Note: Descriptions are shown in the official language in which they were submitted.
CA 02436924 2003-08-11
STUFFING BOX FOR PROGRESSING CAVITY PUMP DRIVE
Field of the Invention
The present invention relates generally to improvements in stuffing box
configurations for progressing cavity (PC) pump drive head installations.
Background of the Invention
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.
Due the abrasive sand particles present in crude oil and poor alignment
between the wellhead and stuffing box, leakage of crude oil from the stuffing
box is
common in some applications. This costs oil companies money in service time,
down
time and environmental clean up. It is especially a problem with heavy crude
oil wells
in which the oil is often produced from semi-consolidated sand formations
since loose
sand is readily transported to the stuffing box by the viscosity of the crude
oil. It is very
difficult to make stuffing boxes that last as long as desirable by oil
production
companies. Costs associated with stuffing box failures are one of the highest
maintenance costs on many wells.
Conventional stuffing boxes are mounted below the drive head. Conventional
stuffing boxes are typically separate from the drive head and are mounted in a
wellhead frame such that they can be serviced from below the drive head
without
removing it. A conventional stuffing box uses braided packing that is split so
it can be
replaced while the polished rod stays inside the stuffing box. Since
conventional
stuffing boxes seal against the polished rod, which is subject to wear, and
due to poor
alignment of the polished rod to the stuffing box, leakage becomes somewhat
-1-
CA 02436924 2007-03-12
inevitable. Due to this experience, users tend to expect stuffing box leakage
if the
stuffing box uses braided packings.
In order to reduce or eliminate the leakage, high-pressure lip seals have been
used running against a hardened sleeve rather than against the polished rod.
Grenke
in Canadian Patent No. 2,095,937 issued Dec. 22, 1998 shows a typical stuffing
box
employing lip seals. These stuffing boxes are known in the industry as
environmental
stuffing boxes because they do not leak at all until the lip seals fail. Since
these high-
pressure lip seals are not split and are mounted below the drive head, they
cannot be
replaced with the polished rod in place so the drive head must be removed to
service
the stuffing box. Since the drive head must be removed to service the lip
seals, the
wellhead frame has been eliminated and the stuffing box is bolted directly to
the
bottom of the drive head on many drive heads now being produced. This type of
stuffing box directly mounted to the drive head is shown in the above
referenced
Grenke patent. This product is made by Grenco Industries. These types of
stuffing
boxes are referred to as integral.
There are many types of rotary lip seals that might be applied to stuffing
boxes
for progressing cavity pumped wells. Grenco and other competitors have had
some
field success with the type described as a flanged VARISEAL in the American
Variseal catalog. American Variseal is a member of Busak and Shamban Inc. This
type of seal is made by a number of competitors. Generally these seals are
machined
from reinforced TEFLON and they have a preload spring between two lips. The
flange is convenient for mounting the seal and stabilizing it. Since the seals
are
TEFLON based, they can operate without lubrication.
Servicing of stuffing boxes is time consuming and difficult. In order to
service
the environmental or integral stuffing boxes, the drive head must be removed
which
necessitates using a rig with two winch lines, one to support the drive head
and the
other to hold the polished rod. To save on rig time, the stuffing box is
typically
replaced and the original stuffing box is sent back to a service shop for
repair.
-2-
CA 02436924 2007-03-12
Recently, Oil Lift Technology Inc. has introduced top mounted stuffing boxes
to
the industry, which allow the stuffing box to be serviced from on top of the
drive head
without removing the drive head from the well. These types of stuffing box are
shown
in Hult Canadian patent application 2,350,047 (the "Oil Lift Stuffing Box").
These top
mounted stuffing boxes use a flexibly mounted "floating" standpipe around
which is a
bearing supported shaft carrying the rotary stuffing box seals. Typically the
primary
rotary stuffing box seal is braided packing since it has proven to last for a
long time
when running against the hardened, flexibly mounted standpipe. Braided
packings
made from TEFLON and graphite fibres and been used most frequently. KEVLAR
cornered packings are often used for the first and last packing rings to
prevent
extrusion. Packings of this type are generally self lubricating which can also
be an
advantage in the present invention. Because the standpipe floats, it self
aligns to the
packing, reducing or eliminating run out and leakage compared to conventional
stuffing boxes. Packings have very low resilience so reduction of run out is
very
important in prevention of leakage. In some cases the stuffing box is counter-
pressurized, preferably by lubricating oil at a higher pressure than the
wellhead
pressure so if there is any leakage through the primary rotary stuffing box
seal,
lubricating oil goes down the well rather than allowing well fluids to leak
into the drive
head. In the most difficult applications, the use of pressurized lubricating
oil has
proven very beneficial in extending stuffing box seal life, demonstrating many
times
the stuffing box seal life compared to non-pressurized stuffing boxes.
Summary of the Invention
Applicant refers the reader to the Applicant's co-pending applications:
Canadian patent application 2,350,047 (Hult) filed on June 11, 2001 and laid
open on
December 9, 2001 and U.S. Patent Application Publication No. US 2001/0050168
filed
on June 11, 2001 and published on December 13, 2001.
