Note: Descriptions are shown in the official language in which they were submitted.
CA 02604998 2007-10-01
1 ACTIVE INTAKE PRESSURE CONTROL OF DOWNHOLE PUMP ASSEMBLIES
2
3 FIELD OF THE INVENTION
4 Disclosed herein are progressive cavity pump systems, including
various pressure control mechanisms.
6
7 BACKGROUND
8 Progressive cavity pumps have long been used downhole for pumping
9 wellbore fluids. When a lone progressive cavity pump is operated in a well
where
free gas or foamy oil is present, the pump does not operate as efficiently and
its run
11 life decreases. To solve this problem, a pump assembly is used having a
charge
12 pump in addition to the main production pump. Referring to Figures 1A and
113, the
13 main pump 106, located at the top of the pump assembly 100, is a high
14 pressure/low volume pump capable of pushing the wellbore fluid the full
length of
the wellbore. The main (progressive cavity) pump 106 includes a rotor 104,
driven
16 by a rotating shaft 102, that turns inside a stator 108 at a fixed rate.
The shaft 102
17 is typically driven by an electric motor (not shown). The charge pump 116,
being a
18 low pressure/high volume pump, is located below the main pump 106 and feeds
it
19 with wellbore fluid through an interconnect 110, such as a pup joint. The
charge
pump of Figures 1A and 113 is also a progressive cavity pump with a rotor 118
and
21 stator 114, but some pump assemblies may instead use an auger for the
charge
22 pump. The effect of adding the charge pump 116 is that, due to the higher
pressure
I
CA 02604998 2007-10-01
1 in the interconnect 110, the gas is compressed to occupy less volume and may
be
2 forced into solution thereby increasing the liquid efficiency of the main
pump.
3 The ratio of the displacements of the pumps in the pump assembly is
4 typically designed according to the gas content of the wellbore fluid, with
the charge
pump having a higher displacement. When the wellbore fluid has a free gas rate
of
6 under 25 percent, a ratio of displacements of approximately 2:1 is commonly
7 employed. With a free gas rate of 25 to 50 percent, the ratio may be
approximately
8 4:1. For example, with free gas in the well at 15 percent, the pump assembly
may
9 use a pump with a 100-barrels-per-day displacement as the main pump and a
pump
with a 200-barrels-per-day displacement as the charge pump.
11 Problematically, the free gas rate of the wellbore fluid is often non-
12 uniform. When the gas content of the wellbore fluid falls below the range
for that
13 the system was designed, the pressure increases dramatically, damaging the
14 charge pump. When the gas content of the wellbore fluid exceeds the
anticipated
range, the pressure decreases, the effect of the charge pump on the pump
16 assembly is nullified, and the pump assembly becomes inefficient. Non-
uniform
17 inflow of water or high viscosity liquids can have the same effect.
18 A current solution to high-pressure events is to create pressure relief
19 ports 120 in the interconnect 110 in various sizes and configurations.
While simple
ports can discharge pressure from the interconnect 110, they are inflexible in
21 response to pressure increases in that the amount of fluid and gas
discharged from
22 a set number and configuration of ports is proportional to the pressure in
the
23 interconnect. These ports 120 also exacerbate the problem of pressure
decreases.
2
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1 Figure 2A is a graph showing the pressure in the interconnect of the
2 main pump 202 in comparison with the fluid viscosity 216 of the liquid being
3 pumped. Curves representing the pressure in the interconnect 202 for each
fluid
4 viscosity 216 are shown for an interconnect alternately having zero (204),
two (206),
four (208), eight (210), and sixteen (212) ports. As is apparent from Figure
2A, the
6 greater the number of ports, the more slowly the interconnect pressure 202
7 increases in comparison to the fluid viscosity 216. In the current ported
8 interconnect method, therefore, using a larger number of ports to avoid a
pressure
9 increase detrimental to the charge pump results in a less than optimal range
of fluid
viscosities that produce an interconnect pressure 202 greater than the minimum
of
11 the efficient range 214, and vice versa.
