Note: Descriptions are shown in the official language in which they were submitted.
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PCT PATENT APPLICATION
TUNABLE PROGRESSIVE CAVITY PUMP
Cross Reference to Related Application:
This application claims priority to provisional application 61/878,367, filed
September 16, 2013, and U.S. Non-Provisional Application 14/486,316, filed
September 15,
2014, the fill disclosure of which is hereby incorporated by reference herein
for all purposes.
Field of the Disclosure:
This disclosure relates in general to progressive cavity pumps for wells and
in particular
to a system that changes the inner diameter of the stator in response to
changes in operating
conditions.
Background:
One type of well pump used in oil wells is a progressive cavity pump. The pump
has a
stator with an elastomeric inner portion. An axial cavity having an internal
helical profile
extends through the stator. A rotor with an external helical profile fits
within the axial cavity. A
motor causes the rotor to rotate, with the interaction of the helical profile
on the rotor and the
helical profile in the stator causing fluid to be pumped upward through the
cavity. The rotation
of the rotor also causes the rotor to orbit within the stator.
The interface between the rotor and axial cavity is sensitive and may change
due to
various conditions in the well. The stator may swell, causing the interference
between the rotor
and the helical profile of the axial cavity to create excessive friction,
increasing the torque and
creating a potential to lock or break of the rotor. On the other hand, if the
stator shrinks, the
cross-sectional area of the axial cavity increases, reducing the interference
between the rotor and
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the axial cavity. Erosive wear may also increase the cross-sectional area of
the axial cavity. If
too large, the interface between the rotor and the stator may allow leakage of
well fluid, reducing
the efficiency of the pump.
The radial shrinkage or swelling of the stator depends on well fluids and
environmental
conditions. For example, the hydrocarbon content of the well fluid may cause
the stator to swell,
decreasing the cross-sectional area of the axial cavity while the pump is
being lowered into the
well. Consequently, manufacturers custom size the interference between the
rotor and the axial
cavity for a particular well. However, if the environmental conditions change,
the axial cavity
geometry may cause the pump to either become less efficient or cease to
function.
Summary:
A well pump assembly includes a progressive cavity pump having a stator with
an
elastomeric inner portion. The stator has an axial cavity with an internal
helical profile. A rotor
with an external helical profile is positioned within the axial cavity. A
motor operatively coupled
to the progressive cavity pump rotates the rotor when supplied with power. At
least one effector
is cooperatively associated with the stator to selectively increase and
decrease a stiffness of the
stator. Preferably, a controller senses operating conditions of the
progressive cavity pump
assembly and controls the effector in response. The change in stiffness may be
caused by the
effector increasing and decreasing a cross sectional area of the axial cavity
in the stator.
The effector may comprises a reservoir within the stator separate from the
axial cavity
and containing a pressure fluid. A reservoir pump for selectively increases
and decreases a
pressure of the pressure fluid in the reservoir. The reservoir may be
elongated and extend along
a length of the stator, separated from the axial cavity.
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Alternately, the stator may contain a reservoir filled with a magneto-
rheological fluid
(MR fluid). A coil generates an electromagnetic field within the MR fluid to
selectively increase
and decrease a viscosity of the MR fluid. The MR fluid reservoir may have two
portions axially
spaced apart and connected by an orifice. A coil generates an electromagnetic
field within the
MR fluid at the orifice to selectively increase and decrease a viscosity of
the MR fluid.
The pump assembly may have a plurality of separate effectors spaced along a
length of
the progressive cavity pump. Each of the effectors is separately controllable
for varying a
stiffness of the stator along the length of the progressive cavity pump.
Brief Description of the Drawings:
The present technology will be better understood on reading the following
detailed
description of nonlimiting embodiments thereof, and on examining the
accompanying drawings,
in which:
Figures 1A and 1B are a sectioned side view, partially schematic, of a
progressive cavity
well pump assembly having a stator with tunable features in accordance with
this disclosure.
Figure 2 is an enlarged transverse cross-sectional view of an alternate
embodiment of the
pump of Figure 1A.