-3-
CA 02436924 2003-08-11
The present invention relates to improving the performance and serviceability
of
the Oil Lift Stuffing Box and to providing a series of stuffing boxes to
retrofit to other
wellhead drives either above or below the drive head.
The present invention relates generally to improvements in stuffing box
configurations. The present invention also relates generally to improvements
in seal
configurations for stuffing boxes.
The present invention is applicable to top mounted stuffing boxes, bottom
mounted stuffing boxes, integral stuffing boxes and stand-alone stuffing
boxes.
Stuffing boxes according to the present invention may either be pressurized or
non-pressurized.
Where the stuffing box is pressurized, the pressure may be applied through a
fluid medium. The fluid medium may be any suitable liquid or gas. In some
applications, the fluid medium is preferably a lubricating fluid such as
lubricating oil so
that the fluid medium is available to lubricate stuffing box or drive head
components
such as seals and bearings.
Where the stuffing box is pressurized, the pressure source may be comprised
of any suitable pressure source, including a hydraulic drive system for the
well, a
separate pump, a pressurized chamber such as a chargeable pressure chamber, a
pressure-intensifying cylinder, or combinations thereof. The pressure source
may also
consist of or be comprised of a hydraulic accumulator for maintaining or
stabilizing the
pressurization of the stuffing box. It is desirable that the pressurization
fluid be 50 to
500 psi above the wellhead pressure so if the primary seal leaks,
pressurization fluid
leaks toward the wellhead rather than allowing well fluid to enter the
stuffing box or
drive head housing.
-4-
CA 02436924 2003-08-11
Where the stuffing box is pressurized, two rotary seals may be used with
pressurization between the two seals. The first seal is a primary seal and has
well
fluid pressure on one side and pressurization fluid, preferably at higher
pressure than
the well fluid, on the opposite side. The second seal is a pressurization seal
for
containing or inhibiting the leakage of pressurization fluid within or from
the stuffing
box. The pressurization seal is subjected to pressurization fluid on one side
and little
or no pressure on the opposite side. Both the primary seal and pressurization
seal
may be comprised of any type of suitable rotary seal, including labyrinth
seals,
chevron packings, braided packings, foil packings, O-rings, lip seals, rotary
oil seals or
combinations thereof. Preferably the primary and pressurization seals are
comprised
of braided packings because of the ease of service. In some cases, such as
using a
pressurization fluid that is different than the lubricating fluid in the
stuffing box or drive
head, even small leakage past the pressurization seal is objectionable. In
these
cases, the pressurization seal is preferably a high pressure lip seal because
these
seals have lower leakage rates than braided packings. Where the stuffing box
is
pressurized, a circulation path is preferably provided for circulating
pressure fluid
which does leak within or from the stuffing box. This circulation path may in
some
applications facilitate lubrication by the pressure fluid of stuffing box or
drive head
components such as bearings or seals.
Where the stuffing box is non-pressurized, a controlled leakage path is
preferably provided for well fluids to prevent or inhibit such fluids from
entering the
stuffing box bearings or the drive head. Two rotary seals are required with a
leakage
path for the escape of well fluids between these seals. The primary seal has
well
pressure on one side and is in communication with the leakage path on the
opposite
side so any well fluid that passes the primary seal escapes to the leakage
path. The
secondary seal is to prevent or inhibit well fluids that escape past the
primary seal
from flowing into the drive head or stuffing box housing, forcing said well
fluids to drain
out through the leakage path. The leakage path may comprise one or more
passages
and one or more holes in components of the stuffing box or the drive head.
Preferably
-5-
CA 02436924 2003-08-11
the leakage path includes a lantern ring disposed adjacent to holes through
the main
shaft thus permitting leakage to exit the drive head or stuffing box.
Stuffing boxes according to the present invention include rotary seals. The
rotary seals may be comprised of any suitable rotary seal, including labyrinth
seals,
chevron packings, braided packings, foil packings, 0-rings, lip seals, chevron
seals,
rotary oil seals or any combination thereof. Preferably the rotary stuffing
box seal is
comprised of braided packings or lip seals or a combination of braided
packings and
lip seals.
Stuffing boxes according to the present invention may utilize a rigidly
mounted
standpipe or a flexibly mounted "floating" standpipe for improving the
performance of
the stuffing box seal. Where a standpipe is utilized, the standpipe may be
either a
single wall standpipe or a double wall standpipe. A double wall standpipe is
useful for
facilitating a pressurized stuffing box in which the pressurization seal is
serviceable
from on top of the stuffing box or drive head. Preferably, the pressurization
seal is
comprised of braided packing or a lip seal or a combination thereof.
In order to pressurize the Oil Lift integral Stuffing Box illustrated by prior
art
Figure 1, a labyrinth seal acting as the pressurization seal has been used
between the
drive gear (Figure 1 illustrates a labyrinth created by a labyrinth ring
sealing against
the drive gear but the inner bearing race, the shaft itself, a bearing spacer
or any
concentric surface that rotates with the shaft can be used) and a labyrinth
ring sealed
to the drive head housing. A labyrinth seal has been used because it is non-
wearing,
but due to its location in the drive head it is impossible to service without
disassembling the drive head. It has also been found that good labyrinth
sealing in
that location is difficult to achieve due to run out between mating parts and
the need
for tight tolerances.
