# & 

# I ENGINEERING ENTERPRISES,INC.

This technical assistance document has been prepared for USEPA Headquarters located in Washington, D.C., and is funded under LOE Contract No. 68-03-3416, Work Assignment No. 2-0-21. The USEPA Work Assignment Manager is currently Mr. Jeff smith. The USEPA LOE Project Officer is Mr. Robert Smith. The objective of this work assignment is to provide EPA with
a technical document which presents and discusses proper cementing practices for the permanent plugging and abandonment of injection wells. This guidance has been prepared as part of the Mid-Course Evaluation (MCE) effort and will assist EPA Regions in the evaluation of plugging and abandonment plans and procedures,
as well as cementing practices currently being utilized by operators of Class II 

### wells.

Work Assignment Manager: Project Manager:

UIC Program Director:

President: 

## i,I**~(')I'** 

# /1;TECHNICAL ASSISTANCE DOCUMENT: CEMENTING FOR THE PLUGGING AND ABANDONMENT OF INJECTION WELLS

PREPARED FOR U.S. ENVIRONMENTAL PROTECTION AGENCY HEADQUARTERS

- WASHINGTON, D.C.

PREPARED UNDER EPA CONTRACT NO. 68-03-3416 WORK ASSIGNMENT NO. 2-0-21

PREPARED BY ENGINEERING ENTERPRISES, INC. NORMAN, OK
SEPTEMBER, 1989TABLE OF CONTENTS SECTION PAGE Acknowledgements••.•..•.•••.••.•••..•.•...•.••....... iv
1.0 INTRODUCTION••.•••.•..••••.•••..••...•.•............• 1 

## - 1 1.1 Background
..................................... . 1 

### - 1 1.2 Purpose
........................................ . 1 

### - 3 1.3 Scope
.......................................... . 1 

## - 3 2.0 INJECTION WELL PLUGGING AND ABANDONMENT••.•........•. 2 

## - 1 2.1 Environmental Concerns
......................... . 2 - 1 2.2 Basic Considerations for Plugging Job Design. '" 2 

### - 2 2.2.1 Geological Environment.
................. . 2 

### - 3 2.2.2 The Mechanical Condition of the Well
..... 2 - 3 2.2.3 Equipment Availaibility and Expense
...... 2 - 4 2.3 Important Points

- Injection Well Plugging and Abandonment.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2 - 5 3.0 EXECUTION OF THE PLUGGING OPERATION..••.............. 3 - 1 3.1 Major Plugging Activities
....................... 3 - 1 3.2 Wellbore Preparation
............................ 3 - 5 3.2.1 Inspection of Well Conditions
............ 3 - 5 3.2.2 Removal of Well Equipment
................ 3 - 7 3.2.3 Remedial Operations
...................... 3 - 11 3.2.4 Establishment of Static i'lC'll**Condition~;** .. ] - ]') 3.3 Important Points

- \':cllhore l'rcpdriltion
......... l - Ii; :.1.4 Well Plugg.ing
................................... l - 1" 3.4.1 Plug**'l'Yre!~** and Locatio!):;
................. 1 - l()

" , 1 .•j . j l' luq:,
....... .

, J . " Inport(lnt !'C,illt:;
- 1'.'('11 1'1\lqqillIJ

........... . 

# . 'TABLE OF CONTENTS PAGE TWO
4.0 SELECTION OF PLUGGING MATERIALS•••••••••••••.••.•••.• 4 - 1 4.1 The Wellbore Fluid System
....................... 4 - 1 4.2 Selection of a cement Slurry
.................... 4 - 5 4.3 Important points

- Selection of Plugging Materials.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4 - 11
S.O SELECTION OF CEMENTING PROCEDURES ..••••.•••....•..... 5 

## - 1 5.1 Cement Mixing Techniques
....................... . 5


### - 1 5.2 Cement Plug Placement Methods
.................. . 5


### - 3 5.2.1 Balance Method
.......................... . 5 

## - 3 5.2.2 Cement Retainer Method
.................. . 5 

## - 6 5.2.3 Two-PIug Method
......................... . 5 

### - 9 5.2.4 Dump-Bailer Method
....................... 5 - 11 5.2.5 Placement of Multiple Plugs
.............. 5 - 13 5.2.6 Tools and Materials to Assist in Effective Plug Placement
................. 5 - 15 5.3 Testing Cement Plugs
............................ 5 - 17 5.4 Guidelines to Ensure Cement Plug Quality
........ 5 - 18 5.5 Sample Procedure and Calculations
............... 5 - 19 5.5.1 Typical Plugging Operation
............... 5 - 19 5.5.2 Other S<1mplc Calculations
................ :> -**2~** 5.6 Important Points

- sC'}cction of Cer.lcntiny Procedures.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ') - 1(,
6.0 REFERENCES..
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 6 - 1
7 • 0 	 GLOS S1\R Y • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• 7 - 1TABLE OF CONTENTS PAGE THREE
LIST OF FIGURES FIGURE PAGE



### 3-1 Well Construction Type A - stages of Abandonment.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 - 2 3-2 Well Construction Type B - stages of Abandonment.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 - 3 3-3 Well Construction Type C - stages of Abandonment.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3 - 4 5-1 Plug Placement

- Principles of the Balance Method
......................................... 5 - 5 5-2 Plug Placement

- principles of the Cement Retainer Method........
. . . . . . . . . . . . . . . . . . . . . . .. 5 - 7 5-3 Plug Placement

- Principles of the Two-Plug Method.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 5

- 10 5-4 Plug Placement

- Principles of the Dump-Bailer Method
...................'
....... . . .. . .. . . . . . . . 5

- 12 5-5 Conventional Well Construction

- Sample Plugging Job Design
............................ 5

- 20

LIST OF TABLES TABLE PAGE



### 4-1 Common Oilfield Cement Types
................... 4 - 7 4-2 Summary of Oilwell Cementing Additives...
...... 4 - 9 4-3 Effects of Additives on the Physical Properties of Cement........................... 4 - ] 0 5-1 

### Potential ApplicaUon:-; of 

### Pluggincj**Hcthod~;** 

### ..... f) - 

### 14Acknowledgments The following persons are responsible for this technical assistance document: Engineering Enterprises, Inc. Authors: Ms. Janet Pearce Mr. J.L. Gray Work Assignment Manager: Ms. Janet Pearce Project Manager: Mr. J.L. Gray Sr. Technical Advisor: Ms. Mary Mercer Ule Program Director: Mr. Talib Syed President: Mr. John Fryberger


### u.s. Environmental Protection Agency Headquarters Work Assignment Managers: Mr. Jeff Smith Mr. Mario Salazar LOE Project Officer: Mr. Robert smith Appreciation is also extended to Ms. Kim Howland and the support staff at EEl for their many hours spent in the preparation of this report.
In addition to the above, Engineering**Enterpri~-.es ,**  Inc. would like to acknowledge industry personnel, service companies,
iJ.n d prof c s s ion i1 lor9aniz a t ion**~;** [ 0 r theire Clnt ri lJ IIt 1 0 n**~;** t 0 available technical literature, "
..bieh**Wtl~;** uti 1 11.f'ti**('xt"n~;ivcly** lrl prepdrinrJ**thi~;** CJuidance document.

iv1.0 INTRODUCTION 1.1 BACKGROUND 

### The U.S. Environmental Protection Agency (EPA) is required by the Safe Drinking Water Act (SDWA) of 1974, as amended, to implement the Underground Injection Control (UIC) program. The objective of the UIC program is to protect underground sources of drinking water (USDWs) from contamination resulting from underground injection practices. The UIC program regulates the injection activities associated with all classifications of injection wells. Since this report is part of the Mid-Course Evaluation (MCE) effort, emphasis is placed upon Class II wells, consisting of those wells which inject fluids: (1) brought to the surface during oil and gas production (Class lID, or disposal); (2) for the enhanced recovery of oil and gas (Class IIR, or recovery); and (3) for liquid hydrocarbon storage (Class IIH). However, plugging procedures described herein are applicable to all well classes. The EPA UIC plugging and abandonment (P&A) regulations for Class II wells are found in 40 CFR, Part 146.10. These regulations state that: (1) The well shall be plugged with cement in a manner which will not alIa'.·; tile movement of fl\lilL; cit**h(~**r 

### into or between**usmoJ~~;**

1 - 1

### (2) Placement of cement plugs in the wellbore shall be accomplished by the: (a) balance method; (b) dumpbailer method; (c) two-plug method; or (d) an alternative method, approved by the Director (Regional
or state), which will reliably provide a comparable level of protection to USDWs; and (3) 

### The well to be abandoned shall be in a state of static equilibrium with the mud weight equalized top to bottom, either by circulating the mud in the well at least once or by a comparable method prescribed by the Director, prior to the placement of the cement plugs.
In accordance with 40 

### CFR, Part 146.24 

### (d), prior to granting approval for the P&A of a Class II well, the Director shall consider: 

### (1) the type and number of plugs to be used; 

### (2) the placement of each plug; (3) 

### the type, grade, and quantity of cement to be used; (4) 

### the method of plug placement; and (5) 

### the procedure used to establish static equilibrium in the well to be plugged. There have been at least two reported cases which indicate the use of inadequate cementing**practice~** 

### ln the plugg

### i 119 0 

### finj 

### e c t ion wells . A 1

### thoII(J11 t 11

### e UTe n° (J II ];IU () 11 : ; c j t ('d 

### above require adequate plugcjill(J of**Clil~;~;** 11 

### inj('ctioll**v/('11~;,** the'), 

### do not :;pccify acceptable critC'rid n'q(lnlinq (,1'W'llt**tYII'-'~;,** Idue;**locatiol1~;** 

### , etc.

1 - 2

### vent interzonal communication and the migration of fluids that might infiltrate and contaminate USDWs. In order to accomplish this objective, proper cementing techniques must be used.
1.2 PURPOSE 

### The purpose of this technical document is to present and discuss proper cementing practices for the permanent plugging and abandonment of injection wells. The document will provide technical assistance to EPA Regional personnel involved in the evaluation of plugging and abandonment plans and procedures submitted by operators of Class II injection wells.
1.3 SCOPE 

### This document presents a discussion on the proper cementing practices utilized in an injection well plugging and abandonment operation. The information which is presented was obtained from professional publications, text books, and EPA technical assistance manuals pertaining to cementing practices recommended for the permanent plugging of injection wells. The following provides a summary of major topics covered in this report: (1) Considerations in Plugging Job Design; (2) Well Preparation Prior to Plugging; (3) Selection of a Plugging FJuid; 

### (4) Cement Types and Add i 

### l i**ve~~;** ( 5 ) f;c·1. pc:t ion 0 f aCement**~;** 1 u r l'
.Y ; 

### ((,) Proper CeI:lcnt Mixing Hcthod:;; <1nci

1 - )2.0 INJECTION WELL PLUGGING AND ABANDONMENT 2.1 ENVIRONMENTAL CONCERNS 

### EPA UIC regulations state that the plugging and abandonment of a Class II 

### injection well must ensure that the well is plugged with cement in a manner which will not allow the movement of fluids either into or between USDWs. In order to achieve a successful plugging operation, provisions must be made for longterm protection against the migration of formation and/or injection fluids into USDW horizons. The plugging practices and cementing methods utilized during the abandonment operation can result in significant environmental problems if not performed properly or sufficiently. The improperly plugged wellbore acts as a potential conduit for fluid movement into USDW horizons. This is clearly illustrated in the various reports of old, abandoned wells, which, according to
numerous sources, have been known to contribute to USDW contamination. Such old wells were plugged under conditions which were considered acceptable at the time of abandonment. The
cause of vertical fluid movement in these old, abandoned wells is often attributed to an increase in reservoir pressure brought about by secondary recovery operations which simply were not considered at the time of abandonment. AlthOlFJh si(Jnificant 

### a dvanc e s h

### a vc**~;**

### ince been mad(' j n p 1u9 Cj i 

### nCj i\ n

### d IIb d t1

### don 1:1c nl 

### technoloCJY, there continues to be a nc'ed fcn- (In'dtcr edn' in both pI

### uggi ng 

### job dC':;l (Jr) and 

### eXcel!lion.

2 - 1

### In order to accomplish the objectives set forth above, the abandonment process must be thoroughly planned prior to initiation of the actual field operation. Ideally, plugging and abandonment operations are designed to ensure the ultimate integrity of the wellbore to be plugged. In general, plugging for abandonment purposes is successfully accomplished through the emplacement of one or more effective cement plugs set through selected depth intervals.
2.2 BASIC CONSIDERATIONS FOR PLUGGING JOB DESIGN 

### An effective P&A plan must address all aspects of the abandonment process and incorporate a variety of factors into the plugging job design. In generating the P&A plan and procedure, consideration must be given to the: (1) geological environment of the well; (2) 

### existing mechanical conditions of the well; and (3) 

### equipment availability and expense. Each of these items will affect the plugging job design and should, therefore, be evaluated thoroughly before determining specific procedures for well preparation and subsequent plugging. As is evident by the variety of plugging procedures available, each well must be evaluated individually so that the most appropriate materials and procedures can be selected for its 

### particular circumstances. The 

### follQ'.o/ing**~;C'ctions** 

### provide (1 brief discussion of each of 

### the ahovc- con:-;iLic·ratiun::.

2 - 22.2.1 Geological Environment 

### Prior to the development of plugging job design, the well's geological environment should be known. Underground sources of drinking water and any potential producing or lost circulation
zones should be identified so that appropriate actions can be taken during the abandonment operation. 2.2.2 The Mechanical Condition of the Well 

### Careful examination of the mechanical condition of the injection well plays an important role in determining whether or not remedial actions may be necessary to ensure the effectiveness of the plugging operation. If an injection well lacks casing or cement integrity, then there already exists a potential for vertical fluid migration. such a condition must be addressed prior to attempting to place cement plugs in the well. other mechanical conditions of the well must be considered for job design purposes. For instance, there may be equipment which cannot be retrieved from the well due to damage which has occurred in the past (e.g. stuck tubing, collapsed casing, etc.). In such cases, the operator must be prepared to utilize alternate plugging methods which will assure adequate protection to USDWs.

2 - 32.2.3 Equipment Availability and Expense 

### Decisions made during the development of an abandonment plan
are generally made with regard to expense and availability of equipment. In many cases, decisions concerning a particular aspect of the abandonment process involve a choice between various materials and/or methods used to accomplish the same basic objectives. An evaluation for each individual situation should be performed to weigh the costs of using specific materials and/or methods against the relative benefits each might offer to the overall plugging operation. Equipment availability is certainly another factor which must be considered when planning a well's abandonment. Prior to specifying a plugging procedure, the operator must be sure that any necessary workover equipment is readily available to fulfill the requirements set forth in the P&A plan.

2 - 42.3 IMPORTANT POINTS INJECTION WELL PLUGGING AND ABANDONMENT
1. ENVIRONMENTAL CONCERNS


### o Prohibit movement into or between USDWs o Unplugged or improperly plugged wellbore is potential migration conduit o Documented cases of USDW contamination via abandoned wells o Successful abandonment 

### = one or more cement plugs through selected intervals o Operational concerns also
2. BASIC CONSIDERATIONS FOR PLUGGING JOB DESIGN


### o Define Geology USDWs Potential producing zones Lost circulation zones o Ascertain Mechanical Condition of Well Casing integrity Cement integrity Junk in hole Stuck tubing Collapsed casing Remedial action necessary?
o Equipment Availability and Expense Workover rig Access to location Fishing tools Cutting and milling tools Service companies Wellbore fluids

2 - 53.0 EXECUTION OF THE PLUGGING OPERATION 3.1 MAJOR PLUGGING ACTIVITIES Plugging for abandonment consists of two major phases: (1) well preparation; and (2) well plugging. Well preparation, as the term implies, consists of those activities necessary to prepare the wellbore for effective plug placement and final abandonment. Such activities may include: 

### (1) inspection of
we 11 cond i t ions ; ( 2) r em0 val 0 f tubi ng, pack er, and/ 0 r salvageable casings; (3) remedial operations such as fishing, milling, squeeze cementing, or plug-back operations; and (4) establishment of static equilibrium. Well plugging consists of those activities associated with the placement of cement and/or mechanical plugs at designated positions within the wellbore. Although there are several cement plug placement methods available, the most common methods involve pumping the cement slurry through a string of drill pipe or tUbing. The plugging job design and abandonment procedures which may be selected for an individual injection well are dependent upon the construction characteristics of that well immediately prior to abandonment. Several common injection well construction typos
are presented in Figures 3-1 through 3-3. Tn order to illu:;trdte the**~~tagos** involved in plurJgir1CJ one! clhdndonmcnt 0pc'r;ltion:;, ('ddl well**con~;tructiCln** type**i~~** depicted in it:;**:~t<ltC'** priur­ tu ',,',-,11 prepd ration, aft('r we 11 Tn-c P**~l**r (It ion, <Illd .I

### rt L'r we 1 1 P1 tlq q i n q d n d j ina 1 abandonw·nt.

3 - 1

### Cement Plug

, 

### . ... , L:.

### USDW Base : Bas'e :',.

Plug. Fluid Plug. Fluid Open Hole
., "".

# .....

... • to • ., 

# .. ..

# ".

...

# ...**~..** 

## .." ..

Plug. Fluid Stub of 

### Cut-off Casing
Bridge Plug Capped with cement

. \ 

### cement '-:-:-:­**~** ... , 

### .'

. 

### WELL PREPARATION AFTER PLUGGING AND ABANDONMENT
•



### • •



## ..

.. 

# .

••• Cement Plug 

### Potential Producing 

### Zone Cement Plug
Bridge Plug

Capped with : -:-:-:-

•.., Injection**Zo·n~** 

### . H**~b ~**  

### ;Iljection Zone ;**~~** c:**~erfora**tions :::: 

### • rr::

### ~ w 

### --_.... ---:-ota1 Depth t-' • 4
.. 

### P1ug. F1uid



# ........ .. 

## :

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### " 

# . .. 

# . .. ,/'

# ......**3~=JRE** 

### WELL PREPARATION AFTER



# . 

# · , • 

# ·. t..:.r.s- Primary Cement 

# · ••



## ..**~.** •

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# ·

. . . '... "**~** .... , ,', 

# .• 

### • L·.·.USDW Base:.:·.·:
.. ·:·.·:·.·· 

# · ­

_.Surface Casing**~-+---Inject;on** 

### Tubing**~--** 

### Long String Casing Borehole**~** I­**~**•**~** - Primary Cement
-,.

### ~ . 1-:If----..**~ ~~njection**  

### Packer i"**----~. ---------------------~----** 

I WELL CONSTRUCTION TYPE A STAGES OF ABANDONMENT-------- 

### 3EFORE WELL PREPARATION AFTER WELL PREPARATION AFTER PLUGGING AND ABANDONMENT

..t" 

### • 9' • • r.. 01 

### Primary Cement 

## " 91: 

# ....
.. •

### 0,.. 

### "USDW Base"', 

# '. USDW Base:"': -"-" 

## . . "

## .. Surface Casing •

a 

### • 

### Plug. Fluid 

### ,L',**~**



### .. • A 

### Primary Cement 1.01

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# .. • 

### Intermediate Casing Cement Plug Injection Tubing _ong String Casing Stub of Cut-off :3orehole Casing**~rimary** 

### Cement

...., H 

### Injection Packer**~** C**.I--------------~--------~--------~----** :n**~** 

### :njection Zone w 

## , Perforat

### ions**~.J ~otal**  

### Depth 

### ..**~·I.** <II**~** , • 

### •**.~~ f~Cement**  

### Plug

1- . •

# _~. 

# {A+**L~' U'S~W** ;-sase '.:':" Cement Plug .r­ • '-;" 

### Plug. Fluid

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### uid


### Cement Plug

" 

### Injection Zone**w~LL** CONSTRUCTION TYPE B STAGES OF ABANDONMENT

### • • 

### ry Cement

- .**~J** 

### Base.:'
..'. e Casing

tion Tubing 

# .. ..**~** 

## .. ..
.. •



## .. 

# .. ..•


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### ,·.L. USDW**Base~** 

# ..1-'---------­**~** ..

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.. 

