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27 September 2004
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FUNCTIONS OFFUNCTIONS OF
DRILLING FLUIDSDRILLING FLUIDS
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Functions Of Drilling Fluid Introduction
Objective of Drilling Operation drill safely evaluate complete
produce Responsibility
Drilling Fluids are critical for successfully achievingthese objectives
Mud Engineer is responsible for maintaining thedrilling fluid system
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Functions
1. Remove Cuttings From The Well Viscosity
The use of shear-thinning, thixotropic fluids with low
shear rate viscosity... Velocity
Annular velocity is key parameter Density
Pipe Rotation higher rotary speeds also aid hole cleaning
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Functions
2. Controlling Formation Pressure
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Functions
3. Suspend and Release Cuttings
Drilling fluids must suspend and release cuttings for efficienct solids control.
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Functions
4. Seal Permeable Formations
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Functions
5. Maintain Wellbore Stability
Wellbore stability is a complex balance.
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Functions
6. Minimize Formation Damage
Protecting the reservoir from damage is a big concern.
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Functions
7. Cool & Lubricate, Bit, and Support Drilling
Assembly & Casing
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Functions
8. Transmit Hydraulic Energy To Tools and Bit
Hydraulic energy can be used to maximize ROP. Provides power for downhole motors and MWD, LWD tools
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Functions
9. Ensure adequate formation evaluation
accurate formation evaluation is essential for the success cuttings logs coring
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Functions
10. Corrosion Control
Dissolved gases can cause serious corrosion problems
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Functions
11. Facilitate Cementing and Completion
The mud should have a thin, slick filter cake.
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Functions
12. Minimize Impact On The Environment
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Functions
Summary Mud Selection Process Mud Properties vs. Functions Functions and Properties will clash
Drilling fluids engineering almost always requires tradeoffs...
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Mud Check / Properties IntroductionMud Check / Properties Introduction
Solids in a mud system determine fluid density,Solids in a mud system determine fluid density,viscosity, gel strengths, filter- cake quality andviscosity, gel strengths, filter- cake quality and
filtration control.filtration control.
Solids and their volumes also influence such factorsSolids and their volumes also influence such factors
as ROP, hydraulics, dilution rates, surge and swabas ROP, hydraulics, dilution rates, surge and swab
pressures, differential sticking, bit life, pump life..pressures, differential sticking, bit life, pump life..
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Measured in: pounds per gallon
kg/m3
SG lb/ft3
Mud Check / Properties DensityMud Check / Properties Density
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Non-aqueous liquids used to formulate OBM &SBM are compressible Fluids. Density increases with pressure
Density decreases with temperature Due to T & P effects, equivalent downholedensity will be different to surface condition
Effects somewhat counter each other Effects more severe when drilling in hightemperature environments
Mud Check / Properties DensityMud Check / Properties Density
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Mud Check / Properties DensityMud Check / Properties Density
R TUAL
HYDRAUL CS
ESD: Equivalent Static Density Profile vs MDUnocal Thailand NPWF
Saraline 200: 2!" l#$%al & '0 (F) T*0+ , " (F) T*TD+ , 2-' (F
2!.00 2!/00 2!"00 2!-00 !000
0
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.
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2
1
.
Equivalent Density *l#$%al+
MeasuredDe2th*
000ft+
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Mud Check / Properties DensityMud Check / Properties Density
R TUAL
HYDRAUL CS
Density versus Pit Te3eratureUnocal Thailand NPWF
0 '0 00 '0 200 2'0 002!2'
2!'0
2!/'
!00
!2'
!'0
Density*l#$%al+
Pit Te3erature *(F+
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Mud Check / Properties Density
UNOCAL SPECIFICATION: 6-1/8 HOLE SECTION
9.2 - 13.0 ppg
TheMud WeightMud Weight will vary but in most cases will be
in this range
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Definition:Definition:Internal resistance to flow of a fluidInternal resistance to flow of a fluid
Mud Check / Properties ViscosityMud Check / Properties Viscosity
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Marsh Funnel
Classic Viscometer
Timed in sec/qt.
UNOCAL SPEC
40 - 80 sec/qt40 - 80 sec/qt
Will vary with temperature!
