Pet E 295 Lab Report #4 & #5
Drilling Fluids
Lab Section H4
Lab Date: March 21st and April 4th 2006
Due Date: April 11th 2006
Prepared by Group #3
Group Members:
……………
Mohammed Abou-Morad
……………
Jackie Chee
……………
Barry Fredrickson
……………
Robert Williamson
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
A. COVER LETTER
B. OBJECTIVE
C. THEORY
I) Density
II) Viscosity
III) Filtration
D. PROCEDURE
I) Preparation
II) Density
III) Viscosity and gel strength
IV) Filtration
E. RECORDED DATA
I) Preparation
II) Mud Density
III) Viscosity
IV) Gel Strength
V) Filtration
F. SAMPLE CALCULATIONS
G. DATA ANALYSIS
I) Viscosity
II) Filtration
H. RESULTS
I. SOURCES OF ERROR
J. CONCLUSION, COMMENTS, REFERENCES
Figure 1: Mud Balance
Figure 2: Flow behavior of Plastic fluid and Newtonian fluid
Figure 3: Schematic diagram of a concentric cylindrical viscometer
Figure 4: Filter Press and Mud Cell
Figure 5: Graph of Filtrate volume vs. Time with corrected linear line
Figure 6: Shear Stress vs. Shear Rate Plot
Based on different rpm on the Fann VG meter
Figure 7: Shear Stress vs. Shear Rate Plot
Based on 600 rpm and 300 rpm readings from normal mud
Figure 8: Shear Stress vs. Shear Rate Plot
Based on 600 rpm and 300 rpm readings from salted mud
Figure 9: Shear Stress vs. Shear Rate Plot
Based on 600 rpm and 300 rpm readings from CMC mud
Figure 10: Volume of Fluid loss vs. Time
Normal Mud
Figure 11: Volume of Fluid loss vs. Time
Salted Mud
Figure 12: Volume of Fluid loss vs. Time
CMC Mud
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Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
NREF 2-052
Markin/CNRL Natural Resources Engineering Facility
116street 91st ave
April 10, 2006
JC Cunha, PhD, P.Eng.
Associate Professor of Petroleum Engineering
Civil & Environmental Eng.
School of Mining & Petroleum Engineering
3-122 Markim CNRL Natural Resources Engineering Facility
Edmonton, Alberta
Canada T6G 2W2
Dear Dr. Cunha,
Drilling mud is important in the petroleum industry. With a big list of functions,
knowing their properties is important. In two 3 hour lab periods, we have learned to
measure the density, viscosity, gel strength, filter cake thickness, and water loss content
of a drilling mud. We also observed how adding different additives, namely, salt and
CMC affects these properties studied.
A test was first done on tap water mixed with 60 grams of bentonite, then 3 grams
of salt with 60 grams of bentonite (to simulate salt water), and finally a test with 1.5
grams of CMC and 60 grams of bentonite. All results yielded a similar density: 1.035
g/cc, 1.040 g/cc, and 1.037 g/cc respectively. The viscosity varied significantly between
all three muds: 23.05 cp, 11.25 cp, and 25.1 cp. The water loss for the first test resulted in
19.2 cc per 30 minutes, the second test lost 35.95 cc per 30 minutes, and the last test gave
out 10.26 cc per 30 minutes. The filter cake thickness for all three runs are as follows,
respectively: 2.567/32 inch, 4.933/32 inch, and 2.067/32 inch.
As shown, a higher viscosity represents less water loss and a thinner filter cake
thickness. The additive of salt does not keep water in the mud well and CMC will not
allow water to be released easily.
I hope these observations will be of good use to you.
Thank you for your time
Sincerely,
……………
……………
Mohammed Abou-Morad
Jackie Chee
……………
……………
Barry Fredrickson
Robert Williamson
Enclosure
Page 3 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
B. OBJECTIVE:
Determination of drilling fluid properties, density, viscosity, gel strength, and
filter cake. We also observe the changes in these properties due to the addition of
different additives. The drilling fluid used adheres to the standard properties of using
900cc of water and 60 grams of bentonite (with other additives added) which is to be
mixed until it is a homogeneous mud.
C. THEORY
Drilling fluid can be classified into three categories: water-base, non-water base
and gaseous (or pneumatic). Most often, bentonite clay is added to give the drilling fluid
more desirable properties. Clay has a few unique properties that are useful in drilling
fluids: they expand to many times their original size when water is added, and they
exhibit thixotropy which is the development of gel strength when fluid is at rest. For a
Newtonian fluid, the gel strength for any given time after it has rested is zero.
