Note: Descriptions are shown in the official language in which they were submitted.
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COMPOSITE SUCKER ROD ASSEMBLY FOR UNDERGROUND WELLS
Related Applications
The present application is a continuation-in-part and claims priority to U.S.
Provisional
Application No. 62/003,437 filed May 27, 2014, and is a continuation-in-part
and claims priority
to U.S. Provisional Application No. 61/903,194 filed November 12, 2013, both
of which are
hereby incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
The present invention relates generally to sucker rod engineering and design.
More
particularly, the present invention relates to a composite sucker rod assembly
for use in down-
hole vertical lift oil extraction.
Sucker rods for use with vertical lift rod pumps, also referred to as surface
units, rocking
horse, or pump jacks are typically made from individual lengths of steel rod
sections that are
connected together by threaded couplings. The individual sucker rods are
typically 25 feet, 30
feet or 37.5 feet in length and are connected together with couplings to form
a sucker rod string.
A typical sucker rod string is from 700 to 10,000 feet or more in length. The
sucker rod string
connects the vertical lift surface device to the down-hole pump unit.
Traditional metal sucker
rods are heavy and subject to corrosion and fatigue failure, particularly at
the threaded
connections or due to stress corrosion cracking. An unexpected broken sucker
rod due to
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corrosion and/or fatigue is expensive to remove and replace. Further, the
weight of a metal
sucker rod string limits its strength and fatigue life and can limit the depth
which even large
surface units can pump. The weight of a steel sucker rod string can also
overload and reduce the
life of the surface unit and its components. Monolithic fiberglass sucker rods
have also been in
use for some time. Fiberglass sucker rods do offer a weight reduction and
corrosion resistance
but have significant stretch and are prone to splitting and failing due to
transient compression in
the rod string.
Current sucker rod technology consists of wrought steel rods that are
typically 3/4 inch
diameter, 7/8 inch diameter, 1 inch diameter, or 1 and 1/8 inch diameter. The
ends of the rods
are formed to include a wrench location and machined threads to interface with
couplings that
join the individual rods together. The typical steel sucker rod lengths are 25
feet and 30 feet. A
string of segmented sucker rods is connected between the vertical lift pumping
unit at the surface
and the down-hole pump at or near the bottom of the oil well. Shorter rods
often called "Pony
Rods" are used to fine tune the overall length of the sucker rod string and
the position of the
pump down-hole. Sinker Bars (larger diameter heavy rods) are used at the
bottom of the well to
weight the entire string for the down stroke. The sucker rods reciprocate up
and down in a tube
that is typically steel and suspended in the wellbore or casing. No well is
perfectly straight.
Steel sucker rods are stiff and often cause excessive wear on the inside of
the well casing where
the well is not straight. Additionally, the flex in the string induced by
pumping causes metal
fatigue which can cause the sucker rod to fail. The highly corrosive
environment worsens the
frequency of rod failures.
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Monolithic fiberglass sucker rods have been developed. The fiberglass rods
have steel-
end fittings bonded over the outside surface of each end of the monolithic
fiberglass rod.
Fiberglass sucker rods are typically larger in diameter compared to their
steel counterparts.
Fiberglass sucker rods have a lower tensile modulus than steel or carbon fiber
and therefore
exhibit more stretch than steel or carbon fiber. Fiberglass sucker rods are
lighter than steel but
have been known to suffer premature failure if subjected to any compression
loading during the
pumping cycle.
A carbon fiber composite sucker rod pultruded as a monolithic bar and meeting
the
typical requirements of a sucker rod would not be attractive because it would
be subject to
compression failures similar to fiberglass and it would be difficult to make
the terminus end
fitting match the strength potential of the carbon fiber composite mid-section
since it would be
merely glued on the outside of the monolithic rod versus tying into the
majority of the fibers.
A continuous length steel sucker rod is also used in a small but increasing
percentage of
oil wells. Steel continuous length sucker rods require large diameter spools
and special handling
techniques. Continuous steel sucker rods are limited in the length that can be
practically used due
to weight, transportation and handling issues. Continuous length steel sucker
rods are heavy,
corrode, and are subject to fatigue failure.
Accordingly, it would be desirable to provide a sucker rod assembly that can
meet or
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exceed all operational requirements and offer significant weight reduction,
complete corrosion
resistance, deeper pumping capability, less maintenance, longer life and
overall improved oil
production economics, thus having pumping performance and service life
advantages over
previous sucker rods.
