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MUD PROPERTIES AND
MEASUREMENTSBY
Dr: Taher ELfakharany
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INTRODUCTION
The continuous circulation of the drilling fluid is very important to
success the drilling operation which un drillable by percussionmethod.
The first rotary drilling fluid was water, when clay- water mixture was
used as a drilling fluid it lined the bore- hole , preventing caving of
quicksand , and allowed drilling to continue.
The selection of drilling fluids depends on the geological conditions and
the ability of mud to perform the functions necessary .
In soft formation , drilling fluids require very precise control of mud
properties and require special chemical additive.
in hard formation special types of mud ( plain water ) considered assuperior mud.
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Testing of drilling fluids
the purpose of testing drilling fluids is to determine
their ability to perform certain necessary functions.
mud engineer is a person whose duty is to prepare
and maintain the properties of drilling fluids
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MUD PROPERTIES AND MEASUREMENTS
BASIC PROPERTIES AND MEASUREMENTS
Density
Rheology
Fluid loss
Inhibition
Solids Content
These must be achieved in an environmentally friendly,
safe and cost effective way.
The main properties of a drilling fluid are:
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MUD PROPERTIES AND MEASUREMENTS
DENSITY
By convention the density iscalled the mud weight
The units are ppg or g/cc
Occasionally lbs/ft3or psi/ft are
used
Correct and frequentmeasurement is essential
Keep balance clean
Check calibration daily
There are two types of balance Pressurized( hydrometer)
Non Pressurized
Derrickman will record density
every half hour( report density in
ppg)
KEEP HOLE
FREE TO EXPEL
MUD
CALIBRATEBY ADDING/
REMOVING
LEAD SHOT
SCALE BAR
SLIDING WEIGHT
SIGHT GLASS
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MUD BALANCE
MUD PROPERTIES AND MEASUREMENTS
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Mud weightbore hole pressure support
When we drill the wellbore we replace acylinder of rock with a cylinder of mud.
The first critical step towards designinga drilling fluid is to establish the mud
weight required to provide the correct
level of bore hole pressure support.
Pm > Pf
Pm - mud pressure
Pf - formation pressure
Bore hole pressure support
MUD PROPERTIES AND MEASUREMENTS
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Mud weightbore hole pressure support
Pore pressure prediction involves the full cooperation ofseveral different engineering disciplines, ie Petrophysical,
Geology, Reservoir & Geomechanics.
It is crucial that rigorous seismic and / or geolog well datainterpretation is done to determine the anticipated pore
pressure regimes in order to identify any pressure reversals
and therefore facilitate appropriate casing design.
Mud weight planning is based on the predicted pore
pressure gradient plus 300 to 500 psi
One of the key elements to successfully drilling a stable, close to
gauge well bore depends upon planning the correct mud weight
overbalance.
MUD PROPERTIES AND MEASUREMENTS
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SHEARRATE
SHEARSTRESS
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Shear stress is directly proportional to
shear rate
Yield stress (stress required to initiateflow) is always zero
Will not suspend cuttings and weighting
materials
Newtonian fluids such as water, gases and
light oils.11
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Viscosity is dependent on the shear rate.Do not exhibit a linear relationship between shearstress and shear rate at constant pressure andtemperature. ( solid suspension, cement slurries,
muds and clay suspensions).
in laminar flow they are thinner at high shear ratesthan at low shear rates.
At low shear rates, particles link together, increasingthe resistance to flow.
At higher shear rates the linking bonds are broken.
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MUD PROPERTIES AND MEASUREMENTS
VISCOSITY HOLE CLEANING
Viscosity is the internal resistance of the fluid to flow
Viscosity is required in addition to flow rate to clean the hole
Several models have been developed to help understand the
behavior of different fluids in laminar flow
Newtonian model - e.g. Water, glycerin, oil
Bingham Plastic Model - Cement, Flocculated fluids : high solids muds
Power Law Model - Low solids polymer muds, Oil based muds
Viscosity =
The units can be dynes/cm2, Pascal S, Centipoise or lbs/100ft2
shear stress (flow pressure)
shear rate (flow rate)
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DYNAMIC VISCOSITY
The dimensions of dynamic viscosity are obtained by
analyzing the forces exerted on a plate are of A,
Moving on a viscous liquid with velocity, V by a force, F
= Shear stress / shear rate
= (F/ A) / (dV/ dL)Flow between plates defining as viscosity
Lower plate is stationary,
The velocity of fluids between blades varies from V at
the top and zero at the bottom
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MOVABLEPLANE (Area=cm )
FORCE
(dynes)VELOI
HEIGHT(cm)
STATIONARYPLANE
VISCOSITY =SHEARSTRESS
SHEARRATE
F/A
V/H
DYNES/cm
cm/sec
cm
DYNE SEC
cm= POISE
=
=
A
B
(cm/sec)
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MUD PROPERTIES AND MEASUREMENTS
INSTRUMENTS USED TO MEASURE VISCOSITY
Marsh Funnel
Results are very temperature
dependent ( thin or thick).