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MUD RHEOLOGY
Mud Check / Properties RheologyMud Check / Properties Rheology
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Rheology is the study of
how matter deforms and flows
Mud Check / Properties RheologyMud Check / Properties Rheology
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Hole cleaning Suspension of solids
Hole stability
Solids control
Equivalent circulating densities
Surge / swab pressures
Factors Influenced by Mud Rheology
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Sleeve
Bob
Dial
Spring
Concentric Cylinder Viscometer
For oilfield viscometers:600 RPM !0"" rec# sec#
$00 RPM %!! rec# sec#
! Dial &nit !#06' lb(!00 s ft
Mud Check / Properties RheologyMud Check / Properties Rheology
Standard MudStandard MudTesting RheometerTesting Rheometer
Fann Model 35Fann Model 35 VG MeterVG Meter 6 speed6 speed
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Dial Units Shear Stress
RPM Shear Rate
Mud Check / Properties VG MeterMud Check / Properties VG Meter
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Plastic Viscosity
Definition:
A measure of the internal resistance to fluid flowattributable to the amount, type, size and shape
of solids present in a given fluid.
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Plastic Viscosity Increased By:
Drill Solids Clays, Shales
Inert Solids Barite, Sand, Limestone, etc.
Colloidal Matter Organophilic Clay, Fluid Loss Additives
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Plastic Viscosity Increased by:
Particles breaking, thus increasing surface areaand more friction
Weight material to increase density
Water Additions
Tightly emulsified water
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Plastic Viscosity
600 DR - 300 DRPV =PV =
PV = Plastic Viscosity, centipoisePV = Plastic Viscosity, centipoise
Measured at Constant Temperature of 150Measured at Constant Temperature of 150ooFF
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Mud Check / Properties Plastic Viscosity
UNOCAL SPECIFICATION: 6-1/8 HOLE SECTION
15 - 35 cps
The above stated range forPlastic ViscosityPlastic Viscosity is
dependent upon mud weights.
Measured At 150oF
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Area Increase by Breaking of Solids
6*inc+ c,be
!*inc+ c,be
!*foot c,be
V-.&M/! c, ft !'" c, in 6*in c,bes !'" c, in!'" !*in c,bes !'" c, in
S&RF1C/ 1R/1! c, ft 62 s) in 6*in c,bes !'" s) in
!'" !*in c,bes !03$6 s) in
!03$6 * 62 4%02 s) in increase
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Plastic Viscosity Decreased by:
Removal of Solids
Shale shaker
Desanders, desilters, and centrifuges Lowering of gel strength allows larger particlesto settle out
Dilution of solids with base fluid or premix
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Yield Point
Definition:
Resistance to initial flow or represents the stress required to start fluid movement.Due to:
dispersion or attraction between solids because of electrical charges located onor near the surfaces of the particles
water phase attraction organophilic clay content
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Yield Point Increased by:
Drilled clay and shale increasing reactive solidscontent
Insufficient treatment with emulsifiers andwetting agents
Adding inert solids (like barite) causing attractiveforces to increase due to crowding of reactivesolids
Addition of gelling agents
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Yield Point Decreased by:
Dilution Solids Removal
Increase in wetting efficiency (sometimes) Emulsifier additions (sometimes)
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Yield Point
300 DR - PVYP =YP =
YP = Yield Point, lb/100 ftYP = Yield Point, lb/100 ft22
Measured at Constant Temperature of 150Measured at Constant Temperature of 150ooFF
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Mud Check / Properties Yield Point
UNOCAL SPECIFICATION: 6-1/8 HOLE SECTION
8 - 18 lb/100 ft8 - 18 lb/100 ft22
Yield PointYield Point to be maintained in the abovestated range.
Measured At 150oF
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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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Gel Strength
Assists in decreasing the settling rate ofcuttings when circulation is interrupted
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Ti3e
4els
PR-5R/SSV/
FR15./
Gel Strength
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Problems Attributed to High Viscosity and Gel Strengths
More pump pressure required
Higher ECDs
Lost circulation by pressure surges
Swabbing of formation fluids into wellbore
Slow gas breakout
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Initial GEL (Dial deflection after 10 seconds ofstatic conditions)
10-minute GEL (Dial deflection after 10seconds of static conditions)
Expressed in lb/100 sq ft
Gel Strengths
M dCh k/P G lS h
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Mud Check / Properties Gel Strength
UNOCAL SPECIFICATION: 6-1/8 HOLE SECTION
4-8 / 7-12 / 12-22 lb/100 ft2
The10 second10 second and1010& 30& 30minute Gel Strengthminute Gel Strengthss tobe maintained in the above stated range.
