Note: Descriptions are shown in the official language in which they were submitted.
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SUCKER ROD COUPLING AND METHOD OF WEAR PREVENTION IN
DRIVEN ROTATION OF A SUCKER ROD STRING IN PRODUCTION TUBING
FIELD OF THE INVENTION
The present invention relates generally to a coupling arrangement
for interconnecting adjacent sucker rods in a string of sucker rods and
preventing
wear of production tubing under driven rotation of the sucker rod string
within a
well bore.
BACKGROUND OF THE INVENTION
In pumping of fluids from a wellbore for production to the surface, a
string of sucker rods connected end to end is used as a mechanical link
between
drive equipment at the surface and a downhole pump in the wellbore for driven
operation thereof. Sucker rods are each externally threaded at pin ends of the
rod and are conventionally interconnected by internally threaded box couplings
each threadingly receiving ends of adjacent rods in the string. The present
application is particularly concerned with wells using rotationally driven
downhole
pumps, where the sucker rod string is rotated to provide the rotational, not
reciprocal, input required to operate this type of pump. A common problem in
such installations is that the sucker rod string does not extend entirely
linearly in
the wellbore, and accordingly box couplings between the rods, which are of
larger
outer diameter than the rods themselves and thus form the radially outermost
extents of the string, will tend to bump or rub against the production tubing
wall
during the driven rotation of the rod string and thus cause significant wear
to the
production tubing. Accordingly, some solutions for preventing or limiting this
wearing of the production tubing have been previously proposed to avoid the
need for costly repair or replacement of damaged tubing.
One prior art solution has been to bond elastomeric materials to the
hard outer surfaces of sucker rod couplers to reduce wear to the tubing, which
is
more difficult and costly to replace than a coupler. However, the coating may
quickly wear away, requiring frequent replacement or recoating of sucker rod
couplers.
U.S. Patent Numbers 4,757,861 and 4,919,202 each teach a
cylindrical shaft-like body that has a vaned cylindrical wheel of elastomeric
material disposed and freely rotatable thereabout. The ends of the body are
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externally threaded in order to each engage a box coupling receiving a sucker
rod therein from the opposite end thereof. The wheel is of greater outer
diameter
than the box couplers and accordingly forms the only contact between the rod
string and the production tubing or well casing, and due to the relative
rotation
allowed between the wheel and the central body, moves very slowly, if at all,
under the driven rotation of the rod string. This lack of significant rotation
and the
use of elastomeric material minimizes wear to the production tubing or well
casing.
However, these two prior art solutions each rely on a three-piece
assembly to achieve both the wear prevention and rod coupling functions. In
other words, the wear prevention structure needs is installed between adjacent
sucker rods using a pair of box couplings. Installation thus requires
threading of
a box coupling on a sucker rod above the wear preventing structure, threading
of
the cylindrical body of the wear prevention structure to that box coupling,
threading of a second box coupling onto the opposite end of the cylindrical
body,
and threading of the second box coupling onto the next sucker rod. It would be
desirable to provide a sucker rod coupling and wear prevention arrangement
that
is easier to install in a sucker rod string.
In view of the forgoing and other shortcomings of the prior art, there
is a desire for improvement in coupling of sucker rods and wear prevention in
driven rotation of sucker rod strings in wellbores.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a
sucker rod coupling comprising:
a coupler unit defined by a unitary body structure having a central
longitudinal axis passing therethrough and comprising first and second
coupling
sections defining opposite first and second ends of the coupler unit, each
coupling section having internal box threading for selective threaded
engagement
with a respective sucker rod at an externally threaded pin end thereof; and
one or two outer members extending about the coupler unit
between the first and second ends thereof, each outer member being rotatable
about the central longitudinal axis relative to the coupler unit and
presenting
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contact surfaces facing outwardly away from the coupler unit at positions
radially
outward therefrom relative to the central longitudinal axis;
each outer member being disposed between a respective one of
the first and second ends of the coupler unit and a respective stop-defining
feature of the unitary body that projects radially outward further from the
longitudinal axis than a portion of the coupler unit around which the outer
member extends without reaching past the contact surfaces of the outer member
so as to block sliding of the outer member past the stop-defining feature
along
the longitudinal axis; and
a respective stop element corresponding to each outer member and
being selectively deployable adjacent the respective one of the first and
second
ends of the coupler unit on a side of the outer member opposite the stop-
defining
feature to project radially outward from an outer surfaces of the coupling
section
without reaching past the contact surfaces of the outer member so as to block
sliding of the outer member past the deployed stop element, the outer member
being slidable off the respective end of the coupler unit when the stop
element is
not deployed.