Used to give trends
Derrick man records results every1/2 hour
The tools must be calibrated with
water which has a funnel
viscosity of 26 +or0.5 sec
Fill mud to mark, 1500 cc
Remove the finger after 950
cc
Torsion Spring
Bob
Variable speed
rotation sleeve
Measure time required
to fill one quart (950) in
second
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MUD PROPERTIES AND MEASUREMENTS
MARSH FUNNEL
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Stormer viscometer:
1-
Fill the cup to within in of the top with the test sample. ifthe sample contains lost circulation or coarse material, pass the
mud through a 20- mesh sieve before pouring into the cup.
2- place cup on viscometer and move it up the grooves in the
support rods . then tighten set screw.
3- release the brake thumb nut and agitate the mud by rapidly
revolving the rotor.
4- set the brake thumb nut and add weights to the plumb lineestimated to cause the rotor to rotate in the cup at 600 rpm( 60
revolution in 6 second)
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5- release the brake thumb nut; agitate , allow the rotor to
make about 20-30 revolutions and then measure the number
of seconds required for the rotor to rotate 60 revolutions( one
complete circle)
6- adjust the weight and repeat step 4 which weight requiredto give 600rpm
7- the no of grams obtained is used to calculate the viscosity
from calibration chart.
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MUD PROPERTIES AND MEASUREMENTS
MULTI SPEED VISCOMETER
6-speed FANN viscometer
Fann Viscometer
Can measure different shear
stresses for different shear rates
Should be used with a heated cup
to give readings at a set
temperature
Also used to measure gel strengths
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MUD PROPERTIES AND MEASUREMENTS
BINGHAM PLASTIC MODEL
PV =Q600 - Q 300 (cps)
Is a part of the resistance to flow caused by
mechanical friction
The plastic viscosity is due to the physical size
and presence of any solids or emulsified droplets
in the fluid. The PV should be as low as possible
To reduce the PV reduce the solids
Yield Point = Q 300 - PV (lbs/100ft2)
The yield point is the viscosity due to the chemical
attraction between the particles. Affected by typesof solids, concentration of solids, and dissolved
salts
To increase the YP add products with attractive
forces.
To reduce add products which reduce attractive
forces
t = ty+ gPV
Q
600
Q
100
ty
PV
Shear rate (g
Sh
earstress
t
)
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V S OS TY
Drilling Fluid Viscosity Varies With Shear Rate.
Funnel Viscosity - Seconds per Quart.
Water = 26 seconds +/- second
Plastic Viscosity - Centipoise. (one gram /cm-sec)PV =
600 -
300
Apparent Viscosity - Centipoise. (6002)
Effective Viscosity - The Measured or CalculatedViscosity at a Given Shear Rate.
Low Shear Rate Viscosity - Centipoise.
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MUD PROPERTIES AND MEASUREMENTS
The Gel strengths refers to the increase in viscosity at
zero shear rate
It is the measure of the attractive forces under static
conditions( quiescence time)
Initial and then subsequent
3 rpm viscometer dial readings,
i.e. 10sec, 10min, 30min= gel strengths
GEL STRENGTHS
Time at zero shear rateMaximums
hea
rstressat3RPM
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GEL STRENGTH
Gel structure develops as a result of charged
particles assuming equilibrium positions (positive
to negative) with respect to each other
Gel strength is a function of time, temperature,concentration and strength of attractive particles
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The electro-chemical attractive
forces between solids under
static conditions.
Closely related to yield point,
i.e. electro-chemical interactions
and the measure of
aggregation, flocculation or
dispersion of the in situ solids.
Initial gel strengths are a goodindicator of low shear rheology
(i.e. 3 rpm viscometer dial
reading).
Gels can be:
Fragile:A 10 min gel strength
that increases but breaks backrapidly after initiating viscometer
shear.
Flat: An initial gel strength that
only increases marginally over
10 mins.