Figure 3 is an enlarged axial cross-sectional view of the pump of Figure 1A
with the rotor
not shown.
Figure 4 is an axial cross-sectional view of an alternate embodiment of the
pump of
Figure 3.
Figure 5 is an enlarged axial cross-sectional view of another alternate
embodiment of the
pump of Figure 1A.
Figure 6 is a schematic, perspective exploded view of the pump of Figure 5.
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Figure 7 is a schematic, perspective exploded view of a portion of the
effector of the
pump of Figure 5.
Detailed Description:
Referring to Figure 1A, a cased well 11 has a wellhead assembly or production
tree 13
mounted at its upper end. Production tree 13 is shown schematically and has a
flow line 15 for
discharging production fluid from well 11. A valve 17 opens and closes flow
line 15. Preferably
the surface equipment includes a flow meter 19 connected into flow line 15 for
measuring the
flow rate of the well fluid. Alternately, flow meter 19 could be located in
the well. An electrical
line 21 connects flow meter 19 to a controller 23 located on the surface
adjacent production tree
13.
Production tubing 25 has an upper end supported by a hanger (not shown) in
production
tree 13 and extends into cased well 11. Tubing 25 may comprises joints of pipe
secured by
threads to each other. Alternately, tubing 25 could be continuous coiled
tubing deployed from a
reel.
A progressive cavity pump 27 secures to a lower end of tubing 25 to pump well
fluid up
to production tree 13. Alternately, progressive cavity pump 27 could be
deployed through tubing
25. Pump 27 has a stator 31 within a cylindrical housing 29, which may be
considered to be part
of stator 31. Stator 31 is fixed against rotation in housing 29, and at least
an inner portion is
founed of an incompressible but resilient elastomeric material. Stator 31 has
an axial cavity 33
extending its length that is formed with a helical configuration. In Figures
lA and 3, axial cavity
33 has two helical lobes, creating a sinusoidal appearance, narrowing and
widening with inward
projecting lobes separated by outward extending valleys. Axial cavity 33 could
have more than
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two helical lobes, such as stator 31' in Figure 2, which has an axial cavity
33' with three helical
lobes.
A rotor 35 rotatably extends through stator axial cavity 33. Rotor 35 is
normally of metal
and has an exterior profile 37 that slidingly engages the profile of axial
cavity 33. Exterior
profile 37 has a single helical configuration that is also sinusoidal in
appearance. However,
when viewed in cross-section, the lobes appear on one side of rotor 35 to be
offset from the lobes
on the opposite side, presenting a sinuous appearance. The transverse cross-
sectional appearance
of rotor 35 is illustrated by rotor 35' in Figure 2.
Exterior profile 37 and the profile of axial cavity 33 are well known and
conventional.
Because of exterior profile 37 and the profile of axial cavity 33, when rotor
35 rotates, it orbits
around axis 39 of pump housing 29. As rotor 35 rotates, an interference fit
with axial cavity 33
causes rotor 35 to deflect or deform elastomeric stator 31 inward and outward
as well fluid is
pushed upward into tubing 25.
A gripping section 40 may be mounted to the upper end of rotor 35 to be
engaged by a
tool for retrieving rotor 35 from stator 31. Normally, the upper end of rotor
35 extends above
stator 31, and the lower end of rotor 35 extends below stator 31.
The interface between rotor 35 and axial cavity 33 is sensitive and may change
due to
various conditions in the well. Stator 31 may swell, causing the interference
between rotor 35
and the profile of axial cavity 33 to create excessive friction, increasing
the torque and creating a
potential to lock or break of rotor 35. On the other hand, if stator 31
shrinks, the cross-sectional
area of axial cavity 33 increases, reducing the interference between rotor 35
and axial cavity 33.
Erosive wear may also increase the cross-sectional area of axial cavity 33. If
too large, the
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interface between rotor 35 and axial cavity 33 may allow leakage of well
fluid, reducing the
efficiency of pump 27.