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### Plug. Fluid 

## -s- Open Hole 

## .. • .,. 6
.. • 

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# ... .. •



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. 

## .. \0
.. 

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### :.:.. ,..... •...L. 

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### ".



# .. ...... ..-

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### :rject'ion Zone Onen Hole AFTER WELL PREPARATION AFTER PLUGGING AND ABANDONMENT

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..... 

# .

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1-
....... ..**~** a A ..... : •• " 

### Cement Plug f 

# .....**,"'--~­**

CI WELL CONSTRUCTION TYPE C STAGES OF ABANDONMENT



## ­3.2 WELLBORE PREPARATION 

### In any plugging operation, care must be exercised in preparing the wellbore for cementing to ensure that effective cement plugs result. Wellbore preparation not only involves activities necessary to ensure a proper environment for setting plugs, but also includes those activities associated with the basic integrity of the well. These activities are essential to achieving an abandonment that will provide long-term prevention of fluid migration into USDWs. As stated earlier, wellbore preparation activities include: (1) inspection of well conditions; (2) removal of downhole equipment; (3) remedial operations; and (4) establishment of static well conditions. Inherent to wellbore preparation activities is the selection of appropriate plugging fluids (Refer to section 4.0).
3.2.1 Inspection of Well Conditions 

### The first step in the abandonment process entails an investigation of available records in an effort to determine the construction characteristics of the well, and to become familiar with local geology. Knowledge of well construction and geological environment is essential to the abandonment design process. Cons t r u c t ion det 

### ail s w h .1 c:

### h**~1** \l**~;** +- 

### b c' 

### con**~~** i cl C'

### r ('d d \l TO i 

### n q wellbore preparation include:

3 -**~**

### (4) perforations or open-hole sections of the well; and (5) any other mechanical equipment (or cement) that may be present in the well prior to abandonment (e.g. packers, cement plugs, etc.). Much of the required well construction data can be derived from permit applications, well completion reports, workover records, and operating and monitoring reports. Additional consideration must be given to constructionrelated factors that might influence the plugging procedure or long-term integrity of the abandoned well (e.g. casing leaks, corroded or collapsed sections of casing, and cement channeling). such potential deficiencies in mechanical integrity may be discovered through a simple review of well records or through conventional mechanical integrity testing methods. The standard annular pressure test can be used to determine the existence of casing leaks, while a temperature survey, casing inspection log, or caliper log can be used to identify the location and extent of such leaks. Annular cement quality can be examined by using a radioactive tracer survey, cement evaluation log, or noise log. The use of specific investigation methods will depend largely on the anticipated condition of the individual well to be 

### plugged. Decisions re(Jilrdinq the need to perform sue11**con~;** 

### t r u

### c t i 011- r 

### e 1

### atedinv c:;t i CJ ;\t**ion~; ~;** 11 0 II 1 cI b C' r.l ,Id c' 

### accorclin(Jly.

3 - 6

### Sufficient information concerning site-specific geological conditions must also be obtained to determine the location and characteristics of USDWs, as well as the formations separating them. Examination of the geological characteristics and pressures encountered in the injection zone and overlying formations also plays an important role in the well preparation process. Such geologic information provides much of the basis for determining: 

### (1) plug type, location, and height; 

### (2) cement slurry and wellbore fluid system design; and (3) 

### casing removal programs. The identification of corrosive zones and injection fluid/formation fluid constituents is also an important part of the planning process, particularly in regard to determination of
an appropriate cement slurry. Geological and hydrogeological data can generally be derived from well records, geophysical well logs, or geologic studies. 3.2.2 Removal of Well Equipment The removal of well equipment is a preliminary step that will influence the overall plugging and abandonment operation. Before removing any equipment from the well, it is necessary to evaluate the impact that such action might have on the effectiveness of abandonment procedures. Injection tubing is almost always removed frum the well prior to plugging. Tubinq serve:-; no practical**p\lr-po:~C'** 

### ,-t1tC'r a b<i ndun n c nt and Cd ni n h i b j t 

### down h0 

### 1 C' ilCt i

### v i t i (':**~** _ in dddit i()n, injC'ction 

### tubing Cdn 

### often**time~~** 

### bC'**~;alvd(J(·d** (I!lei r(·t,\ in('d tor future rcu:;('.

3 - 7

### Associated with the decision to remove injection tubing is the decision regarding whether or not the injection packer should be removed. Many injection packers are readily retrievable, while others are considered permanent installations. Retrievable packers can generally be reused (after minor repairs are made)
. The recovery of a permanent packer, however, is usually not attempted due to the expense of the operation. Permanent packers must be drilled up with a milling tool. The removal of tubing and packer involves setting up a workover rig, unsetting the injection packer, and pulling the injection string out of the hole. Depending on the specific steps outlined in the P&A plan, it is not uncommon to utilize this preliminary step as an opportunity to establish the wellbore plugging fluid system. For instance, operators may unset the injection packer and circulate a clean plugging fluid throughout the wellbore prior to removal of the injection tubing/packer configuration. This operation aids in cleaning the well and, in
some instances, can save the operator time and expense. Selection of an appropriate workover rig is generillly dictated by lifting requirements. Deeper wells which contain
more pipe and consequently, more weight, will usually requIre larger rigs that are capable of ::;;upporting the additioII,tl 

### v,rc·ic;ht. The' 

### mdjol-ity of all v:orkuv(:r**ri(r~~** are equippL'd 

### to: (1) pull tll(' 

### tubinq (or casing) strinq; (?) 

### rotdtc' pipe 

### whi]I' in tllf' Ilu1,'; (\)
stand 

### pipe i nth

### e dC'

### rrick; and**(.~)** 

### c i n:: IIl.1t f' !]

### u i

### d (::) t 

### h r() lj(J

### h()\lt t h f' ',.,',. 1 I b()r C' (Pct r 0 1 ('\l !:l Fxt ('ll:', i "11**~** : ( .r v i ( .(. I 1 'j " ,j)

. II, ,'.': I ' '.,: j ':, I r \

3 - 8

### some oil-producing areas with relatively shallow reservoirs (e.g. Illinois, western Kentucky, Ohio and portions of the Appalachian Basins), cable tool rigs are utilized to perform workover and plugging operations. In order to be able to rotate pipe and circulate fluids, these rigs must be specifically equipped with auxiliary equipment such as hydraulically-operated power swivels and duplex or triplex mud pumps. If tubing and/or packer cannot be successfully removed from the well, the unstuck portion of the tubing string can be severed above the packer and removed. Should the operator desire to remove the portion of tubing and the packer remaining in the hole, each can be drilled up with a mill, and the debris circulated out of the hole. In such instances, however, the operator may be able to satisfy regulatory P&A requirements by setting a mechanical and/or cement plug above the severed tubing string. The removal of screens or liners set across the injection interval may be required in some areas. Although salvaged
screens and/or liners are generally of little economic value,
some state regulatory agencies may prefer their removal to enhance plug placement across the injection zono. 

### Another decision th':"it**mu~:t** 

### be made concern:; the rcmOVd I 01**ca~~!!le;** 

### trom the well. It**i~-;** nc)t UnCOn1I110r1 tC) t ind int('rmt'dirtt(· 

### and/or- long**~~tring** C.:1SlI)qs 

### which tIrE' only pclrti,llly cC'I!1ent.-d 

### in p].:1CC· (i.e. C('p.1Pnt**cl(J('~;** not ('xtf'nd t.o :;\l1'1.1c(-)_

3 - 9

### it is desirable to attempt to cut and salvage the uncemented portion of the casing string. This decision, however, should be made only after careful consideration of a well's individual circumstances and the potential outcome of the casing recovery attempt. Uncemented casings which remain in the well after abandonment may result in future problems. This cannot be 

### over emphasized! 

### By allowing the annulus around the casing to remain uncemented, there exists a conduit through which vertical fluid migration into USDWs can occur. In these cases, fluids could escape through a poor primary cement column or could migrate from pressurized formations exposed in the casing annulus. In order to avoid such a risk, the operator may be required to squeeze cement behind portions of uncemented casings which are to remain in the wellbore. Individual circumstances such as fluid gradients, local geology, etc. will dictate whether or not this is necessary to prevent vertical fluid migration. The removal of uncemented portions of a well's casing may affect the plugging procedures used during abandonment. For instance, the removal of casing will result in the exposure of open hole sections within the well. The existence of any low or high pressure zones Clln affect**sub~;equcnt (lttcI~1pt~;**  

### to**e~;ti1bl** 

### ish static well**condition~;** 

### prior to :;C'tting Cf'r:,'nt pltlCJ!;.

3 - 10

### Uncemented portions of casing strings can be removed prior to pIug-sett ing acti vitie s, depending on the specific circumstances of the injection well undergoing abandonment. However, difficulties may arise when running plug-setting tools into the open hole and then back into the lower portion of the casing string left in the well. Many operators and/or regulators prefer that required plugs be set inside the lower portion of casing prior to cutting and pulling the upper portion. Before casings can be cut and retrieved, a free-point indicator tool is run inside the casing to determine its free point (i.e. where it can be severed). Tools used in casing cutting operations consist of high pressure fluid jet, chemical, mechanical, or explosive cutting devices. Selection of the most appropriate cutting tool will be influenced by casing characteristics, mechanical condition, and internal/external accessibility. 3.2.3 Remedial Operations Prior to plugging a well, a variety of remedial operations may be required to successfully gain access to the intervals which are to be plugged. Remedial**operation~** 

### associated with plugging and abandonment may include: (1) well cleanout**activitie~;** 

### such as "fishin(j" or milling; (2)**ca~:;inCJ** 

### repair
....'or}: such as**~;queeze** 

### cementing; or (1) p1l1q-biWk ofJC'rdt ion:;.

3 - 11Well Cleanout Activities 

### During the abandonment of an injection well, it may be necessary to remove obstructions from the wellbore in order to effectively emplace mechanical or cement plugs. Such obstructions can consist of materials ranging from small particles (e.g. sand) to large objects (e.g. packers or tubulars which have been dropped or stuck) Small particles, such as sand, formation cuttings, etc. can generally be removed through circulation of a workover fluid. Produced saltwater or bentonite muds (gels) are the most commonly used workover fluids. Any small objects such as metal pins, tools, or cuttings can be retrieved through the use of a junk basket retriever. A typical junk basket retriever is a circulation device which is able to catch small pieces inside its cylindrical barrel. Another tool which can be used to retrieve small metallic objects is a "fishing" magnet. For large objects such as packers, tubing, etc. which may be stuck in the well, a variety of retrieval methods may be used. If the top of the pipe is free and is burred or split, a milling device can be used to smooth the top of the pipe. Once the top of the pipe is smoothed, an overshot too] Ciln be lowered over the pipe and tha.n rota.ted to ca.use the tapered**in~;**

### ide of the too1 to engage the pipe ( G c r Ll

### g ht 

### Y and Hill C 1-, J

### n c ., ) C)8 ;:» •

3 - 12Recovery of pipe can also be accomplished by using a spear, which is a tapered tool that is lowered inside the pipe. Once the spear is positioned within the pipe string, several mechanical wedges are released or the tool housing is expanded to engage the pipe for removal. Although fishing techniques are often successful in removing debris, an alternative method of equipment removal consists of milling and/or drilling. Casing Repair A second type of remedial operation that may be performed prior to the abandonment of an injection well is casing repair work. Repair of a damaged casing string is sometimes necessary as a means of access to a zone to be plugged. If the lower part of the hole cannot be reached due to collapsed or buckled casing,
a casing roller or swaging tool can be used to open up the tight place in the casing. Another type of casing repair involves cutting and pulling undamaged casing. Once casing has been cut off, it is useful to grind down or bevel the severed edge to avoid any problems that may occur during plug-setting operations. The most common type of casing repalr is squeeze cementing, which involves the placement of cement slurry**acro~;~;** a perforated
or 1eaking section of casing. Hyclr,Hll ic**prC':~:;u**rc**j~;** then app1 j eel to force**t,hc~ ~';lllr-ry** **again~;t** and into C'xr0:,ccl forni1tion:;.**l\~',** m('11t i 011cdC' d r 1 i c'r, ;.q\le ez c cc';n('ntillq r.ld y d 1**~",** 0 b t.' J,'e 1"":1L'd Tl ('l"('**~** ; : ; d r"y for uncer.lcntc-d**pUl:lion~;** of Cd:;lllq ,,;hicll <In' to n'n,lill ill til., ','H'11

3 - 13

### after abandonment. In these instances, circulation squeeze cementing may be used to ensure that all of the annular void space is filled. Circulation squeeze cementing entails circulation of the cement slurry in the casing annulus in an attempt to extend the cement height behind the casing. It is accomplished in one of two ways. The first method involves pumping cement into one set of perforations placed at the base of the proposed cement column. The cement is pumped under carefully monitored pressure conditions to prevent the hydraulic fracturing of formations exposed in the casing annulus (the calculated treating pressure at the perforations must not exceed the calculated hydraulic fracturing pressure for that particular depth). The second method involves two sets of perforations, one placed at the base of the proposed cement column and one placed at the top. This creates a permeable, low pressure channel through which the pumped cement can flow, thus, forming the desired annular cement column. Plug-back 

### operations Plug-back operations essentially involve plugging back lOiver
zones from the upper portion of the well. In abandonment oper(ltions, this generally consist.:-; of settir1CJ (l mcchanicill bridge plug (lbove the injection zone (or other interval) c·;.:po:;(·d \.;ithin**ttl(~** lc)r1(]**~~tring** casing.

3 - 14A number of plug-back operations are performed during the life of the well some time prior to plugging, thereby eliminating the need to perform such an operation during the well's abandonment. Although it is feasible to plug back lower zones in
a well during the actual plugging process, it is usually more convenient to plug them back during well preparation. For instance, in cases where upper portions of long string casing are to be removed from the well during plugging, it is usually easier to set any injection zone plugs prior to casing removal. This technique may also enhance subsequent attempts to establish static equilibrium in the well. 3.2.4 Establishment of static Well Conditions Once well conditions have been assessed, necessary equipment
removaland remedi a I operat ions are performed. Upon accomplishing these tasks, the well is ready for the final phase of well preparation. During this phase, fluids in the borehole should be brought to a static condition to ensure that fluid movement does not occur during the cement plug placement and setting processes. Any fluid movement in the wellbore during cement slurry placement and setting Cilll result in contamination and/or migration of the cement slurry. Stati c we11 cond i t ions arc c;;t a h 1**i:~**h**(~d** bye 0 nt r 0 11i!lCJ any flow, either into or out of the well. h'hC'11 a v.'c II**i~; CCJI~lP**  1etc-jy

" , r',
..... +-**~-** ,-. 1 \,..**~j** J I '" ,**~** J L tho i n j c'c t 1 0 n Z ()Il(', pr('!:;sure. In !:uch**in~;tance!;,** injectlon zone**pr('~;;'.llrr'** ,Ind rc!;ultdnt flo',·,' t'-tll be' cCJl1troljr'rl thr'()\lqll: ( 1) c i 1't'\l I .It i () 11 ()I d

3 -**1~**

### weighted plugging fluid; or (2) placement of a mechanical plug just above the pressurized interval.
In situations where casing has been removed from the well, fluid flow into and/or out of the well may result from formations exposed in the uncased portions of the hole. static equilibrium, in these cases, can generally be accomplished through the use of
a plugging fluid: 

### (1) which has been specially weighted to
overcome excessive formation pressures; or (2) 

### which contains special materials designed to prevent lost circulation to low pressure formations. Establishment of static well conditions is most readily accomplished through circulation of a new fluid system. The new fluid system will act not only to establish hydrostatic equilibrium in the borehole, but will also serve as the fluid remaining between cement plugs. The main purpose of circulating the hole with a fresh fluid system is to ensure that the wellbore is in a static state. It is particularly important when setting cement plugs by the balance method. By filling the wellbore with a fluid of known and uniform density, the operator should be able to observe any changes in fluid weiCJht caused by potential flm; 

### in the wcllbore. The sec 0 nd pII

### rp0**~~**C 0 

### fanc W 1.-1c'1 ] b()no' fluidsy**~ ~** t C [:1 P('r t itin:; tC) ttlC conclit ion C)t ltlC [JOrell0J C \'Jd 1**l~:** dnd tIlt: dli i 1it ''/ ()1 t htl (:er.1cnt 

### to bond tot

### he ho1 c' 

### and sc·t 

### up pn>I'('r

### 1y. For ill:-.tdllC"f·, In 

### r()tdry-drilled \0,'1"']]::, 

### old drillirvJ [:11;<1 r"n"in:: b"hind tll;'-"::;"llt,-,j

3 - 16

### casings and mudcake may have formed on borehole walls. After casing is pulled, the open hole must be prepared to maximize cement bonding to the formation. This can be accomplished most efficiently by recirculating a fluid which is similar to the drilling fluid in weight and consistency. Additionally, chemicals may be introduced and/or wellbore scratchers (attached to the workover string) may be utilized for mudcake removal. If the wellbore is already in a static state, it is not always necessary to clean the entire borehole prior to cementing. Naturally, the most important portions of the hole are those
across which cement is to be emplaced. Many operators may choose to pump a "spacer" fluid ahead of each cement plug. This fluid acts to ensure that the borehole walls are clean and that the cement slurry is preceded by a fluid which is compatible with its constituents (e.g. will not contaminate it). section 4.0 provides a more detailed discussion of plugging fluids.

