1. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
1
Objectives Objectives for Mud Systems
Upon completion of this section of the course the
student will have instruction in:
1. History of Mud
2. Why do we use it
3. Basic types of drilling mud
a. Fresh water
b. Salt water
c. Oil Base
d. Air/air mist / stable foam
4. Mud check sheet
a. Mud weight
b. Viscosity
c. Plastic Viscosity
d. Yield Point
e. Gel Strength
f. Filtrate
g. Filer Cake
h. Retort solids
i. Sand Content
j. Methylene Blue
k. PH
l. Mud Alkalinity
m.Chloride Measurement
n. Total Hardness
o. Lost Circulation
1. Preventive Measures
p. Shale Problems
2. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
2
Introduction
Mud systems
The birth of modern rotary drilling was born in the
Spindle top area in 1901. Before that time the
industry standard was to pump fresh water down
hole to bring the cuttings to the surface. In the
Spindle top area they encountered down-hole
problems. The quick sand would immediately fall
around the pipe when they would make a
connection. They solved the problem by driving a
herd of cattle through the slush pit, thereby creating
a thick soup of their drilling water. With that
successful action drilling mud was born.
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3. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
3
Why use
drilling
mud?
HOW DOES DRILLING MUD FACILITATE
DRILLING?
Remove the cuttings from the bottom of the
hole and carry them to the surface
Wall the hole with an impermeable mud cake
Support the wellbore
Control subsurface pressures
Hold the cuttings in suspension when
circulation is stopped
Cool and lubricate the bit and drill string
Transmit hydraulic horsepower to the bit using
jet nozzles
Transmit hydraulic horsepower to the mud
motor
Support part of the weight of the drill pipe and
casing
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4. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
4
Types of
Systems
BASIC TYPES OF DRILLING FLUIDS
Fresh water systems
Salt water systems
Oil based and invert emulsion systems
Air/ Air mist/ stable foam circulating systems
Each system has its disadvantages and advantages
depending on which area you are drilling. Although
oil base and invert is widely used in some areas. By
far the most widely use is fresh water and salt water.
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5. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
5
Mud
properties
Mud check sheet
The daily mud engineer’s report is a vital part of the
morning report. The information recorded by the
mud engineer and the information that the derrick
hand inputs on the tour sheet supplies the operating
company and the drilling contractor with vital
information. But what do the numbers mean?
Included in this section is a daily mud engineer’s
report. The first four lines indicate where and when
the sample was taken, flow-line temperature and
depth. All the other items on the sheet are
measurements or calculations from the sample.
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7. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
7
Mud Weight Mud weight
Mud weight is measured with a mud balance scale. The mud
balance scale should be calibrated using distilled water and
should balance at 8.33 ppg (pounds per gallon). The rig’s
mud balance scale should be checked weekly against the mud
engineer’s to ensure both are reading the same.
Mud weight is the most important property, and you are
constantly doing a balancing act between to high of mud
weight and to low of mud weight. If it is to low it can cause
oil and gas, or water intrusion and possible a well control
issue. It also can cause hole instability, tight connections,
bridges or hole enlargements.
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8. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
8
Mud Weight
cont.
The ideal mud weight is as close to formation pressure
as possible.
Clear fresh water allows the fastest drilling possible of any
fluids today. It’s the fastest because it is the lightest. Clear
water weighs 8.33 ppg. Anything that weighs more will slow
the penetration rate down
Mud weight is increased by adding solids to the circulating
system. Solids are from two sources. One is addition at the
surface the other comes from rock formations that you drill.
These solids can be classified as reactive and nonreactive
solids.
Examples of reactive solids added at the surface to purposely
improve mud properties are:
Bentonite Gel
Fluid loss agents
Dispersants
Polymers
Reactive solids that can enter the mud by drilling are:
Anhydrite
Hydratable shales
Salt
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9. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
9
Mud Weight
cont.
Building mud weight by drilling solids is bad. Build mud
weight out of added barite.
Inert solids are those that are chemically inactive. These
solids are generally classified as low gravity solids (specific
gravity less than 3) and high gravity solids ( specific gravity
over 4). The main solid added at the surface is barite, and has
little effect on mud properties. It is a high gravity solid and
has a specific gravity of 4.2.
