U.S. patent application number 13/015732 was filed with the patent office on 2011-08-04 for pressure pulse interaction management in a multiple pump system.
Invention is credited to Rajesh Luharuka, Rod Shampine.
Application Number | 20110189028 13/015732 |
Document ID | / |
Family ID | 44318310 |
Filed Date | 2011-08-04 |
United States Patent
Application |
20110189028 |
Kind Code |
A1 |
Shampine; Rod ; et
al. |
August 4, 2011 |
PRESSURE PULSE INTERACTION MANAGEMENT IN A MULTIPLE PUMP SYSTEM
Abstract
Methods which include operating a plurality of pumps fluidly
coupled to a common fluid line, and modulating a pumping speed of
at least one of the pumps to reduce an amplitude of a pressure
fluctuation in the common fluid line, where the modulating
comprises maintaining an average aggregate pumping rate of the
plurality of pumps.
Inventors: |
Shampine; Rod; (Houston,
TX) ; Luharuka; Rajesh; (Katy, TX) |
Family ID: |
44318310 |
Appl. No.: |
13/015732 |
Filed: |
January 28, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61337041 |
Jan 29, 2010 |
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Current U.S.
Class: |
417/53 |
Current CPC
Class: |
F04B 49/06 20130101 |
Class at
Publication: |
417/53 |
International
Class: |
F04B 49/06 20060101
F04B049/06 |
Claims
1. A method comprising: operating a plurality of pumps fluidly
coupled to a common fluid line; modulating a pumping speed of at
least one of the pumps to reduce an amplitude of a pressure
fluctuation in the common fluid line, wherein the modulating
comprises maintaining an average aggregate pumping rate of the
plurality of pumps.
2. The method of claim 1, wherein the modulating comprises a
modulation behavior selected from the modulation behaviors
consisting of: inducing a random pump rate fluctuation into at
least one of the pumps; inducing a scheduled pump rate fluctuation
into at least one of the pumps; inducing a random pump rate
fluctuation into each of the pumps; inducing a scheduled pump rate
fluctuation comprising a pump offset schedule into each of the
pumps, and further ensuring that each of the pumps operates at a
distinct position in the pump offset schedule; and inducing a
pseudo-random pump rate fluctuation into at least one of the
pumps.
3. The method of claim 1, wherein the modulating is based on a
random seed value for at least one of the pumps, the random seed
value comprising at least one of a pump startup time and a time of
a last command for the pump.
4. The method of claim 1, wherein the maintaining an average
aggregate pumping rate of the plurality of pumps comprises
modulating the at least one pump such that a specified pumped
volume occurs within a specified time period.
5. The method of claim 1, wherein reducing the amplitude of the
pressure fluctuation in the common fluid line comprises an
amplitude reduction operation selected from the amplitude reduction
operations consisting of: minimizing a maximum amplitude of
pressure fluctuation for a range of frequencies of interest;
minimizing an aggregate area under pressure fluctuation pulses for
a range of frequencies of interest; ensuring that a maximum
amplitude of pressure fluctuation for a range of frequencies of
interest is below a specified energy threshold; ensuring that an
aggregate area under pressure fluctuation pulses for a range of
frequencies of interest is below a specified energy threshold;
determining a beat frequency response between at least two of the
pumps, and ensuring that: a maximum amplitude of the beat frequency
response is below a threshold and/or minimized; or an aggregate
area of the beat frequency response is below a threshold and/or
minimized.
6. The method of claim 1, further comprising commanding at least
two of the pumps to pump at a substantially similar nominal pump
rate.
7. The method of claim 1, further comprising operating at least one
pump in all transmission gears and acquiring initial pressure
pulsation data to determine resonance frequencies of the at least
one pump.
8. The method of claim 7 wherein an operator utilizes the resonance
frequencies determined in pump operation to avoid pump speeds which
generate the resonant frequencies.
9. The method of claim 8 wherein the pump operation controlled by
software.
10. A method comprising: determining a first modulation definition
comprising a plurality of modulation instructions, each modulation
instruction corresponding to one of a plurality of pumps fluidly
coupled to a common fluid line; operating the pumps in response to
the first modulation definition; determining a pressure fluctuation
profile and a first fitness function for the first modulation
definition in response to the pressure fluctuation profile;
adjusting the first modulation definition to generate a second
modulation definition; operating the pumps in response to the
second modulation definition; determining the pressure fluctuation
profile and a second fitness function for the second modulation
definition in response to the pressure fluctuation profile; and
comparing the first fitness function and the second fitness
function, and selecting one of the first modulation definition and
the second modulation definition in response to the comparing.
11. The method of claim 10, wherein the determining a first
modulation definition comprises at least one operation selected
from the operations consisting of: determining a stored modulation
definition; selecting a default modulation definition; determining
a modulation definition in response to a pump specific parameter
selected from at least one of a pump identifier, a pump start time,
and a pump last command time; utilizing a modulation definition
from a previous selection of the first modulation definition and
second modulation definition; accepting a user input modulation
definition; determining the modulation definition in response to
user inputs; and scaling a preliminary modulation definition in
response to a designed pumping rate.
12. The method of claim 10, wherein the adjusting comprises
performing at least one adjusting operation selected from the
adjusting operations consisting of: changing at least one of the
modulation instructions, wherein the changing is random,
pseudo-random, and/or scheduled; testing at least one of the
modulation instructions over a specified operating space; and
swapping at least a portion of one of the modulation instructions
with another of the modulation instructions.
13. The method of claim 10, further comprising determining a
sensitivity of the fitness functions to at least one of the
pumps.
14. The method of claim 13, further comprising preferentially
modifying the modulation instructions corresponding to a pump
having a high sensitivity to the fitness functions.
15. The method of claim 10, wherein determining the first fitness
function comprises determining at least one of: a maximum amplitude
of a pressure fluctuation for a range of frequencies of interest;
an aggregate area under pressure fluctuation pulses for a range of
frequencies of interest; a maximum amplitude of a beat frequency
response between at least two of the pumps; and an aggregate area
of a beat frequency response between at least two of the pumps.
