Note: Descriptions are shown in the official language in which they were submitted.
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AUTOMATIC DETECTION OF RESONANCE FREQUENCY OF A DOWNHOLE
SYSTEM
BACKGROUND
[0001] To produce hydrocarbons from a well, an artificial lift mechanism that
utilizes a pump is sometimes used. One type of pump is an electrical
submersible pump
that can be operated at different frequencies. The electrical submersible pump
can be
controlled by a variable speed drive system that is able to vary the
operational frequency
of the electrical submersible pump.
[0002] It is desired that the electrical submersible pump not be run at its
resonance
frequency, as excessive vibration may occur when the electrical submersible
pump is run
at the resonance frequency. The resonance frequency of an object is the
natural
frequency of vibration of the object, determined by the physical parameters of
the object.
[0003] Conventionally, to identify the resonance frequency of the electrical
submersible pump, a manual procedure is performed. The manual procedure
involves
controlling the variable speed drive system (normally located at the earth
surface) to
perform a frequency sweep of the electrical submersible pump. The vibration of
the
electrical submersible pump is monitored by the well operator over the
frequency sweep.
Normally, the frequency associated with the maximum amount of vibration is
considered
the resonance frequency, which is recorded by the well operator conducting the
test. The
variable speed drive system is then manually set to skip the resonance
frequency during
normal operation of the electrical submersible pump.
[0004] Such manual testing of the electrical submersible pump is time-
consuming
and labor intensive, which increases the cost of deploying a completion into a
well.
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SUMMARY OF THE INVENTION
According to the present invention, there is
provided an apparatus comprising: a downhole system adapted
to be run at plural operating frequencies; a drive system to
control an operating frequency of the downhole system; and a
controller to control the drive system to, in a test
procedure, vary the operating frequency of the downhole
system, the controller to automatically detect a resonance
frequency of the downhole system in the test procedure.
Also according to the present invention, there is
provided a method to perform a test procedure in a downhole
tool deployed in a wellbore, comprising: varying, in
response to control of a control module, an operating
frequency of the downhole tool across a predefined frequency
range in the test procedure; receiving, by the control
module, vibration data of the downhole tool as the operating
frequency of the downhole tool is varied across the
predefined frequency range; and automatically determining,
by the control module, a resonance frequency of the downhole
tool based on the vibration data.
According to the present invention, there is
further provided an article comprising at least one storage
medium containing instructions that when executed cause a
control module to: control a drive system to vary an
operating frequency of a downhole tool across a predefined
frequency range during a test procedure; and determine a
resonance frequency of the downhole tool based on
information received from the downhole tool during the test
procedure as the operating frequency of the downhole tool is
varied across the predefined frequency range.
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[0005] In general, a downhole system (e.g., an electrical
submersible pump) can be run at plural frequencies, and a
drive system controls an operating frequency of the downhole
system. A controller controls the drive system to, in a
test procedure, vary the operating frequency of the downhole
system, and to automatically detect a resonance frequency of
the downhole system in the test procedure.
In some embodiments, the controller is also able
to set the detected resonance frequency as an operating
frequency to avoid.
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[0006] Other or alternative features will become apparent from the following
description, from the drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Fig. I illustrates a system with a pump located in a wellbore and a
surface
variable frequency drive and control system having a module to determine a
resonance
frequency of the pump, according to an embodiment.
[0008] Fig. 2 is a flow diagram of a process of detecting the resonance
frequency of
the pump of Fig. 1, according to an embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0009] In the following description, numerous details are set forth to provide
an
understanding of the present invention. However, it will be understood by
those skilled
in the art that the present invention may be practiced without these details
and that
numerous variations or modifications from the described embodiments may be
possible.
[0010] As used here, the terms "up" and "down"; "upper" and "lower";
"upwardly"
and downwardly"; "upstream" and "downstream"; "above" and "below"; and other
like
terms indicating relative positions above or below a given point or element
are used in
this description to more clearly describe some embodiments of the invention.
However,
when applied to equipment and methods for use in wells that are deviated or
horizontal,
such terms may refer to a left to right, right to left, or other relationship
as appropriate.
