Note: Descriptions are shown in the official language in which they were submitted.
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METAL TO METAL PACKOFF FOR USE IN A WELLHEAD ASSEMBLY
BACKGROUND
1. Field of Invention
[0001] The invention relates generally to wellhead assemblies and in
particular to a system and
method for sealing between tubulars in a wellhead assembly.
2. Description of Prior Art
[0002] Wellheads used in the production of hydrocarbons extracted from
subterranean
formations typically comprise a wellhead assembly attached at the upper end of
a wellbore
formed into a hydrocarbon producing formation. Wellhead assemblies usually
provide support
hangers for suspending production tubing and casing into the wellbore. The
casing lines the
wellbore, thereby isolating the wellbore from the surrounding formation. The
tubing typically
lies concentric within the casing and provides a conduit therein for producing
the hydrocarbons
entrained within the formation.
[0003] Wellhead assemblies also typically include a wellhead housing adjacent
where the casing
and tubing enter the wellbore, and a production tree atop the wellhead
housing. The production
tree is commonly used to control and distribute the fluids produced from the
wellbore and
selectively provide fluid communication or access to the tubing, casing,
and/or annuluses
between the tubing and casing. Valves assemblies are typically provided within
wellhead
production trees for controlling fluid flow across a wellhead, such as
production flow from the
borehole or circulating fluid flow in and out of a wellhead.
[0004] Seals are used between inner and outer wellhead tubular members to
contain internal well
pressure. The inner wellhead member may be a tubing hanger that supports a
string of tubing
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extending into the well for the flow of production fluid. The tubing hanger
lands in an outer
wellhead member, which may be a wellhead housing, a production tree, or a
tubing head. A
packoff or seal seals between the tubing hanger and the outer wellhead member.
Alternately, the
inner wellhead member might be an isolation sleeve secured to a production
tree. A seal or
packoff seals between the isolation sleeve and a casing hanger located within
the wellhead
housing.
SUMMARY OF THE INVENTION
[0005] Provided herein is an example of a wellhead assembly that includes an
outer tubular
having a bore that defines a bore wall, an inner tubular insertable into the
bore and selectively set
in a landed position in the bore, a packoff on the inner tubular, and a taper
strategically located in
the bore. When the inner tubular is inserted into the bore, the packoff is in
sealing contact with
the bore wall when the inner tubular is proximate the landed position, and the
packoff is set
radially inward from the bore wall when the inner tubular is above a location
proximate the
landed position. In an embodiment, the packoff includes an energizing ring
with a protrusion, a
seal element having spaced apart legs that terminate on opposing sides of the
protrusion, and a
retaining nut threaded to the inner tubular and on a side of the seal element
distal from the
energizing ring. In this example, the seal element is a generally annular
member. One of the
legs can be spaced radially outward from the protrusion when the when the
inner tubular is above
a location proximate the landed position. Further, one of the legs may be
wedged between the
taper and the protrusion when the when the inner tubular is proximate the
landed position. In
one example embodiment, one of the legs projects radially outward to define a
seal between the
outer tubular and the seal element and another one of the legs projects
radially inward to define a
seal between the inner tubular and seal element. Optionally, the inner tubular
is a tubing hanger
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and the outer tubular is a tubing head. Alternatively, the bore wall projects
radially inward at an
axial location below the taper to define a shoulder on which the inner tubular
lands.
[0006] Another example of a wellhead assembly is provided herein that includes
an outer tubular
having an axial bore, a taper formed in the bore where a surface of the bore
projects radially
inward, a shoulder formed in the bore below the taper, an inner tubular landed
on the shoulder,
and a packoff. In this example the packoff has an outer radius in sealing
contact with the taper
and that is set radially inward from a portion of the bore between the taper
and an upper end of
the bore. An inner radius of the packoff is in sealing contact with the inner
tubular. In one
example, the packoff includes an energizing ring, a seal element with legs
spaced apart by the
energizing ring, and a retaining nut for urging the seal element against the
energizing ring, and
beads on the legs that form a seal against the inner and outer tubulars.
Optionally the seal
element can be metal. The energizing ring can also include a protrusion on
which the legs are
supported. In an example, the inner tubular is a tubing hanger and the outer
tubular is a tubing
head.
[0007] Further disclosed herein is a method of sealing between tubulars in a
wellhead assembly.