Drilled inert solids consist of sandstone, limestone, chert and
other nonreactive rock chips. Drilled solids are almost always
low gravity solids. Unlike barite drilled solids have a adverse
effect on mud properties, down hole conditions and surface
equipment. Because of this controlling or eliminating drilling
solids has a top priority in any mud system. Removing solids
is done mechanically in a properly designed mud system, with
sand traps, shale shakers, desilters, desanders, centrifuges
and by regular cleaning of pits or tanks. Solids can also be
controlled by adding flocculants, dispersants, and thinners.
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10. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
10
Viscosity
Funnel viscosity is measured with a marsh funnel.
The calibration of a marsh funnel is done with fresh
water at 70 degrees. It should take 26 seconds for 1
quart of water to flow out. You should check the
funnel at least every month and should be check
against the mud engineer’s funnel to ensure both
have the same rate of flow.
Viscosity and gel strength increase during drilling
operations.
Penetration of the bit into the formation adds inert
solids, active solids and contaminates to the mud
system. This can cause increases in viscosity and gel
strength to unacceptable levels. In general water and
or chemicals are added to control them.
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11. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
11
Viscosity
If viscosity increases are not controlled, many drilling
problems can occur:
Use of excess pressure to break circulation
Higher pump pressure to circulate the well
Lost circulation from pressure surges and high
circulation pressure
Entrapment to gas in the mud then recirculated
down the hole
Contributes to swabbing of the well during trips
and connections
Sand and cuttings being carried in the mud
causing abrasive wear on equipment
Decrease in penetration rate
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12. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
12
Plastic
Viscosity
Plastic viscosity
Plastic viscosity is a more effect way to check the
flow properties in drilling mud. However its main
disability is that it has to be measured with a Fann-
vg meter carried by the mud engineer. However the
reading of a V G meter can determine the cause of
variations of viscosity and a corrective treatment can
be applied.
Plastic viscosity is that part of flow resistance caused
by mechanical friction. The friction occurs between
the solids and the liquid that surrounds them in the
mud. For field purposes plastic viscosity depends on
the concentration, size and shape of the solids. This
rise in plastic viscosity is cause by solids being
ground up into finer and finer pieces as the mud is
re-circulated. This dehydrates the mud.
An increasing plastic viscosity, with little or no
increase in yield point can be controlled by dumping
tanks and dilution with water or running of solids
control equipment.
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13. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
13
Yield Point Yield Point
Yield Point is also obtained with a V-G meter. It is an
indicator of electrochemical attraction of particles to
each other. These forces are the results of negative
and positive charges located on mud particles
surfaces. High Yield points always results in high
viscosity. Yield point is also an indicator of the ability
of the mud to clean the hole of cuttings while
circulating. In a low solids mud system a relatively
high yield point if desirable. This is accomplished by
adding polymer to the mud system to achieve higher
yield point using lower concentrations. A general
rule is for yield point to be equal to the mud weight
pounds per gallons.
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14. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
14
Yield Point
An increasing yield point, with very little increase of
Plastic viscosity may be reduce or controlled by
chemical treatment only. This can be done with
additives like thinners and dispersants. It is not
economical to reduce yield point by adding water.
For instance, it’s not practical to reduce
contaminated cement. But you can control it with
sodium bicarbonate.
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15. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
15
Gel strength Gel Strength
Gel strength is contained with a V-G meter. Gel
strength differs from yield point. Yield point is an
indicator of the ability of the mud to clean the hole
with the pump on; gel strength is an indicator of the
ability of the mud to suspend solids with the pump
off. As solids and yield point measurements increase
or decrease gel strength usually increases or
decreases in a similar manner. There are two types
of gel strengths, fragile and progressive. The most
desirable one is fragile. A progressive gel maybe
described as low but increases in time. This type of
gel strength is strong and firm and hard to break.
The progressive gel often occurs because of high
concentration of mud solids and can result in a great
number of drilling problems.
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16. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
16
Gel Strength
At the surface high gels will allow sand and cuttings
to remain in the mud, and your solids control
equipment will not take it out. These particles are
then recirculated, damaging pumps, bits, and mud
motors by abrasions. Down hole excessive pump
pressures are required to break circulation, possibly
breaking down formation and causing lost circulation.
Hole swabbing excessive surge pressure can also
result from progressive gels. If it is not controlled
progressive gels can become so bad that the entire
mud system can lock up enough to stick the drill
string.
Build mud weight and other necessary
properties with additives, not containments.
