Casing Design - Module 6 Flashcards
What are the uses of Casing
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
Conductor Casing
6-15m. Prevents erosion of the hole around the base of rig and used to support the well head.
Surface Casing.
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
Intermediate Casing
Is Required with wells
Seals high pressure zones
Protects weak formations or to case off loss circulation zones
Production Casing
Isolate the producing reservoir from undesirable fluids in the producing formation
Main advantage of a Liner
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
Liner Hangers
May be either cemented in place or suspended in the well without cement
Name at least two uses of casing string
Prevent hole from caving in and restricting the production to the wellbore
Which casing string would have the BOP installed on it
Surface Casing
What is the major difference between a liner and casing
Casing extends all the way to surface
Liners stop somewhere in the middle and is tied to another casing string
What are the Three Thread Types
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
Collapse Pressure Conditions
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
CRTRF
Collapse Rating Tension Reduction Factor
Burst Pressure Conditions
Burst pressure is greatest at top of casing string because the external pressure is low
What are the secondary forces acting on casing
Buckling stress
Bending
Axial Compression
Torsion
What is Tension
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
Name the three forces that the casing should be able to withstand
Tension, Collapse and Burst Pressures
Which failure mechanism can result from a cement squeeze job
Collapse because of high pressure differential
What secondary force acts while passing through a dogleg
Bending force
Casing Failure can result from which mechanisms
Shear, Collapse and Corrosion
LOT stands for what
Leak off test
what does the LOT confirm
The strength of the cement bond around the casing shoe to ensure no channeling
it is conducted to find the fracture pressure of formation
LOT procedure
1) Close BOP
2) Pump mud, increasing the pump pressure until the formation breaks / fractures
3) stop pumping
FIT
Formation integrity Test
Why is a FIT conducted
Test the strength of the shoe and formation to the maximum design pressure
LOT vs. FIT
Main difference, LOT is meant to break the formation and the FIT is not
Considerations on which depth to set casing
Geological information
Offset well data
Hole section summaries of similar wells
Pore pressure and fracture gradient prognosis
