sonatrach's cementing

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INTRODUCTION TO HYDROCARBON EXPLOITATION

Development Phase

It is the process by which cement slurry isplaced in the annulus ,bonding the casing to

Conventionally the cement is pumped down the

casing and displaced around the shoe into the

abalt solutions limited - 2005 September October 2005


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Development Phase

Primary functions are :

Provide support to the casings

Zonal isolation-prevent fluid movement betweenzones

Casing protection against corrosive fluids

Support wellbore Protect water zones

abalt solutions limited -2005 September October 2005


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Development Phase

Cement Job Planning

Each cement job must be carefully planned toensure correct additives are being used andsuitable placement technique is being employedfor that application.

The cement engineer must ensure thatCement can be placed correctly using the

available equipment

Cement achieves adequate compressive strength

Cement will isolate zones and support casingthroughout the life ofwell.

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Classification of Cement

Several classes have beenapproved by API

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Development Phase

Classification ofCement

Class AIntended to use from surface to 6000ft (1,830m) When no special properties are required. Similar to ASTM (American Society of Testing

materials) Type I

Cheaper than other classes of cements

Class BIntended to use from surface to 6000ft (1,830m)

Moderate to High sulphate resistance Similar to ASTM Type II

Has lower C3A content than class A



Class C

Intended to use from surface to 6000ft (1,830m)

When conditions require early strength Available in all 3 degrees of sulphate resistance

and similar to ASTM Type III.

Class D

Intended to use from surface to 6000ft (1,830m)to 10,000ft (3050m).

Moderate and High sulphate resistance typesavailable

Under moderately high temperatures andpressures conditions.


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Development Phase


~ Class EIntended to use from 10,000ft (3050m) to

14,000ft (4720m)

Under conditions of High temperature andpressure.

Available in MSR and HSR types

~ Class FIntended to use from surface to 10,000ft

(1,830m) to 16,000ft (4880m). Moderate and High sulphate resistance types

available Extremely 09High temperatures and pressures

conditions.



Class G and H

Intended to use from surface to 8,000ft (2440m)

Can be used with accelerators and retarders tocover a wide range of well depths andtemperatures

Class G Available in MSR and HSR Types, whileClass H is available in MSR Types only.


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Development Phase

me2005 Abalt Solutions Limited. All rights reserved


Properties of Cement

Compressive strength To support the casing

string a compressivestrength of 500 psi isgenerally adequate

WOC (Waiting onCement)-The timerequired for the cement t

attain strength and settlebehind the casing.

The casing shoe should n obe drilled out untilstrength is attained.

Compressive strengthdependsupon Temperature

Pressure

Amount of water mix

Properties of Cement

Thickening Time (Pump ability)Time required for cement slurry to be pumped

and displaced in the annulus. Slurry should have enough thickening time to

allow mixing ,pumping and displacement beforehardening.

Generally 2-3 hours thickening time whichincludes safety factor to allow for delays andinterruptions in operations.


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Development Phase

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Properties of CementWater Loss If water is lost before cement reaches its intended

position???Amount ofwater loss depends upon the type ofcement

jobSqueeze cement jobs require low water loss since the

cement must be squeezed before filter cake builds up Primary cementing is not so critical

Corrosion resistance Formation water may contain Na and Mg sulphates which

react with lime to form calcium sulphoaluminate. These crystals expand and cause cement to crack.

Lowering C3A content increases sulphate resistance types

Slurry Density

Vary between 11 to 18.5 ppg ,depending upon the type offormation

Density is varied for a low to high strength formation.

2005 Abalt Solutions Limited. Allrights reserved

Cementing Additives

Most slurries containadditives to modif theproperties ofthe slurry toproduce a better cement

job.Cement additives can be

used to

Vary slurry density Change compressive

strength Accelerate and retard

setting timeControl filtration and

fluid loss

Slurry viscosity

Additives may be granular

or liquid form, added with

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Development Phase

Cementing Additives

cceleratorsChemicals that reduce thickening time of slurry and

increase early strength Used in conductors and surface casings to reduce WOC Common types of accelerators are :Calcium chloride (CaCl2 )1.5-2%Sodium Chloride (NaCl) 2-2.5%Sea water

extends thickening time of cement slurry to aid properplacement beforehardening.Used in HT wells with Intermediate and production casingsand squeeze cement jobs

Avoids cement setting prematurelyCommon types are:Calcium lignosulphonate 1-1.5%Saturated Salt solutionsCellulose derivativesHydroxycarboxylic acids

2005 Abalt Solutions Limited.Allrights reserved

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Cementineig ting Agents Heavy

dditivesIncreases slurry density.Used when cementing overpressurized zonesTypes are:BariteHematite

Extenders Li ht wei htMaterials that lower slurrydensity and increase yieldto allow weak formations tobe cemented withoutfracturing.Allows more mix water tobe addedTypes are:BentonitePozzolanDiatomaceous earth



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Development Phase

Cementing AdditivesMud Contaminants ___________To Improve slurry properties additives such as Diesel Oil

,thinners etc are added. Prevents undesirable side effects caused by mud on cements

etc.

