Offshore Well construction - Casing Design

Section 3 : Casing DesignSection 3 : Casing Design

WELL CONSTRUCTION COURSEWELL CONSTRUCTION COURSE

1

FUNCTIONS FUNCTIONS OF CASINGOF CASING

WELL CONSTRUCTION

CASING DESIGN

2

1. To KEEPKEEP the hole open and prevent collapse

2. To ISOLATEISOLATE porous different pressure regimes so that production or injection may be controlled from a specific section

3. To PROTECTPROTECT formations from contamination and fracture

4. To CONTROLCONTROL any pressures encountered in the well

5. To provide structural SUPPORTSUPPORT for the BOPsBOPs on the wellhead

6. To ALLOWALLOW the passage of testing and completion equipment

WELL CONSTRUCTION

CASING DESIGN

3

Q. Why not just drill to TD ?

A. Due to the nature of sedimentary basins : • Unstable formations and differing pressures necessitate

casing off the open hole at certain depths to enable the final well objective to be met

• Too long an open hole will collapse and pack off - possible SIDETRACK SIDETRACK or REDRILLREDRILL

• Exposed High and Low Pressure Zones - BLOWOUT- BLOWOUT

WELL CONSTRUCTION

CASING DESIGN

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1.1. Largest tangible costLargest tangible cost on any well

2. Performs critical functions - support, stability

3.3. Errors in calculationsErrors in calculations can impact cost, safety

4. Every design has two areas in common

• Subjective assumptions have to be made concerning maximum loads

• After the loads are calculated a design factor will apply

WELL CONSTRUCTION

CASING DESIGN

5

1. Data is taken from offset wellsoffset wells or local geological knowledge - but actual lithologies may differ

2.2. LOTLOT datadata may be different from the predicted values - need to be able to adjust the wellplan while drilling

3. The controllable kick size must be known at all times while drilling the well - KICK TOLERANCEKICK TOLERANCE

4.4. Inter-relationships MUST be known between LOT, PP, Inter-relationships MUST be known between LOT, PP, potential drilling problems and KTpotential drilling problems and KT

WELL CONSTRUCTION

CASING DESIGN

6

UK North Sea Examples

30”

20”

13-3/8”

9-5/8”

30”

20”

30”

20”

30”

20”

30”

20”

9-5/8”

9-5/8” 9-5/8” 9-5/8”

13-3/8” 13-3/8”

7” Liner 7” Liner 7” Liner 7” Liner

A BC ERD

E

WELL CONSTRUCTION

CASING DESIGN

7

CASING TYPE

COMMON SIZES

FUNCTIONS NORMAL RANGE

Conductor 30”, 26” Conduit for the drilling fluid. Cases off shallow, unconsolidated formations. Allows diverter installation

50 – 1500’

Surface 20”, 13-3/8” A/A plus protect against shallow gas. Case off lost circulation zones. First casing on which a BOP can be run

100 – 5000’

Intermediate 13-3/8”, 9-5/8” A/A plus allows heavier weight muds to be used. Set in transition zone of abnormally pressured formations

1000 – 15000’

Production 9-5/8”, 7” Casing inside which the production casing will be run. Seperates production zones from other reservoir forms

Above of across Reservoir

Liners 7”, 5” A/A plus facillitate testing and act as part of the completion in conjunction with the production tubing.

Across Reservoir

WELL CONSTRUCTION

CASING DESIGN

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1. Shoe depth chosen so that next hole section will not be fractured with higher mud weights