Progressive: An initial gel
strength that increases
significantly over 10 mins and
beyond.
Primary factors that impact gel strength values
MUD PROPERTIES AND MEASUREMENTS
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MUD PROPERTIES AND MEASUREMENTS
EFFECTS OF EXCESSIVE VISCOSITY
Increased pump pressure
Loss of mud at the shakers
Poor efficiency of the solids control equipment
Increased risk of fracturing the formation, especially with high gel
strengths
Poor mud removal for cementing operations
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MUD PROPERTIES AND MEASUREMENTS
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MUD PROPERTIES AND MEASUREMENTS
EFFECTS OF INSUFFICIENT VISCOSITIES
Poor hole cleaning Cuttings bed
Hole fill
Stuck pipe
Cuttings degradation
Overloading of the annulus increasing the hydrostatic
Increased erosion if the fluid is in turbulent flow
Barite sag or settlement
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Gel strengths are measured with either stormer or fan V
G meter as the shear stress necessary to cause spindlemovement at very low shear rate , 3, 6.
The stormer gel strength in grams multiplied by
0.00326 gives the gel strength in Ib/100 squ, Ft.And by using fan viscometer the dial reading gives the
gel strength directly in (lbs/100FT2).
the treating chemicals used for reducing mud viscosityalso reduce the gel strength.
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THIXOTROPY
Thixotropy:The termthixotropy is applied to
the property of water suspensionwith clay which causes it tobecome semisolid gel when it is
left for a time, jelly like mass
This phenomena can be retuned toit is initial condition by agitation
With time a greater force than the
YP is required to get the fluidmoving again
Gel Strength (lbs/100ft2)
Yield Point (lbs/100 ft2)
ShearStress
Gel Strength
Yield Point
Decreasing
Shear Rate
Increasing
Shear Rate
Shear Rate
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The apparent viscosity of a drilling fluids may thus vary over
a wide range depending upon the lattice like coagulation of
suspended clay particles forming the gel.For example :
Drilling fluids in rapid circulation may have an apparent
viscosity 20 centipoises.
After a 10 min period , the same fluid may have an apparentviscosity ,1000 centipoises or more. This property is very
important when circulation is stopped.
For any reason , the pumps are stopped for a time , the gel
strength of the drilling fluids will increase and the drillingcuttings remain suspended.
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Filtration Test
Filtration properties of drilling muds are a measure of the ability
of the solid components of the muds to form a thin, low-
permeability filter cake.The lower the permeability, the thinner the filter cake and the
lower the volume of filtrate from muds of comparable solids
concentration.
This property is dependent upon the amount and physical mud.It has been shown that , when mud of sufficient colloidal content
is used, drilling difficulties are minimized.
In contrast , a mud low in colloids and high in inert solids
deposits a thick filter cake on the walls of the hole.
A thick filter cake restricts the passage of tools and allows an
excessive amount of filtrate to pass into the formation, thus
providing a potential cause of caving
( formation damage)
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MUD PROPERTIES AND MEASUREMENTS
API FILTER PRESS
T- screw
Mud Cup
Framesupport rod
top cap
graduated cylinder
Base cap
thump screw
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Attached to the nitrogen cylinder are a pressure
regulator , a small rubber hose connects this unit to the
filter cell.
Procedure1-Assemble the following dry parts in this order:
base cap, rubber gasket, screen, a sheet of filter paper,
rubber gasket, and cell. Secure the cell to the base cap
2- fill the cell with the sample to be tested to within
0.25in of the top ( necessary to conserve the
compressed gas), set the unit in place in the frame.3- check the top cap to make sure the gasket is in
place. Place the top cap on the cell and secure the unit
with the T- screw.
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4 l d d d li d d h fil
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4-place a dray graduated cylinder under the filtrate
tube.
5- Open the valve to the cell. apply 100 psi pressure to
the filter cell , timing of the test should begin now.6- At the end of 30 min , close the valve to the cell
rapidly and open the safety valve to release the
pressure , return the T- screw.
7- Read the volume of filtrate collected in thegraduated cylinder.
| Results:
i) report the filtrate loss in ml as the API( 30 min)
filtrate loss of the mud.
ii) the filter cake thickness is determined after the filter
cell has been disassembled
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Remarks:
1- after step 5 and before step 6, the amount of
filtrate collected in 7.5 min can be observed and ifmultiplied by two gives a very rough estimate of
what would have been collected after 30 minutes.
