Note: Descriptions are shown in the official language in which they were submitted.
Attorney Docket: Huber-47/P1021
EXTENDED WEAR ROD GUmE AND METHOD
Related Applications
The present appl,'_cation is related to Canadian
Patent File No. 2,119,843, filed March 24, 1994.
Field of the Invention
The present invention relates to a guide for maintaining a rotatable rod
generally aligned within a wellbore of an oil, gas, water, or geothermal well.
More
particularly, this invention relates to an extended wear rod guide for a
rotating sucker
rod commonly used to drive a downhole progressing cavity pump.
Background of the Invention
Those skilled in the hydrocarbon recovery industry understand that pumps at
the lower end of wells are conventionally used to pump oil to the surface via
production tubing positioned within a well tubing. The pump is typically
powered at
the surface, with the power being transmitted through a rod string positioned
within
the production tubing. A rod string conventionally has been reciprocated to
drive the
downhole pump, although a progressing cavity pump driven by a rotating rod has
been used, particularly in wells producing heavy, sand-laden oil or producing
fluids
with high water/oil ratios.
Whether the rod which drives the pump (the sucker rod) reciprocates or
rotates, the rod generally is guided so that it does not rub against the
interior walls
of the production tubing, and thus cause excessive wear on either the sucker
rod, the
sucker rod couplings, or the production tubing. In practice, sucker rods and
production tubing almost never hang perfectly concentric within a well.
Moreover,
few if any wells produce crude oil free of abrasives and water. These
contaminants
increase wear if the sucker rod string contacts the inside of the production
tubing.
Whether the pump driving system utilizes a reciprocating or a rotating rod,
tubing
wear and rod wear accelerate as production rates, hole deviations, water/oil
ratios,
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and sand concentrations increase. While rod guides traditionally have thus
long been
used to generally center the rod within the production tubing, the need for
improved
rod guides increases with the changing variables discussed above.
Rod guides are traditionally spaced along the length of a rod string to
prevent
S the rod string from engaging the tubing string. Various rod guide designs
create a
frictional grip on the rod in order to secure the rod guide in position. Field
installed
rod guides (FIGS) traditionally do not maintain their desired gripping,
engagement
with the rod over a long period of time, particularly when high axial forces
are
encountered by the rod guide and when increasingly more power is transmitted
from
the surface to the downhole pump through the rod. While it is thus desirable
that a
rod guide be installed at the well site or at a location convenient to the
well operator,
FIGS traditionally are not able to achieve reliable engagement with the rod.
Other
versions of FIGS utilize a rubber guide body with a metal C-spring molded
within the
rubber body to supply a supplemental force which increases the frictional grip
of the
guide to the rod, as disclosed in U.S. Patent No. 4,928,472. This latter type
of rod
guide is typically unfinned and has a high pressure drop, and also is
generally
unreliable at securing the guide to the rod. Another type of plastic FIG is
similar in
shape to the rubber rod guide body. The body is machined from UHMW
polyethylene, and does not include a metal C-spring insert. This plastic guide
is
disclosed in U.S. Patent No. 4,858,688.
Rod guides manufactured from plastic have been molded directly onto the rod.
These molded-on rod guides, as disclosed in U.S. Patent No. 4,088,185, thus
have
the advantage of more reliably engaging the rod to maintain the rod generally
concentric within the tubing string. Molded-on rod guides are also relatively
inexpensive to manufacture, although these prior art rod guides have the
disadvantage
of practically requiring that the entire rod be sent from the field to a
molding facility
to remove a worn-out guide and mold on a new guide, after which the rod with
new
guides may then be returned to the field. A rod guide with a diagonal slot
designed
for maintaining a guide on a rod is disclosed in U.S. Patent No. 3,442,558,
while a
similar snap-on guide and scraper is disclosed in U.S. Patent No. 3,282,344. A
field
installable rod guide is disclosed in U.S. Patent No. 4,858,688.
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-3-
U.S. Patent No. 5,191,938 discloses one version of a rod guide including a
cylindrical centralizes body which hinges open during a spreading operation
for
insertion on a mount provided on the rod guide shank. The centralizes body is
returned to its cylindrical shape after installation, and centralizes body is
welded to
S maintain its desired cylindrical form while on the rod. This type of rod
guide has not
proven to result in long life, and the operation of bonding the split body to
its desired
cylindrical form after installation is a drawback to easy field
serviceability. An early
version of a rod guide is disclosed in U.S. Patent No. 3,516,494.
A rotatable rod guide may comprise a rotor which is fixed to the rotating rod,
and a stator which remains generally stationary in the wellbore while engaging
the
tubing to guide the rotor and thus the rod. The rod guide rotor acts to
prevent the
rod guide stator from engaging and thus wearing against the rod itself. Stator
bodies
may be fabricated from UHMW polyethylene or other durable materials, so that
wear
on the stator inner surface is generally not a significant problem. The rod
guide rotor
may be molded on the rod with integral upper and lower stops as disclosed in
U.S.
Patent No. 4,050,514. A significant problem with rotatable rod guides relates
to a
life of the bearing between the outer surface of rotor which is designed for
engagement with the inner surface of the stator or guide body.
Those skilled in the art appreciate that even a relatively insignificant wear
on
a sucker rod may result in a stress point which could cause the rod to break.
Since
rod breakage typically requires significant repair costs and downtime, well
operators
generally are unwilling to allow a stator to directly contact a rotating rod
because of
fear that any rod wear will result in rod breakage. The cost of replacing worn
rod
guides on rotary sucker rods accordingly is a significant factor in the
overall cost of
operating a producing well with a rotating sucker rod.
Improved rotatable rod guides are thus required which will reliably protect
the
rod for extended periods of time. According to the present invention, multiple
rotors
may be securely affixed to a rod at selected positions along the length of
rod, and a
stator then field installed at the well site at a selected rotor position. New
stators may
thus be installed in the field on unused rotors after the originally installed
guide wears
out.