One embodiment of the method includes providing an inner tubular having a
packoff
circumscribing a portion of the inner tubular, providing an outer tubular
having a bore with a
taper so that a portion of the bore above the taper has a radius greater than
a radius of the
packoff, and a portion of the bore below the taper has a radius less than the
packoff, and sealing
between the packoff and the bore by inserting the inner tubular into the outer
tubular at least to a
depth that the packoff contacts the portion of the bore having a radius less
than the packoff. The
method can further include landing the inner tubular in the outer tubular. In
this example, the
packoff includes an energizing ring with a protrusion, a seal element having
spaced apart legs
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that terminate on opposing sides of the protrusion, a soft metal coating on
the seal element, and a
retaining nut threaded to the inner tubular and on a side of the seal element
distal from the
energizing ring.
BRIEF DESCRIPTION OF DRAWINGS
[0008] Some of the features and benefits of the present invention having been
stated, others will
become apparent as the description proceeds when taken in conjunction with the
accompanying
drawings, in which:
[0009] FIG. 1 is a side sectional view of an example of a portion of a tubing
hanger having a
packoff in accordance with the present invention.
[0010] FIG. 2 is a side sectional view of the tubing hanger of FIG. 1 landing
in a tubing head in
accordance with the present invention.
[0011] FIG. 3 is a side sectional view of the tubing hanger landed in the
tubing head of FIG. 2 in
accordance with the present invention.
[0012] FIG. 4 is a side partial sectional view of an example embodiment of the
tubing hanger of
FIG. 1 set in a wellhead assembly in accordance with the present invention.
[0013] While the invention will be described in connection with the preferred
embodiments, it
will be understood that it is not intended to limit the invention to that
embodiment. On the
contrary, it is intended to cover all alternatives, modifications, and
equivalents, as may be
included within the spirit and scope of the invention as defined by the
appended claims.
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DETAILED DESCRIPTION OF INVENTION
[0014] The method and system of the present disclosure will now be described
more fully
hereinafter with reference to the accompanying drawings in which embodiments
are shown. The
method and system of the present disclosure may be in many different forms and
should not be
construed as limited to the illustrated embodiments set forth herein; rather,
these embodiments
are provided so that this disclosure will be thorough and complete, and will
fully convey its
scope to those skilled in the art. Like numbers refer to like elements
throughout.
[0015] It is to be further understood that the scope of the present disclosure
is not limited to the
exact details of construction, operation, exact materials, or embodiments
shown and described, as
modifications and equivalents will be apparent to one skilled in the art. In
the drawings and
specification, there have been disclosed illustrative embodiments and,
although specific terms
are employed, they are used in a generic and descriptive sense only and not
for the purpose of
limitation. Accordingly, the improvements herein described are therefore to be
limited only by
the scope of the appended claims.
[0016] An example embodiment of a tubing hanger 10 is shown in side sectional
view in Figure
1, wherein the tubing hanger 10 includes a packoff assembly 12. In the example
of Figure 1, the
packoff assembly 12 is made up of an energizing ring 14 that is a generally
annular member and
having a base 16 with a substantially rectangular cross-section. Depending
downward from the
base 16 is a lower member 18 that in the example of Figure 1 has a width less
than the width of
the base 16 and tapers axially inward with distance away from the base 16. The
lower member
18 defines a protrusion that extends into a seal element 20 shown disposed on
an outer surface of
the tubing hanger 10 and just below the energizing ring 14. The seal element
20, which is a
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generally U-shaped member, has a base 22 which is generally rectangular in
cross-section and a
pair of legs 24 that project upward and on opposing lateral sides of the lower
member 18.
Optionally, the leg 24 shown facing outward from an axis Ax of the tubing
hanger 10 is spaced
apart from the energizing ring 14 to define a gap 25 between the leg 24 and
energizing ring 14.
Additionally, the spaced apart legs 24 define a space 26. On opposing outer
surfaces of the legs
24 are beads 28 that are raised portions on the inner and outer radial
surfaces of the seal element
20 and as will be described in more detail below, enhanced formation of a
sealing surface
between the seal element 20 and another solid member. A group 30 is provided
on the outer
circumference of the tubing hanger 10 in which the energizing ring 16 and seal
element 20 is
disposed. A lower groove 32 also on the outer surface of the tubing hanger 10
extends
downward from a lower end of the upper groove 30 and as shown in Figure 1 has
a reduced
radius over that of the upper groove 30. Threads 34 extend along the face of
the lower groove 32
and provide connection between the tubing hanger 10 and a retaining nut 36
shown threaded into
placed within the lower groove 32. In one example embodiment, the retaining
nut 36 provides
axial support for the seal element 20.