2. North Sea the average 30” 30” settingsetting depth 340’ below sea 340’ below sea bedbed.

3. Returns to seabed.4. Cemented back to sea bed5. Conductor analysis determines

minimum height of cement to avoid a top up job

6. Can be pile driven on land - often called STOVE PIPESTOVE PIPE

WELL CONSTRUCTION

CASING DESIGN

9

1. Combats weak formations found at shallow depths

2. Usually set in competent rock - hard limestone etc

3. Usually the first casing that the BOP stackBOP stack is set on

4. Normally 20” in the North in the North SeaSea or 18-5/8” in the in the Middle EastMiddle East

WELL CONSTRUCTION

CASING DESIGN

10

1. Usually set to case off a potentially unstable formation - Eocene Shales

2. Good cementation must be ensured - multi-stage cement jobs or multi-stage collars

3. Traditionally 13-3/8”13-3/8” or 9-5/8”9-5/8” casing

4. Connectors are usually Buttress - not premium sealing

WELL CONSTRUCTION

CASING DESIGN

11

1. Production Casing represents the last casinglast casing string

2. Run to isolate producing zones, to provide reservoir fluid control and to permit selective production of specific reservoir zones

3. This is the size through which the well will be completed

4. Usual size is 9-5/8”9-5/8” or 7”

WELL CONSTRUCTION

CASING DESIGN

12

• Does not reach the surface

• Hung off using a liner hanger

• As set on bottom, main criteria is max collapse pressure

• Advantages - lower costs, less pipe, faster running times

• Disadvantages - any leaks, tie-back packer, small bore - difficult to always get a good cement job

WELL CONSTRUCTION

CASING DESIGN

13

Casing is usually described in terms of :

1. Outside Diameter

2. Nominal unit weight and wall thickness

3. The grade of the steel

4. The type of Connection

5. The Range and length of joint

6. The Manufacturing Process

WELL CONSTRUCTION

CASING DESIGN

14

1. The diameter referred to is the pipe body

2. The diameter of the coupling is larger

3. OD tolerance permitted for casing is +1, -0.5%

4. Wall thickness tolerance is +0, -12.5%

5. More specific requirements are set for upset

ends of pipe and tubing

WELL CONSTRUCTION

CASING DESIGN

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• Mechanical and physical properties dependent on chemical composition and heat treatment

• API has defined 8 gradesAPI has defined 8 grades [see API specs 5A, 5AC, [see API specs 5A, 5AC, 5AX]5AX]

• HH4040 JJ5555 KK5555 L L8080 NN8080 CC9595 andand PP110110

• The numbers indicate The numbers indicate MINIMUM YIELD STRENGTHMINIMUM YIELD STRENGTH in in thousands of psi.thousands of psi.

• The letters serve to prevent oral confusion, although The letters serve to prevent oral confusion, although some have additional meaningsome have additional meaning• KK : > minimum ultimate tensile strength than : > minimum ultimate tensile strength than JJ• CC andand L L : ‘Restricted Yield Strength’ : ‘Restricted Yield Strength’• P P :: “High Strength” material “High Strength” material

WELL CONSTRUCTION

CASING DESIGN

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• PHYSICAL PROPERTIESPHYSICAL PROPERTIES: defined in terms of : defined in terms of MinMin and and MaxMax Yield Strength and Yield Strength and MinMin Tensile Strength Tensile Strength

• MINIMUM Yield StrengthMINIMUM Yield Strength: most important in casing : most important in casing design - used to calculate minimum performance design - used to calculate minimum performance propertiesproperties

• P110P110: : can now be used in most normal operations.can now be used in most normal operations.

• API TESTINGAPI TESTING; ; Limited, thus clientsLimited, thus clients may require extra may require extra inspection of critical strings whose failure could have inspection of critical strings whose failure could have serious consequences [i.e., HPHT, sour gas wells]serious consequences [i.e., HPHT, sour gas wells]

WELL CONSTRUCTION

CASING DESIGN

17

• Standardised at API Convention in 1924 - they are:1. API Short Round Thread STC2. API Long Round Thread LTIC3. Buttress Thread BTC4. Extreme Line XL

• BUTTRESS THREADS: surface and intermediate casing

• PREMIUM THREADS: for production casing strings.