The radial shrinkage or swelling of stator 31 depends on well fluids and
environmental
conditions. For example, the hydrocarbon content of the well fluid may cause
stator 31 to swell,
decreasing the cross-sectional area of axial cavity 33 while pump 27 is being
lowered into the
well. Consequently, manufacturers custom size the interference between rotor
35 and axial
cavity 33 for a particular well. However, if the environmental conditions
change, the axial cavity
geometry may cause the pump to either become less efficient or cease to
function.
To avoid these problems, an effector is employed that selectively increases
and decreases
the stiffness of elastomeric stator 31 in response to changes in operating
conditions. A change in
stiffness also changes the interference between rotor 35 and axial cavity 33.
The effector may
also reduce the cross-sectional area of the axial cavity, which in effect,
changes the stiffness of
stator 31.
Referring to Figure 3, in this example, an effector chamber or reservoir 41
within pump
housing 29 is foinied within or outside of stator 31. In this example,
reservoir 41 comprise
several separate axially extending cavities, each folined within stator 31 and
evenly spaced
around axis 39. Each reservoir 41 could have an axis parallel with axis 39, or
each reservoir
could be helical and extend helically around axis 39. Alternately, reservoir
41 could be annular,
extending completely around an outer diameter of stator 31. Effector reservoir
41 may be
elongated, as shown, and could extend all or just part of the length of stator
31. A pressure fluid
43 pumped by a reservoir pump or compressor 45 selectively increases and
reduces fluid
pressure within reservoirs 41. Pressure fluid 43 may be incompressible, such
as a hydraulic
fluid. Pressure fluid 43 may alternately be a compressible fluid, such as air.
Pressure fluid 43
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within each reservoir 41 is isolated or blocked from fluid communication with
well fluid in axial
cavity 33.
Reservoir pump 45 may be located adjacent to production tree 13 and controller
23 (Fig.
1A). Controller 23 (Fig. 1A) controls reservoir pump 45 based on torque sensed
and the flow
rate of well fluid being monitored by flow meter 19. As an alternate to being
mounted adjacent
to production tree 13, the portion of controller 23 that controls reservoir
pump 45 could be
mounted to progressive cavity pump 23 within the well. Reservoir pump 45 draws
fluid 43 from
a tank 47. A valve 48 allows reservoir pump 45 to pump fluid 43 to reservoirs
41 and will hold
the pressure when reservoir pump 45 is turned off. When actuated by controller
23, valve 48
allows flow back of fluid 43 to tank 47.
When the pressure of fluid 43 increases, reservoirs 41 expand and stiffen
stator 31. If
rotor 35 is not present, as shown in Figure 3, the increase in fluid pressure
in reservoirs 41 causes
the dimensions of axial cavity 33 to shrink, as indicated by the dotted lines
49. The flow area of
axial cavity 33 thus shrinks. The difference between the unaltered size of
axial cavity 33 and the
reduced size shown by the dotted lines may only be 0.20 inches or less, as an
example. During
operation, rotor 35 (Fig. 1) will be present, and being metal, it does not
change dimensions in
response to increasing pressure in reservoirs 41. Thus the interference
between rotor 35 and
axial cavity 33 increases in response to increasing fluid pressure within
reservoirs 41.
Referring to Figure 1A, rotor 35 may be driven in various conventional
manners. In this
example, a flex shaft 51 couples to a lower end of rotor 35 via a coupling 53
that allows rotor 35
to stab into engagement with flex shaft 51. Flex shaft 51 rotates within a
connector shaft housing
55 that has a well fluid intake 57 for admitting well fluid to axial cavity
33. A concentric
coupling 59 connects to and causes the lower end of flex shaft 51 to remain
concentric on axis
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39. The upper end of flex shaft 51 and coupling 53 orbit. Flex shaft 51 is
typically formed of a
steel material.
A drive shaft 61 has an upper end that connects to concentric coupling 59.
