Note: Descriptions are shown in the official language in which they were submitted.
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MOTOR/PUMP WITH SPIRAL WOUND STATOR TUBE
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority of U.S. Provisional Application No.
61/239,537 filed on September 4, 2009, the disclosure of which is incorporated
herein by reference for all purposes.
FIELD OF THE INVENTION
The present invention relates to motors and pumps of the type which
include a stator and a rotor which rotates within the stator to either pump
fluid or
to generate mechanical forces from fluid pumped through the motor, e.g., to
rotate a downhole bit. More particularly, the present invention relates to a
relatively low cost stator tube formed by welding a spiral sheet to form the
stator
tube, with an elastomeric layer having a substantially uniform thickness on
the
interior of the stator tube.
BACKGROUND OF THE INVENTION
Various types of downhole progressing cavity or Moineau-style pumps
and motors have been devised for downhole use in hydrocarbon recovery
operations. In one embodiment, the equipment acts as to pump downhole fluid
to the surface, typically by rotating a sucker rod at the surface to rotate
the
downhole rotor. Also, the pump could be configured to run with an electric
submersible motor, which is not driven from the surface using sucker rods. In
other embodiments, the equipment serves as a motor to receive downhole fluids
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pumped from the surface, and uses hydraulic forces to rotate the rotor and
thereby rotate a bit below the motor. Various embodiments of downhole motors
and pumps are disclosed in U.S. Patents 4,386,654, 4,519,712, 4,591,322,
4,773,834, 4,592,427, and 4,991,292. A stator for a positive displacement pump
is disclosed in U.S. Patent 5,145,342, and U.S. Patent 5,474,432 discloses a
pump or motor construction.
A progressing cavity pump is disclosed in U.S. Patent 6,120,267. U.S.
Patents 6,716,008, 6,464,467, 6,398,522, 6,308,549, 6,220,837, and 6,126,032
disclose other embodiments of downhole motor/pumps. U.S. Patent 6,729,391
discloses a progressing cavity pump which is insertable in a tubing string. An
internally profiled stator tube is disclosed in U.S. Patent 6,309,195, and a
method of producing elastomeric stators is disclosed in U.S. Patent 6,158,988.
More recent patents to positive displacement pumps and motors include
U.S. Patents 7,131,827, 7,192,260, 7,226,277, 7,285,885, 7,316,548, 7,329,106,
7,413,416, and 7,473,082. U.S. Patent 6,604,192 discloses a positive
displacement motor with an optimized liner thickness. U.S. Patent 7,137,795
discloses a pump stator formed from interlocking segments. U.S. Publication
2005/0169779 discloses features of a progressing cavity pump, and U.S
Publication 2005/0106004 discloses a stator for a positive displacement pump
with a hollow space in the shape of a double or multiple spiral. U.S.
Publication
2007/0053783 discloses a stator which has multiple spirals for accommodating a
rotor.
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The disadvantages of the prior art are overcome by the present invention,
and an improved progressing cavity pump/motor and in particular a stator for a
progressing cavity pump/motor is hereinafter disclosed.
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SUMMARY OF THE INVENTION
A progressing cavity pump/motor has a stator with substantially the same
shape as the interior wall of the stator, so that an even rubber thickness on
the
stator may cooperate with the rotor profile to generate a pumping action or
generate mechanical torque from fluid transmitted to the motor. The stator is
formed from one or more strips of metal which are rolled and formed into the
desired shape, and welded along the strip seam to produce the desired
configuration.
These and further features and advantages of the present invention will
become apparent from the following detailed description, wherein reference is
made to the figures in the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a portion of a suitable stator tube according to the
present invention.
Figure 2 is a detailed view of a portion of the stator tube shown in Figure
1.
Figure 3 illustrates a side view of a portion of the stator and rotor within
the stator.
Figure 4 illustrates a side view of another embodiment of a stator tube
with a spiraling strip around the seam.
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DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Figure 1 illustrates a spiral shaped stator tube 10 which has an interior
profile intended to generally match the interior profile of the elastomeric
layer
subsequently molded into the stator. The spiral shaped stator tube 10 as shown
in Figure 1 thus provides a significant advantage of enabling a substantially
even
thickness of rubber around the profile of the stator, thereby eliminating
problems
associated with a thick rubber section retaining heat within the stator and
lowering the pressure capability of the pump/motor. While other pump/motor
stators have this general configuration, the present invention substantially
reduces the costs of manufacturing the stator.
