13 -Foamed Cement-NExT

Copyright 2008, NExT, All rights reserved

Foamed Cement

Special Cement Systems

2Copyright 2008, NExT, All rights reserved

Foamed Cement

A stable matrix of gas (air or nitrogen) contained in a cement slurry.

Gas Bubbles

Cement Matrix


Foamed Cement

SlurryMixer

Slurry Pumper

Batch Mixer

Nitrogen Pumper

FoamerPump

WELL


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


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


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


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)


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


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


Compressive Strength


Thermal Conductivity

Density (g/cc)

Density (lb/gal)

Btu

/hr-

ft-o

F

W/m

oK

Foamed Cement

Conventional

Lightweight

Slurries


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


Constant Nitrogen Ratio

� Easy design

� Hole size independent

� Simplified execution

� Varying cement properties

� No flowing zones


� Multiple stages

� Hole size dependent

� Complex execution

� Constant cement properties

� Difficult with small volumes

Constant Density Method

Spacer


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


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)


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)


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


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


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

Documents

13 -Foamed Cement-NExT