Note: Descriptions are shown in the official language in which they were submitted.
CA 02570700 2006-12-08
A CONNECTOR FOR USE IN A WELLBORE
BACKGROUND OF THE INVENTION
Field of the Invention
Embodiments of the present invention generally relate to a connector for
connecting a rod with a component for use in boreholes such as oil and gas
wells.
More particularly, the invention relates to a connector having a stress
reducing design
including opposing planar portions in a substantially cylindrical body. More
particularly
still, the invention relates to a connector and rod having a higher alloy
content.
Description of the Related Art
Modern oil and gas wells are typically drilled with a rotary drill bit and a
circulating drilling fluid or "mud" system. The mud system (a) serves as a
means for
removing drill bit cuttings from the well as the borehole is advanced, (b)
lubricates and
cools the rotating drill bit, and (c) provides pressure within the borehole to
balance
internal pressures of formations penetrated by the borehole. Rotary motion is
imparted
to the drill bit by rotation of a drill string to which the bit is attached.
Alternately, the bit
is rotated by a mud motor which is attached to the drill string just above the
drill bit.
The mud motor is powered by the circulating mud system. Subsequent to the
drilling of
a well, or alternately at intermediate periods during the drilling process,
the borehole is
cased typically with steel casing, and the annulus between the borehole and
the outer
surface of the casing is filled with cement. The casing preserves the
integrity of the
borehole by preventing collapse or cave-in. The cement annulus hydraulically
isolates
formation zones penetrated by the borehole that are at different internal
formation
pressures.
Numerous operations occur in the well borehole after casing is "set". All
operations require the insertion of some type of instrumentation or hardware
within the
borehole. Examples of typical borehole operations include: (a) setting packers
and
plugs to isolate producing zones; (b) inserting tubing within the casing and
extending
the tubing to the prospective producing zone; and (c) inserting, operating,
and removing
pumping systems from the borehole.
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CA 02570700 2006-12-08
Fluids can be produced from oil and gas wells by utilizing internal pressure
within
a producing zone to lift the fluid through the well borehole to the surface of
the earth. If
internal formation pressure is insufficient, artificial fluid lift means and
methods must be
used to transfer fluids from the producing zone and through the borehole to
the surface
of the earth.
The most common artificial lift technology utilized in the domestic oil
industry is
the sucker rod pumping system. A sucker rod pumping system consists of a
pumping
unit that converts a rotary motion of a drive motor to a reciprocating motion
of an
artificial lift pump. A pump unit is connected to a polish rod and a sucker
rod "string"
which, in turn, operationally connects to a rod pump in the borehole. The
string can
consist of a group of connected, essentially rigid, steel sucker rod sections
(commonly
referred to as "joints") in lengths of 25 or 30 feet (ft), and in diameters
ranging from 5/8
inches (in.) to 1-1/4 in. Joints are sequentially connected or disconnected as
the string
is inserted or removed from the borehole, respectively. Alternately, a
continuous
sucker rod (hereafter referred to as COROD ) string can be used to
operationally
connect the pump unit at the surface of the earth to the rod pump positioned
within the
borehole.
A COROD and sucker rods have pin ends for connecting the rod to a pump, a
motor, or another rod. The pin end has a wrench flat section which comprises
four flat
sections in the cross-sectional shape of a square. The wrench flat section
allows an
operator to grab the rod with a wrench and apply torque during connection.
Because
there are four flat sections at 90 angles the operator can move the wrench
from one
flat section to the next with only a quarter turn of the wrench.
Many modern boreholes have a highly corrosive downhole environment.
Traditional rods and connectors have been manufactured with a low alloy
content. The
typical rod has only up to 2% of common alloy elements such as Nickel,
Chromium and
Copper added to their metal chemistry. These low alloy rods are insufficient
for use in
corrosive borehole environments. To solve this problem in the past
manufacturers
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CA 02570700 2006-12-08
applied coatings to the rods to prevent corrosion. However, these coatings
tend to
flake, or scratch off during bending and run in of the rod.
