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wellhead is the topmost point of a well. Wellheads serve a number of functions while a well is being drilled, once it is completed and operational, and when it is shut down, either temporarily or permanently. The wellhead is installed early on in the process so that it can serve as a point of attachment for a blowout preventer, a piece of equipment which prevents catastrophic failure of a well, and once a well is completed, equipment for regulating well operations can be attached at the
wellhead. The wellhead provides pressure sealing as well as room for casing and tubing related to the well, including permanent and temporary equipment introduced into the well. When a wellbore is completed, a pump can be attached to the wellhead or it may be fitted with a device known as a Christmas tree. The Christmas tree holds
valves which are used to control pressure inside the wellbore and to regulate the flow of fluids from the well. This device can also be used as a point of entry to inject things into the well. The term “Christmas tree” is a reference to the shape of this device, which does from a distance resemble a festively decorated tree because it is usually brightly colored for safety and highly branched to make room for valves and pipes. The wellhead is right at the surface and may be partially
buried, while the Christmas tree projects so that it will be accessible to technicians who need to be able to adjust it in order to operate the well successfully. Wellheads can vary in size and complexity depending on the type of well and the location. With things like undersea oil wells, for example, there are substantial pressure and pollution concerns which must be addressed to make the
well as safe as possible. By contrast, with something like a household water well, there are fewer safety concerns and less need for very precise control. Engineers who work with wells want to avoid situations in which wells fail or other problems develop. Control panels are usually located in central areas to provide remote access and the well can also be worked on at the wellhead. When wells need to be temporarily taken offline or maintained, adjustments can be made to the Christmas tree
to address concerns about pressure differentials and other situations which could contribute to the development of workplace hazards. Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AboutMechanics researcher and writer. Mary has a liberal arts degree from Goddard
College and spends her free time reading, cooking, and exploring the great outdoors. Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AboutMechanics researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading,
cooking, and exploring the great outdoors.Recommended
For water well wellheads, see Puteal.
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 gas storage, Etzel Germany
The primary purpose of a wellhead is to provide the suspension point and pressure seals for the casing strings that run from the bottom of the hole sections to the surface pressure control equipment.[1]
While drilling the oil well, surface pressure control is provided by a blowout preventer (BOP). If the pressure is not contained during drilling operations by the column of drilling fluid, casings, wellhead, and BOP, a well blowout 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, which is installed on top of the wellhead, with isolation 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 the production platform it is called a surface wellhead, and if located beneath the water then it is referred to as a subsea wellhead or mudline wellhead.[2][3][4][5]
Components[edit]
The primary components of a wellhead system are:
- casing head
- casing spools
- casing hangers
- choke manifold
- packoffs (isolation) seals
- test plugs
- mudline suspension systems
- tubing heads
- tubing hangers
- tubing head adapter
Functions[edit]
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 blowout preventer during drilling.
- Provides a means of attaching a Christmas tree for production operations.
- Provides a reliable means of well access.
- Provides a means of attaching a well pump,
Design specification[edit]
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 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.
See also[edit]
- Puteal — Water well head
- Pumpjack
- American Petroleum Institute
- Drilling rig (petroleum)
References[edit]
- ^ Schlumberger Limited, oil well
- ^ Croft systems, The Difference Between a Wellhead & Christmas Tree, August 29, 2014 ,by Meisa G
- ^ New Wellhead Design Speeds Up Operations, Schlumberger company, October 12, 2016
- ^ EPA, Wellhead Protection Program
- ^ SFX: Standardized Fatigue-Resistant Wellhead System Solution
External links[edit]
Wikimedia Commons has media related to Wellheads.
- Schlumberger Oilfield Glossary: wellhead
This audio file was created from a revision of this article dated 9 June 2021, and does not reflect subsequent edits.