Note: Descriptions are shown in the official language in which they were submitted.
CA 02831924 2013-10-29
APPARATUS, SYSTEM AND METHOD FOR PUMPING GASEOUS FLUID
1001] BACKGROUND OF THE INVENTION
[002] 1. FIELD OF THE INVENTION
[003] Embodiments of the invention described herein pertain to the field of
electric
submersible pump assemblies. More particularly, but not by way of limitation,
one or more
embodiments of the invention enable an apparatus, system and method for
pumping gaseous
fluid in electric submersible pump down-hole applications.
[004] 2. DESCRIPTION OF THE RELATED ART
[005] Fluid, such as gas, oil or water, is often located in underground
formations. In such
situations, the fluid must be pumped to the surface so that it can be
collected, separated,
refined, distributed and/or sold. Centrifugal pumps are typically used in
electric submersible
pump applications for lifting well fluid to the surface. Centrifugal pumps
impart energy to a
fluid by accelerating the fluid through a rotating impeller paired with a
stationary diffuser.
The rotation confers angular momentum to the fluid passing through the pump.
The angular
momentum converts kinetic energy into pressure, thereby raising the pressure
on the fluid and
lifting it to the surface. Multiple stages of impeller and diffuser pairs may
be used to further
increase the pressure.
[006] Conventional centrifugal pump assemblies are designed to handle fluid
consisting
mainly of liquids. However well fluid often contains gas in addition to
liquid. Currently
available submersible pump systems are not appropriate for pumping fluid with
a high gas to
liquid ratio, also termed a high gas volume fraction (GVF). Particularly,
submersible pump
systems need to be better suited to manage gas contained in well fluid. When
pumping gas
laden fluid, the gas may separate from the other fluid due to the pressure
differential created
when the pump is in operation. The separated gas forms bubbles in the liquid.
If there is a
sufficiently high GVF, typically around 10% to 15%, the pump may experience a
decrease in
efficiency and decrease in capacity or head (slipping). If gas continues to
accumulate on the
suction side of the impeller, gas bubbles may entirely block the passage of
other fluid through
the impeller. When this occurs the pump is said to be "gas locked" since
proper operation of
the pump is impeded by the accumulation of gas. As a result, careful attention
to gas
CA 02831924 2013-10-29
management in submersible pump systems is needed in order to improve the
production of
gas laden fluid from subsurface formations.
[007] A typical impeller of a centrifugal pump is shown in FIGs. 1A and 1B. In
FIG. 1A,
closed impeller 100 is shown with six evenly spaced conventional vanes 105.
For illustration
purposes only, upper conventional shroud 110 and lower conventional shroud 115
are shown
in FIG 1B, but are not shown in FIG. 1A. FIG. 1B shows a cross sectional view
of closed
impeller 100 with two conventional shrouds, upper conventional shroud 110 and
lower
conventional shroud 115. In FIG. 1B, conventional hub 125 is long and hollow
and
connected to lower conventional shroud 115, upper conventional shroud 110 and
conventional
vanes 105. Conventional hub 125 slides over conventional shaft 130 and is
keyed to
conventional shaft 130, which causes closed impeller 100 to rotate with
conventional shaft
130. Closed impeller 100 rotates counterclockwise or clockwise with shaft 130.
Apertures
120 (shown in FIG. 1A) balance the pressure on each side of closed impeller
100.
Conventional closed impeller 100 has a suction specific speed of about 6000.
[008] Closed impeller 100 is paired with a conventional stationary diffuser,
such as that
shown in FIG 2, such that each impeller rotates within (inward of) the
diffuser to which it is
paired. The diffuser does not rotate, but is mounted co-axially with the
impeller and nests on
the diffuser of the previous stage. Typically there is a clearance gap between
the diffuser and
impeller to which it is paired. This conventional clearance gap is typically
about 0.015 inches
to about 0.02 inches in width for conventional semi-open impellers.
