04.politecnico di torino casing programme 2010

8/9/2019 04.Politecnico Di Torino CASING PROGRAMME 2010

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04. CASING PROGRAMME

1

C H A P T E R 4

CASING PROGRAMME


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As said, for an adequate characterization of a formation from a pressure

regime standpoint the following parameters have to be determined:

Pore pressureOverburden pressureFra!ure pressure

These pressures, as seen, are strictly dependent one from the other. In

fact, pore pressures and overburden pressures are related between themby the effective pressure, due to compaction, in accordance with the

effective stress principle and together allow the calculation of fracture

pressures.

The methods in use in the Oil Industry to foresee and calculate these

pressures and gradients have been discussed in hapter ! "Abnormal#ressures$.

4.1. INTRO"#CTION


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4.2. %ASIC CRITERIA IN &E'' P'ANNING

%ased on pressure gradient data, all fundamental information needed to plan drilling

programmes can be obtained because the following parameters can be defined in the most

accurate way:

the dens(!) and r*eo+o,(a+ proper!(es o- !*e dr(++(n, ud/

the op!(a+ dep!*s -or se!!(n, !*e as(n,s&the nuber and d(ae!er o- !*e as(n,sto use&

the ,rade and !*(ness o- s!ee+ -or !*e as(n,sto withstand the stresses induced by the

drilling and production processes&

the dens(!) and r*eo+o,(a+ proper!(es o- een! s+urr(es&

the planning and optimization of the*)drau+( pro,rae'pumps and surface equipment

selection, flow rates, horsepower distribution(& dr(++(n, r(, po!en!(a+, which is related to the geometry 'size, length( and weight of the

casing to run in&

the selection and optimization of dr(++(n, b(!s&

the definition of the e*an(a+ *ara!er(s!(s o- dr(++ s!r(n,sand !ub(n,sfor the )*T

and production tests, acid +obs, hydraulic fracturing&

the choice of thee++*ead and thesa-e!) eu(pen!, such as the %O#s, choe manifold

and surface equipment in general&

the installation of the most suitable equipment and sensors for on!(nuous and (n rea+3!(e

on(!or(n, o- !*e dr(++(n, proess&

the estimation of e++ os!with the relative budget allocation.


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4.$. CASING "ESIGN SE#ENCE 5$ s!eps6

Once the three pressure gradient curves versus depth have been

obtained using the methods previously described, it is possible to tae the

following decisions:-. de-(ne !*e dens(!) !*e ud us! *ave versus dep!*&

. the ne/t step consists in determining the depths at which the various

casing strings shall be run, that is !*e as(n, se!!(n, dep!*s. This also

implies the nuber o- as(n, s!r(n,s reu(red to case the hole from

surface to bottom&

!. nowing the depths of setting and the pressures acting in the well, it is

then possible to a+u+a!e !*e s!resses at which the various casing

strings will be sub+ected during drilling and production and a+u+a!e !*e

e*an(a+ proper!(es the casings should have in order to withstand

these stresses.


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4.$.1. M#" "ENSIT8 "ETERMINATION

The ud e(,*! 5or dens(!)6 s*ou+d be s+(,*!+) *(,*er !*an !*e pore

pressure ,rad(en!'usually -00 g1litre(, when in static conditions 'no mud

circulation(, and be+o !*e -ra!ure ,rad(en! 'plus a certain safetymargin depending on the particular situation(, when in dynamic conditions

'with mud circulation(.

This means that in overpressured zones, the mud density must beincreased with the depth as does the pore pressure gradient.

2or practical reasons, at the rig site the mud density is increased following

step by step patterns, and not continuously, as shown in the ne/t slide.


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9

-.00 -.30 .00 .300

300

-300

-000

!000

300

000

!300

4000

4300

3000

FRACT#RE

GRA"IENT

PORE PRESS#RE

GRA"IENT

M#" "ENSIT8

5a!ua+6

M#" "ENSIT8

5!*eore!(a+6

4.$.1. M#" "ENSIT8 "ETERMINATION


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4.$.2. CASING SETTING "EPTH "ETERMINATION

The ne/t step consists in the determination of the depths at which the

various casing strings shall be run, taing into account safety margins,

nowledge of the area, previous e/periences, e/pected hole problems.

This sequence of calculations will also define the nuber o- as(n,

s!r(n,s reu(redto case the hole from surface down to bottom.


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SE'ECTION CRITERIA AN" PROCE"#RE

The procedure usually followed to determine the casing points is fairly simple and is

based on a


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SE'ECTION CRITERIA AN" PROCE"#RE

4. A first large diameter casing, the ondu!or p(pe '4$, !0$(, is usually set at

around !0530 m with the purpose to protect the shallower formations from caving or

collapsing or for avoiding any eventual stability problem of the drilling rig. If this

casing is driven, it is called the dr(ve p(pe.

3. A second casing, the sur-ae as(n,'!0$, 6$, 0$(, is also positioned at a depth

between -00 and 300 m, with the scope to mae possible the installation of the

%O#s and e/cluding areas with low facture gradients.

6. The number of casing strings required in a well varies between 4 and 7, depending

on the depth, pressure gradients trend and targets to be reached.

7. An e?ap+e o- a+u+a!(onis shown here below.



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E@AMP'E OF CA'C#'ATION

1. &E'' "ATA

5 Total )epth: 3000 m

5 Overpressures Top: -30 m

5 #ore #ressure 8radient at Total )epth: .00 gf1cm1-0 m

5 2racture 8radient at Total )epth: .-3 gf1cm1-0 m

5 9a/imum 9ud )ensity: .06 g 1 litre at Total )epth

5 #ore #ressure 8radient and 2racture 8radient )evelopment: as per slide --

5 9ud )ensity: as per slide --



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-.00 -.30 .00 .300

300

-300

-000

!000

300

000

!300

4000

4300

3000

M#" "ENSIT8

AN" PRESS#RE

GRA"IENTS

"EE'OPMENT



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OPERATIE E@AMP'E 5CASING "ESIGN6

2. CA'C#'ATIONS

2.1 Produ!(on Cas(n, or '(ner

If the well results produ!(ve, the production casing string will be run at

bottom hole '3000 m(

In case the well results dr), it will be plugged and abandoned.

The running of a liner instead of an entire casing string will be evaluated at due

time. In case a liner will appear to be the better solution, it will overlap the last'say the deepest( intermediate casing string for at least 00 m, design

practice.



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2.2. In!ered(a!e Cas(n,

59a/imum 9ud )ensity, df: .06 g1litre at 3000 m

5 Trace a s!ra(,*! +(ne para++e+ !o !*e dep!* a?(s un!(+ (! (n!erse!s !*e -ra!ure

,rad(en! urvein correspondence of a value of .06 gf1cm1-0 m.

5This happens at a depth of 700 m, where the pressure e/erted by the mud in hole

equals that of the fracture pressure: 336. gf1cm. In theory, this should be the setting

depth of the intermediate casing.

5%ut for safety reasons, a ar,(nof some tens of gf1cm'-05!0 gf1cm( should be

maintained in favour of the fracture pressure 'to tae into account friction losses during

mud circulation, surge pressures, etc.(. 2or this e/ample, suppose to need a safety

margin # of about 0 gf1cm 'even a bit less is O;(.

5If the casing is set in correspondence of a fracture gradient< .- gf1cm 1-0 m, which

occurs at $270 , an acceptable safety margin of -=.3 gf1cm

is obtained.In fact:$270 52.12 2.096D10 1>.7 ,-D2

5 *o, !*(s -(na+ (n!ered(a!eas(n, (++ be run a! $270 .



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4 $ 2 CASING SETTING "EPTH "ETERMINATION


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2.$. In!ered(a!e Cas(n,

59a/imum 9ud )ensity at !30 m, df

: -.= g1litre

5Trace a s!ra(,*! +(ne'>ine (, starting from the value of the mud density at !30 m

para++e+ !o !*e dep!* a?(s un!(+ (! (n!erse!s !*e -ra!ure ,rad(en! urve in

correspondence of a value of -.= gf1cm1-0 m.

5This happens at a depth of -330 m, where the pressure e/erted by the mud in hole

equals that of the fracture pressure: =7.6 gf1cm.

5In theory, this should be the setting depth of this other intermediate casing.

5 *upposing to maintain a sa-e!) ar,(n o- abou! 17 3 20 ,-D2 for the same

reasons as before, the casing must be set deeper.

5To obtain a safety margin of -7 gf1cm, the new depth is 2127 , where a fracture

gradient < .00 gf1cm1-0 m can be read:

2127 ? 52.0031.>26D10 1: ,-D2

5 T*(s -ur!*er (n!ered(a!eas(n, (++ be run a! 2127 .




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1:

-.00 -.30 .00 .300

300

-300

-000

!000

300

000

!300

4000

4300

3000


T*eore!(a+ Se!!(n, "ep!*

1770

E--e!(ve Se!!(n, "ep!*

2127

'AST %#T ONE

INTERME"IATE

CASING



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2.4. Sur-ae Cas(n,

59a/imum 9ud )ensity at -30 m, df

: -.!7 g1litre

5Trace a s!ra(,*! +(ne, starting from the value of the mud density at -30 m, para++e+ !o

!*e dep!* a?(s. In this case it can be observed that the fracture gradient curve is not

intersected, neither at the surface.

