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Pet E 367Lab Report #1

Yield of Bentonite and Attapulgite ClaysRheological Characterization of Water-Base Drilling Fluids

Experiment Date: January 31 2007

Prepared by: Jackie Chee (1103396)Group #7Beattie L.Branch T.

Jackie Chee (1103396) February 13 2007Lab Report #1

NREF 2-052Markin/CNRL Natural Resources Engineering Facility116street 91st ave

February 13, 2007

Barkim DemirdalPhD Candidate at Petroleum Engineering Department7-134 Markim CNRL Natural Resources Engineering FacilityEdmonton, AlbertaCanada T6G 2W2

Dear Mr. Demirdal,

Drilling mud is important in the petroleum industry. Drilling mud can be composed of various types of clay. All the clays have their unique properties and when prepared with water, they will exhibit different viscosity, gel strength, and most importantly, the rheological characteristic of the drilling mud. We are required to observe the difference between Bentonite, and Attapulgite clay in both salt water and fresh water. It was also required to differentiate the few non-Newtonian fluid models, and determine the model associated with Bentonite, and Xanthan Gum.

It is clear that Bentonite and Attapulgite give different characteristic to the drilling mud. Bentonite has a low yield of clay and it is highly ineffective in salt water. Attapulgite have a high yield of clay and it does not shown any significant signs of swelling. Bentonite encountered severe swelling when mixed with fresh water. Overall, Attapulgite would be a better choice when making drilling mud.

Bentonite with fresh water exhibits Bingham Plastic properties while the Xanthan Gum with fresh water showed a fluid with a Power Law model.

I hope these observations will be of good use to you.

Thank you for your time

Sincerely,

……………………………..(Jackie Chee)

Enclosure

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Objective

This lab is primarily divided into 2 parts. Part 1 of this lab is to determine how bentonite and attapulgite clay affects viscosity in both water and salt water. Part 2 is to determine the rheological model describing the relation between shear stress and shear rate in a water based drilling fluid.

Theory and concept

Properties of water based drilling mud are controlled mainly by the type of clay added to the drilling fluid to change its properties for better wellbore efficiency. The first part of the lab will produce twelve samples. There will be bentonite or attapulgite added to either salt water or water. The amount of clay added will be 3, 6 and 9% of the weight of water. The density and viscosity will be determined. Density will be determined using the mud balance; and viscosity will be determined using the Fann VG meter (rotational viscometer). There will also be a marsh funnel used to determine relative viscosity to water. Water will only be used for this part of the experiment.

Mud 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 and the hydrostatic pressure the drilling fluid acts at the bottom-hole pressure. A higher density will prevent formation fluid from entering the well bore. 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.

Figure 1Mud Balance

Source: http://www2.mst.dk/udgiv/Publikationer/2001/87-7944-820-8/html/kap01.htm

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Figure 2Schematic diagram of a concentric

cylindrical viscometer


Thixotropy

Thixotropy or the Gel strength is measured at a low shear stress after allowing it to thicken/sit for a given amount of time (10 seconds and 10 minutes by API standards). The strength of the mud cake formed will help in preventing water from entering the wellbore, as well as the drilling fluid circulating in the wellbore to leak out into a fracture.

Viscosity

Part 1

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. Addition of different types of clay will affect the viscosity as well as the use of salt water as oppose to plain water. Using an API standard Fann VG meter, the apparent viscosity is defined as:

μApp=[600 rpmdial reading]

2

Part 2

The Fann VG meter also has various rotation speeds, all of which is useful to determine the drilling fluid rheological model for shear stress to shear rate. The main components will be two cylinders; one will be referred as the Rotor, and the other the Bob. The Rotor is the external cylinder that is connected to the motor giving it a constant angular velocity. The inner cylinder, the Bob is connected to a spring that gives a dial read out. Both cylinders are submerged into the fluid and there is a small annular space in between the Rotor and Bob; when the Rotor is rotating, the fluid will cause a torque on the Bob. Depending on the dimensions, the Fann VG meter used had this relation to shear stress:

τ=θ

Where: τ = shear stress [lbf/100 ft2]θ =Dial reading

The shear rate is determined by:

γ=1.7∗rpm

Where: γ= shear rate [sec-1]rpm = revolutions per minute

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Figure 3Newtonian Model

Figure 5Power Law Model


Most Drilling fluids are non-Newtonian fluids, either viscosity changes with shear rate (ie. Power Law Model or Herschel-Bulkley Model), or a plastic yield must be overcome (ie. Bingham Plastic Model).