In one aspect of the present invention, the need for a non-serviceable
labyrinth
seal located between the housing and main shaft (or an equivalent) in
pressurized
-6-
CA 02436924 2003-08-11
stuffing boxes according to preferred embodiments of the invention has been
eliminated by use of a double wall standpipe and a rotary seal instead of a
labyrinth
acting as the pressurization seal. The principle is an upper primary rotary
seal and a
lower rotary pressurization seal located in the annulus between the standpipe
and the
shaft, with pressurization means connected through passages in the standpipe
communicating with the annular area between the upper and lower seals, said
seals
being field serviceable by removal and replacement through the top of the
stuffing box
or drive head. In the preferred embodiment, the upper and lower rotary seals
are
braided packings separated by a preload spring or a lantern ring because of
the ease
of service and durability of this type of seal. In some cases, such as using a
pressurization fluid that is different than the lubricating fluid in the
stuffing box or drive
head, even small leakage past the pressurization seal is objectionable. In
these
cases, the pressurization seal is preferably a high pressure lip seal because
these
seals have lower leakage rates than braided packings.
Abrasive particles in the well fluid cause wear of the standpipe and it must
be
periodically replaced. Another aspect of the present invention is that the
standpipe
can be inspected and replaced without removing the stuffing box or drive head
from
the well.
Another aspect of the present invention is that in some preferred embodiments,
two different fluids can preferably be used inside the drive head. Hydraulic
pressure,
from the hydraulic system driving the drive head, can preferably be used to
pressurize
the stuffing box. The lower bearings and gears can preferably be lubricated
with gear
oil. Unlike using a labyrinth seal as the pressurization seal, a
pressurization seal such
as braided packings or lip seals can be used in conjunction with a double
walled
standpipe so there is negligible flow of pressurization fluid into the lower
bearings and
gears of the stuffing box or drive head, thus keeping the hydraulic oil out of
the gear oil
in this example.
-7-
CA 02436924 2003-08-11
In another aspect of the present invention, a non-pressurized stuffing box can
be achieved using a flexibly mounted standpipe around which is a rotating
shaft
mounted on bearings in a housing. The primary rotary seal is located in the
annulus
between the standpipe and the shaft. This configuration can be used for a top
mounted stuffing box as part of a drive head or as a stand-alone stuffing box
that can
be retrofitted below existing drive heads, preferably in a wellhead frame
which
supports a drive head above the stuffing box of the present invention. Since
there is
no pressurization system, leakage of well fluids past the primary seal toward
the
stuffing box or drive head will occur. A leakage path is provided to allow
escape of
well fluids. A secondary seal is provided to prevent well fluids from entering
the drive
head or stuffing box housing. Improvements in this system over Hult Canadian
patent
application 2,350,047 are shown in greater detail with reference to the
drawings.
In some cases, it is not economic or practical to provide a pump to pressurize
the stuffing box. In these cases, a pressure intensification cylinder assembly
can be
added in conjunction with the stuffing box so that a pressure fluid is made
available at
a pressure above the wellhead pressure.
In some cases, hydraulic pressure is readily available to provide for stuffing
box
pressurization. However, a standpipe system requires a large main shaft and
large
bearings, which may be too expensive for some applications. In these cases, a
bottom-mounted stuffing box with a pressurization system may be an economic
solution. The stuffing box may be integral with the drive head and mounted on
the
bottom of the drive head by flanges, for example. The stuffing box may also be
a
stand-alone stuffing box mounted in a wellhead frame with the drive head
mounted
above the stuffing box on a wellhead frame.
In another aspect of the present invention, a stuffing box can be constructed
with a non-rotating tubular shaft bearingly supporting a rotating housing. The
bearings
may be lubricated with the pressurization fluid as it travels into the lower
side of the
primary rotary seal. This configuration is simpler to construct than a double
wall
-8-
CA 02436924 2003-08-11
standpipe but it uses more length and does not align the standpipe and the
housing as
well as the double wall standpipe configuration. This is because the housing
is
cantilevered from the bearings.
Brief Description of the Drawings
Aspects of the present invention demonstrating the concepts of the present
invention are illustrated, by way of example in the enclosed Figures:, in
which:.
Figure 1 is a cross sectional view of the prior art stuffing box with floating
standpipe and labyrinth seal shown as Figure 6 in Hult Canadian patent
application
2,350,047.
Figure 2 is a cross sectional view of the prior art stuffing box with floating
standpipe but no pressurization system, shown as Figure 8 in Hult Canadian
patent
application 2,350,047.
Figure 3 is a cross sectional view of the prior art stuffing box pressurized
from
the hydraulic system, shown as Figure 9 in Hult Canadian patent application
2,350,047.
Figure 4 is a cross sectional view of the preferred embodiment of a stuffing
box
including a floating single wall standpipe but without a pressurization
system.
Figure 5 is a cross sectional view of a preferred embodiment of a stuffing box
including a floating double wall standpipe and a pressurization system.
