Cementing

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Introduction to Hydrocarbon Exploitation Development Phase Cementing By Pratap Thimaiah

©2005 Abalt Solutions Limited. All rights reserved

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Cementing It is the process by which cement slurry is placed in the annulus ,bonding the casing to the formation. g n i t n e m e C e s a h P t n e m p o l e v e D

Conventionally the cement is pumped down the casing and displaced around the shoe into the annulus.


©abalt solutions limited - 2005

September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase 3

Cementing

g n i t n e m e C e s a h P t n e m p o l e v e D


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Functions of Cements 


Primary functions are : – Provide support to the casings – Zonal isolation-prevent fluid movement between zones – Casing protection against corrosive fluids – Support wellbore – Protect water zones





Cement Job Planning


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Each cement job must be carefully planned to ensure correct additives are being used and suitable placement technique is being employed for that application.

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The cement engineer must ensure that – Cement can be placed correctly using the available equipment – Cement achieves adequate compressive strength – Cement will isolate zones and support casing throughout the life of well.


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Classification of Cement 

Several classes have been approved by API








Class A – Intended 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

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Class B – Intended to use from surface to 6000ft (1,830m) – Moderate to High sulphate resistance – Similar to ASTM Type II – Has lower C 3A content than class A


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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.

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Class D – Intended to use from surface to 6000ft (1,830m) to 10,000ft (3050m). – Moderate and High sulphate resistance types available – Under moderately high temperatures and pressures conditions. ©2005 Abalt Solutions Limited. All rights reserved






Class E – Intended to use from 10,000ft (3050m) to 14,000ft 14,00 0ft (4720m (4720m)) – Under conditions of High temperature and pressure. – Available in MSR and HSR types

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Class F – Intended 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. ©2005 Abalt Solutions Limited. All rights reserved

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Class G and H – Intended to use from surface to 8,000ft (2440m) – Can be used with accelerators and retarders to cover a wide range of well depths and temperatures – Class G Available in MSR and HSR Types, while Class H is available in MSR Types only.





Properties of Cement 


Compressive strength – To support the casing string a compressive strength of 500 psi is generally adequate – ‘WOC’ ( Waiting on Cement)-The time required for the cement to attain strength and settle behind the casing. – The casing shoe should not be drilled out until strength stre ngth is atta attained. ined. – Compressive strength depends depen ds upon    

Temperature Pressure Amount of water mix Elapsed time


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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 before hardening. – Generally 2-3 hours thickening time which includes safety factor to allow for delays and interruptions in operations.






Water Loss – If water is lost before cement cement reaches its intended intended position??? – Amoun Amountt of water loss depends depends upon the type of cement job  

g n i t  n e m e C e s a h P t n e  m p o l e v e D

Squeeze 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 – Forma Formation tion water may contain contain Na and Mg sulphates sulphates which react with lime to form calcium sulphoaluminate. – Thes These e crystals expand expand and cause cement to crack. – Low Loweri ering ng C3 A content increases sulphate resistance types Slurry Density – Var Vary y between between 11 to 18.5 ppg ,de ,depen pending ding upon the type of formation – Dens Density ity is varied for a low to high strength strength formation. formation. ©2005 Abalt Solutions Limited. All rights reserved

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Cementing Additives 

 g n i t n e m e C e s a h P t n e m p o l e v e D

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Most slurries conta contain in additives to modify the properties of the slurry to produce a better cement job. Cement additives can be used to – Vary slurry density – Change compressive strength – Accelerate and retard setting sett ing time – Control filtration and fluid loss – Slurry viscosity Additives may be granular or liquid form, added with the cement or mixed with water.






Accelerators – Chemicals Chemicals that reduce thickening thickening time of slurry and increase early strength – Used in conductors conductors and surface casings casings to reduce WOC – Commo Common n types of accelerators accelerators are :  Calcium chloride (CaCl2 )1.5-2%  Sodium Chloride (NaCl) 2-2.5%  Sea water

g n i t n e m e C e s a h P t n e m p o l e v e D

Retarders – extends extends thickening thickening time of cemen cementt slurry to aid prope properr placement before hardening. – Used in HT wells with Intermediate Intermediate and production production casings casings and squeeze cement jobs – Avoid Avoids s cement setting prematurely prematurely – Commo Common n types are: are:  Calcium lignosulphonate 1-1.5%  Saturated Salt solutions  Cellulose derivatives  Hydroxycarboxylic acids ©2005 Abalt Solutions Limited. All rights reserved

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n i  t

n e m e C e s a h P t n e m p o l e v e D

Cementing Additives

Weighting Agents Weighting Agents(( Heavy additives) – Increases slurry density. – Used when cementing over pressurized zones – Types are:  Barite  Hematite

Extenders (Light weight) – Materials that lower slurry density and increase yield to allow weak formations to be cemented without fracturing. – Allows more mix water to be added – Types are:  Bentonite  Pozzolan  Diatomaceous earth  gilsonite

Source: Drilling Data Handbook, Editions Technip






Mud Contaminants – To Improve Improve slurry properties properties additives additives such such as Diese Diesell Oil ,thinners etc are added. – Prev Prevents ents undesira undesirable ble side effects caused caused by mud on cemen cements ts etc.