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The disadvantages of the prior art are accordingly overcome by the present
invention, and an improved rod guide suitable for use on a rotating rod string
is
hereinafter disclosed. The rod guide of the present invention is designed for
a
reliable operation over a relatively long period.
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Summar;r of the Invention
The rod guide of the present invention is designed for a use on a rotating rod
string, and more particularly is designed for use on a rod string powering a
progressing cavity pump. A rod guide rotor may include a metal sleeve and
upper
and lower stops affixed to the rod. The rod guide stator preferably has a slot
along
the length thereof and a plurality of radially outward projecting fins. The
slot in the
rod guide stator allows the stator to be spread apart and snapped onto the
rotor, with
the axial position of the stator being limited by the upper and lower stops.
In one
embodiment, the metal sleeve is provided with an axially centered stop ring
which
limits travel of the rod guide stator.
The rotor comprises a metal sleeve which prevents the stator from contacting
the rod and extends the life of the rod guide. Upper and lower plastic stops
may be
injection molded on the rod. A metal snap ring may hold the sleeve on the rod
during the molding process, and also retains the metal sleeve on the rod if a
molded
plastic stop wears away and breaks off while the rod guide is downhole. The
metal
snap ring may be axially recessed slightly with respect to a stop surface on
each
upper and lower stop designed for engagement by the stator. Top and bottom
ends
of the stator may include a plurality of scalloped cut-outs which facilitate
flushing of
the rod guide to keep grit and debris from accumulating within the rod guide
and
thereby interfering with the free rotation of the guided rod within the
stator. The
metal snap rings provide a back-up wear surface for engaging the ends of the
stator
if the plastic stop surface is worn away during use of the rod guide.
The metal rotor sleeve may be formed from one or more pieces, and
preferably covers at least 200° of the 360° circumference of the
rod to adequately
protect the rod from engagement with the stator. End stops may have a
frustoconical
configuration to reduce fluid drag and pressure drop across the rod guide.
Alternatively, the molded stops may be provided with cut-outs so that
circumferentially spaced stop pads are provided for engagement with the ends
of the
stator. Other rotor embodiments secure a metal sleeve to the rod by frictional
engagement, so that both the rotor and the stator may be field installed. The
metal
sleeve may be prevented from engaging the rod by a thin plastic or rubber
layer,
which also desirably increases the friction between the rod and the metal
sleeve. This
_.
-6-
rubber layer also reduces corrosion by galvanic action between the metal rotor
and
the metal rod. The body of the stator may be tapered in the embodiment having
an
axially centered stop ring, so that the center of the stator body has a
diameter greater
than the upper and lower ends of the stator body. A pair of semi-circular ring
members may be clamped around a metal sleeve, and the ends of the two ring
members spot welded together to secure the metal sleeve on the rod. A plastic
or
rubber layer on the inner surface of the metal sleeve shields the rod from.the
welding
process.
It is an object of the present invention to provide an improved rod guide for
protecting an elongate rod of the type commonly used to drive a progressing
cavity
pump. More particularly, the rod guide of the present invention has a
substantially
enhanced life by providing a wear resistant sleeve member to protect the rod
from
being engaged by the stator. The sleeve member exterior surface thus serves as
a
durable bearing surface for engagement with the interior surface of the stator
during
rotation of both the rod and the rotor with respect to the stator.
It is a feature of this invention that the stator may be reliably retained on
the
rod even if a plastic rotor stop breaks off the rod. Another feature of the
invention
is that the metal sleeve may be physically separated from the rod by a
relatively thin
rubber layer. It is another feature of the invention that a plurality of
rotors may be
provided along the length of a rod, so that the user or well operator may snap
a stator
on selected ones of the rotors as new stators are needed.
It is an advantage of the present invention that a metal stop ring may be
utilized to hold the metal sleeve on the rod. Upper and lower plastic stops
may be
molded adjacent each end of the metal sleeve. The metal snap ring may retain
the
sleeve on the rod even if a plastic stop were to break off the rod, and
provides a
back-up hardened wear surface for engaging the pad ends of the stator.
These and further objects, features, and advantages of the present invention
will become apparent from the following detailed description, wherein
reference is
made to the figures in the accompanying drawings.
_7_
Brief Description of the Drawines
Figure 1 is a side view of a rotating rod guide in accordance with the present
invention.
Figure 2 is a cross-sectional view of the rotatable rod guide as shown in Fig.
1.
Figure 3 is a pictorial view of a portion of the metal sleeve generally shown
in Fig. 1, including particularly the groove for receiving the snap ring, and
the
position of the stop surface relative to the snap ring.
Figure 4 is an alternate embodiment of a rod guide, illustrating a cross-
sectional view of the sleeve and one of the stops, with the stator removed for
clarity.
Figure 5 is yet another embodiment of a rod guide, illustrating a cross-
sectional view of the sleeve and one of the stops, with the stator removed for
clarity.
Figure 6 is a side view of another embodiment of a rod guide, partially in
cross-section, with the stator removed for clarity.
Figure 7 is a top view of one-half portion of the stop member as shown in
Fig. 6, illustrating the configuration of the metal retaining ring.
Figure 8 is a cross-sectional view of an upper end member of a rod guide
rotor and a portion of the sleeve as generally shown in Fig. 6, with the rod
removed
for clarity.
Figure 9 is a side view of an upper portion of still another embodiment of a
rotating rod guide.
Figure 10 is a cross-sectional view through the stop member shown in Fig. 9.
Figure 11 is a cross-sectional view of another embodiment of a rotor for a rod
guide.
Figure 12 is a cross-sectional view of the sleeve and one of the stops for the
rotor as shown in Fig. 11.
Figure 13 is a cross-sectional view of another embodiment of a sleeve and one
of the stops for a rotor.
Figure 14 is a cross-sectional view of the rotor as shown in Fig. 13.
