Casing hanger

The surface casing serves as a foundation pile for the well which transfers the hanging load to the earth.

Most casing heads allow for the pressure readings to be taken on the annulus and provide the means to pump out or into if necessary.

The most common size of casing hanger is 13+3⁄8 in (340 mm) with over 155,000 such units installed worldwide in 2014 alone.

The contraction of the oilfield industry throughout 2015 meant that this figure was reduced somewhat to just under 120,000 units, of which 36,822 were "Pos-Grip" casing hangers.

With rank wildcats in geological basins that have not been explored extensively, the first holes might be large enough to provide for a couple of contingency strings of casing.