& 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, 1989 

TABLE 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 	 GLO S S 1\R Y • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• 7 - 1 
TABLE 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 

Reta iner 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) - 14 
Acknowledgments 

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 pro f c s s ion i1 lor9 ani z a t ion ~; [ 0 r the ire Cl n t ri lJ II t 1 0 n ~; t 0 

available technical literature, ".. bieh Wtl~; uti 111.f'ti ('xt"n~;ivcly lrl 

prepdrinrJ thi~; CJuidance document. 

iv 
1.0 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 11 9 0 finj e c t ion well s . A 1 thoII (J 11 t 11 e UTe n°(J II ];I U () 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 aCemen t ~; 1 u r l' . Y ; 

((,) Proper CeI:lcnt Mix i ng 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 d van c e s h a v c ~; inc e bee n mad (' j n p 1 u 9 Cj i n Cj i\ n d II b d t1 don 1:1 c n l 

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

pI ugg i 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 - 2 
2.2.1 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 - 3 
2.2.3 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 - 4 
2.3 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 - 5 
3.0 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 con d i t ion s ; ( 2) r em 0 val 0 f tub i n g, pac k e r, 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 

prep d rat ion, aft(' r we 11 Tn- c P ~l r (I t ion, <Illd .I r t L' r we 1 1 P 1tlq q i n q d n d 

j ina 1 abandonw·nt. 

3 - 1 
Cement Plug 

, . ..., 

L:. USDW Ba se : Bas'e :',. 

Pl ug. 

Fl uid Pl ug. 

Fl uid 

Open Hole ., "". ..... ... • to • .,

.... "....... ~.. .." .. 

Plug. 


Fl uid 


Stub of Cut-off 

Casing 

Bridge Plug Capped 

with cement 

~ . \ ceme nt '-:-:-:­ ... , .' . 

WELL PREPARATION AFTER PLUGGING AND ABANDONMENT 

• 

•

• 

.. 

.. 

. 

••• 

Cement Plug 

Potential 

Producing 

Zone 

Cement Plug 

Bridge Plug 

Capped with 

: -:-:-:- H 

~b •.., Injection Zo·n~ . ~ ;Iljection Zone ; 

c: ~~ :::: • ~erfora t ions

rr:: 

w --_

~ ....---:-ota1 Depth 

t-' 

• 4 .. 

P1ug. 

F1 ui d 

........ .. : ...., .. ". Cement Plug . ". . ".. .. ,/' ...... 

3~=JRE WELL PREPARATION AFTER 

·, .

• ·. t..:.r.s- Primary Cement · •

• 

.. ~. 

•· • · . . . '... " ~ .... , ,', 

.• • 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" 

• • r .. 9' •

01 Primary Cement "91: .... 

.. 

•0, .. 


"USDW Base"', '. 
 USDW Base:" ': -"-". . " 

.. Surface Casing 

• 

a 

• 

Plug. 

Fl ui d 

, L', ~ 

.. 

• 

Primary Cement A

1.01

1.01

.. 

• 

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

, Perfora t ions 
 ~.J ~otal Depth 

..~·I. 

<II ~ , • 

• 

.~~ f~Cement Plug 

1- . • _~. {A+ L~' U'S~W ;-sase '.:':" 

Cement Plug 

.r­ • '-;" 

Plug. 

Fl ui d 

Plug. 


F1 ui d 


Cement Plug 

" 

Injection Zone 

w~LL CONSTRUCTION TYPE B 

STAGES OF ABANDONMENT 
• 

ry Cement • 

- . ~J Base.:' .. '.

e Casing 

tion Tubing 

.. .. ~ .. .. 

.. • 

.. .. .. • 

.. . j>. '" .. ... .. ."

.. ..~ 1-'---------­ ,·.L. USDW Base~

~ 

.. .. 
 .. .. l..... WI!I 

Plug.

Fluid 

-s- Open Hole 

.. • .,. 6 .. • .. .. .. j... ~ ~ .r.- Cement Plug .. ... ..

•

.. Plug . .. \0 .. .. • Fl ui d .. . . .. '.'" ..... .. 

