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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 ...
Casing Diameters of a Borehole Casing Diagram premium gas tight connections on a casing string. Casing is a large diameter pipe that is assembled and inserted into a recently drilled section of a borehole. Similar to the bones of a spine protecting the spinal cord, casing is set inside the drilled borehole to protect and support the wellstream.
The tube well casing houses the inlet, cylinder, piston valves and rising main of a "down-the-hole" type hand pump. Casing to support the external surfaces of the borehole against collapse may be needed, either temporarily or permanently, and is often made of PVC pipe , which has the advantages of being both cheap and inert.
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
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.
In the diagram, these are stands of drill pipe which are 2 or 3 joints of drill pipe connected and stood in the derrick vertically, usually to save time while tripping pipe. Drill string (#25) is an assembled collection of drill pipe, heavy weight drill pipe, drill collars and any of a whole assortment of tools, connected and run into the ...
It is often helpful to visualize the well as a U-shaped tube. Column Y of the tube represents the annulus, and column X represents the pipe (string) in the well. The bottom of the U-tube represents the bottom of the well. In most cases, fluids create hydrostatic pressure in both the pipe and annulus.
Casing is run to protect or isolate formations adjacent to the wellbore. It is generally not possible to drill a well through all of the formations from surface (or the seabed) to the target depth in one hole-size section. For example, fresh-water-bearing zones (usually found only near the surface) must be protected soon after being penetrated.