The main functions of drilling fluid when drilling are:
( 1 ) To remove debris or cuttings from the well bore,
( 2 ) To clean the bottom of the well bore,
( 3 ) To control subsurface pressure,
( 4 ) To cool the bit, drill pipes and drill collar,
( 5 ) Provide a medium to settle out the cuttings,
( 6 ) To form a filter cake on the walls of the borehole,
( 7 ) To prevent caving-in of the formation,
( 8 ) To suspend the cuttings if the drilling is stopped,
The addition of different additives may affect the properties of the drilling fluid.
Two different additives will be added, salt to simulate salt water as oppose to tap water,
and carboxy-methyl cellulose (CMC) into bentonite and tap water. A small amount is to
be added so the density will not change by much, however we shall observe the change in
the fluid properties.
I) Density
Density is the weight per given volume. Measuring the density of the drilling fluid
is important to determine the buoyancy force induced when drilling. A higher density will
prevent formation fluid from entering the well bore. It is also important for the
calculation of the fluid properties like viscosity. In this lab, the density is determined
using the mud balance shown in Figure 1. The mud cup takes a fixed volume of fluid
sample and by adjusting the rider until balanced, a reading can be taken. This apparatus
has to be calibrated using fresh water.
Page 4 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
Figure 1
Mud Balance
II) Viscosity
Viscosity is the fluid’s resistance to flow. The viscosity of the mud determines the
efficiency and even ability to lift cuttings out of the well bore. The higher the density and
viscosity of the mud, the easier it is to lift cuttings. The viscosity of the drilling fluid
behaves as a plastic or non-Newtonian fluid. A yield stress must be overcome before the
mud will shear. The viscosity will depend on the shear rate at which the measurement
was performed. This can be represented by the figure 2 and the comparison between a
Newtonian fluid and Plastic fluid (Plastic being the drilling mud).
Figure 2
Flow behavior of Plastic fluid and Newtonian fluid
In this lab, the Fann VG meter is used to determine the viscosity of the mud. The
drilling fluid is contained in the annular space between the two concentric cylinders as
shown in figure 3. There is a small gap and the distance of the gap will determine the
Page 5 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
constants to obtain shear rate and shear stress. Six shear rates will be used in this
experiment, set by the apparatus in revolutions per minute: 3rpm, 6rpm, 100rpm, 200rpm,
300rpm and 600rpm. During the test, the reading is taken using the highest rpm so that
the viscosity will not skew due to the gel strength when a low rpm is set.
Figure 3
Schematic diagram of a concentric cylindrical viscometer
The outer cylinder rotates at a constant rate (revolutions per minute) which is set.
The shear rate can be determined using this equation:

  rpm *1.7034

Where:  = Shear Rate (sec-1)
rpm = revolutions per minute
The rotation of the outer cylinder will cause the fluid clinging onto the inner
cylinder, “bob” to rotate if the wall shear is overcome. “Bob” is attached to a spring
which will produce a dial reading from the apparatus. The shear stress is related to the
dial reading with this equation:
  D.R.*1.067
Where:  = Shear Stress (lb/100ft2)
D.R. = dial reading
A conversion from lb/100ft2 to Pascals (Pa) can be done by multiplying 
by 0.478803.
The apparent viscosity of the drilling fluid can be calculating using this equation:
Page 6 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids




Where:  = Apparent viscosity in centipoise (cp)
 = Shear Stress in millipascals (mPa)

 = Shear Rate (sec-1)
With the readings obtained, a graph similar to figure 2 can be plotted. The Plastic
viscosity, Bingham Yield, True yield and Apparent (kinematic) viscosity can be
determined. The dial reading is related to the shear stress by a constant factor of 1.067.
Since this is approximately one, it will be neglected in the calculation for the points on
figure 2. The Plastic viscosity is given by:
Plastic Viscosity = [600 rpm reading] – [300 rpm reading]
Where: Plastic Viscosity is in centipoise (cp)
rpm readings are directly off the apparatus and the constant
factor of 1.067 can be neglected. The instrument is adjusted
so that this represents the linear portion of figure 2
The Bingham yield is related by:
YB = [300rpm reading] – Plastic Viscosity
Where: YB = Bingham Yield (lb/100ft2)
rpm reading is directly off the apparatus
Plastic Viscosity is calculated above (cp)
The True yield is then:
Yt = ¾ * YB
Where: Yt = True Yield (lb/100ft2)
YB = Bingham Yield (lb/100ft2)
And the apparent viscosity can be determined by this equation:
 = [600 rpm reading] / 2
Where:  = apparent viscosity (cp)
rpm reading is directly off the apparatus
Thixotropy is the ability of the fluid to develop gel strength with time. The
thixotropy of the mud can be determined by the difference in the 10 minute and 10
second gel strength. The gel strength is determined by allowing the fluid to rest in the
allocated time unit before inflicting a shear rate at 3 rpm on the apparatus. The maximum
dial reading has to be obtained. The reading will increase substantially before gradually
decreasing. It is important to mix the fluid at the highest rpm before each gel strength
test.
