Guidelines for Cement Plug Operations

Guidelines and manuals GM-FPL-CEM-01

Guidelines for cement plug operations

Exploration & Production Rev: 00 Date: 09/10/03 Page: 2 of 18

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GM-FPL-CEM-01 guidelines for cement plug operations rev 00.doc

TABLE OF CONTENTS

1. PURPOSE...................................................................................................................4

2. GLOSSARY ................................................................................................................4

3. REFERENCE ..............................................................................................................4

4. FORMULATIONS AND EQUIPEMENT PREPARED IN ADVANCE ..........................54.1 Slurry test ............................................................................................................................ 54.2 Temperature evaluation....................................................................................................... 54.3 Equipment ........................................................................................................................... 5

5. SLURRY DESIGN LEADING TO HIGH COMPRESSIVE STRENGTH ......................65.1 Slurry density....................................................................................................................... 65.2 Pumpability time .................................................................................................................. 65.3 Filtrate HP / HT.................................................................................................................... 7

6. HEIGHT OF CEMENT : SIDE TRACK OR ABANDON PLUGS.................................7

7. HOLE CONDITIONS...................................................................................................87.1 Hole should be stabilised..................................................................................................... 87.2 Mud in hole should be thin................................................................................................... 8

8. SUPPORT BELOW CEMENT PLUGS .......................................................................88.1 Mechanical support plug...................................................................................................... 88.2 Viscous Pill .......................................................................................................................... 88.3 Mechanical barrier ............................................................................................................... 9

9. SPACERS HEIGHT TO REDUCE CONTAMINATION .............................................10

10. MIXING SLURRY..................................................................................................10

11. PLUG SETTING STRING .....................................................................................1111.1 Cementing string with tubing stinger................................................................................. 1111.2 Diverting Tool ................................................................................................................... 11

12. DISPLACEMENT PROCEDURE ..........................................................................1112.1 Rotation of the cementing string when displacing ............................................................. 11






12.2 Rate of Pumping for Spacers and Slurry.......................................................................... 1112.3 Displacement with specific tools ..................................................................................... 12

13. WAITING FOR CEMENT PLUG STRENGTH. .....................................................12

14. INITIATING THE SIDE TRACK / TIME DRILLING .............................................13

15. ATTACHMENTS...................................................................................................1415.1 Attachment no 1 : Diverter sub ....................................................................................... 1415.2 Attachment no 2 : Parabow ‘’ BJ ‘’ ................................................................................... 1415.3 Attachment no 3 : PPT ‘’ Schlumberger ‘’ ........................................................................ 1515.4 Attachment no 4 : TUBING Abandonment Release Tool ................................................. 1715.5 Attachment No 5 : Indicating Ball catcher : ( Halliburton ) ................................................ 18






1. PURPOSE“ Cement Plugs “ Setting Recommendations- Open hole side track cement plugs- Open hole or cased hole abandon plugsAll the studies conducted in the past have demonstrated that the primary causes offailure for a cementing operation was a combination of the following effects:

* Poor mud removal or cement contamination* Unstable cement slurries* Insufficient slurry volume* Poor job preparation and execution* Poor selection of the interval .

You will find herewith a list of recommendations elaborated commonly betweenFPL/OPS & FPL/EC, and which should ensure the success of your cementingoperation.

2. GLOSSARYBHCT Bottom Hole Circulating TemperatureECD Equivalent Circulating DensityOD Outside diameterP Frac Frac PressureROP Rate Of PenetrationRPM Rotation Per MinuteSG Specific GravityUCA Ultrasonic Cement AnalyserWOB Weight On BitYV Yield Value

3. REFERENCECR FPA 100 Plug and abandon






4. FORMULATIONS AND EQUIPEMENT PREPARED IN ADVANCE

The equipment to be used, and the procedures to be followed for cement placementat different depths should be prepared before the start of the phase/well (to avoiddesigning the slurry at the last moment with insufficient testing) . Do not use liner orcasing formulation .