16. A method comprising: operating a plurality of pumps fluidly
coupled to a common fluid line; interpreting a pumping rate of each
of the plurality of pumps; and adjusting the pumping rate of the
plurality of pumps such that: a total pumping rate is maintained;
and no two adjacent pumps are pumping at the same rate.
17. The method of claim 16, wherein the pumping rate comprises the
rate of pressure pulse application from the pump to the common
fluid line.
18. The method of claim 16, wherein the adjusting the pumping rate
of the plurality of pumps such that no two adjacent pumps are
pumping at the same rate comprises adjusting the pumping rates
according to at least one of: ensuring that the pumps differ in
volumetric rate by at least 0.1 bpm; ensuring that the pumps differ
in plunger strokes per minute by at least 2%.
19. The method of claim 16, wherein adjacent pumps comprise any two
pumps having a shortest relative fluid path through the common
fluid line.
20. The method of claim 16, further comprising operating at least
one pump in all transmission gears and acquiring initial pressure
pulsation data to determine resonance frequencies of the at least
one pump.
Description
RELATED PATENT APPLICATION
[0001] This application claims the benefit of priority from U.S.
Provisional Application No. 61/337,041, filed on Jan. 29, 2010, the
entire contents of which are hereby specifically incorporated by
reference.
BACKGROUND
[0002] The statements in this section merely provide background
information related to the present disclosure and may not
constitute prior art.
[0003] In some subterranean formation processes carried forth in
the field, such as fracturing operations conducted at a well site,
oftentimes high pumping rate requirements make necessary use of
multiple pumps. In such multiple pump jobs, if one or more pumps
are operating at or near the same speed, large pressure
fluctuations or spikes can be produced as the plunger pulses of the
plurality of pumps synchronise and desynchronise. These pressure
spikes or fluctuations, can lead to failure of pressurizing
equipment, such as missile trailers.
[0004] It became know that some failures were due to resonances
manifesting within the piping system, which was excited by these
pressure fluctuations. While chokes may be added to pump inlets on
the missile trailers to significantly abate the problem, such
approach can lead to pump speed synchronization which can increase
the pressure pulsations by up to two orders of magnitude. Such
pulsations may lead to damage the of the treating iron, pumps, or
even engine transmissions.
[0005] It is an objective, of some embodiments of the invention
herein below, to address and at least partially overcome problems
related to pulse synchronisation.
SUMMARY
[0006] In a first aspect, some embodiments are methods which
include operating a plurality of pumps fluidly coupled to a common
fluid line, and modulating a pumping speed of at least one of the
pumps to reduce an amplitude of a pressure fluctuation in the
common fluid line, where the modulating comprises maintaining an
average aggregate pumping rate of the plurality of pumps.
[0007] The modulating may include a modulation behavior selected
from modulation behaviors such as inducing a random pump rate
fluctuation into at least one of the pumps, inducing a scheduled
pump rate fluctuation into at least one of the pumps, inducing a
random pump rate fluctuation into each of the pumps, inducing a
scheduled pump rate fluctuation comprising a pump offset schedule
into each of the pumps, and further ensuring that each of the pumps
operates at a distinct position in the pump offset schedule, and
inducing a pseudo-random pump rate fluctuation into at least one of
the pumps.
[0008] Modulating may be based upon a random seed value for at
least one of the pumps. Some examples of such random seed value
include a pump startup time, a time of a last command for the pump,
and the like.
[0009] Maintaining an average aggregate pumping rate of the
plurality of pumps may include modulating at least one pump such
that a specified pumped volume occurs within a specified time
period.
[0010] In some instances, the amplitude of the pressure fluctuation
in the common fluid line may be reduced by an amplitude reduction
operation such as minimizing a maximum amplitude of pressure
fluctuation for a range of frequencies of interest, minimizing an
aggregate area under pressure fluctuation pulses for a range of
frequencies of interest, ensuring that a maximum amplitude of
pressure fluctuation for a range of frequencies of interest is
below a specified energy threshold, ensuring that an aggregate area
under pressure fluctuation pulses for a range of frequencies of
interest is below a specified energy threshold, determining a beat
frequency response between at least two of the pumps, and ensuring
that: a maximum amplitude of the beat frequency response is below a
threshold and/or minimized; or, an aggregate area of the beat
frequency response is below a threshold and/or minimized.
[0011] Any of the methods described above may further include
commanding at least two of the pumps to pump at a substantially
similar nominal pump rate.
[0012] Further, any of the methods described above may include
operating at least one pump in all transmission gears and acquiring
initial pressure pulsation data to determine resonance frequencies
of the at least one pump. An operator may utilize the resonance
frequencies determined in pump operation to avoid pump speeds which
generate the resonant frequencies. Also, the pump operation may be
controlled by software.
[0013] In another aspect, method embodiments include determining a
first modulation definition by a plurality of modulation
instructions, each modulation instruction corresponding to one of a
plurality of pumps fluidly coupled to a common fluid line, then
operating the pumps in response to the first modulation definition,
determining a pressure fluctuation profile and a first fitness
function for the first modulation definition in response to the
pressure fluctuation profile, adjusting the first modulation
definition to generate a second modulation definition, operating
the pumps in response to the second modulation definition,
determining the pressure fluctuation profile and a second fitness
function for the second modulation definition in response to the
pressure fluctuation profile, and comparing the first fitness
function and the second fitness function, and selecting one of the
first modulation definition and the second modulation definition in
response to the comparing.
[0014] The determining a first modulation definition may include at
least one operation such as, but not limited to, determining a
stored modulation definition, selecting a default modulation
definition, determining a modulation definition in response to a
pump specific parameter selected from at least one of a pump
identifier, a pump start time, and a pump last command time,
utilizing a modulation definition from a previous selection of the
first modulation definition and second modulation definition,
accepting a user input modulation definition, determining the
modulation definition in response to user inputs, and scaling a
preliminary modulation definition in response to a designed pumping
rate.