III) Filtration
Page 7 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
A filtration test is done to determine thickness of the mud cake that will form on
the well bore wall to prevent fluid from the rock beds to flow into the well bore and to
prevent the drilling mud from escaping the well bore. It is also important to determine the
permeability of water in the drilling mud so water does not escape too fast resulting in an
increase in viscosity and hindering drilling mud flow in the well bore system. It is
important to know the water loss under pressure in the drilling mud and the mud cake
thickness.
In this lab, we determined the mud cake thickness and water loss volume using a
filter press, and a sheet of Whatman #50 filter paper. The filter press is shown in figure 4.
The mud cell is to be filled with 400cc of drilling mud into the mud cup and the drilling
mud is forced under a pressure of 100 psig. The water will penetrate the filter paper and
the volume of water is collected in the graduated cylinder. The volume of liquid present
is to be recorded in the following time intervals after the mud is subjected to 100 psig:
1min, 2min, 5min, 7.5min, 10min, 15min, 20min, 25min and 30min. The water loss is to
be reported in cc per minute. After 30 minutes, the mud cell is disassembled to obtain the
filter paper. The filter paper contains a layer of mud that is thicker and higher in viscosity
than the initial mud. That is the mud cake and it is to be measured in the units of 1/32 of
an inch.
Figure 4
Filter Press and Mud Cell
With the recorded data, we have 9 readings which will give a linear line. In the
field, it is easier to take the water loss at 7.5 minutes and double that to obtain a linear
line. This is possible based on the empirical formula:
Page 8 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
t2
t1
Where: V2 = Filtrate loss at t2
V1 = Filtrate loss at t1
t1, t2 = arbitrary times
The recorded data will then be plotted on a graph similar to figure 5, with Filtrate
volume vs. Time. The experimental linear line may not intercept at 0 cc filtrate volume.
This can be done by shifting the line down by how many units the y-intercept is above
the origin.
V 2  V 1*
Figure 5
Graph of Filtrate volume vs. Time with corrected linear line
Page 9 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
D. PROCEDURE
I) Preparation:
Normal mixture (tap water + 60 grams of Bentonite)
1. Obtain 900 cc of tap water using a measuring cylinder.
2. Measure approximately 60 grams of Bentonite using the digital scale.
3. Pour the 900 cc of tap water into the blender and turn it on to low.
4. Slowly, and with small amounts, transfer the Bentonite into the blender
mixing it. Do not put too much Bentonite as it may splash right out or you
may lose some in the process.
5. Mix for at least 10 minutes. This will ensure a homogeneous mixture, where
there will be no lumps or any clay clinging to the surface of the blender. Black
lines may be observed, this is due to the impurities in the Bentonite.
6. After 10 minutes has surpassed, your mud mixture is complete. Check to see
if there are any lumps or unmixed sections. If there are, continue mixing for a
little longer.
Salted mixture (tap water + 3 grams of salt + 60 grams of Bentonite)
1. Obtain 1000 grams of tap water into a measuring cylinder using the digital
scale.
2. Measure 3 grams of salt on the digital scale and add it into the 100 grams of
tap water.
3. Mix thoroughly, shaking it well to ensure a homogeneous mixture of salt
water.
4. From the measuring cylinder, obtain 900 cc of salt water into another clean,
dry measuring cylinder. This can be transferred into the blender and turned on
to low.
5. Measure approximately 60 grams of Bentonite using the digital scale.
6. Slowly, and with small amounts, transfer the Bentonite into the blender
mixing it. Do not put too much Bentonite as it may splash right out or you
may lose some in the process.
7. Mix for at least 10 minutes. This will ensure a homogeneous mixture, where
there will be no lumps or any clay clinging to the surface of the blender. Black
lines may be observed, this is due to the impurities in the Bentonite.
8. After 10 minutes has surpassed, your mud mixture is complete. Check to see
if there are any lumps or unmixed sections. If there are, continue mixing for a
little longer.