:.: .. , ..... •... L. USDW Base.·.· ~ ". .. ...... .. -________~__"__ ...... ·Ir 4 .. "of... ~.t C t P 1 ... ......'_ emen ug I." ...... -~<+----' ,. •• 4 

Plug. 


Fl ui d 


. "" ,. ., 


----

SE~C~E ~ELL PREPARAT:O~ 

. t · ... 

•~ 

~ 

\ot · :...~ 

· • 

• 

.. 

. ~ · 

· 
 t..II 

.. 

H--­

c: 

:r;l 

M 

Prima

I 

L. • USD

I. _Surfac

__+--- Irjec

Sorehole 

I 

I 

! 

i 

K)(~,....,~k:~·~-:njection Packer 

.. :rject'ion Zone 

Onen Hole 

AFTER WELL PREPARATION AFTER PLUGGING AND ABANDONMENT 


). ......... 


..... . . 

-. . '. ., : 

Injection Zone 

....... .., ..... ~ . .... -.....~ Cement Plug .. ,," 4 • 


.. 4" • ..
 .. .. ...... , 

Plug. Potential 


Fl ui d Producing


Zone 


1- ....... .. 


~ a A..... : 

•• " f Cement Plug ..... ,"'--~­

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. 

Con s t r u c t ion de t 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 

perfor m sue11 con~; t r u c t i 011- r e 1 atedinv c:; t i CJ ;\ t ion~; ~; 11 0 II 1cI b C' r.l ,I d 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 n dun n c n t and Cd ni n h i b j t dow n h 0 1C' il C t 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,'; (\) 

s tand pipe i nthe d C' r ric k; and (.~) c i n:: II l.1t f' !] u i d ( :: ) t h r () l j(J h() \l t 

t h f' ',.,',. 1 I b () r C' (Pc t r 0 1 (' \l !:l F x t (' 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 pI ug-sett ing act i vitie s, depending on the spec if ic 

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 - 11 
Well 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 too 1 to 

engage the pipe ( G c r Ll g h t Y and Hill C 1-, J n c ., ) C) 8 ;:» • 

3 - 12 
Recovery 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 1eak i ng sect ion of casing. Hycl r,Hll i c prC':~:;u rc j~; then app 1 j eel 

to force t,hc~ ~';lllr-ry again~;t and into C'xr0:,ccl forni1tion:;. l\~', 

m(' 11 t i 011 cdC' d r 1 i c' r, ;. q \l e e z c c c' ;n(' n tillq r.l d y d 1 ~", 0 b t.' J,'e 1"":1 L' 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 - 14 
A 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 

remova land remed i a I opera t 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. 

Stat i c we 1 1 cond i t ions arc c;; t a h 1 i:~ h (~d bye 0 n t r 0 1 1 i!lCJ any 

flow, either into or out of the well. h'hC'11 a v.'c II i~; CCJI~lP 1 etc-j y 

" , 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 .I t 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 n d p II r p 0 ~~ C 0 fanc W 1.-1 c' 1 ] b () no' flu idsy ~ ~ t C [:1 P (' r t it in:; 

tC) ttlC concli t ion C)t ltlC [JOrell0J C \'Jd 1 l~: dnd tIlt: dli i 1 it ''/ ()1 t htl 

(:er.1cnt to bond tothe ho 1c' 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 - 17 

3.3 	 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 - 18 
3.4 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) ,1 h 0 v (". t h C' 1 0 ',~' C' n~1O:; t 

prod II C t ion and / 0 rillj C' c t 1 0 n Z 0 n e ; (?) d h () '/ c', h (. 1 (J ',,', d !l d / () r 

3 - 19 

through 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(" p1 uq:: 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 n t a i n i n g s tat i c ,",' (> lIe0 nd i t ion S Fl rio't' t U d n d d uri IHj p 1 U CJ 

r; 1 u r r y and b 0 r c h ole f 1 II i d!;; and (3) c 1 c' d n i rt (J C d ~:i IlCJ d n d / () r 

bun-110I(· !;ur'face~; pried' t () pluq plac('·mc·nt. 