5This means that in theory no casings will be required in this section of hole.

5 %ut for what said before, a casing is necessary at around 300 m 'this depth isevaluated case by case depending on lithology, e/perience, e/pected hole problems,

etc.( in order to have the possibility to install the sa-e!) eu(pen!'%O# stac(, thus

ensuring a certain safety margin between the pressure e/erted by the mud in hole and

the fracture pressure, and not to leave a too long section of hole uncased.

5If it is supposed to run this casing at 700 , it results that:

d-a! 700 1.$: ,D+(!re 5a?(u ud dens(!) a! 2170 6G-ra! 700 1.;0 ,-D

2D10

Sa-e!) Mar,(n 51.;0 ? 7006D10 51B$: ? 7006D10 21.7 ,-D2

5 T*(s (s !*e sur-ae as(n, se! a! 700 .




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1>

-.00 -.30 .00 .300

300

-300

-000

!000

300

000

!300

4000

4300

3000



700

S#RFACE

CASING



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2.7. Condu!or P(pe

5 Above the surface casing, in ons*ore e++s, a first large diameter casing, called the

ondu!or p(pe or dr(ve p(pe '4$, !0$(, is usually set at about 0530 m with the

purpose to protect the shallower wea, unconsolidated formations from caving5in or

collapsing or for avoiding any eventual stability problem to the drilling rig itself.

5 The conductor pipe is usually driven into the ground without being cemented at all

????????????????????????.

5 In o--s*ore e++s, the # setting depth, @i, can be calculated 'm( by the followinge/pression:

where:

< rotary table elevation above sea level or "air gap$, m@ < water depth, m

Bsed< overburden density 'e/pected at # shoe(, g1cm!

Bmud< mud density during the ne/t drilling phase, g1litre

( )

( ) mudsed

mudi

HHEH

+

+=

03.167.003.1

03.1




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-.00 -.30 .00 .300

300

-300

-000

!000

300

000

!300

4000

4300

3000



70

CON"#CTOR

PIPE

4 $ 2 CASING SETTING "EPTH A ' I " A T I O N


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"ESIGN E@AMP'E 3 O%TAINE" "ATA

2.9. F(na+ as(n, pro-(+e 5*(* resu+!s !o be a 43s, pro-(+e6

The calculations performed indicate that in the case of this well, with these porepressure and fracture pressure profiles, -(ve as(n, s!r(n,sare required, that is:

1. Condu!or P(pe a! 70

2. Sur-ae Cas(n, a! 700

$. F(rs! In!ered(a!e Cas(n, a! 2127

4. Seond In!ered(a!e Cas(n, a! $270

7a. Produ!(on Cas(n, a! 7000

57b. Ins!ead o- a Cas(n,B a Produ!(on '(ner an be run -ro 7000 up !o $000 B

!*a! (s 270 (ns(de !*e s*oe o- !*e Seond In!ered(a!e Cas(n,6

T*e ne?! s!ep ons(s!s (n !*e ver(-(a!(on o- !*ese as(n, se!!(n, dep!*sB !a(n,(n!o aoun! !*e 7 -a!ors desr(bed (n !*e -o++o(n, s+(des 'C99%CID8

T@AT: the calculations made so far have already considered some of these factors(.

4.$.2 CASING SETTING "EPTH A ' I " A T I O N

4 $ $ CASING SETTING "EPTH A ' I " A T I O N


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After having roughly calculated the depths to which the various

casings must be run, validation must then be carried out to be sure

that these depths are satisfactory.

hecing the accuracy of the casing setting points is based on the

analysis of the following five '3( basic items, including:

1. MA@IM#M PRESS#RE A''O&A%'E AT THE CHOEB P*

2. MA@IM#M "IFFERENTIA' PRESS#REB Pd

$. "RI''ING %A'ANCEB Pdb

4. IC TO'ERANCE

7. E@PECTE"DPOSSI%'E "RI''ING PRO%'EMSREMEM%ER "at the A*ID8$ always means at the TO# of the

ADDE>AC sections

4.$.$ CASING SETTING "EPTH A ' I " A T I O N

4 $ $ 1 MA@IM#M PRESS#RE A''O&A%'E AT THE CHOE P *


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alled also the Ma?(u A++oab+e ANN#'AR Sur-ae Pressure or

MAASP, it represents the ma/imum pressure that can be allowed toaccumulate at the wellhead in case a ic has been controlled, without

causing the fracturing of the formation below the shoe of the last casing

run in hole. It is clear that as mud density increases, #chdecreases.

The minimum acceptable value can be not less than -0 gf1cm for

surface casings and 30 g1litre difference between the fracture gradientbelow the casing shoe and the density of the mud in hole 'or 40530

gf1cm( for the others. In some cases, in particular when deep wells

are drilled, values of #ch very low and sometimes close to zero are

accepted, otherwise the target could not be reached.

At a certain depth, H, the P*

or MAASPis given by the equation:

P* 5G-rBs*oe d-BH6 ? Hs*oeJ D 10

4.$.$.1. MA@IM#M PRESS#RE A''O&A%'E AT THE CHOEB P*


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4.$.$.2. MA@IM#M "IFFERENTIA' PRESS#REB Pd


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It is the difference between the pressure e/erted by the mud at the

ma/imum density foreseen in that given hole section 'generally this is

the value of the mud density at the end of each hole section( and the

pore pressure as a function of depth.

The nowledge of #d is e/tremely important because it can give

indications about the drill string going to get stuc or not, especially in

presence of porous and permeable formations. /perience shows that

#d values can vary from 00 gf1cm and more down to only few

gf1cm depending on local features.

The ma/imum differential pressure Pd as a function of depth is

calculated by means of the formula:

Pd 5d-Ba? GpBH6 ? HJ D 10




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2:

Esually, drilling practices do not fi/ strict reference limits for the values

the differential pressure can assume. This depends on the particularsituation of the area where operations tae place, specifically the

characteristics of formations drilled 'permeability, strength( and

composition and properties of the mud in use.

@owever, it is always necessary to remember that e/cessive

differential pressures can cause:

5 pipe sticing 'vs uncased hole wall(pipe sticing 'vs uncased hole wall(

55 circulation lossescirculation losses

55 low penetration rateslow penetration rates..

B d



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2;

E@AMP'E

The ma/imum differential pressure in the interval -35!30 m

develops as shown in the Table here below.

"EPTHB Gpvs "EPTHB

,-D2D10

MA@ M#" "ENSIT8IN SECTIONB ,D+(!re

PdB ,-D2

2127 1.0$ 1.>2 1;>2700 1.4$ 1.>2 122

2:70 1.77 1.>2 102

$000 1.9; 1.>2 :2

$100 1.:2 1.>2 92

$270 1.:; 1.>2 46

B d

4.$.$.$. "RI''ING %A'ANCEB Pdb


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It is the difference between the pressure due to the drilling mud at its

density and that of the formation, as a function of depth. This measure

indicates how much the pressure e/erted by the mud e/ceeds the pore

pressure. In most case #db increases with depth, if the mud density

and the pore pressure gradient remain constant.

The nowledge of this parameter is very important because it can give

indication about riss of (s ourrene'#dbtoo much close to the

pore pressure, say too low( and about the e--e! on pene!ra!(on ra!e

'too high #db can negatively affect penetration rates(.

The )rilling %alance, Pdb, as a function of depth, H, is calculated with the

equation:

Pdb 5d-Gp6J ? H D 10

db

4.$.$.$. "RI''ING %A'ANCEB Pdb


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E@AMP'E

In the section -35!30 m, the drilling balance varies as shown below.

"EPTHB Gpvs "EPTHB

,-D2D10

M#" "ENSIT8 vs"EPTHB ,D++(!re

Pd%B ,-D2

2127 1.0$ 1.$9 :0

2700 1.4$ 1.90 4$

2:70 1.77 1.:1 44

$000 1.9; 1.;1 $>

$100 1.:2 1.;1 28

$270 1.:; 1.>2 49

4.$.$.4. IC TO'ERANCE


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$1

It represents the vo+ue o- a?(u (n-+u?'ic( that, once entered the

wellbore ' annular space(, can be circulated out by using a "constant

bottomhole pressure$ method without fracturing the formation below theshoe of the previous casing. SEE THE &E'' CONTRO' CHAPTER

This volume (BH is calculated by the following e/pression:

where:

5 Fi,@< ic tolerance, m! 5 Bmud< mud density at @, g1litre

5 a< annular capacity below shoe per unit length, litre1m 5 @ < current depth, m

5 8frac< fracture gradient at the casing shoe, gf1cm1-0 m 5 Bi < density of influ/ fluid, g1litre

5 @shoe< casing shoe depth, m 5 pp< pore pressure at @, gf1cm

It has A>GAH* to be verified at least for the *EC2A and the IDTC9)IAT

casings.

