13- Foam Cement Considerations

8/13/2019 13- Foam Cement Considerations

1/50

FoamCement

Ultra-LightweightCement System


2/50

What is Foam Cement?

Foam cement is an energized systemconsisting of a base cement slurry towhich foamers and nitrogen have beenadded to generate the foamFoam systems are normally light densityFoam systems have distinctive properties(advantages)


3/50

Foam Quality

Quality (expressed in %) of the foamcement slurry is the % of the total volumeoccupied by the Nitrogen. For example:

A bbl of foam cement slurry of 30%quality consists of 0.70 bbls of solids andliquids (water, additives) and 0.30%Nitrogen.


4/50

Why Foam Cement?There are several reasons for using foamcement. For example when encountering lowfracture gradients due to low formationmechanical strength and/or low reservoirpressures.There may be economic benefits of using foamcement. For example, their use can ofteneliminate stage tools thereby saving cost of thetool and saving rig time.There are situations where good strength isneeded, but low densities are required. This isan excellent application for foam cementing.


5/50

Why Foam Cement? (cont.) Another benefit of a compressible system is thatit can prevent annular gas migration.The major distinguishing property of foamcement is that it has high strength at very lowdensities.Conventional water extended cement slurriesachieve densities of no less than 11 lbs/gal and lmaintain acceptable compressive strength for

many applications.Foam cements on the other hand can providesignificant compressive strength at densities aslow as 8 or even 6 lbs/gal.


6/50

Why Foam Cement? (cont.)Foam cements are very compressible.It is possible to maintain low permeability in a foamcement even at densities as low as 8 lbs/gal.Foam systems inherently have low fluid loss which is adesirable characteristic for a cement slurry.Foam slurries are highly viscous. This can increasecirculating pressures and needs to be considered whenwe actually design a job.

Foam cement slurries have very good sweepingproperties due to their high consistencies and theirexpanding properties as they move up the hole.


7/50

Other BenefitsElastic Cement System Resilient / Withstands Pressure Cycling Help Maintain Zonal IsolationHelp Prevent Gas Migration

Compressibility Fluid Loss ControlImproved Mud Displacement

Help Prevent Long Term Gas Migration Minimize Remedial Cementing to Repair Casing


8/50

Other Benefits (cont.)Ultra-Lightweight Cement System

High Strength / Low Density Help Prevent Lost Circulation

Economic saving Eliminate Stage Tool

Save Rig Time

Low Thermal Conductivity


9/50

Physical PropertiesElasticity

High Strength

Compressibility

Low Fluid Loss


10/50

Physical PropertiesHigh Viscosity

Low Permeability

Low Thermal Conductivity


11/50

CementSheath Stress

Fixture

3 in.

3 in.

6 in.

3 in.

48 in.

54 in.

Water Cap

6 in. of 20/40Mesh Sand Pack

Pressure Port

Vent for Annulus

Pressure Gauge

Wire Feed Conduit

Strain Gauge

Data Acquisition

9 5/8-in., 10 3 /4 -in.,13 3/8 -in Outer Casing

5 1/2-in., 7-in.,9 5/8-in Inner Casing

Permeability Inlet

Cement Inlet

Permeability Outlet

CementReturns

PermeabilityInlet

3 in.

3 in.

6 in.

3 in.

48 in.

54 in.

Water Cap

6 in. of 20/40Mesh Sand Pack

Pressure Port

Vent for Annulus

Pressure Gauge

Wire Feed Conduit

Strain Gauge

Data Acquisition

9 5/ 8-in., 10 3 /4 -in.,13 3/8 -in Outer Casing

5 1/ 2-in., 7-in.,9 5/ 8-in Inner Casing

Permeability Inlet

Cement Inlet

Permeability Outlet

Cement

Returns

PermeabilityInlet


12/50

Large Scale Stress Testing - TLW @ 12.5lb/gal


13/50

Large Scale Stress TestingFoamed Cement @ 11.8 lb/gal


14/50

Conclusions from ExperimentsFoamed cements (Q = 0.18 - 0.38) prevent shear failureduring internal casing pressurization Can withstand internal casing pressures up to 10,000

psi without shear failure Compressibility Can withstand mechanical cycling up to 100 times @

90% of shear failure indexFoamed cement generally exhibited no signs of matrixfailure, either radially or circumferentially


15/50

Compressive Strength

0

500

1000

1500

2000

S t r e n g t

h ( p s i )

6 lb/gal 8 lb/gal 10 lb/gal

Standard Cement @ 100 F

12 Hour 24 Hour 72 Hour


16/50


0

500

1000

1500

2000

S t r e n g t

h ( p s i

)


Premium Plus Cement @ 100 F



17/50


0200400600800

1000

1200

S t r e n g t

h ( p s i )


Premium (fine) Cement @ 100 F



18/50


0

200

400

600

800

S t r e n g t

h ( p s i )


Premium (coarse) Cement @ 100 F



19/50

Permeability of Foam CementThe permeability of foam cements issurprisingly low even at a density as lowas 8 lbs/gal.

