IMPROVED SUCKER ROD GUIDE BEARING

PALIER-GUIDE DE TIGE DE POMPAGE AMELIORE

English Abstract

A sucker rod guide bearing with a cylindrical shaft having a threaded stud at each end is connected by couplings to adjacent sucker rods. The coupling has a flat end surface which directly contacts the shoulder of the guide bearing and provides for the transmission of the guide bearing. A vaned cylindrical wheel is slidably mounted over the guide bearing connecting shaft such that the wheel remains stationary while the bearing body rotates within it. The wheel has four vanes, each having a substantially semi- circular cross-section outline. Each vane has an internal lubrication groove running the length of the wheel and the wheel is notched at each end of the groove to allow passage of fluids and extraneous matters such as sand. Preferably the wheel and vanes are made of a very hard polypthalamide resin which resists sand embedment and mechanical failure.

French Abstract

Un palier de guidage avec une tige de pompage d'un arbre cylindrique ayant une tige filetée à chaque extrémité est relié par des joints pour tiges de pompage adjacentes. Le joint présente une surface d'extrémité plate qui est directement en contact avec l'épaulement du palier de guidage et permet la transmission du palier de guidage. Une roue à aubes cylindrique coulissante est montée sur l'arbre du palier de guidage de telle sorte que la roue reste immobile tandis que le corps de palier tourne à l'intérieur de celle-ci. La roue a quatre aubes, chacune présentant une forme sensiblement semi-circulaire en coupe contour. Chaque aube comporte une rainure de lubrification interne s'étendant sur la longueur de la roue et la roue est entaillée au niveau de chaque extrémité de la rainure pour permettre le passage de fluides et de matières étrangères telles que du sable. De préférence, la roue et les aubes sont réalisées en une résine polypthalamide très dure qui résiste à l'enfoncement de sable et aux défaillances mécaniques.

Claims

The embodiments of the invention in which an exclusive property or privilege
is
claimed are defined as follows:
1. A sucker rod guide bearing comprising:
(a) a cylindrical connecting shaft having a threaded stud at each end for
connecting
to a coupling and a shoulder for receiving and transmitting torque;
(b) a vaned cylindrical wheel slidably mounted over the connecting shaft; and
(c) a sucker rod coupling having internal threads at one end for attaching to
the
threaded stud and internal threads at the other end for connecting to a sucker
rod;
wherein the wheel has four vanes, each vane having a substantially semi-
circular cross-section
outline.
2. The sucker rod guide bearing of claim 1 wherein each vane has an internal
lubrication
groove running the length of the wheel and wherein the wheel is notched at
each end of each
groove.
3. The sucker rod guide bearing of claim 2 wherein the wheel and vanes are
fashioned
from a polyphtalamide resin.
4. The sucker rod guide bearing of claim 2 or 3 wherein the wheel and vanes
are
fashioned from a material having a Rockwell Hardness of at least about 120 on
the R scale.
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5. The sucker rod guide bearing of claim 1, 2 or 3 wherein the sucker rod
couplings have
a substantially flat end surface which contacts the shoulder when the coupling
is attached to
the connecting shaft and which is thereby able to transmit at least 1.5 times
the torque
capacity of the sucker rod.
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Description

CA 02225894 1997-12-24
IMPROVED SUCKER ROD GUIDE BEARING
FIELD OF THE INVENTION
The present invention relates to sucker rod couplings and guide bearings.
Couplings
are used to couple together sections of sucker rods for use in an oil well.
Guide bearings are
used to centre the rod and minimize wear on the tubing string.
BACKGROUND OF THE INVENTION
In establishing wells for production of fluid hydrocarbon, a hole is first
drilled into the
ground and then logging equipment lowered into the hole and used to determine
the character
of the formation as a function of depth. A steel pipe or tubing, commonly
referred to as
casing, is then set in the bore hole down to the bottom. The casing is
perforated at selected
locations to allow the fluid in the formation to enter the bore hole.
In cases where the fluid is of high viscosity or where there is a relatively
low pressure,
it is necessary to pump the fluid out of the well. Approximately 90% of all
artificial lift
wells in the U.S. and Canada consist of a down hole pump connected to a
surface power
source by a string of sucker rods. Each sucker rod is typically 25 feet long
with a diameter
of 3/4" or 7/8" and is provided with a threaded pin end and shoulder at each
of its ends. A
cylindrical internally threaded member, typically 4" long and 1 5/8 inches
diameter is used to
couple two sucker rods together. In this way a sucker rod string is made up of
a number of
rods and couplings with the couplings being larger in diameter than the rods.
A sucker rod string passes through a concentric tubing string consisting of 30
foot sections of tubing having an inside diameter of 2 1/2". Rotation or up
and down
reciprocating motion of the sucker rods activate the pumps depending on the
type of pump
employed. In rotary systems, the pump used is often a positive cavity
displacement pump
which consists of two mating pieces, one being stationary and the other
rotating so as to