[009] Currently, gas separators are sometimes used in pump assemblies in an
attempt to
address the problems caused by gas in produced fluid. In such instances, a gas
separator
typically replaces the intake section of a pump assembly in a well containing
fluid with a high
GVF, with the upstream end of the intake including ports to take in well
fluid. Gas
separators attempt to remove gas from produced fluid prior to the fluid's
entry into the pump
section of the assembly. These separators, which also include a rotating shaft
through their
center, employ the inertia of rotating motion to separate fluid of varying
density. There are
two main types of gas separators, vortex and rotary. FIGs. 8A and 8B
illustrate gas separators
of the prior art. FIG. 8A is a rotary gas separator of the prior art. FIG. 8B
is a vortex gas
separator of the prior art. However it is often infeasible, costly or too time
consuming to
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ascertain the correct type of pump and separator combination which might be
effective for a
particular well, and even if the correct arrangement is ascertained, the
separator may not
remove enough gas to prevent a loss in efficiency and/or prevent gas locking.
[0010] In the case of an electric submersible pump (ESP), a failure of the
pump or any
support components in the pump assembly can be catastrophic as it means a
delay in well
production and having to remove the pump from the well for repairs. A gas
separator for a
submersible pump assembly capable of reducing bubble size, homogenizing
produced
gaseous fluid and venting unhomogenized gas would be an advantage in all types
of
submersible assemblies.
[0011] Currently available pump assemblies do not contain components to
satisfactorily
homogenize gas laden fluid and prevent gas locking. This shortcoming decreases
the
efficiency and overall effectiveness of the pump assembly. Therefore, there is
a need for an
apparatus, system and method for pumping gaseous fluid in electric submersible
pump
applications.
BRIEF SUMMARY OF THE INVENTION
[0012] One or more embodiments of the invention enable an apparatus, system
and method
for pumping gaseous fluid.
[0013] An apparatus, system and method for pumping gaseous fluid are
described. An
electric submersible pump (ESP) of an illustrative embodiment comprises a gas
separator, the
gas separator comprising an impeller inward of a diffuser, the impeller
comprising a top side
and a bottom side, the top side open to the diffuser, and wherein the impeller
further
comprises a single shroud located on the bottom side of the impeller and
arranged radially
about a hub, an untruncated vane extending substantially upstream from the
single shroud,
and a truncated vane extending substantially upstream from the single shroud,
and a
centrifugal pump, the centrifugal pump fluidly coupled to the gas separator
and arranged to
receive substantially homogenized fluid from the gas separator. In some
embodiments, the
impeller further comprises an inlet area, the inlet area between about 1.75
and about 2.5 times
a size of a conventional inlet area. In some embodiments, the impeller
comprises at least two
untruncated vanes extending substantially upstream from the single shroud and
at least two
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truncated vanes extending substantially upstream from the single shroud,
wherein each
truncated vane sits at a mid-pitch location between untruncated vanes starting
from the bottom
side of the impeller. In some embodiments, the truncated vanes are between
about 50% and
about 75% of a chord length of the untruncated vanes. In some embodiments, the
gas
separator comprises an increased clearance gap between the impeller and the
diffuser. In
certain embodiments, the increased clearance gap is between about 0.060 inches
and about
0.180 inches wide. In some embodiments, the impeller is configured to operate
at about 8000
to about 12000 suction specific speed.
[0014] A system for pumping gaseous fluid from an underground well of an
illustrative
embodiment comprises a gas separator, the gas separator comprising an impeller
configured
to homogenize at least a portion of a gas and a liquid in a pumped fluid to
obtain
homogenized fluid, the impeller comprising a top side open to the diffuser,
and a truncated
vane located at a mid-pitch location between at least two untruncated vanes
starting from a
bottom side of the impeller; and a gas separation chamber downstream of the
impeller, the gas
separation chamber configured to vent an unhomogenized gas, and a centrifugal
pump
arranged to receive the homogenized fluid from the gas separation chamber. In
some
embodiments the system further comprises a bushing and a flanged sleeve
located directly
upstream of a hub of the impeller. In some embodiments, the impeller comprises
three
untruncated vanes and three truncated vanes, wherein each truncated vane sits
at a mid-pitch
location between the untruncated vanes. In some embodiments the system
comprises a
diffuser, wherein a clearance gap between the impeller and the diffuser is
between about
0.060 inches and about 0.180 inches wide. In some embodiments, the truncated
vane is
between about 50% and about 75% of a chord length of the untruncated vane. In
some
embodiments, the impeller comprises an increased inlet area, the increased
inlet area between
about 1.75 and about 2.5 times a size of a conventional inlet area.