CMC mixture (tap water + 1.5 grams of CMC + 60 grams of Bentonite)
1. Obtain 900 cc of tap water using a measuring cylinder.
2. Measure approximately 60 grams of Bentonite using the digital scale.
3. Measure approximately 1.5 grams of CMC using the digital scale.
4. Pour the 900 cc of tap water into the blender and turn it on to low.
5. Add the CMC into the blender with water.
6. Slowly, and with small amounts, transfer the Bentonite into the blender
mixing it. Do not put too much Bentonite as it may splash right out or you
may lose some in the process.
Page 10 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
7. Mix for at least 10 minutes. This will ensure a homogeneous mixture, where
there will be no lumps or any clay clinging to the surface of the blender. Black
lines may be observed, this is due to the impurities in the Bentonite.
8. After 10 minutes has surpassed, your mud mixture is complete. Check to see
if there are any lumps or unmixed sections. If there are, continue mixing for a
little longer.
II) Density:
1. Once the drilling fluid is well mixed, it is ready to measure the density of the
drilling fluid.
2. Make sure the mud balance is clean and dry. It can be calibrated, but not in
this lab.
3. Pour the drilling mud into the mud cup until a 1/8th of an inch is left between
the fluid and the brim of the cup. Replace the lid of the cup. Some of the
drilling mud should escape through the opening on the lid. Wipe off all excess
mud from the opening and the side.
4. Place the mud balance on the fulcrum and adjust the rider until the level glass
is balanced.
5. On the rider, there is an arrow pointing towards the mud cup, which is the side
the scale should be taken as. The top reading is in lbs/gallon and should be
read to 2 decimal places. The bottom reading is in g/cc and should be read to 3
decimal places.
6. Put the drilling mud back into blender, clean the mud balance and repeat with
the other mud.
III) Viscosity and gel strength
1. After the drilling fluid is well mixed, pour the drilling fluid into the Fann VG
meter cup until the engraved line on the steel cup.
2. Mount the cup onto the platform, ensuring the notch on the bottom lines up
with the opening on the platform.
3. The platform should be raised until the fluid flows into both the holes on the
top of the concentric cylinder containing the bob. This will ensure the fluid
enters and submerges the bob completely.
4. The Fann VG meter supplied should have 6 speed settings: 3rpm, 6 rpm,
100rpm, 200rpm, 300rpm, and 600rpm. There is a diagram on how to operate
each rpm mode in combination with 3 gear settings and 2 speed settings.
5. Turn the meter on to the highest speed (600rpm) and let it sit for a minute.
6. The readings should start from the highest rpm to the lowest rpm, and
switching back to the highest rpm for a minute in between each rpm reading.
This will ensure the drilling mud does not gel strengthen.
7. Starting with the highest speed, which is 600 rpm – observe the dial reading
and wait till it stabilizes before taking a reading.
8. Switch back to the highest rpm and take the next rpm reading. Repeat till all
the rpm settings are done.
9. Once the readings have been obtained, a gel strength test is to be done.
10. Switch the speed to 600 rpm and let it mix for a minute.
Page 11 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
11. Turn the motor off and start the timer.
12. Switch the speed setting to 3 rpm.
13. Turn the motor back on after 10 seconds if the 10 second gel strength is to be
determined, or 10 minutes if the 10 minute gel strength is to be determined.
Take the highest reading once the motor is on.
14. The gel strength can be repeated for accuracy.
15. When all data are obtained, turn off the Fann VG meter and dispose of the
drilling fluid. Clean the bob and cup thoroughly and use an air drier. Repeat
with different muds.
IV) Filtration
1. The filter press, shown in figure 4, needs a sheet of filter (Whatman #50 filter
paper) to be placed on the base of the mud cell. A rubber gasket is to be
placed to avoid leakage between the base cap and the cell.
2. Pouring approximate 400 cc of mud into the mud cell, and fixing it onto the
base. Tighten the “T” screw and make sure all valves are closed.
3. Simultaneously, turn on the gas pressure valve to 100psi and start the
stopwatch.
4. The graduated cylinder below the mud cell indicates the water loss through
the filtrate.
5. Read the water volume level for the following time intervals from the time
pressure was applied: 1min, 2min, 5min, 7.5min, 10min, 15min, 20min,
25min, and 30 min.
6. If necessary, replace the graduated cylinder quickly without losing the drop of
water. The reading on the new graduated cylinder has to be combined (added)
with the reading of the first one graduated cylinder.
