Squeeze Cementing
– Forces cement slurry, under pressure, throughperforations or holes in the casing or liner…..• Used to permanently block entry of undesirable fluids
to the wellbore or to fill channels behind the casing.Water production form watered out zones or leaks areWater production form watered out zones or leaks arecommon targets.
• Also used to set “cement packers” to isolate sections ofthe annulus.
• The cement plug must remain an effective seal fulltemperature, highest pressure and in contact with anyfluid from the well.
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Repair Cementing
• Squeeze Cementing
– Shutting off watered-out perforation intervals
– Filling channels behind the pipe
– Covering pipe annuli that was never cemented– Covering pipe annuli that was never cemented
– Setting cement packers
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Treatment Execution
•Execution of squeeze cementing operations infour basic steps:–Wellbore preparation
–Slurry mixing and pumping–Slurry mixing and pumping
–Squeeze
–Removal of excess cement
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Squeeze Cementing – channel repair
• Objectives
1. Locate the channel
2. Perforate into the channel
3. Inject cement and fill the channel3. Inject cement and fill the channel
Problems
1. locating the channel
2. squeezing into the channel
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Channel Detection
• Cement bond log
• Noise log? - leaks
• Segmented or radial bond log
– Bond differences– Bond differences
– Looking for patterns that represent channels
• Block perforate and squeeze techniques
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Squeeze Types
• Hesitation squeeze – steady application of pressurethought by some to force cement in matrix – mayonly help build size of dehydrated mass or “node”through fluid loss of liquid from the cement slurry.
• Actually – what may be happening in some cases is• Actually – what may be happening in some cases isthat the wellbore is being “restressed” – forming a“stress cage” by solids from mud or cement wedginginto and bridging on the formation. This may allow1 to 5 lb/gal higher fluid gradient weight than initialfrac pressure of the formation.
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Squeeze Types
• Suicide squeeze – This squeezeperforates two spots – high andlow and squeezes from the bottomtowards the top. There is a chance,if slurry volumes are too large, ofif slurry volumes are too large, ofcement spilling out of the upperperforations and sticking theisolation packer or retainer inthe well.
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Fluid Loss Control
• Excessive fluid loss in the slurry can result in bridgingof tubulars by dehydrated cement.
• Slurries with too little fluid loss can result ininsufficient buildup of filter cake on the formation(may also be a function of permeability and(may also be a function of permeability andpressure).
• Fluid loss additives may be required to control fluidloss.
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Cement Node Buildup
Node with minimalintrusion into
Casing Formation
intrusion intowellbore
Primary cementsheath
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Rheology Controls
• Cement slurries have higher viscosity than mostworkover fluids and this significantly reducesmaximum possible pump rate.
• Rheology and stability tests are commonlyperformed:performed:– At surface mixing temperatures, and
– At bottomhole static temperature BHST (caution – makesure mix water temperature is not higher than bottomhole temp.).
• Slurries must stable to provide good rheologycharacteristics that are easily reproducible.
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Slurry Volume
• Volume of slurry prepared depends on:– Length of perforated interval
– Capacity of liner/casing or channel behind pipe
– Void areas behind the perforations
– Force that can be applied to the tubing– Force that can be applied to the tubing
– Configuration of surface mixing / pumping equipment
– Use of cement plugs, pigs or darts (isolation devices)
• Previous squeeze experience provides bestguidelines.
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Depth Control – (with CT)
• In cement squeezing, surface equipment notaccurate enough to position CT nozzle
• Downhole reference point is generally required
• Methods of setting depth reference– Tagging bottom– Tagging bottom
• inaccurate in wells with fill, but viable in certain conditions
– Tagging completion restrictions• tubing end locator (TEL) or tubing nipple locators (TNL)
• commonly used in squeeze cementing
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Cement Contamination Problems
• Contamination can result in:– Unpredictable slurry characteristics
– Reduced compressive strength of the set cement
– Incorrect placement due to change in slurry volume
• To avoid contamination:• To avoid contamination:– Spacer fluid should isolate (ahead of/behind cement)
– Lines should be flushed each time a new fluid is pumped
– Mechanical separation of cement slurry using CT plugs(darts or pigs)
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Reel Manifold Sampling Point andFlush Line
Circulating pressuresensor
To reel core and CTthrough reel isolationvalve
Reel manifoldvalves
From pump unit Flush lineto disposal
Sample point
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Cement Composition and Vol.