[0015] Illustrative embodiments of a method for pumping gaseous fluid
comprises placing an
electric submersible pump assembly into a well containing a gaseous fluid, the
assembly
comprising a gas separator and a centrifugal pump, operating the assembly to
induce the fluid
to flow towards the surface of the well, minimizing phase separation of the
fluid using an
impeller located in the gas separator to obtain substantially homogenized
fluid, removing an
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unhomogenized gas from the assembly in a gas separation chamber of the gas
separator; and
lifting the homogenized fluid to the surface using the centrifugal pump. In
some
embodiments, the pressure differential is reduced by increasing an inlet area
of the impeller.
In some embodiments, the inlet area is increased by replacing an impeller vane
of the impeller
with a truncated vane. In some embodiments, the impeller comprises at least
two untruncated
vanes, and wherein the truncated vane is placed at a mid-pitch location
between the at least
two untruncated vanes starting from a bottom side of the impeller. In some
embodiments the
method further comprises the step of carrying at least a portion of the axial
thrust on the
centrifugal pump with a flanged sleeve and a bushing located directly upstream
of the
impeller. In some embodiments, the method further comprises the step of
causing at least a
portion of the fluid to flow through an increased clearance gap between the
impeller and a
diffuser. In certain embodiments, the increased clearance gap is between about
0.060 inches
and about 0.180 inches wide.
[0016] Illustrative embodiments of an impeller for an electric submersible
pump assembly
comprises a top side and a bottom side, the top side open to a diffuser, a
single shroud located
on the bottom side of the impeller and arranged radially about a hub, at least
two untruncated
vanes extending substantially upstream from the single shroud, at least two
truncated vanes
extending substantially upstream from the single shroud, and wherein each
truncated vane sits
at a mid-pitch location between untruncated vanes starting from the bottom
side of the
impeller.
[0017] In further embodiments, features from specific embodiments may be
combined with
features from other embodiments. For example, features from one embodiment may
be
combined with features from any of the other embodiments. In further
embodiments,
additional features may be added to the specific embodiments described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The above and other aspects, features and advantages of the
illustrative embodiments
will be more apparent from the following more particular description thereof,
presented in
conjunction with the following drawings wherein:
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[0019] FIG. 1A illustrates a plan view of an impeller of the prior art.
[0020] FIG. 1B illustrates a cross sectional view of an impeller of the prior
art.
[0021] FIG. 2 illustrates a perspective view of a diffuser of the prior art.
[0022] FIG. 3 illustrates one embodiment of an exemplary electric submersible
pump (ESP)
assembly.
[0023] FIG. 4A illustrates a perspective view of one embodiment of a semi-open
impeller.
[0024] FIG. 4B illustrates a perspective view of one embodiment of a semi-open
impeller.
[0025] FIG. 5 is a partial cross sectional view taken along line 5-5 of FIG. 9
of one
embodiment of an impeller installed in a gas separator.
[0026] FIG. 6 is a cross sectional view taken along line 6-6 of FIG. 9 of one
embodiment of
an impeller and diffuser pair in a submersible pump assembly.
[0027] FIG. 6A is an enlarged view of the inlet area of an impeller of
illustrative
embodiments.
[0028] FIG. 7 is a flow chart illustrating an exemplary method of pumping
gaseous fluid.
[0029] FIG. 8A illustrates a gas separator of the prior art.
[0030] FIG. 8B illustrates a gas separator of the prior art.
[0031] FIG. 9 illustrates one embodiment of an exemplary electric submersible
pump (ESP)
assembly including a gas separator.
[0032] FIG. 10 is a cross sectional view of one embodiment of an exemplary
rotary gas
separator.
[0033] FIG. 11 is a cross sectional view of one embodiment of an exemplary
vortex gas
separator.