12 Figure 2B is a graph showing the pressure in the interconnect of the
13 main pump 234 in comparison with the free gas rate 236 of the liquid being
14 pumped. Curves representing the pressure in the interconnect 234 for each
free
gas rate 236 are shown for an interconnect alternately having zero (224), two
(226),
16 and four (228) ports. As is apparent from Figure 2B, the greater the number
of
17 ports, the more slowly the interconnect pressure 202 increases as the free
gas rate
18 236 decreases. Again, using a larger number of ports to avoid a detrimental
19 pressure increase results in a less than optimal range of free gas rates
that produce
an interconnect pressure 234 greater than the minimum of the efficient range
214.
21 The pressure curves of Figures 2A and 2B are for example only, as
22 the curves associated with a specific implementation of pump assembly (with
3
CA 02604998 2007-10-01
1 varying main and charge pump displacements, sizes of interconnect, sizes and
2 numbers of ports, etc.) will vary.
3 Changing the port configuration or the displacement from the charge
4 pump when the pressure is approaching the upper or lower limit of the
efficient
range reduces non-uniformity in interconnect pressure. An ideal design,
therefore,
6 would include a mechanism for changing the port configuration or the
configuration
7 of the charge pump in response to the pressure at the inlet port of the main
pump.
8 Disclosed herein are pump assemblies that include these pressure control
9 mechanisms.
11 SUMMARY
12 Disclosed herein are progressive cavity pump assemblies including
13 one or more mechanisms adapted to regulate intake pressure of the main pump
14 between a minimum intake pressure and a maximum intake pressure. In one
embodiment, the mechanism is a sealing member configured to open at a
threshold
16 pressure to discharge wellbore fluid and close after falling below the
threshold
17 pressure. In an alternative embodiment, the mechanism may be a regulator
18 assembly that adjusts the volume of output from the charge pump to the
19 interconnect according to the pressure in the interconnect.
4
CA 02604998 2009-12-01
1 BRIEF DESCRIPTION OF THE DRAWINGS
2
3 Figures 1 A and 1 B illustrate a prior art progressive cavity pump assembly.
4
Figures 2A and 2B are graphs showing pressure in a prior art progressive
cavity pump
6 assembly.
7
8 Figures 3A and 3B are graphs showing pressure in a progressive cavity pump
assembly
9 according to the present disclosure.
11 Figures 4A-D illustrate an exemplary valve for discharging wellbore fluid
according to the
12 present disclosure.
13
14 Figures 5A-H illustrate exemplary stoppers for discharging wellbore fluid
according to the
present disclosure.
16
17 Figures 5J-M illustrate a stopper with multiple stopper ports that align
(in turn) with the
18 pressure relief ports.
19
Figures 6A-C illustrate an exemplary external flap assembly for discharging
wellbore fluid
21 according to the present disclosure.
22
23 Figures 7A-D illustrate an exemplary bladder assembly for discharging
wellbore fluid
24 according to the present disclosure.
26 Figures 8A-8C illustrate a progressive cavity pump assembly having an
exemplary regulator
27 assembly according to the present disclosure.
28
29 Figure 9 illustrates a progressive cavity pump assembly having another
exemplary regulator
assembly.
5
CA 02604998 2007-10-01
1 DETAILED DESCRIPTION
2 Disclosed herein are pump assemblies including one or more
3 mechanisms adapted to regulate intake pressure of the main pump in the
efficient
4 range between a minimum intake pressure and a maximum intake pressure. In
one
embodiment, pressure is decreased by discharging wellbore fluid from the pump
6 assembly. In an alternative embodiment, the mechanism may be a regulator
7 assembly that adjusts the volume of output from the charge pump to the
8 interconnect according to the pressure in the interconnect. Specific design
details
9 have been provided for illustration but should not be considered limiting.
Readers
of skill in the art will recognize that many variations of pump assemblies may
be
11 implemented consistent with the scope of the invention as described by the
12 appended claims.