3 - 21 
3.4.3 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 - 22 
3.5 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 - 23 
4.0 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 

rna tori a 1 between cement pI U(J:~ . 

.. - 1 
The 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 

d uri nCJ the p 1uCJ CJ i n 9 proc e s S, 0 1cl d r ill i n 9 mud md y b.' ( . Il ( . 0l1l1 t c' r co d . 

Man y c 11 C [:1 i Cd 1 ~ usedin d r i 11 i 11 (J mlllb (\ reor gall ie, d II d d ~; : ~. ud I , 

can be v (' !' Y de t rimen t {\ 1 tot h (' :'. (' t tinCJ propert i '-':: U f ,\ r C' 1:\(' n t 

slurry. 

.. - 2 

filtration 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(Jq inq 

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 

flu i d 1co V l' 1 i nthco well c han9 (' : ; Itt11' n Lltic e q u .i 1 i b ci II ;~1 h <t :-. n() t 

4 - 4 
been 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 ) 	 T11 e y can y i e 1 dimpro v (' d b u 11 din q c h a rae t (. t- i ~,; tic ~; and 

minimize damage to :-;lld]t,:; or bC'ntonite. ~;i\IlCl~; by tilt, 

addition of salt. 

4 - 5 
Class 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 

flu ids or high temperu tures that wi 11 f 1 a~:;h set cement) mllS t be 

cons ide red wlwn dc~:; ign i ng the c('mCI1 t !; 1 ul' ry . Tabl e:-; 4 -1 il nd 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 

sp e cia leon d it ion s s u c h u:; I 0:; t c ire ul a t ion <Ill d h i q h 

t l'mp<' r ;.1 t 1I n.':; . 

4 - 6 
TABLE 4-1 


COMMON OILFIELD CEMENT TYPES 1 


'IYPIOJ..C»'»r.'S: 

static Midng Slurry Slurry 


API AS'I)4 Well Depth Te!perature water Weight Y~eld r:.LM"-sif icat lrn '!'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 uni versal 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 mC' n t~. towh i c h the y c ;\ nbc add e d . 

ill u s t rat C' s t h c' (' 1. t (' C t s '!,oJ hie h <1 d d i t i v f' :; h a v (, 0 nthe ph Y!; j c.\ i 

prup('rt i Co!; 0 t CC::H·nt. 

4 - B 
TABLE 4-2 


SUMMARY OF OILWELL CEMENTING.. ADDITIVES (Smith, 1987) 


Type 01 Additove 

Accelerators 

Use 

Reducing woe 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 

lower volume 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 9 
TABLE 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 of Slurry Increases 

Decreases 

Early Strength Increases 

Decreases 

Final Strength Increases 

Decreases 

Durability Increases 

Decreases 

Conductor Casing 

Surface Casing 

Types of Cementing Intermediate Casing 

job applications-­ Production Casing 

Where mostly used Liners 

Sgueezing -.---.------. 

• For temperature 230°F 

X Minor 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 

:l,..... .2 ,...... -C II> ~ ... ex: " ~ c :; 0 :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 - 10 
4.3 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 - 11 
5.0 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 

propo r t ion .i n g and b 1 (' n ding the dry C C' f!H' n t i r1tj mIi t C' r i ;11:::; wit h t hI' 

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

propert i C~;. The ~~y:;t::(,f!l ~~hould include .In (ICCtlrdtc 1:1I.'dI1", o! 

5 - 1 

maintained, 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) recircul ating 

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 " han d - mix i n g " m(> thod ~; for P&,\ c (' :~l (. n tinq 0 p (' r- ,1 t 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 tJ t. r 0 ( ~ () nl rn C~ n d 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 

pl ug-placement techniques are the: (1) bal ance 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 Ii I n II \l:; to (l l:,11 l . \ 1 I ,It. ! • d h (. i LJ h 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 - 4 

PLUG 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 c pic t :; t lH' C (' r:H • n t p 1 de' ( . J~, ( . Il t 

procc'~s us i nCJ the cement-n:ota i 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 n t c~ r t II c' 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 Il 1 i IV] flu i d to 1 1 0,; 11.\ (" k 

into tho placomc·nt tuhing. ]1 neede'd, lh(~ tubill{J ciln th('n lot' 

r a i sod and revc r !eX' C ireu 1 ated t () C' ~ ; t d h Ii:',h the top 0 f t h t' C I.• ;:w 1\ t 

plue;. 

