Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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HIGH TEMPERATURE BACK PRESSURE VALVE
BACKGROUND OF THE INVENTION
I. Field of the invention
[000IJ This invention relates generally to back pressure valves for use in
sealing oil and gas
wells. More particularly, this invention relates to back pressure valves that
seal wells using high
temperature-resistant metal sealing surfaces.
2. Brief Description of Related Art
100021 Back pressure valves are useful for plugging oil and gas wells to
temporarily contain the
wells during, for example, removal of a pressure control adapter (e.g., a
blowout preventer, and
installation of other equipment, such as a production tree). Typically, back
pressure valves are
configured to fit into the opening of the tubing hanger at the wellhead, and
are equipped with
elastomeric or other non-metal seals. Such seals prevent the flow of fluid out
of the top of the
well by sealing the interface between the back pressure valve and the
production tubing.
WM) In general, the elastomeric or other non-metal seals used in back pressure
valves are
adequate for applications having relatively low temperatures, such as about
250 degrees
Fahrenheit or below. However, problems arise with such seals when temperatures
exceed about
450 degrees Fahrenheit or more. For example, in wells where steam assistance
gravity drained
(SAGD) methods are used, temperatures often reach levels higher than 450
degrees Fahrenheit or
more. Under such high heat conditions, elastomeric or other non-metal seals
may fail.
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[00041 Attempts have been made to improve the durability of elastomeric seals
under high heat
conditions by, for example, designing elastomers with higher heat tolerance,
or coating the
elastomeric seals with a heat resistant material. Such attempts, however, have
met with limited
success. Alternatively, attempts have been made to cool the wellhead prior to
installation of
valves having elastomeric seals, such as, for example, by pumping cold water
into the well. The
downside to this approach, however, is that the cooling process can be time
consuming and
expensive. What is needed, therefore, is a back pressure valve that can
effectively seal the
wellhead and that is resistant to high temperature applications.
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SUMMARY OF THE INVENTION
[00051 Disclosed herein is a back pressure valve for sealing a wellbore that
has a cylindrical
body configured for insertion into the opening in a tubing hanger, and that
has tapered metal
sealing surfaces. The surfaces taper inwardly in a downward direction. The
back pressure valve
also has a threaded portion that corresponds to a threaded portion of the
tubing hanger so that
when the threads of the valve engage the threads of the tubing hanger, the
tapered metal sealing
surface is brought into sealing engagement with the tubing hanger. Thus
configured, the
wellbore is sealed because fluid is prevented from flowing between the tubing
hanger and the
metal sealing surfaces of the back pressure valve.
100061 Optionally, the back pressure valve includes a poppet assembly having a
moveable
poppet valve with a poppet valve flange. When the poppet valve flange contacts
and seals
against the cylindrical body, the poppet valve is closed and no fluid can pass
between the poppet
valve flange and the cylindrical body. Conversely, when the poppet valve is
removed away from
the cylindrical body, the poppet valve is opened, and fluid is allowed to pass
between the poppet
valve flange and the cylindrical body. A spring may surround at least part of
the poppet valve
and, absent external forces, is configured to urge the poppet valve flange
into contact with the
cylindrical body. In one embodiment, both the cylindrical body and the poppet
valve flange are
made of metal, and when they contact one another they form a metal to metal
seal.
100071 Also disclosed is a method of sealing a well using a back pressure
valve as disclosed
herein. The method includes the steps of inserting the back pressure valve
through a pressure
control adapter on the well (such as a blowout preventer) so that the metal
sealing surfaces of the
back pressure valve seal against the tubing hanger, thereby sealing the well.
Thereafter, the
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pressure control adapter is removed and a production tree may be installed.
After installation of
the production tree, the back pressure valve may be removed.
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BRIEF DESCRIPTION OF THE DRAWINGS
[00081 The present invention will be better understood on reading the
following de/ailed
description of nonlimiting embodiments thereof, and on examining the
accompanying drawings,
in which:
[0009j Fig. 1 is a side cross sectional view of a back pressure valve
according to one possible
embodiment of the present invention;
100101 Fig. 2 is a side cross sectional view of a back pressure valve
according to the embodiment
shown in Fig. 1, with the poppet valve in an open position;
100111 Fig. 3 is a side cross sectional view of the back pressure valve of
Fig. I inserted into a
tubing hanger that has a blowout preventer mounted to the top thereof; and
[0012i Fig. 4 is an enlarged cross sectional view of the interface between
sealing surfaces of the
back pressure valve and the opening in the tubing hanger according to an
embodiment of the
invention.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
(00133 The foregoing aspects, features, and advantages of the present
invention will be further
appreciated when considered with reference to the following description of
preferred
embodiments and accompanying drawings, wherein like reference numerals
represent like
elements. In describing the preferred embodiments of the invention illustrated
in the appended
drawings, specific terminology will be used for the sake of clarity. However,
the invention is not
intended to be limited to the specific terms used, and it is to be understood
that each specific
term includes equivalents that operate in a similar manner to accomplish a
similar purpose.