7. After the test is complete, turn the pressure valve supply off.
8. Unscrew the “T” screw and remove the cell with the base.
9. Dumping the mud into the garbage and rinsing the cell gently with water.
10. Unscrew the cell from the base and obtain the filter paper.
11. The filter paper contains a layer of mud which is known as the mud cake.
12. Using the appropriate mud cake thickness measuring apparatus, record the
thickness of a few points and average them.
13. Wash the apparatus thoroughly and dry with air.
14. Repeat the filtration with the other drilling muds.
Page 12 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
K. RECORDED DATA
I) Preparation
900cc of water + 60 grams of Bentonite:
Normal mud
Mass of Container
Mass of Container and Bentonite
Mass of Bentonite
Volume of water used with Bentonite
36.05
96.05
60.00
900
Grams
Grams
Grams
Cc
900cc of water + 3 grams of salt + 60 grams of Bentonite:
Salted mud
Volume of water
1000.92 grams
Volume of water and salt
1004.10 grams
Volume of salt
3.18
grams
Volume of water used with Bentonite 900
cc
Mass of Bentonite
60.00
grams
900cc of water + 1.5 grams of CMC + 60 grams of Bentonite:
CMC mud
Mass of Bentonite
60.10 grams
Mass of Bentonite and CMC
61.64 grams
Volume of water used with Bentonite 900
cc
II) Mud Density:
Normal mud
Density Reading 1.035 g/cc = 8.60 lb/gallons
Salted mud
Density Reading 1.040 g/cc = 8.65 lb/gallons
CMC mud
Density Reading 1.037 g/cc = 8.61 lb/gallons
III) Viscosity:
Normal mud Salted mud CMC mud
rpm
Dial readout
600
46.1
22.5
50.2
300
38.1
17.6
38.2
200
33.9
15.9
31.9
100
29.5
13.8
23.5
6
25.1
12.1
8.7
3
26.2
10.4
7.4
For the 3 grams of salt + 60 grams of Bentonite, and 1.5 grams of CMC + 60
grams of Bentonite, the bob fell out half way through the run.
Page 13 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
IV) Gel Strength:
Normal mud Salted mud CMC mud
Run #
Maximum Dial Readout
10 seconds
1st
22
10
6
nd
2
23
10
6
rd
3
23
10
n/a
4th
23
n/a
n/a
Average
22.75
10
6
10 minutes
1st
2nd
Average
36
36
36
13.8
n/a
13.8
24
n/a
24
V) Filtration:
Time (minutes)
1
2
5
7.5
10
15
20
25
30
Normal mud Salted mud CMC mud
Volume of water (mL)
3.1
5.65
<1
4.7
8.45
1.35
7.6
14.16
3.11
9.6
17.50
4.19
11.2
20.37
5.09
14.0
25.10
6.60
16.3
29.29
7.80
18.3
32.77
8.80
19.2
35.95
9.60
Filter Cake Thickness (1/32 inch)
1st
2.6
2nd
2.6
rd
3
2.5
Average
2.567
Page 14 of 24
4.7
5.2
4.9
4.933
1.5
2.4
2.3
2.067
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
F. SAMPLE CALCULATIONS
For Normal mud (60 grams of Bentonite only)
Shear Stress (  )
  D.R.*1.067
 = 46.1 * 1.067
 = 49.1887 lb/100ft2
 = 49.1887 * 0.478803
 = 23.5515 Pa

Shear rate (  )

  rpm *1.7034

 = 600*1.7034

 = 1022.04 s-1
Apparent Viscosity (  )

 

 = 23551.5mPa /1022.04s-1
 = 23.04381cp
Plastic Viscosity = [600 rpm reading] – [300 rpm reading]
Plastic Viscosity = 46.1 - 38.1
Plastic Viscosity = 8
Bingham Yield (YB)
YB = [300rpm reading] – Plastic Viscosity
YB = 38.1 – 8
YB = 30.1 lb/100ft2
YB = 30.1*0.478803 = 14.4120 Pa
True Yield (Yt)
Yt = ¾ * YB
Yt = ¾ * 30.1
Yt = 22.575 lb/100ft2
Yt = 22.575*0.478803 = 10.8089 Pa
Apparent Viscosity (  )
 = [600 rpm reading] / 2
 = 46.1/2
 = 23.05cp
Thixotropy
Thixotropy = [Gel strength @ 10 minutes] – [Gel strength @ 10 seconds]
Thixotropy = 36 – 22.75
Thixotropy = 13.25cp
Page 15 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
G. DATA ANALYSIS
I) Viscosity