3 - 173.3 IMPORTANT POINTS WELLBORE PREPARATION
1. INSPECTION OF WELL CONDITIONS


### o Well records/files o Size, grade, depth of tubulars o Primary cementing program o condition of cement and tubulars o Perforations/open-hole o Downhole equipment o Formation pressure 2. REMOVAL OF WELL EQUIPMENT


### o First step o Requires workover rig o Tubing almost always removed o Some packers not retrievable o cutting uncemented casing Jet Chemical Mechanical Explosive
o Pulling casing o Fishing
3. REMEDIAL OPERATIONS


### o Well cleanout o Casing repair o Plug-back operations
4. ESTABLISHMENT OF STATIC WELL CONDITIONS
o Prevents cement**contamjn~tion** 

### o Proper fluid 

### weight (well control) o CirculZ1tc (It 

### least one .....ellborc VOlUr:ll'

3 - 183.4 WELL PLUGGING 3.4.1 Plug Types and Location 

### The plugs used in the plugging and abandonment operation include mechanical and/or cement plugs. Both are designed to isolate zones for the purpose of preventing: (1) USDW crossflow; (2) 

### surficial flow; (3) 

### contamination of USDWs by oil, gas, or brines; and (4) 

### contamination or disturbance of other formations having potential value. Mechanical plugs generally consist of permanent or retrievable bridge plugs. When used in abandonment operations, they are frequently placed in casing, either: (1) just above the 

### injection zone; or (2) 

### above any well equipment which is not retrievable (e.g. stuck tubing and/or packer). Mechanical plugs set above the injection zone (or other pressurized zone) can provide assurance that there will be no upward fluid movement from the zone. As a safety measure, 50 

### to 100 

### feet of cement should be placed on top of the plug. Although mechanical plugs are commonly used to isolate a pressurized injection zone, cement plugs are the major constituents of an abandoned wellbore. The number and length of cement plugs will vary with the well depth, number of producing formCltions encountered, and the amount of cd:;inq 

### left in 

### the hole. cement plugs Clre often placed: ( 1) ,1h 0 v (". t h C' 1 0**',~'**C'**n~1O:;**t 

### prod II Ct 

### ion and/ 0 rillj C'

### ct 1 0 

### n Z 0 

### n e ; (?) d 

### h()'/ c', 

### h(. 1 (J ',,', d !l

### d / () r

3 - 19through each producing formation and each fresh water strata; (3) at the bottom of intermediate and surface casings; (4) across any casing stubs (pulled casing sections); and (5) at the surface. In relationship to the UIe program, critical containment points that should be isolated are the injection zone, the USDW base, and any point above the USDW base where water quality varies significantly.
A series of plugs separated by an adequate wellbore fluid is generally considered to be adequate protection. Most experts agree that placement of a continuous column of cement from the top to bottom of the well is not necessary to ensure the prevention of fluid migration. In most cases, any benefits that may be derived from the solid cement plug are not justified by the additional expense. However, there are situations where a continuous column of cement would be more economical than a series of plug. For instance, it is sometimes more economical to set a continuous column of cement in a shallow well rather than setting numerous plugs. The rig time and labor expenses incurred
as a result of waiting for each cement plug to set up, etc. can be considerably higher than the expense incurred by the additional cement volume. \\Then selecting the number and ICl1qth of cement pl**ug~;,** the most important point to n·mer.1bcr is th<lt Ul(" p1uq:: li1u:;t be pI dced In i1 m(lnner that \'/111**c:r1~~tlre** tt1(it tllc't-(-**l~',** !1C)**(liI«,(~t** COr.1munication between pe!TH'dble, prodllcinrJ 1<)n:1dt ion:: and l::;lll';

3 - 20

### length of cement plugs vary somewhat among states. Although required cement plugs may range from 25 to 200 feet in length, a 50-foot plug is considered to be a minimum in most cases. 3.4.2 placement and setting of Cement Plugs 

### The design and placement of the cement slurry is one of the most important components of the plugging and abandonment operation. As will be discussed further in section 5.0, the placement of an effective cement plug requires careful planning and considerable skill. caution must be used not only in designing the cement slurry itself, but in placing the cement slurry without contamination. During the selection of a cement slurry, consideration must be given to borehole conditions such as temperature, pressure, potential lost circulation zones, and fluid compatibility. The cement slurry should be designed so that it can withstand longterm exposure to downhole conditions. Plugging fluids left between plugs should also exhibit stability over indefinite periods of time. Some drilling fluids, brines, formation fluids, and injection fluids cun act to inhibit the setting properties of cement. Therefore, cuution must be exercised in plucing the cement slurry without contamination of the cement. The potential for cc·ment contamination C,1l1 

### be minimized by: (1)**f'~~tilbli!;hinCJ** 

### and rna i 

### nt a i n

### i n

### g stati c ,",' (>lIe0 

### nd

### i t ion S Flrio't' t U d n d d

### uri IHj p 1 UCJ

r; 1 u r r y and b 0 r c h

### ole f 1II i d!;; 

### and (3) c 1c'd n i rt(J C d**~:i** IlCJ d n d / () r bun-110I(·**!;ur'face~;** 

### pried' t () pluq 

### plac('·mc·nt.

3 - 213.4.3 Testing of Cement Plugs 

### Testing of cement plugs is performed by 

### "tagging," which consists of running pipe into the hole to locate the plug. After the cement has set up, the pipe is run into the hole to the plug depth and weight is applied to check the position of the plug. Cement plug tagging is discussed further in Section 5.0.

3 - 223.5 IMPORTANT POINTS WELL PLUGGING
1. PLUG TYPES AND LOCATIONS
o Mechanical Plugs Just above injection zone Above unretrievable equipment Bridge plugs Sand or cement on top
o Cement Plugs Above lowermost production or injection zone Through each fresh water strata Across casing stubs At the surface
2. PLACEMENT AND SETTING OF CEMENT PLUGS
o Requires careful planning o Contamination should be avoided o Most effective if: static equilibrium established Spacer fluid utilized Surfaces of casing and borehole clean before placement
o Allow adequate time to set 3. TESTING CEMENT PLUGS
o No simple method o Wait on cement (WOC) 8 to 24 hours o "Tagging the plug" o Testing recommended for: Plugs critical to pressure control or USDW protection Questionablr' pluqr;

3 - 234.0 SELECTION OF PLUGGING MATERIALS 

### Design of the plugging and abandonment operation entails selection of both materials and procedures, such as (1) the wellbore fluid system; (2) cement slurry type; (3) cement mixing, placement, and testing methods; and (4) precautions which should be taken to ensure the effectiveness of cement plugs. The proper selection and use of each of these components is essential to obtaining a satisfactory plugging job. This section will describe criteria for the selection, of basic plugging materials, while Section 5.0 will provide a discussion of available cementing procedures. The two basic materials used in the plugging and abandonment operation are: (1) the wellbore fluid (sometimes referred to as plugging fluid); and (2) the cement slurry used for the plug(s). Proper selection and use of each of these materials is essential in obtaining a satisfactory plugging job. 4.1 THE WELLBORE FLUID SYSTEM 

### The final phase of well preparation consists of the establishment of static well conditions. This is generally accomplished by circulation of a uniform fluid system throughout the wellbore. Of primary importance is the selection and establishment of this fluid system, which will not only provide the necessary environr,H'l1t for**suc,cc·~'.~-~ful C('I~lcnt**  

### pluq placement Clnd setting, but will**ClI~;o ~;crve**  d:; d**:~L!hilizin(j** 

### rnatori 

### a 1 

### between cement pI**U(J:~** .

.. - 1The wellbore fluid system used in the plugging operation should be one which exhibits the following characteristics: (1) sufficient hydrostatic head or weight to prevent any fluid flow into the borehole; (2) ability of the fluid to remain in place
over an indefinite period of time; and (3) chemical and physical stability of the material for an unlimited period of time (Gillespie, et aI, 1973). Sufficient hydrostatic head is required to establish and maintain pressure control and prevent fluid movement during plug placement and setting processes. The ability of the fluid to remain stable and in place over an indefinite period of time is essential to both the success of the plug setting process and post-abandonment integrity of the wellbore. As part of the abandonment planning process, it is important to realize that, in many cases, existing drilling fluids, wellbore fluids, and/or workover fluids are not necessarily designed to meet the above requirements. Therefore, a more suitable fluid system may need to be emplaced in the well prior to cement plug placement. The use of a fresh fluid system will enable the operator to select the necessary constituents of the fluid, enhancing its effectiveness in the plugging**opcr~tion.** In**C<1!~C!;** where open-hole**~;l'ction!;** of the well are expo!;c'U durinCJ the p 1uCJ CJi n 9 proces S, 0 1cl d r ill i n 9 mud m d y b.' ( .Il( .0l1l1t c'rcod . Many c11C [:1 i Cd1**~** usedin d r i 11 i 11(J m lllb (\reor gall ie, d IId d**~;** :**~.**ud I , can be v(' !'Y det riment {\ 1 toth(' :'.('t tinCJ propert i '-':: U f ,\ r C' 1:\('nt slurry.

.. - 2filtration controls and those that have thinners. Unless compensation is made for these mud types, the resultant retardation of the setting properties of the cement could cause a faulty plug. Wellbore fluids and workover fluids found within the typical injection well may also contain constituents that would threaten the effectiveness of the cement slurry.
A recommended fluid for plugging and abandonment purposes would include the following materials: (1) Water, fresh 

### or brine. (2) Bentonite (gel or clay)
. (3) Attapulgite (a type of clay which acts as an extender)
. (4) Lost circulation material (as needed)
. Open-hole, plug-back studies show that the preferred fluid system has a Marsh funnel viscosity of 45 to 80 seconds, a plastic viscosity of 12 to 20 cp, a yield point of less than 5 lbs/100 square feet, and a water loss of less than 15cc (Herndon, et aI, 1976). Detailed hole preparation will depend largely on the plugging job design. In**almo~;t** all cases, hO'.'Jovc'r, a gelled water as described above should prove to be ,an adcqucltc plu(Jqinq fluid.**A~;** mentioned earlier, the ir.1portant tllinq i:; thilt ttl" well be filled with a fluid of uniform weight (p,l!"t il'uLlt-ly important whon u!'"";ing the balanct'**r:~('thod** of pluq pld('(·::i(·nt). Once

4 - 3

### the borehole has been flushed and filled with a suitable fluid system, the operator can observe the fluid level and by doing so, note any fluid movement that may be occurring.
In fully cased wells where pressure control does not appear to be a problem, a specially prepared plugging fluid may not be considered a necessity. In these cases, pressure control may be provided by a simple water or brine solution. In fully cased wells where injection zone pressure is excessive, a weighted plugging fluid may be used for pressure control or the injection
zone can be plugged back through the use of a mechanical plug. If a mechanical bridge plug is selected to seal off injection


### zone pressures, then a simple, low density fluid would be sufficient to maintain the static equilibrium of the well. Establishing an effective plugging environment requires the emplacement of a fluid system which is able to meet the needs of the specific situation. This generally requires that existing wellbore fluids be replaced with the fresh fluid system. This fluid is mixed and circulated into the well using a string of tubing or drill pipe. At least one full circulation is required; several complete circulations arc usually recommended to ensure uniformity of the new fluid**sy~tem.** 

### After circulation**ha~;** 

### been completed, the
....'ell is allowed to !;tdbilize and**i~; ob~;erved**  

### to evalui1tc whether or not static \·;el1**condition~:.** 

### ('xi:;t. 11 the 

### flui d 1coV l'

### 1 i nthco well chan9(': ; Itt 11'

### n Ll

### tic e q u.i 1i 

### bci II**;~1** 

### h<t :-. 

### n()t

4 - 4been obtained and the plugging fluid should be altered and recirculated. After a static well condition has been achieved, cement plug placement activities can be initiated. 4.2 SELECTION OF A CEMENT SLURRY The cement slurry used to plug and abandon a wellbore must be designed so that: (1) it provides sealing to prevent fluid movement between intervals; (2) it possesses good bonding characteristics to the pipe or formation; (3) it demonstrates durability; and (4) a long life may be expected. These conditions can generally be met using a densified cement such as API Classes A, C, G, and H, with a dispersant. These classes of cements are most acceptable due to the following reasons (Herndon, et aI, 1976): 

### (1) They are less subjected to mud contamination and resultant loss of strength; (2) They set and gain strength more rapidly, thus reducing time spent waiting for cement to set; (3) With dispersant added, such slurries control water loss and minimize dehydration of the cement slurry which can result in premature cement setting or fluid movement in the borehole; and (4 ) 	 T11e y can yi e 1dimprov('d bu 11dinq charaet (. t- i**~,;**tic**~;** and minimize damage to :-;lld]t,:; or bC'ntonite.**~;i\IlCl~;** by tilt, addition of salt.

4 - 5Class H cement is used predominantly in Gulf Coast and Midcontinent operations, while Class G cement is used among the West Coast and Rocky Mountain areas. Regarding appropriate cement types for plugging, the following recommendations are made (Herndon, et aI, 1976): 

### (1) For geographical areas which do not contain corrosive waters, a moderate sulfate resistant cement (API Class G or H) would be recommended. (2) In geographical areas where high sulfate or acid waters
are present, a special high sulfate resistant (SR) Class C cement could be used, or 50% pozzolan could be added to either Class C or H cements to provide high resistance to leaching. (3) A dispersant should be used to lower the water content requirement in order to provide better strength and durability. The selection of a cement composition is a function of well depth, temperature, and mud properties. Any special conditions in the well (e.g. lost circulation zones that will drain wellbore fluids or high temperutures that wi 11 f 1**a~:;h** set cement) mllSt be
considered wlwn**dc~:;**igning the c('mCI1 t !;1ul'ry. Tabl e:-; 4 -1 ilnd 4 -:2 provide a summary and description of**~omc** of the**mo~t** connonly used oilfield CC'I:H'nt types and ddditiVt,!; that can count('rdct spe cialeo n d itions s u c h u:; I 0:;t c ireula t ion <Illd h i q h t l'mp<' r ;.1t 1I n.':;
.

4 - 6TABLE 4-1 COMMON OILFIELD CEMENT TYPES1

'IYPIOJ..C»'»r.'S: static Midng Slurry Slurry API AS'I)4 Well Depth Te!perature water Weight**Y~eld** r:.LM"-sificatlrn '!'fpe (ft,) tOp) (gal.lr:J<.) (lb./qal.l (ft. /r:J<.1

{", 'Ccr::-cn**Po~t:a.~)** ! 

### o - 6,000 80

- 170 5.2 15,6 1.18 Frequently used when speCial properties are not required; More econanical than premium cements. !' fCcrron Pcrtlare) II 

### o - 6,000 80

- 170 5.2 15.6 1.18 Used \\hen well conditioos require moderate to high sulfate resistance; More econanical than premium cements. C (High Early) ITT 

### o - 6,000 80

- l70 6.3 14.8 1.32**U~ed ~n**  a higher early compressive strength is needed; More expensive than Portland and unless its special properties are required, should not be used. Generally, Portland with accelerators will give better early strengths.



# .. G (Basic) 

### o - 8,000 80

- 200 5.0 15.8 1.15 Can be accelerated or retarded for use over a wide range of depths and terrperatures; Chemically similar to Class B, but a !rOre uniform product; Used in W. Coast and N. Rocky Mountain areas. 

### o - 8,000 80

- 200 4.3 16.4 1.06 can be accelerated or retarded for use over a wide range of depths and temperatures; Chemically similar to Class B, but a !rOre uniform product; Use prroaninantly along Gulf Coast and in the Mid-continent areas.
static Mixing Slurry Slurry Well Depth**~rature** water Weight**Y~eld** (gal./r:J<• ) ()b./gal.) (ft. 1r:J<.'

____ ___________________**~(~ft~.~,** __________**~(cy~)** ________**~~~~~~~~~~~~~~ruu** ____**~~~~ts~** ___________________________ FCZ20:a.'1ic

- ?or::la.rd 5.75 14.15 1.26 Less expensive than others and perforns**'~.e. S'~.'5:;)**  well with rrost additives; Basically a mix of'Portland cement and Pazzolan; SO/50 Paz. means 50 , Portland and 50% Pazzolan; Has an alllOSt universal application in well cementing; Lower in strength.**;:~zc:an** -**l:~e** >140 4.65 14.00 1.18 Contains no Portland cement; Not normally used at temperatures less than l400p.

1 - Inforrration obtained from"Cementing" by Dwight K. smith, Monograph Volume 4 of the SPE Henry L, Doherty Series and "Halliburton Cementing Tables·,**~.al~:b'JrtOl1** Services.

### Some important design properties to consider when selecting
a cement slurry include: (1) compressive strength; (2) density; and (3) 

### setting time. Cement compressive strength is a measure of the degree of resistance the cement plug has to any forces acting along one of its axes. Compressive strength is achieved after waiting for the cement to set; it will increase with time. A 

### compressive strength of 500 

### psi is generally accepted by industry and regulatory bodies as adequate for most cement plugs. The density of a cement slurry should always be great enough to maintain well control (i.e. control formation pressures); uniformity in slurry density should be maintained for plug placement purposes. Cement setting time is also an important property, particularly when setting multiple plugs. In such a case, the operator must be aware of the amount of time required for each plug to develop the desired compressive strength. 

