OBJECTIVE:



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

A. COVER LETTER Page 3

B. OBJECTIVE Page 4

C. THEORY Page 4

I) Density Page 4

II) Viscosity Page 5

III) Filtration Page 8

D. PROCEDURE Page 10

I) Preparation Page 10

II) Density Page 10

III) Viscosity and gel strength Page 11

IV) Filtration Page 12

E. RECORDED DATA Page 13

I) Preparation Page 13

II) Mud Density Page 13

III) Viscosity Page 13

IV) Gel Strength Page 14

V) Filtration Page 14

F. SAMPLE CALCULATIONS Page 15

G. DATA ANALYSIS Page 15

I) Viscosity Page 16

II) Filtration Page 19

H. RESULTS Page 22

I. SOURCES OF ERROR Page 22

J. CONCLUSION, COMMENTS, REFERENCES Page 24

Figure 1: Mud Balance Page 5

Figure 2: Flow behavior of Plastic fluid and Newtonian fluid Page 5

Figure 3: Schematic diagram of a concentric cylindrical viscometer Page 6

Figure 4: Filter Press and Mud Cell Page 8

Figure 5: Graph of Filtrate volume vs. Time with corrected linear line Page 9

Figure 6: Shear Stress vs. Shear Rate Plot Page 17

Based on different rpm on the Fann VG meter

Figure 7: Shear Stress vs. Shear Rate Plot Page 18

Based on 600 rpm and 300 rpm readings from normal mud

Figure 8: Shear Stress vs. Shear Rate Plot Page 18

Based on 600 rpm and 300 rpm readings from salted mud

Figure 9: Shear Stress vs. Shear Rate Plot Page 19

Based on 600 rpm and 300 rpm readings from CMC mud

Figure 10: Volume of Fluid loss vs. Time Page 20

Normal Mud

Figure 11: Volume of Fluid loss vs. Time Page 20

Salted Mud

Figure 12: Volume of Fluid loss vs. Time Page 21

CMC Mud

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

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.

[pic]

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).

[pic]

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 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.

[pic]

The outer cylinder rotates at a constant rate (revolutions per minute) which is set. The shear rate can be determined using this equation:

[pic]

Where: [pic] = 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:

[pic]

Where: [pic] = Shear Stress (lb/100ft2)

D.R. = dial reading

A conversion from lb/100ft2 to Pascals (Pa) can be done by multiplying [pic] by 0.478803.

The apparent viscosity of the drilling fluid can be calculating using this equation:

[pic]

Where: [pic] = Apparent viscosity in centipoise (cp)

[pic] = Shear Stress in millipascals (mPa)

[pic] = 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:

[pic] = [600 rpm reading] / 2

Where: [pic] = 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

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.

[pic]

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:

[pic]

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.

[pic]

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.

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.

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.

K. RECORDED DATA

I) Preparation

900cc of water + 60 grams of Bentonite:

Normal mud

|Mass of Container |36.05 |Grams |

|Mass of Container and Bentonite |96.05 |Grams |

|Mass of Bentonite |60.00 |Grams |

|Volume of water used with Bentonite |900 |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.

IV) Gel Strength:

| |Normal mud |Salted mud |CMC mud |

|Run # |Maximum Dial Readout |

|10 seconds |

|1st |22 |10 |6 |

|2nd |23 |10 |6 |

|3rd |23 |10 |n/a |

|4th |23 |n/a |n/a |

|Average |22.75 |10 |6 |

| |

|10 minutes |

|1st |36 |13.8 |24 |

|2nd |36 |n/a |n/a |

|Average |36 |13.8 |24 |

V) Filtration:

| |Normal mud |Salted mud |CMC mud |

|Time (minutes) |Volume of water (mL) |

|1 |3.1 |5.65 |< 1 |

|2 |4.7 |8.45 |1.35 |

|5 |7.6 |14.16 |3.11 |

|7.5 |9.6 |17.50 |4.19 |

|10 |11.2 |20.37 |5.09 |

|15 |14.0 |25.10 |6.60 |

|20 |16.3 |29.29 |7.80 |

|25 |18.3 |32.77 |8.80 |

|30 |19.2 |35.95 |9.60 |

| |

|Filter Cake Thickness (1/32 inch) |

|1st |2.6 |4.7 |1.5 |

|2nd |2.6 |5.2 |2.4 |

|3rd |2.5 |4.9 |2.3 |

|Average |2.567 |4.933 |2.067 |

F. SAMPLE CALCULATIONS

For Normal mud (60 grams of Bentonite only)

Shear rate ([pic])

[pic]