SUMMARY OF THE INVENTION
The present invention addresses the aforementioned disadvantages by providing
an
improved sucker rod assembly for use in down-hole vertical lift oil
extraction.
The sucker rod assembly of the present invention comprises a plurality of
parallel
composite strength elements, referred to herein as "strands" to create a light
weight, corrosion
and fatigue resistant sucker rod assembly. Preferably, the strands are made of
carbon fiber, and
will be described primarily as employing carbon fiber. However, other
composite materials may
be employed, and the invention is not intended to be limited to carbon fiber.
In a preferred embodiment, the sucker rod assembly strands are made of carbon
fiber
manufactured by the pultrusion process or variation thereof wherein high
strength fibers are
drawn through a resin bath to impregnate the fibers, and then drawn through
heated dies and
ovens to shape, consolidate and cure the strands into generally round or
polygonal cross-sections
such as hexagons or octagons. Carbon fiber is a preferred material for the
sucker rod assembly
but fiberglass or other high strength fibers may also be utilized so long as
they are tailored to
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meet the strength and stiffness requirements for the sucker rod assembly
application. The fiber
fraction of the strands should be optimized for tensile strength, stiffness,
durability and handling.
Additionally, the plurality of the strands that make up the sucker rod
assembly should be straight
and equal in length in order to maximize the overall strength of the sucker
rod assembly.
In a preferred embodiment, the high strength carbon fibers within a polymer
matrix are
bundled together in parallel to form an elongate rod. Furthermore, by altering
the number of
strands allows for tailoring the mechanical properties of the sucker rod
assembly and the sucker
rod string. A larger bundle of strands is used for the sucker rods at the top
of the well (near the
surface) since the upper sucker rods must carry the weight of the entire
sucker rod string. A
smaller bundle of strands is used for the sucker rods near the bottom of the
well since the tensile
stress is lower, although the weight of the lifted oil must also be taken into
account. The overall
sucker rod string is configured to meet strength and longitudinal stiffness
requirements and
optimize pumping efficiency. A carbon fiber sucker rod assembly of this
configuration has been
demonstrated to be approximately one-fifth the weight of steel sucker rods
while retaining
comparable strength. As a result, the sucker rod assembly of the present
invention will have
pumping performance and service life advantages over conventional steel or
monolithic
fiberglass sucker rods and continuous length steel sucker rods.
The sucker rod assembly includes a terminus fitting at one end of the rod, and
preferably
at both ends of the rod. Preferably, the terminus fittings are made of metal
such as a high carbon
steel. However, other metals or materials may be employed. Each terminus
fitting has a
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proximal end, a distal end, and a central cavity which extends to the terminus
fitting's proximal
end to form a proximal opening for receipt of the elongate rod into the
cavity. The cavity flares
outwardly from the fitting's proximal end toward said fitting's distal end. In
a preferred
embodiment, the terminus fitting's central cavity extends from the fitting's
proximal opening to
the terminus fitting's distal end to form a distal opening. The distal opening
may include a
female thread for affixing to a male threaded member.
The elongate rod's plurality of strands are splayed-out within the terminus
fitting and
encapsulated with a polymer resin or ceramic material which hardens within the
terminus
fitting's cavity to form a tapered wedge that holds the terminus fitting in
place on the plurality of
strands. The terminus polymer or ceramic wedge is cast by injecting the
material into an
injection port which projects through the side of the terminus fitting. When
injected into the
injection port, the material fills the space around the strands. A vent is
provided to allow air to
vent from the central cavity and to give a visual assurance that the tapered
cavity is properly
filled with material.
The tapered cavity is preferably conical and injected or filled with a polymer
material that
adheres to the strands to form a mechanical cone shaped wedge within the
terminus fitting. The
polymer material for the terminus wedge can be epoxy, phenolic or other
thermosetting resin
meeting the performance requirements. For extremely deep wells, a heat
resistant ceramic
material may be used for the terminus wedge. A preferred method for assembling
the carbon
fiber sucker rod assembly is to inject the polymer or ceramic material
directly into the terminus
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fitting. Preferably, two ports in the terminus fitting are used for the wedge
material injection.