### A variety of cement additives are available and may be required to compensate for special conditions in the well. Both high temperature and pressure act to accelerate the setting of cement. If these conditions exist in the well, a retarder should be added to the slurry to prevent premature setting. Fluid loss
or lost circulation is another well condition that**m~y** 

### be encountered. In these cases, filtration (lnd lost-circuldtion control additives can 

### be added to the cement !:..lurry. 'l'ttl>l(' ·1-;:> 

### de:-;cribes con1l'1on cementing additive:;, the'it' ll!"CS 

### and bc'n('t It:;, 

### and the c c 

### m C' n**t~.** 

### towh i c h they 

### c ;\ nbc 

### adde d . illu s t rat C's t h c' (' 1. t ('Ct s '!,oJ

### hieh <1d d i t i v f' :; ha v(, 0 nthe 

### phY!; j 

### c.\ i 

### prup('rt i Co!; 0 t CC::H·nt.

4 - BTABLE 4-2 SUMMARY OF OILWELL CEMENTING
.. ADDITIVES (Smith, 1987)

Type 01 Additove Accelerators Use Reducingwoe time Setting surface pipe Setting cement plugs Combating lost circulatoon Chemical Composition Calcium chloride Sodium chloride Gypsum Sodium silicate Dispersants Seawater Benefif Accelerated setting High early strength Type 01 Cement All APf classes Pozzolans Diacel systems

Retarders Increasing thickening time lor placement Reducing slurry viscosity Lignosulfonates Organic acids CMHEC Modilied lignosulfonates Increased pumping time Bener flow propertIes API Classes D. E. G. and H Pozzolans Diacel systems Weighl-reducing

additives Reducing weighl Combating lost Circulation Bentonite/attapulgite Gilsonlte Diatomaceous earth Perlite Pozzolans Microspheres (glass

spheres) Nitrogen (loam cement) Lighter weight Economy Bener lill-up lower denSIty All API classes Pozzolans Dlacel systems

Heavyweight additives Combating high pressure Increasing slurry weight Hematite Ilmenite Barite Sand Dispersants Higher density API Classes D. E. G. and H

Additives for controlling

lost circulation Bridging Increasing IiIl-up Combating lost circulation Fast-setting systems Gilsonite Walnut hulls Cellophane flakes Gypsum cement Bentonite/diesel oil Nylon fibers Thixotropic additives Bridged fractures Lighler fluid columns Squeezed fractured

zones Treating lost circulation All API classes Pozzolans Diacel systems

Filtration-control

additives Squeeze cementing Setting long liners Cementing in watersensitive formations Polymers Dispersants CMHEC Latex Reduced dehydration lowervolume of

cement Bener lill-up All APf classes Pozzolans Diacel systems
Dispersanls Reducing hydraulic horsepower Densifying cemenl slurries

for plugging Improving flow properties Organic aCIds Polymers Sodium ;hlonde Lignosulfonates ThInner Slurries Decreased flUId loss Bener mud removal Bener placement All API classes Pozzolans Diacel systems

Special cements or

addItives

Salt S,hca flour Mud Kil Rad,oacl,ve tracers Pozzolan lIme S,hca hme Gypsum cement Hydromltll Lalox cr.-ment Th,.otroplC add,ttYos

'-Aud spacers**M~Jd !llJ·~h(·1**  Pnmary cementIng HIgh-temperature cemenlOng Neutralozlng mud·troatlng

chemIcals TraCIng !low patterns locatong leaks Hlgh·teml)<'rature cementing HI\lh-temperature Cflment,n'il Dealing With sP<'C,al

condItIOns Dt'.IIng WIth**5P<'cl~1**

contlltlOns Dealing WIth si"'t,al

con.dltions Covrflrlg**IO~1** «('cutllllon

lone,**Pfevt"nh"~** g.,'n rt1HJ,.\lon
Mlnlm,l'lng**conl.l!'nln~'ll()n** AI(j'rlO If')**dtdlln~** rTlut1 SodIum chlorode Silocon d,o,odo Paralormaldehyde Sc 046 SIlica-lime reaCllons Sdlca·llmeo**rC.1C!Jon~** CalCIum sulldto Hemlhydrale Gyp!.um "",llh**re~ln** LIQUid or rOw!1(·rroJ

lalelll 0'9.\n"**'HWI!lV"~** InorganiC oIiddllr'¥'e\**V~UI."ttllfl** V..1'**"'~'\('** Bener bondIng 10 salt.**shal~s.** sands Stab,hze<! strcn9th lower permeabIlIty Brtter bondIng Greater**~trength**

- lIghter "("ght Ecoroomy ll<Jtltcr we'II"t filllher**5tr~I\'il'h** f**.ut~r** s.tt,nll**~'i'Qhl"** strf'nQth fut., utt,nll fI.lt" bond,"o Conlr()!l4':'d '1IIr.,llon F''''' !.flPthng

.."dlor**g~!.IIIO.n** L.u IAII blck n.oucu kat

CI'(\./I
....1o(,H'''I tUIIIOII'tI (r'flIrnl

(jl\tr ,t'Ij\.(I/1**l\f"~fI'** rThJI1 ft"rr"1 ',", .,: All API classes All API classes API Ciasses A.

B. C. G. and H All API**Ct3S~t'S**

-

--. .­

-­ API Cl.'·.·.,·, A

B. G ,)(,d Ii All Af'l cia,.'••,

AI! Ct"rnrnllf"tJ

5.., ",!",'!I'\. I I (j1!.p1oo1r**~rn~H'1** r\"'I.LIlNi**lo(,)~.l !~"'P"'.loflQ**  If1o( orn"lIi.t,l" (I/j**,~1.11~~'1** 'h,nell 4 9TABLE 4-3 EFFECTS OF ADDITIVES ON THE PHYSICAL PROPERTIES OF CEMENT (Smith, 1987)

Water Requirements Increases Decreases Density Increases Decreases Viscosity Increases Decreases Thickening Time Accelerates Retards Fluid Loss ofSlurry Increases Decreases Early Strength Increases Decreases Final Strength Increases Decreases Durability Increases Decreases Conductor Casing Surface Casing Types ofCementing Intermediate Casing job applications-­ Production Casing Where mostly used Liners Sgueezing -. ---.------.

• For temperature 230°F XMinor Effects 0Major Effects PlugginJl: ,...... U -c .;:: 0 :2 aU**~** 

## e

.. :l**~** ·0

### ~J <......­

X 

### (X)



### (x)

X X**~** ..c CIC U ,...... ·u u 

### '2**;~ ~.~**  0< 0 C l:j>. 

## '" e " 0­ u " trI**tl.~** :x:::x:: 

### (x) X 

### eX) eX) eX) X X X

X
X
X X X X X 

## ® X
X X X X X X X

--­

.,._.­ II> 

## ... u c u .2 :l,..... ,...... -C II>**~** 

## ... "**~** :; 0 

### ex: c :l 

## ...**~** C II> U '" N 0 U u §

### ~ o " ... u 6 G.:**~** .;]

### ,:: .­ > "0 

### ';] lS. U'::: 

# - ... 

## t:a '-" 

### '" 

### '" 

# ,­ "0 U**.~ .~** ::;;"0 C**.~** 

### '" "'Q ::::"0 0"0 

### '" -; u 

### ex: u..,-" u..< ....l< en en en en X X X X X X X 

### (x) 

### eX) X X X X 

### (X) X X X 

### _(X) X X
X 

### eX) X X X X 

### _(X) X X X 

### (x)
X 

### ex)
X X X X X X X X X X X X

-- f---- c----­ --­ X X X X X

- 

### -­**~--** ----... .-­ X X X X --_."

- ,-­ -_._._--­ 

### --­ --­ ---­

# .~

# t-<­ X 

# I

----­ -.-­ ------­ -­ _. ----.­ X

I**~-----.-----.--.-** ...--.- ...- ...-..-.-..-...... 1

4 - 104.3 IMPORTANT POINTS SELECTION OF PLUGGING MATERIALS
1. WELLBORE FLUID SYSTEM PURPOSE


### o Clean hole o static well condition o Uniform throughout wellbore o Necessary environment for successful cement plug setting and placement o Stabilizing material between plugs
2. WELLBORE FLUID SYSTEM PROPERTIES


### o Sufficient weight/density o Ability to remain in place over long period of time o Chemical and physical stability for unlimited time o Recommended fluid would contain: Water Clay Gel Lost circulation material
3. CONSIDERATIONS IN SELECTING PROPER CEMENT SLURRY


### o compressive strength o Weight/density o Additives o Recommended properties: Sealing to prevent fluid movement Good bonding characteristics Durability Long life

4 - 115.0 SELECTION OF CEMENTING PROCEDURES 

### Inherent to plugging job design is the selection of cementing procedures which will adequately fulfill abandonment requirements. The following provides a summary of: (1) cement mixing techniques; (2) 

### cement plug placement methods; and (3) 

### cement testing methods.
5.1 CEMENT MIXING TECHNIQUES 

### Cement should be mixed according to American Petroleum Institute (API) water/cement ratio requirements. Too much water will delay the setting of the cement and will produce a weaker cement with lower resistance to corrosion. Mixing water should be obtained from the purest available source. Ideally, the water supply for mixing cement should be clean and free of contaminants such as soluble chemicals, organic matter, etc. Potable water is always recommended. Clear water is usually suitable. Saline waters should be used with caution since they can act as an accelerator and cause premature setting. This effect can be offset by chemical retarders. It is always Wlse to pretest the cement slurry mixture (using water to be used in actual operation) in the laboratory to ensure that it exhibits the desired setting properties. The cement mixing**sy~tcm** 

### should bC' cdpdblC' of 

### accurdtely propor t ion.i n g and b 1('nding 

### the dry C C'f!H'nt i r1tj m Iit C' r i ;11:::; wit h t hI'

m i >: w

### ate r 

### t h u**~-;** prod tl C i n q a C ('l:i ('nt !.; 1 u r r y \oJ i t h P r (' c! i ( ,t. If;,l '-' I I 

### propert

### i**C~;.** 

### The**~~y:;t::(,f!l ~~hould**  include 

### .In (ICCtlrdtc 1:1I.'dI1", 

### o!

5 - 1maintained, and a high quality cement slurry is pumped. Slurry density should be monitored with a standard mud balance, densimeter, or fluid density balance. Three methods predominantly used to mix cement slurry for "oilfield" cementing are: (1) jet mixing; (2) recirculating mixing; and (3) batch mixing.
Jet mixing is accomplished with equipment consisting of a hopper, mixing bowl, water line, and mixing tub. Dry cement is fed into the hopper, which funnels into the mixing bowl where it meets jetted water. Jetted water acts as the mixing mechanism. The prepared slurry is then transferred to the mixing tub and is ready for use. Recirculating mixing is similar to jet mixing. Mixed cement is recirculated from an agitated vessel and jetted where dry bulk cement is pipe-fed into the system. This process results In a more uniform slurry. Batch mixing differs from jet and recirculating mixing In that most mixing is accomplished with a large vessel. The recirculating technique is used, however, to introduce dry bulk cement to the system. In essence, a "batch" of cement is mixed. Although not considered <.1 common practic(',**som(~ are<l~;**  sti II
u**~-;**c "hand -mixi n g " m (>thod**~;** for P&,\ c('**:~l** (.ntinq 0p('r- ,1t**ion~;** . 'I'll i**~; lJa~;ically**  involves pourinlJ dry cC'l1ient into d tub Ot" b,lr"!"vI, addinq water, and stirrin<] with a wooden**~;tid:.** n tJt. r 0 (**~** () nl rn**C~** nd edt () r**~~** t.. \/ f • !' d 1 r f \ d**~ ~**  () Jl :; :

5 - 2

### water/cement ratio requirements and slurry density are more likely to occur; (2) Such a mixing system provides no accurate method for monitoring the slurry density as the job progresses; (3) 

### Only small batches of cement can be mixed (e.g. one sack at a time), which further contributes to nonuniform characteristics of the cement slurry. All of these factors are likely to produce a cement slurry with unpredictable properties, one which may not meet design requirements, and therefore may not set up properly.
5.2 CEMENT PLUG PLACEMENT METHODS 

### Several methods are available for the placement of cement plugs during well plugging operations. The most commonly used plug-placement techniques are the: (1) 

### balance method; (2) 

### cement retainer method; (3) 

### two-plug method; and (4) 

### dump-bailer method. Cement should not be dumped from the surface as it will be severely contaminated by the wellbore fluid (as the cement migrates downward) and will not set up properly. Each of the accepted methods has advantages as well as limitations. The selection of the most ideal plug placement method is a function of various factors, such as well construction, plug location, well condition, cost, etc. Each of the**~;tandard** 

### plugging techniques is summarized briefly below:
5.2.1 Balance Method Tho 

### bi1]i1nce method cons.ists at 

### runninq tul,iIlq U1' dri 

### 11 plpC' 

### into**c'l~;ing** 

### or open hole ;u1d**di~;p1~lCill(J** Uw c',·w·nt.. 

### slurry**i~j** 

### pumped do'
....

### n the tllbinq 

### or dri 11 pilJ(' ;Ind b,wk 

### up dl()\lnd tilt' d IiIn II \l:; to (l l:, 11 l . \ 1I ,It. ! •d h (. i LJh t '",'h i ('Il ','; r ; \ I 1 ,I L '/d I ":.t It i,',tl I Y

5 - 3

### balance the cement inside and outside the pipe. The tubing is then pulled slowly out of the top of the cement, leaving a solid cement plug in the hole. When the pipe is a considerable distance above the top of the cement plug, the pipe is then cleaned by reverse circulation. In order to achieve success using the balance method, the wellbore fluid system must be in a state of static equilibrium. Any fluid movement can hinder the quality of the cement plug placed by this method. The balance method is by far the most commonly used technique for emplacing cement plugs. However, the method is not necessarily simple to implement. Figure 5-1 

### illustrates the basic steps involved when utilizing the balance method. The success of the balance method requires considerable operator skill in removing the placement tubing without causing significant contamination of the cement slurry. To minimize the possibility of disturbing the slurry while removing the placement string, a small diameter tubing is required. The small diameter tubing increases the size of the annulus between the placement string and casing or borehole wall which allows the withdrawal of the tubing without causing an excessive drop or surge in the cement level that can be brought on by the**sw~bbing** 

### action of pulling the tubing (Geraghty and Miller, Inc., l<)H;n. 

### Balancinq cement l(>vcl:::;**r(>CJllir(':~ c~lrcful**  pldllninq. C.lut ion



### to be sure that an effective**ccmc~nt** 

### pluq w.il1 rC':',ult.

5 - 4PLUG PLACEMENT PRINCIPLES OF THE BALANCE METHOD (Geraghty and Miller, Inc., 1982)

......'+--Cemem slurry 

# LJ Placement tubing Cement-slurry placed run into hole in hole

# I.

I I

":' ',:.**'::',.:::~** . :; :';'.' 

# ....j**/::~;:** '.;..' .:**~ ~.:**  : t'.•.. ' . . I .' .) 

# L Level of**ceme~t:-slu.!"::,y** Placement**t~bi~g** 

### balanced re::::.oved
FIGURE 5-1
5 - 5

### becomes critical in making the necessary calculations. A slight overbalance of cement in the tubing is commonly practiced to compensate for the difficulties involved in precisely matching cement level prior to withdrawal of the placement tubing and in minimizing contamination of the cement during tUbing withdrawal (Geraghty and Miller, Inc., 1982). 

### section 5.5 

### provides sample calculations for implementation of the balance method.
5.2.2 Cement Retainer Method 

### The cement retainer method, a specialized form of the balance method, is used in cased portions of the hole and utilizes a retainer tool. The retainer tool is attached to the 

### placement tUbing and lowered to the bottom of the well. The cement slurry is then pumped through open valves of the tool and back up into the hole until the cement height rises to 50 

### to 100 

### feet above the ultimate setting depth of the tool. The retainer is then retracted to the desired depth and set. After the retainer is set, the cement is forced by pressure into the surrounding formation(s). Upon pumping the desired amount of cement below the retainer, the tubing is then picked up and disengaged from the tool, which causes tool valves to close. Any residual cement in the tubing will then fallout on top of the retainer tool, forming an additional cement plug. Once the tubing has been raised ahove the cemenl top, it if". cloanpd by
reverse circulation. Figure d

### cpict :; t lH' C ('r:H•nt p 1 de'( .**J~,** ( .Ilt**procc'~s** 

### usi 

### nCJ the cement-n:otai 

### ncr r.lcthou.

5 - 6---

-- 

# --1

I. 

# II**::.:~~-** ..

.:.:" :;::; 

# 11 

# II

# flli,:f:i~;~jJ';1 Placement tubing removed 1.1' Heldillel" nlll Cement-slurry Packer set and N I inLu IIDle placed cement squeezed into formation PLUG PLACEMENT PRINCIPLES OF THE CEMENT RETAINER METHOD (Geraghty and Miller, Inc., 1982)

### Although more expensive than the conventional balance method, the cement retainer method offers several advantages which make its application to setting the bottom plug in injection wells favorable. Some of the method's potential advantages are listed below (Geraghty 

### &Miller, Inc., 1982): (1) 

### By forcing cement out under pressure into the surrounding formation, this technique ensures adequate bonding between the plug and the formation. (2) 

### When the plug is to be placed at the bottom of the casing, the cement retainer method creates a more reliable barrier not only to flow inside the casing, but also to flow in the annular space between the casing and formation. (3) 

### In some cases, the cement retainer method may offer an effective alternative to squeeze cementing the lower portion of a casing string when the integrity of a primary cement job is suspect. (4) 

### Once the valve is closed, the cement retainer serves as a barrier to flow past the plug and thereby increases the reliability of the plug. (5) 

### In addition, immediately after the plug 1::; ::;ct, it Cdn be 

### pressure tested. 1'11(> 

### !(·liability 

## or tht' pluq tlltl:: 

### prov ed, 

### the need**t~** 0 r c c nt**c~** r t IIc' h

### ole a1 t (>

### r t IH . phIL) 

### sets for testing is 01**imin~ltpd.**

5 - B

### (6) The method provides excellent control of the cement slurry, and by providing a barrier to gas percolating up through the well, the retainer helps to prevent any potential contamination of the cement while it is setting. 5.2.3 Two-Plug Method 

### The two-plug method utilizes top and bottom cementing plugs to isolate the cement from both the wellbore and displacement fluids in an effort to avoid contamination of the cement slurry. The two-plug method involves a top plug, bottom plug, and a latch-down type plug catcher. The procedure, depicted in Figure 5-3, 

### begins by running the placement tubing with the attached plug catcher into the hole to the depth desired for the bottom of the cement plug. The bottom plug, followed by the appropriate volume of cement slurry, is then pumped into the pipe. The top plug is pumped behind the cement slurry and is followed by a plugging fluid. When the bottom plug reaches the plug catcher, it passes through the catcher and flows out into the well. The cement slurry is then displaced into the well; when the top plug reaches the plug catcher, it is unable to pass through the catcher preventing any further displacement of fluid. The placement tubing can then be slowly rl1ised out of the cone-nt leaving a**~;olid** 

### plug behind. The plug catcher**i~; de~;iCJnC'cl** **~;o** 

### t hat the pre !:;

### sure can be rever:; 0 d, 0 n:1 Il1

### i IV] 

### flui d to 1 10,; 11.\("k 

### into tho 

### placomc·nt tuhing. ]1 

### neede'd,**lh(~** 

### tubill{J ciln th('n lot'
r ai sod and revc r !eX' C

### ireu 1

### ated t () C'**~** ;t d h Ii:',h 

### the top 0 f t 

### ht' C I.•;:w1\t plue;.

5 - 9**.~ :.:~~** **.~**

.....: ..