5 - 9 

.~ :.:~~ .~ .....: ..:: 'U 

.~--+-- Excess slurry, 

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

: 

ill....'---­~~ r~~~:~ent phJQ 

c 

~;?f~;-

[0:· .... ::."'V-,-4.---30"om plUQ

::;.• "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'h isme tho d 0 f P 1 u g P 1 acemen t (il 1 u"tril t (' 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, cae h 1 0 <l d 0 fcc men l 1:\ 1I ~; t b c' S to t 1I P P r i u r' t 0 

5 - 11 
Cump 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 

)< e d u c e d 11 e e d 0 f est a b lIsh 1 n g 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 - Idlr 
setting 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 fir s ttyperc f.1 0 V e s mud c a }: (> wi t h a rot ;1 tin CJ 

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 s1 urry 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 r y, and arc f r c q u (' n t ] Y u !~ C din con j \l I l(' t i 0 II \-.' i thec m(.' II t i 11 q 

5 - 16 

plugs (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 ti n<J on cement to !;('t, it i:; not ,\] ',-;, \ ';/:; 

fC(1siblc or przlctical to tile] ill} cement pluq::. 

on 1 Y day 1 i 9 h t h () U r!.; are w() d: c- d (1 n d the c co mC' 11 t !: (' t - \J P 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. 

PI ug 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 ·.

• 

· 

· 

~ .-.0 

· • 

•

• 

•

• 

• · • 

~ -­

.. .. .' 
..
 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 - 23 
Sample 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. 3Isk. 

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 - 24 
5.5.2 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) 

PLUG BALANCING 


When a cement plug IS to be spotted through 

tubing or dnll pIpe, it IS important to calculate the 

necessary volume of spacer to be pumped 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 

'balancing a plug' 

H 

FIG. 8.5 

Once a plug 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] = 

water ahead [bbl] x tubmg volume [cu ftlsk] 

annular volume [cu fVft] 

3) To calculate the heIght of the balanced cement 

column prior to pulling up the tubing 

slurry volume [cu fl] 

H(ft) = annular volume[cu fVft]+tubmg volume[cu fVft] 

4) 	To calculate the volume of dLSplacement fluid 

DISplacement ITUld volume [bbl] 

=(tubmg length - H) eft] x tubmg volume [bbUft] 

- water behmd from step 2 [bbl] 

As a general rule, it IS advisable to underdlsplace 

the quantity of cement down the tubing by a small 

amount (1/4 to V2 bbl per 1000 ft, depending upon the 

size of the tubular goods). 

EXAMPLE CALCULATIONS 

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

hole. 

- The bottom of the plug IS to be set at 6000 ft. 


- The cement is a neat Class G. 


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


will be used and 6 bbl of water will be pumped 

ahead of the cement slurry. 

- 20% excess cement is bel!eved necessary to 

allo\'/ for hole enlargement. 

1) 	Slurry volume requned 

o3712 eu fUft x200 ft x 1 2 = 89 1eu ft 

2) Sacks of cement 

89 1cu ft ---- =77sk 

1 15 cu fvsk 

3) 	MlX water requIred 

77 sk x 4 '::7 gaL sk ---------- :::: 3 : t t: ~ 

42 ::;.,L eel 

" , ': 

• " • :. : ':',I' - ~ ~ ,:. : .: 

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

."t. :' ," 	 it . ,", ~ 

5 - 26 

6) Displacement volume 

[(6000 ft - 262 ft) 001422 bbl;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. If this was not the 

case. the plug will be over or under displaced. 

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 

open the formatlon so as to pump and dehydrate a 

slurry into the resultmg fractures. 