13
14 I. Discharging Mechanisms
The pressure control mechanism may be a sealing member
16 configured to open at a threshold pressure to discharge wellbore fluid.
Typically,
17 these sealing members discharge pressure from pressure relief ports in the
18 interconnect, but pressure may be discharged from elsewhere in the pump
19 assembly. In various embodiments, the sealing members may be implemented as
valves, stoppers, flaps, and so on.
21 Figures 3A and 3B are graphs showing the interconnect pressure 302
22 in comparison with, alternately, the well fluid viscosity 316 (Figure 3A)
and the free
23 gas rate 336 (Figure 3B). In Figure 3A, a curve representing the
interconnect
6
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1 pressure 302 for each fluid viscosity 316 is shown for an interconnect that
opens
2 two sealing member at 120 psi, two sealing members at 140 psi, a set of four
3 sealing members at 160 psi, and a set of eight sealing members at 180 psi.
The
4 efficient range 314 is shown with a minimum pressure of 100 psi and a
maximum
pressure of 300 psi.
6 In an initial configuration, shown by curve segment 304, the curve
7 exhibits behavior identical to the previously discussed zero-port
interconnect of
8 Figure 2A. This behavior optimizes the range of fluid viscosities that
produce an
9 interconnect pressure 302 greater than the range minimum. The initial
configuration
304 ends at a critical pressure, where the first set of sealing members opens.
11 In the second configuration, the pressure at the inlet port of the main
12 pump 302 builds similarly to the two-port interconnect, as shown by curve
segment
13 306. This behavior optimizes the range of fluid viscosities that produce an
14 interconnect pressure 302 lower than the maximum. If fluid viscosity 316
increases
sufficiently, the interconnect pressure 302 will continue to increase despite
the open
16 ports until the second, third, and fourth sets of sealing members open.
Curve
17 segments 308, 310, and 312 represent subsequent configurations with four,
eight,
18 and sixteen open ports, respectively. The behavior of each configuration is
similar
19 to that of the interconnect of Figure 2A with a corresponding number of
ports. Each
configuration ends at a critical pressure, where the subsequent set of sealing
21 members opens. The number of open ports is increased in each configuration
in
22 order to optimize the range of fluid viscosities that produce an
interconnect pressure
23 lower than the maximum. Thus, by letting pressure build up before releasing
it by
7
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1 opening a sealing member to discharge it, the inlet pressure is kept within
the
2 efficient range over a larger range of fluid viscosities.
3 Figure 3B shows the effect of changing free gas rates on interconnect
4 pressure in an interconnect that opens two sealing members at 120 psi and
two
more sealing members at 140 psi. Thus, the interconnect represented by Figure
3B
6 has a zero-port configuration, a two-port configuration, and a four-port
configuration
7 represented by curve segments 324, 326, and 328, respectively. Each
8 configuration ends at a critical pressure, where the subsequent set of
sealing
9 members opens. The behavior of each configuration is similar to that of the
interconnect of Figure 2B with a corresponding number of ports. In Figure 3B,
11 interconnect pressure 334 increases as free gas rates 336 decline. The
efficient
12 range 314 is shown with a minimum pressure of 100 psi and a maximum
pressure
13 of 300 psi. Thus, the number of open ports is increased in each
configuration in
14 order to optimize the range of free gas rates that produce an interconnect
pressure
within the efficient range.
16 Exemplary sealing mechanisms adapted to regulate intake pressure of
17 the main pump will now be described. Figures 4A-D illustrate an exemplary
valve
18 for discharging wellbore fluid. Figures 4A and 4B show the valves 400 in
the
19 interconnect 110 of the pump assembly 100. Figure 4C shows the valve 400
before
a threshold pressure is exceeded. Figure 4D shows the valve 400 after a
threshold
21 pressure is exceeded. The valve 400 includes a substantially cylindrical
first
22 housing member 402 having a passage 422 running through its longitudinal
axis.