[0015] The adjusting may be accomplished by performing at least one
of changing at least one of the modulation instructions, wherein
the changing is random, pseudo-random, and/or scheduled, testing at
least one of the modulation instructions over a specified operating
space, and swapping at least a portion of one of the modulation
instructions with another of the modulation instructions.
[0016] Any of the above methods may further include determining a
sensitivity of the fitness functions to at least one of the pumps.
Additionally the modulation may be modified by instructions
corresponding to a pump having a high sensitivity to the fitness
functions.
[0017] Determining the first fitness function may include
determining at least one of a maximum amplitude of a pressure
fluctuation for a range of frequencies of interest, an aggregate
area under pressure fluctuation pulses for a range of frequencies
of interest, a maximum amplitude of a beat frequency response
between at least two of the pumps, and an aggregate area of a beat
frequency response between at least two of the pumps.
[0018] In yet another aspect, embodiments may include operating a
plurality of pumps fluidly coupled to a common fluid line,
interpreting a pumping rate of each of the plurality of pumps, and
adjusting the pumping rate of the plurality of pumps such that: a
total pumping rate is maintained; and no two adjacent pumps are
pumping at the same rate. The pumping rate may be determined by the
rate of pressure pulse application from the pump to the common
fluid line.
[0019] The adjusting the pumping rate of the plurality of pumps
such that no two adjacent pumps are pumping at the same rate may
include adjusting the pumping rates according to at least one of
ensuring that the pumps differ in volumetric rate by at least 0.1
bpm, and ensuring that the pumps differ in plunger strokes per
minute by at least 2%.
[0020] Adjacent pumps may be any two pumps having a shortest
relative fluid path through the common fluid line.
[0021] Any of the methods may further involve operating at least
one pump in all transmission gears and acquiring initial pressure
pulsation data to determine resonance frequencies of the at least
one pump.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is exemplary data illustrating a coherent beat
frequency between two pumps operating at a similar nominal speed
(incorporated into the specification text-color).
[0023] FIG. 2 is exemplary data illustrating an incoherent beat
frequency between two pumps operating at a similar nominal speed,
with an imposed modulation on one pump (incorporated into the
specification text-color).
[0024] FIG. 3 is a schematic diagram of a controller for performing
certain operations to modulate pump operations.
[0025] FIG. 4 is a schematic diagram of an alternate controller for
performing certain operations to modulate pump operations.
[0026] FIG. 5 is a schematic diagram of a system having multiple
pumps fluidly coupled to a common fluid line.
[0027] FIG. 6 is an illustration of a scheduled pump
fluctuation.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0028] For the purposes of promoting an understanding of the
principles of the invention, reference will now be made to the
embodiments illustrated in the drawings and specific language will
be used to describe the same. It will nevertheless be understood
that no limitation of the scope of the invention is thereby
intended, any alterations and further modifications in the
illustrated embodiments, and any further applications of the
principles of the invention as illustrated therein as would
normally occur to one skilled in the art to which the invention
relates are contemplated herein.
[0029] Referencing FIG. 5, an exemplary system includes a number of
pumps fluidly coupled to a common fluid line. A controller is in
communication with the pumps, and a number of pressure fluctuation
devices ("P"), which may be accelerometers, high frequency pressure
transducers, or other devices that determine a parameter indicative
of pressure fluctuations at various points in the system. An
exemplary system includes at least two pumps, at least one of which
is in communication with the controller where the controller is
present. The system includes any number of pressure fluctuation
devices, including in certain embodiments no pressure fluctuation
devices. One exemplary system includes a device ("$$") indicative
of a device that is expensive, sensitive to vibrations, critical to
the performance of a pumping job (i.e. failure of the device causes
failure of the job, inconvenience to the job, or otherwise induces
unusual expense into the job). Certain embodiments of the system do
not include a device $$.
[0030] An exemplary procedure with respect to the system includes
operating the pumps fluidly coupled to a common fluid line and
interpreting a pumping rate of each of the pumps. Interpreting as
used herein includes any operation to determine the interpreted
parameter, including at least receiving the parameter as a datalink
or network communication, looking up the parameter value in a
software location, receiving the parameter as an industry standard
communication, determining the parameter from a sensor value,
and/or calculating the parameter based on other parameters received
or known in the system. The procedure includes an operation to
adjust the pump rate of the pumps such that a total pumping rate is
maintained (e.g. 30 barrels per minute (BPM)), and such that no two
adjacent pumps are pumping at the same rate.
[0031] Maintaining the total pumping rate is an operation that is
defined by specific factors related to a job that will be
understood to one of skill in the art contemplating a specific
embodiment of the system. For example, maintaining a pumped volume
to within a specified percentage of a pumped volume over a
specified time period may be acceptable for maintaining the total
pumping rate. The sensitivity of the job to pump rate fluctuations,
the fluid volume within a wellbore down to the formation of
interest, the type of fluid and compressibility of the fluid, and
other parameters known in the art will contribute to the
determination of acceptable percentages. In certain embodiments,
maintaining the pump rate to within a small percentage volume (e.g.
less than 5%, or less than 2%) over a small period of time (e.g.
less than one minute, or less than 30 seconds) will be acceptable
for many wellbore treatment pumping situations.
[0032] A difference between pumping rates that determines that the
pumps are not pumping at the same rate is likewise a
system-specific determination. In certain embodiments, a difference
in pumping rates of 2.5% is sufficient, or a pumping rate of 0.1
BPM is sufficient. One of skill in the art may perform a simple
data sampling to determine how closely synchronised two pumps may
operate and avoid harmonic interaction. It has been observed that
two similar pumps operating at a nominal 5 BPM can experience
harmonic interactions that are 100 times stronger than one of the
pumps operating 0.1 BPM away from the other. In certain
embodiments, the pumping rate is determined by the pump plunger
stroke speed (e.g. in strokes per minute), because pumps having a
different plunger head size will pump different fluid volumes over
time with the same plunger stroke speed. Pumping rate is utilized
herein, and although many examples include volumetric pumping rate,
the use of the term pump rate also includes at least any speed
related to the pumps including at least an engine speed, a plunger
stroke frequency, a volumetric pumping rate, a rate of pressure
pulse application from the pump to the common fluid line (e.g. a
rotational speed of a compressor for a non-positive displacement
pump, or the plunger stroke rate for a positive displacement pump),
and a transmission rotational rate within the pumper system. A
given system may include some of the pump rate concepts and exclude
others, depending on the context of the example and the likely
harmonic interaction factors between pumps for the given
situation.
