Transcript
PLUG CEMENTING
Module CF110 NL08 Sep 99
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ObjectivesBy the end of this module, a trainee will be able to do the followings: List the purpose of setting a cement plugs
List the three different techniques
List the advantages and disadvantages of each
technique
Recognise the job consideration
Select slurry properties to fit with the plug type
Explain step by step the cement plug job procedure
All necessary calculations to perform a balanced plug
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Cement Plugs Introduction Setting a cement plug in a well is a
common oil-field operation.
A cement plug involves a relatively small volume of cement slurry.
And is placed in the wellbore for various purposes:
To side track above a fish or to initiate directional drilling.
To plug back a zone or plug back a well.
To solve a lost-circulation problem during the drilling phase,
To provide an anchor for OH tests.
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Side Track and Directional Drilling
Kick Off PointKick Off Point
CEMENTCEMENTPLUGPLUG
NEWNEWHOLEHOLE
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Plug Back and Depleted Zone
Depleted Zone
Cement Plug
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Lost Circulation
CEMENTCEMENTPLUGPLUG
Thief Zone
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Abandonment
Cement Cement PlugPlug
Cement Cement PlugPlug
Cement Cement PlugPlug
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Examples of Countries Having Drilling and Cementing
RegulationsCountry
Abu DhabiAustraliaAustriaCanada
ColombiaFranceGermanyIrelandItalyJapan
LibyaMalaysiaMozambiqueThe NetherlandsNorwayTurkeyUnited KingdomVenezuela
Agency
Ministry of PetroleumDepartment of MinesOberste BergbehordeOntario-Dept of Mines and Northern affairsAlberta-Oil & Gas Conservation BoardSaskatewan-Dept of Mineral ResourcesMinister of Mines & PetroleumDirection Generale des MinesBureau of MinesOffshore Operating Committee - LondonNational Mining Bureau for HydrocarbonsBureau of Mines
Petroleum Mine Safety RegulationsPetroleum MinistryGeology and Mines DeptThe Ministry of MinesPetroleum DirectoratePetroleum AdminDept of EnergyDept of Hydrocarbons
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Test Anchor
Test String
Zone to be Tested
Weak Formation
Cement Plug
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Plug Placement TechniquesThere are three common techniques for placing cement plugs:
Balanced plug
Dump bailer
Two-plug method
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Balanced Plug
T.O.C with D.P.
T.O.C without D.P.
1. Pump Water Ahead (or CW and/or Spacer)
1. Pump Water Ahead (or CW and/or Spacer)
2. Pump Cement Slurry
1. Pump Water Ahead (or CW and/or Spacer)
2. Pump Cement Slurry
3. Pump Water Behind (or CW or Spacer)
1. Pump Water Ahead (or CW and/or Spacer)
2. Pump Cement Slurry
3. Pump Water Behind (or CW or Spacer)
4. Displace (under-displacement)
1. Pump Water Ahead (or CW and/or Spacer)
2. Pump Cement Slurry
3. Pump Water Behind (or CW or Spacer)
4. Displace (under-displacement)
5. Pull Out Drill Pipe
1. Pump Water Ahead (or CW and/or Spacer)
2. Pump Cement Slurry
3. Pump Water Behind (or CW or Spacer)
4. Displace (under-displacement)
5. Pull Out Drill Pipe
6. Reverse Circulation
Plug Length
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Dump Bailer Method
WIRELINE
DUMP BAILER
CEMENT SLURRY
CEMENT RETAINER
ELECTRICAL / MECHANICAL
DUMP RELEASE
CEMENT PLUG
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Dump Bailer MethodAdvantages:
Depth of cement plug is easily controlled.
Relatively cheap.
Disadvantages:
Not easily adaptable to setting deep plugs.
Quantity of cement limited to volume of dump bailer.
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Two Plug Method
Shear Pin
Plug Catcher
Bottom Wiper Plug & Dart Assy
Top Wiper Plug
Catcher Sub Body
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Two Plug Method
1. Running In
2. Bottom Wiper Plug Landing
3. Shearing Wiper Dart Pin and
Cleaning of Aluminium Tail Pipe
4. Top Wiper Plug Landing -
Shearing Plug Catcher Pin – Pull
String
5. Reverse Circulation
1. Running In
2. Bottom Wiper Plug Landing
3. Shearing Wiper Dart Pin and
Cleaning of Aluminium Tail Pipe
4. Top Wiper Plug Landing -
Shearing Plug Catcher Pin – Pull
String
1. Running In
2. Bottom Wiper Plug Landing
3. Shearing Wiper Dart Pin and
Cleaning of Aluminium Tail Pipe
1. Running In
2. Bottom Wiper Plug Landing
1. Running In the Well
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Two-Plug Method: Tell-Tale Catcher Sub
System
Advantages of this method are:
Isolation ahead and behind the cement.
Pipe cleaned down to the lower end of the tail pipe.
Breakable tail pipe that can be abandoned if stuck.