When we get less than 8 lbs/gal or aquality higher than 50 percent, thepermeability does not increasesignificantly but most foam cement jobsare conducted at densities at around 8 to10 lbs/gal.


20/50

Permeability of Foam Cement

02040

6080

100120

140160

P e r m e a

b i l i t y

( m d )

4 6 8 10

Density (lb/gal)


21/50

Low Permeability


22/50

Low PermeabilityFrom this scanning electron microscope slide you canvisualize how to achieve low permeability even atdensities of 8 lbs/gal.The low permeability is achieved because highcompressive strength, low permeable cement willprovide a barrier between the various bubbles inside thematrix of a foam cement so that anything passingthrough the overall matrix of the foam cement will haveto pass through that low permeability cement in betweenthe bubbles (bubbles are not connected!).

When the foam quality rises above 50 percent, thesebubbles start to interconnect and then you have a flowpath through the matrix of the foam and you see thepermeability increasing.


23/50

Foam Cement


24/50

Thermal Conductivetyof Foam Cement

0

0.05

0.1

0.15

0.20.25

K

- V a l u e

( D r i e

d @

2 3 0 F )

10 11.5 12

Density (lb/gal)

Thermal Conductivity (BTU/HR-FT-F)


25/50

Thermal Conductivity

Thermal conductivity of foam cement isfairly low.

As can seen from this data of dried foamcerment at 230 degrees, thermalconductivities as low as 0.15 BTU degreesFahrenheit.Thermal conductivity decreases as foamdensity decreases.


26/50

Applications of Foam

CementSingle stage cement job across weak formation Prevent lost circulation Saves rig time Deep Water Shallow Flow Control Surface Casing Jobs In Deep Water Applications Helps Prevent Water/gas Influx After Placement


27/50

Applications of Foam

CementSqueeze across weak formation Prevent lost circulation during squeeze Maintain surface pressure indication

throughout job


28/50

Job DesignStatic Model Determine unfoamed slurry volume

Calculate initial nitrogen concentrations

Cement Job Simulator

Determine nitrogen needed for dynamicplacement

Optimize pump rates


29/50

Job DesignWhen designing a foam cement job, two computer models are used.First, the static model is used to determine the volume of unfoamedslurry needed for the job and the initial nitrogen concentrations togenerate foam slurry of a desired specified density.Then a cement job simulator is used to determine nitrogen neededfor dynamic placement. When foam is pumped into place, you haveadditional pressure on the system due to friction.This additional pressure compresses the foam and increases itsdensity, therefore, you need to add additional nitrogen to expandthe foam to the desired slurry density and to fill the entire annulus.The simulator is also used to optimize the pump rates to insuregood displacement throughout the job without exceeding thefracture gradient of the open hole.

E l CEMENT JOB


30/50

Example - CEMENT JOBSIMULATOR

Comparison of Rates In & Out


31/50

CEMENT JOB SIMULATORCalculated Wellhead Pressure


32/50

CEMENT JOB SIMULATORCirculating Pressure / ECD at 5658 ft


33/50

Foam Job ExampleIn the next figure we see an example of a foam cement job.We have a 5 1/2 casing set in an 8 1/2 hole at a depth of 6400feet.Fracture gradient of 10.7 lbs/gal exists at 5800 feet.Normally several stages of foam cement are pumped followed by a

tail cement that is unfoamed. After the plug is bumped, the annulus is closed and an unfoamedcap cement slurry is pumped at the surface to compress the foam tothe desired density and cause the cement to set up quickly at thesurface conditions. This has several advantages. It is possible toaccelerate the cap slurry so that it will set up within 4-6 hours afterplacement allowing the operator to continuew well operations in ashort period of time.


34/50

Foam Cement Example

6400 ft.

1400 ft.