[pic]= 600*1.7034

[pic]= 1022.04 s-1

Shear Stress ([pic])

[pic]

[pic]= 46.1 * 1.067

[pic]= 49.1887 lb/100ft2

[pic]= 49.1887 * 0.478803

[pic]= 23.5515 Pa

Apparent Viscosity ([pic])

[pic]

[pic]= 23551.5mPa /1022.04s-1

[pic]= 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 ([pic])

[pic] = [600 rpm reading] / 2

[pic] = 46.1/2

[pic] = 23.05cp

Thixotropy

Thixotropy = [Gel strength @ 10 minutes] – [Gel strength @ 10 seconds]

Thixotropy = 36 – 22.75

Thixotropy = 13.25cp

G. DATA ANALYSIS

I) Viscosity

Normal mud (60 grams of Bentonite only)

|rpm |Shear Rate [pic] |D.R. |Shear Stress [pic] |Viscosity[pic] |

|600 |1022.04 |s-1 |46.1 |23.5517 |Pa |23.044 |cp |

|300 |511.02 |s-1 |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 |

|6 |10.2204 |s-1 |25.1 |12.8232 |Pa |1254.663 |cp |

|3 |5.1102 |s-1 |26.2 |13.3851 |Pa |2619.297 |cp |

|Plastic Viscosity | |8 | | | |

|Bingham Yield |YB |30.1 |lb/100ft2 |14.4120 |Pa |

|True Yield |Yt |22.575 |lb/100ft2 |10.8089 |Pa |

|Apparent Viscosity |[pic] |23.05 |cp | | |

|Thixotropy | |13.25 |cp | | |

Salted mud (3 grams of salt and 60 grams of Bentonite only)

|rpm |Shear Rate [pic] |D.R. |Shear Stress [pic] |Viscosity[pic] |

|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 |

|200 |340.68 |s-1 |15.9 |8.1230 |Pa |25.544 |cp |

|100 |170.34 |s-1 |13.8 |7.0502 |Pa |51.088 |cp |

|6 |10.2204 |s-1 |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 |[pic] |11.25 |cp | | |

|Thixotropy | |3.8 |cp | | |

CMC mud (1.5 grams of CMC + 60 grams of Bentonite only)

|rpm |Shear Rate [pic] |D.R. |Shear Stress [pic] |Viscosity[pic] |

|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 |

|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 |[pic] |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.

[pic]

[pic]

[pic]

[pic]

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.

[pic]

[pic]

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.

[pic]

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.

H. RESULTS

Drilling mud with 60 grams of Bentonite only:

|Density |1.035 |g/cc |

|Viscosity@600rpm with constant factor |23.044 |cp |

|Bingham Yield | 14.4120 |Pa |

|True Yield | 10.8089 |Pa |

|Apparent Viscosity | 23.05 |cp |

|Thixotropy | 13.25 |cp |

|Water loss from experiment | 19.2 |cc per 30 minutes |

|Water loss with corrected curve | 16.488 |cc per 30 minutes |

|Filter Cake Thickness | 2.567/32 |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:

[pic]

%error = 0.026%

CMC mud:

[pic]

%error = 0.028%

Salted mud:

[pic]

%error = 0.027%

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:

[pic]

%error = 14.125%

CMC mud:

[pic]

%error = 17.105%

Salted mud:

[pic]

%error = 15.983%

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 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”

(April 5th 2006)

Figure 1 source (mud balance): (April 5th 2006)

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[pic]

Figure 1

Mud Balance

[pic]

Figure 2

Flow behavior of Plastic fluid and Newtonian fluid

[pic]

Figure 3

Schematic diagram of a concentric cylindrical viscometer

[pic]

Figure 4

Filter Press and Mud Cell

[pic]

Figure 5

Graph of Filtrate volume vs. Time with corrected linear line

[pic]

Figure 6

Shear Stress vs. Shear Rate Plot

Based on different rpm on the Fann VG meter

[pic]

Figure 7

Shear Stress vs. Shear Rate Plot

Based on 600 rpm and 300 rpm readings from normal mud

[pic]

Figure 8

Shear Stress vs. Shear Rate Plot

Based on 600 rpm and 300 rpm readings from salted mud

[pic]

Figure 9

Shear Stress vs. Shear Rate Plot

Based on 600 rpm and 300 rpm readings from CMC mud

[pic]

Figure 10

Volume of Fluid loss vs. Time

Normal Mud

[pic]

Figure 11

Volume of Fluid loss vs. Time

Salted Mud

[pic]

Figure 12

Volume of Fluid loss vs. Time

CMC Mud

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