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CURRENT VISCOSITY MEASUREMENTS

OF CRUDE OILS OVER THE WIDE

RANGES OF PRESSURES AND

TEMPERATURES Esraa Khaled AliA & Tarek M.Aboul-FotouhB

A: The British University in Egypt

B: Azhar University

Emails: [email protected] , [email protected] [email protected]

ABSTRACT

In this study, current viscosity and density of two Egyptian crude oil samples from Amal and Qarun fields were measured at temperatures ranging from 20 °C to 100 °C. Consequently the results were used to develop graphs to determine the behavior of current viscosity at various conditions. For each sample, the current viscosity, current density and frequency were measure for the specified temperature range at 0, 5 and 10 bars for 200, 40 and 600 RPM. These resulted in a series of conclusions including that by increasing the pressure and temperature the current viscosity decreases. By increasing the frequency of the oil sample, the current viscosity decreased sharply and the highest current viscosity was detected at the highest pressure. Also the increase in pressure had no effect on the decreasing behavior of density with respect to increase in temperature. Finally, the increase in density leads to direct and clear increase in current viscosity.

1. Problem Definition and Objectives

Petroleum fluids have had great importance for many years and in spite of the massive work efforts alread y finished in relation with the oil industry [1], there is still a shortage in the studies available for viscosity behavior against pressure and temperature of some fractions in the petroleum fluids [2]. Considering the importance of viscosity in the planning, development, operation and designing of processes in the petroleum industries; it is of great importance to develop accurate viscosity estimation for estimating viscosity and wide ranges of temperatures and pressures [3].

The principal objective of this research is to simulate the flow of crude oils in pipelines using Process Current Viscometer, measure the current viscosity at any pressure and temperature and also measure the density of oil at any temperature. Then study the effect of temperature and pressure on current viscosity and density of the crude oil.

2. Brief Background / Literature review

Understanding the fluid’s physical properties at different pressures and temperatures is important to determine its performance in pipelines or tubing. An extremely vital physical property that influences and controls the flow of oil thus properly sizing pumps, tubing and pipelines is the crude oil viscosity [4]. Viscosity is a measure of fluid’s internal resistance to flow. It is also a measure of the fluid’s frictional properties and can be termed as a drag force. Viscosity is a function of pressure and temperature [5]. Over the years, values of viscosities at single temperature have been reported in literature and usually there is no mention of whether the fluid is a Newtonian or a non-Newtonian. These data are of little usefulness in real-life processes, where shear rates, pressures and temperatures vary from the conditions of a single viscosity measurement [6].

The device used in this work was Process Current Viscometer which is a measuring device for determining temperature and viscosity in flowing liquids. The base of this measuring system is an oscillating quartz cylinder. The oscillation is depreciated by the viscous properties of the circumfluent liquid [7].

3. Methodology / Approach to the Problem

Two petroleum crude oil samples of different API gravity values were collected from Amal and Qarun production fields. Before analysis, each sample was shaken vigorously to achieve homogeneity. Each crude oil sample was then transferred into a clean pycnometer and their API gravity values were measured according to ASTM standards. Nine runs of experiments have been conducted for each sample and four variables including current viscosity, current density, temperature and frequency were measured in each run over time under the changing conditions.

Figure 1 shows the Process Current Viscometer Apparatus. Sample analysis is also shown in Table 2.

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Table 1: Sample Analysis.

Amal Sample Qarun Sample

API 31.4 15.1

Density (Kg/m3) 869 964

Specific gravity 0.8686 0.9652

α 0.00068 0.66

Fig. 1. Process Current Viscometer Apparatus.

3.1 Current Viscosity Measurement

The Process Current Viscometer is measuring the viscosity of liquids by means of the quartz oscillating dampening and resonance shift by the viscous properties of the surrounding liquid. Beside this, there is also an influence of the density of the medium because of the mass acceleration. The quartz viscometer's microprocessor contains a powerful extrapolation algorithm of the temperature dependent density of the liquid, resulting of a mathematical and physical analysis of the system. In comparison to the variation of the viscosity of a liquid its temperature-density variation is very small. Therefore it is only required to have a rough idea of the value of the reference density of the liquid; everything else is done by the viscometer.

3.2 Experimental Procedures

The steps of using the Process Current Viscometer are shown in Figure 2.