Figure 6 is a preferred embodiment of a stand-alone stuffing box mounted in a
wellhead frame, said stuffing box including a floating double wall standpipe
and a
pressurization system.
-9-
CA 02436924 2003-08-11
Figure 7 is a preferred embodiment of a stand-alone stuffing box including a
floating double wall standpipe and pressurization, said stuffing box mounted
in a
wellhead frame. Said pressurization source is a pressure-intensifying cylinder
built
below the stuffing box, surrounding the polished rod.
Figure 8 is a preferred embodiment of a stand-alone stuffing box mounted in a
wellhead frame using a floating single wall standpipe without a pressurization
system.
Figure 9 is a preferred embodiment of a stand alone stuffing box constructed
with a non-rotating tubular shaft bearingly supporting a rotating housing.
Figure 10 is a preferred embodiment of a drive head with an integral stuffing
box mounted on the bottom of the drive head with a pressurization system.
Figure 11 is a stand-alone stuffing box similar to and using the same
principles
as the integral stuffing box shown in Figure 10.
Description of the Drawings and of Preferred Embodiments
Throughout the descriptions, components that have the same function have the
same number. For example, the function of static seals 126 are described in
the
description of Figure 4 so they are not described again in subsequent Figures,
such as
Figure 8. Since the number 126 is the same in both Figures, the reader may
assume
that the function is the same in this and all other Figures where the same
number
appears.
Figure 1 is a cross sectional view of the prior art stuffing box with floating
standpipe and labyrinth seal shown as Figure 6 in Hult Canadian patent
application
2,350,047. Identification numbers in Figure 1 correspond to Figure 6 of the
patent
application.
-10-
CA 02436924 2003-08-11
Figure 2 is a cross sectional view of the prior art stuffing box with floating
standpipe but no pressurization system, shown as Figure 8 in Hult Canadian
patent
application 2,350,047. Identification numbers in Figure 2 correspond to Figure
8 of the
patent application.
Figure 3 is a cross sectional view of the prior art stuffing box pressurized
from
the hydraulic system, shown as Figure 9 in Hult Canadian patent application
2,350,047. Identification numbers in Figure 3 correspond to Figure 9 of the
patent
application.
Figure 4 is a cross sectional view of the preferred embodiment of a stuffing
box
with a floating single wall standpipe but without a pressurization system. It
is an
improvement compared to Figure 2 since braided packings or high pressure lip
seals
can be used instead of the low pressure elastomeric lip seals shown in Figure
2.
Braided packing materials and high pressure lip seals made from reinforced
Teflon are
self-lubricating whereas elastomeric lip seals are not and as a result they
would wear
out. Additionally, a high pressure lip seal can be fitted above the packings
with
benefits described below.
The preferred embodiment shown in Figure 4 will be used as a reference to
describe in detail the essential elements of a non-pressurized stuffing box
using a
standpipe. Whether the stuffing box is separate from (stand-alone like Figure
6 and
Figure 7) or is integrated into the drive head, the essential elements are
related.
Although Figure 4 illustrates an integral stuffing box, a stand alone stuffing
box can be
constructed with the same elements. A housing 52, often preferred (because of
machining and assembly considerations) with separable upper bearing cap 84,
and
separable lower bearing cap 86, supports a rotating shaft 80. Separable
bearing
caps, if any, are considered part of the housing. A non-rotatable standpipe 92
is
mounted concentrically within the shaft and is detachably secured to the
housing. The
polished rod 26 is received concentrically through the standpipe. Annular
passage
114 between the polished rod and the standpipe contains wellhead pressure.
-11-
CA 02436924 2003-08-11
Annular passage 94 between the standpipe and the shaft can be fitted with
rotary seals. The top of the shaft has a removable drive cap 122 that is
drivingly
connected to the polished rod 26 by a drive clamp 124. Below the drive cap are
static
seals 126 to prevent the escape of well fluids around the polished rod.
Preferably the
static seals are supported in a static seal carrier 110 which is sealed to the
shaft by
seals 236. Seals 236 are preferably O-rings or similar common seals. The
static seal
assembly is hereby defined as the static seals, the static seal carrier and
the seals
236. The drive cap, drive clamp, polished rod, shaft and static seal assembly,
rotate
together around the stationary standpipe. The static seals are referred to as
`static'
because there is no relative rotary motion between the static seals and the
polished
rod and the static seal carrier. The only relative motion in the stuffing box
is the rotary
seals rotating against the standpipe. The standpipe preferably has a hardened
surface to reduce wear of the standpipe and the rotary seals.
By removing the drive clamp, drive cap and static seal assembly, the rotary
seals can be serviced from the top of the drive head or from the top of the
stuffing box.
Spring 118 serves to preload the primary seals 116 which are preferably
braided
packings against the lantern ring 239. Once the spring is removed, the lip
seal
assembly comprised of lip seal 305, lip seal carrier 302, lip seal retainer
303 and 0-
ring seals 304 sealing the lip seal carrier to the shaft can be removed.
Preferably the
lip seal carrier has one or more tapped holes to facilitate removal.