The low pressure technique consists of placing 

cement over a desired 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 

method may be employed. 

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 

relating to calculatIOns often made in the field. 

Consider the 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 entry of water 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 be used 

Class G + 0.2 galisk FLAC· + 0.1 galisk TIC· 

Slurry weight = 158 Ib/gal 

Mix water = 4.97 gals/sack 

Slurry yield = L 15 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 

BRADENHEAD SQUEEZING 

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 - 27 

removed from the annular space by the 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 

negative differential pressures during the shootmg 

and production tests We shall assume that 80% of 

the perforations are open. 

The volume of cement needed to satlsfy the above 

conditIOns may be calculated as follows 

Annular space 

Distance between CBL peaks = 65 ft 

Volume of annular space between CBL peaks 

= 0.0744 cufVft x 65 ft = 4.84 cuft 

Hence, sacks of cement for annular space 

= 4.84 sacks 

Volume of cement left inside casing 

Top of cement at 6980 ft 

0.1305 cufVft x 45 ft = 5.87 cuft 

Hence, sacks of cement = 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 

OF THE 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 =:".: 

5 bhl:< r~l~~l:~'] t~!::~ '.' .. >;:~',.' 50 x 0 O;~2·/~~ 

14 tU 

Height of balanced cement column 

20 sk x 1.15 cu.fVsk = 187.7 ft 

0.02272 cu.fVft + 0.0998 cU.fVft 

DISplacement volume 

Top of water behind cement 

1.14 bbl 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 

Once the 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. 

MAXIMUM ALLOWABLE SURFACE PRESSURE 

The maximum surface pressure that IS acceptable 

at any time while the job is in progress may be 

given by 

MASP = (gr x depth) - (Ph at 7025 ft) + (~Pr) -

(safety factor) 

where, gr = fracture gradient, psi/ft 

Ph = hydrostatIc pressure, psi 

~Pr can be dlsmissed generally, hence bemg an 

extra safety factor 

"'~~f-SALT WATER 

!OO) f t 

FlCB ,. 

5 - 28 
----

CIRCULATING SQUEEZING 

BY·PASS 

PACKER 

-- -:.. 

.' 

FIG. 8 9 

The extent of the hydrostatic pressure present at 

the begmning of the squeezmg may be calculated 

as follows: 

Length of cement plug = 

20 sk x 1.15 ell fVsk 

= 176 ft 

0.1305 ell [Vft 

Length of water spacer = 

(5 bbl + 1.14 bbl) 5.61 eu ft'bbl 

0.1305 ell ftlft = 264 ft 

Length of column 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 maximum aiiowabie surface pressure (MAS?) 


when squeezing begins is therefore: 


[(7025 ft x 0.7 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 of cement column 

= (17.43 cu ft)/(0.1305 cu Nft) 

= 134 ft 

HydrostatIc pressure 

= 0.052 [( 134 x 158) + (264 x 832) 

+ (6627 x 95)] 


= 3498 pSI 


Hence, MASP (fInal) 

= (7025 x 0 7) . (3498) . (5CO) 

= 920 pSI 

In th:s mstance. ',v;th a ccrnr>}ri1tl'le!y low volume 

of cerner,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 

850 

o 	 2 3 4 5 

VOLUME SQUEEZED CU It 

FIG. B.B 

SQUEEZING THROUGH A RETRIEVABLE 

PACKER OR CEMENT RETAINER 

Wherever the packer is run with tail pipe and the 

cement slurry spotted in front of the perforations, 

the balancing of the cement plug and the surface 

pressure calculations are similar to those for 

Bradenhead squeezes 

In some operations, however. the cement 15 

circulated down the hole with the packer's by· 

pass open; before the cement reaches the packer. 

the by-pass is closed causing the fluid ahead of 

the slurry to be squeezed into the formation. If th15 

5 - 29 

operation 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 

plugging any perforations or channels ahead of the

re 

he 

ed 

mg 

hm 

0 

cement. 