• Low or high fluid loss? Depends on depth
• Volume of cement? – depends on channel size
– Often try several small squeezes.
– Pressure?– Pressure?
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Squeeze Success?
• Usually about 50% - but conditions makesuccess vary widely.
• Increases when:
– circulation is possible through the channel,– circulation is possible through the channel,
– Isolation is used fro cement injection,
– cement blending is pod mix,
– the operator is experienced.
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Cement Packer
• Can isolate the annulus
– Water control
– Tubing repair or isolation
– Stabilizing tubing prior to milling window
• Problems and considerations
– Floating the cement in the annulus – there are ways!
– How long a cement column? - 50 to 300+ feet.
– Cement compositions for packers
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Cement Packer
• Perforated annulus at or below point forpacker.
• May need to perforate above top of packerwhen annulus is liquid filled.when annulus is liquid filled.
• Displace cement from a straddle packer orpacker and plug (or retainer) into the annulus.
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Cement Placement With andWithout Retaining “Platform”
Stable cement column
Cement slurry fallsthrough less densefluids
Stable cement columnplaced over the platform
Cement platform
A retainer, mechanical plug, highly gelled mud pill (10 to 20 bbls) or a cement plug maybe used as the “platform”.
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Tool Selection
•Tool strings should generally be kept to a minimum–Connector
• required on all jobs
–Check valves• cannot be used with reverse circulation of excess cement• cannot be used with reverse circulation of excess cement
–Depth correlation• tubing end or nipple locators are commonly used
–Plug catcher• catch and retrieve plugs ahead/behind cement slurry
–Nozzles• developed to improve the slurry placement
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Cementing Nozzle Features
Pins to retainball within thenozzle
Multiplenozzle
Multiplesmall-diameterradial ports
Large-diameter
port
Multiplesmall-diameterradial ports
Largediameterports
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Monitoring RecordingParameters
Pump unit
Coiled tubing• Pressure, rate/volume, string
weight, depth and tubing OD andtubing cycles.
Pump unit• Pressure, density andpump rate/volume
Slurry batch mixer• Monitor density andvolume
Other tankage• Monitor density andvolume
Annulus• Monitorvolume anddensity of allfluids returnedand pumpedthrough theannulus.• Recordpressure.
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Wellbore Preparation
Filtered sea-water or similar
at high rate Choke open
Wellbore cleanand packed –establish leakoffrate.
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Laying In Cement Slurry
Choke open
Slurry pumped atmaximum rate
Nozzle pulled up 50 ftbelow cementinterface
Wellbore pack fluid
Spacer/fresh water
Cement slurry
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Placing Thixotropic Slurries
Choke closed, ifwellbore not fluidpacked, pump slowlydown annulus toprevent U-tubing
Slurry pumped atmaximum rate/pressure
allowed
Nozzle placedabove thief zone
Wellbore pack fluid
Cement slurry
Wellbore pack fluid
Highly gelled mud or other“platform” usually neededexcept in severe fluid loss.
