Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02520758 2005-09-16
FIELD OF THE INVENTION
This invention relates to downhole progressive cavity pumping arrangements and
more
particularly to the polished rod guide assemblies used in the driveheads of
downhole
progressive cavity pumps. The polished rod guide assembly herein described
enables the
CA 02520758 2005-09-16
rotating shaft of the polished rod to be effectively stabilized and aligned
during operation
whilst preventing heat build up and seal degradation.
BACKGROUND OF THE INVENTION
Downhole progressive cavity pumps are used for the conveying of different
types of
fluids, but are especially well suited for the pumping of very viscous or
thick liquids such
as crude oil. A downhole progressive cavity pump is operated by a drive
string, generally
consisting of a polished rod and/or drive string that extends down the well
bore. The
drive string rotates in the stationary production tubing and is suspended from
and rotated
by a drivehead assembly. The drivehead assembly is generally mounted to the
top of a
wellhead, which is attached to the top end of the production tubing. A
polished rod is
attached to the upper end of the drive string and extends through the
drivehead to the
drive string. The pump includes a stator connected to the bottom end of the
production
tubing and a rotor attached to the bottom end of the drive string. Upon
actuation of the
pump by rotation of the drive string, the pumped liquid is forced to the
surface through
the annular space provided between the drive string and the production tubing.
In conventional downhole progressive cavity pump driveheads, a stufFng box is
used to
seal the annular space between the tubing and the polished rod as well as to
align the
polished rod in the well bore between the driven member and the driving
member. The
stuffing box is generally mounted in a bottom end of the drivehead and is used
as both a
guide and a sealing component for the rotating polished rod. The proposed
invention
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eliminates the conventional stuffing box assembly and replaces it with a
polished rod
guide assembly. The polished rod guide assembly herein described is able to
effectively
maintain the alignment between the driving and driven members, eliminating the
rod
wobble associated with such pumping systems. It is a design that does not
generate
excess heat and is therefore able to also provide for a simple and effective
sealing
mechanism.
SUNINIARY OF THE INVENTION
The use of a polished rod and rod string for pumping production wells is well
known in
the prior art. As the polished rod is rotated by a drive motor at the well-
head, the shaft of
the pump drive is rotated in concert with the downhole pump, such a system
must be
provided with an alignment and seal arrangement to ensure that fluids from the
well do
not leak or escape at the well-head.
In the past, various rotary seals have been incorporated into production wells
to prevent
both static and dynamic leakage. In addition to basic rotation seals, advanced
sealing
systems have also been developed which have incorporated additional
functionality
within the seals, however they all incorporate and require various and/or
numerous
quantities and types of packing seals as well as secondary guides and the like
to stabilize
and align the polished rod in the production tubing, all of which have proven
to be non
effective in the long term operation of a downhole pump.
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CA 02520758 2005-09-16
For example prior art such as U.S. patent application 6,739,390 and 09/433,687
describe
a type of gimbal seal and remote guide arrangement for maintaining alignment
and a seal
on the polished rod. The long-term effectiveness of this type of design
remains unproven.
Accordingly, there continues to be a need for way to accurately align and
dynamically
seal a rotating polished rod which will also be effective in providing static
sealing when
the pump is not operating and/or the well is being serviced
Therefore the present invention provides for a rotating polished rod guide
shaft that is
located in a bearing cap that is threadedly connected to the top of the well
pipe, so that
the bearing cap ideally positions and maintains the polished rod in alignment
with the
drive assembly and the driven assembly. Due to the inherent twisting of the
polished rod
when it is being driven it is critical to provide the required support to
prevent
displacement of the polished rod from the most efficient position, that being
in the center
line of the driving member. By employing an assembly with a single large
capacity or
dual or multiple bearing set up, the required alignment is easily kept
consistent without
necessitating the need for an ancillary or secondary bushing or secondary
stationary guide
assembly or redundant sealing or packing arrangements. Such secondary static
guide
assemblies tend to generate heat, which destroys the seals and inevitably the
guides also
wear out. By utilizing an independent rotating polished rod guide shaft
assembly for
effective alignment and sealing, seal degradation is reduced or eliminated and
the need
for a secondary alignment means is also eliminated. By maintaining proper
alignment no
heat is generated from the rotating assembly, prolonging seal life, preventing
leaks and
extending bearing life.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows the upper guide shaft assembly 8, with a dual bearing assembly
12,
bearing spacer 13, polished rod guide cinch cap 15, lower guide shaft assembly
10 with
guide shaft seal assembly 14, shaft to cap seal 17 and lower shaft external
seal 16 and
upper shaft external seal 18.
Figure 2 shows the mounting cap 20 with mounting threads 21, cap to pipe seal
19 and
guide shaft bearing and seal locating surface 23.
Figure 3 shows the upper guide shaft assembly 8 with polished rod cinch cap
locating
threads 25, wrench flat 31, bearing and spacer locating surface 27, upper
external guide
shaft sealing lip 18, upper to lower guide shaft attaching threads 29,
internal polished rod
to guide shaft seal 24, guide shaft to seal and seal to cap locating surface
22.
Figure 4 shows the lower guide shaft assembly 10 with lower to upper attaching
threads
29, lower external guide shaft sealing lip 16 and internal polished rod to
guide shaft seal
24.
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Figure 5 shows guide shaft seal assembly 14, seal assembly to cap seal 17,
lower guide
shaft external seal to guide shaft sealing lip 28, upper guide shaft external
seal to guide
shaft sealing lip 30 and internal guide shaft seals 32.
Figure 6 shows the assembled polished rod guide shaft assembly 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of a polished rod guide shaft in accordance with the
invention
as shown in FIG. 1 is intended for use with a top drive progressive cavity
pump
drivehead, or another suitable rotary pump known in the art.
The two piece guide shaft in the figure 1 assembly includes an upper shaft
section 8 for
locating the bearing assembly 12 and seal assembly 14 and for creating upper
sealing and
seal assembly mating lip 18. Lower shaft section 10 includes sealing and seal
assembly
mating lip 16 for sealing lower shaft to seal assembly 14 as well as for
locking seal
assembly to both upper shaft and lower shaft when assembled. Seal assembly 14
contains
internal sealing elements 32 for sealing seal element 14 to guide shaft units
8 and 10.
Sealing element 14 contains external sealing element 17 for sealing the
sealing assembly
to the mounting cap.
Upper guide section 10 contains internal polished rod sealing element 24 with
bearing
and seal assembly mounting and locating surface 27. Seal assembly locating and
mating
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lip 18 and seal assembly internal mating and locating surface 22 are located
on top of
threaded upper to lower attachment means 24.
Lower guide section 10 contains internal polished rod to guide sealing element
24,
polished rod guide element 10, seal assembly mating, locating and locking lip
26 below
threaded lower to upper guide attachment means 29.
Mounting cap 20 contains bearing and seal mounting surfaces 23 for mounting
and
locating of bearing assembly 12 and seal assembly 14. Cap is threaded 21 to
mount to top
of wellhead and has cap to wellhead sealing element 19.
Changes and modifications in the specifically described embodiments can be
carried out
without departing from the scope of the invention which is intended to be
limited only by
the scope of the claims.
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