[0033] In certain embodiments, the operation to adjust the pumping
rate of the pumps includes adjusting the pump rates such that no
two adjacent pumps have a volumetric rate within 0.1 BPM of each
other, and/or such that no two adjacent pumps have a plunger stroke
rate within 2% of each other. Adjacent pumps, as used herein,
include any two pumps having a shortest relative fluid path through
the common fluid line, or a fluid path through the common fluid
line that does not traverse other pumps. In the example of FIG. 5,
Pump "A" may be considered adjacent to pump "B". Pump "A" may
likewise be considered adjacent to pump "E", although the dynamics
of the common fluid line and the distance between pumps "A" and "E"
may allow the pumps to be considered non-adjacent as well. In one
example, pumps A, C, F, and G run a first pumping rate and pumps B,
D, E, and H run at a second pumping rate, ensuring that no two
adjacent pumps are operating at the same pumping rate. In another
example, pumps A, C run at a first rate, pumps B, D run at a second
rate, pumps E, G run at a third rate, and pumps F, H run at a
fourth rate, again ensuring that no two adjacent pumps are
operating at the same pumping rate, and providing even greater
distance through the fluid path between pumps having similar
pumping rates.
[0034] Other pumping rate combinations are understood herein,
including operating each pump at a different rate, operating pumps
A, G at a first rate, pumps B, H at a second rate, pumps C, E at a
third rate, and pumps D, F at a fourth rate. Certain examples
include operating a lowest number of discrete pumping rates that
still provide a greatest distance between pumps that operate at the
same rate. The number of pumping rates to be utilized may be
determined by a user input, an operation of the controller, and may
further be updated during a treatment operation according to
applicable criteria such as a determination that the vibration
profile can be improved or is too high.
[0035] Referencing FIG. 3, a controller that performs certain
operations for modulating pump rates is shown. The controller forms
a portion of a processing subsystem including one or more computing
devices having memory, processing, and communication hardware. The
controller may be a single device or a distributed device, and the
functions of the controller may be performed by hardware or
software. In certain embodiments, the controller includes one or
more modules structured to functionally execute the operations of
the controller. The exemplary controller includes a feedback
module, a pump modulation module, a randomization module, and a
fitness function module. The description herein including modules
emphasizes the structural independence of the aspects of the
controller, and illustrates one grouping of operations and
responsibilities of the controller. Other groupings that execute
similar overall operations are understood within the scope of the
present application. Modules may be implemented in hardware and/or
software on computer readable medium, and modules may be
distributed across various hardware or software components.
[0036] A procedure for pumping includes operating a number of pumps
fluidly coupled to a common fluid line. The pump modulation module
modulates a pumping speed of at least one of the pumps to reduce an
amplitude of a pressure fluctuation in the common fluid line. The
modulating includes maintaining an average aggregate pumping rate
of the pumps, for example achieving a specified pumped volume
during each specified time period. The pump modulation module may
vary pump rates by inducing a random pump rate fluctuation into at
least one of the pumps, inducing a scheduled pump rate fluctuation
into at least one of the pumps, inducing a random pump rate
fluctuation into each of the pumps, and/or inducing a scheduled
pump rate fluctuation including a pump offset schedule into each of
the pumps. The pump modulation module may operate on a most
sensitive pump, on a pump that is the only pump enabled to respond
to pump rate commands from the pump modulation module, on any
number of the pumps, and/or on all of the pumps. Where the pump
modulation module utilizes a scheduled pump fluctuation, the pump
modulation module ensures that each of the pumps operates at a
distinct position in the pump offset schedule.
[0037] An exemplary pump modulation module induces a pseudo-random
pump rate fluctuation into at least one of the pumps. The
pseudo-random pump rate may be a pump rate fluctuation provided in
a predetermined series, provided by an algorithm that provides a
pseudo-random output, or by other pseudo-random operations
understood in the art. In certain embodiments, a randomization
module provides a random seed value that the pump modulation module
uses for randomizing the pump modulations. The random seed value
may be utilized to seed a random number algorithm, to begin a
scheduled pump fluctuation at a random point within the scheduled
pump fluctuation series, and/or to start the scheduled pump
fluctuation at a random time. The randomization module may
determine the random seed value according to a pump startup time
for each of the pumps, according to a pump identifier (e.g. a pump
index entered by an operator, an ordered value or address for the
pump established during communications with the controller, and/or
a pump serial number established for the pump), and/or according to
a time that a last command was provided to the pump.
[0038] In certain embodiments, the reducing the amplitude of the
pressure fluctuation in the common fluid line includes a fitness
function module determining a fitness parameter and the pump
modulation module modulating the pump rates in response to the
fitness parameter.
[0039] In one embodiment, the fitness function module determines a
maximum amplitude of pressure fluctuation for a range of
frequencies of interest. The frequencies of interest may be
determined by the experience of the operator, by a test of the
lines (e.g. sweep frequency energy and determine harmonic
frequencies of the fluid lines), by observation of pressure
fluctuations during a pumping operation, or by other techniques
understood in the art. The pump modulation module may adjust the
pumping rates to minimize the maximum amplitude of pressure
fluctuation that occurs within the range of the frequencies of
interest. The pressure fluctuation frequency may be a frequency as
determined by a frequency domain transformation (FFT, Fourier,
Z-transform, etc.) of information from a pressure transducer, or a
by a calculated pressure fluctuation frequency according to an
observed beat frequency. The maximum amplitude of a pressure
fluctuation may also be determined by an accelerometer positioned
at a point of interest in the system, where in one embodiment any
responsive frequency of the accelerometer is a frequency of
interest (i.e. the dynamics of the accelerometer may dampen
frequencies that are not of interest).