2- if muds with extremely high sand content , the
filter press may be tilted from its vertical positionto prevent sand from settling on the filter paper.
V2 = V1 * 2/1 , V2 = V1 * 1/2
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Colloidal properties of drilling fluids:
the ability of muds to form a suitable mud line on
the wall of the well ,to seal the pore space , and to
lubricate the drill pipe depends on its colloidal
properties.
For example : clayladen possess colloidalproperties in varying degree, depending upon the
characteristics of the clay used and chemical
constitution of water phase.
Bentonitic clay have colloidal properties higherthan Kaolinites
bentonite marketed under the name of Aquagel.
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There is no unit of colloidity and no method of
measuring the colloidal value of a drilling fluid .the most direct method is that afforded by a wall-
building test instrument.
The ability of a fluids to form a mud cake, under
such conditions in an actual well , may be directly
observed.
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Colloidal suspension:
The terms colloid and colloidal suspension often
used when speaking about drilling fluids, solidssuspension in solution.
Colloidal suspensions of clay solids have a
tendency to gel if circulation is stopped for a
period of time, gel is destroyed by agitation.The suspension formed when bentonite or clay is
mixed with water without making a solution,
because the clay can be separated from the
suspending liquid by the physical process of
filtration.
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Sand content:
all material coarser greater than 200 mesh may be
regarded as sand and for good practice, sandcontent of drilling fluid must be maintained below
5 percent.
Sand content determination of drilling mud is
desirable, because excessive sand may result in thedeposition of a thick filter cake on the wall of the
hole, or may settle in the hole above the tools when
circulation is stopped, thus causing stuck for drill
pipe and bit which lead to twist off.High sand content also may cause excessive
abrasion of pump parts and pipe connections.
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sand content set consists of a 200- mesh sieve, funnel, and
a glass measuring tube calibrated from 0 to 20 % to read
directly the percentage by volumeProcedure:
1- pour mud into sand content tube until it fills up to the
mark mud to here. Then add water to the mark water to
here". Cover mouth of the tube with thumb and shakevigorously.
2- pour this mixture through the screen, being careful to
wash everything out of the tube with clear water through
the same screen. Wash sand retained on screen with a
stream of water to remove all mud and shale particles.
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3-
Fit funnel down over top of screen, invert slowly,turning tip of funnel into mouth of tube, and wash sand
back into tube with a fine spray of clear water on the back
side of screen. allow the sand to settle.
4- Observe the quantity of sand settled in the calibratedtube as the sand content of the mud.
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MUD PROPERTIES AND MEASUREMENTS
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SAND CONTENT
PH value ( acidity or alkalinity) test :
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PH value ( acidity or alkalinity) test :
the degree of acidity or alkalinity of drilling mud is
indicated by the hydrogen ion concentration which is
commonly expressed in terms of pH.A perfectly neutral solution has a pH of 7.0. Alkaline
solutions have pH readings ranging from just above 7
for slight alkalinity to 14 for the strongest alkalinity,
while acid solutions range from just below 7 for slightacidity to less than 1 for the strongest acidity.
The pH measurement is used as an aid in determining
the need for chemical control of the mud as well as anindicating the presence of contaminants such as cement,
gypsum, the optimum pH for any drilling mud is
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Two methods of measuring the pH of a drilling mud
are in use:
1- modified colorimetric method, such as Hydrion
pH Dispenser
2- electrometric method using a glasselectrode
instrument, such as the Beckman or analytical pH
meter( more accurate).
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Basic functions of the drilling fluids
To cool and lubricate the bit and drill string
To remove and transport cuttings from the bottom of the hole
up to the surface(hole cleaning)
To suspend cuttings during times when circulation is stopped
To control encountered subsurface pressure ( pressure
control)
To line the hole with an impermeable filter cake
To support part of the weight of the drill string and casing
To give a good information about the formations penetrated.
