Download - 08 A Cementing
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Cementing
Cementing
• Objectives• Primary and remedial placement techniques• Applicable tools• Job Sequences• Slurry composition• Job design calculations• Required slurry testing
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Cement Job Planning
1. Identify purpose for placing cementa) Primary - casing, liner, or tiebackb) Remedial – sidetrack or abandonment
2. Identify wellbore parametersa) Pressureb) Temperaturec) Fluid typesd) Formations
3. Determine TOC, and cement density and volumea) Coverageb) Fracture limitations
4. Downhole equipment tools and procedures5. Communicate job details to Service Company
Primary Cementing
Definition-Primary cementing is the process of effectively displacing the drilling fluid and placement of cement slurry(s) to form a continuous and competent cement sheath within the wellbore annulus, while maintaining well control.
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Primary Cementing: Objectives
• Support– Tension– Lateral – buckling, pressures
• Isolation – From Surface– Cross flow between zones
• Compliance– Government requirements– Company requirements
Isolation
• Isolation between zones• Isolation to surface• For the life of the well
– Production– Environmental– Well Control
Gas Sand
Aquifer
Isolation
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Intermediate Objectives
Choose cement type and additives for needed density, rheology, filtration, yield, compressive strength, etc. Calculate cement volume required. Design job for best placement.
Deliver slurry volume with performance properties required for job
Calculate hydrostatic pressure effects of fluid columns, Monitor and control U-tube effect
Maintain control of the wellbore
Hole condition, centralizers, spacers/washes, flow rate, wiper plugs, pipe movement
Remove mud / debris from area to be cemented
ActionObjective
Primary Cementing Technique and Issues• Prepare wellbore for casing and cementing operation
– Clean cuttings and debris out of hole– Condition mud for easy removal
• Run casing string with appropriate tools for the job– Float equipment, stage tool, liner hanger– Centralizers, external casing packer, liner top packer
• Mix a dry cement blend on surface with mix water– Cement– Additives– Mix water
• Pump it into place in liquid form from the surface– Mud Removal– Cement coverage– Timing
• Allow the cement to hydrate and harden in place– Time– Temperature
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Running the Casing• Pull wear bushing.• Confirm unobstructed access from v-door to rotary table.
• Rig up casing handling tools – spider, elevator, tongs, hydraulic power, torque turn, fill up line.
• Pick up / make up shoe joints. Test floats.
• Run in hole. Continue running casing, filling as required. Add centralizers.
Float Equipment
• Float Shoe• Float Collar• Acts as check valve• Prevents cement back flow into casing
• Typically run in pairs• Available in differential fill design
• All components drillable
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Float Equipment Valve Operation
Centralizer Types
Bow Type• Welded bow
• Turbolizer
• Spiral Bow
• Rigid Bow
Solid Type• Spiralizer
• Shorty spiral
• Straight
Subs
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Wiper Plugs
• Bottom Plug• Top Plug
Purpose - to mechanically separate fluids (drilling fluids, washes, spacers, cement, displacement fluid) within the drill pipe or casing during cementing operations
Job Types – Conventional Casing
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Job Types – Inner String Casing
Job Types – Liner
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Wiper Plugs – Ahead of Spacers or Behind?
Uncontaminated Spacer and Slurry in “Wiped” casingbehind plug
Uncontaminated Slurry in “Wiped”casing behind plug
Spacer ahead of plug
Drilling Fluid“Film” of Drilling Fluid not wiped from casing ID
Inner String Stab-in Adapters
• Provides hydraulic seal between inner string bore and float equipment.
• Piston effect tries to disengage seals during cementing.
• Inner string handling tools use false rotary mounted on casing.
Latch-In
Screw-In Tag-In
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Stage Cementing Tools
• Also available in hydraulically actuated opening sleeve.
• Closing plug is pumped down as wiper plug after slurry.
• Both plugs are drillable.
External Casing Packer (ECP) / Stage Tool
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Casing Flotation for ERD
• Trapped air pocket above shoe creates buoyant force.
• This reduces drag due to normal force and allows casing to slide longer distances at high angle.
• One time conversion to normal circulation mode.