[0040] In other embodiments, the pump modulation module may adjust
pump rates to minimize an aggregate area under pressure fluctuation
pulses for a range of frequencies of interest (e.g. the largest
peaks in the frequency domain, peaks within a specified percentage
of a largest peak, the top three peaks, etc.). The aggregate area
may be weighted for the energy provided under the peak--e.g.
adjusting for the relative energy provided by a high or low
frequency peak. In other embodiments, the pump modulation module
adjusts pump rates to provide a maximum amplitude of pressure
fluctuation for a range of frequencies of interest that is below a
specified energy threshold (that again may be a frequency-dependent
value), and/or adjusts pump rates to ensure that an aggregate area
under pressure fluctuation pulses for a range of frequencies of
interest is below a specified energy threshold.
[0041] In certain embodiments, the pressure fluctuations are
fluctuations of a beat frequency. The beat frequency may be the
beat frequency between at least two of the pumps (e.g. as measured
between those pumps), and the pump modulation module may adjust
pump rates to ensure that a maximum amplitude of the beat frequency
response is below a threshold and/or minimized, or to ensure that
an aggregate area of the beat frequency response is below a
threshold value, minimized, below an energy threshold value, and/or
has a minimized aggregate energy within the frequencies of
interest.
[0042] In certain embodiments, pumps are controlled to avoid
providing energy to certain portions of the frequency spectrum. The
pumps may be directed into certain frequency portions, for example
one or more pumps spread their energy throughout specific
bandwidths within the frequency spectrum, or sensitive areas of the
frequency spectrum are specifically avoided.
[0043] In certain embodiments, at least two of the pumps are
commanded to operate at a substantially similar nominal pump rate.
The nominal pump rate is the pump rate provided to the pump, by a
controller or operator, before the pump rate command of the pump
modulation module that alters the final pumping rate. The pump rate
that is substantially similar varies with the specific embodiment,
but includes pumps having the same commanded set point, pumps
operating within 2% of each other, pumps operating to within one
significant digit on a display with each other, and pump rates that
if plotted over a period of time exhibit nearly the same average
pump rate and substantial crossover in the plots. Any other
concepts that embody substantially similar pumping rates are
contemplated herein, and certain concepts embodying substantially
similar may not apply to certain embodiments. In certain
embodiments, several pumps or even all of the pumps operate at
substantially similar nominal pump rate. Among advantages provided
by operating pumps at substantially similar nominal pump rates
include simplification of the system for the operator,
standardization in designing pumping treatments where the pumps
perform fungible operations, ensuring that pumps exhibit similar
fuel consumption simplifying logistics, and ensuring that pumps
exhibit similar long-term wear characteristics.
[0044] Referencing FIG. 4, a controller that performs certain
operations for modulating pump rates is shown. A modulation
definition module determines a first modulation definition
including a plurality of modulation instructions, where each
modulation instruction corresponds to one of a number of pumps
fluidly coupled to a common fluid line.
[0045] A pump modulation module operates the pumps in response to
the first modulation definition, and a fitness function module
determines a pressure fluctuation profile (e.g. frequency domain
data showing amplitude peaks, accelerometer peak data with or
without frequency information, etc.) and a first fitness function
for the first modulation definition in response to the pressure
fluctuation profile. A modulation definition adjustment module
adjusts the first modulation definition to generate a second
modulation definition, and the pump modulation module operates the
pumps in response to the second modulation definition. The fitness
function module determines the pressure fluctuation profile and a
second fitness function for the second modulation definition in
response to the pressure fluctuation profile, and a modulation
definition selection module compares the first fitness function and
the second fitness function, and selects one of the first
modulation definition and the second modulation definition in
response to the comparing. The modulation definition selection
module may select the best fitness function between the first
fitness function and the second fitness function (e.g. the one
having a highest value where a higher value indicates greater
fitness), but in certain embodiments the modulation definition
selection module may decline the second fitness function where the
second fitness function is higher but the values are close--for
example to promote system stability and reduce cycling between
operating points.
[0046] In certain embodiments, the modulation definition module
determines the first modulation definition from a stored modulation
definition. The stored modulation definition may be a
manufacturer-provided definition, a modulation definition stored at
a system shutdown, or other stored modulation definition understood
in the art. The modulation definition module may utilize a default
modulation definition as the first modulation definition, for
example at startup, after a hardware change occurs in the system,
and/or after a power down of the system (although the controller
may also save a modulation definition through a power down cycle).
The modulation definition module may utilize a parameterized
modulation definition as the first modulation definition--for
example a modulation definition determined in response to a pump
identifier, pump startup time, and/or pump last command time. The
modulation definition module may determine the first modulation
definition from a previous modulation definition from a prior
execution cycle of the controller (e.g. the selected modulation
definition by the modulation definition selection module), and/or
may determine the first modulation definition in response to user
inputs.
[0047] The modulation definition module may construct the first
modulation definition from a number of sources, including any of
the described sources or other sources understood in the art. In a
non-limiting example, the modulation definition module surveys the
pumps for a pump identifier when communication is initiated between
the pumps and the controller (e.g. a cable from each pump is
plugged into the controller), and where a pump identifier is not
available for a particular pump (e.g. an older pump that does not
publish a pump identifier) the modulation definition module
utilizes a default instruction for the particular pump.
[0048] Certain operations of the controller may be performed by an
operator or in hardware. For example, where a pump is not
compatible for communication with the controller or to receive
commands from the controller, the modulation definition module may
determine the existence of the pump through a user input
identifying the pump, and the pump modulation module may publish a
pump rate command for the pump, where an operator follows the
published pump rate for the pump in question. In the example
embodiment, the modulation definition module and modulation
definition adjustment module may determine that the pump is not
automatically controllable, and assign fixed pump rates to the pump
while assigning rapidly fluctuating pump rates to other pumps that
are automatically controllable. In certain embodiments, a pump may
be responsive to the pump rate commands through hardware devices,
for example a pump may be responsive to a voltage output from the
controller that has a modulated value depending upon the commanded
pump rate. Any pump rate control mechanism understood in the art is
contemplated herein.