Figure 15 is a cross-sectional view of a field-installed rotor according to
the
present invention.
Figure 16 is a cross-sectional view of the rotor as shown in Fig. 15.
- , ~ 1'~ ~ ~,~ ~
-g_
Figure 17 is a cross-sectional view of another embodiment of a rotatable rod
guide according to the present invention.
Figure 18 is a cross-sectional view of the rotor as shown in Fig. 17.
Figure 19 is a cross-sectional view of another embodiment of a rotor.
~~'~352~
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Brief Description of the Preferred Embodiments
Figure 1 depicts a rotating rod guide according to the present invention.
Those skilled in the art will appreciate that the rod guide 10 serves the
purpose of
maintaining the sucker rod 12 substantially centered within tubing 14, which
in turn
is substantially aligned and centered within the casing 18 defining a wellbore
20
extending from the surface to a subterranean formation. An annulus is thus
formed
between the LD. of the casing 18 and the O.D. of a production tubing 14. The
flow
path 16 within the production tubing is conventionally used for passing
contaminated
oil to the surface. For the embodiment depicted in Fig. 1, the rod 12 is
rotated to
drive progressing cavity pump (not shown) at the lower end of the wellbore 20.
The
rod guide 10 prevents the sucker rod 12 and the couplings (not shown) which
interconnect lengths of sucker rods from engaging the inner surface of the
tubing
string 14. The downhole pump, in turn, passes contaminated oil up through the
flow
path 16 in the production tubing 14. Accordingly, the pump must overcome the
pressure loss attributable to the restriction in the flow path 16 caused by
the rod guide
10.
The rod guide 10 comprises a guide body or stator 22 having a generally C-
shaped cross-sectional configuration created by an elongate slot 40 extending
along
the length thereof. The width of elongate slot 40 is thus defined by the
spacing
between the opposing sidewalk 42 and 44 on the stator 22. The slot 40 may be
inclined at a slight angle of approximately 10°, and accordingly the
slot centerline 41
is angled as shown in Fig. 1 with respect to the rod guide centerline 43.
The rod guide 10 also includes a rotor or spool member 25, which comprises
a relatively thin sleeve member 24 and upper and lower end members 26, 28 at
the
opposing ends of the sleeve member 24. Each of the end members 26, 28 has a
frustoconical configuration which reduces the pressure loss across the rod
guide by
providing for streamline flow. Each end member includes planar stop surface
27,
which lies within a plane substantially perpendicular to the central axis 43
of the rod
guide. A gap 66 exists between the upper end of the stator 22 and the stop
surface
27, and a similar gap 68 is shown between the lower end of the guide body and
the
stop surface on the lower end member 28.
~1~~~
- 10-
Figure 2 is a cross-section view through the rod guide 10 shown in Fig. l, and
illustrates the rod guide symmetrically positioned about axis 43. The stator
22
comprises a radially inner body portion 46 having a substantially C-shaped
cross-
sectional configuration, and three ribs, vanes, or fins 48, 50, and 52 equally
spaced
circumferentially about and extending radiaIly outward from the C-shaped
portion 46.
The ribs, fins or vanes 48, 50, and 52 minimize flow resistance around the
guide,
while desirably centralizing the rod 12 within the production tubing 14. A
circle
including the arc segments formed by the outer surface SS of the fins 48, 50,
and 52
preferably has a diameter slightly less than the LD. of the tubing 14.
Alternatively,
the stator as installed on the rotor could have a diameter slightly greater
than the LD.
of the tubing which receives the rod guide. As the rod guide is fitted within
the
tubing, its diameter decreases slightly, thereby maintaining the stator fins
in forced
engagement with the tubing LD. It should be understood that the LD. 57 of the
C-
shaped portion 46 preferably is defined by the cylinder having a diameter
slightly
greater than the O.D. 49 of the sleeve member 24 of the rotor.
The slot 40 preferably has a nominal width (its normal width when the stator
22 is in a relaxed state) which preferably is less than the O.D. 49 of the
sleeve
member 24. The flexibility of the material used for the stator 22 thus allows
the
stator to be snapped on the rotor by simultaneously spreading the width of the
slot 40
and moving the stator 22 radially inward toward axis 43, so that the stator
becomes
positioned on the sleeve member 24 and between the end members 26 and 28 of
the
rotor. The angle between the centerline 41 of the slot 40 and the central axis
43 of
the stator improves the lock-on characteristics of the stator 22 to remain on
the rotor.
The preferred slot angle depends on the length of the stator and the
circumferential
spacing between the fins. If the body 22 is fabricated from less resilient
materials,
such as metal, it would be desirable for the slot to be straight and wide,
thereby
minimizing the amount of flexing required to install the stator.
In one preferred embodiment, the material for the stator 22 is an ultra-high
molecular weight (UHMW) polyethylene material. This material is particularly
preferred for the body of the rod guide according to the present invention,
since the
selected material is highly resistant to abrasion from sand and other
particles
contained in the fluid which is passed by the rod guide. This material has
both good
~1?3~~3
-11-
wear characteristics and a relatively low coefficient in friction when
contacted with
the same or other materials. Because of the UHMW characteristics of the stator
22,
the stator is extruded then machined to its desired form rather than being
injection
molded. It should be understood that the stator could be formed from other
materials. Nylon, Amodel, Hular, PPS, and bronze are examples of other
materials
which may be selected for fabricating the stator 22.
The provision of the slot 40 in the stator renders the rod guide of. the
present
invention essentially field installable. A worn out stator 22 may be easily
snapped
off of the rotor, and a new stator 22 snapped on in a simple and inexpensive
field
operation. In addition to providing this desirable field replaceable
characteristic for
the rod guide body, slot 40 serves another purpose in that the substantial
width of the
slot allows for easy passage of fluid into and out of the annulus formed
between the
LD. 57 of the radially inner body portion 46 of the stator and the O.D. 49 of
the
sleeve member 24 of the rotor. A substantially C-shaped annular gap is thus
formed
by this difference between diameters 57 and 49, and flowing fluid is available
to
continuously "wash" the rod guide when in use. This washing action allows the
stator 22 to freely rotate relative to the rotor, and thus reduces frictional
losses and
abrasion between the inner surface of the stator and the outer surface of the
rotor.