One port is an injection port to inject the polymer or ceramic into the
fitting. The other port is a
vent hole which provides a temporary vent and a sight window to show that
adhesive resin has
filled the tapered cavity. Preferably, the polymer or ceramic wedge material
is injected into the
terminus fitting while the terminus fitting is lying in a horizontal position.
Preferably, at least one spreader plate is positioned within the terminus
fitting's cavity.
The spreader plate is preferably planar and substantially round so as to
define a central axis.
Preferably, the spreader plate is positioned within the terminus fitting's
central cavity with the
spreader plate's central axis coincident with the cavity's central axis.
Preferably, the spreader
plate has a diameter slightly smaller than the diameter of the terminus
fitting's cavity at the
spreader plate's location within the central cavity. The spreader plate has a
plurality of holes
which receives the rod strands so as to splay out the strands in a widened
orientation compared to
where the strands enter the terminus fitting's proximal opening.
Preferably, the spreader plate is constructed of two or more pieces wherein
each piece
includes an engagement edge for engaging an engagement edge of an adjoining
piece.
Preferably, the pieces are held together to form a single spreader plate
simply by the rod strands
forcing the pieces radially together to engage one another. Also preferably,
the engagement
edges of the spreader plate pieces include one or more indents for engaging
indents formed in the
engagement edges of adjoining pieces so that adjoining indents of adjoining
pieces form holes
which receive the strands. In preferred embodiments, the spreader plate pieces
also include a
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peripheral edge where the pieces do not engage an adjoining piece such as
where the spreader
plate periphery is adjacent to the terminus fitting's cavity wall. It is
preferred that the peripheral
edge of each piece include one or more indents for receiving and splaying out
one or more
strands in a widened orientation compared to where the strands pass through
said terminus
fitting's proximal opening.
In an alternative embodiment, an annular spacer is applied over the ends of
the strands to
maintain the strands in a splayed configuration within the terminus fitting
while a polymer is
injected into the fitting and cured. For this embodiment, it is preferred that
the annular spacers
are positioned longitudinally on the strands at approximately the same
location so as to engage
one another. Alternatively, the annular spacers may be longitudinally
positioned at different
locations so as to engage adjoining strands.
The sucker rod assembly includes a connection member for connecting to other
sucker
rod assemblies or other equipment. A preferred connection member has a male
threaded end
which affixes to the terminus fitting's female thread. Preferably, the
connection member
projects into the cavity sufficient such that the connection member engages
the tapered wedge to
place the wedge in a state of compression. This construction results in
putting a pre-load on the
tapered wedge which enhances its ability to handle cyclic tension and
compressive loads.
The preferred method to compress the wedge within the terminus fitting is to
inject the
polymer or ceramic material into the terminus with the threaded connection
member backed out
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slightly from its final (not fully torqued) position. After the wedge is
cured, the threaded
connection member is fully screwed in place and torqued as appropriate.
Another option is to
use a dummy connection member when the polymer or ceramic wedge is injected
into the fitting.
This dummy connection member can be slightly shorter than the final connection
member so a
compressive load is applied to the wedge when the final connection member is
installed.
A minimum number of strands are preferably bundled together to form a length
of the
composite sucker rod assembly. The plurality of parallel strands may be fully
over-wrapped
with an encapsulating layer of composite or polymer material that holds the
bundle together and
provides a wear resistant covering. The over-wrap may also be spaced
incrementally to keep the
bundle together, thereby increasing the overall stiffness of the sucker rod
assembly and providing
tailored dampening for compressive loads. The bundle of strands is preferably
held together
with a composite wrap spaced incrementally sufficient to hold the bundle of
rods together but
allow them to flex between the wrap if the rod experiences a compressive load.
The spacing and
the length of the incremental composite wraps can be used to tailor the
compressive stiffness of
the overall carbon composite sucker rod assembly.
The plurality of parallel strands are preferably bundled in a generally
polygonal or round
package so the sucker rod assembly can be progressively rotated in a well
tubing as typically
done to prevent wear in one spot. It is also necessary for the strands to
splay-out evenly in the
terminus without crossing one strand over another.
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Wear guides and paraffin scrapers may be installed along the length of the
composite
sucker rod assembly after it is assembled. Wear guides are typically used only
on sucker rods
running in a deviated portion of the oil well. A preferred method is to mold a
fiber filled
composite wear guide directly onto the bundle of strands. This can be
accomplished by infusion
molding a relatively thick three dimensional fiber mat that is wrapped around
the strands bundle.