Well Security and Control
• Fracture Gradients• Formation Pressures• Hydrostatic Pressures• Equivalent Circulating Density (ECD)• “U” Tubing, Cement “Free Fall”
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U-Tubing and Cement Free Fall
• Cement slurry density inside pipe is greater than the density of the fluid in the annulus, so it will fall to seek an equilibrium.
• With a closed system this will tend to pull a vacuum at the wellhead.
• How fast will it fall? Depends on density differential and friction factor.
Hold back pressure if needed.
• Modeling with cementing simulator
• When cement is a liquid, it transmits hydraulic pressure like other fluids
• When cement is a solid, it is resistant to hydraulic or gas pressures.
• During the transition phase from a liquid to a solid, cement loses the ability to transmit hydraulic pressure but is not yet able to resist hydraulic or gas pressures
Key Points
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Volume Calculations
• Capacity– annular, between pipe and pipe or pipe and
hole– internal, within a pipe or hole
• Cement Volume– annular volumes– pipe or hole volume– % Excess, accounts for actual hole size
being greater than gauge• Displacement Volume
Annular VolumeTo calculate the annular volume between casing and hole equation is:
CapacityAN x length = volume12-1/4” ID of Hole
2500 ft
9-5/8” ODof pipe
(12.252 – 9.6252) x 0.0009713 == 0.0558 bbl/ft
0.0558 bbl/ft x 2,500 ft =
Capacity in bbl/ft =
((ID2 - OD2) x 0.0009713)
139.5 bbl
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Casing Volume
8.6772 x 0.0009713 = 0.0731 bbl/ft
126 ft
8.677 “ ID
0.0731 bbl/ft x 126 ft. =9.2 bbl
To calculate the internal volume of a casing the equation is: CapacityIN x length = volume
Capacity in bbl/ft =
ID2 x 0.0009713 = bbl/ft
Volume of Cement =
Cased Hole volume+
Open Hole Volume+
Shoe Joint Volume
Cased Hole VolumeVCH = CCH x LCH
Open Hole VolumeVOH = COH x LOH x Ef
Shoe Joint VolumeVShoe Joint= CCasingx LShoe Joint
Volume Calculations
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Cased Hole VolumeCCH x LCH = VCH
Open Hole VolumeCOH x LOH = VOH
Shoe Joint VolumeCCasingx LShoe Jt = VShoe Jt
0.058 bbl/ft x 500 ft = 29 bbls
0.0558 bbl/ft x 2500 ft = 139.5 bbls
+ Excess
1500 ft
4000 ft0.0731 bbl/ft x 126 ft =
9.2 bbls 126 ft
72lb 13-3/8” Casing12.341” ID
47lb 9-5/8” Casing8.677” ID
12-1/4” Hole
TOC @ 1000 ft
% Excess Calculation
Open Volume including Excess
= ((% Excess ÷ 100) + 1) x Volume
For 100% excess this means 2x the calculated volume.
For 50 % excess its 1.5x the calculated volume.
% Excess is used to compensate for hole size being over gauge size.
Generally use standard recommendations for % excess in open hole, unless there is caliper data available or it is otherwise agreed upon to use a different value.
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Recommended % Excess for Open Hole
1525Greater than 18,000
153510,000 – 18,000
15508,000 – 10,000
25754,000 – 8,000
501000 – 4,000
% Excess with OBM
% Excess with WBMDepth (feet)
Volume of Cement =
Open Hole volume+
Cased Hole Volume+
Shoe Joint Volume
279 bbls+
29 bbls+
9.2 bbls=
317.2 bbls
1500 ft
4000 ft126 ft
TOC @ 1000 ft
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Displacement Volume
Capacity =ID2 x 0.0009713 = bbl/ft
(8.677)2 x 0.0009713 = 0.0731 bbl/ft
3,874 ft
8.677 “ ID
Volume =0.0731 bbl/ft x 3,874 ft. =
283.2 bbls
Equation for the Volume of casing is: Capacity x length = bbls
Length =Sfc. to Float Collar @ 3,874 ft
To determine the % excess for an enlarged hole diameter.