Figure 1 also depicts upper cut-outs 62 and lower cut-outs 63 formed in the
upper and lower ends of the stator 22. These cut-outs further serve to
contribute to
the flow of fluid which desirably washes the connection between the stator 22
and the
rotor. Each of the cut-outs has a substantially semi-circular or scalloped
configuration, and is formed extending circumferentially between the gap which
exists
between the ribs 48, 50, and 52. The inclined portion 54 of each rib extends
from
the inner body portion 46 of the stator 22 to the outer diameter surface 55 of
the
respective rib, and contributes to produce a relatively low pressure loss
across the rod
guide. The three cut-outs 62 as shown in Fig. 1 each occur over a
circumferential
length of from about 80° to about 100°, and preferably over a
circumferential length
of approximately 90°. Each of the three pads 60 formed at each end of
the stator by
the cut-outs 62 may be aligned with a respective rib, and may have a
circumferential
width of only about 30°. Each of the pads 60 thus engage the stop
surface 27 on the
end member 26, and this contact area is sufficient to prevent excessive wear
of the
CA 02173523 1999-OS-21
-12-
pads 60. The substantially longer circumferential length of the scalloped cut-
outs 62 (together
totalling approximately 270° in a preferred embodiment) allow for the
desired passage of fluids
to wash between the body 22 and the rotor 25. As shown in the drawing, the
scalloped cut-out
configuration tapers upward to the contact point formed by the pad at the end
of each rib. To
still further provide for this desired washing effect, the substantially C-
shaped gaps 66 and 65
provide a total axial clearance of from about 1 millimeter (mm) to
approximately 3 mm or
greater between the ends of the stator 22 and the stop surfaces on the end
members of the rotor.
The slot 40, in conjunction with the cut-outs 62, 63, the annulus between the
surface 57 and
49 and the gaps 66 and 65, thus all contribute to maximize the flow of fluids
around and
through the rotating and stationary components, thereby reducing high abrasive
rod guide wear.
Figure 3 depicts an upper portion of the sleeve 24 generally shown in Figs. 1
and 2.
The sleeve 24 may be fabricated from a sheet of hardened steel. The material
thickness of the
sleeve 24 is preferably minimized to desirably maintain a minimum diameter of
the inner body
portion 46 of the stator, although the sleeve 24 must be sufficiently thick to
withstand
anticipated wear as it rotates downhole within the stator and thereby prevents
the stator 22 from
engaging the rotating rod 12. The sleeve 24 may be less than 0.20 inches thick
and preferably
has a minimum thickness of from 0.10 inches to 0.1 S inches. If desired, a
uniform stator with
a fixed internal diameter may be used for each size sucker rod. In this case,
the thickness of
the sleeve may be increased from the thickness stated above (which are for the
largest diameter
rod), so that if the rod diameter decreased, the outer diameter of the sleeve
remained
substantially constant for recxiving the uniform stator. As explained
subsequently, a metal
sleeve may be formed from two C-shaped components. The sleeve 24 includes a
circumferential groove 64 formed in the upper and lower ends of the sleeve to
receive a metal
clip 69 which functions to hold the clip components together while the plastic
end members 26
and 28 are molded on the rod 12.
For the embodiment described above, the sleeve 24 is formed by two identical
components 72 each having a 180° circumference. Accordingly, the
elongate sides of the
sleeve components butt into engagement, as shown in Fig. 4. During manufacture
of the rotor
25, the sleeve components 7:Z are placed on a cleaned rod 12 and the clip 69
is slid over the
CA 02173523 1999-OS-21
-13-
ends of the components 72 and into the groove 64, thereby reliably holding the
components 72
in place while the plastic end members 26 and 28 are molded on the rod. Each
end of the
sleeve 24 may include a chamfer 70 to facilitate installation of the clip 69.
The end members
cover the upper and lower ends of the sleeve 24 as shown and also encapsulate
the clip 69.
S The clip 69 is thus spaced axially opposite the stator 22 with respect to
the plastic stop surface
27 on each end member 26 and 28.
After repeated use of the rod guide; the ends of the stator may wear away a
portion
of the plastic end members, so that the plastic stop surface 27 "moves" closer
to the metal clip
69. The primary wear problem in a rotatable rod guide is between the internal
surface of the
stator and the external surface of the sleeve between the end members 26 and
28. The useful
life of a rod guide is thus significantly increased by providing a metal
sleeve on the rod to
resist wear much better than a plastic material sleeve. A lesser wear problem
is encountered
between the ends of the stator and the end members on the rotor which limit
axial travel of the
stator. Nevertheless, the plastic stop surfaces 27 may wear after repeated
engagement with an
end of the stator and particularly the stop surface 27 on the upper end member
26 (due to the
upward force of the flowing fluid in the tubing 14 acting on the stator). A
further advantage
of the clip 69 is that it provides a hardened metal wear surface 67 for
engaging the ends of the
stator if the plastic stop surface 27 were to wear away to expose the
initially plastic-covered
surface 67. If desired, the metal clip 69 could be initially positioned closer
to plastic wear
surface 27, particularly if very limited axial travel of the stator over the
life of the rod guide
were desired.
It is important that the internal diameter of the sleeve 24 mate with the
outer diameter
of the rod 12. Accordingly, it may be desirable to provide sleeve components
each having a
circumference of less than 180°, so that the sides of the components
are spaced apart and thus
cannot interfere with proper installation of the components on the rod. The
total circumference
of the sleeve components preferably is more than 220°, however, so that
the sleeve 24 has the
desired wear material to prevent the stator 22 from contacting the rod 12.
