Supplying API Standard Oil Casings for Various Complex Environments

Surface Casing

This is the second layer of casing, following the conductor casing, typically set at depths between 1,000 and 3,000 feet (300–900 meters).

The primary functions are to minimize shallow well losses; maintain wellbore integrity to prevent borehole collapse; cover weak formations during well control operations; support the blowout preventer (BOP) for well control, and protect shallow freshwater zones from contamination (therefore, surface casing is always anchored at the surface).

Intermediate Casing

Intermediate casing is a specialized type of casing used during drilling operations, positioned between the surface casing and the production casing. Some wells require multiple intermediate casing strings, while others may not need any. It is typically set in the transition zone from normal to abnormal pressure. The primary function is as follows: During drilling operations, numerous challenging formations may be encountered before reaching the production zone. These problematic formations require isolation with intermediate casing, such as lost circulation zones, unstable shale formations, squeezing salt layers, and abnormal pressure zones.

Production Casing

This is the final layer of casing in the oil and gas well casing program, running from the wellhead to below the penetrated oil and gas reservoir. Production casing is used to isolate the production zone and control formation pressure. Additionally, the production casing is designed to withstand injection pressures from operations such as fracturing, gas lift, or waterflood support.

Casing Liner

In a cased wellbore, a casing liner refers to a casing string that is cemented only across the open hole section without extending back to the wellhead. Instead, it is suspended from another casing string. During cementing operations, this method is specifically termed "liner cementing." The casing liner is typically run inside a shallower casing string, with an overlap between the two casing strings usually about 300–500 feet. The casing liner is generally cemented along its entire length. The casing liner is usually run in using drill pipe, which is retrieved after cementing.