The sample is filled into the pressure cell (1) to above the marked level approx.103mL (10), because of the formation of vortex when stirring above 200 RPM. The sensor head is then screwed into the closure head from below using a suitable copper gasket (3). Before closing the unit, place the O-ring seal (2) in the notch on the inner side. A location bolt (4) shows the correct orientation of the flange lid; make sure that the pin enters the corresponding bore (5). After closing the unit, use the 8 screws (6) to close and fix the pressure cell. To improve the temperature regulation, a customized insulation jacket (11) is used. The needle valve (7) is used to pressurize the unit. The pressure inside the unit is displayed on the pressure gauge (8).

At the lower border of the main window is the status line, which displays the settings of "the current measurement". The following values are displayed as shown in Figure 3.

• Given density.

• Given coefficient of thermal expansion

• Number of measurements (or start temperature or measurement duration).

• Temperature (or time) step.

According to the density extrapolation of the samples the process viscometer need to introduce thermal

expansion factor (α) which calculated from the following equation: Where: ρt= the density of the crude oil at final temperature in Kg/m3, ρ15=the density of the crude oil at

15.5°C. α= thermal expansion coefficient. tf = temperature of crude oil at final temperature. t15=

temperature of crude oil at 15.5°C.

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Fig.2. Steps for using the Process Current

Viscometer

Fig.3. Steps of using Process Current Viscometer Control Unit

4. Main results / Achievements

The experimental data of the current viscosity, density, and frequency of two dead heavy oil samples with different API values were measured in the temperature range of 20-100 °C. These values were later plotted in a series of graphs to study the effect of pressure and revolutions per minute on the behavior of current viscosity in an increasing temperature. These figures reveal a general behavior consistent with previous observations made by other authors and by ourselves on different conditions.

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Figure 4 represents the relationship between current viscosity and temperature at different pressures (200, 400, 600 RPM). At 200 RPM Figure indicates that the current viscosity decreases by increasing temperature and pressure. At 400 RPM it shows that the current viscosity decreases by increasing the temperature however, the highest current viscosity value was at 10 bar and decreasing the pressure caused further decrease in current viscosity. At 600 RPM the Figure displays that the current viscosity decreases by increasing the temperature. In addition, the highest current viscosity value was at 10 bar and decreasing the pressure caused further decrease in current viscosity.

Figure 5 illustrates the relationship between current viscosity and frequency at different pressures (200, 400, 600 RPM). At 200 RPM the Figure indicates that current viscosity decreases and frequency increase when the pressure increases. At higher frequencies the behavior at each pressure is the same because they are in the high temperature zone. At 400 RPM the Figure shows that current viscosity decreases and frequency increase when the pressure decreases. And 10 bar indicates the highest current viscosity because high pressure causes the formation of molecules clusters and thus the current viscosity increases. At 600 RPM the Figure reveals that current viscosity decreases sharply with increasing frequency when the pressure decreases. And 10 bar still indicates the highest current viscosity because high pressure causes the formation of molecules clusters and thus the current viscosity increases.

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Fig. 4. Relationship between Current Viscosity and

Temperature at different pressures and RPMs for Fig. 5. Relationship between Current Viscosity

Amal sample and Frequency at different pressures and RPMs for

Amal sample

Figure 6 illustrates the relationship between density and temperature at different pressures (200, 400, 600 RPM). The Figure reveals that density decreases by increasing the temperature however, changing the pressure has no effect on it for the three revolutions per minute.

Figure 7 illustrates the relationship between density and current viscosity at different pressures (200,

400, 600 RPM). At 200 RPM the Figure reveals that by increasing the temperature both the current viscosity and density of the crude oil increase and by decreasing the pressure the density increases. In addition, the Figure reveals at 400 RPM that the highest density value is at 5 bar, followed by 10 bar and finally 0 bar at increasing current viscosity. Besides, the Figure shows at 600 RPM different effect for different pressures with the highest density value at 5 bar.

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Fig. 6. Relationship between Density and

Temperature at different pressures and RPMs

for

Amal sample

Fig. 7. Relationship between Density and Current

Viscosity at different pressures and RPMs for Amal sample

Figure 8 represent the relationship between current viscosity and temperature at different pressures (200, 400, 600 RPM). The Figure indicates that at 200 RPM the current viscosity decreases by increasing temperature and pressure. At 400 RPM the Figure shows that the current viscosity decreases by increasing the temperature however, the highest current viscosity value was at 0 bar and both 5 and 10 bars had no effect on the decreasing behavior of current viscosity. At 600 RPM the Figure displays that the current viscosity decreases by increasing the temperature. In addition, the highest current viscosity value was at 5 and 10 bar which had almost similar effects and decreasing the pressure caused further decrease in current viscosity.