Figure 4 discloses a rod guide rotor 25A similar to rotor 25 described
above. The two arcuate metal sleeve components 72 again are identical, each
having a
- 14-
circumference of about 175°, thereby forming an elongate gap between
the edges of
the two sleeve components. The inner surface of each sleeve component 72 is
covered with a thin rubber layer 73 to significantly increase the static
friction between
the rod 12 and the metal sleeve components and thereby reduce the likelihood
of the
metal sleeve rotating on the rod. This rubber layer 73 also reduces galvanic
corrosion between the metal sleeve and the rod. Preferably, the elongate gap
between
the edges of the sleeve components may also be filled with rubber, so that two
strips
74 of rubber are formed, each having an outer surface approximating the
diameter of
the sleeve components. The rubber strips 74 as shown in Fig. 4 may be formed
by
providing a layer of rubber covering the elongate edge of each metal sleeve
component 72, within this rubber layer being significantly thicker than the
layer 73
provided on the inner surface of each metal sleeve component. By way of
example,
the layer 73 may be from .006 to .020 inches thick, while the edge layer of
rubber
covering the edge of each metal sleeve component may be from .010 to .080
inches
thick. The edge rubber layers are thus pressed into engagement during
installation
of the metal sleeve components on the rod 12, so that mating edge rubber
layers
effectively form each of the elongate rubber strips 74 to fill the gap between
the edges
of the metal sleeve components. The rubber layers 73 and the edge rubber
layers
forming rubber strips 74 may be coated or otherwise bonded to the metal sleeve
components 72 by conventional processes.
Metal clips may be used to hold the components 72 in place while the end
members are injection molded on the rod. It should be understood that other
holding
members, such as a plastic or rubber O-ring, may be used to hold the sleeve
components in place during the operation of molding the end members on the
rod.
Also, the sleeve components may be glued to the rod prior to the end member
injection molding operation. The glue need not retain the sleeve components in
place
during use of the rod guide, however, since the injection molded end members
serve
that purpose once inst<~lled. The lower stop surface 27 for engagement with
the end
pads 60 of the stator is depicted in Fig. 4. Also the plastic material forming
the end
stops could be injection molded to fill the gap or gaps between the sleeve
components.
-15-
For the embodiment depicted in Fig. 5, a single component metal sleeve 76
having a C-shaped cross-sectional configuration is used to form the rotor 25B.
The
sleeve 76 has a circumference of from about 200° to about 320°,
so that a
comparatively wide gap exists between the sleeve sides. This gap, if unfilled,
may
be useful for channeling fluid between the stator and the rotor as further
washing
action. As shown in Fig. 5, however, this gap is filled with plastic 78 during
the
process of injection molding the end members. The material for the sleeve 76
must
be sufficiently flexible to allow the gap between the sleeve sides to spread
apart while
the sleeve is moved radially onto the rod 12, then must allow the sleeve to
spring
back to its original configuration, as shown in Fig. 5, with substantially the
entirety
of the inner surface of the sleeve in engagement with the outer surface of the
rod.
The sleeve 76 need not require any other components to hold the sleeve in
place
during the molding of the end members. The elongate plastic strip 78 prevents
rotating of the metal sleeve 76 on the rod 12. Although not shown in Fig. 5, a
rubber layer on the inner surface of the metal sleeve 76 may be provided in a
manner
similar to the Fig. 4 embodiment. This rubber layer also prevents the metal
sleeve
from direct contact with the rod, thereby minimizing galvanic corrosion and
the
likelihood of stress points on the rod created by scratches or grooves on the
surface
of the sucker rod. As previously noted, the stator as shown in Figs. 1 and 2
may be
installed on the rotor for any of the embodiments discussed above.
Figure 6 illustrates another embodiment of a rotor 110 for receiving a stator
as previously described. The rotor 110 includes a metal sleeve 112 having
identical
sleeve components 114 with sides separated by a slight gap similar to the Fig.
4
embodiment. Each sleeve component 114 includes a metal outer layer 116 and a
thin
rubber inner layer 118 bonded to the inner surface of the metal sleeve
component.
The inner layer 118 substantially increases the static friction between the
rod 12 and
the sleeve components in a manner similar to the Fig. 4 embodiment. Elongate
rubber strips 120 between the edges of sleeve components 114 are similar to
the strips
74 previously discussed. Two sleeve components are positioned on a cleaned rod
during installation, then a pair of identical stop halves 90 as shown in Fig.
7 snapped
together to form each of the end members 92 and 93 which secure the upper and
lower ends of the sleeve components on the rod and effectively replace the
injection
- 16-
molded end members previously discussed. The plastic body 94 of each end
member
may have a curved outer surface 96 as shown in Fig. 6, or may have a
frustoconical
surface as shown in Fig. 3. The metal clip or retaining ring 98 fits within a
groove
provided in the metal sleeve components, as previously discussed.
Figure 7 depicts one of the components 90 which cooperate with a similar
component to form an upper or lower stop member 92 or 93. Each component 90
includes a retaining ring 98 having a generally C-shaped configuration, and a
plastic
body 91 which may be injection or compression molded about the retaining ring.
The
plastic body 91 also has a C-shaped configuration, so that end surface 80 of
one body
91 is pressed firmly against end surface 82 of the mating body 91 to form one
field
installed stop.
The end 100 of the clip 98 extends outward from plastic body surface 80,
while the opposing end 104 of the clip is housed within the plastic body. Each
clip
end has corresponding dog member 102 and 106 for securely interconnecting a
pair
of clip end members and thus the plastic bodies 91 during installation on the
rod 12.
A suitable metal retaining ring according to the present invention is a
interlocking
external Series 5167 ring manufactured by Waldes Truarc, Inc.