Dispersants (Friction Reducing Additives)

Negatively charged polymer molecules that attach themselvesto positively charges in cement grains.

Improves flow properties of slurry Lowers the viscosity so that turbulence will occur at lower

circulating pressure. Types are Polymers 0.3-0.5 lb / sx of cement

SaltCalcium lignosulphonate 0.5-1.5 lb / sx

~ Fluid Loss AdditivesExcessive fluid loss can cause ineffective cement setting Prevents slurry dehydration ,premature setting or reduces fluid

loss to formations Types are:

Or anic o mers 0.5 -1.5 %.

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Cementing Hardware

Used to guide the casingthrough the hole with itsrounded nose.voiding jamming casing

in washed out zones ordeviated wells

Float ShoePrevents the back flow into

the casing once cement isdisplaced behind casing.

Built in check valve that isflapper or ball type.

Float shoe takes extra time torun casing in hole




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Development Phase

Cementing Hardware

Float CollarsThe purpose ofthese landing collars is to

serve as a seat for cement plugs.Run normally 2 or 3joints above the shoe,

known as shoe track.

CentralizersCentring the casing string for the success

ofcement job.Types

Rigid-Positive centralizers aredesigned for a casing-casing annularspace

Flexible or spring bow type are used in

centring in uncased holes. There aretwo types: straight and spiralled They help to

Keep casing out ofkey seats Prevent differential sticking

Improve displacement efficiency


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Cementing Hardware ____________Des gne to separate t e erent u s w enpumped through the casing.Plugs prevent contamination and wipe casing frommudPrevent over displacement of cementGive surface indication that cement placement iscomplete.

Allow casing to be pressure tested.

Bottom PlugBursts when slight over pressure is exerted.

Besides seperating,it scrapes walls as it movesTop Plug

Pumped on the tail end ofslurry and comes torest on bottom plug

ScratchersRun on casing to remove mud cake and break up

gelled mud. Promotes a better bond between cement and

formation Types

Rotating ScratchersReciprocating Scratchers

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Development Phase

Cementing Heads

Provides connection betweendischarge line from cementunit and top of casing

Designed to hold cement plugs Releases bottom plug, mix and

pump down cement slurry

Release top plug and displace

cement without makingconnection.

Cement plug need to installedcorrectly in the heads.

Cementing Baskets

Equipment to minimise losses ofcement slurry in weak zones

Used in shallow to medium depths

Curb fluid passage considerably, but do

not prevent pressure transmission.



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Development Phase

Lowering Casing

The casing must be lowered as fast as possible as time spent isN PT.

Casing string lowering speed is controlled according to surgepressures on wall and bottom.

Carefully organized to prevent casing from being stuck.

Spider and casing elevators are often used.

Lengths of casing are screwed b means of hydraulic tongs.

Driller monitors as casing string is filled up. Mud can be reconditioned and circulated while string is

manoeuvred and scratchers put to work.

Circulation is stopped when mud returns contains no more cuttings Low gas content

No kicks or lost returns

Homogeneous volume of circulating mud


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Cementing Operation~ Primary Cementing

Cement plugs placed correctly in cement head.Pump spacer ahead of cement.

First plug (wiper) pumped down ahead of cementto clean inside ofcasing.Landing collar acts as shoulder for bottom plug.Pressure surge ruptures bottom plug and allowsslurry to pass through and circulate into annulus.

Slurry displaces mud and washes the outside wallof casing as it flows.When slurry pumped down, top plug is releasedand is pushed along down by drilling mud(flushing)Pressure increases and top plug bumps againstlanding collar (not to exceed burst pressure)Displace with spacer and low density mud.


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Development Phase

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Cementing OperationCarried out usually in longer strings in which the

annulus need to filled completely. Requirements ofhigh pump pressures, longer

pumping times and excessive hydrostatic pressurefrom cement column leads to cementing

First stage

~ Simi ar to ear ier proce ure, except t at asma er vo ume is use to cement ower part oannulus depending upon fracture gradient.

Second StageInvolves a stage collar, which is made up into

casing string at pre determined depth.Stage collar are initially closed by inner sleeve,held by retaining pins.After first stage is complete, a special dart isreleased from surface opening ports allowingcommunication between casing and annulus.Circulate through stage collar and pump spacerPump secondary stage slurry and release closingplug.Displace cement with mud.Top plug closes by moving a second sleeve




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Development Phase

rString Cementing

Large diameter casing result in ??????Large displacement volumes

Long pumping times

Cement casing through tubing or drill pipe

Casing run as before

Special float shoe-allows drill pipe to bestabbed

Cement job can then proceed as before. Inner string can be retrieved

Suitable for casings of 13 3/8 and larger

Disadvantage of NTP for running and

retrieving inner string.