A Newtonian model is the simplest. The shear stress is directly proportional to the shear rate as shown in figure 2. Common day liquids are Newtonian like water, honey and oil. The constant proportionality relating the two is called viscosity.

A Bingham Plastic Model is similar to a Newtonian model; however it requires a plastic yield to be overcome before any shearing in the fluid will occur. The relation between shear stress and shear rate is shown in figure 3 and can be expressed as:

τ=τ y+μp∗γ

μp=θ600−θ300

τ y=θ300−μp

Where: = Shear stress τ [lbf/100 ft2]τy = yield point [lbf/100 ft2]μp = Plastic Viscosity [cp]γ = Shear Rate [sec-1]θ600 = dial reading at 600rpmθ300 = dial reading at 300rpm

A Power Law Model is similar to a Newtonian model, however it has no linearity as shown in figure 4. The shear rate and shear stress are related through an exponential term, ‘n’ which is the flow behavior index. A power law model can be expressed as:

τ=K∗(γ )n

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Figure 4Bingham Plastic Model

Figure 6Herschel-Bulkley Model


n=3.322∗log (θ600θ300

)

K=510∗θ300(511)n

Where: = Shear stress τ [lbf/100 ft2]K= Consistency index [lbf/100 ft2]γ = Shear Rate [sec-1]n = flow behavior indexθx = dial reading at x rpm

Flow behavior index ‘n’

Type of fluid

<1 Pseudoplastic, or shear thinning; an increase in shear rate results in a decrease in viscosity

1 Newtonian; shear rate and shear stress are directly proportional

>1 Dilatants, or shear thickening; an increase in shear rate results in an increase in viscosity

A Herschel-Bulkley Model is basically a Power Law model with a Bingham plastic model combined together. A plastic yield is required to initiate flow, and once the fluid is viscous, the relation between shear stress and shear rate is similar to one of the Power Law Model. This can be shown in figure 5. This can be express as:

τ=τ y+K∗(γ )n

Where: = Shear stress τ [lbf/100 ft2]K= Consistency index [lbf/100 ft2]

γ = Shear Rate [sec-1]n = flow behavior indexτ y = Yield Stress [lbf/100 ft2]

With four different models in mind, the selection of the appropriate model is done by plotting shear stress as a function of shear rate will give one of the 4 curves. Linear regression is used to determine the line of best fit. The two lowest rpm reading, usually 3rpm and 6rpm can be neglected from the plotting. The low rpm give an inaccurate reading because the fluid is almost at a stand still and gel strengthening is occurring.

Experimental Procedure

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Part 1

1. Calibrate mud balance using fresh water. (Fresh Water Density at 21 C): 8.3 lb/gal ̊2. Measure the funnel viscosity of water at room temperature. (Water: 26 seconds)3. Twelve samples will be prepared in this lab section. Six of these will be mixed using fresh water, and

the other six with salt water. Half of those six samples, three samples, will be mixed using 3%, 6% or 9% of Bentonite or Attapulgite by weight of water.

Fresh Water Salt Water (20,000 ppm NaCl)Bentonite Attapulgite Bentonite AttapulgiteEach sample will be mixed with 3%, 6% or 9% of clay by weight of water.

4. Obtain 350cc of either fresh or salt water in the mixing cup and start blender.5. Obtain right amount of clay from bulk container.6. Using a spatula, slowly and carefully, add reasonable amounts of clay into the mixing cup while

blender is on. Be careful with spatula hitting the mixer and clay dust puffing into the air. Avoid inhaling clay dust.

7. Mix sample for a minimum of 10 minutes or when sample is well mixed.8. Place sample into Fann VG viscometer and measure apparent viscosity of sample at 600 rpm.

Apparent viscosity can be calculated using formula from theory.9. Measure density of sample using mud balance.10. Dispose of sample properly, clean equipment and repeat with the other samples until done.

Part 2

1. Calibrate mud balance using fresh water. (Fresh Water Density at 21 C): 8.3 lb/gal ̊2. Measure the funnel viscosity of water at room temperature. (Water: 26 seconds)3. Two samples will be prepared in this lab section. Both will use fresh water. One sample will have 35

grams of bentonite, and the either will have 4 grams of Xanthan Gum.4. Obtain 350cc of either fresh or salt water in the mixing cup and start blender.5. Obtain right amount of clay from bulk container.6. Using a spatula, slowly and carefully, add reasonable amounts of clay into the mixing cup while

blender is on. Be careful with spatula hitting the mixer and clay dust puffing into the air. Avoid inhaling clay dust.