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Coiled Tubing Cement Plug Technique
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Job Design Considerations Why is the cement plug being set? At what depth will the plug be set? Across which formations is the plug going to be set? At what density should the slurry be mixed? What is the BHT? What volume should be pumped? What is the required thickening time? How to insure the cement will not be contaminated
by mud? Are pipe centralization and rotation necessary? Waiting on cement time?
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Slurry PropertiesDensity - lighter for Lost CirculationDensity - heavier for SidetrackingDensity - homogeneous - batch mixingRheology - higher for Lost CirculationRheology - lower for placement with Coiled TubingCompressive Strength - higher for SidetrackingCompressive Strength - less important for Lost Circulation
Compressvie Strength - minimum 500 psi for drill outThickening Time - enough for placement - 1.5 to 2 hours
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking).
Poor isolation (plugback, abandonment).
Wrong Depth (all plugs).
Not in place due to sinking to the bottom (all plugs).
Not in place due to loss to thief zone (lost circulation).
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Reasons for Failure Can be Traced to the
Following Slurry not designed for enough compressive strength.
Not enough WOC time.
Inaccurate BHST.
Cement contamination during displacement and POH.
Slurry not designed for the specific problem (lost circulation).
Not enough cement volume.
Difference between cement and hole fluids' densities too high, causing the plug to sink.
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Plug Cementing - ConclusionsPlace the plug in a competent formation (i.e., a hard formation).
Use ample cement.Use a tailpipe through plugback intervals.Use centralizers on the tailpipe where the hole is not excessively
washed out.Use a drill pipe plug and a plug catcher.Condition the well before running the job, using low YP and PV
mud, but of sufficient weight to control the well.Ahead of the cement, run a high-vis pill that is compatible with
the mud and will prevent the cement from sliding down the hole.Use spacers and washes to combat the effects of mud
contamination. Densified cements with a dispersant are also useful.
Allow ample time for the cement to set.
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Diverter Tool
8 holes phased at 450
Bull Plug
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Drill Pipe Centralization & Diverter Tool
DRILLPIPECENTRALIZED
9.0 lb/gal MUD
9.0 lb/gal MUD
SPACER
16.0 lb/gal CEMENT
DIVERTER TOOL
9.1 lb/gal VISCOUS BENTONITE PILL
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Bad Cement Placement Technique
BENTONITE PILL
9.0 lb/gal MUD
9.0 lb/gal MUD
SPACER
Contaminated CEMENT
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Horizontal Well Density swapping won’t occur at horizontal !
“Slumping” tendency can be controlled by increasing of the Mud (limited to allow proper WELLCLEAN
technique)
Contamination of Slurry is likely to occur, pipe rotation will help ensuring only near end of the plug is contaminated.
MUD CEMENT SLURRY
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Reverse Circulating Excess Cement
T.O.C with D.P.
T.O.C without D.P. Plug
Length
1. Plug Balanced1. Plug Balanced
2. Pick up DP to Required T.O.C
1. Plug Balanced
2. Pick up DP to Required T.O.C
3. Reverse Circulation
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Job Procedure - Balanced Plug Test treating lines.
Pump spacer or wash ahead of cement slurry. Mix and pump cement slurry. Pump spacer or wash behind cement slurry. Displace calculated amount of displacing fluid. Under displace 1/2-1 bbl for safety.
Open return lines to the displacement tank on the unit and allow plug to balance itself either by return flow or vacuum.
Pull drill pipe or tubing above the plug. Reverse circulate if conditions allow. POOH and WOC.
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Slurry Volume Calculation
7000
7500
Desired Plug At End of Displacement
Mud
Spacer Cement
Drillpipe/tubing
Lsp2
Lcmt
L
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Slurry Volume Calculation
Volume of Cement, Vcmt
Vcmt = L x Ch x excess factor
where,
L = length of column of cement in open hole
(ft).
Ch = capacity of open hole from standard tables
(ft3/ft).
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Slurry Volume Calculation
Volume of Cement, VcmtVcmt = L x Ch x excess factor, where,L = length of column of cement in open hole (ft).Ch = capacity of open hole from standard tables (ft3/ft).
Length of Balanced Plug (with working string in place).
where,
Can = Capacity of annulus between tubing or drill pipe and open hole(ft3ft).
Ctbg = Capacity of tubing or drill pipe (ft3/ft).
Lcmt = Vcmt
Can + Ctbg
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Slurry Volume Calculation
Volume of Spacer Behind the Cement
Vsp1 = Volume of spacer ahead of the cement
Vsp2 = Vsp
1Can
x C tbg
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Slurry Volume Calculation
Volume of Spacer Behind the Cement
Vsp1 = Volume of spacer ahead of the cement
Length of Spacer
Vsp2 = Vsp
1
Can x C tbg
Lsp2 = length of spacer behind (ft) = Vsp2 / Ctbg
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Slurry Volume Calculation Volume of Spacer Behind the Cement
Vsp1 = Volume of spacer ahead of the cement
Length of Spacer
Displacement Volume
D = depth of work string (bottom of cement plug) (ft)
VVd = Ctbg x [D - (Lcmt + Lsp2)]
V sp2 = V sp
1
C an x C tbg
Lsp2 = length of spacer behind (ft) = V sp2 / Ctbg
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