A CORODO and sucker rods are particularly susceptible to fatigue failure
caused
by continuous use of the rod to operate downhole tools and pumps. Fatigue
failure
occurs with frequency at the fillet of the square wrench flats. The
discontinuity at the
fillet creates a stress concentration. The stress concentration will
eventually cause the
rod to fail which causes loss of time and equipment. Fatigue failure is of
particular
concern when using progressive cavity pumps and deviated wellbore applications
where eccentricity facilitates bending and flexing of the rod connection(s).
There is a need for a connector for connecting a rod to another downhole
component that reduces stress in the connector. There is a further need for a
more
even distribution of stresses in the connector in order to prevent fatigue
failure. There
is yet a further need for a corrosion resistant rod and connector.
SUMMARY OF THE INVENTION
In one aspect a connector for connecting a rod to a wellbore component has a
first end for connecting to the component, a second end for connecting the
body to the
rod and a cross section defining a cylindrical shape with opposing planar
portions for
engagement with a torquing member.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features of the present
invention
can be understood in detail, a more particular description of the invention,
briefly
summarized above, may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however, that the
appended
drawings illustrate only typical embodiments of this invention and are
therefore not to
be considered limiting of its scope, for the invention may admit to other
equally effective
embodiments.
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Figure 1 is a cross sectional view of a wellbore illustrating a rod connector
for
use with a spooled rod.
Figure 2 is a cross sectional view of a wellbore iilustrating a rod connector
for
use with a jointed rod.
Figure 3 is a view of a connector assembly of the present invention.
Figure 4 is a cross-sectional view of the connector assembly of the present
invention.
DETAILED DESCRIPTION
The apparatus and method of the present invention allow for connection of a
rod
for use in a downhole operation with a component. The connector allows the rod
to
operate downhole equipment while reducing the amount of stress in the
connection
which leads to failures.
Figure 1 depicts a cross-sectional view of a wellbore 100. As illustrated, the
wellbore 100 has a string of casing 102 fixed in formation 104 by cured cement
106.
The wellbore 100 also includes a first component 108, shown schematically,
connected
to a rod 110 by a connector assembly 112. In one embodiment the connector
assembly 112 couples the first component 108 to the rod 110, which is a
spooled or
continuous rod (CORODO). The CORODO can be of any diameter that is capable of
being wound and unwound around a spool 114.
In operation the spool 114 with the rod 110 wound around the spool 114 is
brought to the wellbore 100. The connector assembly 112 is then connected to
the first
component 108, described in more detail below, and an end of rod 110. The
spool 114
then actuates and lowers the first component 108 by unspooling the rod 110.
When the
first component 108 reaches a desired depth in the wellbore 100 the spool 114
stops.
In one embodiment the rod 110 is then cut and another connector assembly 112
(not
shown) is coupled to the rod and a second component 200, shown in figure 2. In
one
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embodiment, the end of the rod 110 with the second component 200 is connected
in
the same manner as the end with the first component 108.
Figure 2 shows the rod 110 as a series of rods or joints 202. The joints 202
are
of any length desired. In an embodiment the joints 202 are 25 to 30 feet in
length. The
joints 202 couple together in the same way as the components 108 and 200 are
coupled to the rod with connector assembly 112, described in more detail
below. The
first component 108 couples to the joint 202. The first component is then
lowered into
the wellbore 100, until the top end of the joint 202 is near the top of the
wellbore.
Another joint 202 then couples to the first installed joint. This is repeated
until the rod
110 is the desired length. The second component then couples to the rod 110.
Although rod 110 is shown as a spooled rod and a jointed rod it should be
appreciated that the rod may be any rod for use in downhole operations, such
as a
CORODO, a sucker rod, jointed rod, etc. Further, it should be appreciated that
the rod
110 could be a solid rod or a tubular having a bore through the center. The
rod 110 can
be of any desired diameter in order to meet the specific requirements of the
operation.
The rod 110 and connector assembly 112 may be of any metallurgical make-up.
In an alternative embodiment the rod 110 and the connector 112 have increased
alloy
content. In another embodiment, the rod 110 and the connector 112 have an
intermediate alloy level between stainless steel and low alloy carbon steel.
The alloy
content in another embodiment could be in the range of greater than 21/2% Cr.
to less
than 13% Cr. In another embodiment the alloy content would be approximately
5Cr-
'/2Mo alloy steel, similarly replicating ASME SA193 Grade B5. Although, the
alloy used
is discussed in respect to Cr, it should be appreciated that any alloying
metal could be
used such as nickel (Ni.), molybdenum (Mo.), copper (Cu.), vanadium (V.), etc.