[0034] While the invention is susceptible to various modifications and
alternative forms,
specific embodiments thereof are shown by way of example in the drawings and
may herein
be described in detail. The drawings may not be to scale. It should be
understood, however,
that the embodiments described herein and depicted in the drawings are not
intended to limit
the invention to the particular form disclosed, but on the contrary, the
intention is to cover all
modifications, equivalents and alternatives falling within the scope of the
present invention as
defined by the appended claims.
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DETAILED DESCRIPTION
[0035] An apparatus, system and method for pumping gaseous fluid will now be
described.
In the following exemplary description, numerous specific details are set
forth in order to
provide a more thorough understanding of embodiments of the invention. It will
be apparent,
however, to an artisan of ordinary skill that the present invention may be
practiced without
incorporating all aspects of the specific details described herein. In other
instances, specific
features, quantities, or measurements well known to those of ordinary skill in
the art have not
been described in detail so as not to obscure the invention. Readers should
note that although
examples of the invention are set forth herein, the claims, and the full scope
of any
equivalents, are what define the metes and bounds of the invention.
[0036] As used in this specification and the appended claims, the singular
forms "a", "an"
and "the" include plural referents unless the context clearly dictates
otherwise. Thus, for
example, reference to a vane includes one or more vanes.
[0037] "Coupled" refers to either a direct connection or an indirect
connection (e.g., at least
one intervening connection) between one or more objects or components. The
phrase
"directly attached" means a direct connection between objects or components.
[0038] "Bottom" or "lower" side of an impeller refers to the substantially
downstream side of
an impeller.
[0039] "Top" or "upper" side of an impeller refers to the substantially
upstream side of an
impeller.
[0040] "Downstream" refers to the direction substantially with the primary
flow of fluid
when the centrifugal pump is in operation.
[0041] "Upstream" refers to the direction substantially opposite the primary
flow of fluid
when the centrifugal pump is in operation.
[0042] "Homogenize," means, with respect to a fluid containing gas and liquid,
to
sufficiently reduce the size of gas bubbles in the fluid, such that the fluid
acts substantially
similar to a single-phase liquid as it moves through an ESP pump.
[0043] One or more embodiments of the invention provide an apparatus, system
and method
for pumping gaseous fluid for use in electric submersible pump applications.
While the
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invention is described in terms of an oil or water production embodiment,
nothing herein is
intended to limit the invention to that embodiment.
100441 The invention disclosed herein includes an apparatus, system and method
for pumping
gaseous fluid. Illustrative embodiments of the invention enable substantially
all gases to be
either homogenized with or separated from produced fluid to allow a
submersible pump to
operate without gas locking. In some embodiments, after intake into the pump
assembly, gas
laden fluid may be rotated by an ESP assembly including a semi-open impeller.
In some
embodiments, the semi-open impeller may be located in the centrifugal pump. In
other
embodiments, the semi-open impeller may be located in a gas separator. In some
embodiments, the semi-open impeller includes only a single shroud arranged
radially about a
hub. In some embodiments, a truncated vane and an untruncated vane, which may
be arranged
circumferentially about the hub, may extend substantially upstream from the
single shroud. In
some embodiments, the truncated vane may be located at a mid-pitch location
between two
untruncated vanes starting from the bottom side of the impeller. In certain
embodiments, the
impeller may include two, three or four of each truncated and untruncated
vanes which
alternate around the hub. In some embodiments, the impeller may include an
increased inlet
area. In some embodiments, there may be an increased clearance gap between the
impeller
and a diffuser, through which the fluid may flow. In some embodiments, a gas
separator
including the semi-open impeller of illustrative embodiments may reduce gas
bubble size,
homogenize a portion of the gas laden fluid and vent unhomogenized gas,
sending
substantially homogenized fluid to the centrifugal pump.