Preferably each outer member extends around the coupler unit at a
respective one of the coupling sections at a position past which the internal
box
threading reaches along the longitudinal axis away from the respective end of
the
coupler unit.
Preferably each respective stop element comprises a ring
releasably engagable around the coupler body adjacent the respective end of
the
coupler unit.
Preferably each ring is a snap ring engagable into a respective
groove in the outer surface of the coupling section defining the respective
end of
the coupler unit.
The internal box threading of both coupling sections may be
disposed within a common internal passage extending fully through the coupler
unit along the longitudinal axis. A single internal thread in the common
internal
passage may define the box threading of both coupling sections. Is this right?
Each outer member may be defined by an outer race of a bearing
assembly, the outer face closing fully about the coupler. Each bearing
assembly
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may further comprise an inner race closing about the coupler, whereby the
inner
and outer races and roller elements therebetween are movable together along
the longitudinal axis for selective removal of the bearing assembly from the
coupler.
In use, the sucker rod coupling is coupled between adjacent sucker
rods in a sucker rod string to form a section thereof, the adjacent sucker
rods
comprising upper and lower rods engaged to upper and lower ones of the
coupling sections of the coupling unit and the sucker rod string being driven
for
rotation within production tubing in a welibore, whereby contact of the
contact
surfaces of the outer member of the sucker rod coupling with an inner wall
surface of the production tubing under driven rotation of the sucker rod
string
cooperates with allowed relative rotation between the outer member and the
coupler to avoid direct contact between the production tubing and the rotating
sucker rod string to prevent or limit wear to either thereof.
In one embodiment, there is only one outer member and only one
respective stop element deployable adjacent a bottom end of the coupler unit,
an
upper one of the coupling sections having a larger outer diameter than a lower
one of the coupling sections around which the outer member is positioned and a
step in diameter between the coupling sections forming the stop-defining
feature.
Preferably the larger outer diameter of the upper coupling section of the
coupler
unit is equal to an outer diameter of a portion of the respective sucker rod
to
which the coupler unit is to be coupled. Preferably the larger diameter of the
upper coupling section of the coupler unit is equal to the outer diameter of a
pin
connection shoulder of the respective sucker rod.
In another embodiment, the at least one outer member comprises
separate first and second outer members spaced apart along the longitudinal
axis
and disposed adjacent the first and second ends of the coupler unit
respectively.
The coupler with two outer members preferably comprises a wrench engagable
section defined between the first and second coupling sections, and the wrench
engagable section preferably comprises opposing planar surfaces on opposite
sides of the longitudinal axis.
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According to a second aspect of the invention there is provided a
method of operating and retrieving a sucker rod string within production
tubing in
a well bore, the method comprising:
providing a sucker rod coupling that is in accordance with the first
5 aspect of the invention and has only one outer member and only one
respective
stop element deployable adjacent a bottom end of the coupler unit, an upper
one
of the coupling sections having a larger outer diameter than a lower one of
the
coupling sections around which the outer member is positioned and a step in
diameter between the coupling sections forming the stop-defining feature, and
the larger outer diameter of the upper coupling section of the coupler unit
being
equal to an outer diameter of a portion of the respective sucker rod to which
the
coupler unit is to be coupled;
installing the sucker rod coupling between the respective sucker
rods by engaging the first and second coupling sections of the coupler unit to
the
respective sucker rods to form part of the sucker rod string from the coupler
unit
and the respective sucker rods engaged therewith;
driving rotation of the sucker rod string within the production tubing;
during driven rotation of the sucker rod string, using contact
between the contact surfaces of each outer member of the sucker rod coupling
and an inner wall surface of the production tubing to prevent contact of the
production tubing with the rotating sucker rods and the coupler unit rotating
therewith; and
after failure of the part of the sucker rod string at an upper one of
the respective sucker rods between which the sucker rod coupling is installed,
retrieving the sucker rod coupling and sucker rods therebelow by using the
upper
coupling section thereof of the coupling unit as a fish neck to grip the upper
coupling section with a fishing tool dimensionally compatible with a sucker
rod
size of the sucker rod string.