• PREMIUM SEALS metal to metal sealing, > cost.• Estimated 86% of LEAKS occur on CONNECTIONS

WELL CONSTRUCTION

CASING DESIGN

18

Not equal lengths, API specify the range

Range Length (ft) Average (ft) 1 16 - 25 22 2 25 - 34 31 3 > 34 42

RANGE 3 PIPE; is longer and minimises the number of connections (hence the possible leak areas).

WELL CONSTRUCTION

CASING DESIGN

19

Normally specified as

1. YIELD STRENGTH

1. Pipe Body and Coupling

2. COLLAPSE STRENGTH

3. BURST STRENGTH

• Pipe Body and Coupling

WELL CONSTRUCTION

CASING DESIGN

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PRELIMINARY PRELIMINARY CASING DESIGNCASING DESIGN

WELL CONSTRUCTION

CASING DESIGN

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1. Casing is designed to support three different loads

1. Collapse

2. Burst

3. Tension

2. A standard design process is as follows

WELL CONSTRUCTION

CASING DESIGN

22

Define Load Cases Determine

COLLAPSE and BURST loads

Define Initial Casing String

Determine TENSILE Loads

Adjust Initial Casing String

Determine TRIAXIAL loads if

required

Finalise Casing String

WELL CONSTRUCTION

CASING DESIGN

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1. COLLAPSE is calculated first

• calculations based on pore pressure or mud weight that the casing is set in, with the pipe evacuated.

2. BURST Loads are then calculated

• At shoe – the lessor of PP at next setting depth minus the gas column to the shoe or the FP at the shoe

• At surface – a/a + gas column to surface, minus the decreasing PP (or salt water column) to surface

WELL CONSTRUCTION

CASING DESIGN

24

4. Design Factors are then applied

• See WC manual

5. Initial Casing Selected

• Advise maximum three sections per string

6. TENSILE Loads are then calculated

• Based on selected casing weights

• Buoyed tension compared to pipe body strength and connector strength to ensure design factors OK

WELL CONSTRUCTION

CASING DESIGN

25

Load cases are calculated in the order

that they appear

3. Production

1. Completion / Kill Fluids

2. Tubing Leaks

3. Functioning DST Tools etc

1. Installation

• Casing Running

• Casing cementing

• Plug bump etc

2. Drilling

1. Pressure Testing after WOC

2. Maximum Mud Weight

3. Lost Circulation, Well Control

WELL CONSTRUCTION

CASING DESIGN

26

Load Component Installation Drilling Production

Weight in Air X X X

Buoyancy X X X

Bending (Fb) X X X

Shock Load (Fs) X

Weight of Cement X

Pressure Testing X X

Total

WELL CONSTRUCTION

CASING DESIGN

27

MANUAL

DESIGN FACTORS

Collapse 1.00

Burst 1.10

Tension 1.30

Triaxial 1.25

1. Casing properties are downrated by a design factor to ensure a margin of safety.

2. Note : Local legislation and individual Operators may have different design factors

WELL CONSTRUCTION

CASING DESIGN

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CASING SETTING CASING SETTING DEPTH SELECTIONDEPTH SELECTION

WELL CONSTRUCTION

CASING DESIGN

29

WELL ABCMud Weight Vs Fracture / Pore Presure Curves

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

100006 7 8 9 10 11 12 13 14 15 16

Equivalent Mud Weight (ppg)

Dep

th

Pore Pressures

Fracture Pressures

WELL CONSTRUCTION

CASING DESIGN

30


0

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100006 7 8 9 10 11 12 13 14 15 16


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th

Pore Pressures

Fracture Pressures

DepthLithology

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WELL CONSTRUCTION

CASING DESIGN

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0

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100006 7 8 9 10 11 12 13 14 15 16