[0045] The features of the invention may minimize phase separation of the
fluid by reducing
the pressure differential between the pressure side and suction side of an
impeller vane. This
may reduce gas bubble size, homogenize the liquid and gas in the fluid,
increase the
efficiency and performance of the pump, prevent gas locking and reduce the
producing well's
downtime. When used in a gas separator, the features of illustrative
embodiments may
homogenize at least a portion of the liquid and gas in the fluid, after which
any remaining
unhomogenized gas may be removed from the pump assembly by the gas separator
prior to
the fluid's entry into the pump. Illustrative embodiments of the invention may
homogenize or
remove about 100% of gas in well fluid. Illustrative embodiments reduce the
quantity of
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CA 02831924 2013-10-29
unhomegenized gas, making greater pump and gas separator combinations
effective in
preventing gas locking, and thereby improving the feasibility of finding a
suitable pump and
gas separator combination.
[0046] In some embodiments, the vanes of the present disclosure are arranged
such that there
is a larger inlet area of the impeller than in conventional impeller designs.
Specifically, the
reduction in the number of untruncated vanes and addition of one or more
truncated vanes of
the present disclosure provide for additional open space in the inlet region
of the impeller.
The impeller of an illustrative embodiment may have between about 1.75 and 2.5
times the
size of the inlet area of a conventional impeller. The additional open space
may reduce the
velocity of the fluid passing through the impeller, which assists in
maintaining high positive
pressure at the impeller inlet. The impeller of the present disclosure is
capable of operating
with higher suction specific speed as compared to conventional impellers. In
some
embodiments, the impeller of the present disclosure may operate at about 8000
to about 12000
suction specific speed.
[0047] The invention includes a centrifugal pump, or a gas separator and
centrifugal pump,
for electric submersible pump (ESP) systems. FIG. 3 illustrates one embodiment
of an
exemplary ESP assembly without a gas separator for use in the system of the
invention. FIG.
9 illustrates one embodiment of an exemplary ESP assembly with gas separator
for use in the
system of the invention. In either case, the assembly may be located in an
underground well
during operation.
[0048] As shown in FIG. 3, ESP primary pump 220 and production tubing string
225 are
downstream of ESP charge pump 200. In some embodiments, motor lead extension
230 may
plug into ESP motor 250 at one end and may be spliced to another larger cable
than runs the
length of the well bore to a junction box and/or a control panel on the
surface of the well site.
Production tubing string 225 may be a conduit for the produced well fluid to
flow from the
reservoir towards the surface. ESP seal 240 sits between ESP motor 250 and ESP
intake 210
and may protect ESP motor 250 from well fluid. As shown in the ESP assembly of
FIG. 3, a
semi-open impeller of an illustrative embodiment may be included in ESP charge
pump 200,
which is located downstream of ESP intake 210. Fluid enters the ESP assembly
through fluid
intakes 215 on ESP intake 210. The ESP charge pump 200 of an illustrative
embodiment may
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homogenize fluid prior to the fluid entering ESP primary pump 220. In some
embodiments, a
semi-open impeller of illustrative embodiments may instead be included in ESP
primary
pump 220. Rotating shafts (not shown) pass through the center of the assembly
components,
causing fluid entering the assembly to rotate. ESP primary pump 220 and/or ESP
charge
pump 200 may be centrifugal pumps.
[0049] In some embodiments, a gas separator may be located between ESP intake
210 and
ESP charge pump 200 of FIG. 3 to reduce the gas content of the fluid prior to
the fluid
entering ESP primary pump 220 and/or ESP charge pump 200. In some embodiments,
a gas
separator may eliminate the need for an ESP charge pump. When used, the gas
separator may
be the intake surface for the ESP pump system.
[0050] In certain embodiments, a semi-open impeller of an illustrative
embodiment may be
employed, not in ESP charge pump 200 or ESP primary pump 220, but in a gas
separator to
homogenize gas and liquid and separate unhomegenized gas from the homogenized
fluid,
prior to the fluid's entry into ESP charge pump 200 and/or ESP primary pump
220. FIG. 9
illustrates one embodiment of an exemplary ESP assembly with gas separator for
use in
illustrative embodiments. As shown in FIG. 9, fluid enters port 915 located on
gas separator
910. Gas separator 910 may employ the semi-open impeller of illustrative
embodiments to
first homogenize at least a portion of the gas and liquid in the well fluid,
and may
subsequently vent any remaining unhomgenized gas to the annulus (shown in
FIGs. 10 and
11) of the separation chamber (shown in FIGs. 10 and 11) of gas separator 910,
thereby
reducing or eliminating gas contained in the fluid continuing on to ESP
primary pump 220.
