wellhead

A wellhead is the surface termination of a wellbore or the underwater counterpart that provides the mechanical and pressure-containment interface between the wellbore and surface or subsea production equipment. It anchors the casing strings, supports the tubing and completion hardware, and serves as the connection point for production lines, valves, and control devices.

Typical wellhead assemblies include components such as the casinghead (casing head), tubing head, and various spool pieces. These elements form a stacked housing that seals around the casing and tubing and provides access for cementing, instrumentation, and pressure control. Valves such as the master valve and wing valves are installed to control flow and to permit safe routine and emergency operations. In production configurations, a production tree or Christmas tree is mounted on top of the wellhead to regulate and direct the flow of oil, gas, or fluids from the well. Subsea installations add additional equipment, including a subsea tree and integrated BOP functions, to enable remote operation and enhanced safety.

Wellheads are designed to withstand high pressures and corrosive fluids, accommodate thermal expansion, and allow for maintenance and intervention. They are selected and configured according to well design, depth, expected pressures, and environmental conditions. Standards and specifications from organizations such as the American Petroleum Institute guide the performance, interchangeability, and testing of wellhead equipment.

In practice, the wellhead forms the critical hub for safety systems, production flow, and well integrity, linking the subsurface completion to surface or subsea production infrastructure.