Awellhead is the component at the surface of anoil or gas well that provides the structural and pressure-containing interface for the drilling and production equipment.
The primary purpose of a wellhead is to provide the suspension point and pressure seals for thecasing strings that run from the bottom of the hole sections to the surface pressure control equipment.[1]
Whiledrilling the oil well, surface pressure control is provided by ablowout preventer (BOP). If the pressure is not contained during drilling operations by the column ofdrilling fluid, casings, wellhead, and BOP, a wellblowout could occur.
When the well has been drilled, it iscompleted to provide an interface with the reservoir rock and a tubular conduit for the well fluids. The surface pressure control is provided by aChristmas tree, which is installed on top of the wellhead, withisolation valves and choke equipment to control the flow of well fluids during production.
Wellheads are typically welded onto the first string of casing, which has been cemented in place during drilling operations, to form an integral structure of the well. In exploration wells that are later abandoned, the wellhead may be recovered for refurbishment and re-use.
Offshore, where a wellhead is located on theproduction platform it is called asurface wellhead, and if located beneath the water then it is referred to as asubsea wellhead or mudline wellhead.[2][3][4][5]
The primary components of a wellhead system are:
A wellhead serves numerous functions, some of which are:
The oil industry specifications for wellhead systems (materials, dimensions, test procedures and pressure ratings etc.) are :
In general well heads are five nominal ratings of wellheads: 2, 3, 5, 10 and 15 (×1000) psi working pressure. They have anoperating temperature range of −50 to +250 degrees Fahrenheit. They are used in conjunction with ring type seal gaskets.
In general the yield strength of the materials range from 36000 to 75000 psi.
