Oil Country Tubular Goods are Tubulars used within the global Oil & Gas industry and are manufactured according to API Specification. OCTG is a collective name for Drill pipe, Casing and Tubing and are used both onshore and offshore.
The American Petroleum Institute (API) specifies standardized specifications, which define the properties of Oil Country Tubular Goods and classify them into ten grades. These properties are achieved through the chemical composition of the steel and subsequent heat treatment.
Drill pipe is a seamless tube that rotates the drill bit and circulates drilling fluid. It is hollow to allow drilling fluid to be pumped down the hole through the bit and back up the annulus. The annulus of an oil well is the space between any piping tubing or casing and the piping, tubing or casing immediately surrounding it. The presence of an annulus gives the ability to circulate fluid in the well. Drill pipe is subjected to high torque by drilling, axial tension by its dead weight and internal pressure by purging of drilling fluid.
Casing is large diameter pipe that is assembled and inserted into a recently drilled section of a borehole and typically held into place with cement. It is subject to axial tension by its dead weight, internal pressure by fluid purging and external pressure from surrounding rock formations. When casing is cemented in place it aids the drilling process in several ways:
Prevents contamination of fresh water well zones
Prevents unstable upper formations from caving in and sticking the drill string or forming large caverns
Provides a strong upper foundation to use high-density drilling fluid to continue drilling deeper
It isolates different zones, that may have different pressures or fluids (known as zonal isolation) in the drilled formations from one another
Seals off high pressure zones from the surface, avoiding potential for a blowout
Prevents fluid loss into or contamination of production zones
Provides a smooth internal bore for installing production equipment
Tubing is pipe that is being used to transport crude oil or natural gas from the producing formations to the field surface facilities for processing after drilling is completed. During the extraction process the tubing must withstand the pressure and it must be adequately to resist loads and deformations associated with production and workovers. Generally tubing is manufactured the same way as casing, except and additional process known as “upsetting” which is applied to thicken the pipes.