Casing is a series of steel pipes that are run into a drilled oil well to stabilize the well, keep contaminants and water out of the oil stream, and prevent oil from leaching into the groundwater.Casing is installed in layers, in sections of decreasing diameter that are joined together to form casing strings.
There are five main types of casings:
1.The Conductor Casing or stove pipe
2.The Surface Casing
3.The Intermediate Casing
4 .The Production casing
5 .The Production Liner System – Liner set through the productive interval and landed inside the casing on a hanger or with tieback to the surface