Drive shaft 61
extends through a seal section 63. In this example, a gear reducer 65 secures
to the lower end of
seal section 63 to reduce the rotational speed of drive shaft 61. An
electrical motor 67 couples to
the lower end of gear reducer 65. Motor 67 may be a three-phase type that
rotates typically
around 3600 rpm. Motor 67 has a drive shaft (not shown) that couples to gear
reducer 65 for
rotating drive shaft 61 at a lower rate of speed. A dielectric lubricant fills
motor 67 and also part
of seal section 63. Seal section 63 reduces a pressure differential between
well fluid on the
exterior and the lubricant within motor 67. Seal section 63 may be a
conventional type having a
communication port that admits well fluid to one side of a bag or bellows, the
other side being in
contact with the lubricant. A power cable 69 connects to motor 67 and extends
alongside tubing
25 to the surface where it connects to controller 23. Optionally, a sensing
unit 71 may connect to
motor 67. Sensing unit 71 senses various parameters such as temperature and
well fluid
pressure.
Pump 27 may alternately be driven by a motor located adjacent production tree
13. In
that case, a drive rod (not shown) extends from the surface motor to pump 27.
In operation, controller 23 supplies electrical power to motor 67, which
causes rotor 35
to rotate, pumping well fluid up tubing 25 to production tree 13. Controller
23 monitors the flow
rate with flow meter 19. Controller 23 also monitors the torque required to
rotate rotor 35.
Torque monitoring can be accomplished various ways. In one example, controller
23 monitors
the electrical current supplied via power cable 69 to motor 67. Controller 23
will actuate
reservoir pump 45 to increase the pressure of fluid 43 in reservoirs 41 if the
flow rate drops
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below an acceptable level. Controller 23 will stop reservoir pump 45 from
increasing the fluid
pressure in reservoirs 41, and with valve 48, hold the desired pressure once a
desired flow rate is
reached. Controller 23 will also control valve 48 to bleed off pressure in
reservoirs 41 if the
torque monitored is too high.
The initial interference between rotor 35 and stator axial cavity 33 could be
sized loosely
enough so that once pump 27 has been located in the well, the start up torque
will not be
excessive. That is, possible swelling of stator 31 could be accounted for in
advance by making
the dimensions of stator axial cavity 33 sufficiently large so that expected
swelling would not
cause too much interference between stator 31 and rotor 35. When pump 27 is
first installed,
reservoir pump 45 would not be operating, and the pressure of fluid 43 in
reservoirs 41 would be
equal to the hydrostatic pressure of the well fluid in the well. After pump 27
operates for a
selected duration, controller 23 may increase the stiffness of stator 31 by
causing reservoir pump
45 to increase the pressure of fluid 43 in reservoirs 41, thereby increasing
the flow rate of well
fluid. If the torque becomes too high, controller 23 actuates valve 48 to
bleed off some of the
pressure in reservoirs 41. Controller 23 thus continually tunes pump 27 to
operate with a
desired stiffness of stator 31. As an alternate to automatic control by
controller 23 based on
torque and flow rate, the operator could manually adjust the stiffness of
stator 31 with manual
controls on controller 23 to change the pressure within reservoirs 41.
Referring to Figure 4, progressive cavity pump 27' has more than one stator
portion, and
three portions are shown by the numerals 31a, 31b, and 31c. Stator portions
31a, 31b, 31c are
shown stacked coaxially on each other within a single housing 29', however
they could have
separate housings secured to each other. Each stator portion 31a, 31b, and 31c
has one or more
reservoirs 41a, 41b and 41c, respectively. A separate flow line 74a, 74b and
74c leads from the
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reservoirs 41a, 41b and 41c. A separate valve 48a, 48b and 48c is located in
each flow line 74a,
74b and 74c, respectively. In this example, a single reservoir pump 45 (Fig.
3) supplies pressure
fluid through the separate valves 48a, 48b and 48c to separate flow lines 74a,
74b, and 74c.
Flow lines 74a, 74b and 74c are illustrated on the exterior of housing 29',
but they could extend
upward through the stator portions 31a, 31b and 31c to an upper end of
progressive cavity pump
27'. The pressure fluid in each reservoir 74a, 74b and 74c is isolated or not
in fluid
communication with the pressure fluid in the other reservoirs 74a, 74b and
74c.
