A wellhead is the component at the surface of an oil or gas well that provides the structural and pressure-containing interface for the drilling and production equipment. Wellhead Bohrlochkopf

The primary purpose of a wellhead is to provide the suspension point and pressure seals for the

casing string In drilling technology, casing string is a long section of connected oilfield pipe that is lowered into a wellbore and cemented. The purpose of the casing pipe is as follows: * prevent the collapse of the borehole * prevent formation fluids from ...

s that run from the bottom of the hole sections to the surface pressure control equipment. While

drilling Drilling is a cutting process where a drill bit is spun to cut a hole of circular cross-section in solid materials. The drill bit is usually a rotary cutting tool, often multi-point. The bit is pressed against the work-piece and rotated at ...

the oil well, surface pressure control is provided by a

blowout preventer A blowout preventer (BOP) (pronounced B-O-P, not "bop") is a specialized valve or similar mechanical device, used to seal, control and monitor oil and gas wells to prevent blowouts, the uncontrolled release of crude oil or natural gas from a w ...

(BOP). If the pressure is not contained during drilling operations by the column of

drilling fluid In geotechnical engineering, drilling fluid, also called drilling mud, is used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are als ...

, casings, wellhead, and BOP, a well

blowout Blowout or Blow out may refer to: Film and television *''Blow Out'', a 1981 film by Brian De Palma * ''The Blow Out'', a 1936 short film * ''Blow Out'' (TV series), a TV series on Bravo * "Blow Out" (''Prison Break''), an episode of ''Prison ...

could occur. When the well has been drilled, it is completed to provide an interface with the reservoir rock and a tubular conduit for the well fluids. The surface pressure control is provided by a

Christmas tree A Christmas tree is a decorated tree, usually an evergreen conifer, such as a spruce, pine or fir, or an artificial tree of similar appearance, associated with the celebration of Christmas. The custom was further developed in early modern ...

, which is installed on top of the wellhead, with

isolation valve An isolation valve is a valve in a fluid handling system that stops the flow of process media to a given location, usually for maintenance or safety purposes. They can also be used to provide flow logic (selecting one flow path versus another), a ...

s 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 the production platform it is called a ''surface wellhead'', and if located beneath the water then it is referred to as a

subsea Subsea technology involves fully submerged ocean equipment, operations, or applications, especially when some distance offshore, in deep ocean waters, or on the seabed. The term ''subsea'' is frequently used in connection with oceanography, marin ...

wellhead or mudline wellhead.SFX: Standardized Fatigue-Resistant Wellhead System Solution
/ref>

Components

The primary components of a wellhead system are: *

casing head In oil drilling, a casing head is a simple metal flange welded or screwed onto the top of the conductor pipe (also known as ''drive-pipe'') or the casing and forms part of the wellhead system for the well. This is the primary interface for the ...

* casing spools *

casing hanger In petroleum production, the casing hanger is that portion of a wellhead assembly which provides support for the casing string when it is lowered into the wellbore. It serves to ensure that the casing is properly located. When the casing string has ...

s *

choke manifold In oil and gas production a choke manifold is used to lower the pressure from the well head. It consist of a set of high pressure valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, l ...

* packoffs (isolation) seals * test plugs * mudline suspension systems * tubing heads * tubing hangers * tubing head adapter

Functions

A wellhead serves numerous functions, some of which are: # Provide a means of casing suspension. ( Casing is the permanently installed pipe used to line the well hole for pressure containment and collapse prevention during the drilling phase). # Provides a means of tubing suspension. (Tubing is removable pipe installed in the well through which well fluids pass). # Provides a means of pressure sealing and isolation between casing at surface when many casing strings are used. # Provides pressure monitoring and pumping access to annuli between the different casing/tubing strings. # Provides a means of attaching a

during drilling. # Provides a means of attaching a

for production operations. # Provides a reliable means of well access. # Provides a means of attaching a well pump,

Design specification

The oil industry specifications for wellhead systems (materials, dimensions, test procedures and pressure ratings etc.) are : # API 6A, 20th Edition, October 2010; Specification for Wellhead and Christmas Tree Equipment # ISO 10423:2009 Wellhead and Christmas Tree Equipment In general well heads are five nominal ratings of wellheads: 2, 3, 5, 10 and 15 (x1000) psi working pressure. They have an

operating temperature An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...

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.

References

External links

Schlumberger Oilfield Glossary: wellhead
{{Spoken Wikipedia, date=2021-06-09, En-Wellhead-article.ogg Oil wells Oil platforms Petroleum production Oilfield terminology

Components

Functions

Design specification

See also

References

External links