VOLUMES 

The slurry volume should always be checked 

against the maximum prevailing hydrostatic pressures. The greatest hydrostatic column will exist at 

the moment the preflush comes into contact with 

the lower perforations. 

Length of cement column: 

20 sk x 1.15 eli [tlsk 

002272 eli [tift = 10 12 ft 

Water ahead of the cement slurry = 3 bbl 

Water behind the cement slurry = 3 bbl 

The volume of casing below the packer (packer at 

6900 it) =125 it x0.1305 cu iVit = 16 31 cu ft 

= 291 bbl (3 bbl,say) 

The length of the column of water in the tubing 

3 bbl x 5 5 eli [!!bbl 


= 0.02272 = 740 ft 


Hydrostatic pressure, therefore, 


= 0.052 [(125 x 8.32) + (1012 x 15.8) + (740 x 8.32) 


+ (5148 x 9.5)] 

= 3749 psi 

Formation fracture pressure IS 

7025 ft x 0.7 psilft = 4917 pSI 

The calculated hydrostatIc pressure IS therefo

1.170 pSI below the formatIon fracture pressure 

In our example. therefore 

Packer Placement 

The packer WIll be placed 100 ft above t

perforatIons at 6900 ft and the by·pass left open 

Fluid Volumes 

The volumes of flUId 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 of the bottom of the ~'']Cr:f:r 

20 ,;k x i 1:; ell :1 :~k 

4 : c: ~::Il (2) 561 C'.J ft hr 1 

Fresh water behind = 3.00 bbl (3) 

10.10 bbl total 

Displacement BrIne 

6900 ft x 0.02272 cu.fVft. 

Tbg Vol = = 27.94 bbl 

5.61 cu.ftibbl 

Vol. of brine to be pumped 

to leave the fresh water 

1 bbl 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 1 bbl of the 

packer), the by-pass is closed and we can 

proceed with the squeeze (fig 8.10) 

Fresh water preflush displaced from tubing 

The greatest hydrostatic pressure is applied to 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 of brine needed to be pwnped for the 

cement to reach the perforations. therefore, is 20.9 

+ 2.9 = 238 bbl (see fig812) 

All the cement will be displaced from the tubing 

when 238 bbl + 12 bbl = 250 bbl of brine have 

been pumped (see fig 8 13) 

Maximum displacement 

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' of thiS pc'mr) 

_.. 

:: '.:'II :~ r r: 

br:!l ,~. (:: : • '.:.::!' 

in C(J!'.:'), ; !'·Lr--.' ...;" '·~,i;', '.... ::>. ':'ldl :r:,· r:1,'1:-:.r:',',:::: 

vO!llrn f ' ~,;! r'Jr~r." tr::"lr Cr~d; t~'I" t",:~l.lrj,.:~i L··:-,: .. :,· 

s:(·)pr l1.1 ::. 