Gas separator 910 may be a rotary or vortex type separator.
[0051] FIGs. 4A and 4B illustrate perspective views of one exemplary
embodiment of a
semi-open impeller of an illustrative embodiment. Impeller 30 may include
single shroud 300
arranged radially about hub 310. Truncated vane 320 and untruncated vane 330
may extend
substantially upstream from single shroud 300. In some embodiments, truncated
vane 320 sits
at a mid-pitch location between two untruncated vane 330 starting from the
bottom side of
impeller 30. In certain embodiments, truncated vane 320 alternates with
untruncated vane
330, which vanes 320, 330 are circumferentially disposed about hub 310. In
some
embodiments there are two, three or four of each truncated vane 320 and
untruncated vane
CA 02831924 2013-10-29
330 disposed about hub 310. Greater or fewer number of vanes 320, 330 may also
be used. In
certain embodiments, the number of truncated vane 320 varies from the number
of
untruncated vane 330 and/or the vanes 320, 330 may not strictly alternate. In
FIG. 4B,
balance hole 340 are also shown on impeller 30 and assist in equalizing the
pressure on each
side of impeller 30. In some embodiments, impeller 30 may operate at about
8000 to about
12000 suction specific speed. In some embodiments, truncated vane 320 may
increase the
performance of a pump's head flow and efficiency and maintain high net
positive suction
pressure, without sacrificing suction performance.
[0052] FIG. 5 is a partial cross sectional view taken along line 5-5 of FIG. 9
of one
illustrative embodiment of an impeller for an ESP assembly. FIG. 5 illustrates
one
embodiment of single shroud 300 and the arrangement of vanes 320, 330 disposed
about hub
310 of impeller 30. In some embodiments, truncated vane 320 is between about
50% and 75%
the chord length of untruncated vane 330 (as judged from hub 310 and extending
from the
outer circumference of single shroud 300). In certain embodiments, truncated
vane 320 may
be shorter or longer but always shorter in chord length than untruncated vane
330. In some
embodiments, a centrifugal pump and/or gas separator of an illustrative
embodiment may
include abrasion resistant trim, such as busing 560 and flanged sleeve 570
(shown in FIG. 6)
to increase the lifespan of the centrifugal pump in the instance that solids
are also present in
the produced well fluid.
[0053] In some embodiments the arrangement of vanes 320, 330 create inlet area
610 of
impeller 30 between about 1.75 and about 2.5 times the size of the inlet area
of a conventional
impeller. One embodiment of inlet area 610 is illustrated in FIG. 6A. As shown
in FIG. 6A,
the size of inlet area 610 may be calculated using the formula:
Inlet Area =27tRII ¨ B
where R is mean inlet radius 620 as measured from centerline 640, H is inlet
vane height 630
and B is the vane blockage. The vane blockage may be calculated as follows:
Vane Blockage = NH 7--
sin 13
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where N is the number of untruncated vane 330 in impeller 30, H is inlet vane
height 630, T is
vane thickness 350 (shown in FIG. 5) and 13 is the inlet vane angle (shown in
FIG. 5).
[0054] As truncated vane 320 do not contribute to vane blockage, the
arrangement of vanes
320, 330 of an illustrative embodiment reduce the vane blockage and thereby
increase inlet
area 610.
[0055] FIG. 6 is a cross sectional view taken along line 6-6 of FIG. 9 of one
embodiment of
an impeller of an illustrative embodiment. As shown in FIG. 6, impeller 30 is
implemented in
gas separator 910, but impeller 30 may instead or also be implemented in ESP
charge pump
200 and/or ESP primary pump 220. Impeller 30 may be keyed to shaft 540 at hub
310, such
that impeller 30 rotates with shaft 540. Impeller 30 is paired with diffuser
510. FIGs. 6, 6A
show untruncated vane 330 for illustration purposes, but truncated vane 320
may also be
included in impeller 30 in addition to or instead of untruncated vane 330, for
example as
shown in FIGS. 4A, 4B and/or FIG. 5. In some embodiments, no shroud is present
on top
side 550 of impeller 30. Single shroud 300 is located on the bottom side of
impeller 30.