[0011] Fig. 1 illustrates a system that includes a string deployed in a
wellbore 100,
where the string has a pump assembly 102 that is carried on a tubing 104. In
one
embodiment, the pump assembly 102 is an electrical submersible pump (ESP)
assembly
that is controlled electrically to pump fluids in the wellbore 100 up to the
well or earth
surface 101. The electrical submersible pump assembly 102 is an example of a
downhole
system that is capable of running at various operating frequencies. In other
embodiments, other types of downhole systems are also capable of running at
various
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operating frequencies. Also, instead of a tubing 104, other types of
conveyance
structures can be used for carrying the downhole system into the wellbore 100,
such as
wirelines, coiled tubing, cables and so forth.
[0012] The wellbore 100 is lined by a casing or liner 106 that extends from
the well
surface 101. Wellhead equipment 124 is provided at the well surface 101. A
wellhead
penetrator 122 is provided through the wellhead equipment 124 to enable
electric power
transmission from a surface variable speed drive system 130 to the submersible
pump
assembly 102 through the wellhead equipment 124.
[0013] According to one example, the electrical submersible pump assembly 102
includes a pump 108, a motor 114 for powering the pump 108, a protector 116 to
prevent
wellbore fluid entry into the motor, and an intake/gas separator 112 where
wellbore fluid
enters the pump 108. Also, the electrical submersible pump assembly 102 may
include a
gas handling device 110 for handling an amount of gas that cannot be handled
by the
submersible pump, and a downhole sensor module 118 (connected to associated
transducers) for providing pressure, temperature, flow rate, current, and/or
vibration
readings associated with the wellbore 100 and submersible pump assembly 102.
The
components of the electrical submersible pump assembly 102 are provided for
purposes
of example, as other pump assemblies can have other components.
[0014] The motor 114 is connected to an electric cable 120 that extends
through the
wellhead equipment 124. The cable 120 further extends out from the wellhead
equipment 124 to a control module 126 at the well surface 101.
[0015] The control module 126 includes a controller 128 and the variable speed
drive system 130. Note that other components (not shown) can also be part of
the control
module 126. The variable speed drive system 130 controls the speed at which
the motor
114 runs. The speed control affects the operating frequency of the electrical
submersible
pump assembly 102. The variable speed drive system 130 is connected to the
controller
128, which controls (among others) the speed variation provided by the
variable speed
drive system 130. The variable speed drive system 130 also provides protection
functions for the submersible pump assembly 102.
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[0016] In accordance with some embodiment of the invention, the controller 128
includes a resonance frequency detection software 134 that is executable on a
central
processing unit (CPU) 136. The CPU 136 is connected to a storage 138 for
storing data
and software instructions. The resonance frequency detection software 134
provides an
automated mechanism for automatically detecting the resonance frequency of the
electrical submersible pump assembly 102 (or other type of downhole tool that
is capable
of operating at multiple frequencies). Using the resonance frequency detection
software
134 in the controller 128 to perform the resonance frequency detection enables
a well
operator to automate the resonance frequency detection procedure, such that
the well
operator does not have to manually detect for the resonance frequency and to
make
adjustments in the variable speed drive system 130 for such resonance
frequency. The
resonance frequency detection software 134 works with an electric submersible
pump
assembly 102 that includes a downhole sensor module that is able to measure
vibration at
any point on the submersible pump assembly 102.
[0017] According to some embodiments of the invention, the resonance frequency
detection software 134 is executable to detect the resonance frequency of the
electrical
submersible pump assembly 102, and to automatically set one of the resonance
frequencies that the variable speed drive system 130 will skip, called
"setting a jump
frequency."
[0018] A user station 132 can be coupled to the control module 126. Using the
user
station 132, such as a notebook computer, a desktop computer, a personal
digital assistant
(PDA), or other user device, a user (such as a well operator) can invoke
execution of the
resonance frequency detection software 134 as well as view the results of the
execution
of resonance frequency detection software 134. Also, the user can monitor
operation of
the electrical submersible pump assembly 102. All of these can be accomplished
through
the local user interface on the control module 126.
[0019] In one embodiment, the user station 132 includes a user interface that
displays control elements to control the resonance frequency detection
software 134. The
user interface also displays fields for outputting results of a test conducted
by the
resonance frequency detection software 134 for determining the resonance
frequency of
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the electrical submersible pump assembly 102. Optionally, the user interface
in the user
station 132 can also be used to control the variable speed drive system 130.
[0020] The resonance frequency detection software 134 is an example of a
module
to automatically detect for a resonance frequency of a downhole system such as
the
electrical submersible pump assembly 102. In other embodiments, instead of
being a
software module, a module implemented in hardware or a combination of hardware
and
firmware can be used to perform automated resonance frequency detection.