% Excess = ([(ID22 - OD2) / (ID1
2 - OD2)] -1) x 100
% Excess = ((14.752 – 9.6252) / (12.252 – 9.6252) -1) x 100
= 118 %
ID1 = gauge hole diameter, in. (12.25 in this case)ID2 = enlarged hole diameter from caliper, in. (14.75 in this case)OD = casing size, in. (9.625 in this case)
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Phydrostatic = MWppg x .052 x TVDft
MWppg = Pressurepsi ÷ .052 ÷ TVDft
TVDft = Pressurepsi ÷ .052 ÷ MWppg
Gradientpsi/ft = MWppg x .052
Gradientpsi/ft = Pressurepsi ÷ TVDft
MWppg = Gradientpsi/ ft ÷ .052
Capacitybbl/ft = Hole Diameter2 x 0.0009713
Annular Capacitybbl/ft = (Hole diameter2 - Pipe Diameter2) x 0.0009713
OrAnnular Capacitybbl/ft =
(Hole diameter2 - Pipe Diameter2) / 1029.4
Summary of Calculations
Fluid Column Height in ft = Volume in bbls ÷ Capacity bbl/ft
Volume Excess = Calculated Volume x %Excess / 100
Volume including Excess = ((%Excess / 100)+1) x Calculated Vol
Deq = SQRT((% excess /100+1) x ID2 )-(OD2 x % excess /100))
%Excess = ((ID22-OD2) / (ID1
2-OD2)-1)x100
Casing ID = SQRT[OD2 - (Cwt x 0.3692)]
Cement Slurry Properties
• Density (ppg)• Yield (ft3/sack)• Rheology (PV, YP)• Free Water (%)• Solids Settling• Fluid Loss (cc)• Thickening Time (hh:mm to 100 Bc)• Transition Time (hh:mm)• Compressive Strength (psi)
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Thickening Time
• Thickening Time is dependent upon:1.Temperature2.Water content3.Additives4.Cement type5.Pressure
0
20
40
60
80
100
10 20 30 40 50 60 70 80 90 100 110Time
Bc
120 F150 F
↑ Temperature
↓ Thickening Time
Thickening Time
• What Thickening Time is:
– It is a dynamic laboratory simulation conducted under standard conditions and procedures
– It provides an estimate of time in which cement slurry remains pumpable
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Thickening Time
• What Thickening Time is not:
– It is not an exact simulation of wellbore conditions
– It is not a measurement of cement setting
– It is not the amount of time the cement will remain pumpable if there are any unplanned shutdown periods during the job
Thickening Time Time that is assumed to be available for placing cement
– Mixing and pumping: volume / rate = time– Batch Blending = time– Displacement: volume / rate = time– Safety Factor = time
Static times that are not adequately accounted for in the Thickening Time test
– Planned Interruptions = static time– Unplanned Interruptions = static time
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Transition Time
Definition: Time between which a cement slurry behaves as a liquid and behaves as a solid
– Liquid - fully transmits hydraulic force
– Solid - resistant to any hydraulic force
During this transition time the cement develops gel strength and loses its ability to transmit hydraulic force.
Transition Time
• Generally accepted gel strength values –Initial Set = 100 lb/100ft2 for initial setFinal Set = 500 lb/100ft2
Transition Time = time from 100 lb/100ft2 to 500 lb/100ft2
• The initial set value is now more often referred to as the critical static gel strength. This value can and should be calculated.
• The 500 lb/100ft2 value is a rule-of-thumb, useful for comparison purposes .
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Cementing Materials
• Cement– API– Construction
• Water– Fresh– Sea
• Additives– Generic– Proprietary
Oilwell Cement: Applications
Most common cement for Gulf Coast operations.H
International, standard for oilwell cement.G
Conductor and Surface jobs, when conditions require high early strength.C
North America, Conductor and Surface casing jobs when special properties are not required.B
North America, Limited to local regions of manufacture when conditions require moderate to high sulfate resistance.A
Typical UseClass
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Water
• Fresh water, Drill Water– Standard for API specification test– Typical for land operations– “City” or potable water should be used. Water
from a stream, lake, bayou or irrigation ditch may contain organic compounds which will interfere with the cement performance.
• Sea Water– Typical for offshore operations.– Tends to accelerate so often the switch is made
to fresh water.• Brackish water
– Can be used but must monitor quality.
Oilwell Cement: Units
• 1 sack of cement weighs 94 lbs• 1 sack = 1 cubic foot
• Regardless of whether it is in bulk form or sack the standard unit of measure is the “sack”, and one sack = 94 pounds.
