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PETE 203 DRILLING ENGINEERING. CASING DESIGN. Objectives. Understand primary functions of casing Recognize the various types of casing strings used. Understand the procedures used in the design of casing strings. Types of Strings of Casing. Diameter Example 16”-60” 30”

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Pete 203 drilling engineering

PETE 203DRILLING ENGINEERING

CASING DESIGN


Objectives
Objectives

  • Understand primary functions of casing

  • Recognize the various types of casing strings used.

  • Understand the procedures used in the design of casing strings.


Types of strings of casing

Types of Strings of Casing

Diameter Example

16”-60” 30”

16”-48” 20”

8 5/8”-20” 13 3/8”

1. Drive pipe or structural pile {Gulf Coast and offshore only} 150’-300’ below mud-line.

2. Conductor string. 100’ - 1,600’ (BML)

3. Surface pipe. 2,000’ - 4,000’

(BML)


Types of strings of casing1

Types of Strings of Casing

Diameter Example

7 5/8”-13 3/8” 9 5/8”

4 1/2”-9 5/8” 7”

4. Intermediate String

5. Production String (Csg.)

6. Liner(s)

7. Tubing String(s)


Example hole and string sizes in

Example Hole and String Sizes (in)

Hole Size

Pipe Size

36”

26”

17 1/2

12 1/4

8 3/4

Structural casing

Conductor string

Surface pipe

IntermediateString

Production Liner

30”

20”

13 3/8

9 5/8

7


Example hole and string sizes in1

Example Hole and String Sizes (in)

Hole Size

Pipe Size

36”

26”

17 1/2

12 1/4

8 3/4

Structural casing

Conductor string

Surface pipe

IntermediateString

Production Liner

30”

20”

13 3/8

9 5/8

7


Example hole and string sizes in2

Example Hole and String Sizes (in)

Structural casing

Conductor string

Surface pipe

Intermediate String

Production Liner

Mudline

250’

1,000’

4,000’



CONDUCTOR (1 or 2) (40’ – 300’)

  • Prevent eroding surface sediments and rig foundation by circulating the drilling fluid to the shale shaker.

  • Protects subsequent casing strings from corrosion.

  • Install director system on it.

    SURFACE (300' - 5000')

  • Control caving and washing out of poorly consolidated surface beds.

  • Protect fresh water sands from possible contamination by drilling fluid mud, oil or gas and or salt water from lower zone.

  • Install BOP on it.


INTERMEDIATE CSG (1 or 2)

It depends on well depth and geology in specific area.

Primary Purpose:To seal off troublesome zones which:

  • Contaminate drilling fluid.

  • Jeopardize drilling progress with possible pipe sticking, excessive hole enlargement.

  • Contain abnormal pressure fluids, protect formation below the surface casing from higher pressure credited by mud.


PRODUCTION CSG

1. It is set through productive interval to;

2. Segregate pay zone.

3. Can be used to produce fluid instead of tubing.

DRILLING LINER

1. Lower in cost.

2. Functions like intermediate.

PRODUCTION LINER

1. Lower in cost

2. Functions like production.


6 2 standardization of casing
6.2 Standardization of Casing

API: American Petroleum Institute Standards.

  • Range of length

  • Outside diameter

  • Wt/ft.

  • Type of coupling

  • Steel grade


Classification of csg

Classification of CSG.

1. Outside diameter of pipe (e.g. 9 5/8”)

2. Wall thickness (e.g. 1/2”)

3. Grade of material (e.g. N-80)

4. Type to threads and couplings (e.g. API LCSG)

5. Length of each joint (RANGE) (e.g. Range 3)

6. Nominal weight (Avg. wt/ft incl. Wt. Coupling) (e.g. 47lb/ft)


Length of casing joints

Length of Casing Joints

RANGE 1 16-25 ft

RANGE 2 25-34 ft

RANGE 3 > 34 ft.


  • OUTSIDE DIAMETER (4.5 -20")

    • Tolerance 0.75%

    • Usually slightly oversized.

    • Minimum permissible

    • Wall thickness = 87.5% of nominal wall thickness.

    • Nominal = approximate average

    • Drift diameter : Check ID

      • Minimum mandrel diameter that must pass

      • Unobstructed through the pipe.

      • Insures a bit size less than drift diameter.


  • WEIGHT PER FOOT

    • Nominal wt/ft : is not true wt/ft but is useful for identification purposes as an approximate average (wt/ft)

    • Plain-end wt/ft: is the wt/ft of the pipe body excluding the threaded portion and coupling wt.

