BASIC OF WELLHEAD & FLOW CONTROL EQUIPMENT: Part 1-Casing Program
Wellheads provide the control mechanisms among downhole and break the surface
equipment. In the same way as the well is drilled, casing is placed next to intervals specified by
the well design. The casing setting depth can be unwavering by abnormally pressured zones, lost
distribution zones, sticky formations, or various other reasons as dictated by known factor
Wellhead designs have got to be proficient of withstanding varied ranges of fever and
pressure, as well as various acerbic agents. Standard API pressure ratings pro wellhead
equipment are 2000-, 3000-, 5000-, 10,000-, 15,000-, and 20,000-psi working pressures, While
API fever ratings range from 75° to +250° F (higher pressure and fever ratings are vacant pro
special service). Corrosive environments of carbon dioxide ( CO2 ), hydrogen sulfide ( H2S )
and chlorides ( Cl- ) have got to additionally be considered in the design process.
American Petroleum Institute (API) Specification 6A pro wellhead equipment design.
API 6A establishes the basic necessities pro halt relatives, resources, test procedures, and
pressure ratings so equipment made by various manufacturers will perform at once.
The API specifications additionally outline the essential dimensional data to will allow
wellheads manufactured by an API manufacturer to be interchanged in ground spend.
Manufacturers perform not produce to spend these principles save they be looking for to spend
the API monogram on their products.
wellhead configuration for well with two string wellhead configuration for well with three string
Casing and Casing Programs
The wellhead equipment is designed to suit the casing size and integer of strings
premeditated pro slightly prearranged well. It is therefore essential to increase a basic
understanding of casing and tubing spend in the drilling and producing operations.
Conductor casing, or drive pipe, is a abrupt cord of casing of greater diameter (16 to 48
in.) necessary pro offshore operations, boggy locations, and other conditions in which optional
extra wellhead support is essential. Its principal function is to keep the top of the wellbore
uncluttered and to provide a channel of conveying the drilling fluid returns from the wellbore to
the mud pit. The depth to which it is array varies but is commonly 100 to 400 ft. The part of the
wellhead on the top of the conductor cord is the source plate, which is either an integral part of
the casing head or a fictional (welded-on) plate of steel connected to the casing head by gussets.
The break the surface casing is the paramount cord of casing run on a set down well and
is usually deliberation of as the foundation of the wellhead. The size usually ranges from 8 5/8 to
20 in. Outside diameter (OD), and the piece of this cord varies greatly in distinctive areas, from
200 to several thousand feet. It is array next to a depth sufficient to save from harm all fresh
water-bearing sands and to prevent an underground feast. The join is circulated to the break the
surface on this cord. The part of the wellhead next to the top halt of this cord is the casing head,
which is either screwed or welded against the persist cooperative of casing. The casing head top
connection protuberance is in that case used to install the feast prevention stack, which allows
pro deeper drilling.
(WH with two strings of casing and base plate) (WH with four strings of casing)
The intermediate casing might be the go along with casing cord to is run in a well. Its
goal is to allow pro deeper drilling by isolating weak formations to may perhaps either cause the
fleapit to cave in or lose distribution. The size range pro intermediate casing is typically 7 5/8 to
13 3/8 in. OD. Setting depths vary to run into regulations and geological conditions in a
prearranged well, but commonly range from 3000 to 8000 ft. A well might produce solitary or
two strings of intermediate casing, or it might produce refusal intermediate casing next to all.
The part of the wellhead next to the top halt of an intermediate casing cord is a casing spool.
Some form of isolation seal is used to seal the top halt of this casing to the foundation bowl of
the casing spool. This seal makes feasible the enhance in pressure ratings essential pro the
elevated pressures encountered in deeper drilling. The intermediate casing might be cemented all
the way back to the break the surface, but usually it is cemented back to the halt of the preceding
cord or far back an adequate amount of to separate a individual formation.
The final cord of casing is called the production casing. It is commonly array to or clear
of the formation to is to be produced. Participating in either situation, this will be the of use
overall depth (TD) of the well. The production casing isolates all the other formations from the
producing zone or zones and is usually cemented, like the intermediate casing, back to the halt of
the preceding cord or far back an adequate amount of to provide the essential isolation of the
producing zone or zones. Since the production casing cannot be by far replaced, and since a
minor cord can crop the lubricate in a more efficient mode, tubing is commonly installed inside
the production casing. The tubing can be sealed sour to the inside break the surface of the
production casing by a packer or a number of other sealing device. Production casing typically
ranges in size from 4 1/2 to 9 5/8 in. OD. The part of the wellhead to factory on the top halt of
the production casing is the tubing head. Some form of isolation seal is used among the top halt
of the production casing and the foundation bowl of the tubing head. This seal allows pro
pressure rating enhance and isolates the production casing from the break of the wellhead. The
strength of the production casing cord have got to be sufficient to contain the complete working
pressure of the well.
