Lab 3

Pet E 367 Lab Report #3  Mud

Weight

 Weight

Control

 Solids Determination

Experiment Date: March 7 2007 Prepared by: Jackie Chee (1103396) Group #7 Beattie L. Branch T.

Jackie Chee (1103396)

March 7 2007 Lab Report #3

NREF 2-052 Markin/CNRL Natural Resources Engineering Facility st

116street 91 ave March 7, 2007 Barkim Demirdal PhD Candidate at Petroleum Engineering Department 7-134 Markin CNRL Natural Resources Engineering Facility Edmonton, Alberta Canada T6G 2W2 Dear Mr. Demirdal, In the industry, density control of drilling fluid can be achieved by adding additives like barite, hematite, ilmenite, galena, and lots more. Those are the few most common, however eve ry one has their advantages and disadvantages. We have observed the use o f barite as a density control additive. Our findings show that barite can be used w ith water based drilling fluid and it does not affect the rheological properties of the drilling fluid significantly. There is also a relation in which to determine the amount of barite to add to obtain a desired density for the drilling fluid. It is proven to be valid. The use of the API retort test is crucial in verifying the amount of solid contents in the drilling mud to determine the weighted we ighted solids present in the drilling fluid.

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

The objective of the lab is to familiarize the importance of drilling fluid weight control and the additives used to increase the density of o f drilling fluid. It is also important to note the changes these additives cause on the drilling fluid. The API re tort test can be used to determine the solid content of a drilling fluid.

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Theory and Concept Rheological Properties

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 we ll 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:

  = [600  2  ]

Units in cp

A Bingham Plastic model is determined to be the fluid’s rheological rheologica l property. A plastic yield must be

overcome before any shearing will occur in the fluid. The shear stress to shear rate can be related by this equation:

 =  +  ∗   = 600 − 300  = 300 −  Where:

τ = Shear stress

[lbf/100 ft 2] τy = Yield Point [lbf/100 ft 2]  = Plastic Viscosity [cp] = Shear Rate [sec -1] 600 = dial reading at 600rpm 300 = dial reading at 300rpm

    Solid Control

An important function of drilling fluid is to prevent flow of formation fluid into the wellbore while drilling. As the depth of the well increases, the formation pressure increases as well. I t is important to ensure the wellbore pressure is greater than the formation pressure. A simple way of increasing the wellbore pressure as depth increases is by using the hydrostatic pressure in the fluid. With the addition of clay solids, or heavy clay like barite with a specific gravity of 4.2, mixed into the drilling fluid, the hydrostatic pressure at the bottom of the well increases with depth. This is a very cost effective way of increasing the hydrostatic pressure. There are a few alternative density control additives like hematite with a specific gravity of 4.9-5.3, ilmenite with a specific gravity of 4.5-5.11 and galena with a specific gravity of 7.5.

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There is a drawback with the addition of high density solids into the drilling fluid, in that they are significantly heavier than water and causes the density to increase. This may affect the other important function of the drilling fluid to carry cuttings to the surface, because the total tot al weight of the solids may be so much such that the solids settle to the bottom. This can be solved by altering the rheological properties in the drilling fluid ensuring they are held in suspension. With hematite and ilmenite, they are higher in density than and also twice as hard as barite. These additives will require less addition of additives to increase the weight o f the drilling fluid, but because of their high hardness, they may damage the equipment when circulating in the system. It is also crucial to e nsure that the drilling fluid does not exceed t he fracture gradient in the formation; otherwise it may fracture the formation leading to mud loss or a kick if the formation is not sealed. Typically, the drilling fluid density is not required to exceed 1 9 lbm/gal during normal drilling operations, this density is the average weight of the minerals and fluids present in the earth’s crust. Using Galena to control the density will give an exc ess of 19 lbm/gal drilling mud, which may be required for special drilling operations. With a fracture in the formation, a c asing must be installed or cemented. This is a considerable loss in drilling time and increase in cost. The addition of more clay will change rheological properties and filtration properties in the drilling fluid. The specific gravity of barite is significantly higher than the drill cuttings; because of this, the amount of solids required is less and this decreases the surface area of the solid in the mud. The yield point and non-Newtonian character is dictated by the e lectrical charges in the solid particles and the viscosity is controlled by the total surface ar ea of the solid particles in the mud. It is important to do pilot tests to monitor any changes in the drilling fluid with the increase in clay content. In this lab, a drilling fluid will be prepared and a desired density will be achieved by adding barite. This formula will determine the amount of barite re quired to increase the drilling density to a de sired amount.