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th

Pore Pressures

Fracture Pressures

DepthLithology

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WELL CONSTRUCTION

CASING DESIGN

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0

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9000

100006 7 8 9 10 11 12 13 14 15 16


Dep

th

Pore Pressures

Fracture Pressures

DepthLithology

0

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WELL CONSTRUCTION

CASING DESIGN

33

Construct

1. Mean Pore Pressure gradient curve

2. Mud Weight curve (+ 200 - 400 psi or 0.5ppg)

3. Fracture Gradient curve

4. Add Safety Margin Line (0.3 – 0.5ppEMW less)

5. Check Offset Mud weights and LOT data results

WELL CONSTRUCTION

CASING DESIGN

34

1. Check the mud weight curve at point A

2. Move up vertically to point B

B is the setting depth for

PRODUCTION casing

A

B

WELL CONSTRUCTION

CASING DESIGN

35

3. Move to point C - the mud weight at this depth

4. Move up vertically to point D.

D is the estimated setting depth

for INTERMEDIATE

casing

C

D

WELL CONSTRUCTION

CASING DESIGN

36

5. Move to point E to check the mud weight required. As the pore pressure is normal at this depth casing is not required for mud weight.

E

WELL CONSTRUCTION

CASING DESIGN

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WELL CONSTRUCTION

CASING DESIGN

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1. Shallow gas zones2. Lost circulation zones3. Lithologies4. Unstable formations5. Well profile6. Hole cleaning7. Salt sections or high pressure zones8. Kick Tolerance

WELL CONSTRUCTION

CASING DESIGN

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KICK TOLERANCE KICK TOLERANCE CONSIDERATIONSCONSIDERATIONS

WELL CONSTRUCTION

CASING DESIGN

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TWO TYPES

1. Kick Intensity

2. Kick Volume

WE WILL DO THIS ONE

WELL CONSTRUCTION

CASING DESIGN

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1. Look at the problem in Section 3

2. Draw a brief Well Schematic

We will then work through the problem together

WELL CONSTRUCTION

CASING DESIGN

42

SCHEMATIC

TD = 13,123 ft

8,842 ft

4281ft

WELL CONSTRUCTION

CASING DESIGN

43

KICK

INTENSITY

TD = 13,123 ft

Dwp = 8,842 ft

TD - Dwp = 4281ft

MW = 13.2 ppg

MAASP = 8,842 x (14.3 - 13.2) x .052

506 psi

MAASP

KI = MAASP - ( MW x .052 x Hi )

.052 x TVD

MAMW = 14.3 ppg

* Assumes gas has no weight so it is not included in the formulae.

WELL CONSTRUCTION

CASING DESIGN

44

KICK INTENSITY

TD = 13,123 ft

Dwp = 8,842 ft

TD - Dwp = 4281ft

MW = 13.2 ppg

300 ft

Height of influx based on a 25 bbl kick


.052 x TVD506 psi

MAASP

= 0.44 ppg

KI = 506 - ( MW x .052 x 300 )

.052 x TVD

WELL CONSTRUCTION

CASING DESIGN

45

KICK INTENSITY

13,123 ft

8,842 ft

4281ft

MW = 13.2 ppg

300 ft

Height of influx based on a 25 bbl gas kick

506 psi

MAASP

KI = 506 - ( 13.2 x .052 x 300 ) =

.052 x 13,123

.44 ppg

SO WHAT DOES IT MEAN ?

This is the maximum mud weight increase to circulate out a 25bbl kick without fracturing the weak point.

Mud weight to balance the formation pressure is 13.2 ppg + 0.44 ppg

= 13.64ppg

WELL CONSTRUCTION

CASING DESIGN

46


0

1000

2000

3000

4000

5000

6000

7000

8000

9000

100006 7 8 9 10 11 12 13 14 15 16


Dep

th

Pore Pressures

Fracture Pressures

DepthLithology

0

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

7000

7500

8000

8500

9000

9500

Use the Offset Well Data + your Pore Pressure and Fracture Gradient Plot information to select the 13-3/8” and 9-5/8” setting depths

WELL CONSTRUCTION

CASING DESIGN

47


.052 x TVD

Calculate the Kick Intensity for your selected casing depths for the 12-1/4” and 8-1/2” Sections

Example: for the 12-1/4” hole you need:

1. Your selected setting depth for the 13-3/8” shoe

2. LOT at the 13-3/8” shoe (from your plot)

3. Mud Weight for the 12-1/4” (from your plot)

4. Your selected 12-1/4” TD

5. 8” Collars (Assume 600ft length)

6. Assume 25bbl kick and 0.5ppg minimum KI

WELL CONSTRUCTION

CASING DESIGN

48

HOWEVER !!

