Casing Design - Module 6

Question 1

What are the uses of Casing

Answer 1

Prevent the hole from caving in or washing out
Protect the freshwater sands from contamination
Keep the water out of the producing zones
Confine production to the wellbore
Provides a flow path for produced fluids

Question 2

Conductor Casing

Answer 2

6-15m. Prevents erosion of the hole around the base of rig and used to support the well head.

Question 3

Surface Casing.

Answer 3

Min. 10% of expected well depth or 152m
Supports the BOP’s and protects the fresh water
May be extended to 1500m
25m deeper than the deepest water well within 200m

Question 4

Intermediate Casing

Answer 4

Is Required with wells
Seals high pressure zones
Protects weak formations or to case off loss circulation zones

Question 5

Production Casing

Answer 5

Isolate the producing reservoir from undesirable fluids in the producing formation

Question 6

Main advantage of a Liner

Answer 6

Less cost compared to a full string
Shorter running time which means there is a less chance of becoming stuck
Additional pipe may be tied to the top of the liner back to the surface

Question 7

Liner Hangers

Answer 7

May be either cemented in place or suspended in the well without cement

Question 8

Name at least two uses of casing string

Answer 8

Prevent hole from caving in and restricting the production to the wellbore

Question 9

Which casing string would have the BOP installed on it

Answer 9

Surface Casing

Question 10

What is the major difference between a liner and casing

Answer 10

Casing extends all the way to surface

Liners stop somewhere in the middle and is tied to another casing string

Question 11

What are the Three Thread Types

Answer 11

Rounded Threads - Easy to manufacture and low in cost, most common
Buttress Threads - Tapered, squarer and one straight and one angled flank thread
Extreme Line - Pin and box ends machined as part of the main body of the casing

Question 12

Collapse Pressure Conditions

Answer 12

Highest pressure is seen at the bottom of the casing string
Is most likely to happen during a cement squeeze job
May occur due to excessive bending

Question 13

CRTRF

Answer 13

Collapse Rating Tension Reduction Factor

Question 14

Burst Pressure Conditions

Answer 14

Burst pressure is greatest at top of casing string because the external pressure is low

Question 15

What are the secondary forces acting on casing

Answer 15

Buckling stress
Bending
Axial Compression
Torsion

Question 16

What is Tension

Answer 16

The downward pull of the weight of casing on the pipe body and couplings
Tension is highest at the top of the string
Connection is the weakest part of the string

Question 17

Name the three forces that the casing should be able to withstand

Answer 17

Tension, Collapse and Burst Pressures

Question 18

Which failure mechanism can result from a cement squeeze job

Answer 18

Collapse because of high pressure differential

Question 19

What secondary force acts while passing through a dogleg

Answer 19

Bending force

Question 20

Casing Failure can result from which mechanisms

Answer 20

Shear, Collapse and Corrosion

Question 21

LOT stands for what

Answer 21

Leak off test

Question 22

what does the LOT confirm

Answer 22

The strength of the cement bond around the casing shoe to ensure no channeling
it is conducted to find the fracture pressure of formation

Question 23

LOT procedure

Answer 23

1) Close BOP
2) Pump mud, increasing the pump pressure until the formation breaks / fractures
3) stop pumping

Question 24

FIT

Answer 24

Formation integrity Test

Question 25

Why is a FIT conducted

Answer 25

Test the strength of the shoe and formation to the maximum design pressure

Question 26

LOT vs. FIT

Answer 26

Main difference, LOT is meant to break the formation and the FIT is not

Question 27

Considerations on which depth to set casing

Answer 27

Geological information
Offset well data
Hole section summaries of similar wells
Pore pressure and fracture gradient prognosis