23 The first housing member 402 is welded in the pressure relief port 416 so
as to seal
8
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1 the annulus between the first housing member 402 and the pressure relief
port 416.
2 The axial passage 422 is in fluid communication with the exterior 410 of the
3 interconnect at one end ("the exterior end 415") and the interior 420 of the
4 interconnect at the other end ("the interior end" 417). The first housing
member 402
has two first housing ports 404 in the curved side of the first housing member
402
6 that also connects the passage 422 and the interior 420 of the interconnect.
7 A substantially cylindrical second housing member 406 is slideably
8 mounted inside the first housing member 402 on a pressure bearing (not
shown).
9 The pressure bearing seals the annulus between the first housing member 402
and
the second housing member 406. The second housing member 406 has an axial
11 passage 423 running partly therethrough, the passage 423 closed at one end
by a
12 portion 424 of the second housing assembly transverse to the passage and
open at
13 the other end. The open end 419 of the second housing member is in fluid
14 communication with the exterior end 415 of the first passage 422. The
closed end
418 of the second housing member 406 is oriented towards the interior end 417
of
16 the first housing member's passage. The second housing member 406 is urged
17 towards the interior end 417 of this passage by a biasing member 412, so
that the
18 transverse portion 424 is located between the first housing port 404 and
the interior
19 end 417 of the first passage 422. The transverse portion 422 of the second
housing
member 406 separates the interior 417 and exterior 415 ends of the first
passage
21 422. The second housing member 406 has a second housing port 408 in its
curved
22 side in fluid communication with the second passage 423. The second housing
port
9
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1 408 is located inside the first passage 422 closer to the interior end 417
than the
2 first housing port 404, but farther away than the transverse portion 424.
3 A biasing member 412 is mounted between the second housing
4 member 406 and a seat in the first housing member 402. The biasing member
412
urges the first and second housing ports to the configuration shown in Figure
4C.
6 The biasing member 412 may be, for example, a spring or an elastomer (e.g.,
7 rubber) disc.
8 In the closed configuration, as shown in Figure 4C, the two housing
9 ports 404, 406 are not aligned, and the exterior 410 of the interconnect is
sealed
from the interior 420. Pressure 414 from the interior 420 of the interconnect
acting
11 on the end of the second housing member 406 pushes the second housing
member
12 406 against the biasing member 412, which resists the force. The second
housing
13 member 406 may slide down the first housing member's passage toward the
open
14 configuration, without reaching the open configuration.
When the pressure 414 from the interior 420 of the interconnect
16 exceeds the valve's threshold pressure, the second housing member 406
slides into
17 the open configuration, as shown in Figure 4D, where the first and second
housing
18 ports (404, 408) align, creating a passage 430 from the interior 420 to the
exterior
19 410 of the interconnect, through which wellbore fluid flows, thereby
decreasing the
pressure 414 in the interior 420 of the interconnect. The threshold pressure
is
21 selected to optimize the range of charge pump discharge pressures that
produce a
22 main pump inlet pressure greater than the efficient range minimum and less
than
23 the maximum, as described above with reference to Figures 3A and 3B. After
the
CA 02604998 2007-10-01
1 pressure 414 has dropped below the predetermined threshold pressure, the
force
2 against the closed end 418 of the second housing member 406 is insufficient
to
3 compensate for the biasing member 412, and the biasing member 412 closes the
4 valve.
More than one pressure relief valve may be provided in the
6 interconnect. In the case of multiple valves, discharging may be staggered
for
7 various pressure thresholds. In such an implementation, the valves may be
8 configured to open at different threshold pressures, so that more fluid is
discharged
9 as the intake pressure of the main pump exceeds each different threshold
pressure.