( )[ ]

( )imudp

pmudmudfracshoe

shoefracaHi p

pHGH

HGCV

+

=

1010

4

,

4.$.$.4. IC TO'ERANCE


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$2

IC TO'ERANCE MA@IM#M A''O&A%'E A'#ES

Ho+e S(KeB "(n Ma?(u ( To+eraneo+ue

$ bb+

" L 2$= 40 270

2$= " L 1: 1D2= 24 170

1: 1D2= " L 12 = 19 100

12 1D4= "L ; = ; 70

" ; = 4 27

T*e ( To+erane us! be a+u+a!ed and ver(-(ed -or a++ sur-ae and

(n!ered(a!e as(n,s (n order !o ,uaran!ee 5a! +eas!6 !*ese a?(u va+ues.

4.$.$.7. E@PECTE"DPOSSI%'E "RI''ING PRO%'EMS


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Ghen selecting the casing setting depths, other factors should be taen into

consideration, especially for what regards the shallower casings, such as:

S*a++o Gas

Ho+e A,e(n,'"time dependent$ deformations of the rocs: reep(

#ns!ab+e Fora!(ons

Seepa,es and C(ru+a!(on 'osses

"ev(a!ed or Hor(Kon!a+ "r(++(n,

Produ!(on Reu(reen!s Open Ho+e vs Cased Ho+e

Eono(s

1B0 1B7 2B0 2B70


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$4

CASING POINT

SE'ECTION

Pressure Grad(en!sPressure Grad(en!s

5,-D5,-D22D106D106

Fra!ure

Grad(en!

:=

> 7D;=

Pore PressureGrad(en!

20=

Mud"ens(!)

2000

1700

1000

700

2700

$000

1$ $D;=

4.$.$.9. "ESIGN E@AMP'E


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$7

Pro-.

m

300

-!00

300

Press(one "(--erenK(a+e5 ;g1cmCas(n, Grad(en!( d( Press(one 5 ;g1cm

1-0m Mar,(ne a++a C*oe5 ;g1cm

0

300

-000

-300

000

300

!000

-.0 -.3 .0 .3

#rofonditI

m

0 0 40 60 J0 -00 -0 -40 -60 -J0 00 00 0 40 60 J0

-0

0

-

0

-4

0

-6

0

-J

0

0

0

0

4

0

6

0

20Q

1$ $D;Q

> 7D;Q



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$9

F(na+ Cas(n, Pro-(+e

After having verified the casing setting depths on the basis of the 3 factors previously

seen, five casing strings are required for the well under e/amination, that is:

-. onductor #ipe at 30 m

. *urface asing at 300 m

!. 2irst Intermediate asing at -3 m4. *econd Intermediate asing at !30 m

3. #roduction asing at 3000 m

T*e ne?! s!ep ons(s!s (n !*e de!er(na!(on o- !*e s(Kes 5d(ae!ers6 o- !*e

*o+es !o be dr(++ed and !*ose o- !*e as(n,s !o be run.



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$:

asings are +oints --5-! m long, which, once threaded together, can completely case

the well at the planned depths.

4.$.4. F#N"AMENTA' CASING F#NCTIONS


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$;

Allow the installation of theWellheadand BOPs.

Allow to circulatethe drilling fluid up to the surface.

Isolate formations with different pore pressure and fracture

gradients.

Exclude as soon as possible formations which can cause

drilling problems because of their geological characteristics and

(mainly) their hydraulic features.

Protect potentially productive formations.

4.$.7. CASING T8PES


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$>

K CON"#CTOR PIPE

K S#RFACE CASING

K INTERME"IATE CASINGDS

K PRO"#CTION CASING

4.$.7.1. CON"#CTOR PIPE


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The Condu!or P(pe, CP, is the first string to be run in a well and has the main

functions :to protect the shallower formations from any contamination due to the drilling fluids&

to prevent dangerous wash5outs and erosion of the loose, unconsolidated topsoil,which can, sometimes, result in big problems for the stability of the rig itself&it is of large dimensions, generally from -6, -J531J, 0, 4, !0 and !6$.

The setting depth of the onductor #ipe is usually very shallow '!0530 m and at

ma/imum around -00 m( and is chosen in such a way to permit that the drilling fluid

may be circulated to the mud pits while drilling the surface hole. The # seat must be

in an impermeable formation with enough resistance to fracturing to allow the

circulation of the mud to the surface.

The # can be either driven by a pile driver down to a depth where the casing does not

enter anymore into the topsoil or run in a drilled hole. In this last case, a guide shoe is

usually welded on the last +oint of the # and the cement slurry is pumped through a

swedge, which is screwed to the +oint closest to the surface. The cement slurry isnormally pumped up to the surface.

4.$.7.2. S#RFACE CASING


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41

The second string, which is run immediately after the #, is the sur-ae as(n,B set

usually around -005300 m& its size can range between -!5!1J, -6, -J531J, 0 and 4$.

The main ob+ectives of the surface casing are:to protect the potential fresh5water levels from the contamination of the drilling fluids&

to allow the installation of the %O# stac&

to help supporting the weight of the successive drilling strings and the production

equipment.

Its setting depth should be into an impermeable level below any fresh5water bearing

formation, sometimes as deep as -000 5 -300 m. Of course, if there is the ris to

encounter shallow gas5containing formations or gravel is e/pected, the setting depth of

the surface casing can be shallower. @owever, the setting depth should be deep enough

to allow drilling to the ne/t casing setting point without any ris of fracturing and

providing reasonable assurance that broaching to the surface will not occur in case the

%O# are closed to contain a ic '(n(u *oe ar,(n reu(red 10 ,-D2(.

4.$.7.$. INTERME"IATE CASING5S6


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One or more (n!ered(a!e as(n, s!r(n,s'-5!( are often required to deepen a well

with the purpose:

to seal off troublesome formations, such as wea zones with low fracture gradients,

overpressured intervals, salt beds, sloughing shales, reactive formations, deviated

sections, etc.&

to get closer to the target&

to allow the use of higher density muds, being placed in higher fracture gradient

formations '(n(u *oe ar,(n reu(red 40 ,-D2(&

to install higher performance %O# stac&

to isolate intermediate mineralized formations.

The diameter of these casings normally ranges between -! !1J$ and 7$ and the depth

can reach 3000 m or more. The intermediate casing is often the longest and the

heaviest string run in the well and its role is essential to reach the target.

4.$.7.4. PRO"#CTION CASING


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4$

The produ!(on as(n,or produ!(on +(neris the last and most important string of a

well& its primary functions are:

the isolation and protection of all the zones above and within the production levels&

housing for all the production equipment&

the e/ecution in safe conditions of all those operations which are usually required

during the production life of a well&

the containment of the producing fluids in case of production string 'tubings( failure.

ommon sizes of the production strings vary between = 31J$ to 4 L$ and can be set at

depths from -300 m down to 7300 m and more.

4.$.7.7. 'INERS


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44

'(nersare sections of a casing

string, that cover the hole frombottom up to as certain depth,

but not up to the surface. The

liner top is usually hanged

inside a previous casing string,

'the overlapping length is about00 M 30 metres(.

'INER

TOP

CASINGSHOE

4.$.7.7. 'INERS


45/148


47

The a(n advan!a,esof a liner are:costs containment&decrease of the weight of the tubulars to handle 'effects on rig selection(&

better hydraulics&mechanical integrity when production starts&more fle/ibility in completion schemes.

The a(n d(sadvan!a,esof liner installation are:ris of poor pressure integrity in correspondence of the liner top because

of poor cementation or due to wear of the casing on which the liner is

hanged&ris to cement the liner running equipment& difficulty in obtaining good cementing +obs due to the small clearance

between casing and liner or hole and liner&

need to install a bridge plug above the liner top in case of %O# removalin case the completion string has not been run and landed yet..


46/148

4.$.7.7.1. "RI''ING or


47/148


4:

The setting of a "RI''ING +(ner"RI''ING +(ner is often an economically convenient decision

particularly in deep wells as opposed to running a full string. *uch a decision must

be carefully considered, since it requires that the casing 'run before the liner( is

suitable to withstand the pressure conditions as it were set at the depth of the liner.

If drilling is planned to continue below the drilling liner, then its requirements, in

particular for what concerns the burst resistance, must be further increased. This

well profile, obviously, is e/pensive, because of the higher performances the

intermediate string must possess. 2urthermore, the continuous wear, at which the

intermediate string is sub+ected to, should be carefully evaluated and predicted.

A I M

"r(++(n, or


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4;

If a PRO"#CTION +(nerPRO"#CTION +(neris planned, the intermediate drilling liner is usually tied5bac up

to the surface& good drilling practices '8O2#s( suggest that this operation has to be

accomplished before drilling the ne/t hole section, where the production liner will be

placed. T*a! eans !*a! 5*en neessar)6 (! (s usua+ !o des(,n a drilling liner,

which is tied5bac and then followed 'in time( by the drilling activity leading to run a

deeper production liner.