By utilizing a stator tube that has the same shape but is slightly larger than
the interior profile of the rubber within the stator, the stator may be
manufactured
with an even rubber thickness around its inner profile. At the stator minor
diameter, the rubber is thus thinner than for a conventional cylindrical
stator with
a varying rubber thickness, thereby resulting in the advantages of improved
heat
transfer capability and high pressure capability.
Stators with substantially even rubber thicknesses have been formed by
various techniques, including casting, electrode discharge machining, and
rotary
swaging. Each of these techniques forms a suitable stator tube, but the cost
of
stator manufacturing is a significant disadvantage to the acceptance of such
pump/motors.
As shown in Figures 1 and 2, the stator may be manufactured from metal
strips 12 which are easily rolled and formed into the desired shape, then
welded
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at 14 along the seam of the strips. While each strip may have a desired
configuration to achieve the end results, it is preferable that the seam and
thus
the weld 14 are made at the radially outward portion of each stator lobe
profile,
as shown in Figure 1, so that the seam is easily accessible to a welding
operation. The seam and thus the weld alternatively could be provided in the
"valley" or the radially inward portion of each stator profile. The axial
spacing
between a full revolution of the stator spiral thus coincides with the axial
spacing
between a full spiral of the weld. Two spiraling strips welded together at
this
seam thus forms the completed stator housing. The seam may alternatively be
made between the "hill" and the "valley" of the spiral wound stator tube.
Figure 3 illustrates a portion of a stator 10 with a seam 14 as discussed
above, and a rotor 30 positioned within the stator.
The metal strips 12 which form the body of the stator tube may thus have
a substantially uniform thickness, which may be between 0.040 inches to 0.50
inches. In other embodiments, another thin strip may be welded to the
exterior,
or possibly the interior, of the formed stator tube on each side of the seam,
so
that both the weld 14 and the added strip with a weld on each side of seam 14
thus provides additional mechanical strength and fluid pressure integrity. The
ends of each stator tube may include an adapter so that the spiral tube can be
interconnected by the adapter to tools and tubular with conventional threads.
Referring briefly to Figure 3, the cross-section of the stator 10 is shown,
along with a uniform rubber thickness layer 20 on the interior of the stator
tube
10. Figure 3 also depicts a portion of a suitable rotor 30 positioned within
the
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stator, such that the rotor rotates within the stator to achieve the desired
pumping action or to generate torque from power fluid to rotate a bit.
In one embodiment, an improved downhole motor/pump is provided, the
equipment including a stator tube with a substantially uniform thickness metal
sheet formed and spiral wound to generate an interior profile for the stator.
Adjacent edges of the spiral wound sheet may be secured together by welding.
A substantially uniform thickness elastomeric layer may be formed on the
interior
profile surface of the stator, and a rotor positioned within the stator and
the
elastomeric layer for cooperating with the elastomeric layer during operation
of
the pump/motor. In another embodiment, an improved stator is provided suitable
for use with a pump/motor, with a stator tube having a substantially uniform
thickness metal sheet formed and spiral wound to generate an interior profile,
and adjacent edges of the spiral wound sheet secured together.
Figure 4 illustrates a portion of a stator 11, although in this case the
rubber layer 20 is not shown. The seam between spiraling sheets is connected
by a spiraling strap 36 which may be positioned over a portion of the external
surface of adjacent strips and welded to each strip. As previously noted, the
seam may not be provided in the "high portion" of the stator profile, and thus
the
strips may not enlarge the overall diameter of the stator tube.
Although specific embodiments of the invention have been described
herein in some detail, this has been done solely for the purposes of
explaining
the various aspects of the invention, and is not intended to limit the scope
of the
invention as defined in the claims which follow. Those skilled in the art will
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understand that the embodiment shown and described is exemplary, and various
other substitutions, alterations and modifications, including but not limited
to
those design alternatives specifically discussed herein, may be made in the
practice of the invention without departing from its scope.
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