Note: Descriptions are shown in the official language in which they were submitted.
CA 02784163 2012-07-30
APPARATUSES FOR SEALING AGAINST A WELL TUBULAR
TECHNICAL FIELD
[0001] This document relates to stuffing boxes for wellheads.
BACKGROUND
[0002] Stuffing boxes are used in the oilfield to form a seal between the
wellhead
and a well tubular passing through the wellhead, in order to prevent leakage
of wellbore
fluids between the wellhead and the piping. Stuffing boxes may be used in a
variety of
applications, for example production with pump-jacks, and inserting or
removing coiled
tubing. Stuffing boxes may incorporate a tubular shaft mounted for rotation in
the housing
for forming a stationary seal with the piping in order to rotate with the
piping. The tubular
shaft in turn dynamically seals with the stuffing box housing. Designs of this
type of stuffing
box can be seen in US 7,044,217 and CA 2,350,047. In other designs, the
stuffing box may
instead form a dynamic seal directly against the piping without incorporating
a rotating
tubular shaft. Stuffing boxes may be used for rotating or reciprocating pumps.
[0003] Leakage of crude oil from a stuffing box is common in some
applications, due
to a variety of reasons including abrasive particles present in crude oil and
poor alignment
between the wellhead and stuffing box. Leakage costs oil companies money in
service time,
down-time and environmental clean-up. Leakage is especially a problem in heavy
crude oil
wells in which oil may be produced from semi-consolidated sand formations
where loose
sand is readily transported to the stuffing box by the viscosity of the crude
oil. Costs
associated with stuffing box failures are some of the highest maintenance
costs on many
wells.
SUMMARY
[0004] An apparatus for a wellhead is disclosed, the apparatus defining a
passage for
receiving a well tubular in use, the apparatus comprising: a stuffing box; a
housing mounted
on an upper end of the stuffing box; and one or more seals within the housing
for sealing
against the well tubular in use; in which the housing has two or more
laterally removable
housing segments.
[0005] A method is also disclosed comprising: assembling one or more seals
around
a well tubular received by a stuffing box; assembling a housing around the one
or more seals
by laterally converging two or more housing segments around the one or more
seals; and
mounting the housing to an upper end of the stuffing box.
[0006] A stuffing box for a well tubular connected to operate a
reciprocating pump is
also disclosed, the stuffing box comprising: a housing defining a passage for
receiving the
well tubular; one or more seals at least partially within a removable portion
of the housing
for sealing against the well tubular in use; in which the removable portion of
the housing is
provided in two or more laterally removable housing segments.
[0007] In various embodiments, there may be included any one or more of
the
following features: The one or more seals comprise packing. The one or more
seals are
dynamic seals. The housing is bolted to the stuffing box. The housing is split
into the two or
more laterally removable housing segments along one or more planes running
parallel to and
originating from a stuffing box axis. The two or more laterally removable
housing segments
are secured together with bolts. The upper end of the stuffing box is defined
by a threaded
cap. The apparatus is adapted for production of wellbore fluids. The apparatus
is adapted for
use in a progressing cavity pump application. The apparatus is adapted for use
in a
reciprocating pump application. Each of the one or more seals comprise two or
more
laterally removable seal elements. Before assembling the one or more seals
around the well
tubular: laterally removing one or more of the housing segments from around
the one or
more seals; and removing one or more seals previously assembled around the
well tubular.
The method is carried out without removing either the stuffing box or a drive
head above the
housing. The one or more seals are fully within the removable portion of the
housing.A
second set of one or more seals is located within the housing for sealing
against the well
tubular in use.
[0008] These and other aspects of the device and method are set out in the
description.
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BRIEF DESCRIPTION OF THE FIGURES
[0009] Embodiments will now be described with reference to the figures, in
which
like reference characters denote like elements, by way of example, and in
which:
[0010] Fig. lA is a view of a progressing cavity pump oil well installation
in an earth
formation for production with a typical drive head, wellhead frame and
stuffing box;
[0011] Fig. 1B is a view similar to the upper end of Figure 1 but
illustrating a
conventional drive head with an integrated stuffing box extending from the
bottom end of
the drive head;
[0012] Fig. 2 is a side elevation view, in section, of a known stuffing
box;
[0013] Fig. 3 is a perspective view of a stuffing box with a laterally
removable
housing mounted on an upper end of the stuffing box.