Referring to Fig. 8, the upper end member 92 is shown with an internal
cylindrical surface 84 for fixed engagement with a rod 12. The metal sleeve
components which act as a preferred wear surface for engaging the stator
include an
upper groove and a lower groove for receiving a respective retaining ring. The
interconnecting force of the mating retaining rings may be sufficient to fix
the stop
members and thus the rotor to the metal rod. If desired, however, a rubber
layer
may be provided on the inside of the cylindrical surface 84 of the stop member
to
increase static friction between the stop member and the rod, and thereby
serve a
purpose similar to the rubber layer 73 provided on the inside of the sleeve
component
72 as shown in Fig. 4. This rubber layer 118 would thus be highly compressed
once
the pair of components 90 were snapped together in place on the rod.
Referring again to Fig. 6, it should be understood that the sleeve components
may be placed on a cleaned rod 12, and two components 90 then pressed together
until the mating dogs 102 and 106 lock one of the stop members onto the rod,
with
the retaining ring 98 fitting within the corresponding groove provided in the
metal
- 17-
sleeve components. The other stop member may be similarly snapped together at
the
other end of the metal sleeve components in a relatively simple field
installation. If
the plastic member end surface 108 of the field installed stop as shown in
Fig. 8 were
to wear sufficiently during use of the rod guide, the metal retaining ring 98
would act
as a backup wear surface for engaging the end of the stator. After
installation of the
rotor as described above, the stator may be easily fitted on the rotor using a
conventional tool to spread apart the slot to snap the stator over the sleeve
portion of
the rotor and between the end members.
The embodiment as shown in Figs. 6-8 has a substantial advantage in that the
rotor may be field installed since the end members are not injection molded on
a rod.
Those skilled in the art will appreciate that these embodiments are not
preferred for
many applications, however, because of an increased likelihood that the rotor
will
rotate relative to the rod when the guide is in use. To reduce the likelihood
of
inadvertent rotation of the field installed rotors on the rod, a glue or other
adhesive
may be used to affix the sleeve components and/or the end member to the rod.
Also,
bolts or similar connecting devices may be used to draw the sides of the end
members
closer together, thereby effectively clamping the end members on the rod. Such
clamping devices add considerably to the cost and complexity of a rod guide,
however, and accordingly are not preferred.
Figures 9 and 10 disclose another embodiment of a rotatable rod guide 130.
The stator 132 may be similar to the stator 22 previously discussed, except
that the
ends of the stator need not be cut-out or scalloped to form pads for engaging
stop
surfaces on the end members. Instead, both the upper and lower end members 134
are provided with cut-outs or scallops 136 which extend radially to expose the
end
portion 147 of the sleeve 146 (which may extend axially beyond the scallops),
and
thereby forming end pads 138 for engagement with the end surface 140 of the
stator.
To reduce the likelihood of the stator catching on the end member 134, the
upper and
lower corners of the stator adjacent the ends of the slot 144 may be rounded
at 142,
as shown in Fig. 9. The scallops 136 provided in the end members 134 serve to
facilitate washing action between the stator and the rotor, and prevent the
build-up of
debris between the end of the stator and the end member.
~1~~~~3
- 18-
The configuration of the end members 134 is shown in Fig. 10. Four scallops
136 are provided about the circumference of the end member, thereby forming
four
pads 138 which serve as stop surfaces for limiting axial travel of the stator
with
respect to the rotor. A metal clip may be used to secure the sleeve on the rod
prior
to injection molding the end members, as described above. The end members 134
may be injection molded on the rod 12, and retain the metal sleeve 146 on the
rod
in a manner similar to the Fig. 1 embodiment. The metal sleeve 146 may
alternatively be similar to the Fig. 4 or Fig. 5 embodiment.
Figures 1 l and 12 disclose another embodiment of a rotor 150 for a rod guide.
The stator as shown on Figs. 1 and 2 may be installed on the rotor 150. The
rotor
150 in cross-section may have a substantially C-shaped body 152 as generally
shown
in Fig. 12 circumferentially positioned about 270° of the rod 12. The
annular gap
over approximately 90° between the ends of the body 152 is filled with
plastic when
the end members are molded in place, thereby forming an elongate strip 154
having
an outer surface cooperative with the metal body 152 to form a substantially
uniform
diameter cylindrical surface for engagement with the stator. The upper and
lower
ends of the rotor may be identical.
The metal body 152 may be formed by a stamping operation to form a
shoulder 156 as shown in Fig. 11. Lower bend 158 projects radially outward,
and
upper bend 160 then projects back inward. Extension 162 extends from the upper
bend and has a configuration substantially identical to the body 152. A rubber
layer
164 is bonded on the inner surface of the metal body, and also may
substantially fill
the gap 168 between the lower and upper bends. The upper and lower plastic end
members 166 may totally or partially encapsulate the flanges 156, and are
integrally
connected by plastic strip 154.
The flanges or shoulders 156 may be formed on the ends of the C-shaped body
152 after the rubber layer 164 is bonded to the inner surface of the metal
body. The
body 152 may then be spread apart and snapped onto a rod 12. If necessary, the
metal body may be squeezed to compress the rubber layer 164, and the plastic
end
members 166 then molded on the ends to hold the body 152 on the rod. When the
plastic end members 166 are molded on the rod, the annular gap between the
ends of
the C-shaped body 152 will be filled with plastic, thereby forming strip 154
as shown
_ . ~1?35~~
-19-
in Fig. 12. The lower surface 158 of the flange 156 thus forms a stop surface
for
engagement with the ends of the stator. If the plastic end members 166 fully
encapsulate the flanges, the plastic end members may form a stop surface for
engaging the stator in a manner similar to the embodiment as shown in Fig. 3.
In
this case, the flanges would then provide a metal backup stop surface after
the plastic
stop surface was worn. A metal sleeve with upper and lower flanges could be
formed
from two C-shaped sleeve components in a manner similar to the Fig. 4
embodiment.
