Note: Descriptions are shown in the official language in which they were submitted.
CA 02650199 2011-08-16
METHOD OF HEATING SUB SEA ESP PUMPING SYSTEMS
BACKGROUND
1. Field of Invention
[0002] The present disclosure relates to an electrical submersible pumping
system configured
to heat fluid to be pumped by the system.
2. Description of Prior Art
[0003] Submersible pumping systems are often used in hydrocarbon producing
wells for
pumping fluids from within the well bore to the surface. These fluids are
generally liquids and
include produced liquid hydrocarbon as well as water. One type of system used
in this
application employs an electrical submersible pump (ESP). Submersible pumping
systems, such
as electrical submersible pumps (ESP) are often used in hydrocarbon producing
wells for
pumping fluids from within the well bore to the surface. ESP systems may also
be used in
subsea applications for transferring fluids, for example, in horizontal
conduits or vertical
caissons arranged along the sea floor. When ESP pumps are deployed in seabed
applications
they reside in a cold sea water environment with temperatures in the mid 30 F
to 40 F range.
However, when the ESP pump is energized and it is required to handle
production fluids at
considerably higher temperatures, sometimes in excess of 300 F.
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[0004] One unique problem associated with these large temperature excursions
is difficulty in
starting up the system after a shutdown. Crude oil that is easily pumped at
production
temperatures is often very viscous when it is cooled to sea water temperature,
thereby effectively
locking the pump stages of the ESP so the pump is unable to be rotated. One
way to restart the
system is to heat the crude oil in the pump to sufficiently reduce the oil
viscosity into a range
where the resistance to flow is reduced such that the pump can be restarted. A
similar
temperature related issue is associated with hydrates which accumulate in the
pump when
production fluids are cooled, also locking the pump impellers. Like viscous
crude, this can be
resolved by heating the hydrates and freeing the pump to rotate. In other
situations, depending
on the fluid characteristics of the oil being pumped, there may be some
advantages associated
with reducing the fluid viscosity by heating the pump and motor before fully
starting the system
to reduce the fluid viscosity.
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SUMMARY OF INVENTION
[0005] Accordingly, in one aspect there is provided a method of pumping well
fluid,
comprising providing an electrical submersible pump (ESP) system, the ESP
system having a
pump and a pump motor coupled to the pump by a seal/equalizer section that
reduces a
pressure differential between lubricant in the motor and fluid in a borehole,
the pump motor
having power selectively delivered at a normal operating voltage, a normal
waveform, and a
normal frequency, and an electrical power supply in communication with the
pump motor;
providing the ESP with a heat transfer system including a lower portion
proximate the pump
motor, an upper portion proximate the pump, tubes extending alongside the
seal/equalizer
section between the upper and lower portions, and a working fluid within the
lower portion,
the upper portion and the tubes; immersing the ESP in the well fluid;
supplying a voltage to
the pump motor from the electrical power supply that is less than the normal
operating
voltage to inductively generate heat energy with the pump motor; and
transferring heat
energy generated by the pump motor to the working fluid in the lower portion
of the heat
transfer system, causing the working fluid to vaporize and flow to the upper
portion via one
of the tubes, thereby transferring heat to the pump and surrounding well fluid
and causing the
working fluid in the upper portion to condense and return to the lower portion
via the other of
the tubes.
[0005a] The method can further involve sensing motor and/or fluid temperature.
The
method can further include adjusting inductively heating the motor based on
sensing the
motor and/or fluid temperature. Voltage provided to the pump motor can be
supplied at a
value lower than voltage supplied during normal operation, this can be
performed while
providing power to the pump motor at a frequency higher than during normal
operation. The
method can further include providing power to the pump motor in a waveform
that varies
from the waveform provided during normal pump operation.