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Un desirable properties of drilling fluids
Require excessive pump pressure at the desired
circulation rate
reduce the evaluation of the productivity of the
encountered formations
Adversely affect of the productivity of pay zone
Allow suspension and continual circulation of abrasive
solid
Corrode the drill string
Reduce rate of penetration
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1- Cooling and lubrication of bit and drill string1- The drilling fluid removes heat from the bit which is then dispersed
at the surface( heat generated by the friction between bit and other
contact point)A) Fluid formulations are not changed to improve this function
B)Very occasionally the temperature of the fluid exceeds the flashpoint. In this case it is necessary to improve surface cooling
2- Extra lubrication may be required between the drill string and thecasing or wellbore, especially in directional wells( excessive torque)
A) Liquid additives are used, or Oil base mud( lubricants coat metalsurface with a high strength lubricating film)
B) Solid additives are sometimes used such as glass beads, plasticbeads, graphite or nut plug
C) Drill pipe rubbers are sometimes added to reduce wear between thecasing and drill pipe
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2- Cuttings removal and transportation
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The most important parameter is the
Annular Velocity (A.V.)Where possible the annular velocity
should be 100 ft/min, higher in deviatedholes.
In large hole sections the A.V. can be aslow as 20 ft/min.
If the A.V. is insufficient to clean thehole the viscosity must be increased
For top hole high viscosities must be used
Cuttings removal is harder in deviated
and horizontal holes as the verticalcomponent of the mud is reduced.
A.V.(ft/min)
= Pump rate(bbls/min)/
Annular vol (bbls/ft)
Slip Velocity (ft/min)
=Cuttings velocity -A.V.
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In laminar or viscous flow, cuttings will be in the center ( point ofmaximum velocity) which reach to the surface quickly, whilecuttings close to the walls will move upward slowly.
Most bit cuttings are flattish and will rise and lower exceptions sandgrains.
In turbulent flow, the velocity profile is much flatter and the overturning will not occur.
Low viscosity, low gel strength muds are the most effectiveproperties for lifting cuttings up to the surface.
Equation in laminar and turbulent flow for calculating slip velocityof cuttings ( flat or spherical particles)
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3- Cuttings suspension
Whenever the pumps are switched off, solids will start to settle.
This can result in:Bridging off of the wellbore
Stuck pipe and result in an expensive fishing job
Hole fill
Loss of Hydrostatic
A gel structure is required to suspend the cuttings under zero shear
conditions:
The gel structure is caused by time dependent attractive forceswhich develop in the fluid.
The longer the fluid is static the stronger these forces become
The gel structure should be easily broken
The gel properties are especially important for deviatedandhorizontalwells as the distance solids have to settle is very small
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In hard rock
The penetration rate is low and hence a relatively
small quantity of cuttings in the hole, the effectof gel strength is minor important , we can use a
plain water as a drilling fluid.
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In soft rock
The penetration rate is high and hence the quantity
of cuttings in the hole is quite large, the effect ofgel strength is very important to lift cuttings,
4- Control of encountered subsurface pressure ( pressure
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4 Control of encountered subsurface pressure ( pressure
control)
The pore pressure depends on:
The density of the overlying rockThe pressure of the interstitial fluidWhether the rock is self supporting or is supported bythe fluid.Tectonic activity
If the fluid hydrostatic pressure does not balance the porepressure the following may occur:
Influxes of formation fluid into the wellbore
Lost circulationHole Instability
Stuck pipe
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The pressure balancing the formation
pressure is composed from thehydrostatic pressure under static
conditions:
P = Depth (ft) x Density (ppg) x 0.052
Under circulating conditions the effective
pressure is increased by the pumping
pressure. The forms of the Equivalent
Circulating density (ECD):ECD = Density (ppg) + Ann Press Loss
Depth x 0.052
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PorePressure(Not normallyknown)
Hydrostatic Pressure (psi)= Height (ft) x Density(ppg) x 0.052
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Composition and nature of common drilling muds
In some cases , water or oil are satisfactory as a drilling fluids , however thedesired functions of the drilling fluids require special chemical additive .
Mud consists of :
1- continuous phase ( liquid)
2- dispersed gel forming phase such as ( emulsified liquid ,colloidal solids)
3- inert dispersed solids such as ( weighting material , sand andcuttings)
4- chemical additives necessary ( to maintain or give desiredproperties)
the mud properties affected by temperature and pressure , normallythe effect of pressure is not critical.
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Mud types
1- Fresh water muds:
i- simple clay water mixtures
ii- chemically treated clay water mixtures
iii- calcium treated muds.
2- Salt water muds
3- Emulsion muds
i- oil in water emulsions
ii- water in oil ( inverted ) emulsion
4- oil base muds.5- Surfactant muds.
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1- FRESH WATER MUDS:
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The basic elements of these type are fresh water and suspended clay,various material for specific properties.
1- simple clay water mixtures
The clay will hydrate water when its in contact with water and formcolloidal mixtures.
sodium bentonite has the highest fresh water yield of all clay.
