Tubing and Casing

Posted by Renn Young on December 17th, 2020

Tubing and casing strings are the main parts of the well construction. All wells drilled for the purpose of oil or gas production (or injecting materials into underground formations) must be cased with material with sufficient strength and functionality. Tubing and casing are key portions of OCTG. Tubing is a distinct pipe, installed in production casing after well cementing to allow the oil and gases flow to the ground. Casings are those pipes supporting the wall of oil and gas well. It is mainly divided in 3 major categories- the surface, protection and production casing.

Tubing

Tubing is the conduit through which oil and gas are brought from the producing formations to the field surface facilities for processing. Tubing must be adequately strong to resist loads and deformations associated with production and workovers. Further, tubing must be sized to support the expected rates of production of oil and gas. Clearly, tubing that is too small restricts production and subsequent economic performance of the well. Tubing that is too large, however, may have an economic impact beyond the cost of the tubing string itself, because the tubing size will influence the overall casing design of the well.

Casing

Casing is the major structural component of a well. Casing is needed to:

• Maintain borehole stability

• Prevent contamination of water sands

• Isolate water from producing formations

• Control well pressures during drilling, production, and workover operations

Casing provides locations for the installation of:

• Blowout preventers

• Wellhead equipment

• Production packers

• Production tubing

The cost of casing is a major part of the overall well cost, so selection of casing size, grade, connectors, and setting depth is a primary engineering and economic consideration.