During operation of the embodiment of Figure 4, the well fluid pressure within
stator
cavity 33' caused by the rotation of the rotor (not shown) gradually increases
from the bottom to
the top of progressive cavity pump 27'. Because of the lower pressure within
lower stator
portion 31a, the desired stiffness of lower stator portion 31a may be less
than the desired
stiffness in interniediate stator portion 3 lb. Similarly, the optimum
stiffness in intermediate
stator portion 31b may be less than the optimum stiffness of upper stator
portion 31c. More
interference and stiffness may be desirable in the portions of pump 27' having
higher fluid
pressures. Controller 23 (Fig. 1A) can control pump 45 and valves 48a, 48b and
48c to provide a
different reservoir fluid pressure in each reservoir 41a, 41b and 41c.
Alternately, an operator
could manually control valves 48a, 48b and 48c to maintain different pressures
in reservoirs 41a,
41b and 41c.
Although three separate stator portions 31a, 31b and 31c are illustrated, pump
27' could
have more or fewer. Also, rather than separate stator portions, a single
stator could have several
zones along its length, each zone having a separate reservoir.
Referring to Figures 5 - 7, in this embodiment, two separate stator sections
73a, 73b are
illustrated, but more could be employed. Stator sections 73a, 73b are axially
aligned along a
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longitudinal axis 75 and spaced axially apart from each other a short
distance. Referring more
particularly to Figure 5, each stator section 73a, 73b is of incompressible
elastomeric material
fixed for non rotation within a steel housing 77. The ends of housings 77 may
protrude past the
ends of stator sections 73a, 73b and abut each other. Each stator section 73a,
73b has an axial
cavity 79 for receiving a conventional rotor 80, which is a single-piece
member extending
through both stator sections 73a, 73b.
A stator stiffness effector 81 is mounted between opposing ends of stator
sections 73a,
73b. Effector 81 has a rigid tubular body 83 with one end abutting stator
section 73a and the
other end abutting stator section 73b. Body 83 has an axial bore 85 that is
cylindrical and has a
diameter large enough so that rotor 80 does not contact it as rotor 80 rotates
and orbits. Effector
body 83 has at least one, and preferably several magneto rheological (MR)
passages 87. In this
example, three MR passages 87 are shown in Figure 7, spaced equally around
axis 75. Each MR
passage 87 has a first or upper section 87a and a second or lower section 87b.
Each section 87a,
87b joins a central pocket 88 formed in effector body 83. In this example,
effector body 83 has
three pockets 88.
Mating MR fluid reservoirs 89 are formed within stator sections 73a, 73b to
register with
MR passages 87. Each MR fluid reservoir 89 may have the same diameter as each
MR passage
87. Seals (not shown) seal the interface between MR passages 87 and MR fluid
reservoirs 89.
Each MR fluid reservoir 89 extends parallel to axis 75 a selected distance and
has a closed end
opposite the end joining MR passages 87. The axial length of each MR fluid
reservoir 89 need
not be as long as each stator section 73a, 73b, but could be. MR fluid
reservoirs 89a are located
in stator section 73a and mate with MR passage sections 87a. MR fluid
reservoirs 89b are
located in stator section 73b and mate with MR passage sections 87b.
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An orifice or tube 91extends through each pocket 88 and connects each MR fluid
passage
87a with the corresponding MR fluid passage 87b. Orifice tube 91 seals to MR
fluid passages
87a, 87b and has a flow area smaller than the flow areas of MR fluid passages
87a, 87b, creating
an orifice.
A magneto rheological (MR) fluid 93 is located in MR reservoirs 89, MR fluid
passages
87 and orifice tubes 91. MR fluid 93 is a known liquid that will undergo a
significant change in
viscosity when an electromagnetic field passes through MR fluid 93. One or
more coils or
electromagnets 95 are located within each pocket 88 adjacent to each orifice
tube 91 to impose
an electromagnetic field on MR fluid 93 contained in orifice tube 91. In this
example, two
substantially flat electromagnets 95 are located in each pocket 88, one or
each side of orifice tube
91. Electromagnets 95 are connected by wires (not shown) to a controller, such
as controller 23
(Fig. 1) to selectively supply electrical current.