­

5 - 3
~~~24bbl ""f+-+--25 bbl 

BRINE BRINE BRINE

PUMPED PUMPED PUMPED

t-"_...."-4··--·····_· F\/II 

--.- fW 

FW I 

I 

l 

:.1·:....H--"'-t--27 bbl 

BRINE 

~~- DISPLACEMENT 

BRINE 

(17bbl PUMPED) 

3bbl FRESH ~~~5~;;~. 

WATER 


4bbl SLURRY--+.~~·' 

3bbl FRESH -----f:7BE!?:;:;J 

WATER PREFLUSH 

IFW) WITHIN 

1 bbl 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 - 31 

MAXIMUM ALLOWABLE SURFACE PRESSURE 

When involved in low pressure squeezing, it is 

important to remember that the hydrostatic pressure inside the tubing is applied to the formation 

immediately the packer by-pass is closed. 

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 

.bI .., p,l Pi; ..; .., p" ... .~

0 //igS 101 2177 640 832 62 - - 371 I 700 4 /fH}S III 2543 320 832 - 54 - 3749 670

7 /figS. 121 2897 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 

TABLE 8.4 

900 

MAX ALLOWABLE 

SURFACE 

PRESSURE 

900 I 

700 I . 

900 u~,~---'---'--'---'-_ h) 11 '2 

"'" SOUEEZED 

FIG.8.1S 

The above graph (fig 8 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 - 32 

EXCERPTED FROM "CEMENTING" (Smith, 1987) 

Appendix C 

Plugback Cementing 


C.1 Problem 

Balance a 200-ft cement plug from 5,800 to 6,000 ft after drillpipe is removed. 

C.2 Desired Information 

1. Cement volume-cubic feet of slurry and number of 

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 fli ft. 

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._,., ~Jq''\o/ I-Il Ot(

2. HeighT ofcemenT plug wiTh work STring sTill in plug. 

Equalization point formula: 

N 

h=-­

C+T' 

where 

h = height of balance 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 


sacks x 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,· awl hl'lgirr IIf sputa 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 !If tlu,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):, 

Dr illplpc, ,1n<1 1f"lc"). helVh! 01 111Jld I'd I In ,II1I1Ulll\ 1"'1 

4": In()[) P'l~ III :'11. III hilk lK ~X().1 ft hi" 

5 - 33 
CEMENT HOLE 

AND CONOmONS 

SPACER Hole: 83,. 

well bore fluidAPI Class H 12.8#/gal Cement water base mud 

Slurry Wt.­

16.4#/gal 
 Drill Pipe: 

"'--1t-4-'/z 0.0. 

16.60#1f1 E.U. 

Spacer 200 ft 


In annulus 
 .....,..~~.,..+-:l,..,.~ 5800 ft 

Fresh water 


spacer ahead 


& behind 


cement plug 


Fig. C-1-Plugglng example. 

From handbook ("Capacity"). height of fluid fill inside 4 I

h-in.• 16.60-lbm/ft EU drillpipe =70.32 ft/bbl. 

Height ratio formula: R equals the fill-up factor for the 

work string (feet per barrel) 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 of spacer behind the cemen!. This will change the volume of spacer to be pumped 

ahead of the 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. Spacer height equals volume of spacer times 

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 water equals mixing water plus spacer water 

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 

spacer and cement. The displacement footage required 

behind the spacer and cement equals total work string 

depth minus (height of spacer plus height of cement with 

work string still in plug). 

Displacement footage=6.000 	ft -(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 a cement plug from 5.600 to 6,000 ft for directional 

drilling (whipstock)_ 

C.6 Desired Information 

I. Sacks of cement. 

2. Height of cement with drillpipe and tubing in place. 

3. Height of water in annulus and barrels of water in 

drill pipe 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 a slurry density of 15.6 

Ibm/gal; run 30 bbl of fresh water ahead of the cement 

plug; and run 500 ft of2Y.-in. 00. 4_70-lbm/ft EUE tubing with scratchers and centralizers attached to the bottom of the 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" of crll/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 - 34 

C 

2. Height ofcement plug with work string still in plug. 

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 and height offlush with work string still in 

plug. Calculate the footage of a 2 Ya-in. work string that 

is not covered by cement by subtracting the height of cement 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. 

Calculate the volume of flush in the 2 Ya X 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 ft xO.I344 bbllft =12.81 bbl freshwater flush in 

annulus. 

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

tubing. 

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

Annulus volume (in barrels per foot) equals volume of 