7. Mix sample for a minimum of 10 minutes or when sample is well mixed.8. Record mud temperature using digital thermometer. Place thermometer well in the center of the

mud, avoiding contact with the mixing cup.9. Measure density of sample using mud balance.10. Place sample into Fann VG viscometer and record dial readings at 600, 300, 200, 100, 6 and 3 rpms.11. Determine 10 sec and 10 minute gel strength. 12. Dispose of sample properly, clean equipment and repeat with the other samples until done.

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Results and Calculations

Recorded Data

Part 1

Water PropertiesDensity: 8.3 ppgFunnel Viscosity: 28.54 sec/qt

Mud Apparent Viscosity, µApp

Fresh Water Salt WaterClay Content Bentonite Attapulgite Bentonite Attapulgite

3% 6.5 cp 4.5 cp 3.5 cp 5.5 cp6% 16.6 cp 33.9 cp 3.4 cp 30.2 cp9% 37.0 cp 51.0 cp 6.0 cp 79.0 cp

Mud Density, ρmud

Fresh WaterClay Content Bentonite Attapulgite

3% 8.82 lbs/gal 1.06 g/cc 8.58 lbs/gal 1.03 g/cc6% 8.62 lbs/gal 1.03 g/cc 8.58 lbs/gal 1.03 g/cc9% 8.60 lbs/gal 1.03 g/cc 8.60 lbs/gal 1.03 g/cc

Salt WaterClay Content Bentonite Attapulgite

3% 8.72 lbs/gal 1.04 g/cc 8.64 lbs/gal 1.04 g/cc6% 8.72 lbs/gal 1.04 g/cc 8.51 lbs/gal 1.02 g/cc9% 8.78 lbs/gal 1.05 g/cc 8.70 lbs/gal 1.04 g/cc

Part 2

Bentonite

Added: 35.02g

Density: 8.7lbs/gal

Temperature: 28.4 C ̊

Viscometer

rpm dial reading

600 114.9

300 98.8

200 92.1

100 84.4

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6 68.1

3 68.5Gel Strength

10 sec (average) 57.5 cpRun 1 58.0 cpRun 2 58.4 cpRun 3 56.2 cp

10 min: 63.0 cp

Xanthan Gum

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Added: 4.01g

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Density: 7.5lbs/gal

Temperature: 35.2 C ̊

Viscometer

rpm dial reading

600 104.5

300 90

200 81.5

100 70

6 43.5

3 38.5Gel Strength

10 sec (average) 37.1 cpRun 1 37.1 cpRun 2 37.0 cp

10 min: 43.5 cp

Data Analysis and Discussion

Part 1

All samples had the same viscosity with 3% clay content added. The samples with Attapulgite present gave a high yield of clay compared to Bentonite. With an addition of 3% more, the viscosity of Attapulgite Fresh water and saltwater gave similar results. However, when more attapulgite was added, the salt water mixture continued to become more viscous than the fresh water. The bentonite clay does not build up viscosity in salt water. It will just absorb the water and not change the viscosity at all. The bentonite in fresh water has some affects but it does not increase the viscosity as much as the attapulgite.

Attapulgite is clay that provides a high yield in salt water and reasonable yield in fresh water. Attapulgite in salt water does not provide filtration control though. Bentonite should not be used in salt water at all

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1% 2% 3% 4% 5% 6% 7% 8% 9% 10%0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0 Apparent Viscosity for all 12 Mud Samples

Bentonite Fresh Water Attapulgite Fresh Water Bentonite Salt Water Attapulgite Salt Water

Clay Content (% Weight)

Appa

rent

Visc

osity

(cp)

Figure 7Apparent Viscosity vs. Clay Content for 4 different Mud Compositions


because has no affects on the viscosity and use in fresh water is recommended, however the amount of bentonite clay required to increase the apparent viscosity will be a large amount compared to Attapulgite. Similar to Figure 2 in the lab manual, Bentonite in Salt water increases viscosity so slightly showing a low yield drilling clay. All the other three samples seem to resemble a premium drilling clay. The biggest difference is the affect on viscosity with the amount of clay added.