### :: 

# 'U**.~--+--** Excess slurry,



# 1

# ~-t-:~~i--- PhJQ C01d"oeI"

: 

# ill

.... '---­

# ~~**r~~~:~ent** phJQ c

# ~;?f~;-
[0:·
.... ::."'V-,-4.---30"omplUQ 

## ::;.•"v..' 

# .,

FIGUHE 5-)

5 - 10 PLUG PLACEMENT PRINCIPLES OF THE TWO-PLUG KETHOD (Geraghty and Miller, Inc., 1982)Although more costly, this technique offers several advantages over the balance method (Geraghty and Miller, Inc., 1982) :
(1) The plugs act to separate the plugging fluid and cement slurry, reducing the potential for cement contamination. (2) The bottom plug helps wipe plugging fluid from the inner walls of the placement tubing as it is pushed down into the well in front of the cement slurry, further reducing cement slurry contamination. (3) Most importantly, the two-plug method offers excellent control of the cement and eliminates overdisplacement of cement into the well.
5.2.4 Dump-Bailer Method The dump-bailer method, although available as a plug-setting mechanism, is seldom used for plugging and abandonment operations due to a number of limitations. When using this method, a mechanical bridge plug is normally placed below the location at which cement is to be placed. The bailer, a cylindrical container which holds a fixed amount of cement, is lowered on a wireline and dumps the cement on top of the mechanical plug. 'l'hismethod 0 f P 1ug P 1acement (il 1u"tr ilt ('din F.i (J u r e 5**-,~)** i :, limited by tlll' amount of cC'l:lCnt that ciln he pLlccd \o;jth c!,lch r-tltl. I n add i t ion, caeh 1 0 <ld 0 fccmenl 1:\ 1I**~;** t bc' S to t 1IP P r i u r' t 0

5 - 11Cump**bailer--++~ ,~++--**  Cemem plUQ**~:**..:... 

## r'" PLUG PLACEMENT PRINCIPLES OF THE DUMP-BAILER METHOD (Geraghty and Miller, Inc., 1982)

FIGURE 5-4

5 - 12

### emplacement of an additional load. Since the dump-bailer method
can be time-consuming and inconvenient, it is generally not selected as the primary plugging technique. Table 5-1 (Geraghty 

### & Miller, Inc., 1982) provides a summary of each of the four plugging methods with a description of the potential applications of each. 5.2.5 Placement of Multiple Plugs The majority of abandonment programs require that a series of plugs be placed in the well to be plugged. In executing the operation, certain steps need to be taken during plug placement. In most cases, each cement plug should set up before placement of the next cement plug in the well. This is necessary to allow the cement slurry to solidify in the presence of a static environment. Displacement of cement slurry into the well for setting a second plug will likely disturb the fluid below, increasing the potential for contamination. In addition, it is often necessary to tag the cement plug, thus verifying its position and solidification. This generally requires waiting for 8 

### to 24 

### hours for cement to set up properly. After tagging the cement plug, it may be necessary to recirculate the plugging fluid to ensure that fluid weight 1S 

### equalized throughout the unplugged portion of the wellbore. The plugging fluid is 

### then brought back 

### to a**~tdtic ~;tate**  before**~:(>tting** tt)(! next 

### plug.

!l - 13- - 

### -------------------------- TABLE 5-1 POTENTIAL APPLICATIONS OF PLUGGING METHODS (Geraghty and Miller, Inc., 1982)

Balance Retainer Two-Plug Dump-Bailer Arplication or Use Method Method Method Method 

### Cased wells 3 3 3 3 lIncdsed 

### wells 3 

### 1 3 3 l.dt-'Jl! diallleter wells 3 :3 3 1 !lm,dl didlileler wells 3 :3 3 3 Deep 

### well!:> 2 

### :3 3 1 Shallow wells 3 2 2 3 )<edu c ed 11e ed 0 f establIsh 1 ng s tat

### i

### c equilibrium 1 2 

### 1 1 Reduced 

### need of thorough well cleaning 

### 1 2 

### 1 1 Heduced need of thorough well 

### In!:>pectiull 1 2 

### 1 1 Placement of bottom-hole plugs 3 1 3 3 Placement of intermediate depth plugs 2 :3 2 1 Ability to squeeze cement slurry 1 :3 1 1 Potenl ial fOl­ adequate cement tJonding to formation and casing 2 3 2 2 Preventlon of cement slurry contamination 2 2 3 1 Prevention of cement movement of micJrat 10n 2 3 2 2 Accul-acy 

### uf derth 

### of placement 

### of cement 

### 2 2 2 3 t:asc 01' calculating adequate cement volume 2 :3 3 2**~a~e** ot installing adequate cement vo IlJrlle 3 :3 3 1 Eftectiveness in minimizing time and t:xl'ell:.ie ut plug testin'j :3 1 rJ()te: J

- (Joud L - Idlrsetting multiple plugs generally requires repetition of the above sequence of steps for each plug. However, when plugs are set using the retainer method, the operator can raise the placement tubing to set the next plug immediately after setting the lower plug. This is possible because the retainer assures the position of the plug and isolates the cement below it from any influences in the borehole above the plug. 5.2.6 Tools and Materials to Assist in Effective Plug Placement Regardless of which of the basic plugging techniques is used, the major concern in any plugging operation is to place the cement plug(s) without contaminating the cement. As mentioned earlier, it is essential that prior to the placement of plugs, the wellbore be conditioned through adequate circulation of an appropriate fluid and that the hole be in a static condition with the fluid weight equalized top to bottom. In addition to proper well preparation, there are a number of procedures which can be used to reduce the risks of achieving an ineffective cement plug. preparation of Borehole Walls The use of scratchers and centralizers placed on the lower joints of the placement tubing maximizes displacement efficiency and prepares borehole walls for cement bonding. Scratchers, which are used to remove mudcakc from borehole wdlls,**consi~t** of two types; the firs ttyperc f.1 0 Ves mudc a }: (> wi t h a rot ;1tinCJ motion, while the! other type**u~;e~;** a recipr-oc.lt inc; (up dnd do',:n) r:lUl ion.

5 - 15

### is lowered to emplace the cement slurry. When scratchers are positioned opposite the zones in which the plug is to be set, the pipe is rotated or reciprocated to remove mudcake. Centralizers also may be attached to the bottom of the placement tubing to position it in the center of the hole. This practice is useful in preventing cement from channeling to one side of the annulus in order to permit displacement of the plugging fluid.
In addition to wall scratchers and centralizers, chemical washes may also assist in borehole preparation. These washes, which are pumped ahead of the cement slurry, assist in the removal of mudcake and other deposits from borehole walls. Chemical washes are of two basic types, thinners and acids. Thinners are most effective in water-based plugging fluid systems and act to disperse any flocculated clay particles. Acid washes act to shrink mud particles, thereby dispersing mudcake. Prewashes must be used with caution since they do contain chemicals which can retard or inhibit cement setting. contamination Prevention 

### Cement slurry contamination can often be 

### prevented through the use of spacer fluids. These fluids can be 

### placed ahead of 

### and/or behind t.he cement s1urry as it**i~;** r>l 

### ilcC'd in the tub i llCJ 

### string. Spacers serve to separate the p1uCJC]inq fluid 

### and**C(':~l('nt ~~.1**  

### u r ry, 

### and arc f 

### rc

### q u('n t ] Y u**!~**C

### din con j \l I l('t i 0 II \-.' i thec

### m (.' IIt i 11

### q

5 - 16plugs (e.g. two-plug method). Spacer fluids may be similar to the chemical washes discussed above, or they may be specially designed by service companies.
In addition to prewashes and spacer fluids, small amounts of non-chemically treated drilling muds may also be pumped ahead of the cement slurry. Such muds are used to prevent adverse reactions which might occur when the plugging fluid comes in contact with chemical washes or the cement slurry. These muds generally consist of bentonite, water, and any necessary weighting material. 5.3 TESTING CEMENT PLUGS There is no simple method for accurately testing a cement plug in open hole. The most common way is to simply tag the plug after waiting on the cement to set up and build compressive strength (8 to 24 hours). This is performed by running pipe (tubing or drill pipe) back into the hole to locate the plug by applied weight. Although tagging a plug may give an indication of whether some degree of plugging has occurred at the desired location, it says little about the quality of the plug. A cement plug may be hard on top, but soft farther on down. 

### If the plug is found to be where it is supposed to be, it can still be soft
so that in time, fluids can pass through it.
Due to time spent. wa i tin<J on cement to !;('t, it i:; not ,\] ',-;,\';/:; fC(1siblc or przlctical to tile] ill} cement pluq::.
on1 Y day1i 9 h t h()Ur!.; are w()d:c-d (1n d the ccom C' 11t !:('t - \JP t i tH' i:: ,It

5 - 17

### plugging procedures are followed closely and care is taken in the plug placement process, an effective plug can generally be expected. Cement plugs placed on top of mechanical plugs need not be tested, as isolation is accomplished with the mechanical plug.
PIug testing is recommended for: (1) plugs that are critical to pressure control or USDW protection; (2) plugs which
are suspected to exhibit inferior cement quality; and (3) plugs which are suspected to be contaminated through unsuccessful placement operations.
5.4 GUIDELINES TO ENSURE CEMENT PLUG QUALITY 

### The following recommendations should be helpful in placing a cement plug successfully (Herndon, et at, 1976; Smith, 1987): (1) Circulate the hole sufficiently before performing the job. Use a mud (or gel) of low yield point, low plastic viscosity, and sufficient weight to control the well. (2) Ensure that the wellbore is completely static (no fluid movement) before plugging operations begin. (3) For maximum bonding, place the plug across a competent, hard formation. Caliper logs should bo**con~~ulted** 

### in selecting plug**location~;.** 

### (4) Precede the cement with**:~ufficiC'nl t.lll~·.h**  

### or e.p,:\CC'I' , il
n e c e**~; ~;**  d t'Y .

5 - 18

### (5) Use a densified (low water ratio) cement (API Class A, C, G, or H) that will tolerate considerable mud contamination. (6) To minimize contamination during cement placement, rotate tubing using centralizers and scratchers on tail pipe (lower part of work string) where the hole is not excessively washed out. (7) Carefully calculate cement, water, and displacement volumes. Always plan to use an ample amount of cement. (8) Place the plug with care and withdraw the pipe slowly out of the cement to minimize mud contamination. 5.5 SAMPLE PROCEDURES AND CALCULATIONS 5.5.1 Typical Plugging Operation This section is intended to provide the reader with a practical example of a plugging procedure. Figure 5-5 depicts the sample well, a typical injection well, in its present and proposed condition. It is assumed that the following circumstances exist: All casing, tubing, and cement exhibit mechanical integrity. There are no flo\.JincJ zones nor arC' there any**lo~;t** 

### circulation zones.

5 - 19

### • • 

# ·. • 

# · ... • 

# :

# . ..

.. • 

### \A • 

# ..



# · • 

# · • 

# · • • •**~-**



### I-­

I 1

### ~ 

# /J**t:~** 

# 11

............ ,. 4 

### \. 1

,

# .**~** I. I 

# /:**~:** t..;. ir; 

# · • 

### ." 

# R·

# . • 

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## -­ ..

## ..

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## .. 

## o ",.A .... 

### •



### Surface Casing 8-5/8" 24# J-55 

### Set at 400' Cemented to surface 

### G
Casing Severance at 2,300' 

### EL Injection Tubing 7-7/8" 

### Hole Long String Casing 5-1/2" 17# J-55 

### Set at 2,990' Top of Cement at 2,500'
Injection Packer Injection Zone

2,800-2,850'

Total Depth at 3,000' 50' Surface Plug

Cement Plug from 50' below casing shoe to 50' above casing shoe

Cement Plug from 50' below casing cut to 50' above casing cut

Bridge Plug at 2,750' 

### Capped with 50' cement CONVENTIONAL WELL CONSTRUCTION SAMPLE PLUGGING JOB DESIGN



### ­Equipment removal is feasible. Workover equipment is readily available. Plugs will be placed by the balance method.
A typical plugging procedure for the sample well is presented below: 

### (1) Move in and rig up. Unseat packer and pullout of the hole with injection tubing and packer. NOTE: Injection tubing will be used as the workstring. (2) Rig up a wireline unit and run in the hole with a gauge ring for the 5-1/2" casing (to check for obstructions)
. Pullout of the hole. (3) Run in the hole with a cast iron bridge plug. Set the bridge plug at 2,750'. Pullout of the hole. (4) Run in the hole with a free point indicator tool. Find the free point of the 5-1/2" long string casing (assume at 2,350'). (5) Run in the hole with a jet cutter and shoot off 5-1/2" casing at 2,300'. Pullout of the hole with tool. (6) Pull the 5-1/2" casin(J string out of the holc', Llying it down as corning out of the well.

5 - 21

### (7) Run in the hole with the tubing string to 2,750'. Pull up slightly and circulate the hole with an appropriate preflush to clean hole. (8) Circulate one hole volume (150 bbls.) of gelled plugging fluid to establish static well conditions and prepare well for plugging. Observe fluid level to
ensure that the hole is in a static condition. (9) Assuming that the wellbore is in a static condition, emplace the bottom cement plug 

### (+ 6 sks.). Using the balance method, pump a spacer followed by the cement slurry, spacer, and displacement gel. 

### (10) Pull tUbing slowly out of the cement by about 200'. Reverse circulate any excess cement out of the tubing using gel as the circulating fluid. (11) Pull up to 2,350' and emplace a 100' cement plug 

### (± 23 sks.) using the same technique. utilize 20% excess volume for all cement slurries as a margin of safety. (12) Pull up to 450' and emplace a lOa' 

### cement plug**(~** 

### 32 sks.) across the surface casing shoe using the same placement technique. pullout of the hole with the tubing.**~** - 22

### (13) After waiting 12 hours for cement to set, run in the hole with the tubing and tag the surface casing plug. (14) Assuming that the plug has been successfully tagged, pull up to 50' and emplace the 50' cement plug 

### (± 15 sks.) at ground surface. (15) Mark and restore the well site according to State requirements. Rig down and move off the site.

5 - 23Sample plugging fluid calculations for the job design depicted in Figure 5-5 are presented below: Assume a 20% excess volume required for open hole portions of the well. Plugging Fluid Calculation This calculation assumes that the wellbore is circulated with one hole volume of mud or gel after pulling the long string casing. (2,700'-2,300') (.0232 bbl./ft.) 

## = 9.3 bbls. (5-1/2" csg. ) (2,300'-400') (.0602 bbl/ft.) (1.2) == 114.4 bbls. (7-7/8" D.H. ) (400'-0') (.0636 bbl./ft.) == 25.4 bbls. (8-5/8" csg. ) Approximate Mud Required == 150 bbls. Cement Plug Calculations These calculations assume a cement slurry yield of 1.18 ft.3

### Isk. Plug A. (50')(.1305 ft. 3/ft.) == 6.5 ft. 3 6.5 ft. 3/1.18 ft. 3/sk. 6 sks. cement Plug B. (50' ) ( . 1305 ft. 3/ft. ) == 6.5 ft. 3 (50') (.3382 ft. 3/ft.) (1.2) == 20.3 ft. 3 Total == 26.8 ft. 3 26.8 ft. 3/1.18 ft. 3

### /sk. 

### = 23 sks. cement Plug C. (50') (.3382 ft. 3/ft.) (1.2) == 20.3 ft. 3 (50')(.3575 ft. 3/ft.) == 17.9 ft. 3 Total 38.2 ft. 3 38.2 ft. 3/1.18 ft.3/sk. 32 sks. cement
'3 Plug D. (50')(.3575 ft. 3/ft.) .17.9 ft. 17.9 ft. 3/1.18**ft.3/~k.** Apprl.l>:imatc Cement Hc-qu i rf'd

5 - 245.5.2 Other sample Calculations 

### The remaining pages of this section present detailed sample calculations for cementing procedures associated with plugging and abandonment. These examples have been excerpted from reputable pUblications (See references).

5 -**2~**EXCERPTED FROM "CEMENTING TECHNOLOGY" (Dowell Schlumberger, 1984)


### PLUGBALANCING When a cement plug IS to be spotted through tubingor dnll pIpe, it IS important to calculate the necessaryvolume ofspacerto bepumped behmd the cement slurry. The correct volume ensures that the column of flUId in the annulus (displaced mud, spacer, cement slurry) is adequately balanced by the column of fluid in the tubmg (displacing mud, fluid behind the slurry, cement slurry). It is thIS process that is known as 'balancingaplug'

H

FIG. 8.5 Once aplug has cee:1 spotted. the tubmg 1S**~ul!ed** up unt11 lts end LS pos1t1oned Just above the des1red top of the plL.:g and reverse cnculat:cn 1S establlshed Th1s**::;r~e~at:cn** cuts off the plug cd :he deslred he1ght The steps :n'/::;I·:,.<: ::-. :',:'.]":**balllnc:~'·;** ca!cCl:.":::-.:;**a~e** 1) Tc ceile.:::;::-.:' ':."::::'.: ':C:!'.::::t>**J:.I~: ;~~J::::**  ,: .:**cer.:~nt s.:!,=~** ..**~: ~.'"** **~':~:** ...':**~~:, f;!~**  tr»**:>~'::::".:~i~**.... :**:~.'** L Thus

2) 1'0 instance, WIth fluid of the same denSIty both before and after the slurry, we can use the formula water behmd[bbl] = waterahead [bbl]xtubmgvolume [cuftlsk] annularvolume [cufVft] 3) To calculate the heIght ofthe balanced cement column priorto pullingupthe tubing slurryvolume [cufl] H(ft)

## = annularvolume[cufVft]+tubmg volume[cufVft] 4)To calculatethevolume ofdLSplacement fluid DISplacement ITUld volume [bbl] 

## =(tubmg length - H) eft]xtubmgvolume [bbUft]

- water behmdfrom step2[bbl] As ageneral rule, it IS advisable to underdlsplace the quantity ofcement down the tubing by a small amount(1/4 to V2 bblper 1000ft, dependinguponthe sizeofthe tubular goods). EXAMPLE CALCULATIONS

A 200 ft plug is required In an 8V4 mch open hole.

- The bottomofthe plugIS to besetat 6000 ft.

- Thecementis aneatClassG.

- To spot the plug, a 4V2 inch, 16.6 lblft, drill pipe

will be usedand 6 bblofwater will be pumped aheadofthe cementslurry.

- 20% excess cement is bel!eved necessary to

allo\'/for holeenlargement. 1) Slurryvolume requned 

### o3712 eu fUft x200 ft x 1 2

### =89 1eu ft 2) Sacks ofcement 89 1cu ft

---- =77sk 115cu fvsk 3) MlX water requIred 77 sk x 4'::7 gaLsk

--------- - :::: 3 : t t:**~** 42 ::;.,Leel

" , ': • " • :. : ':', I' -**~ ~**  ,:. : .:

,. " ,

### .. ,t**~:~"** :;, :**~** ..=lt;r-:**~.** ' - J I. I' •

.. ': I' '; " "'" j ."t. :' ," it . ,",**~**

5 - 266) Displacementvolume [(6000 ft

-262 ft) 001422bbl;ft]

- [1.8 bbl]

## =79.9 bbl Note that the total slurry volume. includmg the excess allowed. has been used during the course of this calculatIOn. We must condude. therefore. that the plug will only be well balanced if the estimated excess was accurate. Ifthis was not the case. the plugwillbeoverorunderdisplaced. 