A two piece mold is clamped around the wrapped fiber form. Thermosetting epoxy
is injected
into the mold and flows through the porous spun polyester material. When
cured, the mold is
removed. The three dimensional spun polyester mat impregnated with epoxy forms
a wear
resistant composite particularly suited for application that is permanently
bonded over the sucker
rod. Advantageously, the wear guides can also function as wraps incrementally
spaced to
provide the desired compressive dampening and rod stifthess, as described
above. A preferred
method is to mold the composite wear guide over an incrementally spaced band
in order to
maintain the desired band spacing.
In another embodiment, woven fiberglass, carbon fiber or aramid fiber cloth
tape can be
convolutely wrapped with resin around the bundle of carbon fiber rods such
that it functions both
as a wear band and the banding that holds the plurality of rods together.
Other features and advantages of the present invention will be appreciated by
those
skilled in the art upon reading the detailed description which follows with
reference to the
attached drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded perspective view of a composite sucker rod assembly of
the present
invention;
FIG. 2 is a side cut-away view of a composite sucker rod assembly of the
present
invention;
FIG. 3 is an exploded cut-away view of a composite sucker rod assembly of the
present
invention;
FIG. 4 is a side cut-away view of a composite sucker rod assembly of the
present
invention illustrating a first cavity configuration;
FIG. 5 is a side cut-away view of a composite sucker rod assembly of the
present
invention illustrating a second cavity configuration;
FIG. 6 is a side cut-away view of a composite sucker rod assembly of the
present
invention illustrating a third cavity configuration;
FIG. 7 is a side cut-away view of a composite sucker rod assembly of the
present
invention illustrating injection of resin into the cavity;
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FIG. 8 is an exploded perspective view of a spreader plate of the present
invention;
FIG. 9 is a perspective view of a spreader plate of the present invention;
FIG. 10 is a top view of a first spreader plate of the present invention;
FIG. 11 is a top view of a second spreader plate of the present invention;
FIG. 12 is a top view of a third spreader plate of the present invention;
FIG. 13 is a top view of a fourth spreader plate of the present invention; and
FIG. 14 is a side view of a sucker rod assembly of the present invention
including wear
guides.
DETAILED DESCRIPTION OF THE INVENTION
While the present invention is susceptible of embodiment in various forms, as
shown in
the drawings, hereinafter will be described the presently preferred
embodiments of the invention
with the understanding that the present disclosure is to be considered as an
exemplification of the
invention, and it is not intended to limit the invention to the specific
embodiments illustrated.
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With reference to the figures, the sucker rod assembly 10 includes a plurality
of strands
20 forming an elongate rod 15. The sucker rod assembly 10 further includes a
terminus fitting
30 having a central cavity 33, a spreader plate 22, and connection member 45.
A plurality of
sucker rod assemblies are connected together to form a sucker rod string 11 to
connect a vertical
lift surface device to a down-hole pump unit.
As illustrated in FIGS. 1 ¨ 14, the composite sucker rod assembly 10 comprises
a
plurality of generally round strands 20 that are bundled together to form the
elongate rod 15.
The tensile strength and stiffness of the composite rod assembly 15 is
determined by the
composite materials used for the individual strands 20, the size of the
strands 20, and the number
of strands 20 bundled together to make the rod 15. In preferred embodiment,
the carbon
composite sucker rod strands 20 are manufactured by the pultrusion process or
variation thereof
wherein high strength fibers are drawn through a resin bath to impregnate the
fibers and then
through heated dies and ovens to shape, consolidate and cure the strands 20
into generally round
rods or similar shapes such as hexagons or octagons. Carbon fiber is the
preferred material for
the plurality of parallel strands 20 but fiberglass or other high strength
fibers may also be utilized
so long as they are tailored to meet the strength and stiffness requirements
for the sucker rod
assembly application.
The polymer matrix within the strands 20 may be epoxy, polyester, vinyl ester,
cyanurate
ester, benzoxyzene, phenolic or other suitable thermosetting resins.