As we have offset data we need to use it to plan our well. Recalculate the KI using offset well data

1. Your selected 13-3/8” setting depth

2. The LOT at the 13-3/8” shoe (from your plot)

3. 12-1/4” Mud Weight (estimate from your offset data)

4. Your selected 12-1/4” TD

5. 8” Collars (estimate from the offset data BHAs)

6. Use 25bbl kick and 0.5ppg minimum KI

WELL CONSTRUCTION

CASING DESIGN

49

WORKED EXAMPLEWORKED EXAMPLE

WELL CONSTRUCTION

CASING DESIGN

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1. Calculate for COLLAPSE 1. Collapse drilling Load

2. Selecting casing based on collapse

2. Calculate for BURST 1. Burst drilling Load

2. Selecting casing based on burst

3. Check Tensile Loads

WELL CONSTRUCTION

CASING DESIGN

51

The summary well data for the worked casing design is:

13⅜” casing set at 9,750 ft

External Mud weight (outside) 11 ppg

Internal Mud Weight (inside) 11.2 ppg

Next Section TD (12¼”) 13,360 ft

Draw a Schematic

WELL CONSTRUCTION

CASING DESIGN

52

BASIC WELL DATA

Mud Weight Inside

11.2 ppg

13,360 ft MD

9,750 ft MD

Mud Weight Outside

11.0 ppg

WELL CONSTRUCTION

CASING DESIGN

53

The worst case collapse load during drilling occurs if lost circulation is encountered and the internal hydrostatic pressure decreases. Let us assume Lost Circulation while drilling 12¼” Hole below 13⅜” Casing. The well information is:

13⅜” casing 9,750 ft

External Mud weight 11 ppg

Internal Mud Weight 11.2 ppg

Drilling ahead,12¼” hole 13,360 ft

Losses and fluid drop to 2,528 ft

Schematic

WELL CONSTRUCTION

CASING DESIGN

54

MUD LEVEL INSIDE DROPS

TO 2528 ft

Mud Weight Inside

11.2 ppg

13,360 ft MD

9,750 ft MD

Mud Weight outside

11.0 ppg

2,528 ft MD

MUD LEVELDROPS

WELL CONSTRUCTION

CASING DESIGN

55

Calculate the INTERNAL Pressure Profile

at surface =at 2528 ft =at casing shoe =

= psi

Calculate the EXTERNAL Pressure Profile

at surface =at casing shoe =

= psi

Calculate the NETT Collapse Load at the Casing Shoe

Nett collapse at shoe = ________psi

This is the pressure Acting inside the casing

This is the pressure Acting outside the casing

WELL CONSTRUCTION

CASING DESIGN

56

Internal pressure profile at surface = 0at 2528 ft = 0at casing shoe = (9750’ - 2528’) x 11.2 ppg x 0.052 =

4,206 psi

External pressure profileat surface = 0at casing shoe = 9750’ x 11.0 ppg x 0.052 = 5,577 psi

Nett collapse at shoe = 5,577 psi - 4,206 psi = 1,371 psi

13-3/8 casing 9,750 ftMud weight 11 ppgInternal Mud Wt 11.2 ppgDrilling ahead12-1/4” 13,360 ftFluid drop to 2,528 ft