[0014] Fig. 4 is a section view taken along the 4-4 section lines of Fig.
3.
[0015] Fig. 5 is a perspective view of a stuffing box for a reciprocating
pump and
having a laterally removable housing.
[0016] Fig. 6 is a section view taken along the 6-6 section lines of Fig.
5, and
illustrating a reciprocating pump.
[0017] Fig. 7 is a perspective exploded view of the stuffing box of Fig. 5.
DETAILED DESCRIPTION
[0018] Immaterial modifications may be made to the embodiments described
here
without departing from what is covered by the claims.
[0019] Fig. lA illustrates a known progressing cavity pump installation 10.
The
installation 10 includes a typical progressing cavity pump drive head 12, a
wellhead frame
14, a stuffing box 16, an electric motor 18, and a belt and sheave drive
system 20, all
mounted on a flow tee 22. The flow tee is shown with a blowout preventer 24
which is, in
turn, mounted on a wellhead 25. The drive head 12 supports and drives a drive
shaft 26,
generally known as a "polished rod". The polished rod is supported and rotated
by means of
a polish rod clamp 28, which engages an output shaft 30 of the drive head by
means of
milled slots (not shown) in both parts. Wellhead frame 14 may be open sided in
order to
expose polished rod 26 to allow a service crew to install a safety clamp on
the polished rod
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and then perform maintenance work on stuffing box 16. Polished rod 26
rotationally drives a
drive string 32, sometimes referred to as a sucker rod, which, in turn, drives
a progressing
cavity pump 34 located at the bottom of the installation to produce well
fluids to the surface
through the wellhead.
[0020] Fig. 1B illustrates a typical progressing cavity pump drive head 36
with an
integral stuffing box 38 mounted on the bottom of the drive head and
corresponding to the
portion of the installation in Fig. lA that is above the dotted and dashed
line 40. An
advantage of this type of drive head is that, since the main drive head shaft
is already
supported with bearings, stuffing box seals can be placed around the main
shaft, thus
improving alignment and eliminating contact between the stuffing box rotary
seals and the
polished rod. This style of drive head may also reduce the height of the
installation because
there is no wellhead frame, and also may reduce cost because there are fewer
parts since the
stuffing box is integrated with the drive head. A disadvantage is that the
drive head must be
removed to do maintenance work on the stuffing box. Surface drive heads for
progressing
cavity pumps require a stuffing box to seal crude oil from leaking onto the
ground where the
polished rod passes from the crude oil passage in the wellhead to the drive
head.
[0021] Referring to Fig. 2, a known stuffing box 16 is shown having a
housing 17
defining a passage 19 for receiving a well tubular 52. Mounted within the
passage 19 is a
series of dynamic seals 21 in the form of packing. The seals 21 are mounted
between a first
stop defined by a spring 23 compressed by a stationary sleeve 25, and a second
stop defined
by a threaded cap assembly 27 that defines an upper end 31 of the housing 17.
In use in a
progressing cavity pump application, the pump-driven well tubular 52 rotates,
with seals 21
dynamically sealing against well tubular 52 to prevent axial leakage of fluids
through
stuffing box 16.
[0022] When one or more or all of seals 21 fail, the seals 21 must be
replaced. To do
this cap 27 is axially removed off of well tubular 52, and seals 21 must be
axially removed or
cut off of the well tubular 52. Alternatively, well tubular 52 may be axially
removed. Axial
removal and reinstallation of such components may be accomplished using a
flush by or
workover rig. Once new seals 21 are installed, the stuffing box 16 is
reassembled and well
production resumed.
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[0023] Referring to Figs. 3 and 4, an apparatus 41 for a wellhead 39 (Fig.
4) is
illustrated, the apparatus 41 defining a passage 43 for receiving a well
tubular 52 in use.
Apparatus 41 comprises a stuffing box 42, a housing 45, and one or more seals
47 (Fig. 4).
Like stuffing box 16, stuffing box 42 may comprise a stationary housing 44,
and one or more
seals 48 (Fig. 4). Stationary housing 44 defines a passage 50, for example a
bore, for
receiving a well tubular 52, passage 50 being part of passage 43 when
assembled with
housing 45. In use, stuffing box 42 may be mounted directly or indirectly to a
wellhead 39
(Fig. 4). Housing 45 is mounted on an upper end 49 of the stuffing box 42, and
one or more
seals 47 are within the housing 45 for sealing against the well tubular 52 in
use.
