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PLUG CEMENTING

Module CF110 NL08 Sep 99

2

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

6

Lost Circulation

CEMENTCEMENTPLUGPLUG

Thief Zone

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Abandonment

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)


2. Pump Cement Slurry



3. Pump Water Behind (or CW or Spacer)




4. Displace (under-displacement)





5. Pull Out Drill Pipe





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


1. Running In




4. Top Wiper Plug Landing -

Shearing Plug Catcher Pin – Pull

String

1. Running In




1. Running In


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


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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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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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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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Volume of Spacer Behind the Cement

Vsp1 = Volume of spacer ahead of the cement

Vsp2 = Vsp

1Can

x C tbg

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Volume of Spacer Behind 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


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

cf110 plugcmtg fb

Documents

depth of cement plug

plug type

cement time

quantity of cement

welltwoplug method

cw andor spacerpump

small volume of cement

drill pipepump water