4.1 Slurry testDifferent formulations for significant steps of temperature and pressure should beready , and tested in advance, with the cement additives and water to be used ; thetests should allow to identify in particular :- Sensitivity of setting time versus temperature,- Sensitivity to key additives concentration ;Limitation zone ( temperature range ) for usage of some additive .Density recommendation

4.2 Temperature evaluationIdeally, these tests should be prepared by the contractor, and some of these testscross-checked in PAU. Only adjustment tests would then be done at the last momentProcedures should include a temperature forecast , as precise as possible , for staticand circulating conditions at the different depths . These curves will be upgradedwhile drilling .

4.3 EquipmentEquipment list should include , ready on the rig or available in the near by :

- Diverter Tool or sub (attachment no1) ,- Lengths of slick diameter tubing type 3 ½ ; or lengths of fiberglass /

“aluminium” tubings , dart plugs.- Cement and Additives ,- Batch mixer (recommended option).- Optionally, for enlarged/deviated hole , Parabow ( BJ), ( attachment no2 )

or Cement Inflatable Packer for support - Specific side track bit with concave shape , in case of hard formations.






5. SLURRY DESIGN LEADING TO HIGH COMPRESSIVE STRENGTHIt is recommended to start the preparation of the side track as early as possible :The main element is the FINAL DESIGN OF CEMENTING SLURRY , to be designedas soon as possible .DO NOT USE the liner or casing slurries formulation as a base case .Reduceadditives to a minimum.

5.1 Slurry densityFor side track : As a first approach , slurry at 2.00 SG is recommended :

- Higher slurry density can be considered , 2.05 SG and above as a way toincrease strength when high mud weight is in hole . It should then beobtained with lower water content.

- Avoid Barite or Hematite, as these products reduce the mechanicalresistance of the plug .

For Abandon plugs : Density = 1.90 SG or mud weight plus 10 pointsIt should be designed to obtain the maximum possible strength in a short time ,complex formulation is to be avoided .Order of magnitude for the expected strength is around : 3000 to 4000 psi @ 24h atBHCT , to be adapted to formation hardness . ( Side Track plug ) For temperature above 230 ° F, Silica flour addition is recommended .If sand is available , its addition in the slurry can increase the strength , and may beused , but only for the cases when a very high compressive strength is needed , inhard sandstones ( Experience has shown that adding coarse sand , 12/20 or 20/40mesh sand, increases the problem associated with settling and is difficult to maintainin suspension ).Dense-Crete ( Schlumberger )slurry could be evaluated for special applicationLight slurry can be designed with high strength to reduce the risk of slumping (DeepWater application).

5.2 Pumpability timePumpability time should include a reasonable margin , but not excessive. Work outthe slurry formulation , in order to reach a reasonable , but limited , pumpability time(in general , the forecasted time for normal operations from mixing to reversecirculation , plus 1 hour ) . Re-test formulation of cement slurry with samples of actualproduct to be used , with the temperature determined as accurately as possible . Runcompatibility test with actual mud used .






5.3 Filtrate HP / HTFiltrate HP / HT < 150 mls (permeable zone)

6. HEIGHT OF CEMENT : SIDE TRACK OR ABANDON PLUGS

Typically, length of cement should be between 50 et 200 meters , to modulate as afunction of formation hardness and deviation .

Table of typical length considered as good cement

Hardness offormation

Length ofplug

Soft Medium hard Hard

Vertical hole 50 - 70 m 80 - 100m 100- 130 mDeviated (30°) 60 - 80 m 90 - 120 m 120-150m

Deviated ( > 60°) 70 - 90m 110 - 130 m 140-170m

Table 1

The corresponding slurry volumes will be calculated from hole size and caliperinformation.

Sufficient volume is a key parameter, with a sufficient excess above the theoreticalvolume calculated from table 1.An Excess of 50 % will be applied on these figures on the theoretical volumecalculated.Abandon plugs ( open hole or cased hole ) , excess should be reduced to 50 metersheight or 1 to 2 m³ for mud contamination.It’s recommended to avoid to pump less than 5 m³ of slurry to obtain a success of theoperation in conventional operation . For Slim hole the volume could be re-evaluated.






7. HOLE CONDITIONS

7.1 Hole should be stabilised

The well bore should be completely static ( no gas, no flowing fluid, no lostcirculation).