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[0006] According to another aspect there is provided an electrical submersible
pumping
system for pumping well fluid from a well, comprising a pump having a fluid
inlet; a pump
motor coupled to the pump and having a normal operating voltage, so that when
the pump
motor is operated at a voltage less than the normal operating voltage, heat is
generated by the
pump motor; a seal/equalizer section mounted between the pump and the pump
motor for
reducing a pressure differential between well fluid on an exterior of the
motor and lubricant
within the motor; and a heat transfer system having a lower portion in heat
energy
communication with the pump motor, an upper portion in heat energy
communication with
the pump, transfer tubes extending exterior of the pump, seal/equalizer
section and motor
alongside the seal/equalizer section from the lower portion to the upper
portion, and a
vaporizable working fluid contained in the lower portion, the upper portion
and the transfer
tubes, so that heat generated by the pump motor can be transferred to the
working fluid and
from the working fluid to the pump for reducing resistance of the well fluid
to flow.
[0006a] The lower portion may have a first and second reservoir and tubes
extending
between the reservoirs. The upper portion can include a first and second
reservoir and tubes
extending between the reservoirs. The upper portion may be disposed adjacent
the pump so
that heat energy transferred from the upper portion to the pump can heat fluid
in the pump.
The upper portion is optionally disposed so that heat energy transferred from
the upper
portion flows to fluid outside of the pump. The system may include a variable
speed
controller in electrical communication with the pump motor, so that
manipulating the variable
speed controller adjusts the electrical power delivered to the pump motor for
inductively
generating heat energy. A temperature sensor in communication with the
variable speed
controller can also be included with the system.
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BRIEF DESCRIPTION OF DRAWINGS
[0007] Some of the features and benefits of the present invention having been
stated, others
will become apparent as the description proceeds when taken in conjunction
with the
accompanying drawings, in which:
[0008] The following Figure 1 is a side schematical view of one example of an
ESP disposed
in a sea floor caisson having an associated heating system.
[0009] Figure 2 is a side schematical view of a heat transfer system for
transferring heat
between a pump motor and a pump.
[0010] While the invention will be described in connection with the preferred
embodiments, it
will be understood that it is not intended to limit the invention to that
embodiment. On the
contrary, it is intended to cover all alternatives, modifications, and
equivalents, as may be
included within the spirit and scope of the invention as defined by the
appended claims.
CA 02650199 2009-01-19
DETAILED DESCRIPTION OF INVENTION
[0011] The present invention will now be described more fully hereinafter with
reference to
the accompanying drawings in which embodiments of the invention are shown.
This invention
may, however, be embodied in many different forms and should not be construed
as limited to
the illustrated embodiments set forth herein; rather, these embodiments are
provided so that this
disclosure will be thorough and complete, and will fully convey the scope of
the invention to
those skilled in the art. Like numbers refer to like elements throughout.
[0012] Enclosed herein is a method of handling fluid in a caisson or other
borehole using an
ESP system. In one embodiment, enhanced caisson or borehole fluid flow through
an ESP
system is described herein that includes inductively heating the pump motor of
an ESP system.
The heat energy generated can be transferred, either actively or passively, to
heat the fluid
pumped. The heat can be transferred directly to the pump or the fluid before
it reaches the pump.
The pump motor may be inductively heated by altering the power supplied to the
ESP motor.
Such altering may include altering voltage, altering the frequency, altering
the waveform of
electrical power delivered to the pump motor, or combinations thereof.
[0013] In one example of use, altering includes changing the electrical supply
to the pump
motor from that of a normal or expected operating scenario or a normal or
expected operating
range. For the purposes of discussion herein, electrical supply includes
power, current, voltage,
frequency, and waveform. Reducing voltage supplied to a pump motor while
altering the
supplied electrical frequency and/or supplied waveform from a normal/expected
operating value
or range of values can inductively generate heat in the pump motor stator
stack. Optionally, a
variable speed drive may be employed to perform the altering. It is well
within the capabilities
of those skilled in the art to alter the electrical supply so that heat energy
may be generated using
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an ESP system. When supplying electricity as described above, the
corresponding rotor may not
rotate if the pump is locked by the presence of the viscous fluid or it may
turn at slow speeds
wherein the motor efficiency is very low thereby generating heat.