 −    = 1490 ∗ 35.4 − 2

1

units in grams

2

Where:

2= desired density 1=density of mud

Solids Determination Drilling fluid may either contain low-weight (un-weighted) mud, weighted mud or both. A mud that is low-weight mud is one that does not have barite present. Weighted mud by itself is very rare. If oil is not present in mud, and it is of o nly low-weight mud, then the solid content of the un-weighted mud can be determined directly. However, both weighted and un-weighted mud is present, than a retort must m ust be performed to determine the solid content o f the weighted mud.

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Figure 1 – Relative Amount of Barite and Lower Specific Gravity Solids in the Suspended Solids The mud retort is used to determine the volume fraction of oil, water , and solids in drilling fluids. The mud retort consists of a mud sample holder, a heating element, an aluminum condenser, and a graduated cylinder receiver. The sample is place in the mud sample holder and they come in three sizes, 3

10, 20, and 50 cm . The mud sample holder is heated where oil and water evaporates into a condenser and the liquid is collected in the gr aduated cylinder. Drilling mud may consist of oil, water and solids. The mud retort will give the water volume fraction in the mud, and oil volume fraction if present. The solid volume fraction than can be determined by this equation:

 = 1 −  ∗   −  Where:  = solids fraction  =volume fraction of distilled water collected in the graduated cylinder   =volume increase factor due to loss of dissolved salt during ret orting. This is obtained from table 2.3 and 2.4, page 52 in the Applied Drilling Engineering, SPE Textbook Vol. 2

 =volume fraction of distilled oil. Page 5 of 13



The specific gravity of solids can be obtained using the following formulas: Specific Gravity of Solids:

%     = 100∗% −

Specific Gravity of Mud



=

   Where:

A=8.33 if mud weight is in ppg, or 62.4 if mud weight is in lbm/ft



3

Experimental Procedure 1. Prepare a drilling mud with 350mL of water and 10 grams of bentonite. Ensure the drilling mud is mixed well. 2. Put the drilling mud in the API Standard Fann VG Viscometer and record the 300, and 600 rpm dial readings. 3. Check to see if t he viscosity is between 15 -20 cp. If not, add another 5 grams of bentonite and repeat till the desired viscosity is achieved. 4. Measure the 10 second gel strength. 5. Measure the mud weight using the mud balance. 6. Determine the plastic viscosity and yield point of the drilling mud using recorded data. 7. Calculate the amount of barite to be added to increase the mud weight to 10 ppg. 8. Add the calculated amount of barite to the drilling mud and ensure it is mixed well. 9. Record the 300 and 600rpm 600r pm dial readings on the API Standard Fann VG Viscometer. 10. Measure the 10 second gel strength. 11. Measure the mud weight using the mud balance. 12. Determine the plastic viscosity and yield point of the drilling mud using recor ded data. 13. Run the drilling mud in the Mud Retort to determine the concentration of low solids and high solids in the mud. i.

Prepare the retort assembly.

ii.

Fill the mud into the sample cup, and replace the lid so some mud sips out. Wipe off any external mud or water.

iii.

Lift cover slightly and slide off so that fluid adhering to bottom surface will be scraped back into the sample cup.

iv.

Fill the expansion chamber with steel wool. This prevents a “boil over” ef fect.

v.

Assemble sample cup and expansion chamber together and place i n the respectable spot in the retort device.

vi.

Connect the condenser to the top end of the expansion chamber where gas will exit.

vii.

Place the graduated cylinder to collect liquid from the condenser.

viii.

Plug retort device to a power outlet and leave it on till the rate of water expelled from the condenser is near zero.

ix.

Record the volume of water expelled from the mud.

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x.

At the end of the test, grasp rubber covered connected above the heater and separate retort assembly from condenser. Handling the hot retort by means of connector cord, dip in water to cool.

xi.