7.2 Mud in hole should be thin

The well should be circulated and mud treated to lower viscosity and gel strengthabove support plug to facilitate slurry placement . If possible, make sure the thinnerused will not have a marked effect on the slurry (e.g. ligno-sulfonates may act asstrong retarders ).

8. SUPPORT BELOW CEMENT PLUGS

Either a VISCOUS GEL PILL , or a mechanical support plug should be used belowthe sidetrack or abandon plugs , to avoid uneven slumping .

8.1 Mechanical support plug

The first recommended is to set a strong viscous gel pill , made with active treatedmud.In case of partial failure of side track pill (contaminated cement / ROP to drill cementtoo high) keep a part of this plug (10 to 20 m) to be used as a support plug .

8.2 Viscous PillIt should be obtained with bentonite in water based mud , or with an organo - clay incase of oil base mud . Activation with lime or caustic soda should be avoided . Ifusing polymer , be aware they thin with temperature.If a primary cement plug for support is chosen (a thixotropic cement can be selected), use for the design of slurry spacers , and displacement , the same principlesestablished as for the main side track cement plug .






If a mud treated pill is used , its viscosity should be high ( limit to pumpability) :Values can be in the order of:

Yield Value : Around 100 to 150 lbs / 100 ft2 .Density : Mud Density + 30 points or minimum 1.60 SGGel 10 ‘ : > 70 lbs / 100 ft2Volume / height : +/- 150 to 200 m

The pumping and displacement of the support plug should be done carefully , with anexcess volume , and top to be eliminated by circulation , either in reverse circulation(preferred option , but drawback = ECD) or in direct circulation ( drawback =mudcontamination).

8.3 Mechanical barrier

Mechanical barrier. ( see attachment no 2 )

For severe cases, mechanical device , such as Parabow (BJ) , or Inflatable Packer ,can be used , if available . They have proven to be effective .

If no support is set in place below the side track plug , analysis shows that a largecontamination is likely to occur, especially in low mud density and enlarged hole

86






9. SPACERS HEIGHT TO REDUCE CONTAMINATION

Spacers or washers are important to insure low contamination and adequatedisplacement of mud by the cement slurry : Sufficient volume of spacer isrecommended , length in annulus of around 100 to 150 meters (should be increasedto a length of around 200meters in case of oil base mud or any other muds actingstrongly on cement setting parameters). Volumes, Hole OD and height to be checkedto avoid any errors in displacement .Note : In any case a minimum of 5 m³ of spacer will be pumped ahead the slurry .Spacers design should be kept as simple as possible. The spacer should becompatible with the mud and the cement .In water based mud the tail spacer can be simple pure water, or other spacer withproperties (specific gravity and viscosity ) between the mud and slurry values. Do notuse special additives to clean well bore, they will not have time to act and cancontaminate slurry head .In oil base mud , special care should be taken for the spacers , with reductor ofsuperficial tension . For example :Oil base plus surfactant, in the order of magnitude of 50 meters of hole .Spacer with surfactants, in the order of magnitude of 50 meters of holeA spacer could also be pumped behind, to balance U tube effect at the end ofdisplacement.Main characteristics of spacer :

SG mud < SG Spacer < SG SlurryYV mud < YV Spacer < YV Slurry

10. MIXING SLURRYBatch Mixing is the recommended option.Batch mixing allows for an accurate control of slurry weight and slurry volume. (10m3 capacity minimun with reliable homogenization device )..Note :For batch mixing operations refer also to feed back OPS 12/96Clean Tanks and uncontaminated Cement , is obviously recommended .






11. PLUG SETTING STRING

11.1 Cementing string with tubing stingerSmall diameter tubing tail pipe, with smooth tool joints should be used with a lengthsuperior to the length of cement . ( 3 ½” recommended no less than 2 7/8”) “Aluminium” tubes , or fiber glass , can be an alternative option. ( centralization with2 or 3 centralizers is a good practice )

11.2 Diverting Tool The diverting tool , basically a sub plugged on the bottom with various lateral holesto divert the flow horizontally , has proven efficient , and is recommended to avoidcontamination .Tubing abandonment release tool ( see attachment no 4 ) , this is an option .

