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

Transcript of 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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