Casing is an integral part of the oil drilling and completion process. Typically, casing provides structure and strength to the well bore wall so that it does not collapse on itself. It also ensures that oil or gas does not seep out of the well bore when it is brought to the surface.

You need to plan carefully in order to install the right casing for each well. AUprospect gives you an overview of the types of casing.

Conductor Casing

Conductor casing is installed first, usually before the drilling rig arrives. The hole for the conductor casing is usually drilled with a small auger mounted on the back of the truck. The conductor casing is usually no more than 20 to 50 feet long. It is installed to prevent collapse of the top of the well and to help circulate drilling fluid upward from the bottom of the well. The conductor casing is cemented into place prior to the start of drilling.

Surface Casing

Surface casing is the next type of casing to be installed. It can range in length from a few hundred feet to 2,000 feet and is smaller in diameter than the conductor casing. When installed, the surface casing is mounted on top of the conductor casing. The primary purpose of the surface casing is to protect freshwater sediments near the well surface from contamination by hydrocarbons or brine leaking from deep underground. It also serves as a conduit for the drilling mud to be returned to the surface and helps protect the borehole from damage during the drilling process.

Intermediate Casing

Intermediate casing is usually the longest section of casing in a well. The primary purpose of intermediate casing is to minimize the hazards posed by subsurface formations that may affect the well. These include abnormal subsurface pressure zones, subsurface shales, and formations that may contaminate the well, such as subsurface brine deposits. In many cases, even though there may be no evidence of anomalous subsurface formations, the intermediate casing acts as insurance against the possibility of such formations affecting the well.

HW Casing 3.0m for wireline core drilling.

Production Casing

The production casing, also known as the "tubular column" or "long tubular column", is installed at the end and is the deepest part of the casing in the well. This is the casing that provides the pipeline from the well surface to the oil production formation. The size of the production casing depends on many considerations, including the lifting equipment to be used, the number of completions required, and the possibility of subsequent deeper wells. For example, if the well is expected to be deepened at a later date, the production casing must be wide enough to allow passage of the drill bit at a later date.

Once the casing is set and in most cases cemented into place, the appropriate lifting equipment is installed to bring the hydrocarbons from the formation to the surface. Once the casing is installed, the tubing is inserted into the casing and extended from the open well at the top to the formation at the bottom. The extracted oil travels through this pipe to the surface.

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