12. DISPLACEMENT PROCEDURE

12.1 Rotation of the cementing string when displacingPipe should be rotated while displacing slurry (30 to 40 rpm recommended), but notreciprocated. For this, a rotating head should be made available in advance .(Note: in case of fiber glass tubing ensure that fiber glass thread connection is strongenough for rotation of the cementing string)After the plug is in place, it is important to avoid disturbance to the plug .Hence it isrecommended to pull out slowly to the desired depth for circulation. (2 mins / Stand)

12.2 Rate of Pumping for Spacers and SlurryRate of pumping should be high , in order to reach turbulent flow , when possible ,for the displacement of the spacers and the annular . It can be obtained with the rigpump ; It is not necessary to slow down when the slurry pass into the annular.The compatibility of the ECD with the P Frac of the open hole has to be checked.

Hole Diameter in” Annular Volume in l/m Flow rate in l/min17 ½” 150 1500 - 200016” 125 1200 - 2000

12 ¼” 72 1000 - 15009 5/8” 42 10008 ½” 32 8006” 14 350






The displacement with the cementing unit, (although this presents the advantage ofcontinuity of operation ) , is generally too limited in flow rate, and is notrecommended, except for small diameter.

12.3 Displacement with specific toolsOver displacement should be avoided , as they generate contamination . Dart sub /or ball generally complicate the job , and is not recommended for conventional job .For special application : deep and high deviated , slim hole with small volume theusage of specific tools is recommended .PPT tools – Schumberger ( attachment no 3 )Indicating Ball catcher – Halliburton ( attachment no 5 )

13. WAITING FOR CEMENT PLUG STRENGTH.Give enough time for cement to acquire a good strength, superior to formation .Sufficient Waiting On Cement is to be observed, to be absolutely sure that thecement has acquired a sufficient strength , (especially in the cases when theformation is hard ) .A value of 3000 psi obtained through UCA laboratory tests done at BHCT after 24 to36 hours is recommended .In some particular cases ,when reaming risks is present , it can be recommended torun first a normal light assembly to tag and dress the top of the cement plug at theoptimum depth .To control the strength of top of cement plug the following procedure will be applied :WOB 5000 lbs, no rotation ,flow rate as per drilling flow rate and observe loss ofweight ;If permanent loss of weight ,wait on cement .If not , proceed to side track






14. INITIATING THE SIDE TRACK / TIME DRILLING .- The side track bit should be aggressive.The side track assembly should be made with an agressive side track bit either rockbit (mainly large ,intermediate diameter )or special PDC or diamond side track bit, flator concave, (small intermediate diameter / hard formations ).- The side track Assembly angle should be high enough.Severity of sidetrack Assembly Angle ( bent sub ,...) should be aggressive enough . Itshould be discussed with directional contractor , in view of formation hardness .It will be important however to avoid a too sharp dog leg for the future , if the sidetrack is to be done in the upper part of a deep well ( the dog leg severity will bemostly detrimental in the upper part of the well ).Typically, it should be in the order of 1. 5 °. ( At least : lower values should beconsidered only with care , for soft formations only )- Low side departure is recommended, (near from short axis , if the hole has anellipse shape) .The easier way to start is the lower side , which should be favored each time it ispossible .If the hole is enlarged in ellipse , what is almost always the case in Tectonicenvironment , the trajectory should start as perpendicular as possible to the long axisof the ellipse , in a direction near from the short axis .- Side track parameters WOB – RPM - FLOW as per directional drilling engineerinstructions.- Time drilling with patience.Time drilling should be undertaken with sufficient patience, without taking intoaccount all the time the Martin Decker information. It is reminded, that in areasonably soft formation, a low side departure is nearly always successful, even ifcement plug is not very good , providing the time drilling is done adequately .






15. ATTACHMENTS

15.1 Attachment no 1 : Diverter sub

15.2 Attachment no 2 : Parabow ‘’ BJ ‘’






15.3 Attachment no 3 : PPT ‘’ Schlumberger ‘’











15.4 Attachment no 4 : TUBING Abandonment Release Tool






15.5 Attachment No 5 : Indicating Ball catcher : ( Halliburton )

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Guidelines for Cement Plug Operations