[0049] In certain embodiments, the modulation definition module
determines the first modulation definition by scaling a preliminary
modulation definition in response to a designed pumping rate. For
example, a default modulation definition may include a set of
values for four pumps at a pumping rate of 15 BPM, and the designed
pumping rate may be 20 BPM. In the example, where four pumps are
present in the system, the modulation definition module may provide
modulation definition scaling to the default modulation definition
in response to the designed pumping rate. The scaling may be
applied to some, but not all, of the parameters in the modulation
definition as will be understood to one of skill in the art. For
example, a randomized fluctuation of +/-0.5% may be applied to
either 15 BPM or 20 BPM without regard to the pumping rate, but a
modulation frequency rate may be changed at 20 BPM due to the
change in the forcing frequency provided by the pump. Any source
for the modulation definition may be scaled in response to a change
in the designed pumping rate, including the previous modulation
definition. It is a mechanical step for one of skill in the art,
having the benefit of the disclosures herein, to determine scaling
adjustments to a modulation definition.
[0050] The pump modulation module may perform any adjustments to
the modulation definition understood in the art to stabilize the
system, respond to changes in the system, to achieve set points,
and the like. For example and without limitation, where a change in
the modulation definition indicates a large change in rates, the
pump modulation module may provide rate smoothing to avoid system
disruption, where a large set point change has occurred the pump
modulation module may suspend certain modulation operations that
may reduce system response, etc. Other controller management may be
included in the system, for example gains in various controllers
within the system may be managed to avoid complications with the
modulating or with the changes in set points in response to a
change in the modulation definition. Non-limiting examples include
derivative control elements may be suspended or have target points
adjusted (e.g. changing from derivative of the error to derivative
of a target output or derivative of a nominal non-modulated target
output), integrators may be reset, have values changed, or have
gains increased or reduced, etc. Other adjustments understood in
the art are contemplated herein.
[0051] In certain embodiments, the modulation definition adjustment
module generates the second modulation definition with an operation
such as changing at least one of the modulation instructions,
wherein the changing is random, pseudo-random, and/or scheduled;
testing at least one of the modulation instructions over a
specified operating space (e.g. sequentially manipulating a pump
rate for a pump from a low pumping rate to a high pumping rate at
intervals to test the operating space); and swapping at least a
portion of one of the modulation instructions with another of the
modulation instructions (e.g. swapping a first pump rate and a
second pump rate). Any modulation instructions may be changed,
including at least pump rates, modulation amplitudes and rates,
modulation functions (e.g. random, pseudo-random, selection from
one or more schedules), etc.
[0052] In certain embodiments, the fitness function module
determines a sensitivity of the fitness functions to at least one
of the pumps. The determination of sensitivity may be determined in
the normal course of operations or as an intrusive procedure. For
example, the fitness function may track the magnitude of changes in
the fitness functions in response to changes for various pumps
(including statistically de-convoluting where multiple pumps are
adjusted in each iteration). In another example, the fitness
function module may perform a specific sensitivity analysis,
sequentially adjusting pump commands and determining the magnitude
of changes in the fitness functions in response to the sequential
adjustments. In certain embodiments, the modulation definition
adjustment module preferentially modifies modulation instructions
for high sensitivity pumps. Preferential modification may be a
statistical increase (e.g. the random selector increases the
percentage of adjustments for the sensitive pump) or an explicit
optimization priority selection where the modulation definition
adjustment module manipulates the sensitive pump (or a subset of
the most sensitive pumps) until a determination is made that the
optimal (possibly a local optimum that will change after other
pumps are adjusted) sensitive pump parameters are determined,
whereupon the modulation definition adjustment module proceeds to
optimize the next subset of most sensitive pumps.
[0053] The fitness function may be any pressure fluctuation fitness
parameter described herein or otherwise understood in the art. For
example, and without limitation, the fitness function may be a
maximum amplitude of a pressure fluctuation for a range of
frequencies of interest (including maximum energy under a peak or
the explicit peak amplitude), an aggregate area (including
aggregate energy or explicit area) under pressure fluctuation
pulses for a range of frequencies of interest, a maximum amplitude
of a beat frequency response between at least two of the pumps
(including maximum energy under a peak or the explicit peak
amplitude), and an aggregate area of a beat frequency response
between at least two of the pumps (including aggregate energy or
explicit area). In certain embodiments, the fitness function is
indicative of the pressure fluctuation environment of a sensitive
device in the system (e.g. see "$$" on FIG. 5).
[0054] In certain embodiments, the fitness function assigns certain
pumps to certain portions of the frequency bandwidth (and may
further provide a higher fitness score for the amount of
distribution within each bandwidth). In certain embodiments, the
fitness function protects certain bandwidths by direction the
energy from the pumps away from certain frequency ranges in the
spectrum. The protected frequency ranges may be known problematic
ranges, ranges that are relevant to certain equipment or signal
processing, or ranges reserved for equipment that is not always
present but that may be present on certain occasions.
[0055] Referencing FIG. 6, a randomized sequence is illustrated
that is consistent with certain scheduled pump fluctuations herein.
The randomized sequence includes 1093 values randomly distributed
between +/-0.03. The randomized sequence is a prime number
rendering it unlikely that two pumps proceeding through the
sequence at differing rates (either due to a modulation frequency
command change from the modulation definition, or because the pumps
are pumping at different rates or have different plunger head
sizes) will have a significant harmonic interaction, and also that
any pump having a periodic disturbance (e.g. a secondary pressure
pulse from a valve that is failing) will interact with the
modulation in a simple ratio. However, the randomized sequence need
not include a prime number of elements, as any sufficiently long
sequence will also make interactions unlikely. The randomized
sequence may be stored on the controller in advance, and may be
entered for various pumps at differing positions (e.g. A, B, and C
in the illustration) or at differing times. The amplitude of the
randomized sequence may be scaled, and 3% is provided for exemplary
purposes only.