If salt water is being used in a drilling operation, the use of bentonite clay will have no affect on the drilling fluid. However, the use of attapulgite is suitable for all both salt water and fresh water. Bentonite

maybe suitable in fresh water if the viscosity increase desired is low, otherwise to get a high viscosity for the drilling fluid may require a lot of Bentonite to be added which is not cost effective.

The Bentonite and Fresh Water sample had the highest density at the beginning, but as more clay was added, the density was similar with the other Fresh Water sample of Attapulgite. This is due to the fact that bentonite is swelling. Rather, the Bentonite and Salt water sample hardly changed in density. The Attapulgite in Fresh Water shows a small density increase as more clay is added. The Attapulgite in Salt Water shows a dip at 6% clay content. This may just be bad data since the density shows a concavity in the curve. It should be expected the Attapulgite in Salt Water to have a higher density when compared with Attapulgite in Fresh Water because of the salt crystals present in the water. The density of Salt

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1% 2% 3% 4% 5% 6% 7% 8% 9% 10%1.00

1.01

1.02

1.03

1.04

1.05

1.06

Density for all 12 Mud SamplesBentonite Fresh Water Attapulgite Fresh Water Bentonite Salt Water Attapulgite Salt Water

Clay Content (% Weight)

Dens

ity (g

/cc)

Figure 8Density vs. Clay Content for 4 different Mud Compositions


Water with 20,000 ppm NaCl is 20,250 mg/L, equivalent to 0.02025 g/cc. The difference between Attapulgite in Salt Water and Fresh Water, as seen in Figure 8, is about 0.02 g/cc difference. It can be concluded that the Attapulgite does not swell disproportionally in Salt Water nor Fresh Water.

Yield of Bentonite Fresh Water: 85 bbl per tonClay Content % of Bentonite Fresh Water at 15 cp =5.5%

Yield of Attapulgite Fresh Water: 130 bbl per tonClay Content % of Attapulgite Fresh Water at 15 cp =4.0%

Part 2

Bentonite Density = 8.70 lbs/galμp = Plastic Viscosity = 16.1 cpτy = yield point = 82.7 lbf/100 ft2

τ=τ y+μp∗γτ=82.7+16.1∗γ

Viscometer Shear Rate Shear Stressrpm dial reading γ [sec-1] τ [lbf/100 ft2]

600 114.9 1020.0 114.9

300 98.8 510.0 98.8

200 92.1 340.0 92.1

100 84.4 170.0 84.4

6 68.1 10.2 68.1

3 68.5 5.1 68.5

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150.0 250.0 350.0 450.0 550.0 650.0 750.0 850.0 950.0 1050.080

85

90

95

100

105

110

115

120

R² = 0.992860111919513R² = 0.980159180148684

Shear Rate vs. Shear Stress for Bentonite

bentonite Linear (bentonite) Power (bentonite)

Shear Rate [sec-1]

Shea

r Str

ess [

lbf/

100

ft2]

Figure 9Shear Rate vs. Shear Stress for Bentonite Mud


*reading at 6 and 3 rpm excluded from graph.

According to the R2 values, the best fit line for Bentonite is a linear line. It can be concluded that this bentonite mud is not of the Power Law Model but of the Bingham Plastic Model.

Xanthan GumDensity = 7.50 lbs/galn = flow behavior index = 0.21551K= Consistency index = 11970.68 lbf/100 ft2

τ=11970.68∗(γ )0.21551

Viscometer Shear Rate Shear Stressrpm dial reading γ [sec-1] τ [lbf/100 ft2]

600 104.5 1020.0 104.5

300 90.0 510.0 90

200 81.5 340.0 81.5

100 70.0 170.0 70

6 43.5 10.2 43.5

3 38.5 5.1 38.5

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150.0 250.0 350.0 450.0 550.0 650.0 750.0 850.0 950.0 1050.065

70

75

80

85

90

95

100

105R² = 0.954335325290337R² = 0.999571701953178

Shear Rate vs. Shear Stress for Xanthan Gum

Xanthan GumLinear (Xanthan Gum) Power (Xanthan Gum)

Shear Rate [sec-1]

Shea

r Str

ess [

lbf/

100

ft2]

Figure 10Shear Rate vs. Shear Stress for Xanthan Gum Mud


*reading at 6 and 3 rpm excluded from graph.

According to the R2 values, the best fit line for Xanthan Gum is a power line. It can be concluded that this Xanthan Gum mud is not of the Bingham Plastic Model but of the Power Law Model.