[0024] The housing 45 is provided in two or more laterally removable
housing
segments 45A and 45B. One or more of segments 45A, 45B may be split or semi-
annular in
shape. Segments 45A and 45B may be radial segments defined relative to a
housing axis 51,
such that all segments 45A, B seated within the same plane perpendicular to
housing axis 51
collectively cover three hundred sixty degrees of radial coverage about
housing axis 51. In
further embodiments, each such segment makes up less than or equal to a one
hundred eighty
degree radial portion of housing 45 defined about housing axis 51, so that
each segment may
be removed in a lateral direction 53 (Fig. 3) relative to housing axis 51
(Fig. 4).
[0025] As shown in Fig. 3, the housing 45 may be split into the two or more
laterally
removable housing segments 45A and B along one or more planes, for example the
plane
identified by the section lines 4-4 and shown in Fig. 4, running parallel to
and originating
from stuffing box axis (shown as housing axis 51 in Fig. 4 and illustrated by
section lines 4-4
in Fig. 3).
[0026] By providing laterally removable housing segments 45A and 45B,
housing 45
may be disassembled without interfering with well tubular 52 or other
components mounted
below the housing 45. Thus, segments 45A and 45B may be laterally removed,
each faulty
one of seals 47 replaced, and segments 45A and 45B laterally converged all at
less expense
than repairing faulty seals in a traditional stuffing box such as the stuffing
box 16 shown in
Fig. 2.
[0027] Referring to Figs. 3 and 4, housing 45 may be mounted to upper end
49 of
stuffing box 42, for example bolted using bolts 65 through holes 59 to the
stuffing box 42
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(holes 59 shown in the embodiment of Fig. 7). Other suitable mounting
mechanisms may be
used, such as a threaded connection.
[0028] The two or more laterally removable housing segments 45A and B may
be
secured together, for example with bolts 66. Along each radial face 68
terminating housing
segment 45A as shown in Fig. 4 run a series of holes 69, 71, sized to fit
either a bolt cap 64
or bolt thread 67 (Fig. 7), respectively. Split rings 61 may be positioned
between bolts 66
and holes 69 and 71. Other suitable securing mechanisms may be used here and
in other
parts of the apparatus 41, such as spring, friction, snap fit, or clamp
mechanisms.
[0029] The one or more seals 47 may comprise packing 72 as shown, or may be
other suitable seals such as lip seals (not shown). If seals 47 are used in a
stuffing box
embodiment that uses a rotating tubular shaft, seals 47 may be either dynamic
(seal between
the rotating shaft and the housing 45) or static (against well tubular 52).
Like laterally
removable housing segments 45A, B, seals 47 may be provided in laterally
removable
segments, for example split or semi-annular in shape. Laterally removable seal
segments
may also be secured together by suitable mechanisms such as bolts. Packing 72
is
advantageous as packing 72 may be installed without a flush by unit or
removing well
tubular 52 because the packing 72 can be coiled around well tubular 52. Seals
47 may be
resilient, non-mechanical seals. One or more of a biasing element (not shown)
or an axial
compression mechanism (such as spring 74) may be used to improve sealing. One
or more
rings such as brass rings 78 may be located on either side of seals 47. Brass
rings 78 may be
split (Fig. 7) to allow lateral installation, and may have aligned outer slots
55 for a gasket
such as an o-ring (not shown).
[0030] Referring to Figs. 5 - 7, housing 45 may comprise part of a stuffing
box 42,
for example in a reciprocating pump 76 application. In such an embodiment, the
one or more
seals 47 may be at least partially, for example fully, within a removable
portion, such as
housing 45, of the stuffing box housing 44. A second set of one or more seals
48 may be
located within the housing 44 for sealing against the well tubular 52 in use.
A sleeve 85 may
be positioned within a base cap 84, the lower portion of which may be
connected to a
threaded adapter 90 for connecting directly or indirectly with a wellhead 39
(shown in Fig.
4).
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[0031] Housing 45 may be retrofitted onto the upper end of an existing
stuffing box
42 (Figs. 3 and 4), or supplied as part of a stuffing box 44 (Figs. 5-7).
