13 -Foamed Cement-NExT
Transcript of 13 -Foamed Cement-NExT
Copyright 2008, NExT, All rights reserved
Foamed Cement
Special Cement Systems
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Foamed Cement
A stable matrix of gas (air or nitrogen) contained in a cement slurry.
Gas Bubbles
Cement Matrix
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Foamed Cement
SlurryMixer
Slurry Pumper
Batch Mixer
Nitrogen Pumper
FoamerPump
WELL
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Foamed Cement
Advantages� Easily variable density range
650 to 1750 kg/m3 (6 to 14.5 ppg)
� No blending
� Good mud removal
� Elasticity to absorb stresses
� Relatively high strength, (higher tensile)
� Low thermal conductivity
� Thixotropic behavior
� Two phase ( FL)
Disadvantages :� Difficult to design
� Complex Execution− Personnel− Equipment− Procedure− Back Pressure
� Availability of gas
� Availability of equipment
� Stringent safety requirements
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Applications
� Weak and fractured formations
� Losses to vugs
� Geothermal and steam injection wells
� Casings in permafrost
� Alternative to stage cementing
� Air-drilled wells
� Improved bonding across salt
� Gas and water flow control
� Squeezing depleted zones
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Properties
� Mechanical properties:
− Dependent on foam Quality (porosity)• Ratio of gas to slurry
• 15 to 30 % for improved properties
� Pore size distribution– Quality– Stability
– Mixing Conditions
� Physico-chemical properties:
− Dependent of base slurry density• Cement
• Additives
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Mixing Stable Slurry
� Foaming agent and stabilizer
� Foam generator
− Disperser disk with adequate pressure drop
� Base slurry
− Mixed at optimum water ratio
− Uniform slurry mixing (density control)
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Design Properties
� Density
– Foam quality
– Base slurry density
� Foamability
� Rheology
� Free Fluid
� Fluid loss control
� Compatibility
� Thickening time
� Mechanical properties
– Compressive Strength
– Young modulus
– Poisson coefficient
– Tensile strength
� Shear bonding
� Permeability
� Durability
� Thermal conductivity
• LAB mixing at ambient conditions API / ISO 10426-3
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Rheology
� Foams are different from other fluids
– Compressible
– Bubble structure changes
– Dynamically unstable
� Rheology measurement
– Viscometers are not suitable• Shear changes bubble network
• Foam decays while testing
– Pipe rheometers• Foam is compressible
• Non-Newtonian behavior
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Compressive Strength
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Thermal Conductivity
Density (g/cc)
Density (lb/gal)
Btu
/hr-
ft-o
F
W/m
oK
Foamed Cement
Conventional
Lightweight
Slurries
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Job Design
Wellbore fluids
� Drilling fluid
� Pre-flush
� Cap slurry
� Foamed cement slurries
� Tail slurry
Well conditions
� Low fracture gradients
� Losses
� Hole condition and geometry
� Intervals to cover
� Potential for flow
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Constant Nitrogen Ratio
� Easy design
� Hole size independent
� Simplified execution
� Varying cement properties
� No flowing zones
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� Multiple stages
� Hole size dependent
� Complex execution
� Constant cement properties
� Difficult with small volumes
Constant Density Method
Spacer
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Design Guidelines
� 2 Goals– Control hydrostatic during placement
– Good density profile in annulus at end
� 3 Rules :– Make operation as easy as possible
– Put as much cement in well as possible
– Put minimum amount of nitrogen in well
� 4 Parameters– Number of stages
– Nitrogen ratio for each stage
– Back pressure
– Cap slurry
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Number of Stages
� Sensitive to – Hole geometry
– Hole condition
– Leak off
� Multiple stages make execution difficult– Rate and volume schedules
– Difficult to run excess
– Risk of formation breakdown
� One stage treatment– Always try first
– Easier to design and execute
– Good slurry profile (density/strength)
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Foamed Cement Process Control
0
2 0 0
4 0 0
6 0 0
8 0 0
1 0 0 0
1 2 0 0
1 4 0 0
1 6 0 0
0
108
216
324
432
540
648
756
864
972
1080
1188
1296
1404
1512
1620
1728
1836
1944
2052
2160
2268
2376
2484
2592
2700
2808
2916
3024
3132
3240
3348
3456
3564
3672
3780
T im e (s e c )
0
0 .5
1
1 .5
2
2 .5
3
3 .5
4
4 .5
5
s c f/m in
s c f/b b l
s c f/b b l
b b l/m in
J .Y . F M
fo a m e r
g a l/b b l
B a s e S lu r ry ra te
N 2 s tro k e ra te
N 2 ra t io
F o a m e r ra t io
F o a m e r
� Meters N2 & surfactant rates from
slurry rate
– Foam quality delivered as designed
– Ensures well control
– Slurry properties delivered as designed
– Mass flow meters for mass balance
guarantee
Process control cement unit ( 3 controls)
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Foamed Cement Process Control
Cement Unit
Foamer
Pump
N2
Tank
2000 gals
180 MSCF
N2
Tank
2000 gals
180 MSCF
N2
Pump
Process
Control
Computer
Check Valve
Foam
Generator
Wellhead
Check Valve
Flowmeter
Mixer
Recirc.
Tub
Densitometer
Popoff Valve
Bleedoff w/Choke
Restricted Area
Bleedoff
w/ N2 Choke
N2 Isolation
Valve
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Evaluation
� Temperature survey– WOC 8-24 hr
– Less change than conventional cements
– ID tops of tail and cap
� CBL- Azimuthal sonic tool– Low acoustic impedance -> high amplitude
– Use acoustic impedance charts
� Ultrasonic tool (USIT™)– Calibrate for low acoustic impedance (IMAU, IMAL)
– Compressive Strength is not valid
– Affected by gas -> but uniformly
� Schlumberger Isolation Scanner®
– USIT + Flexural wave attenuation
– Solid, Liquid or Gas
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CBL Interpretation ChartA
mp
litu
de
(m
V)
3-ft Spacing CBL
Ac
ou
sti
c I
mp
ed
an
ce (
Mra
yl)
Density (lb/gal)
7
6
5
4
3
2
1
0
CBL Advisor