[0014] With reference now to Figure 1, one embodiment of an ESP system having
a heating
means is shown in a side schematical view. In this embodiment, an ESP system
20 is disposed in
a vertical caisson 5 bored through the seafloor. A wellhead 8 is provided on
the caisson 5 having
a flow inlet 10 and flow outlet 12. However the caisson 5 may also be a
horizontal or sloped
flow line (such as a jumper line or horizontal pump cartridge) extending along
the sea bed. The
system 20 comprises an ESP motor 22 (or pump motor), a seal/equalizer section
24, an optional
separator section 28 having inlet ports 26 on its outer housing, and a pump 30
on the system 20
upper end. As is known, an ESP system 20 receives fluid to the inlets 26 where
it is directed to
the pump impellers (not shown) for delivery to surface via production tubing
32.
[0015] A variable speed drive 34, which may be disposed on a platform above
sea level; is in
communication with the ESP motor 22 for controlling ESP motor 22 operations.
The variable
speed drive 34 may also be used to alter the supply voltage and frequency to
the ESP motor 22.
The variable speed drive 34 is shown in communication with the ESP motor 22
via line 36. As
noted above, the variable speed drive 34 can adjust the operating parameters
of the ESP motor 22
causing it to generate heat by regulating its voltage, adjusting the power
frequency, adjusting the
supplied power waveform, or combinations of these. These adjustments can cause
the ESP
motor 22 to generate more heat energy than under typical operation. The heat
energy produced
by the ESP motor 22 can be in addition to or in lieu of rotational energy that
is typically
delivered to the pump 30. The heat energy generated by the ESP motor 22 can be
used for
heating the pump 30, heating fluid in the pump 30, or heating fluid to be
pumped by the pump
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30. The fluid to be pumped by the pump 30 may be in a space proximate the
inlets 26, or
optionally further down the system 20 within the caisson 5. The ESP motor 22
may or may not
rotate when inductively generating heat.
[0016] Transferring the heat generated by the ESP motor 22 to the fluid
entering the pump 30
can be accomplished in one of the manners described below. For example, fluid
may be heated
by the ESP motor 22 as it passes the ESP motor 22 after flowing into the
caisson 5. The heated
fluid with lowered viscosity experiences less flow resistance when traveling
to the pump 30 and
through the inlets 26, thereby enhancing pumping flow. Optionally, fluid may
be redirected
from the pump 30 discharge to upstream of the pump motor 22. Similar to the
fluid flowing into
the caisson 5, recirculated fluid absorbs thermal energy from the ESP motor 22
and carries it to
the inlets 26 and pump 30.
[0017] A recirculation line 58 is schematically illustrated communicating with
the pump 30
discharge with an exit 59 below the ESP motor 22. A valve 60 on the
recirculation line 58 can
regulate flow therethrough. The valve 60 is shown communicated with the
variable speed drive
34 via line 62 and line 36, and may be controlled by the variable speed drive
34 or controlled
independently. Similarly, if desired, oil heated in this manner can be
redirected to other
locations to heat such things as valves, pipes, subsea trees etc before being
returned to the to exit
59.
[0018] Temperature sensors may be employed to monitor ESP motor 22 temperature
and
fluids adjacent the ESP motor 22. For example, when the ESP motor 22 reaches a
designated
temperature, the power supply to the ESP motor 22 may be manipulated, such as
by the variable
speed control 34 to slowly rotate the pump shaft thus drawing heated fluid
from adjacent the ESP
motor 22 to the pump intake 26. Examples of such adjustments include changes
to voltage,
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changes to frequency, or changes in waveform. The particular temperature
profiles desired over
a particular time period may dictate if adjusting power supply based on
temperature readings are
performed intermittently or on a continuous circulation basis. A control
algorithm may be
employed for controlling the ESP motor 22; the algorithm may be stored within
the variable
speed control 34 or in a separate controller 38 housed within the variable
speed control 34.
Optionally, the algorithm may be outside of the variable speed control 34. In
this alternative
embodiment algorithm results may be communicated via communication link 40 to
the variable
speed control 34 and used for operating the ESP motor 22.
