to investigate the effect of shear and time dependent behaviours of waxy crude oil during rheological measurements. It is expected that the preliminary work could lead toward a proper rheological measurement guideline for reliable rheological measurement of waxy crude oil.
Highlights
In the oil and gas fields, about 20% of petroleum reserves produced and pipelines are waxy crude oils [1]
This paper aims to first investigate the effect of shear and time dependent behavior of waxy crude oil on the determination of setting parameters for reliable rheological measurement
Typical Arrhenius temperature dependent trend of Newtonian fluid is observed at temperatures above 22oC and 34oC for the cooling and heating curves, respectively while nonNewtonian regions were found to be predominant below the respective temperatures. [10] refer the two temperatures as wax appearance temperature (WAT) and wax disappearance temperature (WDT)
Summary
In the oil and gas fields, about 20% of petroleum reserves produced and pipelines are waxy crude oils [1]. Waxy crude oils are aliphatic hydrocarbon having high molecular weight paraffin consisting of both straight and branched chains with carbon number ranging from C18 to C65 [2]. The solubility of paraffin waxes is dependent on the temperature, i.e. it decreases with decreasing temperature. At reservoir conditions where the temperature ranges around 70 to 150°C with pressure ranges of 50 to 100MPa, the solubility of the paraffins in the crude oil is adequately high. Once the crude oil leaves the reservoir at a high temperature and flows through cold pipelines placed on the seabed with temperature ranging normally from 20qC down to 5°C, the crude oil temperature begins to drop dramatically due to the heat loss to the surroundings
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