Often, the produ!(on +(ner !oo (s bound dur(n, (!s or(n, +(-e !o be !(ed3baup !o !*e sur-ae. If this operation is planned, the intermediate casing string can be

designed to withstand lower mechanical stresses, resulting in running lower level riss

and1or achieving considerable cost savings.

N O T I C E

ementing production liners is usually difficult, because zonal isolation is essential

during the production life of the well and any subsequent wor over activity.

4.$.7.7.2. PRO"#CTION 'INERS


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4>

'INER TOP

'INER TIE3%AC

4.4. CASING AN" %IT SIE SE'ECTION C H A R T


50/148


70

To select the casing and bit sizes, the C*ar! s*on (n !*e -o++o(n, s+(descan

help in this tas. Its ordinary "bottom up$ use is as follows:

-. define the size the casing or the linermust have when the bottom of the hole will be

cased '@* is one of the fundamental data contained inside any official agreement

) M O, usually decided by Os(. This will be the production casing or liner size&

. enter the hartwith that size&

!. follow the arrows on the hart& they indicate the hole sizes that may be required to

run the last casing. If, for instance, the production casing has a 3$ diameter, thehole to be drilled could have a 6 L$ or 6 -1J$ size&

4. continue upwards 'in the well( until surface casing has been selected.


51/148


71

4.4. CASING AN" %IT SIE SE'ECTION


52/148


72


53/148

30" CP



54/148


74

20" CASIN

! # CASIN

$% CASIN

&3 '% CASIN

STAN"AR" CASING PROFI'ESTAN"AR" CASING PROFI'E

2(% )O*E

&(% O+ &$ ,# )O*E

&2 -# )O*E

. ,# )O*E



55/148


77

$0Q CP

20=

s,

> 7D;Q s,

*o+e ; 1D2Q

1$ $D;Q s,

S!andardS!andard

Cas(n,Cas(n,Pro-(+ePro-(+e =7D;

; = :=

9= 7=

Ho+e Cas(n,

2;= 24=1D2

22= 1;=7D;

1:=1D2 19=

14=$D4 1$=$D;12=1D4 512=:D;6 11=$D4

10=7D; >=7D;

;=1D2 :=

9= 7=



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7>

"ESIGN E@AMP'E

9aing reference to the calculation e/ample of *lide - and other ones, the

hole vs casing profile results to be:

-. $9=@ole for $0=onductor #ipe at 30 m

. 29=@ole for 20=*urface asing at '400 m or( 300 m

!. 1: 1D2=@ole for 1$ $D;=2irst Intermediate asing at -3 m

4. 12 =@ole for > 7D;=*econd Intermediate asing at !30 m

3. ; 1D2=@ole for :=#roduction asing at 3000 m

T*e ne?! s!ep (n Cas(n, "es(,n (s !*e a+u+a!(on o- !*e e*an(a+

*ara!er(s!(s !*e var(ous as(n,ss*ou+d *ave (n order !o (!*s!and !*es!resses *(* are ,o(n, !o so+((! !*e dur(n, !*e *o+e +(-e o- !*e

e++.

4.7. APPROACH TO CASING "ESIGN

Cas(n, des(,nCas(n, des(,n actually includes s!ress ana+)s(s proedure The tas


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90

Cas(n, des(,nCas(n, des(,nactually includes s!ress ana+)s(s proedure. The tas

of that procedure is to design a pressure vessel which can withstand a

variety of e/ternal, internal, thermale/ternal, internal, thermal andself weight loading conditionsself weight loading conditions,

while at the same time being sub+ected to wearwearand corrosioncorrosion.It is obvious that loads that can affect casings during the life of the well

can not be e/actly predicted& for this reason they are designed taing

into account the most demanding situations that can realistically occur

according to the policy in force and the e/perience and statistical data

available in each Oil ompany.

It is also necessary to have as much information as possible about:

pressure and temperature gradients&

characteristics of the formations that have to be drilled&

potential hole problems&formation fluid content N characteristics.

It is also necessary to now the mechanical and geometric characteristics of

the tubulars required or available



61/148


91

the tubulars required or available.

The fundamental mechanical features of tubulars must concern and include:

res(s!ane !o (n!erna+ pressure or burs!&

res(s!ane !o e?!erna+ pressure or o++apse&

res(s!ane !o a?(a+ !ens(on.

The mechanical performance of tubulars depends on several factors, such as:

ou!s(de d(ae!er&

a++ !*(ness&

s!ee+ ,rade&

!)pe o- onne!(on.

International Organizations and 9anufacturers too usually provide these data.



62/148


92


63/148



64/148


94

STRESS3STRAIN "IAGRAMME

To determine the behaviour of a material, this is tested. Tests of material

performance may be conducted concerning:

tension&torsion&compression&shear.

The tension test is the most common and is usually represented by plotting the

apparen! s!ress 'the total load applied on the material specimen divided by its

cross5sectional area( on the ordinates against the apparen! s!ra(n 'elongation

between two gauge points mared on the specimen divided by the original gauge

length( on the abscissae.

A typical plot is shown in the ne/t slide, presenting a stress M strain diagram..


65/148

2rom the analysis of the curve, it comes out that: th fi t t f th i t i ht li d d t l ti d f ti



66/148


99

the first part of the curve is a straight line and corresponds to elastic deformations

according to @ooes law and represents the e+as!( re,(on. The slope of the curve 'that

is the ratio between the stress and the strain in the elastic region( is the modulus of

elasticity "$,called also the8oun,Vs odu+us& beyond the elastic limit, peranen! or p+as!( de-ora!(on occurs and the stress5

strain curve assumes a curvilinear trend. If the stress is released in the region between

the elastic limit and the yield strength, the material will contract along a line nearly straight

and parallel to the original elastic line, leaving a permanent set& in steels, a phenomenon, nown as )(e+d(n,, occurs after the elastic limit. It can be

observed, in fact, that once a ma/imum value of stress is reached, a period of

deformation follows, though the stress remains constant or even decreases. The

ma/imum stress reached in this region is called the upper )(e+d po(n!, while the

minimum is called the +oer )(e+d po(n!. In materials that do not e/hibit a mared yield

point, it is customary to identify a quantity called (n(u )(e+d s!ren,!*, which can be

defined as the stress at which the material has a specified permanent set 'a deformation

of 0.P is generally accepted by the Industry(. 2or materials used to produce tubular

goods, the A#I specifies the )(e+d s!ren,!* as !*e !ens(+e s!ress reu(red !o produea !o!a+ e+on,a!(on o- 0.7030.97W 'depending on the grade of the steel( between the

gauge length&


67/148

"ESIGN FACTOR 5"F6

The "F is defined as the ra!(o be!een !*e p(pe res(s!ane to a certain load

4.9. APPROACH TO CASING "ESIGN THE "ESIGN FACTOR "F


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9;

The "F is defined as the ra!(o be!een !*e p(pe res(s!ane to a certain load

'burst, collapse, tension( and theorrespond(n, +oad es!(a!ed inside the well.

)ifferent "es(,n Fa!orsare specified for the three load types and for the varioussteel grades 'high grade steels require higher )2 because they have a smaller

margin between Hield *trength and Tensile *trength(. The following )2s must be

used in casing design calculations:

4.9.1. CASING "ESIGN CRITERIA %#RST

%urs! +oad(n, on the casing is induced when internal pressure

d t l d i th f i b fi t l l ti


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9>

e/ceeds e/ternal pressure and is, therefore, given by first calculating

the probable pressure acting e/ternally to the casing string and the

pressure e/pected internally '*AH inside it(. The burst pressure is,

then, the difference between the e/pected internal pressure and the

e/pected e/ternal pressure

)epending on type of casing, different boundary conditions are

assumed for calculating the stresses which tend to burst the casing&

usually a distinction is made between casings in the following way, in

order to perform the %#RST 'OA" COMP#TATION :

surface casing&

intermediate casings&

production casing&

liners, if any 'drilling or production(.

S#RFACE CASING

In!erna+P

The e++*ead pressure +((! is arbitrary and is generally set equal to that of thei ti f th llh d d %O# i t b t ith i i



70/148


:0

Pressure

O(+ Copan)no *o XGOFP a--e!!*eassup!(onsand !*eonseuen!opu!a!(one!*ods

woring pressure rating of the wellhead and %O# equipment, but with a minimumvalue of -40 gf1cm

Ghen an oversize %O# having a capacity greater than that necessary is selectedor in case of a subsea wellhead, the e++*ead (n!erna+ pressure +((! will be 60Pof the calculated pressure obtained as the difference between the fracture pressureat the casing shoe and the hydrostatic pressure of a gas column up to the well head'methane with a density of 0.! g1dm!is normally considered(. In any case it shallnever be taen less than ,000 psi '-40 gf1cm(. The use of methane for thiscalculation is the "worst case$ when the specific gravity of the fluid is unnown.The bo!!o3*o+e (n!erna+ pressure +((! is set equal to the predicted fracturegradient of the formation below the casing shoe.

onnect both the wellhead and bottom5hole internal pressure valueswith astraight line to obtain the ma/imum internal pressure load versus depth.

