sec year, mud proberties and measurments

8/10/2019 Sec Year, Mud Proberties and Measurments

1/87

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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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


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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


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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.


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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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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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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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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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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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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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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


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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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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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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-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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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

dependent upon the type of mud being used.44


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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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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

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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

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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

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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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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.

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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 % .

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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.

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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.

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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.

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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.

85

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

sec year, mud proberties and measurments

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