The primary rotary seal in the present embodiment is comprised of a lip seal
assembly acting first against well fluids and a set of packings acting once
the lip seal
has failed. The use of a lip seal in conjunction with packings provides
substantial
improvements in stuffing box life. Since lip seals have very little leakage
and do a
good job of excluding contaminants in the well fluid, the lip seal protects
the packing
from any wear until the lip seal fails. The packing stays like new. Once the
lip seal
fails, the packings take over the sealing role. Essentially the stuffing box
has two
seals in series so the stuffing box life is equal to the lip seal life plus
the packing life.
-12-
CA 02436924 2003-08-11
Two lip seals have been used in series in Grenke Canadian patent 2,095,937 but
the
use of packings provides a substantial advantage. When a lip seal fails,
leakage rates
are very high and environmental damage can be severe. A packing starts to leak
slowly and operators have a chance to repair the stuffing box before
substantial
leakage can occur. Use of two lip seals per Grenke provides longer' stuffing
box life
and a resealable inspection port between the two lip seals can indicate when
the first
lip seal has failed. However, if maintenance checks are not done, both lip
seals can
fail, resulting in high leakage rates of well fluids and potential
environmental damage.
Use of packings prevents this.
Lip seals require accurate alignment between the rotating components. Since
the standpipe self aligns to the rotary seals, the lip seal configuration in
the present
invention has substantial life advantages over the configuration used in
Grenke
Canadian patent 2,095,937. The Grenke configuration has a shaft extension that
is
cantilevered from the bearings supporting the shaft. Any misalignment at the
bearings
is multiplied at the rotary seals, unlike the present invention wherein the
shaft is
supported in bearings spanning the stuffing box.
Below the packings 116 is an escape passage for well fluids preferably
comprised of a lantern ring 239 communicating with holes 238 though the shaft.
The
lantern ring preferably has an upper and lower inner diameter to provide a
running
clearance to the standpipe. The lantern ring preferably has an upper and lower
outer
diameter to allow a sliding fit to the inside diameter of the shaft. The inner
diameter
and the outer diameter has a radially relieved section adjacent to radial
holes 242 to
allow well fluid that has leaked past the packings to escape more readily
through holes
242 and then into holes 238 through the shaft.
Below the lantern ring is the secondary rotary seal 300 which is preferably a
set
of packings or another lip seal assembly as described above and shown in
Figure 4 in
the primary stuffing box seal location. Spacer ring 301 has a running
clearance
against the standpipe and serves to prevent the packing from extrusion into
annular
-13-
CA 02436924 2003-08-11
area 94. When a lip seal assembly is used as the secondary rotary seal, the
lip seal
carrier can be integrated with the lantern ring to reduce the number of parts
and the
spacer ring is not required.
Figure 5 is a cross sectional view of a preferred embodiment of a stuffing box
using a floating double wall standpipe pressurization system. The need for a
labyrinth
seal acting as the pressurization seal as shown in Figures 1 and 3 has been
eliminated by use of a double wall standpipe 306 to convey pressurization
fluid above
a rotary seal, preferably a set of braided packings or a lip seal or
combinations thereof,
said rotary seal acting as the pressurization seal. Unlike the previous
labyrinth seal
shown in Figure 1, the pressurization seal in this embodiment can be serviced
in the
field without removing the drive head from the well. Also in this embodiment,
the
standpipe can be removed for inspection and replacement without removing the
drive
head from the well.
In the Figure 5 embodiment, the pressurization fluid is conveyed by a
pressurization means such as a pump 72.
The preferred embodiment shown in Figure 5 will be used as a reference to
describe in detail the essential elements of a pressurized stuffing box using
a double
wall standpipe. Whether the stuffing box is separate from (stand-alone like
Figure 6
and Figure 7) or is integrated into the drive head as shown in this
embodiment, the
essential elements are related. Although Figure 5 illustrates an integral
stuffing box, a
stand-alone stuffing box such as Figure 6 can be constructed with the same
elements.
A housing 52, often preferred (because of machining and assembly
considerations)
with separable upper bearing cap 84, and separable lower bearing cap 86,
supports a
rotating shaft 80. Separable bearing caps, if any, are considered part of the
housing
and will be henceforth referred to as such. A non-rotatable standpipe 306 is
mounted
concentrically within the shaft and is detachably secured to the housing. The
polished
rod 26 is received concentrically through the standpipe. Annular passage 114
between the polished rod and the standpipe contains wellhead pressure.
-14-
CA 02436924 2003-08-11
Annular passage 94 between the standpipe and the shaft can be fitted with
rotary seals. The top of the shaft has a removable drive cap 122 that is
drivingly
connected to the polished rod 26 by a drive clamp 124. The connection between
the
drive cap and the shaft can transmit torque and support axial loads. Below the
drive
cap are static seals 126 to prevent the escape of well fluids around the
polished rod.
Preferably the static seals are supported in a static seal carrier 110 which
is sealed to
the shaft by seals 236. Seals 236 are preferably O-rings or similar common
seals.