E?!erna+Pressure

In wells with surface wellheads, the e/ternal pressure value is taen equal to thehydrostatic pressure of the drilling fluid in which the casing has been run.In wells with subsea wellheads:A! !*e e++*eadGater )epth / *eawater )ensity / 0.- 'gf1cm(

A! !*e s*oe'*hoe )epth 5 Air 8ap( / *eawater )ensity / 0.- 'gf1cm

(Ne! Pressure The resu+!(n, burs! +oad, or ne! pressureBwill be obtained by subtracting, at

each depth, the e/ternal from the internal pressure

S#RFACE CASING 400



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:1

In!erna+ Pressure

at bottomhole: fracture pressure '82.2 ,-D2

at wellhead: %O# G#, C 140 ,-D2

E?!erna+ Pressureat bottomhole: hydrostatic pressure of mud

'-.-0 g1litre(, " 44 ,-D2

at wellhead:E 0 5re+a!(ve pressure6

5R E " *ere STRAIGHT 'INE6

Resu+!(n, burs! +oad 5Ne! Pressure6Internal #ressure 5 /ternal #ressure

at wellhead, C 140 0 140 ,-D2at bottomhole, F 9>.2 44 27.2

,-D2

INTERME"IATE CASINGS 5see one s+(de -or ea* o- !*e6



72/148


:2

In!erna+ Pressure

O(+ Copan)no *o XGOFP a--e! !*eassup!(ons and!*e onseuen!opu!a!(ons

The e++*ead (n!erna+ pressure value is taen as the 60P of the calculatedvalue obtained as the difference between the fracture pressure at the casing

shoe and the pressure of a gas column at the wellhead. If this value is lowerthan -40 gf1cm, the %O# G# of -40 gf1cmis considered at the wellhead.The bo!!o*o+e (n!erna+ pressure +((! is equal to that of the predictedfracture gradient of the formation below the casing shoe.onnect both the wellhead and bottom5hole internal pressure limitswith astraight line to obtain the ma/imum internal pressure load.

E?!erna+ Pressure The e?!erna+ pressure va+ue is taen to be equal to that of the formationpressure.

K Gith a subsea wellhead, at the wellhead, hydrostatic seawater pressureshould be considered.

Ne! Pressure The resu+!(n, burs! +oad, or net pressure, will be obtained by subtracting, ateach depth, the e/ternal from internal pressure. IN THIS CASE THETREN" IS NOT RECTI'INEAR YYYYYYYYYYYYYY

INTERME"IATE CASING 1200

In!erna+ Pressure

t b tt h l f t '- =3 f1 1-0 (



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:$

at bottomhole: fracture pressure '-.=3 gf1cm1-0 m(,A 2$4 ,-D2

at wellhead:

560P of bottom hole fracture pressure minus thehydrostatic head of a column of gas '0.! g1dm!(,

% 0.9 52$4 3 $96 11;.; ,-D2

5%O# G#, C 140 ,-D2

E?!erna+ Pressurepore pressure:

5 at J00 m, "1 51.0$ ? ;006 D 10 ;2.4 ,-D2

5at -000 m, "2 51.20 ? 10006 D 10 120.0 ,-D2

5at -00 m, "$ 51.$:7 ? 12006 D 10 197.0 ,-D2


5at surface. C 140 3 0 140 ,-D2

5at J00 m, 200 3 ;2.4 11:.9 ,-D2

5at -000, 21; 3 120 >;.0 ,-D2

5at -00, 2$4 3 197 9>.0 ,-D2


In!erna+ Pressure at bottomhole fract re press re '- =! gf1cm1-0



74/148


:4

at bottomhole: fracture pressure '-.=! gf1cm1-0

m(, A 4;2.7 ,-D2at wellhead: 60P of bottomhole fracture pressure

minus the hydrostatic head of a column of gas '0.!g1dm!(,

% 0.9 ? 54;2.7 :76 244.7 ,-D2


5 at J00 m, "1 51.0$ ? ;006D10 ;2.4 ,-D2

5 at -J00 m, "2 51.:0 ? 1;006D10 $09.0 ,-D2

5 at 300 m, "n 51.0$ ? 27006D10 27:.7 ,-D2

Resu+!(n, burs! +oad 5Ne! Pressure6Internal #ressure 5 /ternal #ressure5at surface, % 244.7 3 0 244.7 ,-D2

5at J00 m, $$0.0 3 ;2.4 24:.9 ,-D2

5at -J00 m, 410.0 $09.0 104.0 ,-D25at 300 m, 4;2.7 3 27:.7 227.0 ,-D2

PRO"#CTION CASING



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:7

The "worst case$concerning burst

load conditions on produ!(on

as(n, occurs when the well isshut5in and there is a lea in

correspondence of the top of the

tubing, or in the tubing hanger,

and the shut5in well head pressure

is applied to the top of the pacer

fluid 'i.e. completion fluid( in thetubing

'EAAGE

PRO"#CTION CASING



76/148


:9

In!erna+ Pressure

O(+ Copan)no *o XGOFP a--e! !*eassup!(ons and!*e onseuen!opu!a!(ons

The e++*ead (n!erna+ pressure va+ue is obtained as the difference betweenthe pore pressure of the reservoir fluid and the hydrostatic pressure of theproduced fluid which is inside the tubing. In case of uncertainty on the nature

of produced fluid 'hence of its density(, a column of gas having density < 0.!g1dm!will be considered. Actual gas1oil gradients can be used if informationon these is nown. The bo!!o3*o+e (n!erna+ pressure va+ue is obtained by adding thewellhead internal pressure to the annulus hydrostatic pressure e/erted by thecompletion1pacer fluid. 8enerally the completion fluid density is equal to, orclose to, the mud weight in which the casing has been installed. onnect both the wellhead and the bottomhole internal pressure with astraight line to obtain the ma/imum internal pressure.

E?!erna+ Pressure The e/ternal pressure is taen to be equal to that of the formation pressure. Gith a subsea wellhead, at the wellhead, hydrostatic seawater pressureshould be considered.

Ne! Pressure

The resulting burst load, or net pressure, is obtained by subtracting, at eachdepth, the e/ternal from the internal pressure. A'SO IN THIS CASE THETREN" IS NOT RECTI'INEAR YYYYYYYYYYYY

PRO"#CTION CASING $000

In!erna+ Pressure



77/148


::

at wellhead: reservoir pressure minus the

hydrostatic head of the fluid to be produced 'if the

density of the fluid is unnown, consider gas at 0.!

g1dm!(, A $0> 3 >0 21> ,-D2

at bottomhole: wellhead pressure plus the

hydrostatic head of completion fluid,

% 21> Z 51.1 ? $0006D10 74> ,-D2


5 at J00 m, "1 51.0$ ? ;006 D 10 ;2.4 ,-D2

5at -00 m, "2 51.9> ? 21006 D 10 $74.0 ,-D2

5at !000 m, "n 51.0$ ? $0006 D 10 $0> ,-D2


5 at surface, 21> 3 0 21> ,-D2

5at J00 m, 24$ Z ;; ;2.4 24;.9 ,-D2

5at -00, 2;2 Z 2$1 $74 17> ,-D2

5at !000 m, 74> $0> 240 ,-D2

'INERS &ITH INTERME"IATE CASINGS

If d illi li h t b d th i i hi h th li i d d t



78/148


:;

If a drilling liner has to be used, the casing in which the liner is suspended must

withstand the burst pressure that may occur while drilling below the liner.

The design of the intermediate casing string is, therefore, altered slightly:

-( *ince the fracture pressure and mud weight may be greater or lower below

the liner shoe than below the casing shoe, these values must be used to design

both the intermediate casing string and the liner.

( Ghen performing well testing operations or producing through a liner, the

casinginside which the liner is suspended is part of the production stringandmust be designed according to this criterion.

TIE3%AC STRING

In a high pressure well, the intermediate casing string above a liner may be

unable to withstand a tubing lea at surface, according to the production burstcriteria seen before. One solution to this problem is to tie5bac the liner by a

string going from the liner top to surface, thus isolating this intermediate casing.

Co++apse +oad(n, of the casing is induced if the e/ternal pressure e/ceeds the

4.9.2. CASING "ESIGN CRITERIA CO''APSE


79/148


:>

Co++apse +oad(n, of the casing is induced if the e/ternal pressure e/ceeds the

internal pressure. It occurs as a result of either or a combination of:

reduction in internal fluid pressure&increase in e/ternal fluid pressure& additional mechanical loading imposed by plastic formations 'i.e. clay, salt(

movement.

The design of a casing string in collapse mode consists in selecting the lowest cost

pipe that has sufficient strength to meet with the desired design criteria and "designfactor$ )2.

