The wellhead is the assembly at the very top of a well, located at the surface between the casing strings and the rig floor. It serves two core jobs: it suspends and supports the casing run into the well, and it provides pressure seals between casing strings and to the atmosphere. Every well, onshore or offshore, has a wellhead.
The surface termination of a well that hangs off the casing strings and contains seals to control pressure. It forms the foundation on which pressure-control equipment such as the BOP or Christmas tree is mounted.
What the wellhead does
As a well is drilled, successive casing strings are run and cemented. Each string is hung off and sealed at the wellhead using casing hangers and seal assemblies. This builds a stack of nested, sealed strings that isolate the well from surrounding formations and the surface. The wellhead carries the weight of these strings and maintains a pressure barrier throughout the life of the well.
The wellhead is permanent and stays with the well. During drilling, a blowout preventer is bolted on top of it; once the well is completed for production, a Christmas tree is installed in its place.
Wellhead vs. Christmas tree
The wellhead is often confused with the Christmas tree, but they are distinct. The wellhead is the foundational component that hangs the casing and provides seals. The Christmas tree is a separate assembly of valves and chokes mounted on top of the wellhead to control flow during production. In short: the wellhead is the base; the tree is the flow-control crown that sits on it.
Because it is the anchor for all surface pressure-control equipment, the wellhead is a critical safety component throughout drilling, completion and production.
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Frequently asked
A wellhead suspends and supports the casing strings run into a well and provides pressure seals between those strings and to the surface.
The wellhead is the foundational component that hangs the casing and seals pressure. The Christmas tree is a valve assembly mounted on the wellhead to control production flow.
Yes. Every well — onshore or offshore — has a wellhead, which remains a permanent part of the well throughout its life.