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g n i t n e m e C e s a h P t n e m p o l e v e D

Dispersants (Friction Reducing Additives) – Negatively Negatively charged charged polymer polymer molec molecules ules that attach themselves themselves to positively charges in cement grains. – Impr Improves oves flow propertie properties s of slurry – Lower Lowers s the viscosity viscosity so that turbulence turbulence will occur at lower circulating pressure. – Ty Type pes s are are  Polymers 0.3-0.5 lb / sx of cement  Salt  Calcium lignosulphonate 0.5-1.5 lb / sx

Fluid Loss Additives – Excessiv Excessive e flui fluid d loss can caus cause e ineffective ineffective cement setting – Prev Prevents ents slurry dehydratio dehydration n ,premature ,premature setting or reduc reduces es fluid loss to formations – Typ Types es are are::  Organic polymers 0.5 -1.5 % ©2005 Abalt Solutions Limited. All rights reserved

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Cementing Hardware Guide Shoe – Used to guide the casing through the hole with its rounded nose. – Avoiding jamming casing in washed out zones or deviated devia ted wells

g n i t n  e m e C e s a h P t n e m p o l e v e D

Float Shoe – Prevents the back flow into the casing once cement is displaced behind casing. – Built in check valve that is flapper or ball type. – Float shoe takes extra time to run casing in hole





Cementing Hardware 

Float Collars – The purpose purpose of these these landing landing collars collars is to serve as a seat for cement plugs. – Run normally normally 2 or 3 joints joints above the shoe, shoe, known know n as shoe track. track.


Centralizers – Centring Centring the casing casing string string for the success success of cement job. – Ty Type pes s  Rigid-Positive centralizers are designed for a casin casing-casin g-casing g annu annular lar space  Flexible or spring bow type are used in centring in uncased holes. There are two types: straight and spiralled – Th They ey hel help p to  Keep casing out of key seats  Prevent differential sticking  Improve displacement efficiency


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Cementing Hardware

Cement Plug – Desi Designed gned to separate separate the different different fluids when pumped through the casing. – Plugs prevent prevent contamin contaminatio ation n and wipe casing casing from mud – Preve Prevent nt over displaceme displacement nt of cement – Give surface surface indication indication that cement cement placement placement is complete. – Allo Allow w casing to be pressure pressure tested. tested.  Bottom Plug  Bursts when slight over pressure is exerted. g  Besides seperating,it scrapes walls as it moves n i t n  Top Plug e  Provides seal and withstand high pressures m e  Pumped on the tail end of slurry and comes to C rest on bottom plug e Scratchers s a h – Run on casing casing to remove mud mud cake and break break up P gelled mud. t n Promotes otes a better bond betwee between n cement cement and e – Prom m formation p o – Ty Type pes s l e v  Rotating Scratchers e D  Reciprocating Scratchers

Source:weatherford






Cementing Heads – Provides connection between discharge line from cement unit 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 making connection. – Cement plug need to installed correctly in the heads.


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Cementing Baskets – Equipment to minimise losses of cement slurry in weak zones – Used in shallow to medium depths – Curb fluid passage considerably, but do not prevent pressure transmission.





Lowering Casing      g n i t n e m e C e s a h P t n e m p o l e v e D

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The casing must be lowered as fast as possible as time spent is NPT. Casing string lowering speed is controlled according to surge pressures 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 returns contains contains no more cuttings cuttings – Low gas conte content nt – No kicks kicks or lost returns returns – Homo Homogene geneous ous volume volume of circu circulatin lating g mud


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Cementing Operation 


Primary Cementing – Cement Cement plugs placed placed correctly correctly in cement head. head. – Pum Pump p spacer ahead ahead of cement. cement. – First plug plug (wiper) pumped pumped down ahead ahead of cement to clean inside of casing. – Land Landing ing collar collar acts as shou shoulder lder for bottom bottom plug. – Press Pressure ure surge ruptures ruptures bottom bottom plug and allows allows slurry to pass through and circulate into annulus. – Slurr Slurry y displaces displaces mud and washes the outside outside wall of casing as it flows. – Whe When n slurry pumped pumped down, down, top plug is released released and is pushed along down by drilling mud (flushing) – Press Pressure ure increases increases and top plug bumps against against landing collar (not to exceed burst pressure) – Disp Displace lace with with spacer and low densit density y mud.





