q923+rfl+l03

Reservoir Fluid Laboratory Course (1st Ed.)

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http://about.me/Alaminia

mailto:[email protected]

http://bit.ly/Q923-RFL

http://about.me/Alaminia

http://www.iauq.ac.ir/

http://www.iauq.ac.ir/

http://about.me/alaminia

http://about.me/alaminia

1. Initial definitions

2. Measurement of Density

3. Experiments: A. Fluid density using the Pycnometer method

1. Introduction (Theory):

2. Types of fluids

3. Viscometers; A. the falling (or rolling) ball viscometer

B. Capillary Type Viscometer

C. Rotational Viscometers

Viscosity as a rheological property

Rheology is the study of the change in form and flow of matter in terms of elasticity, viscosity and plasticity. A clear understanding of the rheological properties of

fluids is vital in many fields of science and engineering.

Viscosity is the measure of the internal friction of fluid. This internal friction is caused

when a layer of fluid moves in relation to another layer. The greater the friction,

the greater the amount of force required to cause this movement. This movement is known as shear.

Summer 14 H. AlamiNia Reservoir Fluid Laboratory Course (1st Ed.) 5

Deformation of a liquid under the action of a tangential force.To define viscosity

more precisely, let’s take a look at the figure. Two parallel planes of

fluid of equal area “A” are separated by a distance dx and are moving at different speeds V1, V2.


Viscosity definition

The force required to maintain the difference in speed is proportional to the difference in speed through the liquid.

μ is known as the viscosity, usually in units of

centipoises or Pa.s.

dv/dx (or 𝛾) is the shear rate.

Describes the shearing the fluid experiences when the layers move with respect of each other.

Units in reciprocal second, sec-1.

F/A (or τ) is the force per unit area required for the shearing. This is known as

the shear stress and it has units of pressure.

Therefore, we can define viscosity as:


Effect of Pressure on Viscosity

Viscosity of fluids varies with pressure and temperature. For most fluids the viscosity is rather sensitive to

changes in temperature, but relatively insensitive to pressure until rather high pressures have been attained. The viscosity of liquids usually rises with pressure at constant

temperature. • Water is an exception to this rule; its viscosity decreases with

increasing pressure at constant temperature.

• For most cases of practical interest, however, the effect of pressure on the viscosity of liquids can be ignored.


Effect of Temperature and Molecular Weight on ViscosityTemperature has different effects on viscosity of

liquids and gases. A decrease in temperature causes the viscosity of a

liquid to rise.

Effect of molecular weight on the viscosity of liquids is as follows; the liquid viscosity increases with increasing molecular

weight.


Newtonian fluids

A Newtonian fluid is characterized by having a constant viscosity at a given temperature. This is normally the case

for water and most oils.

A plot of shear rate versus shear stress would show a constant slope.

This is the simplest and easiest fluids to measure in the lab.

Shear rate versus Shear stress


Non Newtonian fluids

A non-Newtonian fluid is characterized by not having a unique value for viscosity. That is, the relationship

stress rate/shear rate is not constant.

The viscosity of these fluids will depend on the shear rate applied.

There are several types of non-Newtonian fluid behavior that we can observe in the lab.The most common are

shown in the figure.Shear rate versus Shear stress


types of non-Newtonian fluid behavior

Pseudo plastic fluids: these are fluids like

paints and emulsions, there is a decrease in viscosity as the shear rate increases.

Also known as shear thinning fluids.

Dilatant fluids: these are fluids that

increase their viscosity as the shear rate increases. Examples are cement

slurries, candy mixtures, corn starch in water.

Also known as shear thickening fluids.

Plastic fluids: These fluids will behave

like solids under static conditions. They will start to flow only when certain amount of pressure is applied.

Examples are tomato catsup and silly putty.


Viscosity of different material

Below is a table of viscosity values for some common materials.Material Viscosity (cP)Benzene 0.60Ethanol 1.06Water 1 to 5Mercury 1.55Pentane 2.24Blood 10Anti-Freeze 14Honey 2,000–3,000

Chocolate Syrup 10,000–25,000

Peanut Butter150,000–250,000

the application of (Dilatant materials) shear thickening fluidssome all-wheel drive

(AWD, 4WD, or 4×4) systems use a viscous coupling unit full of dilatant fluid

Body armor


Instrument selection

Viscosity of liquids is determined by instruments called viscosimeter or viscometer.

Most instruments designed to measure viscosity can be classified in two general categories: tube type and

rotational type.

The selection of a particular instrument must be based on the type of analysis required and the characteristics of the fluid

to be tested. For example,

rotational methods are generally more appropriate for non-Newtonian fluids,

while glass capillary viscometers are only suitable for Newtonian fluids.

In this lab, we will use one instrument to measure viscosity: the Ruska Rolling Ball

viscometer.


the falling (or rolling) ball viscometer

An instrument commonly used for determining viscosity of a liquid is the falling (or rolling) ball viscometer, which is based on Stoke’s law for a sphere falling in a fluid under effect of gravity.

A polished steel ball is dropped into a glass tube of a somewhat larger diameter containing the liquid, and the time required for the ball to fall at constant velocity through a specified distance between reference marks is recorded.


The calculation

The following equation is used

µ = absolute viscosity, cp

t =falling time, s

ρb = density of the ball, gm/cm3

ρf = density of fluid at measuring temperature, gm/cm3

K = ball constant.

The ball constant K is not dimensionless, but involves the mechanical equivalent of heat.

The rolling ball viscometer will give good results as long as the fluid flow in the tube remains in the laminar range. In some instruments of

this type both pressure and temperature may be controlled.


Instruments to measure rheological properties (Ruska falling ball)

Schematic diagram of the falling ball viscometer. Ruska falling ball viscometer


Ruska Apparatus

The Ruska rolling ball viscometer is used to determine the viscosity of bottom hole and surface samples at elevated temperatures and pressures, up to 10,000 psi and 300 °F. This instrument operates on the

rolling ball principle, where the roll time of a ¼ inch diameter ball is used to obtain viscosity data.

The viscosity is calculated as

μ: viscosity K: constant ρ ball: Density of the ball

ρ fluid: Density of the fluid t: roll back time

The driving force in this instrument is the difference in density between the fluid and the ball.

At a fixed temperature, the difference in ball and fluid density will be constant.

The viscosity Will be directly proportional to the roll back time.

The constant of the viscometer must be determined by previous calibration using a liquid of known viscosity.


Operating Procedure

Choose the correct ball size. If the fluid viscosity is

estimated to be between 0 and 5 cP, a 0.252 or 0.248 inch diameter ball should be used.

Above 25 cP, the 0.234 inch diameter ball will be appropriate

Clean the test assembly with kerosene and vent air to ensure the chamber is

free of dust.

Place the ball

in the bottom of the empty measuring barrel.Evacuate the test

assembly. This is done by opening

the vacuum pump valve at the lower end of the unit and closing the charging valve.

Charge the test sample fluid in the viscometer. The vacuum valve should

be closed while the high pressure charging valve is reopened.


Operating Procedure (Cont.)

Rock the test assembly to obtain a single phase sample. The presence of gas bubbles inside the chamber can prevent the ball

from moving freely and stop the experiment completely.

Set the temperature of the viscosimeter to the desired value. Allow 3 hours for the temperature to stabilize.

Bring the ball to the hold position, by rotating the test unit 180 degrees.

Turn on the coil and switch to HOLD. The yellow light must be on

Rotate the assembly to the desired angle (70°, 45°, or 23°), this will depend on how viscous the fluid is.

Switch to FALL. The green light must be on. The ball is released and the time to travel is displayed. When the ball hits the bottom, a sound alarm will be triggered.

Calculate the viscosity by using the equation. With the appropriate values for the constant.


Ostwald viscometer

One type of viscometer for liquids is the Ostwald viscometer. In this viscometer, the viscosity is

deduced from the comparison of the times required for a given volume of the tested liquids and of a reference liquid to flow through a given capillary tube under specified initial head conditions. During the measurement

the temperature of the liquid should be kept constant by immersing the instrument in a temperature-controlled water bath.

Two types of Ostwald viscometers.


Calculations for the Ostwald viscometerIn this method

the Poiseuille’s law for a capillary tube with a laminar flow regime is used

t is time required for a given volume of liquid V with density of ρ and viscosity of μ to flow through the

capillary tube of length l and radius r by means of pressure gradient ΔP.

The driving force P at this instrument is ρgl. Then

or

The capillary constant is determined from a liquid with known viscosity.


Description of the Liquid Viscosity Measurement using Capillary TypeThe main objective of

the Liquid Viscosity Measurement is to determine the kinematic

viscosity of Newtonian liquid petroleum products.

