Note: Descriptions are shown in the official language in which they were submitted.
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CENTRIFUGAL PUMP WITH INDUCER INTAKE
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates in general to electrical submersible well pumps, and in
particular to a centrifugal pump with an impeller and diffuser located before
the first
impeller of the pump.
2. DESCRIPTION OF THE RELATED ART
A common electrical submersible well pump of a type used for oil wells has a
centrifugal pump that is driven by a downhole electrical motor. The pump has a
large
number of stages, each stage having an impeller and diffuser. These pumps work
well
for delivering large volumes of liquid, principally oil and water, of medium
viscosity.
Significant amounts of gas present can present problems because a centrifugal
pump does not operate efficiently with large amounts of entrained gas. A gas
~ separator may be incorporated into the pump assembly for separating out gas
prior to
reaching the first pump stage. Still, in some cases, the fluid pressure is
inadequate at
the first stage due to the presence of gas in the well fluid.
High viscosity well fluid can also present problems for centrifugal pumps
because the viscous fluid may not feed adequately into the first stage.
Inadequate
feed pressure at the first stage may also occur in highly deviated or
horizontal wells.
BRIEF SUMMARY OF THE INVENTION
According to the present invention, a centrifugal pump for use in an
electrical
submersible well pump assembly is provided that includes a mufti-stage
submersible
pump having impellers for displacing well fluid. An inducer is attached to the
pump
for inducing well fluid to flow into the pump. The inducer has a helical
flight similar
to an auger. A diffuser is provided between the inducer and the first impeller
of the
pump for channeling flow from the inducer into the eye of the impeller. The
diffuser
is a mixed flow type, having passages that incline inward from the upstream
end to
the downstream end.
The inducer converts rotational energy to head and flow. The diffuser converts
the rotational energy from the inducer into velocity head and channels the
flow into
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the eye of the first impeller of the pump. These attributes are useful in high
gas
environments and high viscosity environments.
In accordance with one aspect of the present invention there is provided an
electrical submersible well pump assembly comprising:
a centrifugal pump having a housing with a well fluid inlet and a plurality of
pump stages contained in the housing, the stages including an inlet stage
having an
impeller located downstream from the inlet;
an inducer mounted in the housing upstream of the impeller of the inlet stage,
the inducer having a helical flight that is rotatable in unison with the pump;
and
a diffuser positioned between the inducer and the impeller of the inlet stage.
In accordance with another aspect of the present invention there is provided
an
electrical submersible pump assembly, comprising:
a centrifugal pump having a housing containing a rotatably driven shaft that
drives a plurality of impellers, the housing having a well fluid inlet;
an inducer having a helical flight, the inducer being located in the housing
and
rotated by the shaft; and
a diffuser stationarily mounted in the housing downstream of the inducer and
upstream of a first one of the impellers, the diffuser having a plurality of
passages
extending from an upstream end of the diffuser to a downstream end of the
diffuser,
the passages being spaced farther from the shaft at the upstream end of the
diffuser
than at the downstream end.
In accordance with yet another aspect of the present invention there is
provided a method of pumping well fluids comprising:
flowing well fluids into a housing of a centrifugal, pump assembly;
rotating an inducer in the housing to cause the well fluid to flow through the
housing; then
passing the well fluid through a diffuser located in the housing; and then
passing the well fluid into an impeller of a first stage of the centrifugal
pump
assembly.
In accordance with still yet another aspect of the present invention there is
provided an electrical submersible well pump assembly comprising:
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a centrifugal pump having a housing with a well fluid inlet and a plurality of
pump stages contained in the housing, the stages including an inlet stage
having an
impeller located downstream from the inlet;
an inducer mounted in the housing upstream of the impeller of the inlet stage,
the inducer having a helical flight;
a rotatable shaft extending through the inducer and the stages of the pump for
rotating the inducer and the impellers; and
a diffuser positioned between the inducer and the impeller of the inlet stage;
wherein,
the housing and the shaft define an annular sealed enclosure between the
inducer and the diffuser, so as to require all well fluid entering the inlet
to flow to the
diffuser.
In accordance with still yet another aspect of the present invention there is
provided an electrical submersible pump assembly, comprising:
a centrifugal pump having a housing containing a rotatably driven shaft that
drives a plurality of impellers, the housing having a well fluid inlet for
receiving a
well fluid containing liquid and gas;
an inducer having a helical flight, the inducer being located in the housing
and
rotated by the shaft; and
a diffuser stationarily mounted in the housing downstream of the inducer and
upstream of a first one of the impellers, the diffuser having a plurality of
passages
extending from an upstream end of the diffuser to a downstream end of the
diffuser,
the passages being spaced farther from the shaft at the upstream end of the
diffuser
than at the downstream end; wherein
the housing and the shaft between the inducer and the diffuser defining a
closed annular passage so as to require all of the gas and liquid flowing into
the inlet
to flow to the diffuser and the impellers.
In accordance with still yet another aspect of the present invention there is
provided a method of pumping well fluids containing liquid and gas,
comprising:
providing a pump having a housing, a helical vane, and a plurality of stages,
each stage having a diffuser and an impeller;
rotating the helical vane and the impellers;
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flowing liquid and gas into the housing, and conveying the liquid and gas
through the helical vane;
after passing from the helical vane, directing all of the flow of liquid and
gas
axially and radially inward, relative to an axis of the pump, into the stages
of the
pump; and then
pumping all of the flow of liquid and gas through the pump with the stages of
the pump.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment of the present invention will now be described more fully
with reference to the accompanying drawings in which:
Figure 1 is a schematic view illustrating an electrical submersible pump
assembly installed in a well and having a diffuser in accordance with this
invention.
