casing types casing seating depth and casing design

casing

1. CASING

2. The main functions of the casing in any well are:
1.Maintain hole integrity
2.Isolate abnormally pressured zones
3.Protect shallow weak formations from heavier mud weights
required in the deeper portions of the hole
4.Prevent contamination of freshwater-bearing strata
5.Support unconsolidated sediments
6.Along with cement hydraulic seal

3. Common Casing Designs

4. Conductor Casing
•Sealoffunconsolidatedformations
atshallowdepths
•Stopwashoutsunderthedrillingrig.
•Protectfreshwatersands.
•Togiveabaseandsupportforthe
nextstringofcasing
•Setbeforetherigissetup

5. SURFACE CASING
Surfacecasingisthefirststringofcasingusedafterthe
conductorpipe.
Itisrequiredinsomeinstancesbylaw(toprotectgroundwater)
andisnormallycementedfulllength.
SurfacecasingsupportstheBOPstackandsubsequentcasing
andtubingstrings.
Itisnormallytheonlystringdesignedtocarrycompression
loads.

6. SURFACE CASING
•Protect,watersands
•SupportthewellheadandBOP
equipments
•Caseunconsolidatedformations
•Supportothercasings
•Caseofflostcirculationzones

7. INTERMEDIATE CASING
Intermediatecasingisanystringbetween
thesurfaceandproductionstring.
Intermediatecasingmayormaynotbe
cementedfulllength.Inmanythecases
intermediatecasingiscirculatedby
regulations

8. INTERMEDIATE CASING
Intermediatecasingmaybeusedto:
1.Sealoffweakerzones
2.Protectpreviouscasingstringsfrom
higherburstpressure.
3.Providesupportforlinercasing

9. PRODUCTION CASING
Theproductioncasingisusedtocontrol
thehydrocarbonbearingzonesthatwill
beproduced.Thisstringofpipeadds
structuralintegritytothewellboreinthe
producingzones.
Productioncasingshouldbesetbefore
completingthewellforproduction.It
shouldbecementedinamanner
necessarytocoverorisolateallzones
whichcontainhydrocarbons.

10. PRODUCTION CASING
Every well does not have all the strings.
Depending on depth and conditions.
Surface and Production are in almost every well.

11. The PIPE
Thesizeofthecasingreferstotheoutside
diameter(O.D.)ofthemainbodyofthetubular
(nottheconnector).
Casingsizesvaryfrom4.5"to36"diameter.
TubularswithanO.D.oflessthan4.5”arecalled
Tubing.

12. STANDARDS
Length
TheAPIstandardsrecognizethreelength
rangesforcasing:
Range1(R-1):16–25ft
Range2(R-2):25–34ft
Range3(R-3):>34ftusuallyabout42ft
CasingisrunmostofteninR-3lengthsto
reducethenumberofconnectionsinthe
string.Sincecasingismadeupinsinglejoints,
R-3lengthscanbehandledeasilybymostrigs.

13. STANDARDS
Weight
Itisconventionaltospecifycasingdimensionsbysizeandweightperfoot.
•NominalWeight:Basedonthetheoreticalcalculatedweightperfootfor
a20ftlengthofthreadedandcoupledcasingjoint.Thisisnotatrue
weightperfoot.
•PlainEndWeight:Theweightperfootofthejointofcasingwithoutthe
threadsandcouplings(pipebody).
•Averageweightperfoot:isthetotalweightofanaveragejointof
threadedpipe,withacouplingattachedpower-tightatoneend,dividedby
thetotallengthoftheaveragejoint.

14. STANDARDS
Forexample:therearefourdifferentnominal
weightsperfootof95/8’’casing.

15. STANDARDS
Eachgradeisdesignatedbyaletter,andanumber.
Theletterreferstothechemicalcompositionofthematerialandthe
numberreferstotheminimumyieldstrengthofthematerial.
N-80casinghasaminimumyieldstrengthof80000psiandK-55hasa
minimumyieldstrengthof55000psi.
Hencethegradeofthecasingprovidesanindicationofthestrength
ofthecasing.
Thehigherthegrade,thehigherthestrengthofthecasing.(Cost)

17. STANDARDS

18. STANDARDS
Proportionality limit: Stress is proportional to
strain (Hooke’s law). If stress is removed --> it
returns to original length. s= Ee(E: elastic
modulus or Young’s modulus. For steel E =
30,000 psi)
Elastic limit (yield point): Beyond the elastic
limit, permanent deformation will occur. The
lowest stress at which permanent deformation
can be measured is defined as elastic limit or
yield point.
Typical yield behavior for non-
ferrous alloys.
1: True elastic limit
2: Proportionality limit
3: Elastic limit
4: Offset yield strength
Yield point

19. STANDARDS
TensileStrength
Itistheultimate
strengthofa
givenalloyor
product that
determineshow
muchloaditcan
withstandbefore
breaking,orbeing
pulledapart.

20. STANDARDS
Connections
Connectionrepresentlessthan3%ofthepipelength.
Morethan90%ofpipefailuresoccurintheconnection.
Connectionsrepresent10%-50%ofthetotaltubularcosts
Individualjointsofcasingareconnectedtogetherbyathreaded
connection.Theseconnectionsarevariouslyclassifiedas:API;premium;
gastight;andmetal-to-metalseal.
InthecaseofAPIconnections,thecasingjointsarethreadedexternallyat
eitherendandeachjointisconnectedtothenextjointbyacoupling
whichisthreadedinternally.

21. STANDARDS

22. STANDARDS
Connections
ThestandardtypesofAPIthreadedandcoupledconnectionare:
•Shortthreadconnection(STC):
-8threadsperinchandthreadshaveroundedcrestsandroots
•Longthreadconnection(LTC):
-8threadsperinch;threadshaveroundedcrestsandroots;thread
sectionislongersohasbettersealabilityandtensilestrengththanSTC.

23. STANDARDS
Connections
Buttressthreadconnection(BTC):
- 5threadsperinchandnot
symmetricfortheloadandstabflanks

24. STANDARDS
Connections
•Metal-to-metalseal:ThreadandCoupled(MTC):
-Generallyhaveburst,collapse,andtensionratings
equaltothepipebody.