The static seal assembly is hereby defined as the static seals, the static
seal carrier
and the seals 236. The drive cap, drive clamp, polished rod, shaft and static
seal
assembly, rotate together around the stationary standpipe. The static seals
are
referred to as `static' because there is no relative rotary motion between the
static
seals and the polished rod and the static seal carrier. The only relative
motion in the
stuffing box is the rotary seals rotating against the standpipe. The standpipe
preferably has a hardened surface to reduce wear of the standpipe and the
rotary
seals.
By removing the drive clamp, drive cap and static seal assembly, the rotary
seals can be serviced from the top of the drive head or from the top of the
stuffing box
in the case of a stand-alone stuffing box, without removal from the well.
The primary rotary seals are preferably packings 116 or a combination of
packings and lip seals as shown in Figure 4. Below the packing 116 is a
packing
pusher ring 308 which has a running clearance against the standpipe and serves
to
prevent the packing from extrusion into annular area 94. Preload spring 118
acts with
the pressurization fluid to push the packing toward the static seal carrier
110.
Below the spring is the pressurization rotary seal 307 which is preferably a
set
of packings or a lip seal assembly as described above and shown in Figure 4 in
the
primary seal location. Spacer ring 308 above the packing 307 and spacer ring
301
below packing 307 have a running clearance against the standpipe and serve to
-15-
CA 02436924 2003-08-11
prevent the packing from extrusion into annular area 94. The spacer rings are
not
required when a lip seal assembly serves as the pressurization seal.
The standpipe in this embodiment is called double walled because that is the
preferred method of its construction. Other methods of construction would be
possible
as long as the standpipe functions to communicate pressure from a pressure
supply to
the stuffing box between the pressurization rotary seal and the primary rotary
seal as
described herein. Functionally, the double walled standpipe has internal
passages to
communicate pressure from the pressurization system to the annular area 94
between
the primary rotary seal and the pressurization seal. A pressure connection to
a
passage in the housing is made where the standpipe is secured to the housing.
Generally the inner wall is sealed to the housing and the outer wall is sealed
to the
housing and fluid is conveyed from the housing between these two seals, shown
as
items 354 and 355. Fluid is then conveyed in the annulus 321 between the outer
and
inner wall of the standpipe and then is conveyed radially through hopes or
passages
322 through the outer wall into annular passage 94 between the primary seal
and
pressurization seal.
By use of a double walled standpipe, both the pressurization seal and the
primary seal can be replaced in the field without removing the drive head or
stuffing
box from the well. This is not possible with the labyrinth located in the
position of
Figure 1.
Abrasive particles in the well fluid cause wear of the standpipe and it must
be
periodically replaced. Another aspect of the present embodiment of the
invention is
that the standpipe can be inspected and replaced without removing the stuffing
box or
drive head from the well by releasing retaining fastener 309 which is
preferably a
special bolt that fits radially into a retention hole or other suitable shape
310 in the
standpipe. When the retaining fastener is in place the standpipe is prevented
from
rotation or axial movement. The retaining fastener is fitted with clearance
into the
-16-
CA 02436924 2003-08-11
retention hole to permit the standpipe to tilt to better align the standpipe
to the rotary
seals carried by the shaft.
The principle of configuring the standpipe securing means so the standpipe can
be inspected or replaced can also be applied to the single wall standpipe
shown in
Figure 4. In this case the standpipe requires only a single seal and a
retention hole so
it can be radially secured as described herein. Figure 8 illustrates the
principle.
Figure 6 is a preferred embodiment of a stand-alone stuffing box mounted in a
wellhead frame using a floating double wall standpipe and pressurization
system. The
drive head in this and all stand alone stuffing boxes is mounted on the top of
the
wellhead frame.
The essential elements of this stand-alone stuffing box are the same as a
stuffing box integrated into the drive head in Figure 5. The description of
Figure 5
applies to this stuffing box as well.
The principle whether integrated into a drive head or in a stand-alone
stuffing
box is an upper primary rotary seal and a lower rotary pressurization seal
located in
the annulus between the standpipe and the shaft, with pressurization means
connected via inlet passage 316 through passages in the standpipe
communicating
with the annular area between the upper and lower seals, said seals being
field
serviceable by removal and replacement from the top of the stuffing box or
drive head.
In the preferred embodiment, the upper and lower rotary seals are preferably
braided
packings separated by a preload spring or a lantern ring because of the ease
of
service and durability of this type of seal. In some cases, the pressurization
seal is
preferably a high pressure lip seal because these seals have lower leakage
rates than
braided packings and they take less axial length. In the preferred embodiment,
the
stuffing box would be pressurized off the hydraulic system that is powering
the drive
head. The pressure from the hydraulic system is preferably reduced down to 50
to
500 psi above the wellhead pressure by the built in pressure-reducing valve
315. A
-17-
CA 02436924 2003-08-11
check valve 393 is preferably used with pressurized stuffing boxes since it
locks fluid
into the annular area between the primary and pressurization seals and
prevents
shifting of these seals when well servicing may cause high wellhead pressure.
Pressurization fluid that escapes past the pressurization seal is preferably
returned to the pressurization source though fluid passage 317.