Figures 2A and 2B comprise an enlarged sectional view of a Iower portion of
the pump of Figure I .
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Refernng to Figure 1, an electrical submersible pump assembly 11 is shown
installed within a well 13. Well 13 contains a well fluid I S, which flows
inward from
perforations 17. In the application of this invention, well fluid I S will
typically be a
heavy viscous crude or it may contain a large percentage of gas.
Pump assembly 11 includes a centrifugal pump 19 which has a well fluid inlet
or lower intake 21. Pump 19 is suspended by a string of production tubing 20,
and its
lower end is mounted to a conventional seal section 23. An electrical motor 25
is
supported on the lower end of seal section 23. Seal section 23 seals well
fluid from
lubricant within electrical motor 25 and also reduces the pressure
differential between
the hydrostatic pressure in the well and the internal pressure of the
lubricant in the
motor. Additionally, seal section 23 has thrust bearings for absorbing axial
thrust
generated by pump 19. Electrical motor 25 is a large AC motor which is
supplied
with electrical power through a power cable (not shown) extending down from
the
surface.
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Referring to Figure 2B, the lower end of pump 19 has a pump base 29 affixed
thereto. Pump base 29 is secured by bolts (not shown) to seal section 23 (Fig.
1 ).
Pump base 29 is a tubular member having a sidewall 30 that defines a bore 28.
Intake ports 21 are located in sidewall 30.
An axial shaft 43 extends through pump base 29. Shaft 43 couples to a shaft
(not shown) extending upward from seal section 23 (Fig. 1), which is driven by
electrical motor ZS (Fig. 1). An inducer 4S is mounted to shaft 43 and located
within
bore 28. Inducer 4S is a helical screw pump, having a hub 47 that slides over
shaft 43
and rotates with shaft 43 by means of a key. A flight 49 extends outward from
hub
47. Flight 49 is helical and has an outer periphery in close proximity to
sidewall 30 of
pump base 29. lnducer 4S has a length that is less than the length of pump
base 29.
Pump base 29 has a set of exterior threads S 1 on its upper end. A tubular
housing S3 secures pump base 29 to an upper portion of pump 19. Pump base 29
may
be considered to be a lower portion of housing S3. Pump 19 has a large number
of
substantially identical pumping stages, each stage having a rotating impeller
SS and
stationary diffuser S7, as shown also in Figure 2A. Unlike a conventional
centrifugal
pump, the lowermost element of pump 19 is one of the diffusers S7, not one of
the
impellers SS. The first stage of a typical prior art pump will have an
impeller SS as
the upstream element rather than a diffuser S7.
Pump 19 is preferably a mixed flow type as opposed to a radial flow type.
That is, each stage creates significant axial flow as well as radial flow. A
radial flow
stage principally creates radial flow. Each diffuser S7 has a plurality of
diffuser
passages S9, each having a lower or upstream end 61 and an upper or downstream
end
63. The upstream ends 61 axe spaced radially from shaft 43 a greater distance
than
2S the downstream ends 63. Being a mixed flow type, the passages S9 incline
radially
inward from the upstream ends 61 to the downstream ends 63. A significant
axial
distance exists between upstream ends 61 and downstream ends 63. Conversely,
in a
radial flow diffuser (not shown), the passages extend principally radially and
not
axially.
A guide vane 6S is optionally mounted between inducer 4S and the first
diffuser S7. Guide vane 65 is keyed to shaft 43 for rotation therewith and has
a
plurality of blades 67. Guide vane 6S serves to prevent fluid pre-rotation as
the fluid
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passes from inducer 45 into the lowermost diffuser 57. However, guide vane 65
could
be omitted, allowing flow to pass directly from inducer 45 into the lowermost
diffuser
57.
In operation, electrical power is supplied to motor 25 to drive pump 19. As
indicated by the arrows in Fig. l, well fluid 15 flows into intake ports 21.
Inducer 45
rotates with shaft 43, acting as a low pressure pump stage to induce flow into
the
lowermost diffuser 57.
Guide vane 65, if employed, receives the flow from inducer 45 and tends to
reduce swirling of the well fluid. The well fluid flows through passages 59 of
the
lowermost diffuser 57, then into the eye or inlet of the lowermost impeller
55. The
lowermost diffuser 57 converts the flow from inducer 45 into velocity head.
The invention has significant advantages. In high gas environments the
invention mixes the gas and liquid and raises fluid pressure at the entrance
of the first
pump stage. In high viscosity environments the invention positively feeds
fluid to the
first pump stage. In a horizontal application, the inducer and diffuser
increase the
feed pressure at the first pump stage. Another benefit is that pressure and
flow will be
provided to the first impeller even if there is partial blockage of the intake
of the first
impeller since inducer is a positive displacement device.
While the invention is shown in only one of its forms, it should be apparent
to
those skilled in the art that it is not so limited, but is susceptible to
various changes
without departing from the scope of the invention. For example, a gas
separator may
also be employed with the pump assembly.