N O T I C E

Ghen maing a selection, if a choice e/ists between a lower grade heavy pipe and a

higher grade but lighter pipe, both of them providing adequate strength at similar cost,

the higher grade 'lighter( pipe should be chosen due to the reduction of tension

loading.


80/148


81/148

INTERME"IATE CASING

In!erna+Pressure

The worst case for collapse loading occurs when a loss of circulation isencounteredwhile drilling the ne/t hole section. This results in the mud level insideth i d i t ilib i l l h th d h d t ti h d l



82/148


;2

O(+ Copan)no *o X

GOFP a--e!!*eassup!(onsand !*eonseuen!opu!a!(one!*ods

the casing dropping to an equilibrium level where the mud hydrostatic head equalsthe pore pressure of the thief zone. onsequently, it will be assumed that thecasing is empty to the height '@(calculated as follows:

5 '@loss5 @( / dm< @loss / 8p 5 @ < @loss'dm 5 8p(1dm


83/148


;$

F+u(d He(,*! Copu!a!(on

'@ loss5@( / dm< @ loss/ 8p

@ < @ loss'dm5 8p( 1 dm

If 8p< -.0! gf1cm1-0m

then

H H +oss 5d3 1.0$6Dd

or

H H +oss513 GpDd6

@

INTERME"IATE CASING 1200 In!erna+ Pressurein case the depth at which circulation losses are

t d i th l l d i l l t d



84/148


;4

e/pected is nown, the level drop is calculated

with: H H+oss51 GpD dud6

If:dmud < -.J0 g1litre

8p< -.0! gf1cm1-0 m

@loss< 300 m

the well will be empty down to H 109>.4 5a! sur-ae. 05a! 109>.4 0

5a! 1200 512003109>.46?1.;0?0.12$.7 ,-D2

E?!erna+ Pressure5pressure of the mud used to run the casing

% 51.4; ? 12006 D 10 1::.9 ,-D2

Resu+!(n, o++apse +oad 5Ne! Pressure6

5/ternal #ressure 5 Internal #ressure5at surface, A 05at -06=.4 m, F 17;.$ ,-D2

5at -00, E 51::.9 3 2$.76 174.1 ,-D2


In!erna+ PressureIf the depth of e/pected circulation losses



85/148


;7

is unnown, it is assumed the casing half

void and half filled with the mud to be used

in the ne/t hole section at its ma/imumdensity:

5 from 05600 m, C 0

5 at -00 m, d f,ma/ ne/t phase / L @

" 51.;0?9006D10 10; ,-D2

E?!erna+ Pressurepressure of the mud used to run the

casing, % 51.4;?12006D10 1::.9 ,-D2

Resu+!(n, o++apse +oad 5Ne! Pressure6/ternal #ressure 5 Internal #ressure5at surface, A 05at 600m, F 51.4;?9006 D 10 3 0;;.; ,-D2

5at -00 m, E 51::.9 3 10;.06 9>.9 ,-D2


I ! + P



86/148


;9

In!erna+ Pressure5casing half void and for the remaining half

the mud at its ma/imum density3 -ro 031270 0

3 a! 2700 51.1?12706D10 1$:.7 ,-D2

E?!erna+ Pressure5pressure of the mud used to run the

casing, % 51.;?27006 D 10 470 ,-D

2

Resu+!(n, o++apse +oad 5Ne! Pressure6/ternal #ressure 5 Internal #ressure5at surface, A 05at -30 m, F 51.;?12706 D 10 227 ,-D2

5at 300 m, E 470.0 3 1$:.7 $12.7 ,-D2

PRO"#CTION CASING

In!erna+ The worst case occurs when the casing is completely empty. It is in fact probable



87/148


;:

Pressure

O(+ Copan)no *o XGOFP a--e!!*eassup!(onsand !*eonseuen!opu!a!(on

e!*ods

that during the productive life of a well, tubing leas often occur. Also wells may beon artificial lift or have plugged perforations or very low internal pressure values

and, under these circumstances, the production casing string could be partially orcompletely empty. This must be taen into consideration in the design and theideal solution is to design for zero pressure inside the casing which provides fullsafety.In particular situations, the Gell Operations 9anager may consider that thelowest casing internal pressure is the level of a column of the lightest densityproducible formation fluid.

E?!erna+Pressure

Assume the hydrostatic pressure e/erted by the mudin which casing is installed.In case of salt sections, consider uniform e/ternal loading equal to theoverburden pressure at the true vertical depthof the relevant point.

Ne! Pressure In case of the casing being empty the resultant collapse load, or net pressure, isequal to the e/ternal pressureat each depth.

In other cases, it will be obtained by subtracting, at each depth, the internal fromthe e/ternal pressure.

PRO"#CTION CASING $000

In!erna+ Pressure casing completely void



88/148


;;

casing completely void

3 a! sur-ae 0

3 a! bo!!o*o+e 0

E?!erna+ Pressure5pressure of the mud used to run the

casing, % 51.1 ? $0006 D 10 $$0

,-D2

Resu+!(n, o++apse +oad 5Ne!

Pressure65/ternal #ressure 5 Internal #ressure5at surface, A 0 5re+a!(ve pressure65at !000 m, % $$0 ,-D2

'INERS AN" INTERME"IATE CASINGS

-( If a drilling liner has to be used, the casing above, in which the liner is



89/148


;>

suspended, it must withstand the collapse pressure that may occur while drilling

below the liner. Therefore the design of the intermediate casing string is slightly

altered.( Ghen well testing or producing through a liner, the casing above the liner is part

of the production casing5liner string and must be designed according to this

criterion.

TIE3%AC STRING

If the intermediate string above the liner is unable to withstand the collapse

pressure calculated according to the production collapse criteria, it will be

necessary to run and tie5bac a string of casing from the liner top to the surface.

Tens(+e -a(+ureoccurs if the longitudinal force e/erted on a pipe e/ceeds either the tensile strength

of the pipe or of its connections. 8enerally, the connection used in a string of casing is stronger

than the pipe body although this must always be checed out.

4.9.$. CASING "ESIGN CRITERIA TENSION


90/148


>0

2or situations where a connection coupling has to be of special clearance type 'i.e. smaller

diameter than the normal( or if a flush +oint pipe must be used, the connection will be weaer thanthe pipe body.

Cas(n, !ens(+e +oadsare usua++) (posed b)-( T*e e(,*! o- !*e p(pe (!se+-. The highest tensile stresses will occur at the uppermost portion

of the pipe. The tension is the weight of the pipe in air less buoyancy.

( %up(n, a een! p+u,.

!( %end(n,.4( S*o +oad(n,:

K Ghile lowering casing through unstable formations such as cavings where the casing string may

get temporarily stuc before suddenly slipping through, thereby inducing tensile shoc loads.

K Ghen landing casing in a subsea wellhead from a floater.

3( #pard and donard re(proa!(n, oveen!scarried out where there is a tendency to

become differentially stuc. To free the pipe considerable pull may be necessary.

6( H(,* (n!erna+ pressurewill induce tensional stresses caused by radial e/pansion and, hence,

a/ial contraction.

Esually, mainly the first three parameters are taen into consideration when designing a casing.

%#O8ANC8 FORCE

The effect of buoyancy is generally assumed to be the redu!(on (n e(,*! of the



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>1

casing string when it is suspended in a liquid compared to its weight in air.

The buoyancy or reduction in string weight, as observed on the blocs of the rotarytable, is the resultant of pressure forces acting on all the e/posed horizontal faces of a

body and in calculations is defined as negative as it acts upwards, hence reducing the

pipe weight.

The areas referred to are the tube end areas, the shoulders at point of changing casing

weights and, to a smaller degree, the shoulders on collars. The forces acting on theareas of collar shoulders are for practical purposes negligible in casing design as the

upward and downward facing shoulders countered each other over short distances.

%uoyancy 2orce < Geight in Air / '9ud )ensity1*teel )ensity(

Apparent Geight < Geight in Air / R'*teel )ensity M 9ud )ensity(1*teel )ensityS

Apparent Geight < Geight in Air / %uoyancy 2actor

%uo)an) Fa!or 1 5ud dens(!)6D5s!ee+ dens(!)6

*teel )ensity < 7.J3 g 1 litre *teel *pecific Geight < 7.J3 g force 1 litre

%EN"ING

Ghen calculating tensile loading, the effect of bending must also be considered, if

li bl Th b di f th i dditi l t i th ll f th i



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>2

applicable. The bending of the pipe causes additional stress in the walls of the pipe.

%ending causes tension on the outside of the pipe and compression on the inside of

any bend, assuming the pipe is not already under tension.

%EN"ING

%ending is caused by any deviations in the wellbore from the vertical resulting from

side5tracs, build5ups and drop5off angles. *ince bending load increases the total tensile



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>$

, p p g g

load, it must be deducted from the usable rated tensile strength of the pipe.