For example, an interconnect may have three valves with threshold
11 pressures of 100 200, and 300 [Evan: please provide actual numbers] pounds
per
12 square inch (psi) respectively. Thus, upon reaching a pressure of 100 psi
(assumed
13 here to be a marginally high pressure), only the first valve is open, to
marginally
14 counteract the increase in pressure. Upon reaching a detrimentally high
pressure
of 300 psi, all three valves are open for maximum pressure release. The
specific
16 break pressures provided above are for example only. Many configurations of
17 pumping assembly are possible, with each configuration having its own
design
18 parameters.
19 Figures 5A-D illustrate an exemplary stopper 500 for discharging
wellbore fluid. Figures 5A and 5B show the stopper 500 in the interconnect 110
of
21 the pump assembly 100. Figure 5C shows the stopper 500 before a threshold
22 pressure is exceeded. Figure 5D shows the stopper 500 after a threshold
pressure
23 is exceeded. The stopper 500 includes a substantially cylindrical manifold
504
11
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1 coaxially mounted in the interconnect 502 and moveable along the
longitudinal axis
2 of the interconnect 502. The manifold has stopper ports 508 corresponding to
3 pressure relief ports 506. A surface 511 may be attached to the manifold
504. The
4 surface 511 is preferentially perpendicular to the manifold, but may be
otherwise
oriented. The interconnect 502 also includes a surface 510 substantially
6 perpendicular to its main axis. Biasing member 512 sits between the
perpendicular
7 surfaces 510 and 511 and urges the manifold 504 towards the closed
configuration.
8 In the closed configuration, as shown in Figure 5C, the stopper ports
9 508 and pressure relief ports 506 are not aligned, and the exterior 525 of
the
interconnect is sealed from the interior 530. Pressure 514 from the interior
530 of
11 the interconnect, acting on surface 511, pushes the stopper 500 against the
biasing
12 member 512, which resists the force. As the pressure 514 from the interior
530 of
13 the interconnect increases, the stopper 500 may slide axially in the
interconnect 502
14 toward the open configuration, but does not reach the open configuration
until after
the pressure has reached the threshold pressure.
16 When the pressure 514 in the interior 530 of the interconnect exceeds
17 the stopper's threshold pressure, the pressure 514 exerted on surface 511
slides
18 the stopper 500 into the open configuration, as shown in Figure 5D, where
the
19 stopper ports 508 and pressure relief ports 506 align, creating a passage
520 from
the interior 530 to exterior 525 of the interconnect 502, through which
wellbore fluid
21 flows, relieving pressure. After the pressure 514 has dropped below the
threshold,
22 the force against the perpendicular surface 511 of the stopper 500 is
insufficient to
23 compensate for the biasing member 512, and the biasing member 512 urges the
12
CA 02604998 2007-10-01
1 stopper 500 closed. The threshold pressure is selected to optimize the range
of
2 discharge pressures from the charge pump which result in a main pump inlet
3 pressure in the efficient range.
4 The interconnect may have multiple pressure relief ports and/or the
stopper may have multiple stopper ports. In the case of multiple ports,
discharging
6 may be staggered for various pressure thresholds. Figures 5E-H illustrate a
stopper
7 501 with stopper ports 505 that align with multiple pressure relief ports
507a and
8 507b. Figure 5E shows the stopper 501 at a nominal pressure in closed
9 configuration. Figure 5F shows the stopper 501 before a threshold pressure
is
exceeded. Figure 5G shows the stopper 501 after a first threshold pressure is
11 exceeded. Figure 5H shows the stopper 501 after a second threshold pressure
is
12 exceeded. The manifold has stopper ports 509 corresponding to pressure
relief
13 ports 507a and 507b. Other than the ports, stopper 501 operates similarly
to
14 stopper 500. In the closed configuration, as shown in Figures 5E and 5F,
the
stopper ports 509 and pressure relief ports 507a and 507b are not aligned, and
the
16 exterior 525 of the interconnect is sealed from the interior 530. As the
pressure 514
17 from the interior 530 of the interconnect increases, shown in Figure 5F,
the stopper
18 501 slides axially in the interconnect 502 toward the open configuration,
but does
19 not reach the open configuration.