### SQUEEZE CEMENTING Squeeze cementmg is covered more fully m Chapter 12. For this chapter, however, the followmg facts should be considered. The high pressure technique involves breaking openthe formatlon so as to pumpand dehydratea slurryinto the resultmgfractures. The low pressure technique consists of placing cement over adesired interval. and then applymg just sufficient pressure to dehydrate the cement into the perforation channels and surrounding voids. Both techniques may be employed by using isolating tools such as packers and cement retainers. Alternatlvely, the Bradenhead squeeze methodmaybeemployed. CBl 

### o mV 50 

# j 

# l 1**~** 

# II I !; I 

### !\ 

## I ..' I' .l . I I \ 5**~~:..** l E 7000**~:**

...**702~** ': 

# [I l_

# ----~**~.-.--~-** .--­ FIG 8.6 In order to demonstrate such techniques more fully, let us conSider an example using data relatingto calculatIOnsoften made inthe field. Considerthe following: An evaluatIon of a pnmary cementmg job has shown poor isolation in front of the productlon zone with the result that production tests have yielded high gas and water cut 011. To work the well in an economically viable manner, it is necessary to eliminate the entryofwater and gas into the wellbore by more effectively isolatmg the oil interval. WELL DATA Total depth 

## =7050 ft Casmg = 5Y2 mch. 17 Ib/ft, O. 1305 cu ftlft Tubing = 2 mch 

### ro, 4 lb/ft. 0.02272 cu ftift Open hole = 6% mch dnlled through pay Formation fracturing

gradIent 

## =0 7 psilft BHCT 

## = 130 F FLUID DATA Cement slurry to beused Class G 

### + 0.2 galisk FLAC· 

### + 0.1 galisk TIC· Slurry weight = 158 Ib/gal Mix water = 4.97 gals/sack Slurry yield = L15 cu ftisack Thickening time at 130 F SHCT = 120 min Completion Fluid NaCl bnne 9.5 lb/gal Workmg WIth thIS data we shall develop field calculatIons for the purposes of low pressure squeeze Jobs The Sradenhead techmque shall be used In our first example and In shall conSIder the calc:Jlatlons through a packer the second. for a sque we eze
BRADENHEADSQUEEZING SLURRY VOLUME 1'he oc;ec! of th:s exe:::sc :s q'J:rE-**s~;:'.rl ·/**  tc**~::!** any ';c:js ,n the ann:J!3: S;'.::>? ',':::h**c(~l;·!dr,.::e:i** c..**~·::;**.. :**~'.:** 

### v":h
..::n ane**~~~;-'**::**~: '~~** **S'.~:~ ~~**  J:-'. ::**r.',~~: ~** \1:::::r:**[-.o·:/~·.c,":_: :JL~** **s~.,::ulc ['~~** **r]':;~d":** :::**ir.f~' r-'~~~~~=-.~:-~:** 

f".'r**.~: ;~** **'.J;;;,(~)r:~:)** ':"t,": "" -:,:**t,~~'** ••.J ",::1:: _OJ:**I-=,',j~_'t_'** .. ,**'1,'hlC~! t~:tj**  ,_'en:E:r:t :!I :: - ;,' ::-::!'**::~~. r,~j''''** **~:**

### ..**:'~.,_~ L(,l~'**  ::**~:('~ J;~"!** **~C,(;I-_·t:h~~r** \ •**.I;!~: ~~>.** **,"~:** ::!.r>;**~:'**..1'::**~':',1:"~ ~**  t:t-<l

5 - 27removedfrom the annularspace bythe producing fluids. An injection test, performed with clean fluids, demonstrated a fair injection rate at a low pressure. The perforations may be considered as clean, as they have been subjected to high negativedifferentialpressuresduringthe shootmg and production tests We shall assume that 80% of the perforationsareopen. Thevolumeofcement neededto satlsfy the above conditIOns maybecalculatedas follows Annularspace Distance betweenCBL peaks = 65 ft Volumeofannularspace betweenCBL peaks 

### = 0.0744 cufVft x65 ft 

### = 4.84 cuft Hence, sacksofcementforannularspace = 4.84 sacks Volume ofcementleft inside casing Top ofcement at 6980 ft 0.1305 cufVft x 45 ft = 5.87 cuft Hence, sacks ofcement 

### = 5.10 sacks i.e. total sacks = 9.94

Add 20% excess cement - 1.99 Therefore total cement in sacks= 11.93 sk say 12 sk As can be seen, even haVing taken into account the fact that 100% of the annular space has to be cemented, the reqUIsite volume of dry cement remains relatively small For the purposes of thls hypothetIcal Job, therefore, the recommended approach v'louId be to mlX 20 sacks of cement and reverse out the excess above the 6920 f[ level SPOTTING THE CEMENT SLURRY IN FRONT OFTHE PERFORATIONS If::lne lS to**a'J('~d sc;~;.>::::r.~l~i;j:;1a'J!"q**  ::ulds ahead of t!1('**sl~rr'i t[:~":.\** **Cf'~~j'-.:·r;( r:ll..!S~**  be**r:.;rc~erl·" ta!(~d~C,?C1**  ;n**frc~lt** ':,1: :;,(:**;Je;::..~rdt:c~r~s l~he** **r;l'~~** CU.iC-l;::'--·**':~(-::j ~-'I--:"** **C:d"'~11('"i~(~d :):~'~s;dlng**  tc**th~.:** r.-1e!:--:cd**sr.,:,·:;~. '~'"lr:,f':**  ::1**::1:~~ ('~,~~_'!j-_'r** **1~he res~**  of**~r:f"' c~11c'Jlar:,.:~'.:)** **;".J!r>,_'~,j~,~~~ ..1~)**  :ullu'oI-:s**\VJt~'r J~,f-"dd**  ::;f:h,·**:~:'.':::'** ':::;>':rr',l = 5**bcl:~ \~/~lte,:** **t:'~'hlr:d r~.('** **'.::~··r·~·'~···:,~ ~~!** **~!r'l** =:".: 5bhl:<**r~l~~l:~'] t~!::~**  '.'
..**>;:~',.'** 50 x 0**O;~2·/~~** 14 tU Heightofbalancedcement column 20 sk x 1.15 cu.fVsk = 187.7 ft 0.02272 cu.fVft 

### +0.0998 cU.fVft DISplacementvolume Topofwater behindcement 1.14bbl

### x5.61 cu[Vbbl 7025 ft-187.7 ft- -------= 6555.8 ft 0.02272 cu.fVft

(6555.8 x 0.02272)= 149 cu.ft = 26.5 bbl Oncethe cement has been balanced. the tubing lS then pulled above the plug, the BOP rams are closed and the requislte amount of pressure is applied through the tubing in order to start the squeezmg of the cement slurry through the perforations. MAXIMUMALLOWABLESURFACEPRESSURE The maximum surface pressure that IS acceptable at any time while the job is in progress may be givenby MASP = (grxdepth) - (Ph at7025 ft) 

### +**(~Pr)** - (safetyfactor) where, gr = fracturegradient, psi/ft Ph = hydrostatIcpressure, psi**~Pr** can be dlsmissed generally, hence bemg an extrasafety factor**"'~~f-SALT** WATER

!OO) ft

FlCB ,.

5 - 28

# ---- CIRCULATING SQUEEZING

BY·PASS

PACKER



# -- -:

# .. .'

FIG. 8 9 The extent of the hydrostatic pressure present at the begmningofthe squeezmg may be calculated as follows: Length ofcement plug = 20 sk x 1.15 ell fVsk 

## = 176 ft 0.1305 ell [Vft Length ofwater spacer 

## = (5 bbl + 1.14 bbl) 5.61 eu ft'bbl 0.1305 ell ftlft 

## =264 ft Length ofcolumn of brine = (7025

- 176

- 264) 

### = 6585 ft Therefore, Total hydrostatic pressure = 0.052 [(176 x 15.8) 

### + (264 x 8.32) 

### + (6585 x 95)] = 3512 psi The maximumaiiowabie surface pressure (MAS?) when squeezing begins is therefore: [(7025ft x0.7 psi/ft)
-(3512 psi) -(500 psi)]= 906 psi The MASP at the end of the squeezing may be calculated as follows: Cement volume inside the casing = (20

- 4.84) sk x (1.15 cu fVsk) = 17.43 cu ft Length ofcement column = (17.43 cu ft)/(0.1305 cu Nft) 

### = 134 ft HydrostatIc pressure = 0.052 [( 134 x 158) + (264 x 832) 

### + (6627 

### x95)] = 3498 pSI Hence, MASP (fInal) 

## = (7025 x07)

.(3498)
. (5CO) 

## =920 pSI In th:s mstance. ',v;th a ccrnr>}ri1tl'le!y low volume ofcerner,t to be**sc;ue'::~.'d** the difference between the hydr::::st<ll:c pressur,:: at the beq:nnmg and at the enc ,:)f th(' ]ch IS r,,";t 'J"r'l slQnlflcant and Vlrl'Jilll','**:r:-lf~~'S:~lhlt"** Ie rl1<lfl:::,r Ther': are cases, h::;',ve';'C'! In '::h:e:: ,1 ;:,;,,:1): Ir
..,**~::\SP** agamst the voil:r:le**S':llJ(.'t:~:·.,~d** IS of '::,,:·t::,:.;'.:('!.lbk, importance

_. espec::dl',I · ...·here s,lch a**;~:lct** CJrl 

## ce used to**deti::rn~lr·;",i ~h{~**  l:rnll3 ')!1**,~:~** ..'**~~~lifdC(,** pressure at any :"ll'/E'!')**}]C:~'I:** :L**:r:,::.~** :;_'r MAX SURfACE PRESSURE pSI
950

900

850o 2 3 4 5 VOLUME SQUEEZED CU It FIG. B.B SQUEEZINGTHROUGHA RETRIEVABLE PACKERORCEMENTRETAINER Wherever the packer is run withtail pipe and the cement slurry spotted in front of the perforations, the balancing ofthe cement plug and the surface pressure calculations are similar to those for Bradenheadsqueezes In some operations, however. the cement 15 circulated down the hole with the packer's by· pass open; beforethe cement reaches the packer. the by-pass is closed causing the fluid ahead of the slurry to be squeezed into the formation. Ifth15

5 - 29operation is to succeed when using low pressure squeezing, the fluid ahead of the cement slurry must be clean and free of solids, so as to avoid plugginganyperforationsorchannelsaheadofthe

re

he

ed mg hm

0 cement. VOLUMES The slurry volume should always be checked against the maximum prevailing hydrostatic pressures. The greatesthydrostaticcolumnwill exist at the moment the preflush comes into contact with the lowerperforations. Lengthofcementcolumn: 20 sk x 1.15 eli [tlsk 002272 eli [tift 

### = 1012 ft Wateraheadofthe cement slurry = 3bbl Water behindthe cementslurry = 3bbl The volume ofcasing belowthe packer (packerat 6900 it)

### =125 it

### x0.1305 cu iVit

### = 16 31 cu ft = 291 bbl (3 bbl,say) The lengthofthe columnofwaterinthe tubing 3bblx5 5eli [!!bbl 

## = 0.02272 = 740 ft Hydrostatic pressure, therefore,
= 0.052 [(125

### x8.32) 

### + (1012 

### x 15.8) 

### + (740 

### x8.32)



### + (5148 

### x 9.5)] = 3749 psi Formationfracture pressure IS

7025 ft 

### x0.7 psilft = 4917 pSI The calculated hydrostatIc pressure IS therefo 1.170 pSI belowthe formatIon fracture pressure Inour example. therefore Packer Placement The packer WIll be placed 100 ft above t perforatIonsat 6900 ft and the by·pass left open Fluid Volumes The volumes offlUId ShO'lI:1 b::lO'I: ,,:ill bf..: pump In the follcwlng order. WIth :hc b'!'pac,::; rernaln open until the fresh 'Nater**~lr{':l:dl** v.,;r:1C·c; 'IJlt one bhl ofthe bottom ofthe**~'']Cr:f:r**

20 ,;k x i 

### 1:; ell

## :1**:~k** 4 :

### c:**~::Il** (2) 561 C'.J ft hr 1 Freshwater behind = 3.00 bbl (3) 10.10 bbl total Displacement BrIne 6900 ftx0.02272 cu.fVft. TbgVol= = 27.94 bbl 5.61 cu.ftibbl Vol. of brine to be pumped to leave the fresh water 1bbl from the packer = (27.94 - 10.10

- 1.00)bbl 

## = 16.84 saY,l7bbi (4) Once the 17 bbl of brIne have been pumped (bringing the preflush water to Within 1bbl ofthe packer), the by-pass is closed and we can proceed with the squeeze (fig8.10) Freshwaterpreflushdisplacedfromtubing The greatest hydrostatic pressure is appliedto the formation at the point when all the leading fresh

_••_.__ \..
.... _ 1.-.
..... __ ...,J;
....._1
....... ___...J •___ .\...
.........t-..;....._ fT1\.-..
....... V\'dlt::l lld;::' Ut::t::ll Ul;::'jJlC1"t::U !lU111 Ult:: lUUlll'"J. lllt:: total volume of brine required to achieve this dISplacement is (17 + 1

### + 3) bbl = 20.9 bbl (see fig.8. 11) Cement at perforations The cement will reach the perforations when 2.9 bbl of it (the volume of the casing below the packer) has been pumped from the tubing. The total volume ofbrine neededto bepwnpedfor the cement to reach the perforations. therefore, is 20.9 

### + 2.9 = 238 bbl (see fig812) Allthecementwillbedisplacedfromthetubing when 238 bbl 

### + 12 bbl = 250 bbl of brine have been pumped (see fig8 13) Maximumdisplacement The process of squeezing should stop v.'hen there IS about 20 ft of cement sllli standmg above the perforaw.ns (Prcsurmng th,-j( final pres..sur.,; hiiS not be,,-.·" reached !n ildvanc':C' ofthiS pc'mr)

_ .. :: '.:' II**:~**r

### r: b r:!l**,~.** (:: : • '.:.::!' in C(J!'.:'), ; !'·Lr--.'
...;"**'·~,i;',** '
....::>. ':'ldl :r:,· r:1,'1:-:.r:',',:::: vO!llrnf '**~,;! r'Jr~r."**  tr::"lr**Cr~d; t~'I"** **t",:~l.lrj,.:~i** L··:-,:
..:,· s:(·)prl1.1 ::. ­

5 - 3**~~~24bbl** ""f+-+--25bbl BRINE BRINE BRINE PUMPED PUMPED PUMPED

t-"_

...."-4··--·····_· F \/II

--.- fW

FW I 

# I 

# l :.1·:
....H--"'-t--27bbl BRINE**~~-** DISPLACEMENT BRINE (17bbl PUMPED) 3bbl FRESH**~~~5~;;~.** WATER

4bbl**SLURRY--+.~~·'**

3bbl FRESH-----f:7BE!?:;:;J WATER PREFLUSH IFW)WITHIN 1bbl OF PACKER PACKER AT -+-- 6)OOft

BRINE!SWI

# ~1'f~~I~~~~~~:T FIG. 8.10 FIG. 8.11 FW PREFLUSH**t:\~~\ti0~0t--21** bbl BRINE 

### M PUMPED**~~;;+--** FW BEHIND SLURRY**~~+---** SLURRY

BRiNE BELOW PERFS

FIG. 8.12 FIG 8 13 iF; S ].I
5 - 31MAXIMUMALLOWABLESURFACEPRESSURE When involved in low pressure squeezing, it is important to remember that the hydrostatic pressure inside the tubing is applied to the formation immediatelythe packerby-pass isclosed. The maximum allowable surface pressure, (neglecting friction pressures) is (as previously): 

### MASP = (gf x perf. depth)- (safety factor) - (Ph at perfs) This varies according to the cumulative volume pumped into the tubing after the by-pass valve is closed.


### , 

# .. CUMUlA,TlV( HYDROST PRESSURE TIJ81kO HYDROST ""USURI CA$'PIIO VOlUME 0 

## .. , I'UIr,("fOAFTfllt sw FW sw FW s 

### • eM' eM' 

## .. CLOSING IYPASS L


# .., p,l 

# .., .bI Pi; 

# ..; 

## ...**.~** p" 640 2177 62 0 //igS 101 371I 832 700 - - 54 2543 4 /fH}S III 320 832 3749 670 - - 2897 7 /figS. 121 320 242 103 3562 860 - 

### - 8 (ltt}813J 3042 320 103 3465 950 - - 

### - 

## I 10/fig8141 3269 122 

### I - I - I 35 37 

### I 34631950 

### I TABLE8.4

900 MAX ALLOWABLE SURFACE PRESSURE

900 I

700 

## I .

900

# u~,~---'---'--'---'-_ h) 11 '2 "'" SOUEEZED FIG.8.1S The above graph (fig8 15), made by plotting the Max:rnum Allo',vable Surface Pressure (Table 84) aga:nst the Cumulatlve Volume Pumped after c\oslnq the by'pass can be used to mOnltor the maX";,Ui;l s'Jr:Llce pressure**d~:r:;Y-1** the jeD

5 - 32EXCERPTED FROM "CEMENTING" (Smith, 1987) 

# Appendix C 

# Plugback Cementing

C.1 Problem Balance a 200-ftcementplug from 5,800 to 6,000 ft after drillpipe is removed. C.2 Desired Information 1. Cementvolume-cubicfeet ofslurryandnumberof sacks.

2. Cement column height and spacer column height with the drillpipe in the plug.

3. Spacer volume. 4. Mixing water volume (for cement. spacer. and 20-bbl cleanup).

5. Displacing fluid volume. C.3 Well Conditions (see Fig. C-i)

Hole size-8.75 in. Drillpipe size-4.5 in. 00. 16.60 Ibm/ft. Plug set-6.000 to 5.800 f1. Mud in hole-water based. 12.8 Ibmlgal. Spacer--200 ft of fresh water. Cement-API Class H. Slurry weight-16..l Ibm/gal. C.4 Calculations

I Ct'/IIO!f l·n/UlIlt'. Cap;JCity of8"·In.**h()k~'0.4176·** cu flift.

CCnll·nt \ olume cquah cap;l(lI) f.l(\ur tllllC\**hCI~h(** of dc\ircd plut:



### o 417t) (lJ**ftl!.~** 200,·83 52 (U f( C\'ment v()luIlie eyu:tl, API CI.1" II ;11 I() 4 Ibfll/},::d '" 1.06 ell II,**\;IC'~**

5.1(1, of cemcnt equal, cubic fcc! celnen! dlvldcd by cubic fee!**~Iurry** per**~Jck**

S.I .'i:? eU II

•J lot: Ic.." l1\at .. '. """'l./)·,.......' ....,. t•••" I,r......, ( ."'
....,"'\1**'.t~** •• ....**,'.6~,** .. ""m H
...... t.I.t
...... "()oI'I -;"'r._,., Ot(**~Jq''\o/** I-Il 2. HeighTof cemenTplug wiTh workSTring sTill inplug. Equalization point formula: N h=-­ C+T' where

h = height ofbalance cement column. 83.52 cu ft 0.3071 cu ft/ft+0.07980 cu ft/ft =215.87 cu ft. N = required cement slurry (cubic feet). 78.79 sacksx 1.06 cu ft/sack=83.52 cu ft, C = cubic feet per linear foot of space between tubing (or drillpipe) and casing (or hole) found in the handbook tables under "Volume and Height." 0.3071 cu ftift. and T = cubic feet per linear foot inside tubing (or drillpipc or**cJ~ing)** found in the handbook t.lbks under "Capacity."**0.079~** cu ftift. 3. I/()/IIIII,· awlhl'lgirrIIfsputa ill rht' al/l/lI/l11 1\rth 1\Ii,).:. srrrn\i .1111/111 [,lug**Annlllll~** tlll·up factor for 4 '
..: ·111 OD pipe in JII X', In. 11llic 0 OS·l7 bblift.