Measured At 150oF
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Plastic Viscosity & Yield Point
Both Effected by Temperature & Pressure ChangeBoth Effected by Temperature & Pressure Change
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Plastic Viscosity & Yield Point
Unocal Thailand
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VG Meter Dial Reading
Direct Reading 600 rpm 300 rpm 200 rpm 100 rpm 6 rpm (Low Shear Rate Rheology) 3 rpm
Indirect Calculation LSYP (Low Shear Yield Point) = 2 x 3 rpm 6 rpm DR
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HTHP Fluid Loss Effected By:
Viscosity of the continuous phase Temperature oil- or synthetic fluid ratio
high ratios require more dedicated FLadditives
tightness of the emulsion water-wetting of solids
solids content amount of fluid loss additive
Mud Check / Properties HTHP Fluid LossMud Check / Properties HTHP Fluid Loss
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Problems With High HTHP FL: Stuck Pipe Formation Damage
Mud Check / Properties HTHP Fluid LossMud Check / Properties HTHP Fluid Loss
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HTHP Fluid Loss Procedure 350oF or Formation Temperature 500 psi differential Testing started after reaching test temperature Time: 30 minutes
Report: Total Filtrate collected times 2 Report Cake Thickness in 32nd inch
Water in Filtrate is Indication of Weak Emulsion
Mud Check / Properties HTHP Fluid LossMud Check / Properties HTHP Fluid Loss
M dCh k/P ti HTHPFlidL
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Mud Check / Properties HTHP Fluid Loss
UNOCAL SPECIFICATION: 6-1/8 HOLE SECTION
< 3.0 mls at TD
The HTHP Fluid Loss is measured at 350oF 500 psidifferential pressure
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Heat In Retort (+/- 900oF) Pass Vapor Through Condenser Collect Fluid In Graduated Cylinder Record On Mud Check
SF % by Volume Water % by Volume Solids % by Volume
Calculate SF/W Ratio and
Solids Analysis
Mud Check / Properties Composition AnalysisMud Check / Properties Composition Analysis
Water
Solids
Synthetic Fluid
MudCheck/PropertiesLowGravitySolids
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Mud Check / Properties Low Gravity Solids
UNOCAL SPECIFICATION: 6-1/8 HOLE SECTION
40 - 50 ppb
LGS to be maintained by efficient use of thecentrifuges. In most instances, this will require
continuous operation.
MudCheck/PropertiesElectricalStability
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Mud Check / Properties Electrical Stability
The electrical stability is an indication of howtight the water is emulsified in the oil orsynthetic phase
MudCheck/PropertiesElectricalStability(Volts)
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Mud Check / Properties Electrical Stability (Volts)
Oil and SF do not conduct electricity In the electrical stability test, the voltage (electricpotential) is increased across electrodes on a
fixed-width probe until the water dropletsconnect to form a continuous bridge This completes the circuit Record voltage at which the connection is made
M dCh k/P ti EltilStbilit
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Mud Check / Properties Electrical Stability
Factors Effecting ES Water Content Water-wet solids
Emulsion Strength (larger droplets, lower ES) Temperature (higher temp., lower ES) Salt Content (slight reduction in ES with high salt) Weight Material
MudCheck/PropertiesElectricalStability
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Mud Check / Properties Electrical Stability
The electricalstability of a oil- orSDF should be usedto indicate trends... UNOCAL SPEC:
> 500 volts
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MudCheck/PropertiesCaClContent
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UNOCAL SPECIFICATION: 6-1/8 HOLE SECTION
35% By Wt.35% By Wt.
Mud Check / Properties CaCl2Content
Conclusion
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Conclusion
Solids removal is one of the most importantSolids removal is one of the most importantaspects of mud system control.aspects of mud system control.