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Fig. 8. Relationship between Current Viscosity and

Temperature at different pressures and RPMs

for

Qarun sample

Fig. 9. Relationship between Current Viscosity and

Frequency at different pressures and RPMs for

Qarun sample

Figure 9 illustrates the relationship between current viscosity and frequency at different pressures (200, 400, 600 RPM). The Figure indicates that at 200 RPM current viscosity decreases and frequency increase when the pressure increases. At higher frequencies

the behavior at each pressure is the same because they are in the high temperature zone. The Figure also shows that at 400 RPM current viscosity decreases and frequency increase when the pressure decreases. And 0 bar indicates the highest current viscosity. On the other hand, both 5 and 10 bars had the same effect on the decreasing behavior of current viscosity. At 600 RPM the Figure shows that current viscosity decreases sharply with increasing frequency when the pressure decreases. The highest current viscosity value is at 5 bar. Also, 5 and 10 bars have almost the same effect on the behavior of current viscosity.

Figure 10 illustrates the relationship between density and temperature at different pressures (200, 400, 600 RPM). The Figure reveals that density decreases by increasing the temperature however, changing the pressure has no effect on it for the three revolutions per minute.

Figure 11 demonstrates the relationship between density and current viscosity at different pressures (200, 400, 600 RPM). The Figure also reveals that at 200 RPM, increasing the temperature increases both the current viscosity and density of the crude oil increase and by decreasing the pressure the density increases. In addition, the Figure reveals that at 400 RPM both 5 and 10 bars have the same effect and they have the highest density value at increasing current viscosity. Besides, at 600 RPM it shows different effect for different pressures with the highest density value at 10 bar.

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Fig. 10. Relationship between Density and

Temperature at different pressures and RPMs

for

Qarun sample

Fig. 11. Relationship between Density and Current

Viscosity at different pressures and RPMs for

Qarun sample

5. CONCLUSIONS

• The continuous increase in temperature leads to sharply decrease in current viscosity. Also by increasing the pressure, the current viscosity increases until reaching the high temperature zone where pressure has no effect and the three conditions behave the same.

• By increasing the frequency, the current viscosity decreases steeply this indicates high mobility of liquid oil sample molecules at lower viscosities. Besides, the current viscosity decreases sharply with increasing frequency when the pressure decreases. At 10 bar the highest current viscosity was detected because high pressure causes the formation of molecules clusters and thus the current viscosity increases.

• With the continuous increase in temperature, the density of the oil samples declined steeply. Moreover, changing the pressure had no effect on the decreasing behavior of density over the increase in temperature.

• The increase in density leads to increase in current viscosity directly and clearly.

REFERENCES:

[1]. Esraa Khaled Ali, Tarek Aboul-Fotouh. Current Viscosity Measurements of Crude Oils. Germany : Lambert Academic Publishing, 2016. 978-3-659-93337-0.

[2]. C. Boned, C.K. Zeberg-Mikkelsen, A. Baylauq, P.Dauge. High pressure dynamic viscosity and density of two synthetic hydrocarbon mixtures representative of some heavy petroleum distillation cuts. Pau Cedex, France : ELSEVIER, 2003.

[3]. Viscosity prediction in selected Iranian light oil reservoirs: Artificial neural network versus empirical correlations. Mohammed Soleimani Lashkenari, Majid Taghizadeh, Bahman Mehdizadeh. 2013, Springer, pp. 126-133.

[4]. New correlations for prediction of viscosity and density of Egyptian oil. A.N. El-hoshoudy, A.B. Farag, O.I.M. ALi, M.H. El-Batanoney, S>E>M. Desouky, M. Ramzi. 2013, ELSEVIER, pp. 277-282.

[5]. Viscosity estimation of binary mixtures of ionic liquids through a multi-layer perceptron model. Pablo Diaz-Rodriguez, John C. Cancilla, Gemma Mutate, Jose S. Torrecilla. 2015, ELSEVIER, pp. 1350-1353.

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[6]. Effect of Temperature on Viscosity of Fruit Juices and Purees . Saravacos, G. D. 1970, Food Science, p. 1. [7]. Laboratory Viscometer. Wunstorf : F5 Technologie GmbH, 2013.