Wellhead system

The improved wellhead system includes a wellhead housing with an internal annular shoulder having a plurality of removed arcs to form an interrupted support shoulder. A casing hanger is provided with an external annular shoulder having a plurality of removed arcs which correspond with those on the wellhead housing. In a first orientation, the removed arcs of the casing hanger shoulder align with the arcs of the support shoulder in the wellhead housing to allow the casing hanger to pass through the wellhead housing or the wellhead housing to be lowered below the casing hanger. In a second orientation the remaining shoulder arcs of the casing hanger align with the support shoulder arcs to support the casing hanger. The casing hanger also includes a thread for attaching a tool whereby the casing hanger and casing attached thereto can be tensioned. An alternate embodiment of the improved wellhead system includes a wellhead housing with an internal support groove. A casing hanger with a contractible split ring allows the casing hanger to be suspended from the internal support groove of the wellhead housing. A ring compression tool which allows the contractible split ring to be compressed allows selective engagement of the casing hanger with the internal support groove of the wellhead housing. This feature allows the casing hanger to pass through the wellhead housing or the wellhead housing to be installed over the casing hanger.

BACKGROUND 
This invention relates to the field of wellhead apparatus, more 
particularly to wellhead housings and casing hangers which allow the 
wellhead housing to be installed over the casing hanger. 
Prior wellhead systems are based on drilling the borehole of the well in 
successively smaller diameter sections and lining these sections with 
correspondingly smaller diameter sections of casing. Usually the wellhead 
housing is secured to the outermost string of casing and therefore the 
largest diameter casing lines the first section of the borehole of the 
well. The subsequent successively smaller diameter strings of casing are 
supported by casing hangers which sit on annular shoulders in the wellhead 
housing. Since the shoulders are machined in the wellhead housing, they 
limit the size of tools which can be passed through the wellhead housing. 
These dimensions and constraints do not allow the wellhead housing to be 
run after the casing hanger or the casing hanger to be run prior to the 
wellhead housing. 
Prior oil and gas well completion operations in offshore locations often 
used a mudline wellhead positioned on the ocean floor with a few sections 
of casings, called a tie back string connected to a second wellhead 
located on a platform or similar structure. This type of completion 
required an adjustable sub to allow tensioning of the tie back string. The 
present invention eliminates the need for this adjustable sub by allowing 
the casing hanger to land below the landing shoulder in the wellhead 
housing. The tie back string is then tensioned by a tool connected to the 
casing hanger and the wellhead housing is then rotated to a position 
supporting the casing hanger. 
In the event of the wellhead housing being damaged during drilling 
operations, previous wellhead systems prevented removal and replacement of 
the damaged wellhead housing due to the above-described configuration of 
the wellhead housing and the casing hangers. The improved wellhead system 
of the present invention overcomes the deficiencies of the prior art and 
provides a wellhead system which allows a wellhead housing to be installed 
over a previously installed casing hanger. 
An example of a wellhead with a retractable seat is the D. L. Martin U. S. 
Pat. No. 3,902,743 which shows a radially movable split ring that provides 
a full opening through bore in its expanded position and a substantially 
continuous landing seat in its extended position. 
The B. F. Baugh et al. U.S. Pat. No. 4,488,740 discloses a wellhead housing 
and a removable casing hanger support member with a plurality of 
circumferentially spaced breech block teeth disposed on each. The breech 
block teeth allow the wellhead housing to maintain a larger through bore 
with the casing hanger support member removed. Installation of the support 
member provides sufficient bearing area for the subsequent casing hangers. 
SUMMARY 
The improved wellhead system includes a wellhead housing with an internal 
annular shoulder having a plurality of removed arcs to form an interrupted 
support shoulder. A casing hanger is provided with an external annular 
shoulder having a plurality of removed arcs which correspond with those on 
the wellhead housing. In a first orientation, the removed arcs of the 
casing hanger shoulder align with the arcs of the support shoulder in the 
wellhead housing to allow the casing hanger to pass through the wellhead 
housing or the wellhead housing to be lowered below the casing hanger. In 
a second orientation the remaining shoulder arcs of the casing hanger 
align with the support shoulder arcs to support the casing hanger. The 
casing hanger also includes a thread for attaching a tool whereby the 
casing hanger and casing attached thereto can be tensioned. An alternate 
embodiment of the improved wellhead system includes a wellhead housing 
with an internal support groove. A casing hanger with a contractible split 
ring allows the casing hanger to be suspended from the internal support 
groove of the wellhead housing. A ring compression tool which allows the 
contractible split ring to be compressed allows selective engagement of 
the casing hanger with the internal support groove of the wellhead 
housing. This feature allows the casing hanger to pass through the 
wellhead housing or the wellhead housing to be installed over the casing 
hanger. 
An object of the present invention is to provide an improved wellhead 
system which allows removal and replacement of a wellhead housing after 
installation of casing hangers within the wellhead housing. 
Another object of the present invention is to provide an improved wellhead 
system which allows the spacing and tensioning of a tie back casing string 
from a mudline wellhead to a wellhead positioned on a platform or similar 
surface support structure.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to FIG. 1, casing risers of 20", 13 3/8" and 10 3/4", 
denoted by numerals 10, 12 and 14 respectively, extend from a mudline 
wellhead (not shown) to the platform structure 16. The lower ends of 
casing risers 10, 12 and 14 are connected to the mudline wellhead in a 
manner well known to those skilled in the art. Outer casing string 14 is 
connected to platform structure 16 by suitable means as welding. 