Further, the metallurgy described above can be used on any rod and any
connector
used in downhole operations.
Figure 3 depicts a view of the connector assembly 112 according to one
embodiment of the present invention. The connector assembly 112 includes a
body
300, a first end 302 and a second end 304. In one embodiment, the first end
302 has
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CA 02570700 2006-12-08
threads 306. As shown, the threads 306 are the male or pin of the connection;
however, it should be appreciated that the threads 306 could be in any form to
facilitate
connection to another member such as a female or box end, a clamp, a flange,
etc.
The first end 302 adapts for easy connection to the components 108 and 200 or
another connector assembly 112. The first end 302 couples to the body 300.
The body 300 is substantially cylindrical and has two full diameter sections
308
on each end of the body 300. Between the full diameter sections 308 is an
engaging
section 310. The engaging section 310 includes planar portions 312. The planar
portions 312 are substantially parallel and adapted to be engaged by a tool
400, shown
in figure 4. The tool 400 is any tool for applying or resisting torque in the
rod 110 such
as a wrench, spanner, etc. As shown in figure 4 the planar portions 312 are
arranged
at edges 402 to transition smoothly from flat to the natural cylindrical
diameter of the
body 300. This differs from prior connectors that had a square arrangement,
thus
having four 90 angles. It should be appreciated that when applying torque to
a rod or
tubular the highest stress concentrations are on the outer edge of the rod or
tubular. In
an arrangement with sharp angles the torque load is further concentrated at
the angles.
Thus, the engaging section 310 reduces stress concentrations in the connector
assembly 112 by having tangential edges 402 rather than the angles of the
prior art. It
should be appreciated that the body 300 can be of any size and configuration
so long
as the edges 402 of the planar portions 312 have a smooth transition to the
rest of the
body.
The body 300 couples to the second end 304 of the connector assembly 112.
Each end of the second end 304 adapts to couple to the rod 110 and the body
300
respectively. The second end 304 may be adapted to be the same diameter as the
rod
110, and further be adapted to match the diameter of the body 300 on the other
end.
The second end 304 is welded directly to the rod 110, although it should be
appreciated
that any connection could be used such as clamps, threads, flanges, etc.
The first component has an adapter 116 shown schematically. The adapter 116
is arranged to connect to the first end 302. In one embodiment the adapter 116
is a
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female or box connection attached to a shaft that couples to the first
component 108.
The adapter 116 with the first component 108 is then brought into engagement
with the
first end 302. The tool 400 then engages the planar portions 312. The
connection is
made between the adapter 116 and the first end 302 by rotating the adapter 116
while
the tool 400 prevents rotation of the connector assembly 112. In another
embodiment
the connection is made when the adapter 116 is held stationary while the tool
400
torques the connector 112. It should be appreciated that the adapter could be
any
connector adapted to connect to the first end 302. The connection of the
connector
assembly 112 to the second component 200 or another connector assembly is
performed in the same manner as described above and thus will not detailed
here.
In one embodiment the first component is a downhole pump such as a
reciprocating pump, a progressive cavity pump. The second component is a motor
for
rotating the rod 110. As the second component 200 rotates the rod 110, the rod
110
turns and torques the connector 112 and transfers rotation to the adapter 116
and thus
transfers rotation to the shaft of the pump, not shown. As described above due
to the
improved design of the connector assembly 112, stresses in the connector
assembly
112 and the risk of failure are greatly reduced over the life of the rod.
Although the first component 108 is described as a pump, it should be
appreciated that the first component 108 could be any tool or component used
in
downhole operations such as a packer, an expander, a cutting tool, a valve, an
anchor,
etc. It should further be appreciated that the second component 200 could be
any tool
or component used at the surface of a wellbore such as, but not limited to a
spider, a
rotary table, a pipe spinner, a power tong, a top drive, an elevator, the
spool, a human
operator, etc.
While the foregoing is directed to embodiments of the present invention, other
and further embodiments of the invention may be devised without departing from
the
basic scope thereof, and the scope thereof is determined by the claims that
follow.
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