Types of Casings and Functions
There are five main types of casings
- The Conductor Casing or stove pipe
- The Surface Casing
- The Intermediate Casing
- The Production casing
- The Production Liner System – Liner set through the productive interval and landed inside the casing on a hanger or with tieback to the surface
The main function of these casings are:
1. To furnish a permanent and gauge wellbore of precise diameter through
which subsequent drilling, completion and production operations can take
place
2. To allow selective production from heterogeneous formations without
interformational flow
3. To allow the a means of attaching the wellhead system and Xmas tree to
control and handle the produced fluid.
More specifically, the conductor/surface easing is used to :
- Control caving and washing out of poorly consolidated surface formations
- Furnish the means of handling the return flow of drilling fluid
- Protect fresh water sands from possible contamination by drilling fluid, oil/gas or formation water.
- Allow the attachment of BOP systems.
The main function of the intermediate easing is to seal off troublesome zones, which contaminate the drilling fluid or jeopardise drilling progress with possible hole problems
The production string or liner provides the means of segregating the pay
section from all other zones and allow for selective production.