Casing and tubing

Casing is run in sections as the well gets deeper. It holds the hole open and it separates the zones the well has drilled through. Cement, not the pipe alone, makes the seal. Tubing is then run for production or injection. Both are oil-country tubular goods. The usual specification, when the customer names it, is API Spec 5CT, with the outside diameter, the weight, the grade, the connection and the length range written on the order.

The photograph is casing stored at a rig site. Tubing is smaller and is specified on its own line even when it is the same enquiry. Wellhead equipment, which hangs these strings and holds the pressure at surface, is quoted to API Spec 6A when that standard is required. A wellhead photograph is not on this page.