When the pressure 514 in the interior 530 of the interconnect exceeds
21 the stopper's first threshold pressure, the pressure 514 exerted on surface
511
22 slides the stopper 501 into the half open configuration, as shown in Figure
5G,
23 where the stopper ports 509 and pressure relief ports 507a align, creating
a
13
CA 02604998 2007-10-01
1 passage 521a from the interior 530 to the exterior 525 of the interconnect
502,
2 through which wellbore fluid flows, relieving pressure. After the pressure
514 has
3 dropped below the first threshold, the biasing member 512 closes the stopper
501.
4 If pressure 514 continues to increase despite the release of fluid
through passage 520a, the pressure 514 exerted on surface 511 slides the
stopper
6 501 into the full open configuration, as shown in Figure 5H, where the
stopper port
7 509 and pressure relief port 507b align in addition to the stopper ports 509
and
8 pressure relief ports 507a, creating a passage 521 b from the interior 530
to exterior
9 525 of the interconnect 502, through which wellbore fluid flows, relieving
more
pressure than passage 521a alone. After the pressure 514 has dropped below the
11 second threshold, the biasing member 512 returns the stopper to the half
open
12 configuration above.
13 Figures 5J-M illustrate a stopper 503 with multiple stopper ports 509a
14 and 509b that align (in turn) with a pressure relief ports 507. Figure 5J
shows the
stopper 503 at a nominal pressure in closed configuration. Figure 5K shows the
16 stopper 503 before a threshold pressure is exceeded. Figure 5L shows the
stopper
17 503 after a first threshold pressure is exceeded. Figure 5M shows the
stopper 503
18 after a second threshold pressure is exceeded. The manifold has stopper
ports
19 509a and 509b corresponding to pressure relief ports 507. Other than the
ports,
stopper 503 operates similarly to stopper 500. In the closed configuration, as
21 shown in Figures 5J and 5K, the stopper ports 509a and 509b and pressure
relief
22 port 507 are not aligned, and the exterior 525 of the interconnect is
sealed from the
23 interior 530. As the pressure 514 from the interior 530 of the interconnect
14
CA 02604998 2007-10-01
1 increases, shown in Figure 5F, the stopper 503 slides axially in the
interconnect 502
2 toward the open configuration, but does not reach the open configuration.
3 When the pressure 514 in the interior 530 of the interconnect exceeds
4 the stopper's first threshold pressure, the pressure 514 exerted on surface
511
slides the stopper 501 into the half open configuration, as shown in Figure
5L,
6 where stopper ports 509a and pressure relief ports 507 align, creating a
passage
7 523a from the interior 530 to exterior 525 of the interconnect 502, through
which
8 wellbore fluid flows, relieving pressure. After the pressure 514 has dropped
below
9 the first threshold, the biasing member 512 closes the stopper 503.
If pressure 514 continues to increase despite the release of fluid
11 through passage 523a, the pressure 514 exerted on surface 511 slides the
stopper
12 503 into the full open configuration, as shown in Figure 5M, where the
stopper ports
13 509b and pressure relief ports 507 align in addition to the stopper ports
509a and
14 pressure relief ports 507, creating a passage 523b from the interior 530 to
exterior
525 of the interconnect 502, through which wellbore fluid flows, relieving
more
16 pressure than passage 523a alone. After the pressure 514 has dropped below
the
17 second threshold, the biasing member 512 returns the stopper to the half
open
18 configuration above.
19 In other configurations, at a particular threshold pressure, multiple
pressure relief ports may be aligned with multiple stopper ports. Thus, in
each of
21 the implementations above, more wellbore fluid is discharged as the intake
pressure
22 of the main pump exceeds each different threshold pressure.