The final cord of tubular goods to goes into the well is the production tubing. Unlike
casing, it is not cemented in the well. It is supported and sealed by killing it inside the top bowl
of the tubing head, and it can be packed sour down beneath with a packer. The packer seals the
OD of the tubing cord to the inside diameter (ID) of the production casing. Tubing can be
replaced what time damaged; additionally, the well can be deepened or plugged back and a up-
to-the-minute tubing cord used to accommodate the up-to-the-minute depth. The annular
freedom among the OD of the tubing and ID of the production casing can additionally be used to
filch the fluids artificially from the well or to inject chemicals what time the well is being
produced. The parts of the wellhead next to the top halt of the tubing are the tubing head adapter
and the production tree. Tubing size might range from 1 to 7 in. OD, and the irk size of the tree is
Table 1 (below) summarizes the type of wellhead pro apiece tubular classification and the OD,
setting depth and pressure ratings to would usually correspond. Figure 1 (wellhead configuration
pro well with two strings of casing),
String Depth Set (feet) Wellhead Pressure Range (psi)
Base Plate Fitted or Attached to
Conductor 16-48 100-400* 500-1500
Surface Casing 8 5/8-20 200-2000* Casing Head 2000-3000
7 5/8-13 3/8 5000-8000* Casing Spool 2000, 3000, 5000
Production Total Depth 3000, 5000, 10,000,
4 1/2-9 5/8 Tubing Head
Casing 10,000* 15,000
Production Tubing Head Bonnet and Production 3000, 5000, 10,000,
1-7 Near Total Depth
Tubing Tree 15,000
Table 1. Tabular Goods and Wellhead Components
The casing head, which is additionally called the first head or bradenhead, serves as an
intermediate connection among the casing, well control equipment (e.G., feast preventers) and
ensuing casing and tubing spools. The casing predetermine and anticipated pressure ranges will
determine the basic casing head design.
Since the casing head is the lowest section of the wellhead meeting, it is area of interest
to the influence of all impending casing and tubing strings, plus the influence of slightly added
break the surface equipment. The casing head additionally provides a channel by which the
subsequently casing cord can be centered, supported, and sealed. This is achieved by a load
shoulder and controlled irk on which the casing hanger is supported and the annular seal
effected. Participating in addition to this, the casing head have got to provide a channel to adapt
and link up well control equipment and seal the irk from the surroundings. And, last but not least,
the casing head have got to provide a channel of controlled access to the wellbore pro pressure
control and fluid returns in drilling operations. A source plate might be used to help effectively
distribute the influence what time extreme loading, due to casing size and fleapit depth, is
incurred. The source plate 'nay be forged as an integral part of the casing head or attached
independently with welded gussets. Participating in the situation of offshore wells, the source
plate is supported by the conductor pipe. On set down wells, the source plate might break on the
ground or on a definite block prepared pro this goal.
Casing heads are vacant with either a threaded or slip-on join foundation. Participating in
broad, the join connection is preferred what time present is a hazard to the casing will stick in
height. With the welded connection, the casing can be scratch next to slightly desired statement.
The top connection can be either a protuberance or a clamp heart. The spend of clamped relatives
is usually attributed to their much more rapidly frame, lighter influence, and minor OD.
Casing heads commonly produce two border outlets to are the same size; in rare
instances, solitary outlet might be bigger than the other. Four types of outlets are vacant:
Threaded, flanged, studded protuberance, and clamp heart ( Figure 1 ).
Bowl designs vary by manufacturer, but two widespread designs exist. One includes a
load shoulder designed to bear the load of the casing transferred via the casing hanger; and a
vertical or near-vertical profile, provided that a metal-to-metal seal area to separate the casing
annulus shaped by the subsequently casing cord. The other profile offers a lessened seal area
both to provide the seal and store the load.
Metal-to-metal seals are preferred pro in height pressures and acerbic surfaces. However,
they are very susceptible to injury from the rough therapy to lubricate ground equipment is often
prearranged. While the exact type might vary by manufacturer, metal-to-metal seals are typically
interference-energized; therefore, if they start leaking past the well is producing, present is nearly
nothing to can be complete on it. However, folks to are appropriately installed with undefective
components are very steadfast and impart tremendous service. They are particularly applicable
everyplace movement of the wellhead components is likely due to fever variations.
Weld-on heads are commonly welded next to two points: Next to the foundation of the
casing head and next to the amalgamation of the casing top and casing load shoulder of the
casing head. After welding and allowing the join area to cool, the welds are tested by channel of
a test seaport connected to the in-house area among the two welds ( Figure 2 ). The pressure
practical in the test ought to not exceed 80% of the yield strength of the casing in spend.