CA 02225894 1997-12-24
create a chain of cavities moving from the bottom of the assembly to the top.
Such systems
have the capability to remove troublesome sand and other solids from the bole
hole as well as
being able to achieve high lifts at slow rotation speeds. Typical rotation
speeds encountered
are in the area of 600 revolutions per minute at depths of up to 4,000 feet.
Various types of couplings between sections of sucker rods are employed to
centralize
the sucker rod string. One common type of coupling has an exterior hard
surface that turns
with the rod and tends to wear out the casing. An elastomeric material is
sometimes bonded
to the outer surface of the coupling to reduce the wear of the casing which is
more expensive
and difficult to replace than is the coupling. Couplings having an elastomeric
outer surface
provide only a partial solution to wearing through of the casing in as much as
the elastomeric
surface wears away quickly and then the coupling must be replaced or be
resurfaced.
U.S. Pat. No. 4,757,861 issued to Klyne discloses a sucker rod coupling
assembly
having a free turning vaned wheel of soft resilient material, a steel shaft
with soft resilient
sleeve bonded thereto and coupling and faces with soft resilient rings bonded
to the ends
thereof. The sleeve and rings prevent sand from reaching and abrading the
steel surfaces of
the shaft and coupling end faces. However, given than the sleeve and rings are
soft and
resilient, the torque transfer takes place across the stud threads rather than
across the rings and
sleeve to the steel shaft. Moreover, excessive wear or breaking of the wheel
places the steel
box end couplings in contact with the well casing or tubing resulting in
wearing of the latter
rather than the couplings.
U.S. Patent No. 4,919,202 issued to Clintberg discloses a sucker rod guide
bearing
having a vaned cylindrical wheel slidably mounted over a bearing body which is
connected by
couplings to adjacent lengths of sucker rod.
The vaned wheel in Clintberg spaces the coupling away from the sides of the
casing
and reduces wear on the casing by remaining stationery while the bearing body
rotates within
it. Figure 1 is sectional view of the prior art Clintberg sucker rod guide
bearing and Figure
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CA 02225894 1997-12-24
2 is a sectional view taken through the bearing wheel and casing. Torque is
transferred from
sucker rod to a coupling, to a torque transfer washer, to a central body, to a
lower torque
transfer washer, through another coupling and finally to the adjacent sucker
rod. The torque
transfer washers are necessary because attaching a standard coupling to the
central body does
not provide sufficient contact area for effective torque transfer. The washers
also provide
alternative sacrificial wear surfaces in the event the vaned wheel wears or
breaks away. As
may be seen in Figure 2, the vaned wheel permits through-flow of fluid between
the vanes
and the casing.
The sucker rod guide bearing disclosed in U.S. Patent No. 4,919,202 may be
improved
upon further. It was found that sand would embed in the vaned wheel in between
the wheel
and the connecting shaft (referred to as the central body in the '202 Patent).
As the
connecting shaft rotated, the embedded sand would quickly abrade the
connecting shaft and
eventually cause the wheel or the shaft to fail. Also, the use of torque
transfer washers or
belled couplings provided very little secondary wear surface in the event the
vaned wheel was
worn away or broken. Lastly, it was found that fluid flow through the vaned
wheel and
resistance to rotation of the wheel within the casing could be improved by
altering the design
of the wheel. Accordingly, there is a need in the art for an improved sucker
rod guide
bearing which addresses the disadvantages in the prior art.
SUMMARY OF THE INVENTION
In general terms , the invention is an improved sucker rod guide bearing,where
the
improvement lies in the following:
(a) the vaned wheel is improved by having only form vanes of reduced cross-
sectional area and by including an internal lubrication groove with each vane;
(b) the vaned wheel is fabricated from a very hard resin which resists sand
embedment and mechanical failure;
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CA 02225894 1997-12-24
(c) the torque transfer contact area between the couplings and the central
body or
connecting shaft is enlarged by modifying the couplings.
BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiment of the invention will now be described with reference
to the
drawings in which:
Figure 1 is a sectional view of a prior art sucker rod guide bearing.
Figure 2 is a sectional view through 1-1 of the prior art sucker rod guide
bearing
in Figure 1.
Figure 3 is a sectional view of a portion of the preferred embodiment of the
present invention showing the connecting shaft, the vaned wheel and the
couplings.
Figure 4 is a sectional view taken through 4-4 of Figure 3 showing the vaned
wheel and connecting shaft in cross-section within a casing.
Figure 5 is a sectional view of the modified coupling and showing the flat
contact surface which abuts the connecting shaft.
DETAILED DESCRIPTION
In the following description, like referenced numbers in the different figures
refer to
like parts. Referring to Figure 3, there is shown a portion of well tubing