According to a third aspect of the invention there is provided a
sucker rod coupling comprising:
a coupler unit extending having a central longitudinal axis passing
therethrough and comprising first and second coupling sections defining
opposite
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first and second ends of the coupler unit, each coupling section being
configured
for selective attachment to a respective sucker rod; and
at least one outer member extending about the coupler unit
between the first and second ends thereof, each outer member being rotatable
about the central longitudinal axis relative to the coupler unit and
presenting
contact surfaces facing outwardly away from the coupler unit at positions
radially
outward therefrom relative to the central longitudinal axis.
The at least one outer member may comprise first and second outer
members spaced apart along the longitudinal axis and disposed adjacent the
first
and second ends of the coupler unit respectively, in which case first and
second
internal passages may extend into the first and second coupling sections from
the
first and second ends of the coupler unit respectively to engagingly receive
ends
of the respective sucker rods, the first and second outer members extending
about the coupler unit at positions along the first and second internal
passages
respectively.
Preferably each internal passage is threaded for selective threaded
engagement with a matingly threaded end of the respective sucker rod.
Preferably there are provided stops defined at ends of the first and
second coupling sections opposite the first and second ends of the coupler
unit
and projecting radially outward from outer surfaces of the coupling sections
where the outer members extend thereabout to limit sliding of the outer
members
toward one another along the longitudinal axis.
Preferably there are provided stop elements selectively deployable
at positions between the first and second outer members and the first and
second
ends of the coupler unit to project radially outward from the outer surfaces
of the
coupling sections where the outer members extend thereabout to limit sliding
of
the outer members away from one another, the outer members being slidable off
the ends of the coupler unit when the stop elements are not deployed.
According to a fourth aspect of the invention there is provided a
method for preventing wear under driven rotation of a sucker rod string within
production tubing in a well bore, the method comprising:
providing a sucker rod coupling comprising a coupler unit extending
along a central longitudinal axis passing therethrough and comprising first
and
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second coupling sections defining opposite first and second ends of the
coupler
unit, each coupling section being configured for selective attachment to a
respective sucker rod; and at least one outer member extending about the
coupler unit between the first and second ends thereof, each outer member
being
rotatable about the central longitudinal axis relative to the coupler unit and
presenting contact surfaces facing outwardly away from the coupler unit at
positions radially outward therefrom relative to the central longitudinal
axis;
installing the sucker rod coupling between the respective sucker
rods by engaging the first and second coupling sections of the coupler unit to
the
respective sucker rods to form part of the sucker rod string from the coupler
unit
and the respective sucker rods engaged therewith; and
driving rotation of the sucker rod string within the production tubing;
during driven rotation of the sucker rod string, using contact
between the contact surfaces of each outer member of the sucker rod coupling
and an inner wall surface of the production tubing to prevent contact of the
production tubing with the rotating sucker rods and the coupler unit rotating
therewith.
Preferably the sucker rod coupling comprises a wrench engagable
section defined between the first and second coupling sections at a position
spaced from each outer member along the longitudinal axis and each coupling
section of the coupler unit is threaded for engagement with a matingly
threaded
end of the respective sucker rod, the method comprising using a wrench to
rotate
the coupler unit about the longitudinal axis at the wrench engagable section
to
loosen or tighten threaded connection of the coupler unit within the rod
string.
The wrench engagable section of the coupler unit may comprise
opposing planar surfaces on opposite sides of the longitudinal axis.
Alternatively,
the wrench-engagable section may be circular in cross-section and engagable by
a pipe wrench to effect rotation of the coupler unit.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, which illustrate exemplary
embodiments of the present invention:
Figure 1 is a side elevational view of a central body of a sucker rod
coupling according to a first embodiment of the present invention.
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Figure 2 is an overhead plan view of the central body of the sucker
rod coupling of Figure 1.