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17. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
17
Gel Strength Fragile gels occur when the initial strength increases
slightly with time. This type of gel strength is easily
broken resulting in fewer drilling problems. These
gels also provide adequate solids suspension cuttings
in the bore-hole then allowing proper particle
settlings in the mud pits. Gel strength in mud is very
important and should be controlled at the lowest
practical value. The only rule-of-thumb for gel
strengths is to keep them from becoming excessively
high or progressive.
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18. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
18
Filtrate Filtrate
Filtrate is another very important measurement of
chemical and physical properties of drilling mud. A
good water loss value and deposition of thin filter
cake are often the determining factors of successful
performance of drilling mud. Filtrate is measured by
an API approved filter press carried by the mud
engineer. During drilling operations there is two
types of filtrations, dynamic and static. Dynamic
filtration occurs while drilling fluid is being circulated.
There is no adequate means of measuring dynamic
filtration in the field. However increasing fluid loss
increases the penetration rate. This may help with
increase drilling speed but high filtration rates can
spell disaster for other wellbore properties such as
hole stability and pay zone penetration. Always
follow the mud engineer’s treatment instructions
closely each shift.
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19. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
19
Filtration The mud engineer can only measure static fluid loss
at the well site. However, the information gained
from this test is very important. In static filtration the
filter cake becomes the thickest and this is when
problems can occur. Excess filtration into a pay zone
can cause formation damage by adverse reaction of
the formation clays, imbibition of the filtrate water
causing water blockage, or by invasion and clogging
of the pore throats with solids from the mud. Filtrate
invasion of a shale can lubricate the fracture planes
and can cause sloughing or facilitate hydraulic
erosion of the well bore. From a drilling standpoint,
excessive filtration rate can cause differential sticking
across any lower pressured porous zone. There are
no rules-of-thumb for the fluid loss test run in the
field. Filtrate can be controlled by the addition of
fresh bentonite, starch, colloids, polymers, oil, and
dispersants to the mud systems. Add to system what
is needed- if need to control water loss, and then
add products to keep water loss down.
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20. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
20
Filtration High Temperature-High Pressure Filtrate
(HTHP Filtrate)
Is a much more accurate measurement of the true
fluid loss of a drilling mud because it performs the
test at temperature and pressures much closer to
actual bottom hole conditions. However, it is not
used much on moderate depth wells because the
equipment is complicated, expensive, and somewhat
dangerous for a tired mud engineer to run. However,
on some wells where HTHP information is critical, it
is run on a daily basis.
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21. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
21
Filter Cake Filter Cake
Runs hand-in-hand with filtrate. It is obtained with
the same instrument as filtration. A filter cake
develops when filtrate is lost to a porous formation.
It consists of the solids presents in the mud, both
drilled solids and mud additives from the surface
mixing operation. In general, poor filtration control
results in a thick filter cake. From a drilling
standpoint, filter cake accumulation on sand faces
causes more problems than the filtration itself. A
thick filter cake can cause many problems downhole,
such as tight hole, swabbing while tripping, and
differential sticking. In some extreme cases, the filter
cake can become so thick that is actually reduces the
hole diameter to less than the size of the drill bit.
In general, filter cake composed mainly of
drilling solids is thick and fluffy, and exhibits
high fluids loss. It is much more desirable to
build a filter cake out of mud products added
to the system. Adding chemicals to control fluids
loss (gel, drispac, starch, etc.) will serve to toughen
the wall cake, and make it thin and tight.
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22. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
22
Retort Solids
and Retort
Liquid
Retort Solids and Retort Liquid
Retort Solids and Retort Liquid are derived by
calculations performed by the mud engineer. Solids
content can only be reduced by either by water or by
use of solids control equipment. In a low-solids
drilling fluid, the solids content cannot be reduced
without lowing the mud weight. If the mud weight
needs to be maintained and the solids lowered, the
only practical way to do this in a freshwater system
is with the additional of barite.
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23. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
23
Sand
Content
Sand Content
Sand content is a measure of sand in the drilling
mud. It is measured by the mud engineer during his
daily mud check. Sand it extremely abrasive and
causes erosion of centrifugal pumps, mud pumps,
high-pressure lines and hoses, swivel, drill pipe, drill
collars, mud motors, and drill bits. Because of this, it
is important to keep the sand content as low
as possible at all times. Frequent dumping of the
sand trap and mud tanks and constant use of the de-
sander should be performed whenever mud is in the
tanks.
