Classification, Specifications and Functions of Casing Pipe

Casing pipe is a steel pipe that supports the walls of oil and gas wells. Each well uses several layers of casing based on different drilling depths and geological conditions. Cement must be used to cement the casing after it is lowered into the well. Unlike oil pipes and drill pipes, it cannot be reused and is a one-time consumable material. Therefore, the consumption of casing accounts for more than 70% of all oil well pipes. According to the usage, casing can be divided into: conduit, surface casing, technical casing and oil layer casing, and their structure in the oil well.
 

① Conduit

Mainly used for drilling in oceans and deserts to separate seawater and sand to ensure smooth drilling. 

The main specifications of this layer of casing are: ∮762mm (30in) × 25.4mm, ∮762mm (30in) × 19.06mm.

② Surface casing
It is mainly used for the first drilling to drill through the soft strata on the surface to the bedrock. In order to seal this part of the strata from collapse, it needs to be sealed with surface casing. 

The main specifications of surface casing: 508mm (20in), 406.4mm (16in), 339.73mm (13-3/8in), 273.05mm (10-3/4in), 244.48mm (9-5/9in), etc. The depth of down pipe depends on the depth of soft stratum, generally 80~1500m. The external pressure and internal pressure it withstands are not large, and K55 steel grade or N80 steel grade is generally used.

③ Technical casing
Technical casing is used in the drilling process of complex formations. When encountering complex areas such as collapse layers, oil layers, gas layers, water layers, lost circulation layers, salt-gypsum layers, etc., technical casing needs to be installed for sealing, otherwise drilling will not be possible. conduct. Some wells have deep and complex formations, and the drilling depth reaches several thousand meters. Such deep wells require several layers of technical casing, which require very high mechanical properties and sealing properties, and the steel grades used are also higher. In addition to K55, N80 and P110 steel grades are mostly used, and some deep wells also use Q125 or even higher non-API steel grades such as V150. 
The main specifications of technical casing are: 339.73mm (13-3/8in), 273.05mm (10-3/4in), 244.48mm (9-5/8in), 219.08mm (8-5/8in) 193.68mm ( 7- 5/8in), 177.8mm (7in), etc.

④ Oil layer casing
When drilling reaches the target layer (layer containing oil and gas), the oil and gas layer and the upper exposed stratum must be completely sealed with oil layer casing. The inside of the oil layer casing is the oil layer. The oil layer casing has the deepest depth among all types of casing, and its mechanical properties and sealing performance requirements are also the highest. The steel grades used include K55, N80, P110, Q125, V150, etc. 
 

The main specifications of oil layer casing are: 177.8mm (7in), 168.28mm (6-5/8in), 139.7mm (5-1/2in), 127mm (5in), 114.3mm (4-1/2in), etc.

Read more: What are the Grades of OCTG Casing Material?

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