Figure 3 is a schematic illustration of the sucker rod coupling of
Figure 1 in use within a wellbore to couple together sucker rods in a string
and
prevent wear to the production tubing in which the sucker rods are used.
Figure 4 is a perspective view of the central body of the sucker rod
coupling of Figure 1.
Figure 5 is a perspective view of a sucker rod coupling according to
a second embodiment of the present invention.
Figure 6 is an exploded side elevational view of the sucker rod
coupling of Figure 5.
Figure 7 is a schematic illustration of the sucker rod coupling of
Figure 5 in use within a wellbore to couple together sucker rods in a string
and
prevent wear to the production tubing in which the sucker rods are used.
DETAILED DESCRIPTION
Figure 1 shows a central coupler unit 10 of a sucker rod coupling of
a first embodiment of the present invention. The coupler unit 10 is defined by
a
single integral unitary body of solid material having an elongated shape
oriented
to lie lengthwise on a longitudinal axis 12 passing centrally therethrough.
Along
its length, the body 10 features a first coupling section 14 defining a planar
first
end 16 of the body, a second coupling section 18 defining an opposite planar
second end 20 of the body and a middle wrench section 22 interconnecting the
coupling sections along the longitudinal axis 12. Each coupling section 14, 18
features a cylindrical portion of the body that has been hollowed by formation
of a
bore 24 extending into the body from the respective planar end face of the
body
defined by that cylindrical portion in order to form an internal passage in
the
coupling section into which the end of a sucker rod can be inserted. The bore
24
has a circular cross section concentric with the circular cross section of the
cylindrical portion into which it extends and, as shown in the partially
sectioned
illustration of Figure 3, is threaded according to the thread pattern of an
externally
threaded male or pin end 26a of a conventional sucker rod 26 to facilitate
threaded engagement of the sucker rod end 26a into the internally threaded
female or box end section of the coupler body 10.
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At a distance along the longitudinal axis 12 from each end face 16,
20 of the coupler body 10, the outer diameter of the coupling section 14, 18
increases by a single step to form a larger cylindrical portion 28 concentric
and
end-to-end with the smaller cylindrical portion 30 defining the respective end
face
16, 20 of the coupler body 10. A shoulder formed at this change in diameter of
each coupling section 14, 18 defines a ledge in the form of an annular stop
face
or surface 32 projecting radially outward from the smaller diameter portion 30
of
the coupling section in a plane normal to the longitudinal axis 12. A
circumferential groove 34 in the outer peripheral surface of the smaller
diameter
portion 30 of each coupling section 14, 18 extends fully therearound about the
longitudinal axis at a location therealong a short distance inward from the
respective end face 16, 20 of the coupler body 10.
With reference to Figure 3, the final structure of the sucker rod
coupling of the first illustrated embodiment is completed by installation of a
bearing 36 and snap ring 37 on each coupler section 14, 18 of the coupler body
10. Each bearing 36 is of a conventional structure having an inner race member
38, an outer race member 40 and a plurality of rolling elements 42 disposed
therebetween. Each bearing 36 is disposed about the smaller diameter portion
30 of the respective coupler section 14, 18 so that the annular or hollow
cylindrical inner race member 38 is frictionally engaged with the outer
peripheral
surface of the coupling section at this small diameter portion thereof, and
the
annular or hollow cylindrical outer race member 40 is accordingly rotatable
relative to the fixed-together inner race member and coupler body 10 about the
longitudinal axis 12 due to the roller elements 42 between the races. The
first
illustrated embodiment features needle bearings having elongated cylindrical
roller elements, but it will be appreciated that other known rolling element
bearing
types may alternatively be used to allow relative rotation between the outer
race
member and the coupler body 10. Furthermore, other embodiments may lack an
inner race member engaged to the coupler body 10, and instead may have roller
elements disposed directly between an outer race member and the coupler body
10, relying on outer surfaces of the coupler body to define the inner race of
the
bearing assembly.