CA 02604998 2007-10-01
1 Figures 6A-C illustrate an exemplary external flap assembly 600 for
2 discharging wellbore fluid. Figure 6A shows the external flap assembly 600
in the
3 interconnect 110 of the pump assembly 100. Figure 6B shows the flap assembly
4 600 before a threshold pressure is exceeded. Figure 6C shows the flap
assembly
600 after a threshold pressure is exceeded. The flap assembly 600 includes a
base
6 602 attached to the exterior of the interconnect 614, for example, by
welding, and a
7 flap 606 for blocking the pressure relief port 612 movably attached to the
base 602
8 by an attachment member 608 such as a hinge, tether, membrane, etc. The flap
9 assembly 600 also includes a biasing member 604 (e.g., a spring) that biases
the
flap 606 against the exterior of the interconnect 614 to block the pressure
relief port.
11 When the pressure 610 in the interior of the interconnect reaches a
12 threshold pressure, the pressure pushes against the resistance of the
biasing
13 member 604 to rotate the flap 606 away from the pressure relief port 612
providing
14 a path 620 for wellbore fluid to discharge from the interconnect, as shown
in Figure
6C. Similarly to the other sealing members discussed above, the threshold
16 pressure is selected to keep the main pump inlet pressure in the efficient
range, and
17 the selection may be influenced by hysteresis effects.
18 Figures 7A-D illustrate an exemplary bladder assembly 700 for
19 discharging wellbore fluid. Figures 7A and 7B show the exemplary bladder
assembly 700 in the interconnect 110 of the pump assembly 100. Figure 7C shows
21 the bladder assembly 700 before a threshold pressure is exceeded. Figure 7D
22 shows the bladder assembly 700 after a threshold pressure is exceeded. The
23 bladder assembly 700 includes a pliable bladder 706 inside the interconnect
708
16
CA 02604998 2007-10-01
1 with a first opening 710 at a first end in fluid communication with the
charge pump
2 outlet port and a second opening at a second end (not shown) in fluid
3 communication with the main pump intake port (not shown). The bladder 706 is
4 preferably made of an elastomeric material, such as rubber, and includes
slits 704
aligned with the pressure relief ports 702.
6 As shown in Figure 7C, as long as the pressure 710 inside the
7 interconnect 708 is below the threshold pressure, the slits 702 remain
closed, and
8 the exterior 716 of the interconnect is sealed from the interior 714. When
the
9 pressure 710 in the interior 714 of the interconnect 708 exceeds the slits'
threshold
pressure, the pressure 710 forces the slit 702 open, as shown in Figure 7D,
11 allowing wellbore fluid to escape. After the pressure 710 has dropped below
the
12 threshold, the slits 702 close. Hysteresis effects may result in a lag
between the
13 pressure dropping below the threshold and the slits closing. The threshold
pressure
14 may be selected to account for these hysteresis effects.
The opening characteristics for the slits may be varied to provide a
16 staggered pressure relief as discussed above. These opening characteristics
17 include threshold pressure, deformability, size of the opening at a
pressure, or
18 recovery time once pressure has subsided. The bladder assembly may include
19 more than one bladder. Some of these multiple bladders may be made of less
flexible materials, made thicker, or be stretched less to increase threshold
pressure
21 and decrease the size of the slit upon deformation from pressure. The
opposite
22 effect may be achieved by the opposite action. Threshold pressure of a slit
may
23 also be decreased by increasing the size of the closed slit.
17
CA 02604998 2007-10-01
1
2 II. Charge Pump Output Control
3 Other methods besides discharging wellbore fluid are used to
4 regulate intake pressure of the main pump. For example, intake pressure in
the
main pump may also be controlled by a regulator assembly that adjusts the
6 pressure capability of the charge pump according to the pressure in the
7 interconnect.
8 Figures 8A-8C illustrate a progressive cavity pump assembly having
9 an exemplary regulator assembly. Figure 8A shows a progressive cavity pump
assembly at a nominal pressure. Figure 8B shows a progressive cavity pump
11 assembly during a high pressure event. Figure 8C shows a progressive cavity
12 pump assembly during a low pressure event. The progressive cavity pump
13 assembly has a rotor 118 that may be longitudinally displaced relative to
the stator
14 114. Thus, a varying portion of the rotor 118 may be within the stator 114,
which
effectively controls the pressure capability of the pump by changing the lift
of the
16 pump. The regulator assembly includes a substantially cylindrical guide 802
coaxial
17 with the interconnect 110 on which stator 114 is slidably mounted with a
mounting
18 collar 804. Biasing member 806 axially biases the rotor 118 within the
stator 114.