12-in. hole (barrels per foot) minus volume of 3 '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: 30 bbl-12.8 bbl-8.96=8.24 bbl 

freshwater flush in annulus between 3 'll-in. drill pipe inside 9 'h-in. hole. 

Fill-up factor (feet per barrel) 3 'h-in. drillpipe inside 

9'h-in. hole = 13.1976 ftlbbl (handbook volume and height 

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 =annulus freshwater flush + 2%-in. 

freshwater flush volume + 3 'll-in. freshwater flush 

volume. 

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

bbl=31.7 bbl. 

4. Freshwater requirements. Mixing water per sack of 

Class A cement at 15.6 Ibm/gal=5.2 gallsack. 

Mixing water equals water-per-sack factor times total 

sacks: 

5.2 gal/sack x 266.24 sacks = 1.384 .448 gal. 

Mixing water= 1.384.448 gah-42.00 gallbbl=32.96 

bbl. 

Total freshwater flush volume = 3 1.7 bbl. 

Cleanup or washup=20 bbl. 

Total fresh water=32.96 bbl + 31.7 bbl +20 bbl=84.66 

bbl. 

5. Displacement volume-capacity of mud behind 

spacer and cement. Displacement footage equals total 

work string depth minus (height of spacer plus 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:Jpac iry factor of work 

string timc~ displJcemcnl foolJgc rninlJ~ O.007·C bblifl x 

S,3~ 1.38 ft' 39Ag bhl. -.-­

5 - 35 

5.6 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 - 36 
5. 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 - 37 
6.0 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 Abandonll • 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 - Pl u99.i!l9....E.D9.Aba ngoTJ.JJ1£nt ___LQLgf.tJ. Prepa red for 

U.S. EPA, Washington, D.C. 1988. 

Env i ronmen ta 1 and Ground \'1 a to r Institute. proc0.cd i ng s ..9J ,tho 

Eirst __l'Is-:!t. i . .9J}S~<::'_ClD f!?XQJ}~_o:... _.0.fL_?b <lo<iClnC(j ,..,\~i' 11~,~ :__ Prob 1er:l ~-;.._illlS:i 

;;.9_1~t.i ,0 n ~2. • Pre son ted inc 0 0 p 0 rat ion wit h 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/ • 

Gera CJ h t Y & r·l ill f' r, Tn r . 'j'f'(-hrli(':11 H,II1U.ll Inj,'ct l()n \·/,'·11 

Ah:1 n d () n :'" ' n t. 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= 

() - 2 
7.0 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 ann u 1 u ~.~ i~; the 5 pac e b C' t '.' p (' nthe 10 n q ~; t 1- i n q and t h (. 

~;urrolll1d ing borehol e) . 

"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 direct 1 y into the cas i neJhcCld . 

-; - 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 n t ric r 0 lIsu r f tI C C s, (> d C h 0 f ",' h i C' h 1: ; d !', : ~ c' rl h 1 (' d ','; i t 11 iI 

!; e r .i c s 0 [ h (' ,I V Y - d u t. y r 0 lIe r-:; . 

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

"1 - 3 
on 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; 


ope rations . The rcarese v (' r dId i ~~ tinc t l YP(' ~; 0 f c (' ;:1 (' tl t 1 n q Ii J u CJ ~ ~ • 


Thoy arc used to : 


p r () cos S (('. q. mud, c (' m0 nt, dis pIa C (' 171 c' n t 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 n j e c t i on we 11 ~; . 

7 - 6 
crossflow: 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 

be e n po s sib 1 c fro m nat 1..1 r alp res sur e 0 r p II mpin CJ 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 

be t wee nthe in j e c t ion tub i n g / cas in g wall 0 r in j 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 - 9 
injection 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 nth i spaper ,refers t. 0 il part j ill 1 (' n(J t h P 1 P(> !.-; t r i 11 CJ 

ext(' n dinq fro 1':1 the bot t 0 r.1 0 f t h c· b U 1 d101 (' t 0 i1 II (' 1 \ . \' ,It j CJ II , II )() \' l ' 

the b CJ t t 0 r.1 0 t the pre v i 0 U !~ C a" i n CJ :; t r i n(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] 1cd the 1unnt'] 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 mix i n g tub and v i bra t C'd tor C' m0 v c' any finc' I y C' n t 1- d PIi (; d 

air buhblc~--; frOT:1 the mlxc:r. 

7 - 12 
mudcake: 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 suitab I c to r d rink ing or coo}; j neJ pll rpu:;(':', 

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 d ll".'.rn the II n nul II" lind up d IIdOll t () f t 11 C' t ul) i n q u ! P 1I)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 val ve, 0 r !~ h \l tot tar\I r:1 r t 0 ( , C' d : : C' i n j t.-, ( • t i Cl n 

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

7 - 16 
slurry: 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 ft 3 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 - HI 
two-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 - 19 
wellbore: 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