2or determination of the effect of bending, the following formula should be used:

T% 17.72 [ \ [ " [ A-

where:

5 < build5up rate or drop5off rate 'degrees 1 !0 m(

5 ) < outside diameter of casing 'in(

5 Af < cross5sectional area of casing 'cm(

5T% < additional tension due to bending 'g force(.

*ince bending load, in effects, increases tensile load at the point applied, it must be

deducted from the usable strength rating of each section of pipe that passes the point of

bending. The section which is ultimately set through a bend must have the bending loaddeducted from its usable strength up to the top of the bend. 2rom that point up to the

top of the section the full usable strength can be used.

E@AMP'E OF %EN"ING CA'C#'ATION

"a!a

K asing: O) -! !1JU, 7 lbf1ft '-07.-4 gf1m(, Af< -!!.= cm, 73, %TC

K )irectional well with casing shoe at ,000 m '9)(

;i ff i t t !00



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>4

K ;ic5off point at !00m

K %uild5up rate: !V1!0m

K 9a/imum angle: !0V reached at 600 mK 9ud weight : -.- gf1dm!

K #ipe body yield strength: -,33J,000 lbf '707 t force(

K )esign factor : -.7 707 1 -.7 < 4-3 t force

Ca+u+a!(on

-( asing weight in air 'Ga(

Ga< -07.-4 / ,000 < -4 t force( asing weight in mud 'Gm(

Gm< -4 / 0.J3= < -J4 t force

!( Additional tension due to the bend(n, e--e!'T%(

T% 17.72 ? $ ? 1$.$:7 ? 1$$.>2 ;$441 , -ore

This stress will be added to the tensile stress already e/isting on the curved section of hole

4( Tension in the casing at !00 m due to its weight< 0.J3= / '-700 / -07.-4( < -36 t force

3( Total tension in the casing at !00 m 'weight in mud W bending( < -36 W J! < != t force6( Tension in the casing at 600 m due to its weight < 0.J3= / '-400 / -07.-4( < -= t force

7( Total tension in the casing at 600 m 'weight in mud W bending( < -= W J! < - t force


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"ESIGN PROCE"#RE

-( alculate the e(,*! o- !*e as(n, s!r(n, (n a(r.



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>:

( alculate the e(,*! o- !*e as(n, s!r(n, (n ud by multiplying theprevious weight by the buoyancy factor '%2( in accordance with the mud

weight in use.

!( Add the additional load due to bup(n, an) een! p+u, to the casing

string weight in mud. Tae into account possible pressurization when

performing operations such as opening1closing )F valves and settingpacers.

No!e T*(s +oad an be a+u+a!ed b) u+!(p+)(n, !*e e?pe!ed bup3p+u,

pressure b) !*e orrespond(n, as(n, (nner se!(on area.

4( In deviated wells, calculate the additional tension due to bend(n,.

3( ompare the obtained weight value to the csg body H* 'including )2 effect(

S#RFACE CASING 400

TENSION

30 -00 t2

%"

4.:.$.$. CASING SE'ECTION E@AMP'E TENSION


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>;

TENSION

asing >ength: 400 mGeight in Air, A%< '400 / -3J.47( < 6!.! t force

Geight in 9ud 'dm< -.-0 g1litre(, ) < 34.4 t force

AC

There is no reliable methods of predicting casing wear and determining the reduction

in casing burst and collapse properties due to the reduction in the thicness of casing

walls. @owever, when needed, some theoretical models can be applied to mae a

4.9.7. CASING "ESIGN CRITERIA CASING &EAR


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>>

, , pp

prediction about possible wear occurrences.

In ver!(a+ e++s, casing wear usually occursin the first few +oints below the wellhead

or in correspondence of intervals with a high dogleg severity 'abrupt variations of

inclination and direction of the wellbore tra+ectory(. In casing design, usually casing

wear in vertical wells is not considered unless specific cases.

In dev(a!ed e++s, wear will occur in correspondence of the build5up and drop5off

sections. The casing covering these sections has to be of a higher grade or heavier

wall thicness, in particular when long drilling times are e/pected.

The ma+or factors affecting casing wear are:

K Cotation of drill pipes

K Tool +oint lateral load and diameter



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100

+

K )rilling rate

K Inclination of the holeK *everity of dog legs

K *teel wear factor.

?? %i5center bit employment

The wear factor depends upon several

variables including:

K 9ud properties

K >ubricants

K )rill solids

K Tool +oint roughness

K Tool +oint hardness.

CORROSION

)uring the drilling phase, if there is any lielihood of a sour corrosive fluid influ/,

consideration should be given to setting a sour service casing string before drilling into

4.9.9. CASING "ESIGN CRITERIA CORROSION


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101

the reservoir. The %O# stac and wellhead components must also be suitable for sour

service.

O?),en 5O26 O/ygen dissolved in water drastically increases its corrosion action

potential. It can cause severe corrosion at very low concentrations of less than -.0 ppm.

Carbon d(o?(de 5CO26#ressure increases the solubility of Oand lowers the p@ of

drilling fluids, while temperature decreases its solubility raising the p@. orrosion causedby dissolved O is commonly called "sweet$ corrosion. The partial pressure of carbon

dio/ide can be determined by the formula:

Par!(a+ Pressure To!a+ pressure ? Mo+ Fra!(on o- CO2(n !*e ,as.

Esing the partial pressure of O as a reference to predict corrosion, the following

relationships have been found:

K partial pressure Q!0 psi usually indicates high corrosion ris.K partial pressure between 75!0 psi may indicate medium corrosion ris.

K partial pressure X7psi generally is considered non corrosive.

H)dro,en Su+p*(de 5H2S6 @ydrogen sulphide is very soluble in water and when

dissolved behaves as a wea acid and usually causes pitting. Attac due to the presence

of dissolved hydrogen sulphide is referred to as "sour$ corrosion.

4.9.9. CASING "ESIGN CRITERIA CORROSION


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102

Other serious problems which may result from @* corrosion are hydrogen blistering andsulphide stress cracing.

The S.S.C. 5Su+p*(de S!ress Cra(n,( phenomenon is triggered off when, at

temperatures below J0V and in the presence of tension stress, the @* comes into

contact with @O freeing @W ions. Temperatures above J0V inhibit the *.*..

phenomenon, therefore if the temperature gradient is nown, this may be useful in theselection of the tubular materials most suited to resist @* attac. valuation of the

problem depends on the type of well.

The combination of @* and O is more aggressive than @* alone and is frequently

found in oilfield environments.

It should be pointed out that @* also can be generated by microorganisms '*C%( which

attac sulphur5containing chemicals used in the formulation of drilling fluids

Tepera!ure E--e!s: 2or deep wells, reduction in yield strength must be considered

due to the effect on steel by *(,* !epera!ures. If no information is available on

temperature gradients in an area, a gradient of .35!V1-00m should to be assumed.

4.9.:. CASING "ESIGN CRITERIA OTHER EFFECTS


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10$

Operations at +o !epera!uresrequire tubulars made from steel with high ductility toprevent brittle failures during *EC2A transport and handling.

There is a wide range of casings available from *uppliers, which goes from

plain carbon steel for standard applications to e/otic duple/ steels 'duple/

stainless steels are called "duple/$ because they have a two5phase

4.:. CASING SPECIFICATION AN" C'ASSIFICATION


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104

stainless steels are called duple/ because they have a two phase

microstructure consisting of grains of ferritic and austenitic stainless steel(

for e/tremely sour service conditions.

The available casings can be classified under two main specifications:

API SPECIFICATION 5Aer(an Pe!ro+eu Ins!(!u!e6

non3API SPECIFICATION 'materials out of A#I *pecifications have been

developed to meet demand for higher classes of casings able to cope with

e/treme conditions beyond the range of application of A#I casings(

The Aer(an Pe!ro+eu Ins!(!u!e 5API( has an appointed ommittee on

*tandardization of Tubular 8oods which publishes, and continually updates, a

series of *pecifications %ulletins and Cecommended #ractices covering the



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107

series of *pecifications, %ulletins and Cecommended #ractices covering the

manufacture, performance and handling of oilfield tubular goods. They also

licence manufacturers to use the A#I 9onogram on products which meet with

their published specifications.

The %ulletin regarding tubular goods specifications is the API 7TR C$DISO

10400 "Technical Ceport on quations and alculations for asing, Tubing,

and >ine #ipe Esed as asing or Tubing& and #erformance #roperties Tablesfor asing and Tubing, 2irst dition 'Identical to I*O -0400:007(, dition: 7th

American #etroleum Institute 1 0-5)ec500J 1 !7J pages 'based on the %ull

3 "%ulletin on #erformance #roperties of asing, Tubing and )rill #ipe$,

-st dition, October -===(.

It should not be interpreted that only A#I tubulars and connections may be

used in the field& in fact, there are situations, which can be solved only if

special materials, not yet addressed by A#I specifications, are used.



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109

special materials, not yet addressed by A#I specifications, are used.