Most of the solids remaining in retort will adhere to the heater where removal is easy. Use spatula to scrape out cup and e xpansion chamber. Run short length of pipe cleaner through condenser hole and retort drain t ube to remove oil residue.

xii.

Calculate the specific gravity of solids

xiii.

Using Figure 1, with the specific gravity of solids calculated; determine the weight percentage of high gravity solids and low gravity solids.

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Results and Calculations

Recorded Data Clay Added

Viscometer Reading

Grams

300rpm

600rpm

Plastic Viscosity

Yield Point

10

6.5

9.1

2.6

3.9

15

13.0

17.5

4.5

8.5

20

24.0

29.7

5.7

10 second gel strength

Density

1st

2nd

average

ppg

18.3

13.0

13.5

13.25

8.61

17.9

16.5

15.5

16.00

10.02

Drilling mud of 10 ppg ( added 85 grams of barite) 24.7

31.5

6.8

Mud Retort Water Volume =

9.1cc

Percentage Volume Water =

91%

Percentage Volume Solid=

9%

Specific gravity of mud=

1.202881

Specific gravity of solids=

3.254235

Obtained from Figure 1 Percentage weight High Gravity Solids=

56%

Percentage weight Low Gravity Solids=

44%

Specific Gravity of Solids mixed (Theoretical) Specific Gravity

Mass

Bentonite

2.6

20

grams

Barite

4.2

85

grams

3.895238

105

grams

Mixture

Page 7 of 13



Sample Calculations For 20 Grams

Plastic Viscosity

Yield Point

 = 600 − 300  = 29.7 − 24.0  = 5.7cp

 = 300 −   = 24.0 − 5.7  = 18.3 lbf/100 ft

2

Amount of Barite required making 10 ppg

 −    = 1490 ∗ 35.4 − 2

1

2

10 −8.61   = 1490 ∗ 35.4 −8.61 

  = 81.5 81.53 3  Added 85 grams

Percentage Volume Water = 9.1 / 10 * 100 = 91% Percentage Volume Solid = 100% - Percentage Volume Water = 9 % Specific Gravity of Mud

  = 8.33 

=



= 1.20 1.2028 28

10.02 8.33

Specific Gravity of Solids %     = 100∗% −

− 91%  = 100 ∗ 1.2028 9%  = 3.25 3.2542 42

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Shear Stress Vs. Shear Rate Comparing the Addition of Barite Bentonite

Bentonite + Barite

Linear (Bentonite)

Linear (Bentonite + Barite)

33

31 y = 0.013x + 17.9

29 ] 2 t f 0 0 1 / f b l [ s s e r t s r a e h S

27 y = 0.011x + 18.3 25

23

21

19

17

15 0

200

400

600

800

1000

Shear Rate [sec-1]

Figure 2 Page 9 of 13





Analysis and Discussion Theoretical

Density (ppg) Specific Gravity of Solids

Retort

% Error

10.00

10.02

0.2

3.895238095

3.254235

16.45607

When 20 grams of be ntonite was added, the apparent viscosity of the drilling mud was 14.85cp (29.7/2), which is short of the 15-20 15 -20 cp required. It is observed that the addition of 5 grams of bentonite increases the apparent viscosity by 5cp. If 2 5grams of bentonite was mixed, the apparent viscosity might be greater than 20cp. The density of drilling fluid after adding the barite is 10.02, w hich is a 0.2% error. The calculations required an addition of 81.53 grams of barite, however to accommodate the barite loss during mixing, it would be safer to add an addition 3 grams. This shows the equation to calculate the amount of barite required is very accurate.





