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Casing that is cemented in place aids the drilling process in several ways: [2] Prevents contamination of fresh water well zones. Prevents unstable upper formations from caving in and sticking the drill string or forming large caverns. Provides a strong upper foundation to allow use of high-density drilling fluid to continue drilling deeper.
A liner is a casing string that does not extend to the surface, being hung instead from a liner hanger set inside of the previous casing string but usually within about 300 feet (91 m) of its bottom. Other than the obvious cost savings, the liner installation allows larger drill pipe or production tubing to be used in the upper portions of the ...
Sometimes, the process of running in and cementing the casing is also included. After a well has been drilled, should the drilling fluids be removed, the well would eventually close in upon itself. Casing ensures that this will not happen while also protecting the wellstream from outside incumbents, like water or sand. [1] Perforated shoe
Production casing is the final casing string set in a well and usually reaches from the surface to Target Depth (TD). The type of casing used depends upon the different conditions in the well. Commonly, production casing sizes range from 4 + 1 ⁄ 2 in (110 mm) to as large as 9 + 5 ⁄ 8 in (240 mm). It is the last string cemented in a well ...
Steel casing pipe is often specified as ASTM A-252 which is a structural grade material that does not require hydrostatic testing and the inspection requirements are not stringent and it usually costs less than other grades such as A-53, [2] A-139 or API 5L. Used natural gas line pipe is also used as casing on many projects because it is often ...
When the well has been drilled, it is completed to provide an interface with the reservoir rock and a tubular conduit for the well fluids. The surface pressure control is provided by a Christmas tree, which is installed on top of the wellhead, with isolation valves and choke equipment to control the flow of well fluids during production.
The outer portions of the float shoe are made of steel and generally match the casing size and threads, although not necessarily the casing grade. The inside (including the external taper) is usually made of cement or thermoplastic, since this material must be drilled out if the well is to be deepened beyond the casing point. [2] [3]
In a completed well, there may be many annuli. The 'A' annulus is the void between the production tubing and the smallest casing string. The 'A' annulus can serve a number of crucial tasks, including gas lift and well kills. A normal well will also have a 'B' and frequently a 'C' annulus, between the different casing strings.