Thermoplastic polymer
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matrices such as PEI, PEEK, PPS or other suitable polymers may also be used by
modifying the
pultrusion process to heat, consolidate and shape, and chill the polymer and
fiber matrix into
usable composite strands. The fiber fraction of the strands 20 should be
optimized for tensile
strength, stiffness, durability and handling. The ideal size of the strands 20
is roughly from 1/8th
inch diameter to 3/16th inch diameter although other sizes may be used and the
ideal size may be
dependent on processing and assembly requirements.
Generally, the smaller the diameter of the strands, the faster it can be
pultruded because
of faster resin curing. A thick pultruded cross section is slow to cure.
Additionally, a larger
number of strands can be pultruded at the same time when they have a small
diameter versus a
large diameter. The cross sectional area of typical sucker rods can be
pultruded at roughly 10
times the through-put speed when they are made as a plurality of strands
versus as a monolithic
rod, as such this lowers production cost. Even with the additional steps to
cut and bundle the
strands, the overall production cost of a carbon fiber composite sucker rod
made from a plurality
of strands is generally lower than an equivalent monolithic version. However,
it is also
necessary for the strands to be large enough in cross section for ease of
handling and to lay
straight in the tooling used for assembly of the sucker rod. Thus, the
plurality of the strands 20
that make up the rod 15 should be straight and equal in length in order to
maximize the overall
strength of the rod 15. If one strand is shorter than the others in the
bundle, then that strand is
loaded more than the others and would fail prematurely under a tensile load
condition.
Experience has shown that it is preferred that the strands 20 be approximately
1/8 inch or larger
in diameter to be stiff enough to be assembled in typical assembly tools
maintaining equal length
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and straightness of the strands 20 without methods to pre-tension the strands.
Unlike prior
manufacturing processes, tensioning the strands 20 during assembly is not
necessary as that
would be time consuming and costly.
A minimum number of strands 20 are preferably bundled together to form a
length of the
elongate rod 15. As illustrated in FIG. 14, the bundle of strands 20 is
preferably held together
with composite wraps 50 spaced incrementally sufficient to hold the bundle of
rods together, but
allow them to flex between the wrap 50 if the rod experiences a compressive
load. The spacing
and the length of the incremental composite wraps 50 can be used to tailor the
compressive
stiffness of the overall carbon composite sucker rod 50. Experience has shown
that spacing the
composite wraps 50 and/or wear guides at approximately 10-30 times the bundle
diameter is
ideal to provide compressive dampening yet make the overall rod stiff enough
for handling.
Even more preferably, the composite wraps 50 and/or wear guides (described
below) are spaced
at 15-25 times the bundle diameter, and the preferred distance between wraps
is approximately
20 times the bundle diameter.
The plurality of parallel strands 20 are preferably bundled in a generally
polygonal or
round package so the sucker rod assembly 10 can be progressively rotated in a
well casing as
typically done to prevent wear in one spot. It should be noted that the
diameter of the carbon
fiber sucker rod assembly 10 is significantly less than its equivalent steel
counterpart. For
example, the equivalent carbon fiber sucker rod assembly 10 replacing a 1-1/8
inch diameter
steel sucker rod is just under 1 inch diameter.
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The sucker rod assembly's terminus fittings 30 may be affixed at one or both
ends of the
sucker rod assembly 10. The terminus fittings are preferably made of metal,
and more preferably
made of a high carbon steel. Other materials including carbon fiber may be
employed.
However, they are not preferred. Each terminus fitting 30 has a proximal end
31 and a distal end
32. A cavity 33 extends the length of the terminus fitting from its proximal
end to its distal end
so as to form a proximal opening 35 and a distal opening 36. The cavity 33 has
a tapered
construction so as to have a smaller diameter at its proximal opening 35 than
toward its distal
end. In a preferred embodiment, the central cavity has a conical section 37
towards the terminus
fitting's proximal end 31 and a substantially cylindrical section 38 towards
the terminus fitting's
distal end 32. The cavity's proximal opening 35 is sized to receive one end of
the elongate rod
15 and its individual strands 20. Preferably, the cavity's distal opening 36
includes a female
thread 41 for affixing to a male threaded member.
