This article presents the definition of the various casing types: conductor, surface casing, intermediate casing, production casing and liner.
Marine Conductor (Offshore)
This is for offshore drilling operations from jack-up rigs. It consists of a pipe driven, jetted, or cemented in a pre-drilled hole to provide structural strength, to cover very soft formations below the seabed, to serve as a circulation system for the drilling fluids, and to guide the drilling and casing strings into the hole.
Conductor Casing String (Onshore)
The conductor casing string is used to cover unconsolidated surface formations, to seal off shallow water sands, and to provide protection against shallow gas flows. The string is cemented to surface and is the first casing on which one or more BOP could be installed.
Surface Casing String
The surface casing string is used to provide blow-out protection, to seal off water/hydrocarbon formations, and to prevent loss of circulation. This string is normally cemented to surface or seabed.
Intermediate Casing String
The intermediate casing string is usually set in the transition zone of abnormal pressured formations and used to protect weak formations, to case off circulation losses, hole sloughing, caving, reservoir formations, and to provide blow-out protection. Cement fill to shut off hydrocarbon zones and flowing salt sections.
Production Casing String
The production casing string is used to separate the productive zones from other reservoir formations or for testing purposes.
Liners
Liner, other than production liners, are used as an intermediate casing string to permit deeper drilling, to separate the productive zones from other zones, or for testing purposes. A liner is always cemented to its top.