Normal mud (60 grams of Bentonite only)

rpm
D.R. Shear Stress 
Viscosity 
Shear Rate 
600 1022.04 s-1 46.1 23.5517 Pa
23.044 cp
-1
300
511.02 s
38.1 19.4646 Pa
38.090 cp
200
340.68 s-1 33.9 17.3189 Pa
50.836 cp
100
170.34 s-1 29.5 15.0710 Pa
88.476 cp
-1
6 10.2204 s
25.1 12.8232 Pa 1254.663 cp
3
5.1102 s-1 26.2 13.3851 Pa 2619.297 cp
Plastic Viscosity
Bingham Yield
YB
True Yield
Yt
Apparent Viscosity 
Thixotropy
8
30.1
22.575
23.05
13.25
lb/100ft2 14.4120 Pa
lb/100ft2 10.8089 Pa
cp
cp
Salted mud (3 grams of salt and 60 grams of Bentonite only)

rpm
D.R. Shear Stress 
Viscosity 
Shear Rate 
600 1022.04 s-1 22.5 11.4949 Pa
11.247 cp
300
511.02 s-1 17.6
8.9915 Pa
17.029 cp
-1
200
340.68 s
15.9
8.1230 Pa
25.544 cp
100
170.34 s-1 13.8
7.0502 Pa
51.088 cp
-1
6 10.2204 s
12.1
6.1817 Pa 594.164 cp
3
5.1102 s-1 10.4
5.3132 Pa 1039.721 cp
Plastic Viscosity
4.9
Bingham Yield
YB 12.7 lb/100ft2 6.0808 Pa
True Yield
Yt 9.525 lb/100ft2 4.5606 Pa
Apparent Viscosity  11.25 cp
Thixotropy
3.8 cp
CMC mud (1.5 grams of CMC + 60 grams of Bentonite only)

rpm
D.R. Shear Stress 
Viscosity 
Shear Rate 
600 1022.04 s-1 50.2 25.6463 Pa 25.093 cp
300
511.02 s-1 38.2 19.5157 Pa 36.962 cp
200
340.68 s-1 31.9 16.2972 Pa 51.249 cp
100
170.34 s-1 23.5 12.0057 Pa 86.998 cp
6 10.2204 s-1
8.7
4.4447 Pa 427.209 cp
3
5.1102 s-1
7.4
3.7805 Pa 739.801 cp
Page 16 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
Plastic Viscosity
12
Bingham Yield
YB 26.2 lb/100ft2 12.5446 Pa
True Yield
Yt 19.65 lb/100ft2 9.4084 Pa
Apparent Viscosity 
25.1 cp
Thixotropy
18 cp
Figure 6 shows a plot of the calculated shear stress at all the shear rates for all 6
rpm levels during the experiment. Because the drilling fluid is non-Newtonian, a line of
best fit cannot be used to represent the relation between the shear stress and shear rate.
Rather the Bingham yield has to be determined and the true yield as well. A better
representation is on Figure 7, 8 and 9 for all three different drilling muds.
Shear Stress vs. Shear Rate
30
25
Shear Stress (pa)
20
15
10
5
0
0
200
400
600
800
Shear Rate (1/s)
Normal Mixture
Salt Mixture
CMC Mixture
Figure 6
Shear Stress vs. Shear Rate Plot
Based on different rpm on the Fann VG meter
Page 17 of 24
1000
1200
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
Shear Stress vs. Shear Rate
25
Shear Stress (Pa)
20
15
10
5
0
0
200
400
600
800
1000
1200
Shear Rate (1/s)
600rpm and 300rpm
Bingham Yield
True Yield
Linear (600rpm and 300rpm)
Figure 7
Shear Stress vs. Shear Rate Plot
Based on 600 rpm and 300 rpm readings from normal mud
Shear Stress vs. Shear Rate
12
10
Shear Stress (Pa)
8
6
4
2
0
0
200
400
600
800
1000
Shear Rate (1/s)
600rpm and 300rpm
Bingham Yield
True Yield
Linear (600rpm and 300rpm)
Figure 8
Shear Stress vs. Shear Rate Plot
Based on 600 rpm and 300 rpm readings from salted mud
Page 18 of 24
1200
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
Shear Stress vs. Shear Rate
30
25
Shear Stress (Pa)
20
15
10
5
0
0
200
400
600
800
1000
1200
Shear Rate (1/s)
600rpm and 300rpm
Bingham Yield
True Yield
Linear (600rpm and 300rpm)
Figure 9
Shear Stress vs. Shear Rate Plot
Based on 600 rpm and 300 rpm readings from CMC mud
II) FILTRATION:
The water loss vs. the time has been plotted and is shown in figure 10, 11
and 12. Figure 10 shows the water loss for the normal mud. The best fit line
obtained from the data points indicated a water loss at 30 minutes of 20.991cc.