19 An expandable chamber 810 connected to the stator 114 lengthens as pressure
increases. In the illustrated embodiment, the expandable chamber comprises the
21 interconnect 110 and the charge pump 116. Some embodiments may also include
22 a damping member (not shown) to curtail pressure oscillation.
18
CA 02604998 2007-10-01
1 During operation with a nominal chamber pressure, shown in Figure
2 8A, the biasing member 806 is partially compressed by the pressure in the
chamber
3 810 so that a portion of the rotor 118 is outside of the stator 114. The
lift of the
4 charge pump at this configuration is the nominal lift for which the pump
assembly
has been designed. The nominal lift is typically the optimal lift for the gas
6 percentage of wellbore fluid most likely to be present in the well, but may
also be an
7 optimal lift for the average gas percentage, or some other lift. The optimal
lift could
8 also be the maximum lift of the charge pump.
9 During a high pressure event in the chamber 810, as shown in Figure
8B, the force exerted by the pressure on the expandable chamber 810 increases,
11 further compressing the biasing member 806 and sliding the stator 114
further
12 downward so that the rotor 118 is drawn farther out of stator 114. Thus,
the pump
13 effectively has a lower lift and thus a lower pressure capability at a
given speed.
14 The lower lift decreases the interconnect pressure, thus regulating the
main pump's
inlet pressure. In essence, the regulator assembly provides negative feedback
to
16 hold the main pump's inlet pressure in the desired range.
17 Upon a low pressure event in the chamber, as shown in Figure 8C,
18 the force exerted by the pressure on the expandable chamber 810 decreases
from
19 normal, lessening the compression of the biasing member 806 and sliding the
stator
114 further upward from its nominal position so that the rotor 118 is
displaced
21 farther into stator 114. This effectively increases the charge pump's lift,
and thus,
22 pressure capability at a given speed, increasing the main pump's inlet
pressure.
19
CA 02604998 2007-10-01
1 Figure 9 illustrates a progressive cavity pump assembly having
2 another regulator assembly 900. The regulator assembly 900 includes a
gearbox
3 904 linking the drive shaft 112 to a rotor 118, an actuator 902 for
selecting a gear, a
4 pressure sensor 908, and a controller 906 operatively coupled to the
pressure
sensor 908 and the actuator 902. The controller may be connected to the
gearbox
6 904 and the actuator 902 by hydraulic lines, electrical wires, fiber optic
cables,
7 tension cables, or a combination of these, or other known control links.
8 The controller 904 receives pressure information from the pressure
9 sensor 908. The controller 904 selects a higher gear if the pressure
registered by
the pressure sensor 908 is below a first threshold pressure. Alternatively,
controller
11 904 selects a lower gear if the pressure registered by the pressure sensor
908 is
12 above a second threshold pressure. By selecting a higher gear, the rotor
118
13 rotates at a higher speed, increasing the pump's capacity. Selecting a
lower gear
14 has the opposite effect. It may be desirable that the pressure exceed the
particular
threshold for a period of time before the controller 904 selects another gear.
16 Further, the amount of time may vary as a function of the amount by which
the
17 threshold pressure is exceeded.
18 It should be understood that the invention concepts disclosed herein
19 are capable of many modifications. Such modifications may include, but are
not
limited to, modifications in the number, configuration, and sizes of ports,
pump size
21 and displacement, and in particular the use of pumps other than progressive
cavity
22 pumps for either the main pump or charge pump. To the extent such
modifications
CA 02604998 2007-10-01
1 fall within the scope of the appended claims and their equivalents, they are
intended
2 to be covered by this patent.
21