WELL CONSTRUCTION

CASING DESIGN

57

Pressure

Depth

Nett Collapse Line

1371 psi 4206 psi 5577 psi

1446 psi 2528 ft

0 ft

9750 ft

WELL CONSTRUCTION

CASING DESIGN

58

1. The following casings are available – 13-3/8”, 68lb/ft K55 and 13-3/8”, 72lb/ft, N80.

2. The Transocean design factors for collapse is 1.0

Size

ins

Grade Wt per foot

lbs

Inside Diameter

ins

Collapse Resistance

psi

Body Yield Strength

x1000 lbs

Burst Pressure

psi

Downrated Burst Pressure

(Transocean DF = 1.1)

Coupling

Buttress Thread

psi

13-3/8” K55 68 12.415 1,950 1,069,000 3,450 3,450

13-3/8” N80 72 12.347 2,670 1,661,000 5,380 5,380

WELL CONSTRUCTION

CASING DESIGN

59

Casing Wear• reduces wall thickness

Fill-up of casing strings while running• inadequate fill-up can result in casing

collapse

WELL CONSTRUCTION

CASING DESIGN

60

The worst case Burst Load occurs either during pressure testing or during a well control event. Let us assume the 13-3/8” casing is being pressure tested to 3,000psi

13-3/8 casing 9,750 ftMud weight 11.5 ppg

Top of Cement (TOC) at 3000’ Previous Casing shoe at 1500’ Pressure test to 3000 psi Note: assume that, in the

annulus, the cement has deteriorated to normal Pore Pressure at 8.6ppg EMW and the mud has deteriorated to ‘brackish’ water at 8.33ppg EMW.

Schematic

WELL CONSTRUCTION

CASING DESIGN

61

PRESSURE

TESTING TO

3,000 psi

9750’

11.5ppgMud

Surface

TOC at 3000’

TOC

‘Water’(8.33ppg)

‘Cement’(8.6ppg)

3,000 psi PRESSURE TEST

WELL CONSTRUCTION

CASING DESIGN

62

Calculate the INTERNAL Pressure Profile [psi]at Surface = psiat Casing Shoe = psi

Total = psi

Calculate the External Pressure Profile [psi]

at Surface = __________psi

at TOC = ______________________________psi

at Casing Shoe = ______________________________psi

Total = ________psi

Calculate the NETT Burst Load at surface and the casing shoe [psi]at Surface = psiat Casing Shoe = psi

WELL CONSTRUCTION

CASING DESIGN

63

at surface = 3000 (ie, the casing test pressure)

at casing shoe = 3000 psi + (9750 x 11.5 x .052)

= 8,831 psi

WELL CONSTRUCTION

CASING DESIGN

64

at surface = 0

at TOC= 3000ft x 8.33 ppg x 0.052 = 1299 psi

Between TOC at 3000 ft & the shoe at 9750 ft

= 6750 ft x 8.6 ppg x .052 = 3019 psi

Total = 4,318 psi

WELL CONSTRUCTION

CASING DESIGN

65

at surface = 3000 psi

at shoe = 8831 psi – 4318 psi

= 4,513 psi

WELL CONSTRUCTION

CASING DESIGN

66

Production Casing Surface Tubing LeakProduction Casing Surface Tubing Leak

Load at shoe = gas at surface + HH of fluid

Development DrillingDevelopment Drilling

Can use oil gradient for invading fluid if no gas present

Pressure TestingPressure Testing

Lowest of Max WH pressure, 80% of burst, WH or

BOP rating

Surface Equipment LimitationsSurface Equipment Limitations

WELL CONSTRUCTION

CASING DESIGN

67

Surface

9750 ft

TOC – 3000 ft

3000 6000 9000

3000 psi

PRESSURE (psi)

DEPTH (ft)

4513 psi

Nett Burst

WELL CONSTRUCTION

CASING DESIGN

68

1. The following casings are available – 13-3/8”, 68lb/ft K55 and 13-3/8”, 72lb/ft, N80.

2. Note: The Transocean design factors for burst is 1.1, so downrate the burst pressure accordingly.

Size

ins

Grade Wt per foot

lbs

Inside Diameter

ins

Collapse Resistance

psi

Body Yield Strength

x1000 lbs

Burst Pressure

psi

Downrated Burst Pressure

(Transocean DF = 1.1)