[0021] According to one embodiment, to enable the test procedure for finding a
resonance frequency by the resonance frequency detection software 134, a
downhole
sensor module 118 is provided in the electrical submersible pump assembly 102.
The
downhole sensor module 118 is connected to the cable 120 through the motor
104, while
one or more transducers can be located at any point on the electrical
submersible pump
assembly 102.
[0022] As depicted in Fig. 2, to perform the test procedure, the resonance
frequency
detection software 134 is executable to receive or generate (at 202) minimum
and
maximum operating frequency values that define a frequency range over which a
frequency sweep is to be performed in the test procedure. In one
implementation, the
minimum and maximum operating frequencies can be entered by a user at the user
station
132 or through the user interface of the controller 128. For example, the user
interface
presented by the resonance frequency detection software 134 can have fields
for
receiving various parameters, including the minimum and maximum operating
frequencies.
[0023] Alternatively, the minimum and maximum operating frequencies can be
generated by the resonance frequency detection software 134 based on various
data
associated with the electrical submersible pump assembly 102. For example, the
electrical submersible pump assembly 102 can be associated with motor
"nameplate"
data, including the maximum horsepower of the motor 114, and the motor
nameplate
frequency. The motor nameplate frequency is typically 50 Hz or 60 Hz,
depending on
power supply frequency. The maximum frequency for the frequency sweep is then
derived using the following equation:
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Motor Nameplate Frequency *
MaxFreq - Motor Nameplate HP / HP Consumption At Motor Nameplate Frequency
[0024] The HP consumption at motor nameplate frequency refers to the expected
horsepower consumed by the pump 108, gas handling device 110 (if present), and
intake/gas separator 112 being run by the motor at the motor nameplate
frequency. The
HP consumption at motor nameplate frequency can be entered by a user (such as
through
the user station 132), or can be derived from other information such as
pressure or flow
rate information from transducers located on the electrical submersible pump
assembly
102.
[0025] After receiving or generating (at 202) the minimum and maximum
operating
frequencies at 102, the resonance frequency detection software 134 causes (at
204) the
controller 128 to control the variable speed drive system 130 to run the
electrical
submersible pump assembly 102 from the minimum operating frequency to the
maximum
operating frequency. During this frequency sweep, the resonance frequency
detection
software 134 receives (at 206) vibration data from a sensor.
[0026] The vibration data is stored (at 208) and correlated to the operating
frequencies. For example, the vibration data and corresponding operating
frequencies
can be stored in a table format. Based on the received vibration data, the
resonance
frequency detection software 134 determines (at 210) the resonance frequency,
which is
the frequency at which maximum vibration is detected (from the vibration
data).
[0027] The detected resonance frequency is then stored (at 212) and optionally
reported to the user at the user station 132. Also, the controller 128, based
on the
resonance frequency determined by the resonance frequency detection software
134, sets
(at 214) the variable speed drive system 130 to skip the resonance frequency.
For
example, the variable speed drive system 130 can be associated with a jump
frequency or
jump frequencies that is or are to be skipped over during operation.
[0028] Instructions of the resonance frequency detection software 134 (Fig. 1)
are
stored on one or more storage devices in the controller 128 and loaded for
execution on a
processor (such as CPU 136). The processor includes microprocessors,
microcontrollers,
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processor modules or subsystems (including one or more microprocessors or
microcontrollers), or other control or computing devices. As used here, a
"control
module" refers to hardware, software, or a combination thereof. A "control
module" can
refer to a single component or to plural components (whether software or
hardware).
[0029] Data and instructions (of the software) are stored in respective
storage
devices, which are implemented as one or more machine-readable storage media.
The
storage media include different forms of memory including semiconductor memory
devices such as dynamic or static random access memories (DRAMs or SRAMs),
erasable and programmable read-only memories (EPROMs), electrically erasable
and
programmable read-only memories (EEPROMs) and flash memories; magnetic disks
such as fixed, floppy and removable disks; other magnetic media including
tape; and
optical media such as compact disks (CDs) or digital video disks (DVDs).
[0030] While the invention has been disclosed with respect to a limited number
of
embodiments, those skilled in the art, having the benefit of this disclosure,
will appreciate
numerous modifications and variations therefrom. It is intended that the
appended claims
cover such modifications and variations as fall within the true spirit and
scope of the
invention.
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