(0014) Referring to Fig. 1, there is shown a back pressure valve 2 according
to one example
embodiment of the present technology. The back pressure valve 2 has a
cylindrical body 4
configured to be inserted into the opening 6 in the tubing hanger 8 of a
wellbore (shown in Fig.
3). The cylindrical body 4 may have internal shoulders 22. The back pressure
valve 2 also
includes a metal sealing surface 10 that in an example tapers inwardly from an
upper end 12 to a
lower end 14 thereof. In one example embodiment, the sealing surface 10 may be
tapered at an
angle of about 3 to 10 degrees relative to the longitudinal axis 16 of the
back pressure valve 2.
In certain embodiments, such as that shown in Fig. 1, the back pressure valve
2 may also have a
hydraulic sealing groove 13 that circumscribes the back pressure valve 2 and
bisects the metal
sealing surface 10.
100151 The back pressure valve 2 additionally has means for attachment of the
valve 2 to the
tubing hanger 8, as well as means for energizing the metal sealing surface 10
into sealed
engagement with surfaces of the tubing hanger 8 (shown in Fig. 3). For
example, with respect to
the means for attachment, in the embodiment shown in Fig. 1 the back pressure
valve 2 includes
threads 18 that may be configured to correspond to threads 42 (shown in Fig.
3) in the opening of
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the tubing hanger 8. Furthermore, with respect to the means for energizing,
the back pressure
valve 2 may have internal threads 20 positioned on an inner surface 21 of the
back pressure valve
2. These internal threads 20 may be configured for engagement with an
installation tool (not
shown). Once the installation tool is engaged with the internal threads 20,
the installation tool
can rotate the back pressure valve 2 until threads 18 fully engage the
corresponding threads 42 in
the opening of the tubing hanger 8.
100161 Fig. I also shows a poppet valve 24 that may be included in the back
pressure valve 2.
The poppet valve 24 may include a poppet valve flange 26, and an elongate
member 31 that
extends from the poppet valve flange 26 to at or near the bottom end 38 of the
back pressure
valve 2. In addition, the poppet valve 24 may include a spring 28, or other
biasing mechanism.
The poppet valve flange 26 may have a seal 30 that prevents fluid from passing
between the
poppet valve flange 26 and shoulders 22 on the cylindrical body 4 when the
poppet valve is
closed, as shown in Fig. 1, and as fiuther described below.
100171 A spring 28 may surround at least a portion of the elongate member 31
of the poppet
valve 24 to help control the movement of the poppet valve 24. The spring 28 is
bounded at a
bottom end by a spring retention shelf 40 in the cylindrical body 4, and at an
upper end by
protrusions 33 extending outwardly from an upper end of the elongate member
31.
Alternatively, the protrusions 33 may be omitted, and the upper end of the
spring 28 may be
bounded by the poppet valve flange 26. The spring 28 is biased so that, in the
absence of
external forces, it urges the at least one flange 26 of the poppet valve 24
into engagement with
the shoulders 22 on the cylindrical body 4.
100181 Thus configured, the poppet valve 24 has at least a closed position and
an open position.
The closed position is the position shown in Fig. 1, with the poppet valve
flange 26 contacting
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the shoulders 22 on the cylindrical body 4. When in the closed position, the
at least one poppet
valve flange 26 forms a seal with the shoulders 22, and fluid is prevented
from flowing between
the poppet valve flange 26 and the shoulders 22. In an example embodiment,
both the flange 26
and the shoulders 22 are metal, so that the seal between them is a metal to
metal seal. Seals 30
may supplement this seal and may be made of an elastomer or any other suitable
material.
[001.9I Application of an external force may cause the poppet valve 24 to move
into an open
position, as shown in Fig. 2. For example, an axial pressure differential on
poppet valve 24 may
exert a force on the poppet valve 24 in a downward direction D. When the
magnitude of this
downward force exceeds the upward force exerted on the poppet valve flange 26
by the spring 28
a.nd well bore pressure, the poppet valve 24 will move downward relative to
the cylindrical body
4. As this happens, the poppet valve flange 26 will move downward into an open
position, away
from the shoulders 22 on the cylindrical body 4, and fluid will be able to
flow therebetween.
Hence, the back pressure valve assembly can be removed from inside the hanger
with a
lubricator tool.
100201 Referring now to Fig. 3, there is shown a back pressure valve 2
according to an
embodiment of the invention, inserted into an opening 6 of a tubing hanger 8.