Annulu, 'illume !Iftlu,fi-c'qlu], fill·up Llctur lilli'" rc' qlllrcd fdl

0.05,1",: hhl. tl.-**~()()** tl' 1(1),\ hhl Determine thc' fdl·up r;lIlo tx-t,q:l'n the hell',h! of flUid in the annulll\ and !tw**hCll~h(** llf thlld in the v,ork \trlng

From h.Hh!hoo\, I' '\'"lulI1c .1Il.! HClt:tI! Ikl\H','1l (',1'<1[1):, Drillplpc, ,1n<1 1f"lc"). helVh! 01 111Jld I'dI In ,II1I1Ulll\ 1"'1 4": In()[)**P'l~** III :'11. III hilk lK**~X().1** ft hi"

5 - 33CEMENT HOLE AND CONOmONS SPACER Hole: 83,. wellborefluidAPI Class H 12.8#/gal Cement water base mud SlurryWt.­ 16.4#/gal Drill Pipe: "'--1t-4-'/z0.0. 16.60#1f1 E.U. Spacer200 ft In annulus 

# ....**.,..~~.,..+-:l,..,.~** 5800 ft Fresh water spacerahead & behind cement plug
Fig. C-1-Plugglng example.
From handbook ("Capacity"). height offluid fill inside 4 I h-in.• 16.60-lbm/ft EU drillpipe=70.32 ft/bbl. Height ratio formula: Requalsthe fill-up factor for the work string (feet perbarrel) divided by the fill-up factor fer the annulus (feet per barrei): 70.32 ft/bbl

----- ==3.85. 18.2804 ftlbbl Annulus volume divided by R equals tubing volume: 10.94+3.85=2.84 bbl. For this example. use 3 bbl ofspacer behind the cemen!. This will changethe volumeofspacerto bepumped ahead ofthe cement plug.

New annulus volume equals tubing volume times fillup ratio:

3 bblx3.85=11.55 bbl (round up to 12 bbl). Spacer height should be equal inside and outside the work string. Spacerheight equals volume ofspacertimes fill-up factor:

12 bbl x 18 2804 ft/bbl=219 ft. 4.**Fr('~h,,"l1ler** requirements (lor CCmt'lIl-JI'l1Ca alld ('quipmcnl CIt·OllIlP). Mixing WJter per**~ad** of**CL1~\** H cement at 16.4 Ibrn/gal"-4.3 galhal"k

Mixing water equal\galr;-;r), p<:r \.ll'k tlll1n totJI sacb. 4.3 x 7S.793.19gal. 339 gal 42 gal/bhl ==8.07 bbl W;Jtcr (I)r**~p;Kcr** equal\ \p;J(cr .dlcHl pill' '(>.I(cr be hind (Clllcnt**plu!~·** 10.')4 I:' S-I I] 7H bill Total fresh waterequals mixing waterplusspacerwater plus cleanup water:

8.07 bbl+ 13.75 bbl +20 bbl (cleanup water variable) ==41.82 bbl total. 5. Displacement volume-capaciry of mud behind spacerand cement. The displacement footage required behind the spacer and cement equals total work string depth minus (heightofspacerplus heightofcementwith work string still in plug).

Displacement footage=6.000ft-(215.87+200 ft) =5.584 ft. Capacity factor:**4~-in.** EU 16_60 lbm/ft drillpipe=0_OI422 bbllft_ Displacement volume equals capacity factor of work string times displacement footage:

0_01422 bbllftx5.584 ft=79.41 bbl. C;5 Balanced Plug for Whipstock Set acement plug from 5.600to 6,000 ft for directional drilling (whipstock)_ C.6 Desired Information

I. Sacks ofcement. 2. Heightofcementwith drillpipeandtubing inplace. 3. Height ofwater in annulus and barrels ofwater in drillpipe and tubing_

4. Total water (including mixing water. spacer. flush, and 20-bbl cleanup).

5_ Barrels of displaced fluid. C.7 Conditions Cement. Class A cement mixed at aslurrydensity of 15.6 Ibm/gal; run 30 bbl of fresh water ahead ofthe cement plug; and run 500 ft of2Y.-in. 00. 4_70-lbm/ftEUE tubing with scratchers and centralizers attached to the bottom ofthe drillpipc" Hole. 9 Ih-in. drilled hole washed out to an average 12-in. hole from 5.430 to 6.145 ft: 3'/,-in.-OD, 13.30-lhm/ft EU drillpipc; and wellhore fluid is lOS-Ibm/gal native mud. C.S Calculations I Volulllt" ofcrll/nll FrUIIl h.lf1Jb(){)J... C;Jp.lllty LI(tor for J 12 in Iwk eyu.li., O.7H'i·t ell ftifl

Cemcnt volumc cqll.lh clp.""lty L,c·tor IlfIle,**hl'l!~~lt** III dcmed plu):

0.7854 eu ftnt :.: ·WO It J**I·~** 16 eu ft. O;J\\ A l'CIllt"nt 1111**~("d** .It I') I, Ihm/g.d

.IS c"U It/·
..**ll·~ S.lC~\**  (It crllll·,,1 COil","', cub,,· fert of celtH'lIt dlv"h"d by cuhl!. krt LIt ·.IUI I! pC! \.Ie I.

5 - 34C 2. Heightof cementplug with workstringstillinplug. Equalization point formula: N h =--­ C+T' where hb = height of balance column. 314 cu ft 0.7546 cu ft/ft+0.02171 cu ft/ft =404.48 ft. tV = required cement slurry: 314.16 cu ft. C = space between tubing (or drillpipe and casing/hole): 12-in. hole capacity factor minus 2Ya-in. hole capacity factor=0.7546 cu ft/ft. and

-­ T = cubic feet per linear foot inside tubing or drillpipe or casing=0.02171 cu ft/ft.
3. Volume andheight offlush with workstring still in plug. Calculate the footage ofa 2Ya-in. work string that is notcoveredby cementby subtracting the heightofcement with work string in the plug from the total length of 2Ya-in. tail pipe.

Tubing not covered with cement=500-404.68 ft =95.32 ft. where h=41 1.73.

Calculatethe volume offlush in the 2YaX 12-in. annulus and the volume of flush in the 2¥a-in. work string.

Annulus capacity factor=0.1399 bbl/ft-0.0055 bbl/ft. 95.32 ftxO.I344bbllft

### = 12.81 bbl freshwater flush in annulus.

95.32 ftxO.00387 bbl/ft=0.37 freshwater flush in tubing.

Annulus volume 3Il-in. drillpipe and 12-in. hole (5,430 ' to 5.500 ft).

Annulus volume (in barrelsper foot) equals volume of 12-in. hole (barrels per foot) minus volume of3' Il-in. hole (barrels per foot):

0.1399 bbl!ft-0.0119 bbllft=0.128 bbl/ft. Barrels of flush between 5,430 and S.500 ft ="(S.SOO ft- 5.430 ft)xO.128 bbl/ft=8.96 bbl Calculate the remaining flush that will have to be balanced. Total flush minus flush used with 2Y.-in. annulus work string equals remaining flush for 3'h-in. drillpipe inside 12-in. annulus: 30bbl-12.8bbl-8.96=8.24bbl freshwater flush in annulusbetween 3'll-in. drillpipe inside 9'h-in. hole.

Fill-up factor (feet perbarrel) 3'h-in. drillpipe inside 9'h-in.hole= 13.1976ftlbbl (handbookvolumeandheight between casing. drillpipe. and hole):

13.1976 ft/bblx8.23 bbl=108.62 ft. (70 ft+ 108.62 ft)xO.00742 bbl/ft

= 1.33 bbl freshwater flush in drillpipe. Total freshwater flush=annulusfreshwater flush+2%-in. freshwater flush volume+ 3'll-in. freshwater flush volume.

Total freshwater flush volume=30bbl+0.37bbl+ 1.33 bbl=31.7 bbl.

4. Freshwaterrequirements. Mixing waterpersackof Class A cement at 15.6 Ibm/gal=5.2 gallsack.

Mixing water equals water-per-sack factor times total sacks:

5.2 gal/sackx266.24 sacks= 1.384.448 gal. Mixing water= 1.384.448 gah-42.00 gallbbl=32.96 bbl.

Total freshwater flush volume=31.7 bbl. Cleanup or washup=20 bbl. Total fresh water=32.96bbl+31.7bbl+20bbl=84.66 bbl.

5. Displacement volume-capacity of mud behind spacer and cement. Displacement footage equals total work stringdepth minus (height ofspacerplus height of cement with work string still in the plug):

6.000 ft-(95.32 ft+70.00 ft+ 108.60 ft+404.68 ft)

=5,321.38 fl. Capacity factor: 3'h-in. ElJ, 13.30-lbm!ft drillpipe= 0.00742 bbl'ft. Displacement volume equah C:Jpaciry factor of work string**timc~** displJcemcnl foolJgc**rninlJ~** O.007·C bbliflx**S,3~** 1.38 ft'39Ag bhl. -.-­

5 - 355.6 IMPORTANT POINTS SELECTION OF CEMENTING PROCEDURES 1. CEMENT MIXING PROCEDURES


### o Importance of proper mixing Proper proportions Predictable properties
o Mixing water from purest available source Potable water recommended Clear water suitable
o Mixing Methods Jet Recirculating Batch Bulk
2. CEMENT PLUG PLACEMENT METHODS


### o Balance method a Cement retainer method a 

### Two-plug method o Dump bailer method 3. PLACEMENT OF MULTIPLE PLUGS
a 

### Most jobs require multiple plugs a 

### Each plug should set before next plug is placed (8 

### to 24 

### hours) a 

### Should tag plug to verify location and setting a 

### Recirculate plugging fluid before placing each plug (static condition) a 

### Repeat procedure for each plug
4. TOOLS AND MATERIALS TO ASSIST IN PLUG PLACEMENT
a 

### Scratchers a 

### Centralizers o**Chcmic~ll** 

### ....**'ashc·~;** a**Spaccr~::;** to pr(·vent contamination

5 - 365. GUIDELINES TO ENSURE CEMENT PLUG QUALITY


### o Circulate the hole sufficiently.
o Use wellbore fluid having a low yield point, low plastic viscosity, and sufficient weight.
o Establish and maintain static well conditions.
o Place cement plugs across a competent, hard formation.
o Precede the cement slurry with flush or spacer. o Use a low water ratio cement (API Class A, C, G, or H)
. o Use the tools necessary to minimize contamination.
o Carefully calculate cement, water, and displacement volumes.
o Place the cement plug with care, withdrawing pipe from plug slowly to minimize contamination.

5 - 376.0 REFERENCES Alguire, Samuel L. "Why a Need Exists for More Uniform and Proper Plugging Methods of Abandoned Wells," Minutes from itA symposium on Plugging to Abandon ll Michigan Department of • Natural Resources. 1973. American Petroleum Institute. Glossarv of Oilfield Production Terminology. Washington, D.C. 1988. American Petroleum Institute. The Language of Energy: A Glossary of Words and Phrases Used in the Energy Industry. American Petroleum Institute. Specification for Materials and Testing for Well Cements. API Spec. 10. Washington, D.C. 1988. Barkis, Bruce. Open-Hole Cement Plugs. World oil. 1952. Booz, Allen and Hamilton, Inc. Development of Procedures and Costs for Proper Abandonment and Plugging of Injection Wells. Prepared for u.S. EPA, Washington, D.C. 1980. Bradford, Ben, C.M. stout, and G.A. Massick. "Problems to be Overcome in Setting Cement Plugs," Minutes from "A Symposium on Plugging to Abandon". Michigan Department of Natural Resources. 1973. Clark, J.E., M.R. Howard, and D.K. Sparks. "Factors That Can Cause Abandoned Wells to Leak as Verified by Case Histories from Class II In-jection, Texas Railroad Commission Files," Proceedings**fro~** "International Symposium on Subsurface Injection of Oilfield Brines". Sponsored by UIPC and USEPA. 1987. Dowell Schlumberger. cementing Technology. London, England. 1984. Engineering Enterprises, Inc. SurveY--QJ'**~j:._.?_t_e ,Cl,<;l~.-lJ**  __**,1JI~** Programs

- Plu99.i!l9....E.D9.AbangoTJ.JJ1£nt

___

### LQLgf.tJ

. Prepared for U.S.EPA, Washington, D.C. 1988. Envi ronmenta 1 and Ground \'1ator Institute. proc0.cd i ngs .

### .9J ,tho E

irst

__l'Is-:!t.i .**.9J}S~<::'_ClD f!?XQJ}~_o:...** _.0.fL_?b<lo<iClnC(j , ..**,\~i' 11~,~** :__ Prob1er:l**~-;**.._illlS:i**;;.9_1~t.i** ,0n**~2.**• Presonted inc 0 0p0 ration with t h (' lJ. S. 

## r:P A {\!ld the National Water Well**A~~ociation.** ]9R4. Cass, Tyler E., -J,IY H. Lehr, and Ililrolcl i-J.**I!(~i!:!;,** .Jr_ Ndt ional \'/i.1ter Wc'11**k:;!C~ociation.** Inp,\C't of ,\hlnclnl1('d \,:,,11:: nn Cl[)Ul1d 1 (3F/ • GeraCJht Y & r·l ill f'r, Tn r . 'j'f'(-hrli(':11 H,II1U.ll Inj,'ct l()n \·/,'·11 Ah:1n d()n:'" ' nt. 1'1 ,.P" !-c·d 1 (Jr,-**tj.~~~** 1-:1'j\,**h·d:~.hln(Jt(~f1,** D.C'.**1(j/~~'1.**

6 - 1

### Gillespie, AI, Norman Tschirley, and Russell Duke. "Properties Needed for an Effective Plugging Fluid," Minutes from "A Symposium on Plugging to Abandon". Michigan Department of Natural Resources. 1973. Greenfield, Lou and Jack Cain. "Mud Treating Chemicals and How They Affect Cement Plugs," Minutes from "A SYmposium on Plugging to Abandon". Michigan Department of Natural Resources. 1973. Herndon, Joe, and Dwight K. smith. Plugging Wells for Abandonment - A state-of-the-Art Study with Recommended Procedures. Union Carbide Corp., Nuclear Division, Oak Ridge, Tennessee. 1976. Moseley, Neal F. "Advantages and Disadvantages of using Cement, Cast Iron Plus Cement, and Cement Retainer Plugs in Plugging to Abandon," Minutes from "A Symposium on Plugging to Abandon". Michigan Department of Natural Resources. 1973. Petroleum Extension Service. A Primer of Oilwell Service and Workover. University of Texas at Austin. 1979. Scott, John. "Completion Technology Includes Plugging, Too,H Petroleum Engineer. 1971. Smith, Dwight K. Cementing. Monograph Series, Society of Petroleum Engineers of AIME. Volume 4. Dallas, Texas. 1987. Warner, D.L. and J.H. Lehr. An Introduction to the Technology of Subsurface Wastewater Injection. EPA-600/2-77-240. 1977=

() - 27.0 GLOSSARY - A ­ abandon: to cease efforts to produce oil or gas from a well (or inject fluids into a well). See "temporary abandonment" and "permanent abandonment". accelerator: a material which accelerates or speeds up the normal rate of reaction between cement and water, resulting in an increase in the development of early strength, and, in some cases, a decrease in the setting time or thickening time. annular: referring to the annulus. annular pressure test: a test method used to demonstrate the mechanical integrity of casing, tubing, and packer in a conventional well configuration. When using the test, tubing and packer are set inside the casing string to be tested. Pressure is then applied to the liquid-filled casing/tubing annulus for a specified period of time. If a significant pressure drop occurs during the test period, then one of the well components (casing, tubing, or packer) is leaking. annulus (or annular space): the space surrounding one cylinder within another cylinder. This term can refer to the space around
a**!"c~C'ction** of pipe within a larger pipe or borehole (c.(j. the lonq ;.t r i n 9 annu 1 u**~.~ i~;**  the 5 pace b C' t '.' p ('nthe 10n q**~;**t 1- i n q and t h(.**~;urrolll1d** ing borehole)
.

"l - 1

### - B ­ balance method (cementing): involves the pumping of a desired quantity of cement slurry through drill pipe or tUbing until the level of cement outside is equal to that inside the string. The drill pipe or tubing is then pulled slowly from the slurry, leaving the plug in place. bit: cutting or boring element used in drilling operations. borehole: the hole made by drilling or boring a well. bridge: restricting objects placed in the well to provide an obstruction upon which cement plugs may be set. bridge plug (BP): a mechanical plug which is run inside casing
or tUbing for the purpose of isolating or sealing off a zone from the upper section of the well. brine disposal: the practice of disposing of highly saline waters produced in association with oil or natural gas. brush plug: restricting object (brush) placed in the well to provide an obstruction upon which cement plugs may set. bullhead pumping method: cement placement method by which cement is pumped direct1 y into the casineJhcCld
.

-; - 2

### - c ­ cable-tool drilling: a method of drilling in which a weighted bit at the bottom of a cable falls against the formation being penetrated, thereby using a percussion action to break the rock. A bailer is used to retrieve the rock particles from the bottom of the hole. caliper log: a well log which measures hole diameter. Also called a "section gauge," the multi-armed tool measures the corrosion of casing and tubing. cased hole logging: refers to any log run to determine characteristics in subsurface zones already confined by casing; to determine well conditions, especially of cemented or perforated intervals; or to determine the condition of the casing itself. casing: pipe, usually steel, used in oil wells to seal off fluids from the borehole and to prevent the walls of the hole from sloughing off or caving. API 

### casing sizes range from 4 1/2 

### in. 00 to 20 in. 00 inclusive. casing inspection log: a cased hole log which utilizes induced electrical current to detect corrosion or other damage in casing. casing roller: d 

### rugged tool composed of i1 

### I:),Hldrc'l ,'lith 

### a**~,l'ri(':~** o f ('C C e nt 

### ric r 0 lIsu r f tIC C s, (>d C h 0 f ",'h i C'h 1:; d !', :**~**c' rlh 1('d ','; i t 11 iI !;e r .i c s 0 [ h (' ,I V Y - dut.y r 0 lIer-:; . 