[0056] Gap 530 is between untruncated vane 330 and/or truncated vane 320
(shown in FIG.
5) of impeller 30 and diffuser 510. In some embodiments, gap 530 is an
increased clearance
gap. The width of gap 530 may be increased by machining the face of diffuser
510 that sits
parallel to the face of impeller 30. In some embodiments, increased clearance
gap 530 is
between about 0.060 inches and about 0.180 inches wide, as required for
various gas to liquid
ratios. In certain embodiments, increased clearance gap 530 may be wider or
narrower
depending on the size of the pump and type of well and/or fluid being pumped.
In some
embodiments, increased clearance gap 530 is at least wider than about 0.020
inches. Increased
clearance gap 530 allows the high pressure fluid to circulate and mix with low
pressure fluid.
Balance hole 340 assist in equalizing the pressure on each side of impeller
30.
[0057] In some embodiments, bushing 560 and flanged sleeve 570 located
upstream and/or
downstream of hub 310 assist in stabilizing impeller 30 and/or holding
impeller 30 in place
during operation. In some embodiments, bushing 560 and flanged sleeve 570 are
located
directly upstream and downstream of hub 310. Bushing 560 and/or flanged sleeve
570 may
assist in carrying at least a portion of the axial thrust load on impeller 30,
such as upthrust
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and/or downthrust. Bushing 560 and/or flanged sleeve 570 may be made of
tungsten carbide,
silicon carbide or any other material having similar properties or known to
those of skill in the
art. In some embodiments, bushing 560 and flanged sleeve 570 comprise abrasion
resistant
trim.
[0058] As shown in FIG. 6, when impeller 30 is in operation, fluid may flow
downstream
and/or upwards through passage 580 towards successive stages of impeller 30
and diffuser
510 pairs and then to ESP charge pump 200 and/or ESP primary pump 220,
eventually
passing through production tubing 225 to a pipe, conduit, tank, collection
container or other
desired location.
[0059] In some embodiments, ESP charge pump 200, ESP primary pump 220 and/or
gas
separator 910 comprises multiple stages of impeller 30 and diffuser 510 pairs,
which are
stacked on shaft 540. In certain embodiments, ESP charge pump 200 and/or ESP
primary
pump 220 includes between about 10 and about 100 stages of impeller 30 and
diffuser 510
pairs. In some embodiments, gas separator 910 includes between about one and
about five
stages of impeller 30 and diffuser 510 pairs, depending upon the GVF in the
produced fluid.
In some embodiments, the inclusion of impeller 30 and diffuser 510 pairs in
one component
of an ESP assembly obviates the need for their inclusion in another component.
For example,
in some embodiments, if gas separator 910 includes between about one and about
five stages
of impeller 30 and diffuser 510 pairs, then impeller 30 and diffuser 510 pairs
may not be
necessary in ESP charge pump 200 or ESP primary pump 220.
[0060] FIG. 10 is an illustrative embodiment of impeller 30 in a rotary gas
separator. FIG. 11
is an illustrative embodiment of impeller 30 in a vortex gas separator. As
shown in FIGs. 10
and 11, fluid with a high GVF enters port 1010. Once the fluid enters port
1010, it may pass
through flow inducer 1015 and proceed to impeller 30. Impeller 30 may rotate
with shaft 540
and may homogenize at least a portion of the gas and liquid passing through
one or more
stages of impeller 30 and diffuser 510. Once the fluid is at least partially
homogenized, it
proceeds to separation chamber 1020 where unhomogenized gas exits at annulus
1025. The
homogenized fluid may then proceed to ESP primary pump 220 with a reduced or
eliminated
risk of gas locking. In some embodiments, the gas separator of illustrative
embodiments may
include increased clearance gap 530 between impeller 30 and diffuser 510. In
some
13
CA 02831924 2013-10-29
embodiments, bushing 560 and flanged sleeve 570 may assist in stabilizing
impeller 30 and/or
holding impeller 30 in place during operation in the gas separator.