• Bulk # of sacks x 94lb/sk = pounds of cementPounds of cement / 94lb/sk = # of sacks
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Oilwell Cement: Water requirement
Water Content %
Com
pres
sive
Stre
ngth
30 40 50
PumpableNot Pumpable
Hydration Water
Standard Water
Settl
ing
6,000
2,000
From Schlumberger
•Tricalcium Aluminate in the cement grain begins to interact with the water.
•A layer of Calcium Silicate Hydrate forms over the grain, causing osmotic pressure to increase as water diffuses inside the grain.
•Calcium Silicate Hydrate fibrils form and grow and interlink between grains, thereby increasing strength and decreasing permeability.
Cement Hydration
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Water Requirement for API Cements
Type of Cement Water Requirement
API Class C 6.3 gal/94-lb sack or 56%
API Class A 5.2 gal/94-lb sack or 46%
API Class G 5.0 gal/94-lb sack or 44%
API Class H 4.3 gal/94-lb sack or 38%
• Definition: A cement additive is any material added to cement for the purpose of modifying the physical or chemical properties of the cement slurry or the set cement.
• Physical forms of additives are:– Dry powder, granules and flakes.– Liquids and liquid emulsions.
Cement Additives
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Cement Additives
– Density– Rheology– Free water– Solids settling– Fluid loss– Thickening time
– Transition Time– Compressive Strength – Strength Retrogression– Expansion– Bond Strength
What properties of the cement slurry or set cement can be controlled by additives?
Cement Additives: Categories
• Extenders - ↑ Yield, ↓ Cost, ↓ Density• Weighting Agents - ↑ Density, Maintain well control• Fluid Loss Control - ↓ Dehydration• Accelerators - ↓ Thickening time• Retarders - ↑ Thickening time• Dispersants - ↓ Viscosity • Lost Circulation - ↓ Slurry loss to formation • Strength Retrogression Preventatives - ↓ CS Loss• Gas Control - ↓ Transition time• Anti-foam - ↓ Air entrainment
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Cement Additives: Inconsistencies
• Salt accelerates at concentration below 10%, but at concentrations above 10% it retards
• Some Fluid Loss additives viscosify, but others disperse
• Most retarders disperse, but some viscosify
• Dispersants almost always retard, but at low temperatures they can accelerate
Cement Additives: Inconsistencies
• High temperatures require high concentration of retarder, but in some cases excessive retarder decreases pump time
• With slurry designs containing large amounts of additives, 5 or more, the synergistic effects often overcome the primary effects
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Cement Additives: Units of Addition
• Dry– bwoc, by weight of cement– lb/sk, pound per sack of cement– bwow, by weight of waterExample: 1% bwoc = 1 x 94 / 100 = 0.94 lbs
• Liquid– gps or gal/sk, gallon per sack of cement– gphs, gallon per hundred sacks of cement
Slurry Design
Cement Slurry design consists of determining the optimum mix of Cement, Water and Additives to providethe required properties for placement and long termperformance of the cement sheath.
• Design Concepts• General Designs• Basic Requirements• Special Conditions
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• Designs should be simple – Minimum additives– Easier to take from lab to field
• Designs should be consistent– Same blends, similar additive
• Designs should be flexible– Not sensitive to minor fluctuations in additive
concentration or well conditions• Designs must meet requirements
Design Concepts
Wellbore Conditions vs Slurry Properties
Parameters Properties
Pore and fracture pressures - DensityLost circulation
Temperatures, BHST, BHCT - Thickening Time
Hole and casing geometries - Rheology
Formation properties - Fluid Loss
Mud Properties - Compatibility
Cement Fill - Volume, Yield
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Lead, Tail and Single Slurries
• Lead Slurries– Extended, higher yield per sack, lighter weight– Lower cost, lower performance
• Tail Slurries – Mixed at normal density– Optimized properties
• Single Slurries– One slurry at one density
Slurry Design Guidelines
• When there is oil or synthetic mud in the hole– Must test compatibilities
• Across salt zones –– Cement slurry must be salt tolerant
• For temperatures greater than 250° F – Silica sand or flour must be added
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Slurry Design Priorities