[0017] Figure 2 illustrates in side sectional view, one example of the tubing
hanger 10 being
inserted within a tubing head 40 for assembly of a wellhead assembly (Figure
4). In this
example, the outer radial surface of the tubing hanger 10 is shown sliding
into a bowl 42 formed
in the tubing head 40. A shoulder 44 is defined at a lower end of the bowl 42
where the inner
surface 46 of the bowl 42 extends radially inward towards axis Ax. Above the
shoulder 44 is a
taper 48 that is defined where the inner surface 46 depends radially inward
for an axial distance.
As shown, as the tubing hanger 10 is being inserted within the tubing head 40
the beads 28 on
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the outer leg 24 are set radially inward from the inner surface 46 as long as
the beads 28 are at a
location above the taper 48.
[0018] As shown in Figure 3, the tubing hanger 10 has landed within the tubing
head 40 and the
lower lateral edge of the nut 36 is being supported on the shoulder 44.
Further, the respective
locations of the taper 48 and ridges 28 are strategically disposed so that
when tubing hanger 10 is
in the landed position of Figure 3, the ridges 28 are at a depth where the
inner surface 46 is set
radially inward so that the beads 28 are in compressive contact against the
inner surface 46. As
such, a sealing surface is formed between the seal element 20 and inner
surface 46, the sealing
surface against the tubing head 40, in combination with a sealing surface
between beads 28 and
groove 30 defines a sealing barrier between the tubing hanger 10 and tubing
head 40. Further,
the gap 25 (Figure 1) has disappeared due to the radial inward movement of leg
24 against the
lower member 18. In this instance, the lower member 18 provides support for
legs 24.
[0019] A side partial sectional view of an example of a wellhead assembly 50
having the packoff
assembly 12 is illustrated in Figure 4. In this example, the wellhead assembly
50 is made up of a
production tree 50 set above the tubing head 40 and over a bore hole 54. In
the example of
Figure 4, the bore hole 54 extends through subterranean formation 56. Further
included with the
wellhead assembly 50 is a string of tubing 58 shown mounted on a lower end of
tubing hanger 10
and projecting into the bore hole 54.
[0020] Optionally, a soft metal, such as silver, may be set over the seal
element 20 provide a
lubricating coating for when the tubing hanger 10 is being landed within the
tubing head 40.
One example of operation, the packoff assembly 12 (Figure 1) is formed onto
the tubing hanger
by first sliding the energizing ring 14 into upper groove 30 and then adding
the annular seal
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element 20 into upper groove 30 so that the lower member 18 extends between
the legs 24 for
providing support for the legs 24. In one example, the outer leg 24 of the
seal element is sized to
have an outer circumference just less than the inner circumference of the
radius of the inner
surface 46 so that during landing, up until the seal element 20 contacts the
taper 48, the seal
element 20 is spaced radially inward from the inner surface 46. Reducing the
amount of sliding
contact between the seal element 20 and inner surface 46 reduces chances of
damage before the
tubing hanger 10 is landed within the tubing head 40. After installing the
seal element 20, the
retainer nut 36 is screwed into place thereby locking the packoff assembly 12
to the tubing
hanger 10. Again, as the tubing hanger 10 is being landed within the tubing
head 40 the strategic
location of the taper 40 then engages the seal element 20 to create the seal
between the tubing
hanger 10 and tubing head 40. Although the energizing ring 14 may lift
slightly during
engagement of the seal element 20 with inner surface 46, the energizing ring
14 provides a
backup force for legs 22 and prevent legs 24 from collapsing. Optionally,
outer diameter of the
seal element 24 is electively changed to fit a particular size of the bowl 42.
Moreover, in one
example, the seal element 24 includes a flexible material, such as metal, so
that when landing in
tubing heads having asymmetric bowls 42, the elasticity and flexibility of the
seal element 24 can
from a full seal around the entire circumference of the interface between the
tubing hanger 10
and tubing head 40. An example of using a seal element 24 made from a metallic
material over
that of an elastomer is the ability to be deployed in lower depth but higher
temperature wells.
[0021] The present invention described herein, therefore, is well adapted to
carry out the objects
and attain the ends and advantages mentioned, as well as others inherent
therein. While a
presently preferred embodiment of the invention has been given for purposes of
disclosure,
numerous changes exist in the details of procedures for accomplishing the
desired results. These
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and other similar modifications will readily suggest themselves to those
skilled in the art, and are
intended to be encompassed within the spirit of the present invention
disclosed herein and the
scope of the appended claims.
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