The corrected curve requires a shift of 4.5027 units down and the water loss at 30
minutes for this is 16.488cc.
Page 19 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
Volume of Fluid vs. Time
25.0
20.0
Volume of Fluid (cc)
y = 0.5496x + 4.5027
Experimental Data
15.0
y = 0.5496x
Corrected Curve
10.0
5.0
0.0
0
5
10
15
20
25
30
35
Time (Minutes)
Figure 10
Volume of Fluid loss vs. Time
Normal Mud
Volume of Fluid vs. Time
45.00
40.00
y = 1.0068x + 8.1066
Experimental Data
35.00
Volume of Fluid (cc)
30.00
y = 1.0068x
Corrected Curve
25.00
20.00
15.00
10.00
5.00
0.00
0
5
10
15
20
Time (minutes)
Figure 11
Volume of Fluid loss vs. Time
Salted Mud
Page 20 of 24
25
30
35
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
Figure 11 shows the water loss for the Salted mud. The best fit line
obtained from the data points indicated a water loss at 30 minutes of 38.311cc.
The corrected curve requires a shift of 8.1066 units down and the water loss at 30
minutes for this is 30.204cc.
Volume of Fluid vs. Time
12.00
10.00
y = 0.2835x + 1.7594
Experimental Data
Volume of Fluid (cc)
8.00
y = 0.2835x
Corrected Curve
6.00
4.00
2.00
0.00
0
5
10
15
20
25
30
35
Time (minutes)
Figure 12
Volume of Fluid loss vs. Time
CMC Mud
Figure 12 shows the water loss for the CMC mud. The best fit line
obtained from the data points indicated a water loss at 30 minutes of 10.264cc.
The corrected curve requires a shift of 1.7594 units down and the water loss at 30
minutes for this is 8.505cc.
Page 21 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
H. RESULTS
Drilling mud with 60 grams of Bentonite only:
Density
1.035
Viscosity@600rpm with constant factor
23.044
Bingham Yield
14.4120
True Yield
10.8089
Apparent Viscosity
23.05
Thixotropy
13.25
Water loss from experiment
19.2
Water loss with corrected curve
16.488
Filter Cake Thickness
2.567/32
g/cc
cp
Pa
Pa
cp
cp
cc per 30 minutes
cc per 30 minutes
inch
Drilling mud with 3 grams of salt and 60 grams of Bentonite only:
Density
1.040 g/cc
Viscosity@600rpm with constant factor
11.247 cp
Bingham Yield
6.080 Pa
True Yield
4.5606 Pa
Apparent Viscosity
11.25 cp
Thixotropy
3.8 cp
Water loss from experiment
35.95 cc per 30 minutes
Water loss with corrected curve
30.204 cc per 30 minutes
Filter Cake Thickness
4.933/32 inch
Drilling mud with 1.5grams of CMC and 60 grams of Bentonite only:
Density
1.037 g/cc
Viscosity@600rpm with constant factor
25.093 cp
Bingham Yield
26.2 Pa
True Yield
19.65 Pa
Apparent Viscosity
25.1 cp
Thixotropy
18 cp
Water loss from experiment
10.26 cc per 30 minutes
Water loss with corrected curve
8.505 cc per 30 minutes
Filter Cake Thickness
2.067/32 inch
I. SOURCES OF ERROR
Comparison of the viscosity obtained from the 600rpm reading with constant
factor and viscosity without the constant factor:
Normal mud:
%error 
CMC mud:
23.044  23.05
23.044
%error = 0.026%
*100
Page 22 of 24
%error 
25.093  25.1
25.093
%error = 0.028%
*100
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
Salted mud:
%error 
11.247  11.25
11.247
%error = 0.027%
*100
All three muds yielded a low percentage of error between using the constant
factor and not. Therefore, the viscosity, at high shear rate can be determined easily using
this apparatus by diving the reading by two.
The actual water loss from the experiment compared to the water loss after
deriving a linear relation yields such errors:
Normal mud:
%error 
19.2  16.488
19.2
%error = 14.125%
CMC mud:
10.26  8.505
%error 
*100
10.26
%error = 17.105%
*100
Salted mud:
%error 
35.95  30.204
35.95
%error = 15.983%
* 100
All three muds gave a reasonably high percentage of error. However, due to some
other factors that might affect the water loss volume, the linearized curve can be accepted
as a way of determining the water loss at any given time, especially at 30 minutes.