Sample Calculations

Part 1

Apparent Viscosity:

μApp=[600 rpmdial reading]

2

[600rpm dial reading] for 3% Bentonite Fresh Water = 13

μApp=132

=6.5cp

Unit Conversion:

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1 lbs/gal = 0.119826427 g/ccDensity for 3% Bentonite Fresh Water = 8.82 lbs/galDensity for 3% Bentonite Fresh Water = 8.82 * 0.119826427 Density for 3% Bentonite Fresh Water = 1.06 g/cc

Part 2

Bentonite:

μp=θ600−θ300

μp=114.9−98.8=16.1cp

τ y=θ300−μp

τ y=98.8−16.1=82.7 lbf/100 ft2

Xanthan Gum:

n=3.322∗log (θ600θ300

)

n=3.322∗log(104.590.0 )=0.21551

K=510∗θ300(511)n

K= 510∗90.0(511)0.21551

=11970.68 lbf/100 ft2

Shear Rate:

γ=1.7∗rp mWhere: γ= shear rate [sec-1]

rpm = revolutions per minuterpm of 600

γ=1.7∗600γ=1020 sec-1

Sources of Errors:

The use of Bentonite was not pure. When preparing the mud, dark lines appeared on Bentonite mud showing impurities in Bentonite clay. These impurities may not be homogenous throughout the entire

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Bentonite bulk container. If research is done on drilling fluid, pure Bentonite should be use, however to stimulate real field mixing, it is not significant.

When using the mixer in preparing the mud, there was a lot of powder from the clay that was not mixed in the mixing cup and even some that blew away onto the table. The actual amount of clay added may be less than prepared. An alternative way of adding the exact amount of clay is by having the clay in tabulate forms or pill forms so that the clay cannot be blown away.

Conclusions

Bentonite works well in Fresh Water; however it does swell a few times its own size. Bentonite should not be used with Salt Water as has a low yield of clay.. Attapulgite on the other hand has a high yield of clay in both Fresh Water and Salt Water, and it does not swell too much.

Drilling mud is a non-Newtonian fluid. To determine which type of model the fluid follows cannot be approximated using eye judgment. A graph must be constructed and linear regression or power law regression must be performed to determine the rheological character of the drilling mud. Bentonite mixed with fresh water will give a Bingham Plastic fluid and Xanthan Gum gives a Power Law fluid.

References:

http://www.glossary.oilfield.slb.com/Display.cfm?Term=gel%20strength, February 10 2007http://en.wikipedia.org/wiki/Newtonian_fluid, February 10 2007http://www.glossary.oilfield.slb.com/DisplayImage.cfm?ID=373, February 10 2007

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Assignment

Apparent Viscosity using Power Law Laminar Flow Equations

Approach 1

μApp=K∗(Dh−D p)

1−n

144∗va1−n ∗(

2+ 1n

0.0208)

n

Where: μApp= apparent mud viscosity, cpva= average annular mud velocity, ft/secDh= hole diameter, inchD p= pipe outer diameter, inchK= consistency index, equivalent cp

Pipe Rheological Parameters

np=3.322∗log (θ600θ300

)

np=3.322∗log(10065 )=0.62150

K p=510∗θ300(511)np

K p=510∗65(511).62150

=687.376

For va= 150 ft/min

μApp=687.376∗(8.5−4.5)1−.62150

144∗2.51−.62150∗(2+ 1.621500.0208

)

.62150

μApp=140.551 cp

Annular rheological Parameters

nAnn=0.657∗log (θ100θ3

)

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nAnn=.657∗log( 323.0 )=0.67541

K Ann=511∗θ3(5.11)n Ann

K Ann=511∗3.0

(5.11).67541=509.406

For va= 150 ft/min

μApp=509.406∗(8.5−4.5)1−.67541

144∗2.51−. 67541∗(2+ 1.675410.0208

)

.6 7541

μApp=130.857 cp

ft/min ft/sec Pipe Rheological Annular Rheologicalva U (cp) n k U (cp) n k % error of u

180 3 131.1794 0.621502 687.377 123.3385 0.675415 509.4061 6.357202

150 2.5 140.5516 0.621502 687.377 130.8579 0.675415 509.4061 7.407796

120 2 152.9382 0.621502 687.377 140.6875 0.675415 509.4061 8.707753

90 1.5 170.5316 0.621502 687.377 154.4574 0.675415 509.4061 10.40693The pipe rheological viscosity is higher than the annular rheological viscosity. The % error of

viscosity is small when the annular velocity is highest. As the velocity decrease, the error increases.

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