To lock the strands 20 within the terminus fitting's cavity 33, the strands
are splayed out
so as to have a diameter greater than the terminus fitting's proximal opening
35. To maintain the
strands 20 in a splayed out condition, the sucker rod assembly 10 includes a
spreader plate 22
positioned within the terminus fitting's cavity 33. The spreader plate is
preferably planar and
substantially round so as to define a central axis. In addition, the spreader
plate 22 has a plurality
of holes 23 for receiving the rod strands 20 so as to splay the strands in a
widened orientation
compared to where the strands enter the terminus fitting's proximal opening
35. To position the
spreader plate within the terminus fitting's central cavity, the spreader
plate has a diameter
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slightly smaller than the diameter fitting's cavity 33 where the spreader
plate has been positioned
within the cavity 33. Furthermore, preferably the spreader plate's central
axis is coincident with
the cavity's central axis. As would be understood by those skilled in the art,
the diameter of a
preferred spreader plate would be smaller when positioned within the cavity's
conical section 37
than if the spreader plate 22 were positioned in the cavity's cylindrical
section 38.
As illustrated in FIGS. 8 ¨ 13, the spreader plate 22 is constructed of two or
more pieces
24 wherein the pieces can be arranged to adjoin one another to form a single
spreader plate 22.
Each of the spreader plate pieces 24 include an engagement edge 25 where it
engages the
engagement edge of an adjoining piece 24. Preferably these engagement edges 25
include
indents 27 which align and adjoin indents formed in adjoining pieces to form
holes 23 for
receiving the rod strands 20. Moreover, the spreader plate pieces 24 also
include a peripheral
edge 26 where the pieces do not engage an adjoining spreader plate piece 24.
It is preferred that
these peripheral edges also include indents 27 sized for receiving a rod
strand 20. As illustrated
in FIGS. 2 and 3, strands within the peripheral edge indents are constrained
by the terminus
fitting's cavity sidewall. The peripheral edge indents 27 also maintain the
strands 20 in a
widened orientation compared to where the strands pass through the terminus
fitting's proximal
opening 35. The sucker rod assembly 10 may include any number of spreader
plates so as to
maintain the strands 20 properly aligned and positioned to prevent withdrawal
of the elongate
rod 15 from the terminus fitting 30. For example, FIG. 5 illustrates a sucker
rod assembly 10
with two spreader plates 22.
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In an alternative embodiment, the sucker rod assembly includes a plurality of
annular
spacers wherein an annular spacer is applied over the ends of each the strands
to maintain the
strands in a splayed configuration. For this embodiment, the annular spacers
may be positioned
longitudinally upon the strands at approximately the same location so that the
periphery of each
annular spacer engages the periphery of an adjoin spacer. Alternatively, the
annular spacers may
be longitudinally positioned at different locations so that the periphery of
an annular spacer
engages adjoining strands.
As illustrated in FIGS. 5 and 6, terminus fitting's tapered cavity 33 may
include a conical
section 37 and a cylindrical section 38. If it is desirable to minimize the
size of the terminus
fitting 30, the cavity's conical section 37 can be shorter in length provided
the overall cavity
length is retained. More specifically, shortening the length of the conical
section 37 while
retaining the overall length of the cavity 33 enables one to maintain the
wedge effect of affixing
the rod 15 to the terminus fitting 30 and thus maintain the overall adhesive
shear strength of the
wedge 21 to the rod 15 when the size of the fitting is constrained. For
example, FIG. 7 illustrates
a terminus fitting where the conical portion 37 is shorter than the
cylindrical portion 38.
Conversely, FIG. 6 illustrates a terminus fitting where the conical portion 37
is longer than the
conical portion illustrated in FIG. 5.
The terminus fitting's cavity 30 (as illustrated in FIG. 7) is preferably
injected or filled
with a polymer material that adheres to the strands 20 and forms a mechanical
tapered wedge 21
within the terminus fitting 30. The polymer material for the wedge 21 can be
epoxy, phenolic or
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other thermosetting resin meeting the performance requirements. For extremely
deep wells, a
heat resistant ceramic material may be used within the terminus cone. In
contrast to traditional
potted steel wire rope terminations where resin or molten metal is poured into
the open end of
the terminus, the preferred method for assembling the carbon fiber sucker rod
10 is to inject the
polymer or ceramic resin material directly into the terminus fitting 30.