Retaining rings could be provided above and below the flanges to secure the
metal
sleeve on the rod prior to injection molding the end members on the rod,
thereby
encapsulating the retaining rings in plastic. Since the flanges rather than
plastic
surfaces on the end members and/or the retaining rings serve as the stop
surfaces for
engaging the ends of the stator, a rubber O-ring, clamp, or other removable
holding
device may be used to secure the two opposing metal sleeve components on the
rod
while the plastic end members are molded in place. The holding devices may
then
be removed after the molding operation, and may be reused on another rotor.
Figures 13 and 14 illustrate yet another embodiment of a stator 170. The
metal sleeve 172 again includes a rubber layer 174 bonded thereon, and
substantially
encircles the rod 12. The sides of the metal sleeve, and more preferably the
rubber
layer covering the sides of the metal sleeve, may be butted together as shown
in Fig.
14. A thin elongate gap 175 between the sides of the metal sleeve may thus be
filled
with rubber. The upper and lower ends of the metal sleeve include side
connections
which are deformed to form interconnecting S-ends which hold the metal sleeve
in
place on the rod prior to molding the stops on the rods. Each of the S-ends
176 may
be similar to the interconnection of a sheet metal joint, and each connection
176 is
encased in the plastic end member 178 which is subsequently molded on the rod.
Upper and lower tab ends of the metal sleeve are bent to form bearing tabs
180. As with other embodiments described above, the plastic end members 178
could
fully encapsulate the bearing tabs 180, in which case the metal bearing tabs
180
would provide a backup metal stop surface for engaging the stator. From two to
four
bearing tabs may be equally spaced around the circumference of the rod, and
three
such bearing tabs are shown in Figs. 13 and 14. The lower end of the rotor 170
may
~1°~~~23
-20-
be constructed similar to the depicted upper end. The stator as previously
described
and as shown in Figs. 1 and 2 could be snapped in place on the rotor 170.
Figure 15 discloses a rotor 210 comprising two substantially identical metal
bodies 212 each covering 180° of a rod. Each metal body 212 includes a
rubber
inner layer 214 bonded thereto. A slight gap between adjoining sides of the
metal
bodies may be filled with rubber in a manner similar to the Fig. 4 embodiment.
Each
body also includes a flange 216 having a pair of passageways 218 therein. The
two
bodies 212 may be placed on a rod, and a pair of roll pins 220 as shown in
Fig. 15
then pressed into passageways 218 to hold the bodies in place on the rod. The
plastic
end members 222 may then be molded on the rods, partially encapsulating the
flanges
216.
The rotor 210 as shown in Figs. 15 and 16 may be modified so that the rotor
is field installable. For this embodiment, the plastic end members 222 may be
molded on each body 212 before the bodies are installed on a rod. After
fitting
elongated roll pins in the passageways 218, the ends of the roll pins
extending from
the passageways 218 may be deformed, thereby securely fixing the metal halves
on
the sucker rod. When deforming the ends of the roll pins, the metal body
halves may
be squeezed together, thereby compressing the rubber layer 214.
Figure 17 discloses yet another embodiment of a rod guide 230. The rod
guide includes a metal sleeve 232 preferably having a rubber or other
elastomeric
layer 234 on the inner surface thereof. The rotor also includes a metal ring
member
236 affixed to the metal sleeve and spaced approximately midway between the
upper
and lower ends of the metal sleeve. As explained subsequently, the metal
sleeve
includes stop surfaces 237 and 239 which limit axial travel of the stator with
respect
to the sucker rod 12.
As shown in Figure 18, the metal sleeve 232 may be formed in substantially
the same manner as the sleeve discussed above and shown in Fig. 4. The ring
member 236 replaces the purpose of the retaining clips and the plastic end
members
used in that embodiment to hold the metal sleeve on the sucker rod 12. The
ring
member includes a pair of substantially identical short metal sleeve
components 237
which are welded together at radially opposing welds 238. Preferably, the
welds 238
are circumferentially spaced from the adjacent sides of the components which
form
-21 -
the metal sleeve 232, as shown in Fig. 18. The metal sleeve 232 prevents the
welds
238 from damaging the metal sucker rod 12. A clamp or other suitable securing
member (not shown) may be used to retain the metal sleeve 232 on the sucker
rod 12
while compressing the elastomeric layer 234 prior to the welding operation.
The stator 240 includes a radially inner body having an axially extending slot
therein (not shown) for mounting the stator on the rotor as previously
discussed, and
also includes a plurality of vanes as shown in Fig. 1 extending radially
outward from
the body. The stator body includes a radially inner ring-shaped cavity sized
for
receiving the ring member 236. The otherwise generally cylindrical inner
surface 241
of the stator may be slightly larger than the outer diameter of sleeve 232 to
facilitate
rotation of the rotor about the stator. The stop surfaces 237 and 239 on the
ring
member 236 thus limit axial travel of the stator. The central portion of the
stator
adjacent the ring member 236 may have a generally cylindrical outer surface
242.
The upper and lower surfaces 244 and 246 between the cylindrical surface 242
and
the ends of the stator may be slightly tapered as shown in Fig. 17 to reduce
the mass
of the stator while providing a smooth contour for promoting streamline fluid
flow
and reducing the pressure drop across the stator. Since upper and lower end
members with stop surfaces thereon are not utilized for limiting axial travel
of the
stator, scallops at the ends of the stator 240 need not be provided.
It is also possible to spot weld the edges of the metal sleeve components
together. For this embodiment, the metal component edges are in contact, as
shown
in Fig. 2, or are separated by a very narrow elongate gap. The metal sleeve
components are protected from engaging the rod 12 by a thin rubber or plastic
layer,
as shown in Fig. 4. The rubber or plastic layer shields the rod from the
welding
process, and serves the further purposes described above. As the weld cools
and
contracts, the sleeve is secured to the rod in the manner of a shrink fit.