Cementing Operation


Source: drilling,NGUYEN


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Cementing Operation

Stage Cementing – Carri Carried ed out usually usually in longer longer strings in which which the annulus need to filled completely. – Requi Requiremen rements ts of high pump pressures pressures,, longer pumping times and excessive hydrostatic pressure from cement column leads to cementing 

First stage  Similar to earlier procedure, except that a smaller volume is used to cement lower part of annulus depending upon fracture gradient.

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Second Stage • Invo Involves lves a stage stage collar, collar, which is made up into casing string at pre determined depth. • Stage collar collar are initially initially closed by inner sleeve, sleeve, held by retaining pins. • Afte Afterr first stage stage is complete, complete, a special dart is released from surface opening ports allowing communication between casing and annulus. • Circ Circulate ulate through through stage collar collar and pump spacer • Pump secondary secondary stage stage slurry and release closing closing plug. • Displ Displace ace cement cement with mud. mud. • Top plug closes closes by moving moving a second sleeve sleeve






Cementing Operation Risk of channelling and poor cement bond may arise ???



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Inner String Cementing – Large diamete diameterr casi casing ng result result in ??? ?????? ???  

Large displacement volumes Long pumping times

– Ceme Cement nt casing casing through tubing tubing or drill pipe


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Casing run as before

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Special float shoe-allows drill pipe to be stabbed

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

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Suitable for casi Suitable casings ngs of 13 3/8” and larger

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Disadvantage of NTP for running and retrieving inner string.






Liner cementing – Has a full length length float float collar collar , landing collar collar and and shoe installed. – Landi Landing ng collar collar catches the the cement wiper wiper plug. – Wipe Wiperr plug is held held on end of the the tail pipe pipe by means of shear pins. – Line Linerr is run on drill drill pipe pipe and hanger hanger set at at correct point inside previous casing string. – Mud is circula circulated ted out to ensure ensure it is free of debris. – Befo Before re cementing, cementing, setting setting tool tool is backed off. spacer ahead ahead and followed followed by slurry. slurry. g – Pump spacer n – Relea i Release se pump dow down n plug and displ displace ace cement cement t n out of liner. e down plug releases releases wiper wiper plug. plug. m– Pump down e move down until until Landing Landing collar. collar. C – Both move - – Bump plugs plugs with with 1000 psi pressu pressure. re. e – Bleed off off and check check for for back flow. flow. s a – Exce Excess ss cement cement used to seal seal top of liner. liner. h P – Once cement ce ment is se set, t, setti setting ng tool is picked up picked t out of liner n e – With tail tail pipe above above liner, excess excess cement cement is m reversed circulated p o l e v e D


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Cementing Operation

Liner Cementing


Source: drilling,NGUYEN





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Cementing Operation Problems with cementing Liners – Minimal annular spaces 

Clearance between 7” OD liner and 8-1/2” hole.

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Difficult to run liner Lost circulation problems


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Difficult to centralise Cement placement poor (channelling)

– Mud contamination – Lack of pipe movement-due to risk of setting tool sticking


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Cementing Job 


Recommendations – Use centralise centralisers rs at critical points along the casing string – Moving the casing casing-rotatio -rotation n rather than reciprocation – Befor Before e cementing, cementing, ensure mud has good flow properties – Displace Displace cement cement under turbulent turbule nt condi conditions tions if poss possible ible – Spa Space cers rs to prevent prevent mud contamination in annulus.





Secondary Cementing Operation Squeeze Cementing


“Process by which hydraulic pressure forces cement slurry through holes in casing into annulus and formation” 

Often used as a remedial operation in work overs


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Secondary Cementing Operation 


Applications – To seal off gas and water producing zones and maximize oil production from completion interval. – Repair casing failure through leaking joints and corrosion. – Seal off lost circulation zones. – Remedial work on a poor primary cement job. – Abandonment.






Processes of squeezing cement – Hig High h Pressure Pressure


– Low Pres Pressure sure


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Secondary Cementing Operation High Pressure Squeeze – Breaking Breaking down the formation formation and allowing cement slurry into fractured zone. – Carrie Carried d out by solids solids free fluids fluids – water or brine. – Fract Fracture ure occurs occurs along plane perpendicular to direction of least compressive stress. At depths g n i >3000 ft, vertical stresses are t n greater than horizontal stresses. e m– After breaking breaking formation, formation, slurry slurry of e C cement is spotted adjacent to formation and pumped slowly. e s a – Inje Injection ction pressure pressure gradually gradually builds h P up. t n – Press Pressure ure released released for back flow. e m– High Pressu Pressure re squeeze squeeze jobs are p o l recommended for very dense and e v impermeable formations. e D






Low Pressure Squeeze – Efficient method to seal unwanted zones – Slurry of finely divided solids in liquid is forced into formation without fracturing. – Liquid is forced into formation and solids build up cake. – Reverse circulate out excess cement. – Often used for repairing primary cement job.