    • Average wt/ft: total wt. of avg. joint of threaded pipe with a coupling attached power tight of one of avg. joint.

      For design calculation nominal wt/ft. is often used.


6.3 Type of Coupling

  • A coupling is a casing connector which is made of casing material.

  • Most common types of casing. Joints are externally threaded from each end.

  • API specification the coupling should be of the same grade as the pipe body.


Casing threads and couplings

Casing Threads and Couplings

API round threads - short { CSG }

API round thread - long { LCSG }

Buttress { BCSG }

Extreme line { XCSG }

Other …


  • CSG & LCSG

    These connectors have the same basic design:

    • Threads are round shaped and are spaced to give eight threads/inch.

    • Sometimes they are called API 8-round threads.

    • Threads are cut with a taper of 3/4 in/ft.

    • These are commonly used connectors because of their proven reliability, ease of manufacture and low cost.

    • Cut with a 60 angle, and has round peaks and roots.

    • Thread compound must be used to fill the voids and obtain a seal.

      Tensile strength of the joint

    • Joint Efficiency = < 100%

      Tensile strength of the pipe body


API BCSG CONNECTOR

  • Joint efficiency is 100% in most cases.

  • It is tapered but longer thread run out ¾ inch/ft. for upto 75/8 inch.

  • Thread shape is square to reduce unzipping tendency.

  • 5 threads cut to the inch.

  • 1 inch/ft for 16 inch csg.


  • API XCSG CONNECTOR

    • It is integral joint.

    • Pipe thicker near the wall.

    • OD is less than other API couplings

    • Sealing mechanism is metal to metal seal between the metal and the box.

    • Much more expensive.



  • STRENGTH

    • Strength is designated by casing GRADE

    • Grade code : Letter and number H-40, J-55, C-75, L-80

    • Letter is arbitrary.

    • Number designates the minimum yield strength of steel in thousands of psi.

    • Yield strength :tensile stress required to produce a total elongation per unit length of 0.005 on a standard test specimen.

    • Minimum yield strength = 80% of average yield strength observed.


s

e




Tensile force balance on pipe body

Tensile force balance on pipe body

Example 7.1:

Compute the body-yield strength for 20-in., K-55 casing with a nominal wall thickness of 0.635 in. and a nominal weight per foot of 133 lbf/ft.


Tensile force balance on pipe body1

Tensile force balance on pipe body

K55

Solution:

This pipe has a minimum

yield strength of 55,000 psi

and an ID of:


Tensile force balance on pipe body2

Tensile force balance on pipe body

Thus, the cross-sectional area of steel is

and a minimum pipe-body yield

is predicted by Eq. 7.1 at

an axial force of:



Pipe body yield strength1

Pipe Body Yield Strength

Example

What is yield strength of body of 7”, 26 #/ft, P-110 casing?

(to the nearest 1,000 lbf).

…agrees with Tables


Internal yield pressure for pipe burst

Internal Yield Pressure for Pipe (Burst)

FT

FP

where

FP = DLP

FT = 2tLYP

DLP = 2tLYP


Example

Example

For 7”, 26 #/ft P-110 pipe

(to the nearest 10 psi)

…agrees with Tables.





Casing design burst from internal pressure

Casing Design - Burst API CASING (from internal pressure)

Internal Yield Pressure for pipe

Internal Yield Pressure for couplings

Internal pressure leak resistance

Internal Pressure

p

p


Casing design burst

Casing Design - Burst API CASING

Example 1

Design a 7” Csg. String to 10,000 ft.

Pore pressure gradient = 0.5 psi/ft

Design factor, Ni=1.1

Design for burst only.


Burst example

Burst Example API CASING

1. Calculate probable reservoir pressure.

2. Calculate required pipe internal yield

pressure rating


23 lb/ft API CASING

26 lb/ft

N-80


Example1

Example API CASING

3. Select the appropriate csg. grade and wt. from the Casing tables:

Burst Pressure required = 5,500 psi

7”, J-55, 26 lb/ft has BURST Rating of 4,980 psi

7”, N-80, 23 lb/ft has BURST Rating of 6,340 psi

7”, N-80, 26 lb/ft has BURST Rating of 7,249 psi

Use N-80 CSG, 23 lb/ft


Api design factors typical

API Design Factors (typical) API CASING

Required

10,000 psi

100,000 lbf

10,000 psi

Design

11,250 psi

180,000 lbf

11,000 psi

Collapse 1.125

Tension 1.8

Burst 1.1


Table 3
Table 3 API CASING

(4)


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