Type of casing pipe

There are five different types of casing pipe: Conductor Casing, Surface Casing, Intermediate Casing, liner String, Production Casing.

Casing pipe is an integral part of the oil drilling and completion process.

In general, casing provides structure and strength to the walls of the well hole so that it doesn’t collapse on itself. It also ensures that there is no seepage of oil or natural gas out of the well hole as these are brought to the surface.

Careful planning is required so that the proper casing for each well is installed. Subsurface characteristics, the diameter of the well, and the pressures and temperatures experienced throughout the well, are all taken into account when planning the various casing strings.

Below is a list of standard API5CT specifications, all of which we supply.

We are also able to supply casing with non-API specifications for special situations, including those with semi-premium and premium connections.

Conductor Casing

Conductor casing is installed first, usually prior to the arrival of the drilling rig. The hole for conductor casing is often drilled with a small auger drill, mounted on the back of a truck. Conductor casing is usually no more than 20 to 50 feet long. It is installed to prevent the top of the well from caving in and to help in the process of circulating the drilling fluid up from the bottom of the well. Onshore, this casing is usually 16 to 20 inches in diameter, while offshore casing usually measures 30 to 42 inches. The conductor casing is cemented into place before drilling begins.

Surface casing is the next type of casing to be installed. It can be anywhere from a few hundred to 2,000 feet long, and is smaller in diameter than the conductor casing. When installed, the surface casing fits inside the top of the conductor casing. The primary purpose of surface casing is to protect fresh water deposits near the surface of the well from being contaminated by leaking hydrocarbons or salt water from deeper underground. It also serves as a conduit for drilling mud returning to the surface, and helps protect the drill hole from being damaged during drilling. Surface casing, like conductor casing, is cemented into place. Regulations often dictate the thickness of the cement to be used to ensure that there is little possibility of freshwater contamination.

Intermediate Casing

Intermediate casing is usually the longest section of casing found in a well. The primary purpose of intermediate casing is to minimize the hazards that come along with subsurface formations that may affect the well. These include abnormal underground pressure zones, underground shale, and formations that might otherwise contaminate the well, such as underground salt-water deposits. In many instances, even though there may be no evidence of an unusual underground formation, intermediate casing is run as insurance against the possibility of such a formation affecting the well. These intermediate casing areas may also be cemented into place for added protection.

Liner Strings

Liner strings are sometimes used instead of intermediate casing. Liner strings are commonly run from the bottom of another type of casing to the open well area. However, liner strings are usually attached to the previous casing with 'hangers', instead of being cemented into place. This type of casing is thus less permanent than intermediate casing.

Production Casing

Production casing, alternatively called the 'oil string' or 'long string,’ is installed last and is the deepest section of casing in a well. This is the casing that provides a conduit from the surface of the well to the petroleum-producing formation. The size of the production casing depends on a number of considerations, including the lifting equipment to be used, the number of completions required, and the possibility of deepening the well at a later time. For example, if it is expected that the well will be deepened at a later date, then the production casing must be wide enough to allow the passage of a drill bit later on.

Well casing is a very important part of the completed well. In addition to strengthening the well hole, it provides a conduit to allow hydrocarbons to be extracted without intermingling with other fluids and formations found underground. It is also instrumental in preventing blowouts, allowing the formation to be 'sealed' from the top should dangerous pressure levels be reached. For more technical information on blowouts and their prevention. Once the casing has been set, and in most cases cemented into place, proper lifting equipment is installed to bring the hydrocarbons from the formation to the surface. After the casing is installed, tubing is inserted inside the casing, running from the opening well at the top to the formation at the bottom. The hydrocarbons that are extracted go up this tubing to the surface. This tubing may also be attached to pumping systems for more efficient extraction, should that be necessary.

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