Housing 52, non-rotatable standpipe 306, polished rod 26, annular passage
114, annular passage 94, static seals 126, static seal carrier 110, seals 236,
static seal
assembly, primary rotary stuffing box seals 116, packing pusher ring 308,
preload
spring 118, pressurization rotary stuffing box seal 307 and spacer ring 308
function as
described in the description of Figure 5.
When the stuffing box is integrated into the drive head, the polished rod
clamp
supports the polished rod load and transmits torque from the drive head to the
polished rod. When the stuffing box is a stand-alone version, the polished rod
is still
supported and driven by the drive head. However, for the stand-alone version,
the
stuffing box is driven by the polished rod. Very little torque is required to
drive the
stuffing box so the drive clamp and its connection to the drive cap do not
need to be as
robust. The bearings 312 and 313 are not large enough to support the axial
load of
the polished rod so it is important that the rod clamp 124 does not rest
against the
drive cap 122 and apply axial load. Axial clearance space 323 should be
visually
apparent so an operator can be sure axial load is not being applied to the
stuffing box
bearings. The stuffing box functions the same in both cases.
Removable drive cap 122 is preferably secured to shaft 80 by fasteners 318.
Preferably the fastener is an Allen head bolt that can protrude above the
drive cap and
be driven by corresponding recesses in drive clamp 124. Alternately, the drive
cap
and static seal carrier might be combined and the main shaft could be
internally
threaded to connect the combined static seal carrier/drive cap to the shaft.
Other
methods of connecting the drive cap to the shaft and transmitting torque from
the drive
-18-
CA 02436924 2003-08-11
clamp to the drive cap can be used. Determination of which connection is
preferable
depends on cost and space considerations.
In the preferred embodiment, spacer ring 301 has been eliminated but rather
the shaft is made with a close running fit at location 320.
The passage 321 between the inner and outer walls of the standpipe and the
passage 322 through the outer wall leading to the area between the seals are
more
readily apparent in Figure 6 than in Figure 5 but the passages are present in
both
embodiments and function the same in both.
Figure 7 is a preferred embodiment of a stand-alone stuffing box mounted in a
wellhead frame using a floating double wall standpipe similar to Figure 6. The
stuffing
box functions identically to Figure 6, only the source of pressurization is
different. In
this embodiment, the pressurization source is a pressure-intensifying cylinder
assembly located below the stuffing box, surrounding the polished rod. Grease
or oil
under pressure is pumped through valve 338 into the upper chamber 336 to push
the
piston 325 down. Wellhead pressure in annular passagel 14 pushes on the bottom
of
the piston, urging the piston upward. Since the piston area on the wellhead
side is
larger than on the stuffing box side, oil or grease feeds into the stuffing
box through
passage 341 at higher pressure than the wellhead pressure. By mounting the
cylinder
assembly between the stuffing box and the wellhead, heat is conducted into the
cylinder to prevent the cylinder from freezing. There are no separate fluid
lines to
freeze off in cold weather or be damaged during well servicing. It will be
appreciated
that this pressurization system can be used whether the stuffing box is a
stand-alone
version or is built into the drive head. This pressurization system could be
used with
any stuffing box that can employ a pressurization system.
Pressurization fluid that escapes past the pressurization seal is preferably
returned to the pressurization source though fluid passage 395.
-19-
CA 02436924 2003-08-11
Components of the pressure intensification cylinder are a piston 325 fitting
into
cylindrical bore 328 of intensifier housing 326. The intensifier housing has a
smaller
diameter at bore 327 than at 328. The piston is shown at the bottom of its
stroke.
Seal 331 located between the inside of the piston and extension tube 324 acts
against
well pressure. Well pressure also acts against seals 330 between the piston
and bore
328 of the intensifier housing. Fluid contained in cavity 336 acts on the
small side of
the piston and is therefore at a higher pressure than the well fluid. Seal 329
between
bore 327 and the piston and seal 398 between the extension tube and the inner
diameter of the piston are acted on by the pressurization fluid.
Extension tube 324 may be part of housing 326, but for ease of manufacturing
it
may be sealed to and secured to the housing. Figure 7 illustrates an O-ring
seal 339
with bolts 340 securing the tube to the housing but many other methods are
possible.
Passage 337 is a breather hole to allow air to escape or flow into the area
between the
external seals on the piston. O-ring seals 354 and 355 have the same function
as with
all the double wall standpipe embodiments. They act to seal the standpipe to
the
housing in two places with pressurization fluid flowing into the passage 321
between
the two seals.
For ease of manufacturing, Figure 7 illustrates a step in the cylinder housing
bore but a piston having a larger area on the bottom side than the top side
can also be
achieved by a stepped extension tube and a cylinder housing with a straight
bore.
Figure 8 is a preferred embodiment of a stand-alone stuffing box mounted in a
wellhead frame using a floating single wall standpipe with a pressurization
system.