Preferably, an injection
port 39 and vent port 40 are used for the resin material injection. The
injection port 39 is
provided to inject the polymer or ceramic resin into the fitting 30. The vent
port provides a
temporary vent and a sight window to show that adhesive has filled the cavity
30. Preferably,
the polymer or ceramic material is injected into the injection port 39 while
the terminus fitting 30
is lying in a horizontal position. It is important to assemble the composite
sucker rod 10 in a
horizontal position with the plurality of strands 20 supported substantially
straight and in the
desired bundle configuration with the terminus end fittings 30 properly
aligned before the resin
material is injected into the terminus fitting's injection port 39. It is also
important for the
splayed orientation of the strands 20 to be configured properly and
consistent.
As illustrated in FIGS. 3 - 7, in a preferred embodiment, the sucker rod
assembly 10
includes a threaded connection member 45 to interface with a standard sucker
rod coupling that
connects rod to rod to form a sucker rod string. In another embodiment, the
threaded connection
member 45 can be applied on only one end of the sucker rod 10 and no threaded
connection
member is affixed to the other end. This enables one sucker rod 10 to be
coupled to another
without the use of traditional sucker rod couplings. Instead, the connection
member 45 of one
sucker rod assembly 10 threads into the female threaded opening 36 of the
other sucker rod
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assembly 10.
Further, in a preferred embodiment, it is desirable to compress the hardened
resin wedge
21 with the male threaded portion of the connection member 45 as a means to
firmly hold the
wedge 21 in position within the terminus fitting 30, especially when it is
anticipated that the
sucker rod assembly will experience compressive loads. The preferred method to
compress the
wedge 21 within the terminus 30 is to inject the polymer or ceramic resin into
the terminus 30
with the threaded connection member 45 backed out slightly, for example,
approximately 1/8 to
1/2 turn, from its final position or not fully torqued. As a result, the
wedge 21 will be in-situ
molded within the terminus 30. After the wedge 21 is cured, the threaded
connection member 45
is fully screwed in place and torqued as appropriate. This method results in
putting a pre-load on
the wedge 21 which enhances its ability to handle cyclic tension and
compressive loads. Another
option is to use a dummy connection member (not shown) when the polymer or
ceramic wedge
is injected into the fitting 30. This dummy connection member can be slightly
shorter than the
final connection member 45 so a compressive load is applied to the wedge 21
when the final
connection member 45 is installed.
As illustrated in FIG. 14, wear guides 50 and/or paraffin scrapers may be
installed along
the length of the composite sucker rod assembly 10. Wear guides 50 are
typically used only on
sucker rods running in a deviated portion of the oil well. Traditional wear
guides are made from
a thermoplastic polymer and are pre-molded and snapped in place or injection
molded directly
onto the steel sucker rod. Traditional wear guides often do not stay in place
during operation.
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For a preferred sucker rod 10 of the present invention, a fiber filled
composite wear guide
50 is molded directly onto the bundle of strands 20. This can be accomplished
by infusion
molding a relatively thick three dimensional fiber mat that is wrapped around
the strands bundle.
In a preferred example, the fiber form is a wear resistant spun polyester mat
made by 3M that is
from 1/4 to 3/8 inch thickness. In one example, a 3 - 4 inch wide by 9-12 inch
long strip of 1/4 inch
thick spun polyester mat is wrapped around the plurality of strands 20 of the
sucker rod assembly
at the location desired for the wear guide 50. A two piece mold is clamped
around the
wrapped fiber form. Thermosetting epoxy is injected into the mold through an
injection port to
flow through the porous spun polyester material. When cured, the mold is
removed. The three
dimensional spun polyester mat impregnated with epoxy forms a wear resistant
composite
particularly suited for application that is permanently bonded over the sucker
rod assembly 10.
Advantageously, as illustrated in FIG. 14, the wear guides 50 can also
function as wraps
incrementally spaced to provide the desired compressive dampening and rod
stiffness, as
described above. In another embodiment, woven fiberglass, carbon fiber or
aramid fiber cloth
tape can be convolutely wrapped with resin around the bundle of carbon fiber
rods such that it
functions both as a wear guide and the banding that holds the plurality of
rods together.
While several particular forms of the invention have been illustrated and
described, it will
be apparent that various modifications can be made without departing from the
spirit and scope
of the invention. Therefore, it is not intended that the invention be limited
except by the
following claims. Having described my invention in such terms so as to enable
person skilled in
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the art to understand the invention, recreate the invention and practice it,
and having presently
identified the presently preferred embodiments thereof we claim:
