The document describes an experiment to measure the gel strength of drilling mud using a rotational viscometer. Gel strength is a measurement of the forces within a drilling mud under static conditions that cause its viscosity to increase over time. The experiment procedure involves stirring a mud sample, then measuring the torque required to rotate a disk in the sample after 10 seconds and 10 minutes to determine the gel strength.

1. Drilling Engineering-I
Pet-E-211L
Lab Instructor :
Engr. Muhammad Awais Qureshi
Department of Petroleum &
Gas Engineering 5/5/2021

2. Experiment # 05
• Objective:
1) Measurement of gel strength of drilling mud by
viscometer.
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3. Apparatus
• Rotational viscometer,
• Bentonite,
• Water,
• Graduated Cylinder,
• Stirring Rod,
• Balance,
• Beakers
• PPE’s (Personal Protective Equipments)
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4. Related Theory
• Thixotropy :
• The characteristic of a liquid, such as a drilling mud, to form a gelled
structure over the time at static condition and then to liquefy when agitated.
• Gel Strength :-
• The shear stress measured at low shear rate after a mud has set
quiescently for a period of time
(10 seconds and 10 minutes in the standard API procedure. Although measurements after 30 minutes
or 16 hours may also be taken)
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5. • The time-dependent forces in the drilling mud cause an
increase in viscosity as the fluid remains quiescent for a
certain period.
• The gel strength is a measurement of the electrochemical
forces within the fluid under static conditions.
• Its field unit is the same as that of the yield strength.
• The strength is a function of suspended solids, solid contents,
temperature, chemical content and time.
• Usually it is caused by the high concentration of clay.
• Functions of gel strength:
• Gel Strength decreases the settling rate of cuttings when
circulation is stopped/ interrupted.
• Units are lbf/100 sq. ft
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6. 1) More pump pressure required
for "Break Circulation's
2) Lost circulation by pressure
surges.
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Problems Attributed To
High Gel Strength

7. Rotational Viscometer
• Rotational viscometer uses the
idea that the torque required to
turn an object in a liquid is a
function of the viscosity of that
liquid.
• It measures the torque required
to rotate a disk or bob in a liquid
at a known speed.
• Rotational viscometers are
commonly used for measuring
viscosity of Non-Newtonian fluids
.
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8. OFITE-8 SPEED
VISCOMETER
• The Model 800 8-Speed Electronic Oilfield Viscometer is
designed and exclusively manufactured by OFI Testing
Equipment, Inc. It is extensively used worldwide in both
the field and laboratory for precisely measuring the
rheological properties of drilling fluids and cement.
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9. Features
• Speeds are easily changed with a control
knob
• Shear stress values are displayed on a
lighted magnified dial for ease of reading
• Suitable for both field and laboratory use and
uses a motor-driven electronic package to
provide drilling fluid engineers with an
extremely accurate and versatile tool
• Operates anywhere in the world without
flipping switches or re-wiring
• Threaded rotor - mechanically attaches to
the unit the same way every time
• Available with retractable legs for placement
in kits
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10. 5/5/2021

11. Measurement Procedure
1) Stir the sample again for 10 seconds.
2) Set the speed to “GEL” and immediately shut off the
power.
3) As soon as the sleeve stops rotating, wait 10 seconds
and turn the power on while looking at the dial. Record
the maximum dial deflection before the gel breaks. This
is the 10 second gel strength.
4) For the 10 minute gel strength, re-stir the fluid and wait
10 minutes before recording the maximum dial
deflection
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12. Demonstration
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13. Observation and
Calculations
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Time Gel Strength Readings
(lbf/100 sq. ft )
t ( 10 sec)
T (after 10 mins)

14. Precautions
1. Sleeve and bob should be washed after each operation.
2. The rotor bob assembly should be lowered slowly into
the beakers up to the mark.
3. Wear relevant Personal Protective Equipment (PPE)
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15. Viva Voce
Q1) Which role does Gel Strength play in the drilling
process?
Q2) What type of fluids does drilling fluid belong to?
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