Slide 1

CASINGDESIGN

At the end of the lesson, you should be able to:

State the functions of casingDefine the terms: conductor, surface, intermediate andproduction casingList and describe the loads which must be considered inthe casing designDesign casing setting depths and select casing sizesCalculate burst and collapse loads on a production casingSelect casing weight, grade and connection

IntroductionCasing Configuration & FunctionsCasing PropertiesCasing Design

Casing Setting DepthsCasing Sizes SelectionCasing Loads

Casing costs is one of the largest cost items of adrilling projectRepresent up to 30% of the total cost of the wellTherefore proper planning of casing settingdepths and casing selection is importantSize and setting depths depends almostentirely on the geological and pore pressureconditionsCasing must be designed to withstand theanticipated load during installation, drillinganother hole and production

Casings are pipes that isrun in a wellbore afterdrilling a hole.

They have various sizes tosuit different hole sizes foreach section of drillingoperations.

Normally, casing will becemented in a wellbore.

WHY RUN CASING ?Reasons for running casing : Consolidate unstable formations prevent cave-ins Separate different pressure orfluid regimes Control the pressure encounteredavoid fracturing weaker zones Protect the formation from anycontamination Provide production and operationconduit support for thewellhead & BOP

Casing string consists of individual joints of steel pipe which areconnected together by a threaded connectionsGuide / casing shoe attached to the bottom of the casing stringCasing hanger Allows casing to be suspended from the wellhead,attached to the top of casingOthers: float collar, centralizers, scratchers

Conductor (20 30 OD)Surface Casing(13- 3/8 20 OD)Intermediate Casing(9-5/8 16 OD)Production Casing(4-1/2 9-5/8 OD)Liner(4-1/2 13-3/8 OD)

HOLE SIZE

36

26

17

12

8 CASING SIZE

30

20 or 18-5/8

13-3/8

9-5/8

7DESCRIPTION

Conductor

Surface Casing

IntermediateCasing

ProductionCasing

Liner

Casing TypeFunctionsSetting Depths(from seabed)ConductorTo seal off unconsolidatedformations to prevent erosionEnables circulation of drillingfluid150 600 ftSurface CasingSeal off any fresh water sands

Support the wellhead and BOPequipmentPrevent lost circulation1000 5000 ft

Casing TypeFunctionsSetting Depths(from seabed)IntermediateCasingIsolate troublesome formationsbetween surface and productioncasing

Normally set in the transitionbetween normal and abnormalzone

Depends on the number ofproblems encountered1,000 10,000 ftProduction Casing

Separate producing zones fromother formations

Conduit for production andtesting tubingSet across orabove pay zoneTYPICAL CASING FUNCTIONS & SETTINGDEPTH RANGES

Casing Type

Liner

(less than 5000ft casing stringwhich issuspendedfrom a linerhanger (200 400ft)Functions

Replace intermediatecasing for deeperdrilling economic Separate producingzonesSettingDepths(fromseabed)

As requiredTYPICAL CASING FUNCTIONS & SETTINGDEPTH RANGES

Sizes (OD)

Vary from 4.5 to 36If less than 4.5, it is called tubingLength of JointRange 1, 2, 3

Casing Weight per ft

Casing Grade (H-40, J-55, L-80, N-80, C-90 and etc)

ConnectionsShort Thread (STC), LTC, buttress, IF, EFCasing is generally classified according to:

Involves three distinct operationsCasing Setting Depths SelectionCasing Sizes SelectionSelection of Casing Weight, Grade and Coupling

Casing must be able to withstand maximum loadanticipated during landing, drilling andproduction.Design must be based on the worst anticipatedloading conditions.Minimal cost can be achieved by using lowestpossible wt/ft and lowest coupling grades combination string.

Main factors that govern the setting depths are:

Formation pressures (normally, abnormally)Fracture PressuresGovernment Legislation or Company Policy

Casing setting depths are selected for the deepest string tobe run and then successively from the base of the well tosurfaceThe first selection criteria for selecting deeper setting depthsis to permit the mud weight to control formation pressureswithout fracturing any overlying formationsPlot pressure (pore, fracture and mud weight) against depthprofile

Required mud density todrill to aProd casing is set hereIntermediate casing is sethere to prevent fracturingRequired mud density todrill to cSurface casing is set hereto prevent fracturing

Casing sizes and string configuration are dictatedby the size of the smallest casing string to be runOnce it is known, all subsequent casing and holesizes are selectedSelection of the smallest casing string is based onoperational considerationsDrilling engineer will collate this information fromgeology, reservoir engineering and productionengineeringThe objective of the drilling engineer is to use thesmallest casing sizes possible

CASING SIZES SELECTION

(contd)The bit size to drill a certain interval must be slightly largerthan the casing OD (Table 7.7)To drill the lower interval, the bit size must fit inside thecasing. in turns it determines the min size of the seconddeepest casing string (Table 7.8)

Same process continues

CASING SIZES SELECTION(contd)

Each casing string has to be designed for burst,collapse and tensionThus, its grade and coupling must be able towithstand the loadsDesign load conditions vary from one casing stringto anotherShould consider the design loads for collapse andburst firstThen evaluate the tension load and upgrade thepipe section if necessaryFinally check for biaxial effect

Collapse Load,P e P iP cBurst Load,P i P eP bExternal pressure may be caused by: Pore pressure Mud weight Column of cementInternal pressure may be caused by: Full evacuation Hydrocarbon influx Tubing leak

Tension Load,

Total Tensile Load = Cumulative Wet Weight carried by topjoint + Shock load

Yp

WhereShock load = 3200 x WnYp= Joint yield strength

Collapse Load assume that: well is in the last phase of production Casing is empty Fluid SG outside pipe is the mud SG Beneficial effect of cement is ignored Design Factor of 1.0

Collapse Load at Surface:P e

P i0.052 17.95 0 0 psi

0 psiP e P iP c0 psiCollapse Load at Casing Shoe:P e

P i

P c0.052 17.95 19000 17735 psi

0 psi

P e P i 17735 psiFrom Table 3.3, all grade satisfy the requirement.

Burst Load assume that: well has a BHP equal to the formation porepressure and the producing fluid is gas Production tubing leaks gas (0.1 psi/ft) Fluid SG inside casing/tubing annulus is the mudSG Fluid SG outside casing is the saturated salt waterSG (gradient 0.465 psi/ft) Design Factor of 1.0

P e0.052 8.94 0 0 psiBurst Load at Surface:P i P eP c24241 psiPi = Shut in BHP Pressure due to Gas Column

P i 17.45 0.052 19000 0.1 1900015341 psiP bP i P e 15341 psiBurst Load at Casing Shoe:P e0.052 8.94 19000 8835 psiPi = Pressure due to Fluid Column + Surface Pressuredue to gas leak

P i 17.95 0.052 19000 15341 33076 psi

From Table 3.3, only grade SOO meet the burst requirement.0

2000

40006000

8000

10000

12000

14000050001000015000200002500030000PcPbV-150 38#V-150 41#V-150 46#MW-155SOO-140SOO-15516000

18000

20000

Check for tensile loading (SF=1.8):06000 V-15038#6000143038165528564828121600686428 2.0832486000 12000 MW-15512000 19000 V-15046#60007000159213443846165528233772399300233772121600147200520900 3.056249380972 3.527818SFDepth(ft)From ToTotalTensileGradeLengthYp(1000lb) Wn(lb/ft)Wet Weight TotalWet(BF=0.726) WeightShockLoadSince calculated SF exceed minimum SF of 1.8, all sections satisfy

tensile load requirement.

Need to check for pressure testing, biaxial effect and costs.