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24. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
24
Methylene
Blue
Capacity
Methylene Blue Capacity (MBT)
Methylene Blue Capacity is a measurement of
bentonite in the mud system in lb/bbl. With the
results of this test, the mud engineer can estimate
how many drilled solids are in the mud and devise a
treatment based on this data. The range for
bentonite content in a low-weight system would be
from 12-18 lb. /bbl., while in a weighed system the
range would be 10-14 lb./bbl. Testing MBT is not
usually performed on the average well with
acceptable mud properties and not every mud
engineer carries the kit to test for MBT.
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25. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
25
PH
PH Balance
The PH of a mud system is determined by testing a
sample of mud with litmus paper. Almost all mud
systems have a PH of above 7 in order to minimize
drill pipe corrosion and maintain mud stability.
Extremely high PH is good for corrosion and good for
drilling in H2S environments, but bad for mud
proprieties, formation clays, and down hole stability.
A PH above 11.5 will burn away the polymer in a
modern mud system, reducing it to a fresh water gel
system. This will drastically lessen the inhibitive
effects of the mud and can de-stabilize the well bore.
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26. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
26
Mud alkalinity
Mud alkalinity and filtrate alkalinity
Mud alkalinity (PM) and filtrate alkalinity (MF/PF) are
more detailed and specialized tests of PH in a mud
system. In general the Mf should be 3 times the PF.
If the ratio gets higher it can be an indication of an
alkalinity problem in the mud system.
The PF/Mf spread should be low -around 3.
Another indication of contamination is skyrocketing
PM. Generally salt and anhydrate contamination will
cause PM to decrease.
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27. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
27
Chloride
Measurement
Chloride Measurements
Chloride measurement is a test for salt. Salt content
can affect the performance of water-based mud
systems. A low solids non-dispersed mud system is
an inhibited mud system with very desirable flow
properties. However, it is not very tolerant of salt
contamination, and the total chlorides approach
10,00 ppm, it will start to clabber and become very
thick. At that point, the mud system is much more
tolerant of salt than a non-dispersed mud. It does
not protect the producing formations or inhibit the
hydration of shales in the well bore. When the
chloride level reaches about 20,000 ppm, it is time to
change over to a true salt water based mud system.
All solids in any mud system are considered
contaminate a low solid non-dispersed mud system
can only be weighted up with barite to about 12.0
ppg. If a higher mud weight is needed, the system
must be a dispersed. In a dispersed system can be
weighted to about 18.0ppg.
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28. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
28
Total
Hardness as
calcium
Total Hardness as Calcium
Total Hardness as Calcium is a measure of the
hardness of the water in the mud system. Water
containing a large amount of dissolved calcium or
magnesium salts is referred to as “hard water”. The
most common indicator of hard water is the difficulty
of soap to lather up. Hardness in the mud system
can come either from the water that you start with
or from the formations penetrated while drilling.
Some sources for calcium are anhydrite, gypsum,
some shales, and cement plugs. Bentonite gel and
other drilling clays have low yields when mixed with
hard water. Also extensive calcium contamination
results in high water loss and fast gel rate. Hardness
is usually treated with caustic soda or soda ash.
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29. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
29
Lost
Circulation
Lost Circulation
Lost circulation can be a very troublesome and costly
problem in the drilling industry. Yearly the cost of
materials, man hours, and lost holes amount to
millions of dollars.
Lost circulation, or lost returns, is the loss to
subsurface formations of drilling fluid used dring
drilling operations. The loss may vary from a gradual
lowering of the mud level in the pits to a complete
loss of returns.
Loss of drilling fluids can occur in four types of
formations:
Unconsolidated or highly permeable formations
Natural fractures
Induced fractures
Cavernous formations
Mud losses to induced fractures are the most
troublesome because they can occur in any
formation. It is difficult to prevent mud losses to
induced formation because further parting of the
formation will destroy the seal.
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30. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
30
Lost
circulation
Preventive Measures
When in area of known lost circulation, the driller can
increase his chances of success by taking the
following preventive measures:
Use a light mud weight as possible
Lower viscosity, gel strengths, and yield point
within safe limits
Slow pumps to minimum rate necessary to
clean the hole
Pull and run pipe at slow rates
Drill don’t spud bridge
Break circulation cautiously after engaging the
rotary or while pulling pipe
Don’t speed up the pump until circulation has
been established
If lost- circulation zones are expected, pre-treat the
mud with lost circulation materials before drilling into
the zone.