[0056] As is evident from the figures and text presented above, a
variety of embodiments according to the present invention are
contemplated.
[0057] An exemplary pumping situation includes a fracturing
operation with high pumping rates utilizing multiple pumps. In
these multiple pump jobs, if one or more pumps are operating at or
near the same speed, large pressure fluctuations are produced as
the plunger pulses of the pumps go into and out of synchronization.
The pressure fluctuations have been observed to be powerful enough
to break missile trailers, and otherwise increase wear, cause
damage to, and increase the chance of failure of treating iron,
pumps, transmissions, and other equipment. One mechanism understood
to cause failures are pressure fluctuations from the multiple pumps
that match the resonance of the piping system, or other equipment
vibrationally connected to the pumped fluid. Certain mitigating
techniques such as choking pump inlets and missile trailers can
assist with the issue, but such techniques may be undesirable due
to fluid frictional losses, and operator behavior such as operating
all pumps at the same speed can still increase wear and cause
failures. Pumps operating at synchronised speeds have been observed
to increase pressure pulsations by two orders of magnitude.
[0058] An exemplary operation includes operating a control
algorithm on an individual pump to prevent pump synchronization.
The control algorithm modulates the pump rate randomly up and down,
and may be performed any number of the pumps, including a single
pump, all pumps, or any number of the pumps.
[0059] An exemplary control algorithm applies the pump rate
modulation, determines a feedback signal, and adjusts the pump rate
modulation in response to the feedback signal. The pressure
modulation may be random (e.g. determined on an output from a
random function generator or white noise algorithm), pseudo random
(e.g. determined from a pre-stored randomized sequence), or
scheduled. Examples of a scheduled sequence include a
pre-determined sequence that does not repeat within the sequence
itself (e.g. based on the values of .pi., e, or other non-repeating
sequence), a sequence having a prime number of variation settings
(in certain embodiments, a large prime number), and/or any other
sequence determined such that, for a finite number of pumps
following the sequence and positioned at different places serially
within the sequence, the pumps will not experience significant
harmonic interactions.
[0060] The feedback signal may be a vibration level from any
portion of the system in vibrational communication with the pumped
fluid of the pumps, including at least the discharge piping or the
pumps. An alternate or additional feedback signal may be a measure
of the pressure fluctuation, including an amplitude of the pressure
fluctuation in either the time or frequency domain. The frequency
domain may include a description of the power of pressure
fluctuation peaks, including an amplitude or an area under one or
more peaks, and may include frequencies of interest, predetermined
frequencies, or frequencies determined during pumping operations.
The frequency measure may include a description of a combined beat
frequency between two or more pumps, or it may be a pressure
fluctuation as measured at a single sensor.
[0061] Another exemplary control algorithm utilizes a selection
algorithm that searches the pumping rate or pumping rate modulation
operating space, providing improving response as the pumping
continues.
[0062] Another exemplary control algorithm includes selectively
changing pump rates on adjacent pumpers (or on pumpers most likely
to be vibrationally coupled, including pumpers having a shortest
vibrational path through the pumped fluid) to NOT match the pump
rate of the adjoining pumper(s). In certain embodiments, a feedback
signal or signals may be utilized to determine an optimal or
improved pump rate during a job. In one embodiment, the control
algorithm utilizes two pump rates, with one alternating set of
pumps at a first speed and another alternating set of pumps at a
second speed. In another embodiment, opposing pumps may be operated
at differing pumping speeds, and the control algorithm may utilize
a number of pumping speeds such that no opposing, adjacent, or
otherwise closely proximate pumps operate at the same speeds. In
one example, even-numbered pumps operate at 5 barrels per minute
(BPM), and odd pumps operate at 5.1 BPM. Pump rates described
herein may refer to volumetric pump rate, or plunger stroke rate
(e.g. in plunger strokes per minute). As will be understood in the
art, pumps operating at different volumetric pump rates having
different sized plungers may nevertheless be operating at a similar
plunger stroke rate.
[0063] Another exemplary pump modulation operation is described.
The pump rate (or equivalently, the engine speed) is modulated up
and down using a random, pseudo-random, or pre-defined series
structured so that when the volume pumped in an interval (e.g. one
minute) is summed and divided by the time interval that the average
rate is equal to the rate that the pump was set for. In one
example, pumps at a rate at least 0.1 BPM apart can reduce the
pulsations by 2 orders of magnitude (100 times), so In certain
embodiments a modulation of +/-0.1 BPM is sufficient.
[0064] The modulation occurs at a frequency to avoid spending any
significant time at a given potentially damaging frequency, and to
minimize the energy input at any given point in the frequency
spectrum. In one embodiment, a modulation series designed to spread
the pumping energy evenly across a given band (such as +-0.1 BPM)
is utilized. In another embodiment, a series designed to give a
distribution is not even across the frequency band is utilized. In
certain embodiments, a modulation series designed to reduce a
maximum amplitude of any single peak is utilized.
[0065] An alternate or additional embodiment includes minimizing
pumping energy at a specified range of frequencies, and further
including minimizing pumping energy at a range of frequencies that
are observed to occur with other pumps in the system that do not
have a control algorithm modulating the pumping rate. In one
example, a first pump is fluidly coupled to a system having other
pumps that operate in an open loop response to a pump rate set
point, a feedback signal determines the pumping energy frequencies
of the open loop pumps that are realized at the fluid outlet (or
other position in proximity to the first pump), and a control
algorithm modulates the first pump in response to the feedback
signal. An exemplary modulation includes minimizing a pumping
energy frequency of the first pump at the pumping energy
frequencies of the open loop pumps as realized at the fluid outlet
(or other position in proximity to the first pump).