Yielddefined as the No of barrels with 15 centipoise viscosityobtained per ton clay. For bentonite the yield is 100 bbL.
In sodium bentonite Na is dominant ion which absorb high amount ofwater , give high viscosity with low clay content than other clay and
give better colloidal properties.The natural clays encountered in some areas have sufficient quality to
form satisfactory fresh water muds without commercial claysadded.
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Si l t l d it bl f h ll d illi i
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Simple waterclay muds are suitable for shallow drilling in areaswhere contaminating beds are no problem, LCM, weighingmaterials may be added as needed.
2- Chemically treated clay water mixtures
when the formations are contaminated with ( salt ( NaCl), gypsumCaso4. Nh2o), or anhydrite ( Caso4 ), bentonite treated muds areunsatisfactory.
These contaminants are a source of calcium ions which causeflocculationof the clay particles.( particles form an open network
type of structure).Flocculation causes an increase of water loss, viscosity and gel
strength which considered un desirable properties.
When the amount of calcium contamination is small such as
cement plug, the system can be treated directly by usingsodium bicarbonate or barium carbonate which removesoluble calcium and replaced by calcium carbonate.
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Viscosity reducer
Polyphosphates , caustic soda ( NaoH), quebracho, lignin (
CARONOX)or humic compoundsThe mud treated with causticquebracho mixture turned to red
and commonly called red muds.
Water loss reducer
Organic colloids , such as pregelatinized starch or ( CMC)
Carboxyl methyl cellulose
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3- CALCIUMTREATED MUDS.
if the formations encountered contaminated with calcium ion ( Ca++) the mud
system must be treated with calcium.This type of muds classified according to calcium source, the manner and
degree of treatment.
Therefore the difference between calcium contaminated and calcium treated
mud in that : the latter allowed to remain the calcium in mud for special
benefits.
These muds tolerate other flocculating salts ( up to 5 % Nacl) which contain
high solid % at low viscosity and relatively easy and maintain for filter loss
and gel strength.
Filter loss may be controlled with starch or CMC
Starch for mud having p H >12 and salinity >25
CMC for all types of muds except those of high salinity
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Lime treated muds Ca ( OH)2
1- High lime treated muds
2- Low lime treated muds
High lime treated muds
61
Materials additives Percentages
Caustic soda 2 to 4 Ib/ bbL
Organic thinner 2 to 4 Ib/ bbLSlaked lime 2 to 20 Ib/ bbL
pH Above 12
Advantages of high lime treated muds
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Advantages of high lime treated muds
1- Low viscosity and gel strength
2- Easily maintained low filter loss
3- High resistance to contamination
4- May be weighted up to 20 Ib / gal
5- may contain high solids concentrations at low viscositiesDisadvantages of high lime treated muds
The tendency to solidify at high temperatures which lead to
use low lime
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LOW LIMETREATED MUDS
Low lime muds contain less caustic soda , lime and clay
pH is normally from 11.5 to 12.5.
this type of mud give high viscosity than high lime muds.
other classifications of calcium treated muds
gypsum- treated muds which used for drilling gypsum andanhydrite beds.
This types of mud is maintained at low pH ( around 9.5 ) gel
strength and flow properties being easily maintained.
The higher calcium content in muds the higher inhibitive to clayswelling which desirable for drilling bentonite shale sections.
used in drilling high temperature formations
63
Salt water muds
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Salt water muds
The principal use of salt water muds :
The areas where salt section or bed must be drilled or in areas where
salt water is available such as off shore , swamp and sea sidelocations.
The difference between fresh and salt water muds is the type of clay
used as the gelforming phase.
Sodium bentonite does not form a satisfactory colloid in salt water.
Salt concentrations neutralize the electric charge on dispersed
bentonite particles.(positive charges surrounding the solid are
driven closer to negative charges) allowing flocculation
properties.
Salt clays dont exhibit desirable wall building properties of
bentonite, but exhibit thick mud cakes and high water loss.
Starch or CMC are used for filtration control.64
OIL IN WATER EMULSIONS
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This type is the most common emulsion muds , in which the oil is the dispersed phaseand exists as small individual droplets.
The base mud may be any type of fresh or salt water mud.
The stability of such emulsions dependent upon emulsifying agents used such as soaps, lignin compounds, organic colloids such as starch or CMC and other colloidalsolids.