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The larger diameter portion 28 of each coupler section 14, 18 of the
coupler body 10 locates the respective bearing 36 along the longitudinal axis
12
under sliding of the bearing 36 onto the coupler body 10 from the respective
end
16, 20 thereof during assembly of the sucker rod coupling, this large diameter
5 portion 28 acting as a stop to limit movement of the bearings toward each
other
and toward the middle wrench portion 22 of the coupler body 10 when the end
face of the bearing reaches the ledge or stop surface 32 at the juncture of
the
small and large diameter portions of the respective coupling section of the
coupler body 10. The snap ring of each coupling sections 14, 18 is then
engaged
10 into the groove 34 on the side of the respective bearing 36 opposite the
large
diameter stop-defining portion 28 of the coupling section 14, 18 to complete
the
positioning of the bearing 36 along the longitudinal axis 12 by blocking
movement
of the bearing 36 away from the middle section and the opposite bearing to the
respective end 16, 20 of the coupler body 10. The snap rings 37 thus provide
removable stop elements that can be installed and removed as needed to allow
for possible removable of the bearings 36 if required, the installation of the
snap
ring 37 forming a stop deployed on the coupler body 10 to project radially
outward from the outer peripheral surface of the smaller diameter portion 30
of
the respective coupling section 14, 18 to block sliding movement of the
installed
bearing 36 past it along the longitudinal axis. It will be appreciated that
other
selectively deployable stop elements may be used in place of snap rings to
position the bearings when deployed and allow removal of the bearings when not
deployed. For example, the end of the coupling body could be externally
threaded for engagement with an internally threaded nut or stop ring to allow
installation and removal of the nut on the side of the bearing opposite the
fixed or
permanent larger diameter stop-defining portion 28 of the respective coupling
section. However, the snap ring has the advantage that it will maintain it
position
along the longitudinal axis regardless of any inadvertent rotation thereof
since the
axial position of the snap ring is locked by its positive positioning within
the
groove. Also, use of an internally threaded nut or stop would require that
such
piece be sufficiently small so as not to project further from the coupling
unit that
the bearing to ensure that only the bearing contacts the production tubing
surrounding the coupling.
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Figure 3 shows the sucker rod coupling in use within the bore 100
of a well. The threaded internal passage 24 of the first coupling section 14
has
been engaged with the externally threaded pin end 26a at the bottom of a
sucker
rod 26 disposed above the coupling in the well bore 100, and the threaded
internal passage of the second coupling section 18 has likewise been engaged
with the externally threaded pin end at the top of a sucker rod disposed below
the
coupling in the well bore 100 so that the coupling body 10 acts to couple the
two
sucker rods together and accordingly forms part of the overall sucker rod
string
that is driven for rotation to operate a downhole pump. The bearings 36 of the
coupling extend outwardly beyond any and all portions of the coupler body 10
in
radial planes normal to the longitudinal axis 12 thereof. The outer peripheral
surfaces of the outer race members of the bearings 36 facing outwardly away
from the coupler body relative to the longitudinal axis 12 accordingly define
the
radially outermost extents of the coupling, and therefore define cylindrical
contact
surfaces that will contact the surrounding cylindrical inner wall surface of
the
production tubing 102 before any portion of the two sucker rods and the
coupler
body therebetween is allowed to reach the production tubing 102 under
movement of this rod string portion out of alignment with a central axis of
the
section of the production tubing string 102. With frictional contact between
the
outer race of one of the bearings and the surrounding tubing wall 102 closing
thereabout, the outer race is stationary with respect to rotation about the
longitudinal axis while the inner race, and the coupler body 10 on which it is
fixed,
are rotated about the longitudinal axis 12 by the driven rotation of the
sucker
rods. Accordingly, there is no relative movement between the bearing contact
surfaces that make contact with the production tubing, and so wear of the
tubing
that would otherwise occur under contact of any part of the spinning rod
string
with the production tubing is avoided. If the outer race of the bearing does
rotate
somewhat under the driven rotation of the string, it will be at significantly
reduced
speed compared to that of the string, and so the degree of wear is still
reduced
from what would occur without use of the coupling.