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Development Phase

Cementing Operation

~ Li ner cementingHas a full length float collar , landing collar andshoe installed.

Landing collar catches the cement wiper plug. Wiper plug is held on end ofthe tail pipe by

means ofshear pins. Liner is run on drill pipe and hanger set at

correct point inside previous casing string.Mud is circulated out to ensure it is free of

debris. Before cementing, setting tool is backed off. Pump spacer ahead and followed by slurry. Release pump down plug and displace cement

out of liner. Pump down plug releases wiper

Both move down until Landing collar.

Bump plugs with 1000 psi pressure.

Bleed offand check for back flow.Excess cement used to seal top ofliner.Once cement is set, setting tool is picked upout ofliner

With tail pipe above liner, excess cement isreversed circulated




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Development Phase

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blems with cementing LinersMinimal annular s aces

Clearance between 7 OD liner

and 8-1/2 hole.

Difficult to run linerLost circulation problems

Difficult to centraliseCement placement poor(channelling)

Mud contamination

Lack ofpipe movement-due torisk ofsetting tool sticking


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Cementin Job

ecommendationsUse centralisers at critical

points along the casing stringMoving the casing-rotationrather than reciprocation

Before cementing, ensure mudhas good flow properties

Displace cement underturbulent conditions if possible

Spacers to prevent mudcontamination in annulus.




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Development Phase

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Secondary Cementing Operation

Squeeze Cementing

Process by which hydraulic pressure forcescement slurry through holes in casing intoannulus and formation

~ Often used as a remedial operation in workovers



~ Applications

To seal off gas and water producing zones andmaximize oil production from completion i nterva l.

Repair casing failure through leaking joints and

corrosion. Seal off lost circulation zones.

Remedial work on a poor primary cement job.

Abandonment.


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Development Phase

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~ Hig Pressure Squeeze

Breaking down the formation andallowing cement slurry intofractured zone.Carried out by solids free fluids water or brine.Fracture occurs along planeperpendicular to direction of leastcompressive stress. At depths>3000 ft, vertical stresses are

greater than horizontal stresses.

ter rea ng ormat on, s urrycement is spotted adjacent toformation and pumped slowly.Injection pressure gradually buildsup.Pressure released for back flow.High Pressure squeeze jobs arerecommended for very dense andimpermeable formations.




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Development Phase

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~ Low Pressure Squeeze

Efficient method to seal unwanted zones

Slurry of finely divided solids in liquid is forcedinto formation without fracturing.

Liquid is forced into formation and solids build upca ke.

Reverse circulate out excess cement.

Often used for repairing primary cement job.




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Development Phase

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den head SqueezePumping cement through drill pipewithout the use of packer. Cementstopped at required depth andpressure build up is obtained byclosing BOPS at surface.

Displacing fluid is then pumped

down, forcing cement intoperforations

Generally used for low pressure

cement squeeze job.Disadvantages

It is difficult to place cementaccurately.

Cannot be used for squeezingoff one set of perforations ifother are still open.


Procedure for squeezingRun packer on drill pipe and set atdepth to with bypass openPump cement slurry ,displace cementand allow fluid to flow through by passportsClose port when cement slurryreaches packer. Applysqueeze pressureRelease pressure and check back flowRelease packer, pick up and reversecirculate.

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Secondary Cementing OperationRetrievable PackerCan be set and released as many times

on one trip.

pressure is being applied.

Can be either compression set or tensionset.By pass ports allow annularcommunication

Generally set 30-50ft above perforations.

Sometimes tail pipe is used below packerto ensure only cement is squeezed

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Development Phase

Cement Plu s

lanced PlugMethod achieves anequal level of cement inthe drill pipe andannulus.Preflush, cement slurryand spacer fluid arepumped down the drillpipe and displaced withmud.Displacement continuesuntil level of cementinside and outside issame.Drill pipe retrievedleaving plug in place.


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Cement Evaluation Tools

~ Cement job can be considered a failure if:

Cement does not fill annulus to required height.

Cement does not provide good seal at shoe. Cement

does not isolate undesirable zones.


Development Phase

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Cement Plugs

Dump Bailer MethodSet permanent bridge plug belowplug back depthCement bailer containing slurry isthen lowered down the well Whenbailer reaches bridge plug theslurry is released and set on to p

Advanta esBetter depth controlReduced risk of contamination

DisadvantagesOnly small volume of cement

can be dumped and therefore

several runs requiredNot suitable for deep wells

unless retarders used.

2005 Abalt Solutions Limited. All rights reserved

2005 Abalt Solutions Limited. All rights reserved



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Development Phase

48 Cement Evaluation Tools~ Cement Bond Logs

Indicate presence of

cement and bond.

Tool emits sonic signalsand receives at receiver.Amplitude indicateswhether bond is strongor weak.

Channelling can also bedetected.

ioactive surveys

Radioactive tracers canbe added to cementslurry before it ispumped.Carnolite is commonlyused and detects the topofcement in annulus.



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