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Placement Techniques – Bra Braden den head Squeez Squeeze e – Retr Retrievable ievable squeeze squeeze packer packer – Dri Drillab llable le cem cement ent ret retaine ainerr






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Secondary Cementing Operation Braden head Squeeze – Pumping Pumping cement cement through drill pipe without the use of packer. – Cement Cement stopped at required required depth and pressure build up is obtained by closing BOPS at surface. – Displacing Displacing fluid fluid is then pumped down, forcing cement into g n i perforations t n e – Generally Generally used used for low pressure pressure m e cement squeeze job. C Disadvantages ges e – Disadvanta s a  It is difficult to place cement h P t accurately. n e  Cannot be used for squeezing m p o off one set of perforations if l e v other are still open. e D


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Secondary Cementing Operation Retrievable Packer – Can be set and releas released ed as many many times on one trip. – Isola Isolate te casing casing and well head while while high pressure is being applied. – Can be either either compressio compression n set or tension tension set. – By pass ports ports allow annul annular ar communication – Gene Generall rally y set 30-50ft above perforatio perforations. ns. Sometime times s tail pipe is used below below packer packer g – Some n i to ensure only cement is squeezed t n e m e C e s a h P t n e m p o l e v e D

Procedure for squeezing  Run packer on drill pipe and set at depth to with bypass open  Pump cement slurry ,displace cement and allow fluid to flow through by pass ports  Close port when cement slurry reaches packer.  Apply squeeze pressure  Release pressure and check back flow  Rele Release ase packer, packer, pick up and reverse reverse circulate. ©2005 Abalt Solutions Limited. All rights reserved




Secondary Cementing Operation Drillable Retainer

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– Contains Contains two two way valves valves to prevent flow in either or both directions. – Used for primary primary cement cement jobs as well as closing water producing zones. – Run on drill drill pipe or wireline, wireline, once cement has been squeezed, the drill pipe can be removed, closing back pressure valve. – Can be used used once then then drilled out. – In multiple multiple zones, zones, retainer retainer isolates lower perforations



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Cement Plugs Cement Plugs – Designed to fill a length of casing or open hole to prevent vertical fluid movement – Used for: 


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Abandoning depleted zones Seal lost circulation zones Providing KOP for directional wells Isolating zone for formation testing Series of plugs for well abandonment

– Precautions    

Selection of clean hole to prevent contamination Condition mud prior to placing plug Pre-flush fluid ahead of cement Densified slurry to be used. ©2005 Abalt Solutions Limited. All rights reserved




Cement Plugs



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Cement Plugs 

Balanced Plug – Method achieves an equal level of cement in the drill pipe and annulus. – Preflush, cement slurry and spacer fluid are g n pumped down the drill i t n pipe and displaced with e m e mud. C e – Displacement continues s a until level of cement h P t inside and outside is n e same. m p o l – Drill pipe retrieved e v leaving plug in place. e D ©2005 Abalt Solutions Limited. All rights reserved




Cement Plugs 

Dump Bailer Method – Set permanent permanent bridge bridge plug below plug back depth – Cemen Cementt bailer containing containing slurry slurry is then lowered down the well – When bailer bailer reaches reaches bridge plug plug the slurry is released and set on top – Advan Advantages tages g n i Better depth control  t n e  Reduced risk of contamination m e Disadvanta vantages ges C – Disad  Only small volume of cement e s a can be dumped and therefore h P several runs required t n  Not suitable for deep wells e m unless retarders used. p o l e v e D


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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.








Temperature surveys – Running a recording thermometer in the casing after cementing. – Thermometer responds to heat generated by cement hydration to detect top of cement.


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Cement Bond Logs – Indicate presence of cement and bond. – Tool emits sonic signals and receives at receiver. – Amplit Amplitude ude indica indicates tes whether bond is strong or weak. g n i t – Channelling can also be n detected. e

m e C  e s a h P t n e m p o l e v e D

Radioactive surveys – Radioactive tracers can be added to cement slurry before it is pumped. – Carnolite is commonly used and detects the top of cement in annulus. ©2005 Abalt Solutions Limited. All rights reserved



Cementing

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