including a section
of a sucker rod string contained therein. The series of sucker rods (20) are
interconnected by
means of a sucker rod guide bearing (10) coupled at each end by a standard
sucker rod
coupling (18). The bearing (10) consists of central cylindrical body (12)
having a shank (26)
connected to a threaded stud (30). The shank (26) has a diameter less than the
threaded stud
(30).
The vaned wheel (14) is preferably made of an extremely hard polyphthalamide
resin
such as Amodel' . Amodel' is available from Amoco Polymers in Alpharetta,
Georgia,
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.CA 02225894 1997-12-24
U.S.A. The vaned wheel (14) is fitted slidable over the cylindrical body (12)
and is of a
length slightly less than that of the body (12) leaving slight gaps between
the wheel (14) and
the upper coupling (18a) and the lower coupling (18b).
Upon tightening of the couplings (18) over the threaded studs (30) it may be
seen that
the end of the coupling abuts the shoulder (13) of the connecting shaft (12).
Torque is
transferred from the upper coupling (18a) directly to connecting shaft (12)
and directly out to
the lower coupling (18b). Standard sucker rod couplings are not suitable for
this purpose
because the end surfaces mating or contacting with the connecting shaft
shoulder (13) are
bevelled or tapered. Tightening of a standard coupling will result in the
shoulder (13)
slipping inside the coupling and flaring the coupling outward. Accordingly,
modified
couplings (18) are used in the present invention. The couplings (18) are
modified by
"facing" the ends to provide greater flat contact area with the shoulder (13).
Figure 5 shows the faced end of the coupling (18) and the dotted line
represents the
outline of a standard coupling. As a result the inside diameter edge (19) of
the coupling (18)
contacts the shoulder (13) closer to the centre of the connecting shaft (12)
than in a standard
coupling. With the degree of facing shown in Fig 5., the coupling (18) is able
to transmit at
least 1.5 times the torque capacity of the sucker rod in the preferred
embodiment.
The vaned rotatable wheel (14) is shown in cross-section Figure 4. Compared
with the
prior art vaned wheel (15) seen in Figure 2, there are four vanes (32), each
having a flow-
through lubrication groove (34) within each vane (32). The vanes (32) are also
rounded in
cross-section as opposed to the square shape (33) shown in the prior art
Figure 2. The result
of the reduced number of vanes (32) and the rounding of the vanes (32) is a
reduced cross-
sectional area. The increased cross-sectional area between the casing (40) and
the wheel (14)
permits improved through-flow of fluid (42). As well, the internal lubrication
grooves (34)
also allows passage of fluids and extraneous matters such as sand. The
lubrication grooves
(34) help prevent abrasive material build-up on the inside of the wheel (14),
which extends
the life of both the wheel (14) and the connecting shaft (12).
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CA 02225894 1997-12-24
The use of Amodel' or similar polyphthalamide resins as the wheel material
significantly increases wheel life by resisting sand embedment and offers a
significantly lower
co-efficient friction between the wheel (14) and the connecting shaft (12).
The Rockwell
Hardness of the resin used in the preferred embodiment is 120 on the R Scale.
The vaned wheel (14) of the preferred embodiment is a further improvement in
that it
is less prone to rotation within the casing (40) as the sucker rod string
rotates in normal
operation. In normal use, the wheel (14) rests against the casing (40). The
increased
resistance to rotation is a result of a wider stance between the two points of
contact between
the wheel (14) and the casing ( shown as A and B in Figure 4). It is readily
seen that the
stance A - B is close to 90 degrees of the circumference of the casing (40)
whereas in the
prior art shown in Figure 2, the stance is approximately 30 degrees.
In the event the vanes (32) of the wheel (14) wear down significantly or the
wheel
(14) breaks, the outer cylindrical surface (19) of the sucker rod couplings
(18a, 18b) act as
alternative sacrificial surfaces. As shown in prior art Figure 1, the
sacrificial surface consisted
only of torque transfer washer (16). By eliminating use of the torque transfer
washer (16) as
shown in Figure 3, significantly greater secondary wear surface is provided.
At the same
time, sufficient torque transfer surface is provided between coupling body 18
and connecting
shaft (12).
It is seen in Figure 3 that the edges of the vaned wheel are chamfered to
facilitate
insertion and extraction of the sucker rod string. Also, at the upper and
lower end of each
vane, a notch (36) is provided to permit flow of fluid through the lubrication
grooves even
when vaned wheel abuts coupling bracket (18).
Accordingly, this invention has been described with reference to a preferred
embodiment. However, this description is not intended to be limiting in that
various
modifications and variations will be apparent to persons skilled in the art.
It is contemplated
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CA 02225894 1997-12-24
that the appended claims will cover any such modifications or embodiments as
fall within the
scope of the invention.

Representative Drawing