[00191 As shown in Figure 1, temperature probes 52, 54, 56 are disposed in the
caisson 5 and
configured for monitoring fluid temperature within the caisson 5 and adjacent
the ESP system
20. The temperature probes 52, 54, 56 are in communication with the line 36
via respective lines
48, 46, 44. Accordingly, discreet temperature measurements may be taken at
fluid points within
the caisson 5 communicated to the variable speed control 34. Additional or
alternative
temperature measurements may as well be recorded at other locations where
temperature
readings may be relevant or of interest. Optionally, the ESP motor 22
temperature may be
obtained by the lines 36, 50 directly connected to the ESP motor 22. A similar
line 42 provides
temperature communication between the line 36 and the pump 30. The line 36,
which can
provide three-phase power to the ESP motor 22, can also have data signals
superimposed thereon
for transmission to the variable speed control 34. The data signals can
emanate from the
temperature sensors in the fluid, sensors on the equipment, or the valve 60.
The variable speed
drive 34 may be utilized so that steps programmed therein can be undertaken so
that the ESP
motor 22 operations can be adjusted based on real time readings of
temperature.
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[0020] Optionally, when the ESP system 20 is not in use, the variable speed
control 34, or
other surface control scheme, may monitor fluid temperature and/or motor
temperature for
determining if an appropriate pumping temperature exists. The variable speed
control 34 may be
further configured to energize the ESP motor 22 for heating the ESP system 20
to maintain
proper pumping temperature in the system 20. In this example of use, the pump
30 and pumping
system 20 is continuously heating even in situations when the ESP system 20 is
not otherwise
operating.
[0021] With reference to Figure 2, a schematical view is shown illustrating a
heat transfer
system 64 for transferring heat from the ESP motor 22 to the pump 30. The heat
transfer system
64 as shown comprises a lower/liquid portion 66 arranged proximate to the ESP
motor 22. The
lower/liquid portion 66 comprises a first and second reservoir 68, 69 disposed
at different
locations along the surface of the ESP motor 22. Tubes 70 are illustrated
extending between the
reservoirs (68, 69). In this schematical representation, the heat transfer
system 64 is a sealed
system with vaporizing and condensing fluid circulating within the sealed
system.
[0022] Heat energy from the ESP motor 22 is graphically represented as by the
arrow and Q;,,
shown entering the tube 70. In this stage of the process, the heat Q;,,
entering the tube 70
vaporizes the working fluid therein as it is entering into the exit reservoir
69. The heated
vaporized fluid then flows from the reservoir 69 through the flow line 71 to
an
upper/vaporization portion 72. The upper/vaporization portion 72 also includes
corresponding
reservoirs 74, 75 with tubes 76 extending therebetween. In this step of the
cycle, the vaporized
fluid flows through the tubes 76 transferring heat to the pump 30 and
condenses the working
fluid within the tubes 76. QOUt and its associated arrow represent the heat
transferred from the
CA 02650199 2009-01-19
fluid in the tubes 76 to the pump 30. The condensed fluid flows from the tubes
76 into the
collection reservoir 75 and is directed through flow line 65 to reservoir 68.
[0023] It should be pointed out that the manner of transferring heat from the
ESP motor 22 to
the pump 30, or to other components of the system such as valves, trees, or
pipes etc, is not
limited to the schematic example provided in Figure 2. Instead embodiments
exist that include
any type of sealed system circulating a working heat transfer fluid between
the pump 22 and ESP
motor 30 (or other components to be heated). The scope of the present
disclosure includes the
use of any type of heat tube as well as any thermo-siphon system is one option
possible for
application with the system and apparatus herein described. Additionally,
means for generating
heat is not limited to the inductive manner of heating the ESP motor 22
described, but can
includes other modes of heating the pump motor, such as by resistance heating
of the motor
windings.
[0024] It is to be understood that the invention is not limited to the exact
details of
construction, operation, exact materials, or embodiments shown and described,
as modifications
and equivalents will be apparent to one skilled in the art. In the drawings
and specification, there
have been disclosed illustrative embodiments of the invention and, although
specific terms are
employed, they are used in a generic and descriptive sense only and not for
the purpose of
limitation. Accordingly, the invention is therefore to be limited only by the
scope of the
appended claims.
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