Retrofitting an existing
stuffing box 42 may be carried out in a variety of suitable ways. Referring to
Fig. 4 for
example, threaded cap assembly 27 (Fig. 2) may be removed, and a threaded base
cap 84
threaded onto the upper end 49 of stuffing box 42. Next, an inner flanged
sleeve 85 is nested
within threaded base cap 84, sleeve 85 having an upper sleeve extension 87 for
receiving and
axially aligning housing segments 45A and 45B. Sleeve 85 may act as an upper
stop for seals
48 and a lower stop for existing stuffing box 42 seals 47 as shown. Next,
seals 47 and split
rings 78 are installed, and housing segments 45A and 45B laterally converged
and mounted
by bolting to threaded base cap 84. In other embodiments, an existing stuffing
box 42 may
be retrofitted by modifying the threaded cap assembly 27 as required, for
example by drilling
axial holes (not shown) in threaded assembly (shown in Fig. 2) and mounting
housing
segments 45A and B.
[0032] Referring to Fig. 4, as eluded to above the embodiments described
herein may
be installed by the following sequence. The one or more seals 47 may be
assembled around
well tubular 52. Well tubular 52 may be initially received by a stuffing box
42 if the method
is a method of retrofitting an existing stuffing box 42. Next, housing 45 is
assembled around
the one or more seals 47 by laterally converging the two or more housing
segments 45A and
45B around the one or more seals 47. Next, the housing 45 is mounted to an
upper end 49 of
the stuffing box 42, or directly or indirectly to wellhead 39, depending on
the application.
[0033] The method described above may form part of a method of replacing
the one
or more seals 47. In such an embodiment, one or more previously installed
seals 47 may
need replacing, and the following sequence carried out. One or more of the
housing
segments 45A and B may be laterally removed from around the one or more seals
47. Next,
the faulty seal 47, or all of seals 47 are removed from around the well
tubular 52.
Afterwards, the initial stages of the method may be carried out, for example
by assembling a
new set of the one or more seals 47 followed by assembling the housing 45 and
mounting the
housing 45. The method may be carried out without removing either the stuffing
box 42 or a
drive head above the housing 45.
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[0034] Stuffing box 42 may be used for production of wellbore fluids, such
as
production in a progressing cavity pumping application. Stuffing box 42 may be
adapted to
be retrofitted into a wellhead 39, for example below the drive head (not
shown). In other
cases stuffing box 42 may be adapted for an integral application, for example
in the style
shown in Fig. 1B.
[0035] Referring to Fig. 4, it should be understood that various other
components
may be incorporated into stuffing box 42. For example, primary seals 92 may
provided at
various points between well tubular 52 and housing 44. Similarly, o-rings 86,
gaskets,
packing and other components may be used.
[0036] In general, where the word seal is mentioned in this document, one
or more
seals may be provided to effectively operate as a single seal, for example
observed in the
stacking of plural lip seals 48(Fig. 6) provided as the stationary seals for
sealing against well
tubular 52 in use. In addition, it should be understood that various other
components may be
provided with the stuffing box 42 for various wellhead applications to be
carried out. For
example, wellhead 39 may include any one or more of the other components
illustrated in
Fig. lA or 1B. In some applications, a drive head may rotate a well tubular
52, while other
applications may incorporate a pump jack attached to reciprocate well tubular
52 as a
polished rod. Stuffing box 42 may also be used for injection or pulling of
tubulars, for
example in a coiled tubing application. Stuffing box 42 may also be used in a
slew pump
application. Stuffing box 42 may incorporate a lubrication system (not shown)
for lubricating
various components, such as the one or more seals 47.
[0037] Various components discussed herein may include various sub-
components,
such as the plural sleeves that thread together to make up the housing 44 of
Fig. 4.
Connections between components, or the mounting of one component to another,
may be
done through intermediate parts.
[0038] Figures may not be drawn to scale, and may have dimensions
exaggerated for
the purpose of illustration.
In the claims, the word "comprising" is used in its inclusive sense and does
not exclude other
elements being present. The indefinite article "a" before a claim feature does
not exclude
more than one of the feature being present. Each one of the individual
features described
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here may be used in one or more embodiments and is not, by virtue only of
being described
here, to be construed as essential to all embodiments as defined by the
claims.
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