As best seen in FIG. 2, an optional annulus cap 18 is disposed in the 
20".times.13 3/8" annulus and attached to casing risers 12 and 14 by 
suitable means as welding. Casing hanger 20 is connected to the upper end 
of casing riser 10 by suitable means as welding or cold forging. An 
external thread 22 is formed on the upper exterior of casing hanger 20 for 
purposes to be described hereinafter. The lower exterior of casing hanger 
20 has annular support shoulder 24 formed thereon with portions removed to 
form support shoulder arcs 26 as best seen in FIG. 3. 
Referring to FIG. 4, wellhead housing 28 is located on the upper end of 
casing riser 12 and attached thereto by suitable means as welding. Support 
shoulder 30 is formed on the interior of wellhead housing 28 with portions 
removed to form support shoulder arcs 32 as best seen in FIG. 5. As shown 
in FIG. 4, support shoulder arcs 26 on casing hanger 20 are disposed 
between and below support shoulder arcs 32 on wellhead housing 28. A 
casing tensioning tool (not shown) is attached to thread 22 of casing 
hanger 20 and casing 10 is tensioned sufficiently to allow wellhead 
housing 28 to be rotated 90.degree. to the position shown in FIGS. 6 and 7 
The tension on casing 10 is released and support shoulder arcs 26 of 
casing hanger 20 rest on support surfaces 32A defined by the support 
shoulder arcs 32 of wellhead housing 28 to support casing 10 in tension. 
Annulus packoff 34 is then installed as shown in FIG. 8 and completion of 
the well can continue in a manner well known to those skilled in the art. 
In the event of wellhead housing 28 being damaged during subsequent 
completion operations, the above-described sequence of operations can be 
reversed to allow installation of a new undamaged wellhead. Annulus 
packoff 34 is first removed and the casing tensioning tool is reattached 
to thread 22 of casing hanger 20. Sufficient tension is applied to stretch 
casing 10, thereby lifting support shoulder arcs 26 off support shoulder 
arcs 32 and allowing wellhead housing 28 to be rotated to the position 
shown in FIGS. 4 and 5. Wellhead housing 28 can then be stripped over 
casing hanger 20 and a replacement wellhead housing installed as 
previously described. 
FIG. 9 shows an alternate embodiment of the improved wellhead system. Those 
items which are unchanged from the preferred embodiment carry the same 
numeral designation. As in the preferred embodiment, casing risers of 20", 
13 3/8" and 10 3/4", denoted by numerals 10, 12 and 14 respectively, 
extend from a mudline wellhead (not shown) to the platform structure 16. 
The lower end of casing risers 10, 12 and 14 are connected to a mudline 
wellhead (not shown) in a manner well known to those skilled in the art. 
Outer casing string 14 is connected to platform structure 16 by suitable 
means as welding. 
Optional annulus cap 18 is disposed in the 20".times.13 3/8" annulus and 
attached to casing risers 12 and 14 by suitable means as welding. Casing 
hanger 40 is connected to the upper end of casing riser 10 by suitable 
means as welding or cold forging. An external thread 42 is formed on the 
upper exterior of casing hanger 40 for purposes to be described 
hereinafter. The lower exterior of casing hanger 40 has annular groove 44 
formed thereon with radially contractible split ring 46 positioned 
thereon. Casing hanger 40 is connected to the upper end of casing riser 10 
by suitable means as welding or cold forging. 
Ring compression tool 48 is threaded onto thread 42 of casing hanger 40 
until split ring 46 is in the compressed position shown in FIG. 10. 
Referring to FIG. 11, wellhead housing 50 is positioned on the upper end 
of casing riser 12 with support groove 52 positioned therein. Initially 
split ring 46 is positioned below support groove 52 as seen in FIG. 11A. 
Ring compression tool 48 is partially unthreaded from thread 42 of casing 
hanger 40 to allow split ring 46 to expand. Tension is then applied to 
ring compression tool 48 and casing hanger 40 until casing 10 is tensioned 
sufficiently to allow split ring 46 to engage support groove 52 as seen in 
detail in FIG. 12A. Alternatively, as best seen in FIG. 12, a casing spear 
54 is landed in the interior of casing 10 and casing 10 is tensioned 
sufficiently to allow compression ring tool 48 to be unthreaded and split 
ring 46 to engage support groove 52 as seen in detail in FIG. 12A. The 
tension on casing 10 is released and split ring 46 rests on support groove 
52 of wellhead housing 50 to support casing 10 in tension. Annulus packoff 
34 in then installed as shown in FIG. 13 and completion of the well can 
continue in a manner well known to those skilled in the art. 
In the event of wellhead housing 50 being damaged during subsequent 
completion operations, the above-described sequence of operations can be 
reversed to allow installation of a new undamaged wellhead. Annulus 
packoff 34 is first removed and the casing spear 54 is reattached to the 
interior of casing 10. Sufficient tension is applied to stretch casing 10, 
thereby lifting split ring 46 off support groove 52. Ring compression tool 
48 is then threaded onto thread 42 and split ring 46 is compressed, 
allowing wellhead housing 50 to be stripped over casing hanger 40 and a 
replacement wellhead housing installed as previously described. 
The construction of our improved wellhead system and the methods of its 
application will be readily understood from the foregoing description and 
it will be seen we have provided an improved wellhead system which allows 
the installation of a wellhead housing after installation of casing 
hangers within the wellhead housing. Furthermore, while the invention has 
been shown and described with respect to certain preferred embodiments, it 
is obvious that equivalent alterations and modifications will occur to 
others skilled in the art upon the reading and understanding of the 
specification. The present invention includes all such equivalent 
alterations and modifications, and is limited only by the scope of the 
appended claims.