Stator sections 73a, 73b may be secured together with effector 81 sandwiched
between in
various manners. If desired, effectors 81 could also be located at the upper
end of stator section
73a and lower end of stator section 73b. A collar or clamp 99 is schematically
illustrated as
enclosing effector 81 and joining stator housings 77. Effector body 83 may
have an outer
diameter smaller than the inner diameter of housings 77, as illustrated, and
fits within the
portions of housings 77 that extend beyond stators 73a, 73b. Rather than a
collar 99, the abutting
ends of housings 77 could be welded to each other or secured in other manners.
During operation of the embodiment of Figures 5 ¨ 7, rotation of rotor 80
exerts radial
outward forces on each stator section 73a, 73b, causing lobes within axial
cavity 79 to deflect
radially back and forth. The deflection force transmits through stator
sections 73a, 73b and acts
radially on MR fluid reservoirs 89a, 89b, alternately squeezing and relaxing
reservoirs 89a, 89b.
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This alternating force on MR fluid reservoirs 89a, 89b causes a pumping action
of MR fluid 93,
causing it to flow in an oscillating manner through orifice tubes 91. At the
same time, the
rotation of rotor 80 pumps well fluid through axial cavity 79 up from stator
section 73a.
If controller 23 (Fig. 1A) senses from flow meter 19 that the flow rate of
well fluid is too
low, it will send a signal to electromagnets 95, which impose an
electromagnetic field on MR
fluid 93 flowing through orifice tube 91. The viscosity of MR fluid 93 within
each orifice tube
91 increases as a result, which slows the flow rate between MR fluid
reservoirs 89a, 8911 The
fluid pressure within reservoirs 89a, 89b increases as the helical lobes of
rotor 80 exert radial
outward forces on stator sections 73a, 73b. The increased pressure resists the
outward deflection
of stator sections 73a, 73b, thereby increasing the stiffness of stator
sections 73a, 73b. The
increased stiffness effectively increases the interference between rotor 80
and stator sections 73a,
73b, thereby increasing the flow rate.
If controller 23 senses that the torque to rotate rotor 80 is too high, it
will cut off the
voltage supplied to electromagnets 95. The viscosity of MR fluid 93 within
orifice tubes 91
rapidly drops, lowering the pumping pressure within MR fluid reservoirs 89.
The stiffness of
stator sections 73, 73b thus decreases to reduce the torque. Rather than
automatically controlling
the stiffness with controller 23 based on torque and well fluid flow, an
operator could manually
vary the stiffness with manual controls on controller 23 to supply voltage to
electro magnets 95.
The embodiment of Figures 5 ¨ 7 could also be incorporated into separate
zones, in a
manner similar to the embodiment shown in Figure 4. Controller 23 (Fig. 1A)
could supply
voltages to electromagnets 95 in one or more of the zones to increase or
decrease the viscosity
and not to other of the zones. Also, the zones could be manually controlled.
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The foregoing aspects, features, and advantages of the present technology will
be further
appreciated when considered with reference to the following description of
preferred
embodiments and accompanying drawings, wherein like reference numerals
represent like
elements. In describing the preferred embodiments of the technology
illustrated in the appended
drawings, specific teoninology will be used for the sake of clarity. However,
it is to be
understood that the specific terminology is not limiting, and that each
specific teon includes
equivalents that operate in a similar manner to accomplish a similar purpose.
For example, other effectors to increase and decrease the stiffness of the
stator in
response to changing conditions are feasible. Shape memory gel and shape
memory alloys
change shapes in response to voltage changes. Piezoelectric crystals, voice
coils or any other
media or elements that alter geometry in response to changing conditions
sensed could also be
used.
Although the technology herein has been described with reference to particular
embodiments, it is to be understood that these embodiments are merely
illustrative of the
principles and applications of the present technology. It is therefore to be
understood that
numerous modifications may be made to the illustrative embodiments and that
other
arrangements may be devised without departing from the spirit and scope of the
present
technology.
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