All types of oil have been used however diesel oil is the most common used for : Un cracked , for stability
High flash point, to minimize fire hazard
High aniline number>155 to reduce the rubber parts failure circulation system
Low pour point ,for use in varying temp.
have color and fluorescence
The quantity of oil added to the base mud near (10 %) dependent on the desiredproperties
65
THE ADVANTAGES OF OIL IN WATER
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EMULSIONS
Increase the rate of penetration
Give better lubrication of bit and drill string
Reduce the drill string corrosion
Improve mud properties such as reduce viscosity, pump
pressure ,and water loss and give thin and smooth filter
cake
Reduce the formation damage ( pay zone)
Less hole trouble , such as bit balling, heaving shales,
and hole enlargement.
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h di f il i l i
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the disvantages of oil in water emulsions
Additional cost of oil and the problems of cuttings analysis.
The water loss test is a good indicator of emulsion stability:
if no free oil appears in the filtrate paper , means the oil
molecules are still dispersed in the solutions.
67
WATERIN OIL ( INVERTED ) EMULSION
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( )
In this type , water is the dispersed phase. This type of mud is not
commonly used because their additional cost. this type contains
from 30 to 60 % water and the oil may be diesel or crude oil.
Emulsifying agent is generally added and mixed with oil also
weighting materials may be added if desired.
We can change the percentages of oil and water as required.This type of muds have low gel strength, high viscosity, filtration
rates are quite low and more stable at temp approximately 200 F.
advantages: easy of handling and mixing , lower cost than OBM
any water and most crude oils may be used as materials.
Disadvantages: instable at temp above 200 F, possible reversion to an
oil in water type if excess solids or weighting material accumulate,
And require closer supervision.68
Oil b d
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Oil base muds:
Oil base muds are expensive and used in special purpose as a
drilling fluids.
In this type , high flash diesel oil is the continuous phase,
also contains oxidized asphalt to give colloidal
properties, and provide the wall building property,
organic acids and alkaline forms an unstable soap
which give the viscosity and gel strength required .
Organic acid thin the mud where the alkaline make it
thick, and various stabilizing agentsWater as dispersed phase from 2 to 5 % .
69
WHY WE USE OIL BASE MUDS
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WHY WE USE OIL BASE MUDS
1- drilling and coring of possible productive sections, to reduce the
formation damage of pay zone by water influx2-Drilling heaving shales which continually hydrate , swelling and
slough when contacted with water.
3- High temp drilling where possible solidification or otherproblems make other muds un desirable.
4- used as perforating fluids to prevent contamination of thesection after it is perforated.
5- Numerous prevention uses, such as freeing stuck pipe, corrosionprevention, and remedial work of producing wells.
The primary advantages of all muds having oil as continuousphase are minimum contamination of pay zone and insensitiveto the common contaminant.
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D illi h d
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Drilling hazards
There are certain hazards of drilling may be avoided or overcome
by proper control of mud properties.Some of hazards which may be encountered during drilling:
Salt section hole enlargement
Heaving shale problems
Blowouts
Lost circulation.
72
Salt section hole enlargement
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When salt section or salt bed encountered during drilling and thesis
section must be penetrated , solution and erosion of these beds can
cause excessive hole enlargement which in turn causes some
trouble :
The enlarged hole make fishing operations more difficult , when
the drill string failure.
The enlarged hole require larger volume of muds to fill the system ,hence the total cost increased.
The enlarged hole require larger cement volume for casing
operations
To avoid these problems we must prepare salt saturated mud to drillthe salt sections.
73
HEAVING SHALE PROBLEMS
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HEAVING SHALE PROBLEMS
Some areas are characterized by shale sections containing bentonite or other
hydra- table clays which continually adsorb water, swell and slough intothe hole causes severe drilling hazards when encountered such as pipe
sticking, excessive solid build up in mud and hole bridging.
There are various treatment methods may be used:
Changing mud system to inhibitive ( high calcium content) type such as
lime ,gypsum, which reduce the tendency of mud to absorb water.
Increasing the rate of penetration for rapid removal of cuttings.
Increasing mud density for greater mud cake.
Decreasing water loss of mud
Changing to oil emulsion mud
Changing to oil base mud.
treatment methods depend upon the degree of severity.74
BLOWOUTS
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Blowout is the most expensive and highly feared hazard of drilling.
blowout occurs when the encountered formation pressure exceedthe mud column pressure which allows the formation fluids to
blow out of the hole. Blowout also may be caused by too rapid
withdrawal of the drill string this is known as ( swabbing).