[00611 FIG. 7 is a flow chart illustrating an exemplary method of pumping
gaseous fluid of
an illustrative embodiment. At step 710 a centrifugal pump assembly, including
ESP primary
pump 220, seal section 240, gas separator 910, ESP motor and/or ESP charge
pump 200, is
placed into a well containing gaseous fluid. The pump may then be operated to
induce the
fluid to flow towards the surface of the well at step 720. At least a portion
of the fluid may
flow through increased clearance gap 530 between truncated vane 320 and/or
untruncated
vane 330, and a diffuser 510, at step 730. At step 740, phase separation of
the fluid may be
minimized and/or bubble size may be reduced by reducing the pressure
differential between
the pressure side and suction side of truncated vane 320 and/or untruncated
vane 330. In some
embodiments, steps 730 and 740 occur in ESP primary pump 220 and/or ESP charge
pump
200. In some embodiments, steps 730 and 740 occur in gas separator 910.
[0062] In some embodiments, the fluid flow may be caused by rotating an
impeller
comprising truncated vane 320 and at least two untruncated vane 330 extending
substantially
upstream from a single shroud 300, wherein a truncated vane 320 sits at a mid-
pitch location
between untruncated vane 330 starting from the bottom side of impeller 30. In
some
embodiments, the pressure differential between the pressure side and suction
side of truncated
vane 320 and/or untruncated vane 330 may be reduced by increasing impeller
inlet area 610.
In some embodiments, unhomogenized gas may be vented from the pump assembly by
gas
separator 910 at step 745. Fluid may then be lifted towards the surface, a
transport conduit,
pipe, tank, collection container, or any other desired location at step 750.
[0063] The centrifugal pump of the invention may be suitable for a variety of
types of
submersible stages known in the art for use in submersible pumps. For example,
mixed flow
submersible pump stages, as well as radial flow submersible pump stages, may
make use of
the centrifugal pump of the invention. Both these and other submersible stages
suitable for
use with an ESP system may benefit from the centrifugal pump of the present
disclosure.
[0064] The gas separator of the invention may be suitable for a variety of
types of
submersible stages known in the art for use in submersible pumps. For example,
mixed flow
submersible pump stages, as well as radial flow submersible pump stages, may
make use of
14
CA 02831924 2013-10-29
the gas separator of the invention. Both these and other submersible stages
suitable for use
with an ESP system may benefit from the gas separator of the present
disclosure.
[0065] Various embodiments of the invention may comprise various numbers and
spacing of
truncated vane 320. ESP primary pump 220, ESP charge pump 200 and/or gas
separator 910
may benefit from the semi-open impeller of the invention. One or more
impeller/diffuser
stages within ESP primary pump 220, gas separator 910 and/or ESP charge pump
200 may
benefit from illustrative embodiments of the invention. In some embodiments,
the invention
described herein may be suitable for pumping fluid having a gas to liquid
ratio of up to about
90% by volume, depending on the bubble size of the gas. The impeller of the
invention may
have between about 1.75 and 2.5 times the size of the inlet area of a
convention impeller. In
some embodiments, the impeller of the invention may operate at about 8000 to
about 12000
suction specific speed. In an illustrative example, in some embodiments
incorporating a gas
separator, if fluid with a 70% GVF enters port 915, the impeller of the
invention may
homogenize the fluid such that there is between about 30% and about 40% GVF in
separation
chamber 1020, which is vented such that the fluid entering ESP primary pump
220 has about
0% GVF. In some embodiments, small quantities of unhomogenized gas may remain
in fluid
entering ESP primary pump 220, although enough gas may have been homogenized
or
removed to significantly decrease the risk of gas locking.
[0066] While the invention herein disclosed has been described by means of
specific
embodiments and applications thereof, numerous modifications and variations
could be made
thereto by those skilled in the art without departing from the scope of the
invention set forth in
the claims. The embodiments described in the foregoing description are
therefore considered
in all respects to be illustrative and not restrictive. The scope of the
invention is indicated by
the appended claims, and all changes that come within the meaning thereof are
intended to be
embraced therein.
