decreasing mud density by diluting it with water

1. 1
Petroleum department
3rd stage
Group (A)
Drilling Lab
3rd
Experiment:
Dilution
Date of experiment: November 26th
2015
Supervised by:
Mr. Pshtiwan Jaf
Prepared by:
Muhammad Faisal

2. 2
Aim of experiment:
The aim of dilution is to reduce the muds density, which
reduces the Hydrostatic pressure.

3. 3
Theory:
Misreported mud weights may erroneously call for mud weight
adjustments, which can lead to well kicks, the fracturing of a
formation, and higher mud drilling costs. The most common causes
of such errors are:
• Lack of calibration of the mud balance.
• Air/gas cut mud.
• Improper procedures followed in measuring mud weight.
Mud weight control is Controlling of mud weight within a
specified range in the field is one of the major concerns in the
implementation of an optimum drilling-mud program. Drilled
solids, particularly those of micron and submicron size, are the most
detrimental to the rate of penetration (drilling rate). If these solids
are not removed from the mud system, they will adversely affect the
weight and other important properties of the mud. The control of
mud weight in the field is accomplished by:
• Utilization of effective solids removal equipment.
• Addition of chemical flocculants at the flow line.
• Dilution with water.
Mud weight control is dilution by water is less effective
supplementary technique. A continuous but small regulated stream
of water should be added at the flow line, as excessive dilution will
result in excessive treatment costs. In oil-based muds, dilution for
the purpose of reducing the mud weight is costly and detrimental
to the drilling rate and therefore must be avoided. (Azar & Samuel, 2007)

4. 4
Introduction:
In this experiment we reduce the mud weight by adding more
water to the mud. The same apparatus and materials used in the
previous test (Mud Balance) are going to be used in this experiment
again. Especially the mud balance which is the essential instrument
in any density relevant experiment.

5. 5
Apparatus & materials:
Mud balance Electronic balance Beaker
Syringe
Electric mixer & steel vessels

6. 6
Water Bentonite
Calibration:
1. Remove the lid from the cup.
2. Fill the cup with fresh water around 70°F (21°C).
3. Put the lid back on the cup, (water should come out from the
lids hole).
4. Set the rider on 8.3 ppg or 1 specific gravity.
5. Add or remove steel shot from the Shotwell until the
instrument is in balance and the bubble in the level rests in the
center of the level glass.

7. 7
Procedures:
1. Weigh 25.05 gm of bentonite on the electric balance.
2. Pour 489.97 cc of water into a 500 ml beaker.
3. Pour the water into two vessels and stir the water with the
mixer.
4. Slowly add the bentonite to the stirring water.
5. Leave the mixer running for few minutes till we have a good
mixed mud.
6. Mix the mud in one of the vessels with the mud in the other.
7. Place the mud balance base (preferably in carrying case) on a
flat level surface.
8. Fill the clean, dry cup to the top with the freshly obtained mud
sample to be weighted.
9. Place the lid on the cup and set it with a gentle twisting
motion. Be sure that some mud is expelled through the hole in
the cap as this will ensure the cup is full and also will free any
trapped air or gas.
10. Cover the hole in the lid with a finger and wash all mud
from outside of the cup and arm. Then thoroughly dry the
entire balance.
11. Place the balance on the knife edge and move the rider
along the outside of the arm and leave it on 8.58 ppg (the
expected mud density) and wait till the cup and arm are
balanced as indicated by the bubble.

8. 8
12. Obtain 325 cc of water by the beaker and syringe.
13. Mix the water with 300 cc of the mud that we prepared
previously, by using the electric mixer again.
14. Pour the diluted mud into the mud balance cup, then
place the lid on the top (some mud should expelled from the
lids hole.
15. Put the rider on 8.45 ppg and observe the level bubble till
it settles in the center.
16. Clean and dry the mud balance when finished.
Discussion:
The pressure exerted by the drilling fluid should be kept in a
certain range so that we avoid any undesirable events such as kicks,
blow outs or formation damage. We used barite to weight the mud
and the water to dilute it, but water is only effective to dilute clean
bentonite water based muds. It is not very efficient in the field
drilling fluid dilution. In formations where we have shale layers mud
dilution with fresh water is not acceptable because it causes big
damages. Some times in the field we have a diluted mud which has
low density about 8.42 ppg (too light), and we have to increase the
density as quick as possible to about 15 ppg, to prevent a sudden
kick by the formation fluid. We are not able to directly add barite
to the mud, and we cannot add bentonite to reach the density of 15
ppg. In this situation other actions must be taken.
Q1) when does a kick or a blowout occur?
A1) kicks and blow outs occur when the formation fluids (oil and
gas) pressure is bigger than the drilling fluids pressure.
Q2) when does formation damage (fracture) occur?
A2) it occurs when the drilling fluids pressure is bigger than the
fracture pressure of the formation rocks.
Q3) in what range the muds hydrostatic pressure should be kept?

9. 9
A3) the hydrostatic pressure must be larger than the formation
fluids pressure and smaller than the fracture pressure and the
hydrostatic pressure is controlled by mud weighting and dilution.
Q4) why water is not very efficient in the field drilling fluid dilution?
A5) because in well drilling operation the mud beside containing
bentonite, it carries out sand, rock cuttings and other solid particles
from the bottom hole to the surface. These materials are in soluble
in water so they have to be segregated from the mud by
mechanical means. These equipment utilize high-speed screen
shakers with 50 mesh size or finer, followed by desanders, desilters,
and mud cleaners for unweighted muds. Centrifuges, which can
discriminate among solids on the basis of their specific gravities, are
used for weighted muds; centrifuges are also used in unweighted
muds if a true low-solids mud system is to be maintained. Flow-line
flocculation through the addition of chemicals is also used to
enable the solids removal equipment to extract submicron-size
drilled solids and is an essential means of controlling the mud
weight.
Q6) why mud dilution with fresh water is not acceptable while
drilling shale formations?
A6) because shale contains clay which reacts with fresh water and
swells which sticks the drill pipe. That’s why we have to use salt
water to dilute mud because salt doesn’t react with shale.
Q7) what actions must be taken when we need to do mud
weighting for a low density mud?
A7) when we need to do mud weighting for a low density mud, we
cannot directly add barite. Because barite is inert and insoluble in
water and it precipitates after a while if the percentage of bentonite
to suspend barite particles in the mud is too small. And we can’t
increase the density by adding bentonite, because bentonite

10. 10
increases density till a certain point (about 8.6 ppg) after that
viscosity increases as well. In this situation the density is increased
by bentonite till a limit then barite is added for mud weighting.
References:
Azar, J. J. & Samuel, R., 2007. Drilling Engineering. Tulsa, Oklaoma:
PennWell Corporation.
Committee, A. S. S., 2011. Drilling Fluids Processing Handbook.
s.l.:Elsevier.
Mian, M. A., 1992. Petroleum Engineering Handbook for the
Practicing Engineer. Tulsa(Oklahoma): PennWell Books.