For capillary viscometers the time is measured in

seconds for a fixed volume of liquid

to flow under gravity through the capillary at a closely controlled temperature.

The kinematic viscosity is the product of

the measured flow time and the calibration constant of the viscometer. =(Const.*t)

The dynamic viscosity can be obtained by multiplying

the measured kinematic viscosity by the density of the liquid.=Kinematic viscosity* ρ=(Const.*t)*ρ


Definitions, Unit and dimensions:

Dynamic viscosity (μ) is the ratio between the applied shear stress and

the rate of shear and is called coefficient of dynamic viscosity μ.This coefficient is thus

a measure of the resistance to flow of the liquid; it is commonly called the viscosity of the liquid.

Kinematic viscosity (υ) is the ratio μ/ρ where ρ is fluid density.


The experiment procedures:

Select a clean, dry calibrated viscometer having a range covering the estimated viscosity (i.e. a wide capillary for a very viscous

liquid and a narrower capillary for a less viscous liquid).

The flow time should not be less than 200 seconds.

Charge the viscometer: To fill, turn viscometer upside down. Dip tube (2) into the liquid to be

measured while applying suction to tube (1) until liquid reaches mark (8).

After inverting to normal measuring position, close tube (1) before liquid reach mark (3).

Viscometer apparatus


The experiment procedures: (Cont.)

Allow the charged viscometer to remain long enough to reach the room temperature. Read the calibration constants-directly from the viscometer.

Measuring operation: Open tube (1) and measure

the time it takes the liquid to rise from mark (3) to mark (5). Measuring the time for rising from mark (5) to mark (7)

allows viscosity measurement to be repeated to check the first measurement.

If two measurements agree within required error (generally 0.2-0.35%), use the average for calculating the reported kinematic

viscosity.


The experiment Calculations:

Calculate the kinematic viscosity υ from the measured flow time t and the instrument constant by means of the following equation:υ = kinematic viscosity, cSt C = calibration constant,

cSt/s t = flow time, sθ = Hagenbach correction

factor, when t < 400 seconds, it

should be corrected

according to the manual. t > 400 seconds, θ = 0.

Calculate the viscosity μ from the calculated kinematic viscosity υ and the density ρ by means of the following equation:

μ = dynamic viscosity, cpρ avr = average density in

g/cm3 at the same temperature used for measuring the flow time t.

υ = kinematic, cSt.


The experiment report:

Report test results for both the kinematic and

dynamic viscosity.

Calculate the average dynamic viscosity.


the rotational viscosimeter

Other often used viscometers especially for non-Newtonian fluids are the rotational type consisting of two concentric cylinders, with the annulus containing the liquid whose viscosity is to be measured. Either the outer cylinder or the

inner one is rotated at a constant speed, and the rotational deflection of the cylinder becomes a measure of the liquid’s viscosity.

Schematic diagram of the rotational viscometer


Calculations for the rotational viscosimeterWhen the distance between

the cylinders d, is small, we can define the viscosity gradient for laminar flow regime as

R is radius of the inner cylinder (bob) and ω is angular velocity of the outer cylinder (rotor) defined by ω = 2π n.

When the rotor is rotating at a constant angular velocity ω and the bob is held motionless, the torque from the torsion spring on the bob must be equal but opposite in direction to the torque on the rotor from the motor.

The effective area of the applied torque is 2 π.R.h h is length of the cylinder.

The viscous drag on the bob is k.θ.R, k is the torsion constant of the

spring and θ is angular displacement of the instrument in degrees.

which gives

K is the instrument’s constant which is determined by calibration.


1. (KSU) M. Kinawy. “Reservoir engineering laboratory manual" Petroleum and Natural Gas Engineering Department, King Saud University, Riyadh (2009).

2. “Dilatant.” Wikipedia, the free encyclopedia 1 July 2014. Wikipedia. Web. 5 Aug. 2014.

3. (ABT) Torsæter, O., and M. Abtahi. "Experimental reservoir engineering laboratory work book." Department of Petroleum Engineering and Applied Geophysics, Norwegian University of Science and Technology (NTNU), Trondheim (2003). Chapter 4

q923+rfl+l03

Engineering

viscosity viscosity

viscosity temperature

constant viscosity

liquid viscosity

viscosity definition

newtonian fluids

layer of fluid

fluid density