Space is often a constraint when retrofitting stuffing boxes to existing
equipment. In
general terms, the sealing system is equivalent to Figure 4, except the
pressurization
seal 347 has been removed from the annulus between the shaft and the standpipe
and is relocated to the annulus between the shaft and the housing. The lantern
ring
has been eliminated since the leakage path past the primary rotary seal is
between the
shaft and the standpipe. Elimination of the lantern ring and relocating of the
secondary seal saves axial length and this is an advantage where space is
-20-
CA 02436924 2003-08-11
constrained. However, the pressurization seal cannot be field serviced without
removal and disassembly of the stuffing box.
Pressurization fluid is introduced through fluid passage 399. Pressurization
fluid pressure may be indicated on pressure gauge 314. Pressurization seal 347
is
preferably a high pressure lip seal. It may be fitted into a groove or
retained by, for
example, a spacer ring 348 and a retaining ring such as a snap ring 349. A
single wall
standpipe 92 is secured to housing 52 by special fastener 309 which prevents
rotary
and axial displacement. The special fastener is sealed to housing 52 to
prevent loss
of well fluids. As with embodiments shown in Figures 4, 5, 6, and 7, the
standpipe can
be fastened to permit inspection and replacement through the top of the
stuffing box
stuffing. Figure 4 is not shown with the upwardly removable standpipe but it
can be
done in the same manner illustrated by Figure 8.
Preferably, the primary seal is comprised of a high pressure lip 305 seal
acting
first against wellhead pressure in series with packings 116 acting once the
lip seal has
failed. The principles have already been described under the description of
Figure 4.
Alternately, only the high pressure lip seal or only packings may be used. The
advantage of packings is that they are split and can thus be replaced without
removing
the drive head from the wellhead frame 311.
In this embodiment, bearings 312 and 313 are preferably greased. Grease
nipple 346 and grease relief 345 are for purposes of adding grease to the
housing.
Alternately, the bearings may be in an oil bath. Housing cap 344 can be
removed for
repair of seals or bearings. Primary seals 305 and 116 can be serviced from
above
the stuffing box as previously described.
Figure 9 is a preferred embodiment of a stand alone stuffing box constructed
with a non-rotating tubular shaft 357 bearingly supporting a rotating housing
356. The
bearings 358 and 359 can be lubricated with the pressurization fluid as it
travels
toward the lower side of the primary seal 116 along fluid passages 368 and
369. This
-21-
.................
CA 02436924 2003-08-11
configuration is simpler to construct than a double wall standpipe but it uses
more
length and does not align the standpipe and the body as well as the double
wall
standpipe configuration because the primary seal and pressurization seal are
outside
the bearing supports and self alignment is not possible. The primary rotary
seal 116 is
field serviceable without removing the stuffing box from the well but the
pressurization
seal 360 is not. It may be preferable to use a high pressure lip seal as the
pressurization seal to save axial space. Pressurization fluid that escapes
past the
pressurization seal is preferably returned to the pressurization source though
fluid
passage 367. Collection of leaked pressurization fluid is provided for by oil
seal 361
which is preferably protected by flinger seal 362.
Figure 10 is a preferred embodiment of a drive head with an integral stuffing
box mounted on the bottom of the drive head with a pressurization system. In
some
cases, hydraulic pressure is readily available to provide for stuffing box
pressurization.
However, the standpipe system requires a large shaft and large bearings, which
may
be too expensive for some applications. In these cases, a bottom-mounted
stuffing
box with a pressurization system may be an economic solution. This can be done
with
the stuffing box integral with the drive head or as a stand-alone stuffing box
mounted
in a wellhead frame as shown in Figure 11. In this preferred embodiment shown
in
Figures 10 and 11, there are a pressurization seal and a primary seal
preferably
comprising two sets of packings separated by a packing preload spring that
acts as a
lantern ring. The packings run on a hard sleeve that is supported on an
extension 383
of the main shaft 80 of the drive head. The main shaft is supported by
bearings 379,
380 and the stuffing box is fitted to the drive head with a pilot diameter 400
to align the
rotating shaft with the rotary stuffing box seals. Although alignment is not
as good as
with a floating standpipe, this is a cost effective solution, suitable in
conditions where
stuffing box wear is not severe. In this embodiment the primary rotary seal
384 is
located at the bottom of the stuffing box. The upper seal 385 is the
pressurization
seal. Since the pressurization seal is sealing against lubricant, wear of the
pressurization seal and shaft extension 383 is generally not severe. It may be
-22-
CA 02436924 2003-08-11
preferable to use one or more lip seals as the pressurization seal rather than
packings
because they need less space and have no leakage.
Lubricant leakage passing through the pressurization seal should not be
allowed to enter the housing 52 through the lower shaft seal 387. For this
reason a
spacer ring 386 is placed above the pressurization seal 385 to allow
pressurization
fluid to escape through passage 382. Pressurization fluid enters the stuffing
box
through passage 381 and pushes against both sets of packings together with
preload
spring 118. Packing pusher 372 loads the pressurization packing 385 while
spacer
ring 389 pushes against primary packing 384. Spacer ring 388 or an equivalent
shape
in stuffing box housing 401 prevents packing extrusion.
Figure 11 is a stand-alone stuffing box similar to and using the same
principles
as the integral stuffing box shown in Figure 10 except in this case the
stuffing box is
driven by the polished rod.
-23-