The density of muds is the principal factor for avoiding this
problem.
The magnitude of pulling drill pipe depend upon the speed of
withdrawal, hole- pipe clearance, mud viscosity and gel strength.
75
Lost circulation:
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Lost circulation:
Lost circulation is defined as the loss of quantities of
whole mud to an encountered formation. Lostcirculation may be partial(10 % from total volume), or
complete loss.
Lost circulation occurs when formation permeability issufficiently great to accept whole mud; voids are too
large to be plugged by the solids in mud or when the
hydrostatic pressure is greater than the formation
pressure.
76
Undesirable effects of lost circulation
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Undesirable effects of lost circulation
Continuance drilling without returns, increase the mud cost.
The drop in annular mud level may cause a blowout
No information about the formation being drilled.
The possibility of stuck pipe with a resulting fishing job is
increased
Loss of drilling time the total cost increased
If the lost circulation zone is the pay zone , productivity
damage may result.
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There are a relations between the permeability of
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formations and the loss of mud solids into the
formations.
faulted , jointed and fissured zones can be considered asthe most common source of lost circulation.
When the mud column pressure exceeds the stress
holding a fracture , it opens and accepts the mud andloss of circulation occurs. The bad handling of drill
string (run in) may cause fracture and loss.
Cavernous or open fissured formations are the most severe
case of lost circulation (blind drilling or drilling withoutreturns for some distance below the cavernous section
is continued, then casing must be set through this zone
and cemented.79
Methods of combating lost circulation
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Methods of combating lost circulation
The operations requires some knowledge about the zone
which obtained by down hole surveying devices.
First of all we can change the properties of drilling fluids
to cure some lost circulation problems, or we can use
air, gas and aerated mud ( gasified fluid) for thisproblems.
Spotting plugs containing mud, cement, LCM opposite
the permeable zone is a common cure.
80
LCM USED FOR COMBATING LOSS
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LCM USED FOR COMBATING LOSS
Fibrous materials : hay, sawdust, bark, cotton seed,
hulls and cork.
Lamellate (flat, platy) materials : mica and cellophane
Granular material : nut shells, perlite, and ground
plastic.Fibrous and lamellate materials are most effective in
coarsely permeable rocks where voids are relatively small
Granular materials are used in larger openings which
required to form a bridge across the void.
81
MUD CALCULATIONS
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MUD CALCULATIONS
1- volume Vs = ( )
( )
* Vs + m1 =
2- weight *Vs =( )
( )
ol % =( )
( )
Wt % = ( )( )
82
BUOYANCY
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BUOYANCY
Archimedes principle states that a body submerged either wholly or
partially in the liquid is buoyed up by a force equal to the weight of the
liquid displaced.
In drilling operations, the hole is usually full with drilling fluid,
this buoyant force can be calculated by assuming the weight
of 1 ft of drill pipe immersed in drilling mud would be:
Wpm = WpaWm
Wpa =/4*( - )p
Wpm =/4*( - )m
Where:Wpm , Wpa : weight of drill pipe in mud and in air,Ib/ft
Wm weight of equivalent volume of mud Ib/ ft
m, p, density of mud and steel, Ib/ cu,ft83
Wpm =Wpa (1- m / p)
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Effect of buoyancy on drill pipe
Several opinions have been expressed:i) buoyancy acts along the entire length of the pipe which reduce
the weight of the pipe, but not affect the neutral point( the point
where the axial stresses were zero) of the pipe.
ii) buoyancy acts on the bottom of the pipe, and affect on neutralpoint.
Buoyancy may cause buckling to the drill string.
The neutral point in the pipe will move upward as the density of
the immersed fluid increased. Or the neutral point affected bythe fluid density
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If the drill pipe suspended in air the neutral point will
be at the bottom of the pipe.
Buoyancy acts on the bottom of the pipe , if the pipe
becomes stuck at some point up the hole, then
buoyancy are not acting above the stuck point.
The weight of the pipe down to the stuck point will be
the weight of the drill pipe in air and not in mud
which is very important in fishing operations.
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Weight indicator:
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Weight indicator:
Is the device used to show the weight of equipment
hanging from the travelling block usually attached to the
dead line.
this device was designed to prevent over loading on the
derrick.
The function of this device :
i) show the weight on bit
ii) Show the friction loads during lifting the tools from the
holethe reading of indicator dependent upon the number of line
in the travelling block and the size each one.
The weight indicator must be calibrated if the line changed.86
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THE END
Thank you
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