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
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INTRODUCTION TO HYDROCARBON EXPLOITATION
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
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INTRODUCTION TO HYDROCARBON EXPLOITATION
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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INTRODUCTION TO HYDROCARBON EXPLOITATION
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
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Classification ofCement
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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INTRODUCTION TO HYDROCARBON EXPLOITATION
Development Phase
Classification ofCement
~ 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.
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Classification ofCement
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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INTRODUCTION TO HYDROCARBON EXPLOITATION
Development Phase
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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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INTRODUCTION TO HYDROCARBON EXPLOITATION
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.
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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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INTRODUCTION TO HYDROCARBON EXPLOITATION
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
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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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INTRODUCTION TO HYDROCARBON EXPLOITATION
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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INTRODUCTION TO HYDROCARBON EXPLOITATION
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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INTRODUCTION TO HYDROCARBON EXPLOITATION
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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INTRODUCTION TO HYDROCARBON EXPLOITATION
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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INTRODUCTION TO HYDROCARBON EXPLOITATION
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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INTRODUCTION TO HYDROCARBON EXPLOITATION
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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INTRODUCTION TO HYDROCARBON EXPLOITATION
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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INTRODUCTION TO HYDROCARBON EXPLOITATION
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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INTRODUCTION TO HYDROCARBON EXPLOITATION
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
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Secondary Cementing Operation
~ 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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INTRODUCTION TO HYDROCARBON EXPLOITATION
Development Phase
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Secondary Cementing Operation
~ 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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INTRODUCTION TO HYDROCARBON EXPLOITATION
Development Phase
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Secondary Cementing Operation
~ 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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INTRODUCTION TO HYDROCARBON EXPLOITATION
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.
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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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INTRODUCTION TO HYDROCARBON EXPLOITATION
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.
INTRODUCTION TO HYDROCARBON EXPLOITATION
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.
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INTRODUCTION TO HYDROCARBON EXPLOITATION
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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