It may be necessary to change your nozzle size to
allow the lost circulation material to be pumped.
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31. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
31
Lost
circulation
Loss circulation zones can be classified as:
Seeping losses
Partial losses
Complete loss with hole full or mud within sight
down hole
Complete loss with mud level over 500 ft. down
the hole
Match the lost circulation material to the type
occurring. For example most seepage losses occur
because the lost circulation agents in the mud are
not fine enough to complete the seal. The size of
material should match the severity of loss.
No advantage is gain if the concentration of lost
circulation material exceeds 25 lb. per bbl.
Mechanical failure of the pump, and plugging of the
drill string is likely when you exceed this limit.
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32. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
32
Lost
circulation
As the severity of the loss zone increases, only
the size of the lost circulation increases, not
the concentration.
If a reasonable amount of lost circulation material is
in the mud system and has not helped, it is useless
to increase the concentration of the same material.
The next step would be to increase the size of the
lost circulation material. If necessary you must adjust
your jets to pump the material, in extreme cases it
might be necessary to run the pipe in open-ended.
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33. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
33
Lost
circulation
When partial or complete loss occurs, it is usually
best to fight the loss zone from above rather than
with the drill string on bottom.
If the mud column is at surface but the well will not
circulate, an accepted procedure would be to trip half
way out of the hole then try to break circulation.
Continue to tripping half way out until circulation is
regained. Once circulation has been established
begin staging in the hole and establish circulation at
each stopping point until the zone has been sealed.
If possible don’t keep lost circulation material in the
mud while drilling ahead. Over time the materials
grind down to the point where they are useless as
lost circulation material. As mud properties
deteriorate circulation pressure increases, and a risk
of lost circulation returns.
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34. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
34
Shale
problems
Shale problems
Maintaining well- bore stability while drilling shale
sections can be tricky. Shales causing trouble have
been describe as:
Sloughing shale
Heaving shale
Running shale
Bentonitic shale
Mud Making shale
Plastic flow shale
Gas bearing shale
Pressured shale
The factors which influence how shale reacts to the
drill bit are:
Degree of hydration
Cementing material binding to the shale
Inclination of bedding planes in the shale
Pressure acting on or within the shale
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35. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
35
Shale
problems
Drilling problems associated with shales are:
Hole enlargement
Hole cleaning
Stuck pipe
Bridges and unwanted fill
Increased mud cost
Poor cement jobs
Difficulty with logging
Shale problems can’t be solved with drilling mud
alone. The mechanical factors which can contribute
to shale problems are:
Erosion due to high annular velocities
Pipe whipping of drill string by rotating to fast
While tripping, pressure surges ,swabbing, or
wall contact
Internal forces within the formation(tectonics)
Gas pressure within the shale
Mud filtrate or whole mud invasion of shale
bedding planes or fractures
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36. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
36
Shale
problems
Solving a shale problem caused by pressure is
simple. Increase the mud weight. There are other
drilling practices that will help in this situation:
Keep the hole full
Low viscosity, low gel strengths, and thin wall
cake will aid in preventing swabbing
Pull slowly through the problem interval
Another problem encountered is the effect of mud
chemistry on the shale. Mud making and bentonitic
shales are examples although there are many other
types of clays present in shales. These shale can
either hydrate or dehydrate, depending on whether
water from the mud moves into the shale, or water
from the shale moves into the mud. In either case
the shale can become unstable. Field experience has
shown that fewer problems occur when fluid loss is
kept to a minimum. It should be pointed out that
once a problem is created by high water loss it is
more difficult to stop.
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37. Instructor Guide Trinidad Drilling
Drillers Program
Section 12
37
Shale
problems
Another factor influencing shale stabilization is PH.
A PH of 8.5 to 9.5 gives better well-bore stability
than a high PH such as found in lime muds. High Ph
seems to promote rather than alleviate shale
problems of this type.
Many problems shales are time sensitive especially
the ones affected by mud chemistry. Many shatle
problems are not as severe when the hole is drilled
in as a short time as possible.
To summarize, when drilling shale problem shale:
Drill with sufficient mud weight
Control the water loss at a low value
Keep the mud in the correct PH range
Keep the shale exposure as short as possible
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