In the first illustrated embodiment, the middle wrench section 22 of
the coupler body 10 is concentric with the coupling sections and is square in
cross-section with a corner-to-corner diameter less than the circular diameter
of
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both the small and large diameter portions of the equally dimensioned coupling
sections. This square wrench section provided two pairs 22a, 22b of parallel,
planar opposing faces across the longitudinal axis 12, each pair of opposing
faces thus defining wrench flats by which the wrench section can be engaged by
opposing jaws of a wrench in order to rotate the coupler body 10 about its
central
axis 12 to effect tightening and loosening in threaded coupling and decoupling
of
the coupler body 10 with a sucker rod. It will be appreciated that other non-
square cross-sections may be used in the wrench section of the coupling body
while still presenting at least one pair of opposing planar surfaces or wrench
flats.
Alternatively, a circular or other curved peripheral shape may be used in the
cross-section of the middle part of the coupler body, and still be engagable
by a
pipe wrench to effect rotation of the coupler body relative to a sucker rod in
coupling or decoupling therefrom.
The coupler body is preferably a single integral unitary body of
steel, for example 4140 HTSR steel machined to shape the different sections,
but
those of skill in the art will recognize alternate materials and production
methods
that may be used to form the coupler body having the different sections
described. For example, a coupler body formed by multiple pieces rigidly fixed
together during production of the coupling could similarly form a one-piece
coupler unit for direct connection between sucker rods without additional
coupling
pieces separate from the coupler unit. Timken B-2420 and B-2824 are examples
of bearings that may be used, and suitable dimensioning of stops and bearing-
carrying portions of the coupler body for cooperation with such bearings is
within
the ambit of those skilled in the art. These differently sized exemplary
bearings
having different outer diameters illustrate how sucker rod couplings of the
present
invention may be produced in different sizes to better fit differently sized
production tubing. The size of the bearing is selected to have an outer
diameter
less than the inner diameter of the production tubing, thereby leaving space
between the bearing and the tubing wall through which the fluid being produced
by operation of the downhole pump can pass, even when part of the bearing's
outer surface is in contact with the tubing wall. Other bearings may be used,
or
sleeves or wheels of metal, plastic or other materials may be fitted about the
coupler body using an interface other than rollers elements but of low enough
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friction between the sleeve and body to allow relative rotational motion
therebetween about the longitudinal axis. The use of any such rotatable outer
member disposed about a central body that not only forms the spinning core or
shaft carrying the outer member but also forms coupling sections for direct
connection to sucker rods without requiring separate additional couplers
between
the body and the sucker rods presents advantage over prior art arrangements
requiring fastening together of multiple separate pieces to achieve both a
wear
preventing function and coupling of adjacent sucker rods.
Accordingly, embodiments using only one outer member rotatable
relative to the central coupling body would still provide such advantage over
the
prior art, just as embodiments lacking a specific section for engagement by a
wrench would share this advantage. The first illustrated embodiment provides
further benefit by using two outer members at spaced positions along the
central
body to better resist deviation of the body's axis sufficiently out of line
with the
well bore axis to, and even further benefit by providing a central wrench
engagable portion disposed between, and thus left uncovered and unobstructed
by, the two outer members.
Figures 5 and 6 show a second embodiment sucker rod coupler
that uses a single plastic sleeve to provide the contact area of the coupler
with
the production tubing instead of the two bearings of the first embodiment.
Carrying only a single sleeve, the coupler unit of this embodiment is
significantly
smaller than that of the first embodiment and has a simpler overall structure,
meaning that the coupler may be produced at a lower cost and marketed as a
more cost efficient option than the first embodiment.
With reference to the exploded view of the coupling in Figure 6, the
coupler unit 10' of the second embodiment is again defined by a single
integral
unitary body of rigid material having an elongated shape oriented to lie
lengthwise on a longitudinal axis 12' passing centrally therethrough. Along
its
length, the body 10' features a first coupling section 14' defining a planar
first end
16' of the body and a second coupling section 18' defining an opposite planar
second end 20' of the body. The second embodiment lacks the wrench section
of the first embodiment. Each coupling section 14', 18' features a respective
cylindrical portion of the body that has been hollowed by formation of a
single
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bore 24' extending fully through the body from the on planar end face thereof
to
the other to form a single internal passage into each end of which the pin end
of a
sucker rod can be received. The bore 24' has a circular cross section
concentric
with the circular cross section of the cylindrical body portions through which
it
passes and, as shown in broken lines in Figure 6, is threaded according to the
thread pattern of an externally threaded male or pin end of a conventional
sucker
rod to facilitate threaded engagement of the pin ends of two sucker rods into
the
threaded internal passage from opposite ends of the coupler body 10'.