### buc}:led,**collap:~cd,** or dcforrlC,d ca:;itHJ. 1\ Cd:; i nq r 0 1 1('r i: ; t \l II

"1 - 3on tubing or drill pipe to the depth where casing lS deformed, and is rotated slowly, which allows the rollers to contact all sides of casing. casing shoe: a short, heavy section of steel pipe with a rounded bottom that is placed on the end of a casing string to assist in guiding casing into the hole. For purposes of this paper, this term refers to the bottom of the casing string. casing stub: uppermost portion of casing, remaining in hole subsequent to cutting and pulling upper section of uncemented pipe.
cast iron bridge plug (ClBP): a mechanical plug composed of cast iron which is run on wireline inside casing for the purpose of permanently sealing off a zone from the upper section of the well. A CIBP must be drilled out for removal.
cement dump bailer: a cylindrical container with a valve that is used to release small batches of cement downhole.
cement evaluation log: a cased hole log which is used to measure cement quality. Cement evaluation logs consist of two major types: the cement bond log (eBL) and the cement evaluation tool (CET)

. The cement bond log (CBL)**measurc~:;** the general e:..:tcnt oj cement and**it~;** bonding quality throuCJh the induction of**<lcoll~;ti('** signals and obscrvati.on of**o;iqll~ll** re"poli:-,C' dt it**p<l~;~;t'~;** thrOtlCjh ('>:isting medium (e.g. fluid, pipe, ceI:1cnt, ,ll1d fOl'lll"tiol1). Till' cpmc-nt evaluation tool (eFT)**u::;e~.;** d di t jC'rC'nt**mC'iI:-,llr-l'j~l(,llt**

7 - 4

### principle; the CET uses a pulse of ultrasonic energy to investigate the cement radially and measure cement existence and quality, casing diameter, casing roundness and tool eccentricity. It is able to provide data which the CBL 

### cannot provide.
cement 

### plug: a portion of cement placed at some point in the well to effect a sealing action.
cement retainer: a tool set in the casing or well during squeeze cementing and other remedial cementing jobs. The cement retainer tool is run on tUbing and allows the passage of cement when valves are open. with tubing removed, the valves close, preventing the passage of cement below the tool.
cement retainer method: a method of cement placement by which cement is pumped through open valves of a retainer tool and into the hole. The tool is then set and the cement is forced by pressure into the exposed formation. Upon removing the tubing from the tool, valves close and cement can no longer pass through the tool, but is emplaced on top of the retainer, forming an additional cement plug.
cement slurry: the plastic fluid which IS 

### produced by the mixture of dry cementing materials with water. cementing plugs: pluqs which arc US('cl durinq cemellt inc; 

### operations . The rca

### resev ('

### rdIdi**~~**

### tinc

### t l YP('**~;** 0 f c (' ;:1('tlt 1 nq IiJuCJ**~ ~**  • 

### Thoy arc used 

### to : p r () cos S (('. q. mud, c ('m0 nt, dispIaC (' 171 c'nt 

### r 1 u i d' etc.);**(:~)**

7 - 5

### clean casings of fluids or particles which can contaminate cement; and (3) provide a seal or shutoff so that fluid cannot bypass the plug. centralizers: guides which are attached to the outside of the casing and which serve to keep it centered in the hole. Centralizers are also used to maintain proper centralization of cased hole logging tools. circulation: refers to the process by which a fluid is moved from and back to the same point (e.g. from the surface, through the wellbore, and back to the surface). compressive strength: the degree of resistance of a material to force acting along one of the axis in a manner tending to crush it, usually expressed in pounds of force per square inch of surface affected. confining zone: a geological formation, group of formations, or part of a formation that is capable of limiting fluid movement above an injection zone. conventional completion or operation: an injection well construction type having cemented surface casing, cemented long string casing, and injection tubing and packer which arc set 

### above the injection**interv~l.** 

### In a conventional operation, fluicL; arc 

### inject.ed thr-ouqh the injection tubinq and 

### into the' 

### inject.ion zone. This**i~;** 

### the prcdominillll ",,'{'II**con~;trllcti()n** j()!­ i nj e c t i 

### on we 11**~;** 

### .

7 - 6crossflow: 

### refers to the movement of fluids from one zone to another.
- D ­ dehydration: 

### removal of free or combined water from a material. densimeter: 

### an automated device used to weigh drilling fluids and oilfield cements. The densimeter is installed in the discharge line between the mixing unit and the wellhead, and continuously records fluid weight throughout the operation. dispersant: 

### a cement additive which reduces the initial consistency of slurries. dump-bailer: 

### a cylindrical container with a valve that is used to release small batches of cement downhole. dump-bailer method: 

### a means of slurry deposition or fluid displacement usually in association with cementing or completion work.
- E ­ enhanced oil recovery: 

### injection of water, steam, gases or chemicals into underground reservoirs to cause oil to flow toward producing wells, thus permitting more recovery than would have bee n pos sib1 c from nat 1..1

### r alp ressure 0 

### r p II

### m pinCJ 

### a 1 0 n('
.

7 - 7- F ­ fishing: operations for the purpose of retrieving pipe, collars, junk, or other obstructions from the wellbore. fishing magnet: a powerful permanent magnet designed to recover metallic objects lost in a well. flocculation: the coagulation, coalescence or aggregation of finely divided suspended particles. fluid density balance: a portable device which measures the density of a cement slurry under sufficient pressure to compress entrained air. It is believed to be a more accurate than when the cement sample is taken directly from the mixing tub. formation fluid: a fluid that naturally occurs in an underground geologic formation. free point indicator tool: a tool designed to measure the amount of stretch in a string of stuck pipe, thereby, indicating the deepest point at which the pipe is free.

- G - gel: a term used to designate highly colloidal, high-yielding, viscosity-building commcrciQl clays, benton i tc lind nttnpulgitc clays. gelled water:

7 - 8

### - H ­ hopper: a device used to hold or feed fluid additives (e.g. dry cement and additives). hydration: the chemical reaction between hydraulic cement and water forming new compounds most of which have strength-producing properties. hydrostatic equilibrium: a static state (e.g. no fluid movement)
. hydrostatic head liquid. Hydrostatic head is commonly expressed as "feet of liquid."
- I ­ injection fluids: fluids injected via a well into an underground geologic formation. injection packer: the device on the end of the injection tubing which, when set, isolates the injection fluids by forming a seal bet weenthe inj e c t ion tubi n g / casing wall 0 r inj e c t ion tubing/borehole wall, while still allowing fluid movement to
occur through its internal opening, or bore. In cilsing, packers
are generally retrievilble. In open holo, pilckcrs ilrc generally pcrmilnont installations. See "packer". injection string: the entirc· lC'nqth of trw tllhinq or**C"~·.lnq** u:;(·d to inioct fluids into a well.

7 - 9injection tubing: small diameter pipe used to inject fluids into
a subsurface formation. injection zone: the geological formation into which fluids are injected.
interformational flow: refers to the movement of fluids from one formation to another. intermediate casing: the casing string between surface and long string casings frequently used to support and seal off problem sections encountered in a wellbore while drilling.

- J ­ jet cutter: a tool used to sever pipe in a well. The tool
severs the pipe through detonation of a specially shaped explosive, which generates horizontal cuts around the pipe. jetted water: water forced through a "jet" or port. junk retriever: a cylindrical tool used to retrieve metal debris lost in a well.
- L ­ leaching: a process by which soluble materials are removed through contact with a liquid (e.g. wilshiny out). liner: i nthi spaper,refers t.0 il part j ill 1('n(J t h P 1P(> !.-; t r i 11CJ ext('ndinq fro 1':1 the bott 0 r.1 0 f t hc· b U 1 d101 (' t 0 i1 II (' 1 \ .\' ,It j CJ II ,II)()\' l ' the b CJt t 0 r.1 0 t the prev i 0 U**!~** Ca"i nCJ :;t r in(J •

7 - 10

### zones and water bearing formations. A liner mayor may not be cemented in place. Although not used as such in this paper, the term "liner" may also refer to a smaller diameter casing run inside of existing casing, extending from the surface to the top 

### of the productive zone. It mayor may not be cemented, and is frequently run when the existing casing string develops leaks or mechanical problems. liquid hydrocarbon storage: the storage of hydrocarbons (which
are liquid at standard temperature and pressure) in porous underground geologic formations. long string casing: the casing string that runs from the surface to the total depth of the well (or to just above the target zone, if an open hole completion). It is generally referred to as the injection or production casing, and normally contains injection tubing and packer, or production tubing. lost circulation: the loss of quantities of fluids to a formation, evidenced by the complete or partial failure of the fluid to return to the surface as it is being circulated in the well.
- M ­ 

### Marsh funnel viscosity: COr.1:TIon 1 Y C,l] 1 cd the 1 unnt'] visco:; i t y.
required tur a 

### given f]uid to ! lOT,,' 

### iu n n (-, ] .

-; - 11

### mechanical integrity: an injection well has "mechanical integrity" if its state of repair is such that no significant leaks are present in the well's tubing, packer, or casing; and there is no significant fluid movement into a USDW through vertical channels adjacent to the injection wellbore (e.g. cement)
. 

### mechanical plug: a plug which is generally run inside casing or tubing for the purpose of isolating or sealing off a zone from the upper section of the well. 

### milling: the process by which a mill is used to cut or grind metal objects in a well. A 

### mill is a downhole tool with rough, sharp, extremely hard cutting surfaces. 

### mud: a fluid circulated through a well during both drilling and remedial operations. Mud is composed of liquids and solids and is used to: (a) cool and lubricate the drill bit, (b) suspend formation cuttings for ease in bringing them to the surface, and (c) provide a hydrostatic fluid column which can be "weighted" to assist in pressure control and stability of the wellbore. See 

### "gel". mud balance: a balance used to measure fluid density. In u::,ing
a mud b,llance during cementing,**:;ample~~** arc**~_;clcctiv('ly** tilkt'n 

### fro m the 

### mixi n g tub and 

### v ibrat C'd torC'm0 vc' 

### any fin c' Iy C' nt 1- d PIi(;d air**buhblc~--;** frOT:1 

### the mlxc:r.

7 - 12mudcake: the solid material deposited along the wall of the hole resulting from filtration of the liquid part of the drilling fluid or cement slurry into the formation.
- N ­ noise log: a cased hole log which measures the borehole audio signals caused by the flow of fluids.
- 0 ­ open hole: portion of the well in which casing has not been set. overshot tool: a fishing tool which is attached to tubing or drill pipe and lowered over the outside wall of pipe lost or stuck in the wellbore. A friction device in the overshot firmly grips the pipe, allowing the stuck pipe to be pulled from the well.

- p ­ P&A - abbr: plug and abandon. packer: downhole equipment consisting of a sealing device, a holding or setting device, and an inside passage for fluids. It is used to block the flow of fluids through the annular space between the tUbing and the borehole wall (or bctwcell tubing and casing) by sealing off the space between them. paraffin: a wax-like**sub~;t(lnce** 'which is**d('po~;itc'd** troD ;,DDt:' crude cd**l~; ;I~;**  they flo',o; throlHJh till'
....**'(,llb(Jn~.**

7 - 13

### perforations: holes which are shot in the casing string either for the purpose of producing fluids from, or injecting fluids into a formation, or for the purpose of performing remedial cementing operations. Holes are formed in the casing by a perforating gun, which is an explosive device utilizing bullets
or shaped charges. permanent abandonment: to place cement plugs across critical
zones in a well to abandon it. permeability: a property of geologic formations whereby fluid movement can occur through the pore spaces, fissures, and or fractures in the rock. plastic viscosity: a measure of the internal resistance to fluid flow attributable to the amount, type, and size of solids present in a given fluid. plug and abandon: See "permanent abandonment". plug-back: to place mechanical and/or cement plug in or near the bottom of a well to isolate a lower zone from the upper portion of the well. plug-back total depth (PBTD): 

### the depth at which the well is pI

### ugcJcd back. potable water: WQ

### ter suitabI c to

### r drinking or coo}; j neJ pllrpu:;(':', 

### from both h0alth and 

### ile:;thetic cOll::irl\·I.ltions. 

### production casing: ::c(' "long string casing".

7 - 14- R ­ radioactive tracer survey: 

### a survey commonly performed in injection wells to monitor the movement of injection fluids in the wellbore. The tool injects a slug of radioactive material into the injection fluid stream and, through detectors on the tool, traces its movement throughout the wellbore.
reservoir: 

### a subsurface porous and permeable rock body that contains oil and/or gas. Most reservoir rocks are limestones, dolomites, sandstones and/or a combination of these.
retarder: 

### a chemical which is added to cements or slurries to lengthen thickening time.
retrievable bridge plug (RBP): 

### a retrievable mechanical plug which is run inside casing or tubing for the purpose of isolating
a zone from the portions of the well above the zone. A RBP is designed so that it can be taken out of the well with ease. retrievable packer: 

### a packer which, after set, can be retrieved from the hole by reversing the setting process. Most packers used in conventionally completed injection wells are retrievable. Sec "packer".

reverse circulation: 

### a**procc,~~~** 111 

### which the norn);ll**cour~;('** uf 

### fluid circuliltion is 

### reversed. I!1 n'vc'**r-~;**e c ireu 1 d t i ()n , 

### fluid 1 ,­ .' p u m pcd dll".'.rn 

### the IInnul II" 

### lind up d IIdOllt () f t 11 C' t 

### ul) i

### n q u ! 

### P1I)j , .

7 - I!>

### rotary drilling: the method of drilling wells that depends on the rotation of a bit attached to a column of drill pipe to cut the rock. A fluid is circulated to remove the cuttings.



### - s ­ sack: standard package for cement (94 

### lb. of dry cement). This term is used informally as a measurement for the amount of dry cement used to mix a cement slurry_ scratcher: a device fastened to casing which aids in removal of mudcake from the annulus while the pipe is being moved during the cementing operation.

screen: a well screen serves as the intake section of a well. The screen is a pipe with small holes or slots that allow fluids to enter the well, but prevent or minimize the entry of sand particles into the wellbore. secondary recovery: any method by which an essentially depleted reservoir is restored to a producing status by the injection of liquid or gases into the reservoir. This process produces energy, which enables the movement of reserves through the reservoir and to the producing wellbore. shoot off: refers to tubing or casing severance. This 

### can be performed by: ((1) an 

### explosive chdrqC' or (b) a Ch('r:lical ',:hieh 

### "cut**~~"** the me>LIl
. 

### shut-in: toe 1 0 ::, C' ,I 

### valve, 0 r**!~**h \ltot

## tar\Ir:1

## r t 0 ( , C'd : :C' i n j t.-, ( •t i Cln 

### into, or' prod\lction fn)J':1 a 

### well.
7 - 16slurry: suspension of solids in water, oil or mixture of both. slurry yield: the volume of slurry which is produced from one sack of cement (e.g. 1 sack of Class A cement mixed with 5.2 gallons of water produces a slurry yield of 1.18 ft3 of slurry/sack of cement).
spacer: a fluid which is used to separate two incompatible fluids, while being compatible with both.
spear: a tool used to retrieve pipe lost in a well. The spear is lowered into the lost pipe and, through a series of mechanical movements, grips the inside wall of the lost pipe; enabling its retrieval from the well.
squeeze cementing: a remedial cementing operation in which pressure is applied to "squeeze" or force cement into or against
a formation through holes or perforations in the casing string. static fluid level: the level to which reservoir fluids rise when the well is shut-in. This fluid level can be used to estimate the reservoir pressure. See "fluid level". string: refers to the entire length of casIng, tubing, or drill pipe (e.g. the casing string, etc.). surface casing: thc first strirH] of**ca~;incJ** to be set In a ","'cll. Its principal**purpo~;e** is to protc'c:t**lrl'~~h** ,,'dtc-r :-;,111<1:;. swaging tool:

7 - 17

### - T ­ TA - abbr: 

### temporarily abandon
TDS - abbr: 

### total dissolved solids temporary abandonment: 

### to cease operations on an oil or gas well without permanently plugging. Some wells are "temporarily abandoned" by shutting the well in. others are "temporarily abandoned" by subsurface equipment removal and surface valve shut-in, etc. Future considerations for the utility of the well often contribute to the decision to delay permanent plugging and abandonment. temperature survey: 

### an operation to determine temperatures at various depths in the hole. The results of the survey are often used to identify suspected fluid entry into the wellbore. tertiary recovery: 

### a term which refers to enhanced oil recovery methods other than waterflooding, especially when steam, gases, or chemicals are used to provide the recovery mechanism.
total depth (TD): 

### the maximum depth reached in a well. tubing: 

### small diameter pipe run in a well to provide a conduit for the injection or production of fluids.
tubular 

### goods:**~ny** 

### kind of pipe. oi 1 

### field tubular gomb iIWl wk 

### tubing,**ca~-;** i nC], 

### drill pipe, and line pipe.

7 - HItwo-plug method: a means of placing a plug with less likelihood of overdisplacing or contaminating. Wiper plugs are run above and below the cement slurry. A plug catcher tool, run on the bottom of the string, seats the top plug and indicates that the cement has been placed at the desired depth.



### - u ­ uncased hole: that portion of the well which is not covered by a string of casing. unconventional completion: any completion type that does not conform to a conventional completion type. See "conventional completion".
- V ­ viscosity: the internal resistance offered by a fluid to flow. This phenomenon is attributable to the attractions between molecules of a liquid, and is a measure of the combined effects of adhesion and cohesion to the effects of suspended particles, and to the liquid environment. The greater this resistance, the greater the viscosity.


## - w ­ water loss: the volume of water filtrllte**lo~t** to the perr.wilble material due to the process of filtrdtiun. waterflooding: one r:wthod of enll,II11'(·j tt'c'uv,'ry in ,</llic'h ',:,It "t" 1:: injected into an oil reservoir to pLl!:.h ddditiolldl oil throucJh tIll' re:,ervoir rock ;tnd into the proc1u(-illq**'~;i'llhClt'I'::,**
7 - 19wellbore: 

### the hole drilled. This can refer to cased or uncased holes. wiper plug: 

### a rubber device which fits the internal diameter of
a pipe string and is used in cementing operations. When inserted ahead of cement, the wiper plug wipes drilling fluid off the internal casing walls to prevent cement contamination. When inserted after the cement, the plug wipes cement off the casing walls and lands in a special fitting, which provides a surface pressure indication that the cementing operation is complete. wireline: 

### a slender, wire-wrapped electric line used to run equipment and tools in and out of a well. A wireline is generally 3/8 in. to 3/4 in. in diameter and is frequently used for well logging, perforating, etc. workover fluid: 

### fluid used during workover operations (e.g. circulation or drilling fluid used during remediation).

- y ­ yield point: 

### thc resistance to initial flow, or the stress rcquired to initiate fluid movement.

7 - 20