Also shown is a
blowout preventer 46 mounted above the tubing hanger 8. In this embodiment,
the opening 6
includes threads 42 that are configured for engagement with the threads 18 of
the back pressure
valve 2. In addition, an upper portion 44 of the walls of opening 6 is tapered
outwardly, from a
smaller diameter at a downward position toward the lower portion of the tubing
hanger 8 to a
larger diameter at an upward position toward the upper portion of the tubing
hanger 8. As the
back pressure valve 2 enters the opening 6, the threads 18 of the back
pressure valve 2 engage
the threads 42 of the opening 6. An installation tool (not shown) then
continues to provide
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torque to the internal threads 20 until the back pressure valve 2 is fiilly
threaded into the opening
6 and the metal sealing surface 10 of the valve 2 contacts the tapered upper
portion 44 of the
walls of the opening 6. With the back pressure valve 2 fully in place, the
contact between the
metal sealing surface 10 and the walls of the opening 6 in the tubing hanger 8
form a seal. In
embodiments having a hydraulic sealing groove 13, the hydraulic sealing groove
13 may serve to
enhance the seal and clean the tapered sealing surface, when the metal sealing
surface 10 fully
contacts the walls of the opening 6. With the back pressure valve 2 in place
in the tubing hanger
8 as shown in Fig. 3, the opening 6 of the tubing hanger 8 is sealed and
blocks fluid flow
between the walls of the opening 6 and the metal sealing surface 10 of the
back pressure valve 2.
100211 Fig. 4 show an enlarged view of an example interface between the metal
sealing surface
of the back pressure valve 2 and the tubing hanger 8. In Fig. 4, an example of
the taper of the
metal sealing surface 10 can clearly be seen. As discussed above, in one
example embodiment,
the metal sealing surface is tapered at an angle of about 3 to 9 degrees.
100221 One advantage to the back pressure valve disclosed herein is that the
seal between the
valve 2 and the tubular hanger 8 is metal to metal. This means that no
elastomeric or other type
of seal is required to seal the interface between the components. The
elimination of elastomers
or other non-metal seals is beneficial because inany of those materials cannot
withstand high heat
applications. In fact, elastomeric and other non-metal seals are generally not
adapted for use in
applications where temperatures reach 450 degrees Fahrenheit or more.
Moreover, while some
specialized elastomeric seals may be able to withstand higher temperatures,
such seals often
cannot be used because of econonaic or other considerations.
[00231 Some wellhead applications, however, do generate high heat. For
example, steam
assistance gravity drained (SAGD) wellhead applications can generate
temperatures of up to 650
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degrees Fahrenheit or more. Therefore, to use elastomeric or non-metal seals
in those
applications requires time-consuming cooling processes, such as pumping cold
water through the
wellhead. Because the seals of the valves disclosed herein are made of metal,
and can therefore
withstand much higher temperatures, the cooling processes are urmecessary.
[00241 In addition to the apparatus and assembly shown in Figs. 1-4, another
embodiment of the
invention provides a method of sealing a well with the back pressure valve
described above. In
practice, the back pressure valve of the present embodiments may be used to
plug a well during
the transition of wellhead operations to production operations, when the
pressure control adapter
such as a blowout preventer (shown in Fig. 3) is removed from the wellhead,
and a production
tree (not shown) is installed.
[00251 Initially, the back pressure valve is introduced to the tubing hanger
at the wellhead by
attaching the valve to an installation tool and inserting the valve through
the pressure control
adapter. For example, referring to Fig. 3, if the pressure control adapter is
a blowout preventer
46 or lubricator adapter, the back pressure valve 2 is inserted through the
opening 48 that
provides access from the top of the blowout preventer 46 to the opening 6 in
the tubing hanger 8.
During this step, the installation tool may engage the internal threads 20 on
the inner surface 21
of the back pressure valve 2, and may turn the back pressure valve 2 so that
the threads 18 of the
back pressure valve 2 engage corresponding threads 42 in the tubing hanger 8.
The tool will
continue to turn the back pressure valve 2, thereby further engaging the
threads, until the metal
sealing surfaces 10 of the valve 2 contact the tubing hanger 8.
100261 Once the back pressure valve 2 is in place and a seal is achieved, the
pressure control
adapter may be removed and a production tree may be installed without fluid
leaking from the
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well. Mier the installation of the production tree, the back pressure valve 2
may be removed by
reversing the above process to allow oil or gas to flow out of the wellhead.
[0027) While the invention has been shown or described in only some of its
forms, it should be
apparent to those skilled in the art that it is not so limited, but is
susceptible to various changes
without departing from the scope of the invention. Furthermore, it is to be
understood that the
above disclosed embodiments are merely illustrative of the principles and
applications of the
present invention. Accordingly, numerous modifications may be made to the
illustrative
embodiments and other arrangements may be devised without departing from the
spirit and
scope of the present invention as defined by the appended claims.
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