Still referring to Figure 6, at a distance along the longitudinal axis
12' from each end face 16', 20' of the coupler body 10', the outer diameter of
the
coupling section 14, 18 features a single step change, decreasing from the
upper
first coupling section 14' to the lower second coupling section 18'. A
shoulder
formed at this change in diameter of between the two coupling sections 14',
18'
defines a [edge in the form of an annular stop face or surface 32' projecting
radially outward from the smaller diameter lower coupling section 18' in a
plane
normal to the longitudinal axis 12'. A circumferential groove 34' in the outer
peripheral surface of the smaller diameter lower coupling section 18' extends
fully
therearound about the longitudinal axis at a location therealong a short
distance
inward from the bottom end face 20' of the coupler body 10'.
With reference to Figure 5, the final structure of the sucker rod
coupling of the second illustrated embodiment is completed by installation of
a
sleeve 36' and snap ring 37' on the lower coupler section 18' of the coupler
body
10'. The plastic sleeve 36' has a cylindrical outer surface closing around the
longitudinal axis 12' and a cylindrical inner bore centered thereon. The
sleeve
36' is disposed about the smaller diameter lower coupling section 18' with the
bore diameter of the sleeve 36' slightly exceeding the outer diameter of the
lower
coupling section 18' so that the sleeve 36' is accordingly rotatable relative
to the
coupler body 10' about the longitudinal axis 12'.
The larger diameter upper coupler section 14' of the coupler body
10' locates the sleeve 36' along the longitudinal axis 12' under sliding of
the
sleeve 36' onto the coupler body 10' from the bottom end 20' thereof during
assembly of the sucker rod coupling, this large diameter coupling section 14'
acting as a stop to limit movement of the sleeve toward the top end 16' of the
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coupler body 10' when the end face of the bearing reaches the ledge or stop
surface 32' at the juncture between the coupling sections 14', 18'. The snap
ring
37' is then engaged into the groove 34' on the side of the sleeve 36' opposite
the
large diameter stop-defining upper coupling section 14' to complete the
5 positioning of the sleeve 36' along the longitudinal axis 12' by blocking
movement
of the sleeve 36' away from the upper coupling section 14' to the bottom end
20'
of the coupler body 10. The snap ring 37' thus provides a removable stop
element that can be installed and removed as needed to allow for possible
removable of the sleeve 36' by sliding off the bottom end of the coupling unit
if
10 required, the installation of the snap ring 37' forming a stop deployed on
the
coupler body 10 to project radially outward from the outer peripheral surface
of
the smaller diameter lower coupling section 18' to block sliding movement of
the
installed sleeve 36' past it along the longitudinal axis.
Figure 7 shows the sucker rod coupling in use within the bore of a
15 well. The threaded internal passage 24' of the coupling unit 10' has been
engaged at its top end with the externally threaded pin end 126a at the bottom
of
a sucker rod 126 disposed above the coupling in the well bore 100, and at its
bottom end with the externally threaded pin end at the top of a sucker rod
disposed below the coupling in the well bore 100 so that the coupling body 10
acts to couple the two sucker rods together and accordingly forms part of the
overall sucker rod string that is driven for rotation to operate a downhole
pump.
The sleeve 36' of the coupling extends outwardly beyond any and all portions
of
the coupler body 10' in radial planes normal to the longitudinal axis 12'
thereof.
The outer peripheral surfaces of the outer sleeve 36' facing outwardly away
from
the coupler body relative to the longitudinal axis 12' accordingly define the
radially outermost extents of the coupling, and therefore define cylindrical
contact
surfaces that will contact the surrounding cylindrical inner wall surface of
the
production tubing 102 before any portion of the two sucker rods and the
coupler
body therebetween is allowed to reach the production tubing 102 under
movement of this rod string portion out of alignment with a central axis of
the
section of the production tubing string 102. With frictional contact between
the
sleeve and the surrounding tubing wall 102 closing thereabout, the sleeve is
stationary with respect to rotation about the longitudinal axis while the
coupler
CA 02772666 2012-02-29
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16
body 10' is rotated about the longitudinal axis 12' by the driven rotation of
the
sucker rods. Accordingly, there is no relative movement between the sleeve
contact surfaces that make contact with the production tubing, and so wear of
the
tubing that would otherwise occur under contact of any part of the spinning
rod
string with the production tubing is avoided. If the sleeve does rotate
somewhat
under the driven rotation of the string, it will be at significantly reduced
speed
compared to that of the string, and so the degree of wear is still reduced
from
what would occur without use of the coupling.