1. Density 2. Thickening Time 3. Mixability4. Rheology5. Fluid Loss Control6. Compressive Strength7. Free Fluid and Settling
Slurry Design: General Requirements
Density+ 1.0 ppg > drilling fluid density+ 0.5 ppg > spacer density< Equivalent Circulating Density (ECD) to
fracture formationThickening TimeJob time plus safety factor, one hour plusProduction / gas control - right angle set
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Slurry Design: General Requirements
RheologyConductor / Surface - mixable and pumpable,
thixotropic for lost circulationIntermediate PV < 150, YP < 40Production PV < 100, YP < 20Fluid LossSurface < 500cc/30minIntermediate < 250 cc/30minProduction < 100 cc/30minGas Control < 50 cc/30min
Slurry Design: General Requirements
Compressive Strength
8 hours maximum for WOC, 500 psi
24 hr, 1000 psi
Perforating, 1500 to 2000 psi
Free Water
Surface strings < 1.0
Deviated wellbores 0 %
Production strings 0 %
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SLURRY
PROPERTIES
Conductor and
Surface Casings
Intermediate
Casings and
Drilling Liners
Production
Casings and
Liners
Deep Production
Liners and for
Gas Control
+ 1 lb/gal > drilling fluid density DENSITY
< Equivalent Circulating Density (ECD) to fracture formation
Job time plus at least one hour for safety factor
THICKENING TIME For Production casings or for gas control, the TT chart should display a right angle set
(transition from 40 to 100 Bc less than 15 minutes)
FREE WATER < 1.0% < 0.5 % 0 % 0 %
FLUID LOSS NA < 250 < 100 < 50
< 150 < 150 < 100 < 100 RHEOLOGY
PV
YP < 50 < 40 < 25 < 20
< 12 < 8 < 8 < 8 Compressive Strength
WOC (hrs to 500psi)
24 hr 1,000 2,000 2,000 2,000
Thickening Time When specifying Thickening Time requirement:
• Calculate, Do Not Estimate– Temperature. Use simulators as necessary.– Time to mix and pump lead and tail. Time to drop
plugs. Displacement time. Safety factor• Evaluate risks
– TT must be long enough to insure placement.– Excessive TT increases the risk of well control
problems and poor isolation• Remember lab test is a dynamic test
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Densified Slurries
• Cement Slurry density be increased by using less water through the use of dispersants to maintain rheological properties
• Class G cements can be mixed at up to 16.5 ppg and Class H cements can be mixed at up to 17.2 ppg.
• Hematite common weighting agent.
Remedial Cementing• Squeeze - The placement of a cement slurry, under
pressure, against a permeable formation causing the slurry to dehydrate and create a cement seal across the formation face. – Repair a primary cement job or casing leak– Add height to cement column to produce upper zones– Eliminate water from the hydrocarbon zone– Reduce the producing gas:oil ratio– Seal the annulus of a liner top or casing shoe– Plug zone(s) in a multi-zone injector or production well
• Balanced Plug - The placement of a cement slurry, under normal circulation, to provide isolation between the lower and upper portion of the wellbore.– Sidetrack– Plug back– Abandonment
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Spacers for Plugs• Separate mud and cement with an adequate
volume of spacer or wash
• WBM: Chemical wash or spacer
• SBM: add surfactant to water wet surfaces
• Volume of spacer/wash ahead to be equivalent to 500ft of annular fill
• Spacer behind at volume calculated to balance
• Always calculate the loss in hydrostatic pressure when using water or base oil/synthetic ahead of a cement plug assuming gauge hole
Plug Cement Volume
• Use a caliper log to determine the cement volumes and where to set the plug
• Set plug in a near gauge section of the hole• If no caliper, use the recommended excess• Actual excess should account for knowledge of the particular
area and hole conditions
20306 – 8-1/2203012-1/4205014-3/4 – 17-1/2-10024-30-20030-26
% Excess (SBM)% Excess (WBM)Hole Size (in)
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USI CBL comparison
Good interpretation Ambiguous Very ambiguous or not detectable
Gas ChannelContaminatedMud ChannelMud LayerLiquid microannulusDe-bonded, dry microannulusVery light, good bondHeavy, medium, good bond
CBLUSICement
Acknowledgements
• Thanks to Unocal for their assistance in the preparation of this material
• Many of the casing tool examples are from Davis-Lynch company.
• Many of the casing handling tool examples are from Varco and BJ as provided by Weatherford.
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