Definition
Casing — Casing is the large-diameter steel pipe cemented into a wellbore to line and support the hole, isolate formations, and provide a pressure-tight conduit, manufactured to API Spec 5CT and run in successively smaller strings with depth.
Also known as: casing string, well casing
What casing is
Casing is the permanent steel liner of a well. After a hole section is drilled, casing is run and cemented in place to support the borehole wall, seal off unstable or fluid-bearing formations, and contain wellbore pressure. It is manufactured to API Spec 5CT and installed as a telescoping series — conductor, surface, intermediate and production strings — each smaller than the last.
Because casing is cemented and left in the well, its collapse, burst and tensile ratings are matched carefully to the pressures and loads of each section. Casing accessories such as centralizers, float equipment and stop collars ensure a good cement job.
Key attributes
- Grades — API 5CT grades (H-40 through P-110 and beyond) chosen for pressure and, in sour service, NACE MR0175 compliance.
- Drift diameter — the guaranteed minimum ID that later tools and tubing must pass through.
- Running — installed with elevators, slips and casing running tools, then cemented.
Renting casing accessories
While casing itself is usually purchased, the tools and accessories to run it are commonly rented. Explore casing accessories and completion applications, or contact us for your casing job.