Coupling

Buttress Thread

psi

13-3/8” K55 68 12.415 1,950 1,069,000 3,450 3,136 3,450

13-3/8” N80 72 12.347 2,670 1,661,000 5,380 4,891 5,380

WELL CONSTRUCTION

CASING DESIGN

69

0 ft

9750 ft

Nett Collapse Nett Burst

CONCLUSION

Both are suitable for CollapseOnly N80 suitable for Burst

RECOMMENDATION

Select 72ppf, N80

13-3/8” N80 - 72 ppf 2. Collapse 2670 psi4. Burst 5380 (4891 downrated for DF)

13-3/8” K55 – 68 ppf1. Collapse 1950 psi3. Burst 3450 (3136 downrated for DF)

1446 psi

1371 psi 4,271 psi

3,000 psi

WELL CONSTRUCTION

CASING DESIGN

70


Weight in Air X X X

Buoyancy X X X

Bending (Fb) X X X

Shock Load (Fs) X

Pressure Testing X X

Total Load (lbs)

Once the casing meets collapse and design criteria, it is necessary to ensure that it will meet the Tensile design. It needs to withstand installation, drilling and production loads. It is assume that the casing is fixed at the surface but free to move at the shoe.. The following loads need to be considered.

WELL CONSTRUCTION

CASING DESIGN

71

Load cases are calculated in the order that they appear

1. Installation

2. Drilling

3. Production

Production

1. Completion / Kill Fluids

2. Tubing Leaks

3. Functioning DST Tools etc

Installation

• Casing Running

• Casing cementing

• Plug bump etc

Drilling

1. Pressure Testing after WOC

2. Maximum Mud Weight

3. Lost Circulation, Well Control

WELL CONSTRUCTION

CASING DESIGN

72

Let us assume two load scenarios:

1. The maximum installation (or running) load when running the 13-3/8” casing to 9,750ft. • Inside diameter 12.347”• Mud weight 11.0 ppg• Instantaneous Velocity 5 ft/sec

2. The maximum drilling load when cementing the 13-3/8” casing at 9,750ft.• Top of Lead Slurry 3,000 ft• Weight of Lead Slurry 11.6 ppg• Top of Tail Slurry 9,000 ft• Weight of Tail Slurry 15.8 ppg• Plug Bump Pressure 3,000 psi

Calculation: Use the data above + the attached handout (from the Well Construction Manual,

Section 3, to calculate the tensile loads and fill out the table on the next page.

WELL CONSTRUCTION

CASING DESIGN

73


Weight in AirFair = W x TVD

Buoyancy (note: needs to be subtracted)

Fbuoy = (Pe x Ao) – (Pi x Ai)

Bending (Fb)Fbend = 64 x DLS x OD x W

Shock Load (Fs)Fshock = 1,780 x V x As

Pressure TestingFptest = Pptest x Ai

Total Tensile Load (lbs)

WELL CONSTRUCTION

CASING DESIGN

74


Weight in Air 702,000 702,000 702,000

Buoyancy (subtract) 115,821 168,425 115,821

Bending (Fb) 61,632 61,632 61,632

Shock Load (Fs) 184,832

Pressure Testing 359,198 359,198

Total Tensile (lbs) 832,643 lbs 954,405 lbs 954,405

WELL CONSTRUCTION

CASING DESIGN

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Weight in Air 702,000 702,000 702,000

Buoyancy 115,821 168,425 168,425

Bending (Fb) 61,632 61,632 61,632

Shock Load (Fs) 184,832

Pressure Testing 359,198 359,198

Total [lbs] 832,643 954,405 954,405

13-3/8” N80 Tensile

From tables = 1,661,000 lbs

Design Factor = 1.3 1.3 x 954,405 lbs= 1,277,923 lbs

Thus Tensile Design is OK

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CASING DESIGN

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CASING DESIGN

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Documents

Offshore Well construction - Casing Design