PETE 411 Well Drilling

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PETE 411Well Drilling
Lesson 17Casing Design
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Casing Design

• Why Run Casing?
• Types of Casing Strings
• Classification of Casing
• Wellheads
• Burst, Collapse and Tension
• Example
• Effect of Axial Tension on Collapse Strength
• Example

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Read Applied Drilling Engineering, Ch.7
HW 9 Due 10-18-02
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Casing Design
What is casing?
Casing
Cement

• Why run casing?
• 1. To prevent the hole from caving in
• 2. Onshore - to prevent contamination of fresh
  water sands
• 3. To prevent water migration to producing
  formation

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Casing Design - Why run casing, contd

• 4. To confine production to the wellbore
• 5. To control pressures during drilling
• 6. To provide an acceptable environment for
  subsurface equipment in producing wells
• 7. To enhance the probability of drilling to
  total depth (TD)
• e.g., you need 14 ppg to control a lower
  zone, but an upper zone will fracture at
  12 lb/gal.
• What do you do?

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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 mudline.
• 2. Conductor string. 100 - 1,600
• (BML)
• 3. Surface pipe. 2,000 - 4,000
• (BML)

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Types of Strings of Casing
Diameter Example

• 4. Intermediate String
• 5. Production String (Csg.)
• 6. Liner(s)
• 7. Tubing String(s)

7 5/8-13 3/8 9 5/8
4 1/2-9 5/8 7
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Example Hole and String Sizes (in)
Hole Size
Pipe Size
Structural casing Conductor string Surface
pipe IntermediateString Production Liner
30 20 13 3/8 9 5/8 7
36 26 17 1/2 12 1/4 8 3/4
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Example Hole and String Sizes (in)
Hole Size
Pipe Size
Structural casing Conductor string Surface
pipe IntermediateString Production Liner
30 20 13 3/8 9 5/8 7
36 26 17 1/2 12 1/4 8 3/4
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Example Hole and String Sizes (in)
Structural casing Conductor string Surfac
e pipe IntermediateString Production Liner
Mudline
250 1,000 4,000
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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. 47 lb/ft)

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Length of Casing Joints

• RANGE 1 16-25 ft
• RANGE 2 25-34 ft
• RANGE 3 gt 34 ft.

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Casing Threads and Couplings

• API round threads - short CSG
• API round thread - long LCSG
• Buttress
  BCSG
• Extreme line XCSG
  
• Other
• See Halliburton Book...

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API Design Factors (typical)
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

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Abnormal
Normal Pore Pressure Abnormal Pore Pressure
0.433 - 0.465 psi/ft gp gt normal
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Design from bottom
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Press. Gauge
X-mas Tree
Wing Valve
Choke Box
Master Valves

• Wellhead
• Hang Csg. Strings
• Provide Seals
• Control Production from Well

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Wellhead
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Wellhead
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Casing Design
Tension
Tension
Depth
Burst
Collapse
Collapse
STRESS

• Burst Assume full reservoir
  pressure all along the wellbore.
• Collapse Hydrostatic pressure increases
  with depth
• Tension Tensile stress due to weight of
  string is highest at top

Burst
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Casing Design

• Collapse (from external pressure)
• Yield Strength Collapse
• Plastic Collapse
• Transition Collapse
• Elastic Collapse

Collapse pressure is affected by axial stress
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Casing Design - Collapse
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Casing Design - Tension
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Casing Design - Burst (from internal pressure)

• Internal Yield Pressure for pipe
• Internal Yield Pressure for couplings
• Internal pressure leak resistance

p
Internal Pressure
p
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Casing Design - Burst

• Example 1
• Design a 7 Csg. String to 10,000 ft.
• Pore pressure gradient 0.5 psi/ft
• Design factor, Ni1.1
• Design for burst only.

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Burst Example

• 1. Calculate probable reservoir pressure.

2. Calculate required pipe internal yield
pressure rating
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Example

• 3. Select the appropriate csg. grade and wt.
  from the Halliburton Cementing 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

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23 lb/ft 26 lb/ft N-80
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Collapse Pressure

• The following factors are important
• The collapse pressure resistance of a pipe
  depends on the axial stress
• There are different types of collapse failure

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Collapse Pressure

• There are four different types of collapse
  pressure, each with its own equation for
  calculating the collapse resistance
• Yield strength collapse
• Plastic collapse
• Transition collapse
• Elastic collapse

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Casing Design

• Collapse pressure - with axial stress
• 1.

YPA yield strength of axial stress
equivalent grade, psi YP minimum yield
strength of pipe, psi SA Axial stress, psi
(tension is positive)
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Casing Design - Collapse

• 2. Calculate D/t to determine proper equation to
  use for calculating the collapse pressure

Yield Strength Collapse Plastic Collapse
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Casing Design - Collapse, contd

• Transition
• Collapse
• Elastic Collapse

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Casing Design - Collapse

• If Axial Tension is Zero
• Yield Strength Plastic Transition
  Elastic

J-55 14.81 25.01
37.31 N-80 13.38
22.47 31.02 P-110
12.44 20.41 26.22
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Example 2

• Determine the collapse strength of 5 1/2 O.D.,
  14.00 /ft J-55 casing under zero axial load.
• 1. Calculate
• the D/t ratio

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Example 2

• 2. Check the mode of collapse
• Table on p.35 (above) shows that,
• for J-55 pipe,
• with 14.81 lt D/t lt 25.01
  
• the mode of failure is plastic collapse.

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Example 2

• The plastic collapse is calculated from

Halliburton Tables rounds off to 3,120 psi
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Example 3

• Determine the collapse strength for a 5 1/2
  O.D., 14.00 /ft, J-55 casing under axial load of
  100,000 lbs
• The axial tension will reduce the collapse
  pressure as follows

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Example 3 contd

• The axial tension will reduce the collapse
  pressure rating to

Here the axial load decreased the J-55 rating to
an equivalent J-38.2 rating
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Example 3 - contd
compared to 3,117 psi with no axial stress!
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