Types of casing pipe

Casing‌ pipe is one of the key equipment used in the oil drilling process. It is mainly used to support the well walls of oil and gas wells, prevent collapse, and ensure deep well formation pressure balance and oil production operations. It usually consists of multiple sections of steel pipe connected by threads and is used with drilling rigs and other equipment related to the petroleum industry. Generally speaking, there are six main types of OCTG Casing pipe used in onshore and offshore oil wells:

1. Structural Casing
Structural Casing can solve problems of additional lost circulation, hole caving and minimize kick problems from shallow gas zones. Typical depths range from 600 - 1000ft.

2. Conductor Casing
Conductor casing is used to support the well by preventing collapse of the loose soil near the surface during drilling operations. It's diameters varies from 18 to 30''.

3. Surface Casing
There are some strict regulations in some countries due to environmental issues. Surface casing can isolate freshwater zones from oil well so that these areas are not contaminated during drilling and completion.

4. Intermediate Casing
Usually, intermediate casing is the longest section of casing in a well. Intermediate casing is used to minimize hazards that underground formations may pose to a well. It also helps to maintain hydrostatic pressure at a appropriate level to prevent blowouts.

5. Production Casing
Production casing is the final interval and the deepest section of casing in a well. It can provide a conduit from the petroleum producing formation right up to the surface.

6. Casing Liner
Essentially, casing liner is a string of intermediate casing that does not extend all the way to surface. It is hung off in or above the previous casing shoe and is usually cemented over its entire length to ensure it seals within the previous casing string. 

Read more: Casing pipe vs Drill pipe or API 5CT Steel Casing and Tubing Chart