Analysis and Discussion Theoretical

Density (ppg) Specific Gravity of Solids

Retort

% Error

10.00

10.02

0.2

3.895238095

3.254235

16.45607

When 20 grams of be ntonite was added, the apparent viscosity of the drilling mud was 14.85cp (29.7/2), which is short of the 15-20 15 -20 cp required. It is observed that the addition of 5 grams of bentonite increases the apparent viscosity by 5cp. If 2 5grams of bentonite was mixed, the apparent viscosity might be greater than 20cp. The density of drilling fluid after adding the barite is 10.02, w hich is a 0.2% error. The calculations required an addition of 81.53 grams of barite, however to accommodate the barite loss during mixing, it would be safer to add an addition 3 grams. This shows the equation to calculate the amount of barite required is very accurate. The specific gravity of the solids through calculations predicts the mixture of bentonite and barite, with their respective mass mixed, to have a specific gravity of 3.895. It is found the specific gravity of the solids obtained from the mud retort is 3 .254. This yields a 16.5% error, which is considerably large. The reason for such a high error may be because the graduated cylinder used in the experiment was cracked at the brim, and a few drops of water escaped through the side. Recalculating the specific gravity of the solid, using a water volume of 9.3cc yields a specific gravity for solids to be 3.898. The mud retort can be reliable in determining the water, and solid volume fraction, however due to its ability to take a small sample, the e rror in the data may be quite high. It would be better if a 50cc mud retort is available. On the other hand, with more mud sample, it may take longer for the process to evaporate all the liquid in the mud. The addition of Barite did not change the fluid rheological properties significantly. The apparent viscosity did increase by 1cp, and the yield point was not affected. This is shown in Figure 2, a comparison of the shear stress and shear rate of the two drilling mud, without barite and w ith barite. The noticeable change in rheological property is the ge l strength, where the addition of barite increased it by 2.5 cp. The increase in gel strength is because of the additional solid particles, barite, which has se ttled. A possible source of error is when using the mixer in preparing the drilling 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 le ss than prepared. An alternative way of adding the exact amount of clay is by having t he clay in tabulate forms or pill forms so that the clay cannot be blown away.

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Conclusion 1. The equation used to calculate required barite is valid and can be used to obtain any desire density drilling fluid. 2. Barite is an excellent density contro l additive; it increases the density well and does not affect fluid rheological properties significantly.

3. The mud retort is a very accurate device to determine specific gravity of solid, however, limited by the amount of sample used, it may c arry high errors.

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References

Bourgoyne, Millheim, Chenevert, Young: Applied Drilling Engineering Engineering Vol.2, pg 51 , 66-68, 1986 Pet E 367 – Winter 2007, Experiment 3: Mud Weight – Weight Controls – Solids Determination Lab Manual http://www.glossary.oilfield.slb. http://www.glossa ry.oilfield.slb.com/Display.cfm?Te com/Display.cfm?Term=retort rm=retort

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Assignment Volume of wellbore 0 - 10500ft

4315.75

cubic ft

10500ft - 14000ft

1379.22

cubic ft

Drill Collar Volume 1500 349.7476

ft cubic ft

Drill Pipe Volume 12500 457.8642

ft Cubic ft

Mud Tanks each volume

1440

cubic ft

all 3

4320

cubic ft

Total Mud Capacity (including tank) 9207.36 cubic ft 260.723 cubic m 1639.9 bbl

Total Mud Capacity (excluding tanks) 4887.357 cubic ft 138.3945 cubic m 870.4755 bbl

If 10 stands are pulled out 1 stand = 3 Drill Pipes 1 Drill Pipe =30 feet 1 stand = 90 feet 10 stands = 900feet Volume of mud in wellbore=

4887.357

cubic ft

Volume of Drill Pipe Pulled Out 32.96622

cubic ft

Volume of drill pipe pulled out = volume of empty space in wellbore height=

88.0521

feet

Volume of drill pipe pulled out = volume of empty space in mud tanks height=

0.18315

feet

for 1 tank

height=

0.06105

feet

for all 3 tanks

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Volume required to increase the tanks by 3 inch Volume =

W2 (ppg)

135

cubic ft

3.82277

cubic m

24.0445

bbl

Barite Req (grams)

10

0

10.5

29.9197

11

30.5328

11.5

31.1715

12

31.8376

12.5

32.5328

13

33.2589

13.5

34.0183

14

34.8131

14.5

35.6459

15

36.5196

Barite Requirement to to increase Density of mud by 0.5 ppg increments 40 35 ) s 30 m a r g 25 ( d e r i u 20 q e R 15 e t i r a 10 B

5 0 10

10.5

11

1 1 .5

12

12.5

13

Desired Density (ppg)

Page 13 of 13

1 3 .5

14

1 4 .5

15

Lab 3

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