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Commencing Squeeze
Choke back returnsmonitoring pressureand volumes
Low rate continuouspumping or hesitation
Wellbore pack fluidNozzle pulled up>50 ft abovecement interface
Wellbore pack fluid
Cement slurry
Spacer/fresh water
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Completing Squeeze
Choke back returnsincreasing final squeezepressure
Displacement fluid pumpedat maximum rate/pressure
allowed
Nozzle movedcontinuously orfrequently
Wellbore pack fluid
Cement slurry
Spacer/fresh water
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Contaminating Excess Slurry
Returns choked tomaintain pressure onsqueezed zone
Contaminant pumpedat maximum
rate/pressure
Nozzle penetrates slurry ata rate which provides a50% mix of contaminant
Contaminated slurry
Cement slurry
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Reverse Circulating Excess Slurry
Open returnsfrom CT
Fluid pumped at maximumrate/pressure for allowable
differential (1500 psi)
Nozzle penetratescontaminated slurry at arate which provides a50% mix ofcontaminated slurry andpack fluid
Contaminated slurry
Wellbore pack fluid
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Reverse Circulating Live Slurry
Open returnsfrom CT
Fluid pumped at maximumrate/pressure for allowable
differential (1500 psi)
Nozzle penetratesslurry at a rate whichprovides a 50% mix
Wellbore pack fluid
Cement slurry
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Wellbore Circulated Clean
Returns choked tomaintain pressure onsqueezed zone
Fluid pumped atmaximum rate/pressure
Nozzle reciprocatedthrough treatmentzone to TD
Differential pressuremaintained againstsqueezed zone
Wellbore pack fluid
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Wellbore Preparation
•Wellbore preparation operations include–Slick-line work, e.g. fitting dummy gas-lift mandrels
–Pressure test the production tubing annulus
–Establish hang-up depth or TD using slick line
–Confirm and correlate depths with CT and flag the tubing–Confirm and correlate depths with CT and flag the tubing
–Remove fill from rat hole below perforated interval
–Perform pretreatment perforation wash or acidizing
–Place a stable platform for cement slurry
–Ensure wellbore fully loaded with filtered water (orequivalent)
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Slurry Mixing and Pumping
•Key points in the slurry mixing and pumping processinclude–Batch mix and shear the slurry
–Conduct job-site quality control tests–Conduct job-site quality control tests
–Prepare contaminant and spacer fluids as required
–Confirm CT depth
–Lay in cement slurry following pumping schedule
•When using thixotropic cements–Do not stop pumping while cement is inside the work string
–Place CT nozzle above thief zone and pump down productiontubing/CT annulus while squeezing the cement
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Squeeze
•Downhole generation of filter cake aided byperforming hesitation type squeezes–For example, 10 min at 1000 psi, 15 min at 1500 psi,
20 min at 2000 psi...
•As fracture pressure exceeded–Filter cake prevents formation from fracturing
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Removal of Excess Cement
•Efficient removal of excess cement
–Critical to timely completion of job
•Achieved using several methods:•Achieved using several methods:–Reverse circulation of live cement
–Circulation of contaminated cement
–Reverse circulation of contaminated cement
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Reverse Circulation of Live Cement
•Reverse circulation of live cement slurry can beperformed if–Designed slurry thickening time (including safety factor)–Designed slurry thickening time (including safety factor)
allows for completion of the reversing phase
–CT penetration rate controlled to effectively dilute theslurry as it is removed
–Maximum density of reversed fluid is 10 lb/gal
–Reversing is continued until clean returns observed atsurface
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Rev. Circulation of ContaminatedCement
•Contamination of excess cement is often necessary to:
–Extend slurry thickening time• allows cleanout operations to be completed safely
–Allow cleanout operations to be delayed until cement nodeshave increased compressive strength
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Typical Cement SlurryContaminant Composition•TYPICAL CEMENT SLURRY CONTAMINANT
COMPOSITION
• Borax/Bentonite
• 10 to 20 lb/bbl Bentonite
• 20 lb/bbl Borax
• 3 gal Cement Retarder
• Bio-Polymer Gel
• 1.5 lb/bbl Biozan gel
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Circulation of ContaminatedCement
•Conventional circulation used when:–Operating conditions cannot safely support reverse
circulation of excess slurry
•Example:•Example:–Operations performed through 1-1/4-in. work strings cannot
employ reverse circulation techniques
–Reason: excessive friction pressure encountered
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Evaluation of Squeeze
•Methods used to evaluate depend on treatmentobjectives
•Initial step in evaluation process–Confirm condition of wellbore in the treatment zone–Confirm condition of wellbore in the treatment zone
•If wellbore is obstructed–Drilling/under-reaming may be required
•Additional check–Ensure the rat hole is debris or cement free
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