The Purpose of an Oil and Gas Well Casing

When oil is to be extracted from the earth, wells are required. The act of well drilling, however, will only take place on a site that has been selected as a location for oil. Geologists who specialize in this field often use a seismograph, as well as other types of equipment, to determine the geological structure of the ground being investigated.

A well that is drilled in the correct location will then be used for production. However, certain things need to be done in order to ensure that the well does not collapse. A well on its own, even though it may have been cut through rock or other sturdy material, will not be strong enough. A well casing is therefore used to support the sides of the hole. Casings can be compared to the spine of a human. Just as the spine protects the spinal cord, a casing provides support to a well.

Quite a complex process is used to case a well, but those experienced are capable of completing the task in a short period of time. Tubing, or pipes made of steel, will be placed alongside the inside walls of the well. The pipes that are used are fastened to the well with cement. Cement will fill the gaps between the tubing and the walls of the well.

The type of casing used will mainly depend upon the structure and depth of the well. A simple metal pipe that stretches from the top to the bottom of the hole may be adequately used for smaller wells, however, most wells need more complicated casings for better support. Wells considered as particularly unstable, or those that may have pressure problems, will require many pipes of different widths. The pipes at the bottom are narrower than those at the top.

Since there are pipes of different diameters, there are multiple sections within a single casing. These sections can also be referred to as joints, and each is often about forty feet in length. The pipes that are all screwed together form what is known as a casing string.

The pipes within the casing string are able to fit together tightly because they have male and female threads that interlock. A thread protector is also another part of the casing pipes, and it serves the purpose of protecting the male threads. To ensure that the threads are well secured, a thread compound is used.

A well casing will begin at the bottom of the bore hole and end at the top, where its entire weight is transferred to casing hangars. The joints are connected one by one, and they get progressively wider as they near the surface. Once the pipes have been put into place, a cement slurry fixes them to the inside wall of the well.

On occasion, a well is not completely drilled at one time. For this kind of well, a casing program is used. Each casing is then set into place before the next section of well is drilled.