casing heads

A casing head is an adapter between the first casing string and either the BOP stack (during drilling) or the wellhead (after completion). This adapter may be threaded or welded onto the casing, and may have a flanged or clamped connection to match the BOP stack or wellhead. It is the primary interface for the pressure control equipment. When installed, a casing head is typically tested to very strict pressure and leak-off parameters to insure viability under blowout conditions, before any surface equipment is installed.