Casing head options include an inner seal (e.G., an 0-ring) to seal among the casing and casing
head, and lockdown screws to keep down bowl protectors.
Casing spools function in much the same way as casing heads, with two essential
differences: (1) the spool provides a foundation bowl to seal the preceding cord of casing, and
(2) the foundation connection have got to be compatible with the top connection on the
preceding head or spool. Casing spools are manufactured to run into the same necessities as the
casing head and are identified by the following: Size (bottom bowl ordinary size as reflected by
the casing OD on which the casing spool will normally seal), pressure rating (as unwavering by
the top connection), type (bowl design), foundation connection, top connection, and
miscellaneous details (e.G., size and type of outlets, plastic injection ports, and special material
Like a casing head, the casing spool has a top bowl, which holds the casing hanger to
suspends the subsequently cord of casing. Again, two border outlets are provided and might be
threaded, clamp-hub, protuberance, or studded. These outlets are a good number often fitted with
gate valves, although a valve amputation (VR) plug--which allows installation and amputation of
valves under pressure by channel of a lubricator--and blind protuberance might be installed.
Unlike a casing head, a spool additionally has a foundation bowl with a packoff seal and
a protuberance or clamp heart pro mounting it on top of a casing head or preceding spool. These
foundation dishes are designed to accommodate a packoff meeting to seals around the casing
bash and forms pardon? Is often called a "secondary seal" among the current casing cord and the
The minor protuberance of the casing spool additionally serves as a test seaport pro
pressure tough the casing seals and protuberance relatives.
The top bowl configuration is usually identical to the casing head design pro apiece
individual manufacturer. Since intermediate strings commonly produce a elevated cord
influence, dishes cooperative casing hangers with less important killing competence might not be
unfilled in casing spools.
Casing hangers allow the influence or tension load of a casing cord to be transferred to a
casing head or spool. Casing hangers additionally spotlight the casing cord in the head or spool
and provide a pressure-tight seal hostile to the inside of the casing head or casing spool bowl to
contain pressure in the annulus among its casing cord and the preceding cord. Participating in a
number of personal belongings, a separate seal ring or packoff bushing is necessary to provide
There are two major types of casing hangers: Slip-type hangers, which are installed
around the casing past it is run; and mandrel-type hangers, which are made up into the cord.
Mandrel-type hangers (boll weevils) are threaded top and foundation and are made up promptly
into the halt of the casing cord. If refusal sticking crisis occurs while running casing, the
mandreltype casing hanger can be used. The chief help of the mandrel casing hanger is its down-
to-earth design pro killing and sealing pipe. If the pipe sticks, a slip-type casing hanger is
Slip-type hangers (wraparounds) are hinged or halved to facilitate wrapping around the
casing and might be dropped through the feast preventer (BOP) stack, assuming sufficient
clearance is impart, prearranged the ID of the stack. This allows the sealing sour of the annulus
past to nippling down the BOPs.
Slip-type hangers produce slips in serrated segments. The slips produce a lessened back
to matches the taper on the. Inside of the slip bowl. When the hanger is wrapped around the
casing, the slip teeth engage the casing. In the same way as the casing is lowered, it pulls the
slips down with it. The lessened bowl forces the slips hostile to the casing (with a wedging
action) as they move down, so their grip on the casing increases as the casing influence
increases. The casing hangers ought to be designed so to the inward force of the slips will not
crush or draw away the casing clear of acceptable limits next to many equal to the strength of
API round-thread cooperative relatives. For killing extreme many from casing heads or spools,
two sets of slips in tandem might be necessary to distribute the load on a bigger area of casing.
If the casing influence is sufficient, a slip-type automatic-seal hanger is used with a
compression-type seal procedure to is involuntarily actuated by the influence of the casing.
When casing influence is insufficient to actuate the seal, as in shallow wells what time the casing
is cemented back to the break the surface, the hanger design might incorporate a sealing element
located exceeding the slips to is mechanically activated with cap screws ( Figure 1 ).
Manufacturer specifications might vary, but in broad, automatic-seal hangers require next to
slightest 3 in. Of downward casing movement to engage the slips fully and a lowest amount
40,000-lb load to actuate the compression-type seal.
Slip-type hangers can be installed sooner than or past the casing has been cemented.
Participating in broad, this depends on the piece of the casing cord. Shallow intermediate strings
are commonly on the edge from the hanger and in that case cemented all the way to break the
surface. Deeper intermediate or production strings are commonly cemented while the casing is
on the edge in tension from the rig roaming hinder. Then, past the join has cured, the roaming
hinder is used to draw a calculated amount of tension on the uncontrolled pipe exceeding the
join. At this statement, the slip-type hanger is installed.