5 1/2 inch8 7/8 inch

BHCT = 96 F

10.7 lb/galFrac Grad

5800 ft


35/50

Example Foam Cement Job

The following figure shows nitrogen ratevariation in four stages to achieve anaverage density of around 8.5 lbs/gal.The top stage has 160 scf/bbl of nitrogen.The next stage has 485 scf/bbl, the next570 scf/bbl and the last on 920 scf/bblBelow the last stage, there is a tail cementat 12.5 lbs/gal.


36/50

Foam Cement Example

Nitrogen0

160485

570

920

0

Density (lb/gal)12.5

8.08.9

8.7

8.5

12.5

Depth (ft)700

1400

4000

5000

6400

2700


37/50

Slurry Design ExampleThe base slurry consists of cement mixed at its normal mixing waterrequirement.If the cement slurry needs to be accelerated for application in cooltemperatures, calcium chloride can be added to the baseformulation.For deeper hotter applications, if the slurry needs to be retarded, anon-dispersing retarder can be used. This is not a typical ligno-sulfanate retarder which affect the stability of the foam.For some applications, fluid loss additives are added to the baseslurryTo the slurry, 1.5% by volume of foaming agent and 0.75% of foamstabilizer are injected through the suction side of the downholepumpThese surfactants are used to generate and maintain a stable foam.Foam slurry stability is tested in the lab


38/50

Foam Cement Testing

Tests conducted withunfoamed base slurry:

Thickening time Rheology (simulators

use it to predict foamrheology)

Fluid loss

Free fluid

Tests conducted withfoamed slurry:

Compressive Strength Foam stability


39/50

Performing a Job

Foam Generator

Nitrogen Unit

Cement Pump Truck

FoamChemicalPump

Injection Unit


40/50

Performing a JobTypically the layout of the job consists of a cementpump truck to mix the base cement slurryNext, an injection unit to inject the foamer and stabilizerinto the suction side of the downhole pump.

The cement slurry is then pumped to the foamgenerator.In the nitrogen unit, the nitrogen is vaporized andmetered as specified for the job.

The nitrogen is also pumped to the foam generator.The generated foam cement slurry is then pumped tothe well.


41/50

Automated Foam CementSystem

Recent technology includes automation of the nitrogenrate control, base cement density control and surfactantinjection control.It is possible to automate the nitrogen rate to proportiona specified amount of nitrogen from the nitrogen pumptruck. This eliminates any operator error that could beencountered when relying on simple verbalcommunication during the job.It is also possible now to automate the cement slurrydensity control. This regulates bulk cement delivery andmix water rates and eliminates operator error. Also automated is the amount and rate of injection ofsurfactants into the unfoamed slurry.


42/50


43/50

Offshore CapabilityNitrogen ConverterSkid

Self-contained

Automatic rate

control 8 x 8 x 10

3000 scf/min maxrate

17,000 psi maxpressure

100 scf/minminimum rate


44/50

Automatic Density

Control


45/50

Backpressure Control

When conducting a cement job, one thing thatneeds to be controlled is back pressure, even iffoam cement is not expected to return tosurface.

Without back pressure control, uncontrolledexpansion of the foam at the surface can causewhats known as a cement blowout.The highly energized foam cement underpressure can expand quite a bit when itencounters atmospheric pressures. This mustbe prevented and in order to do that, it isimportant to maintain back pressure control.


46/50

Backpressure ControlMust be able to control the annularflow of a foam cement job

Without backpressure uncontrolledexpansion of foam at surface willcause Cement Blowout

Subsea use can be controlled at

seabed by hydrostatics


47/50

Backpressure control

Annulus chockingCement slurry cap pumped after the job

Offshore, water hydrostatic is oftenenough


48/50

Foam Cement Quality

ControlSlurry Density and Rate Measurement

Nitrogen Rate MeasurementSurfactant Metering

Foam Generator

Foam Density Measurement

F C t


49/50

Foam Cement mayImprove Job Cost

N2 Unit

Chemicals

No Stage Tool

Reduced Rig Time

Less remedial work


50/50

Bond LogEvaluationEvaluation of Foam

Cement Jobs CannotBe Done WithConventionalInterpretation

MethodsSVP ProcessProvides Means toEvaluate Foam

Date post:	03-Jun-2018
Category:	Documents
Upload:	joan-corso
View:	218 times
Download:	0 times

13- Foam Cement Considerations

Documents