Figure 19 discloses yet another embodiment of a rotatable rod guide. The
embodiment as shown in Fig. 19 is substantially the same as the embodiment
discussed above, except that the metahring member 236 in Fig. 18 has been
replaced
with a one-piece plastic ring member 252. The metal sleeve 232 may thus be
placed
on the rod 12 and held in place by any suitable securing member, such as
rubber O-
rings sized to slip over the upper and lower ends of the metal sleeve 232. The
sucker
- ~ . ~~?353
-22-
rod 12 with the metal sleeve thereon may then be passed through a mold, and
the
plastic ring member 252 injection molded on the metal sleeve. If desired, a
one piece
or two piece component metal sleeve may be used. Any substantially wide gap
between sides of the metal sleeves may be filled with plastic while the ring
member
S is molded in place.
In other embodiments, a sleeve may be molded or otherwise retained on the
rod. The sleeve may include a plurality of elongate notches or splines which
interrupt
the circumference of the sleeve. These grooves, indentations, or notches form
additional washout or cleansing channels which minimize the likelihood of
debris
becoming trapped between the stator and the rotor.
Those skilled in the art will appreciate that any number of fins or vanes may
be provided on a guide body, although preferably at least three and less than
seven
such fins are provided. For many applications, three circumferentially spaced
fins
are preferred. The design of the rotating rod guide according to the present
invention, along with the selection of material as discussed above, provide
high
protection for the rod and maximize the benefit to the fluid pumping operator.
The
field serviceability feature of the rod guide is a significant advantage of
this invention
compared to prior art designs. If a rod guide stator becomes worn down to the
point
that the rod or rod coupling contacts the tubing, the rod guide stator can be
snapped
off the rotor and a new stator snapped on the rotor in its place. This is a
significant
feature when using more durable metal rotors which have a much longer life
than the
prior art plastic material rotors. The rod need not be returned to the shop
for
installation of the guide bodies, and the replacement operation is easily
accomplished
in the field.
The design of the rod guide according to the present invention also allows for
a number of different materials to be utilized to form the rotor. The outer
sleeve
portion of the rotor may be fabricated from metal sheet stock, as described
above, but
also could be fabricated from a ceramic material. An elastomeric material
other than
rubber may be used to increase frictional engagement between the outer wear
resistance sleeve material and the sucker rod, and prevent galvanic corrosion.
The
body of the end members of each rotor may be plastic, with the retaining clip
being
a hardened metal. Various mechanisms may be used to bond or secure the rotor
to
', '
-23-
the rod. Various alternative techniques may thus be used to form a suitable
rotor and
mechanically fix the spool to the rotor, either permanently or temporarily.
Those
skilled in the art will further appreciate that the sleeve member of the rotor
may
extend substantially, although perhaps not completely, between the end
members,
S while still providing the desired purpose of positioning the stator about
the rod.
As previously noted, the material for the stator is a significant feature of
the
present invention, although various moldable or machinable materials. other
than
UHMW polyethylene may be provided. Any polymer resin or alloy of polymers that
provide suitable performance in tensile strength, elongation, impact
properties and
low coefficients of friction may be used. Polymers having molecular weight
above
500,000 are likely candidates. Bronze and brass are likely candidates for
fabricating
a metal stator, and these metal materials would make the stator more wear
resistant
than if fabricated from standard plastic materials. The stop surfaces on the
rotor end
members also may be spaced apart axially a distance substantially greater than
the
axial length of the stator.
According to the method of the present invention, excess rotors may be
initially molded on a rod, e.g., rotors in excess of the number of stators
desired along
that length of rod may be provided above or below the rotor intended for
initial use
with a stator. A rubber sleeve or adhesive tape (not shown) may be placed over
an
unused rotor to simply protect the rotor from wear, with this rubber sleeve
having an
outer diameter only slightly greater than the rotor and thus not serving to
centralize
the rod within the production tubing. If one or more of the rotors should
become
excessively worn, the stator may be removed from the worn rotor, the
protective
rubber sleeve removed from the previously unused rotor spaced above or below
the
worn rotor, and a new stator then snapped onto the unused rotor. This feature
even
further reduces the overall cost of maintaining the rod string centered within
the
tubing string, since the return of sucker rods to the manufacturing facility
for molding
on new rotors is substantially reduced or eliminated.
According to the method of the present invention, a rod guide is positioned
on a sucker rod by securing a rotor and a stator to the sucker rod. The stator
is
formed having a passageway therein for receiving the sleeve portion of the
rotor, with
the stator having a slot with a width selected as a function of the
construction material
- ~, . ~1~~~23
- 24 -
for the stator and the diameter of the sleeve portion of the rotor. The stator
may then
be moved radially inward with respect to the sleeve member of the rotor, and
the
spreading force then released to allow the stator slot to substantially return
to its
original width. The passageway in the stator may have an interior diameter
greater
than the diameter of the sleeve member of the rotor, and the slot has a width
sufficient to facilitate flow in and out of an annulus between the stator and
the rotor.
Cut-outs may be formed in the stator to provide communication to and from the
annulus between the stator and the sleeve member of the rotor, with the cut-
outs
providing a plurality of pads for engagement with stop surfaces on
corresponding
rotor end members.
The concepts of the present invention, while particularly well suited for
protecting a rotating rod used to drive a downhole progressing cavity pump,
may also
be applied for protecting other tubular goods which are rotating within a
wellbore.
The rod guide may be used as a field installed guide or scraper on a
reciprocating
sucker rod. The extended wear rotor according to this invention could also be
used
for a rod guide wherein at least a substantial length of the internal surface
of the
stator and the external surface of the rotor are sealed rather than being
exposed to
well fluids. The concepts of the present invention may thus be used to devise
a guide
for protecting a drill pipe rather than a sucker rod, since engagement of a
rotating
drill pipe with a casing string or open hole also results in excessive wear on
either
the drill pipe string yr the casing string.
The foregoing disclosure and description of the invention are thus
illustrative,
and changes in both the apparatus of the rod guide and in the method of
constructing
and operating a rod guide as described above may be made with departing from
the
present invention.