The sources of these errors may come from the water used. In the experiment, tap
water was used which contains a lot of impurities that may have reacted with the mud,
affecting the mixture. The water temperature may also affect mud homogeneity because a
higher water temperature will mix the bentonite better. A way to prevent such error is to
ensure that all tests use the same source of water and the same water temperature for all
the experiments.
The bentonite used in this experiment was not pure bentonite. When mixing the
mud, black lines appeared from the standing wave. These black lines show the impurities
in the mud. Even though pure bentonite is not used in the drilling rig, the same type of
bentonite or the same source (brand) is to be used to ensure the drilling muds have the
same composition of impurities and bentonite. Small amount of impurities can yield a
potentially large difference in results.
When determining the density of the mud, it is quite possible that some dried mud
was on the side of the cup. Such impurities may have skewed the balance scale. There
may have also been some mud stuck in some hard to clean spots. The mud balance may
also have some dents which adds more mud volume. Both of these errors may result in a
higher density recorded.
In the viscosity calculations, the data results corresponding to the lowest shear
rate are neglected. This is because the bob may be slipping and it does not represent the
Page 23 of 24
Group #3
Pet E Lab Report #4 & #5
Drilling Fluids
shear stress that the fluid is experiencing. Rotation speeds less than 6 rpm should be
neglected. Because the rpms are so slow, thixotropy may be occurring in which the mud
is strengthening up (gel strength). The mud is not experiencing enough movement, or
shearing, the mud may be standing still and strengthen. In the experiment with the Fann
VG meter, the bob fell off twice with the salted mud and CMC mud. This occurred at low
rpms showing the shear stress inflicted on the mud by the bob cannot overcome the mud
after it has gel strengthened. Only high rpm readings are valid.
During the filtration test, especially with the salted mud run, the stopwatch time
and the time from the pressure is applied may be out of sync. This is due to a human error
in which a valve was left open. This caused a bit more water to filtrate through before
starting the time. This test required a person to take a water level reading when the time
interval has surpassed. There may be inaccuracy in the human reading because of the
limited time allowed for the person to take the reading. The first few minutes of reading
were difficult because the water dripping was at a high rate. Each drop of water made the
meniscus to “wave” and taking a reading was difficult. There were also a few times when
an air bubble was trapped and taking an accurate reading would be hard. For the salted
mud run, because a lot of water filtrate was extracted, two different graduated cylinders
had to be used. When switching, a few drops landed on the side of the cylinders, and did
not fall straight down. This may have reduced the amount of water measured. A possible
way of preventing such tedious readings would be to measure the mass of water present
using a digital scale. A mass reading would be more accurate; however the density of the
water extracted needs to be determined.
The filter cake measurement was very difficult. The surface was not uniformly
flat. Running the filter paper with water may have resulted in a small loss in height of the
filter cake. Direct water contact will wash away some of the filter cake. This can be easily
prevented by dipping the filter cake into a basin of water and gently rinsing. The faucet
on the sink only gave turbulent water flow.
The time between each reading may not have been sufficient for the mud to
stabilize. It is very important to be patient and give sufficient time for the reading to
stabilize, especially in the viscosity test, where the dial reading fluctuates with time.
J. CONCLUSION, COMMENTS, REFERENCES
Adding different additives can change the property of drilling mud. In this lab, we
examined a simple 60 grams of bentonite mixture (tap water mixture), a 3 grams of salt
and 60 grams of bentonite mixture (salt water mixture), and a 1.5 grams of CMC and 60
grams of bentonite mixture (CMC mixture). The addition of salt is to simulate salt water
mixed with bentonite.
With the normal mixture, water loss is ample and this produces a pudding like
mixture with a high viscosity. With the salt water mixture, the amount of salt water
absorbed by the bentonite is less because the rate of water loss was high. This will
produce a chocolate milk-like mixture with a lower viscosity. The CMC mixture allows
for more water to be absorbed by the bentonite due to the low rate of water loss and this
creates a honey like mud with a really high viscosity.
Data Source:
Pet E 295 Lab Manual “Drilling Fluids”
th
2006)
www.wikipedia.org (April 5
Figure 1 source (mud balance): http://www.mst.dk/udgiv/Publikationer/2001/87-7944-820-8/html/kap01.htm (April 5
Page 24 of 24
th
2006)