The second embodiment coupler thus operates similar to the first
embodiment and shares the same advantage of direct coupling to the sucker
rods it connects in order to avoid use of box connection pieces separate from
the
single body piece around which the outer member (whether a bearing or sleeve)
rotates. The two illustrated embodiments also share the advantage that each
such outer member is selectively removable from the coupler unit for
replacement, by disengagement of the snap ring from the groove adjacent the
end of the coupler unit to allow sliding of the outer member off that end of
the
unit. Both embodiments make use of the lower coupling section to not only
provide the threaded coupling to the respective sucker rod, but also to
provide a
bearing or sleeve carrying portion of the coupler, with the first embodiment
likewise having such dual functionality of the upper coupling section. This
dual
functionality provides material savings in reducing that size of the overall
coupler,
thus saving on production cost.
With reference to Figure 7, the second embodiment provides further
advantage by having the outer diameter of the upper coupling section 14' equal
to the outer diameter of the pin shoulder 126b of the sucker rods 126 in the
string. This way, should there be a failure at the pin connection 126a of the
sucker rod 126 above the coupler to the coupler unit 10', a conventional
overshot
fishing tool suitably dimensioned for compatibility in drawing out the size of
sucker rod used in the string by its pin shoulder 126b can be used to fish out
the
coupler and the sucker rods connected below it by gripping the coupler unit
10' at
the outer peripheral surface of its upper coupling section 14'. This way, no
new,
different or specialized fishing tool is required to retrieve the remaining
rod string
portion stuck in the wellbore, as an existing sucker-rod fishing tool
configured for
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17
the known sucker rod size can be employed in the conventional manner to grip
the upper coupling section 14' of the sucker rod coupler in the same manner as
it
would typically be used to grip the pin shoulder of one of the sucker rods. As
shown in Figure 7, the overall length of the coupler unit only slightly
exceeds the
combined length of the pins of the two sucker rods connected by it, which
combines with the dual functionality of the lower coupling section 18' to make
efficient use of material in the smaller resulting coupling. The lower
coupling
section 18' is just long enough to fit the axial length of the sleeve 36'
between the
groove positioned at the bottom end of the coupler unit and the shoulder-like
stop
defined the joint of the two coupling sections 14', 18'.
A prototype of the second embodiment coupler uses a roller-like
piece of virgin ultra high molecular weight polyethylene (RecoTM UHMW-PE
natural virgin from Redwood Plastics Corporation) to provide a sleeve having a
high impact strength, high chemical and wear/abrasion resistance and low
coefficient of friction, but it will be appreciated that sleeves of other
materials may
alternatively be employed. Likewise, although the illustrated sleeve 36'
features a
continuously curved cylindrical outer surface, it will be appreciated that
other
sleeve shapes of non-circular cross section may be similarly employed to
provide
tubing contact surfaces radially outward from the rest of the coupler. For
example, U.S. Patent Numbers 4,757,861 and 4,919,202 show how a vaned
wheel of elastomeric material or fluted and/or notched tubular sleeve of soft
resilient abrasion resistant material may be used to contact the well tubing
around a sucker rod string while providing significant open areas in the wheel
or
sleeve's cross section to ensure that fluid can flow past it. Such material
and
shape configurations may similarly be employed in the present invention in
place
of the illustrated second embodiment sleeve of substantially cylindrical shape
(purely cylinder outer surface, except at short tapered end portions of the
sleeve)
or illustrated first embodiment bearing(s).
Since various modifications can be made in my invention as herein
above described, and many apparently widely different embodiments of same
made within the spirit and scope of the claims without department from such
spirit
and scope, it is intended that all matter contained in the accompanying
specification shall be interpreted as illustrative only and not in a limiting
sense.