@owever, when using non5A#I pipes and connections, the designer mustchec the methods by which the strengths have been calculated. Esually it will

be found that the manufacturer will have used the published A#I formulae

'reported in the above mentioned A#I 3TC !(, baced up by tests to prove if

the performance of the product conforms or e/ceeds these specifications.

*ometimes, the non5A#I manufacturers claim the performances of theirmaterials be better than those calculated using the A#I formulae& in these

circumstances, claims must be critically e/amined by the designer.

If needed, an end5user can specify more stringent chemical, physical and

testing requirements on orders.

A casing is classified according to:

ou!s(de d(ae!er: generally e/pressed in inches

4.:.1. API CASING SPECIFICATIONS


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10:

no(na+ un(! e(,*!: e/pressed in lb force 1 ft 'g force 1 m(

,rade o- !*e s!ee+: indicated by a letter ';, #, Y( and a number '40, 73, --0,

etc.(, which represents the yield strength of the material divided by -000

a++ !*(nessand (ns(de d(ae!er&

e*an(a+ proper!(esof pipe body and couplings

!)pe o- onne!(on: A#I Cound Thread '*hort or >ong(, %uttress, /treme

>ine

An e/amples of casing designation is as follows: = 31J$ #--0 47 lb force 1 ft

%T Z73J 'shoe depth in feet(

API PRO"#CTS

There are eleven A#I casing grades and seven tubing grades.

4.:.1.2. API CASING GRA"ES


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10;

CASINGS T#%INGS

H340 H340

]377 ]377

377

M397

N3;0 N3;0

'3;0 '3;0

C3>0 C3>0

C3>7

T3>7 T3>7P3110 P3110

3127


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4.:.1.$. API CASING CONNECTIONS


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110

NON3#PSET CO#P'ING

#PSET CO#P'ING

API THREA"E" CONNECTIONS

The four most common A#I threaded connections are:'(ne P(pe T*reads ; R d S* ! '*TN( d ' '>TN( T* d



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111

; Round S*or!'*TN( and 'on,'>TN( T*reads

%u!!ress'%T(E?!ree '(ne T*reads

>ong and short threads are identical e/cept for thread length.

These connections are of a type called interference connections, i.e. the

connection seals by the wedging action 'interference( of two tapered surfacescoming into contact. @owever the surfaces are not in full contact over their

entire area. *ealing of the clearance area of both eight round and buttress

threads is accomplished with A#I modified thread lubricant 'and sometimes by

"premium$ thread lubricants.(

'INE PIPE THREA"S



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112

RO#N" 5'ONG AN" SHORT6 THREA"S4.:.1.$. API CASING CONNECTIONS


113/148


11$

%#TTRESS THREA"S



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114

E@TREME3'INE THREA"S4.:.1.$. API CASING CONNECTIONS


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117

4.:.1.4. API CASING TA%'ES


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119

API Ran,e 'en,!*B

C*e(a+

Copos(!(on

o- API

Tubu+ars

4.:.1.4. API CASING TA%'ES


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11:

4.:.2. NON3API CASING SPECIFICATIONS


118/148


11;

CASING PROFI'E

4.:.$. CASING SE'ECTION E@AMP'E


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11>

1. CAON"#CTOR PIPE $0= AT 70

2. S#RFACE CASING 20= AT 400

$. FIRST INTERME"IATE CASING 1$ $D;= AT 1200

4. SECON" INTERME"IATE CASING > 7D;= AT 2700

7. PRO"#CTION CASING := AT $000

20= CASING4.:.$. CASING SE'ECTION E@AMP'E


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120

20= CASING4.:.$. CASING SE'ECTION E@AMP'E


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121

S#RFACE CASING 20= AT 400

Resu+!(n, burs! +oad 5Ne! Pressure6Internal #ressure 5 /ternal #ressure at wellhead, C 140 0 140 ,-D2

4.:.$.1. CASING SE'ECTION E@AMP'E %#RST


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122

at wellhead, C 140 0 140 ,-D

at bottomhole, F 9>.2 44.0 27.2 ,-D2

%#RST RESISTANCE

"es(,n Fa!or 1.07

[533 =4 lbf1ft: --0 psi


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12$

5at surface, A 05at bottomhole, %< 44 3 0 44 ,-D2

CO''APSE RESISTANCE

"es(,n Fa!or 1.10

[533 =4 lbf1ft: 30 psi < !6 gf1cm, ')2


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124

]377 109.7 +b-D-!'-3J.47 g force 1 m(asing body Hield *trength: -6J3000 lbf < 74= t

force

')2 < -.70( 440.3 t force

asing >ength: 400 m

Geight in Air, A%< 400 / -3J.47 < 6!.! t force

Geight in 9ud 'dm< -.-0 g1litre(, asing GG 0 Z >06 vs 440.7 OAC

]77

10

9.7

+bD-!E

440

!

1$ $D;== CASING



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127

1$ $D;== CASING



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129

INTERME"IATE CASING 1$ $D;= a! 1200

Resu+!(n, burs! +oad 5Ne! Pressure6Internal #ressure 5 /ternal #ressure5at surface. C 140 3 0 140 ,-D2



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12:

5at J00 m, 200.0 3 ;2.4 11:.9 ,-D25at -000, 21; 3 120 >; ,-D2

5at -00, 2$4 3 197 9> ,-D2

%#RST RESISTANCE

"es(,n Fa!or 1.07

]377 74.70 +b-D-! 2:$0 ps( 1>2 ,-D2B5"F1.0761;$ ,-D2

[533 6- lbf1ft: !0=0 psi


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12;

at -06=.4 m, F 17;.$ ,-D

5at -00, E 1::.9 3 2$.7 174.1 ,-D2

[533 34.30 lbf1ft: --!0 psi


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12>

N3;0 :2 +b-D-! 510:.1$ ,-D6

P(pe %od) 8(e+d S!ren,!* 1.991.000 +b-

:72 ! -pre 5"F 1.:06 442 ! -ore

asing >ength: -00 m

Geight in Air A% < -00 / -07.-! < -J.3 t

force

Geight in 9ud 'dm< -.4J g1litre(, '%2


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1$0

OTHER S'I"ES

Ghen needed, the position and magnitude of volumetric wear in a casing string can be

theoretically estimated by calculating the energy imparted by the rotating tool +oints to

the casing at different casing points and dividing this by the amount of energy required

to wear away a unit volume of casing. The percentage of casing wear at each point

along the casing is then calculated once the volumetric wear has been obtained.



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1$1

The vo+ue!r( ear is proportional to an empirical "wear factor$, which is defined as

the coefficient of friction divided by the volume of casing material removed per unit of

energy input. The Gear Folume, F, equals:

590 ? ^ ? F ? ' ? " ? N ? S6DPwhere:F < Gear Folume #er 2oot 'in!1ft(

2 < Gear 2actor 'in1lbf(> < >ateral >oad on )rill #ipe #er 2oot 'lbf1ft(

) < Tool [oint )iameter 'in(

D < Cotary *peed 'C#9(* < )rilling )istance 'ft(

# < #enetration Cate 'ft1hr(

No!e T*e *e(a+ a!(on o- ,ases su* as H2SB CO2 and O2!ends !o redue !*e

sur-ae *ardness o- s!ee+ andB !*usB on!r(bu!es s(,n(-(an!+) !o !*e ra!e o- ear.

The reoended proedure to determine the wear effect on casing mechanical

performances is the following

-( conduct the casing design as previously seen&

( in correspondence of the wear points, calculate the allowable reduction in wall5



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1$2

thicness of the casing that maes the burst or collapse resistance of the casing equal tothe calculated burst or collapse loads, including the appropriate )esign 2actors&

!( estimate the wear rate in terms of loss of wall thicness per operating day. A wear

percentage below 7P is considered acceptable&

4( from the loss in wall thicness and the rate of wear, calculate the allowable operatingtime in the casing string:

5 If the allowable operating time is less than the planned operating time, use

heavier casings or increase their grade -00 m above and to 60 m below the

wear point until the allowable operating time e/ceeds the anticipated operating

time.

5 If the allowable operating time is greater than the planned operating time donot include a wear allowance.

"ETECTION OF CASING &EAR

)etecting casing wear can be achieved by two methods:

K use of magnets in the mud flow return in order to catch any piece of metal present in the

drilling fluid.

K recording of caliper logs immediately after the casing has be run into the hole in order to



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1$$

provide a base log. A wear log can then be run at any time while drilling the ne/t holesection.

CASING &EAR RE"#CTION

If there are fears about casing wear, the following drilling practices can be applied to

minimize this occurrence:K use of down hole motors and turbines&

K use of rubber protectors on drill pipes&

K use of drill pipes without hard5facing&

K minimization of doglegs&

K minimization of sand content inside the mud&

K use of oil5based mud.

API PRO"#CTS

H340

@540 is the lowest strength casing and tubing grade in the specifications, with minimum yield strength

of 40 si, and a minimum tensile strength of 60 si. @540 is a carbon type steel

04.politecnico di torino casing programme 2010

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