[0066] In one embodiment, one or more modulation series are
structured, and pumps are introduced into the one or more
modulation series, such that no two pumps run the same series at
the same point in the series. In one embodiment, a random series is
generated and utilized, and in an additional embodiment a long
series is entered at a random point or initiated at a random time.
In certain embodiments, a parameter is utilized as a random seed,
such as a pump startup time, a pump identifier (such as a serial
number or an operator entered value), and/or a time of a last
command instruction to the pump.
[0067] FIGS. 1 and 2 provide exemplary data illustrating a pump
modulation. FIG. 1 illustrates two pumps operating at similar
speeds, where the yellow trace is the sum of the pumping rates. A
coherent beat frequency is observed, which would show an
identifiable high-amplitude peak in the frequency domain (not
shown--but the determination of frequency domain information from
time domain information as illustrated in FIG. 1 is a mechanical
step for one of skill in the art). FIG. 1 illustrates a first pump
operating at a constant speed, with a second pump operating at the
same average volumetric pumping rate with time, but with a +/-0.8%
random modulation applied. Again the yellow trace shows the summed
pumping rates. In the illustration of FIG. 2, a beat frequency
component is barely present, and it is clear that a frequency
domain analysis would show a number of diffuse peaks with much
lower amplitudes than the dominant beat frequency from FIG. 1. In
some instance, inventors discover that averaging effect of
randomizing across a high number of pumps, such as 10 to 14 pumps,
on actual job may have even a greater effect than shown, possibly
leading to lower peak to peak pressure fluctuations in the
discharge line.
[0068] Another exemplary embodiment includes randomly adjusting
pump speeds during a pumping operation with a selection algorithm
to adjust a combination of pump speeds that obtains an improving
discharge line harmonics profile (or other harmonic feature). For
example, a first set of pumping parameters may be tested and
compared to a second set of pumping parameters, and a fitness value
assigned to each set of parameters. The pumping parameters having
the superior fitness value are selected for a next iteration of the
selection algorithm. The generation of new pumping parameters to
test may be random or scheduled. The pumping parameters may include
pumping rates, modulation values, or modulation methods, or any
other pumping parameters understood in the art. The scheduled
adjustments to the pumping parameters may include testing the
pumping operating space (e.g. testing values from a minimum to a
maximum pump rate), testing how many different pumping rates are to
be utilized (e.g. two rates on alternating pumps, four rates
including differing rates for alternating and opposing pumps, a
unique rate for each pump, etc.), and/or testing whether randomized
pump modulation or pump rate offset values provide superior
response.
[0069] In certain embodiments, the fitness function includes a
maximum observed frequency peak response (typically where a lower
maximum is better), an area under frequency peak responses through
a frequency range of interest, a combination of these parameters
(e.g. minimized area combined with a specified maximum peak
threshold that is not to be exceeded). Further, the frequency
ranges of interest may vary between maximum peak values and the
area under frequency peak responses (e.g. to minimize a specific
resonance with the maximum peak, and to minimize total energy
through a different frequency range, to protect from different
failure modes). Still further, the fitness function may incorporate
a number of pressure pulse measurements--for example a first
pressure pulse measurement may be taken between a first and a
second pump, and a second pressure pulse measurement may be taken
between the second pump and a third pump--and the pressure pulse
measurements may be weighted or otherwise combined into a fitness
function result. Where a number of pressure pulse measurements are
combined, the combination may determine any type of data from each
(e.g. peak maximums, peak areas, etc.), and may weight the data in
any manner without limitation. Non-limiting examples include
weighting pressure pulse measurements more heavily near expensive
or sensitive equipment, selecting frequency ranges of interest
according to observed or expected frequency resonance values (e.g.
lower frequencies where a discharge line is longer, etc.).
[0070] In one embodiment, pumps may be adjusted individually or in
subsets of the total number of pumps, and the selection of the
individual pumps may be random or selected. In one example, out of
10 pumps on location, pumps 3 and 8 are selected. The selection of
pumps 3 and 8 may be random, or in one example they are selected
according to a high sensitivity to a fitness function (e.g. a small
fluctuation in pumps 3 and 8 is observed to induce a large change
in the fitness function). In one embodiment, the speeds of pumps 3
and 8 are swapped, keeping the same aggregate pumping rate, and the
fitness function is determined. If the fitness function improves
(e.g. harmonics are reduced at a position in the system), the
swapped rates are kept; otherwise the old rates are restored. A
next iteration of the algorithm utilizes the new rates as a
baseline, and may test the same pumps, test different pumps,
re-check some or all of the pumps for sensitivity to the fitness
function, or perform other operations. The iterations of the
control algorithm to improve the fitness function may be performed
for a specified time, a specified number of iterations (e.g.
hundreds, thousands, or more), until a threshold fitness function
value is achieved, until an optimal fitness value is achieved (e.g.
a specified number of iterations occur without improvement or with
only improvement below a threshold value--although any convergence
criteria understood in the art may be utilized), performed
periodically (e.g. a number of iterations, a specified pause, and
then repeated), and/or may be performed periodically throughout a
pumping operation.
[0071] Alternatively or additionally, the control algorithm may be
performed in response to a user input. For example, a number of
pumps may be connected to a wellbore and a number of operations
performed over a period of time. After each shutdown, the hardware
configuration may be identical at startup, and the previously
determined pumping rates or modulation values may be acceptable.
However, a given operation may involve a change in the hardware
(e.g. a pump is added, removed, swapped out, moved, etc.) or a
change in the job design (e.g. a different pumping rate than a
previous job) and an operator may activate the control algorithm to
re-optimize the pumps. The control algorithm may also determine
that a change has occurred (e.g. by determining a change in the
fitness function value) and re-optimize the pump rates or pump
modulation values automatically.
[0072] Yet another control algorithm includes selectively changing
pump rates on adjacent pumpers to NOT match the pump rate of a
reference pumper. For example, the control algorithm may be
implemented as a rule that no alternate pumps may have same pump
rates. The control algorithm may additionally search for optimal
pump rates during a pumping operation, utilizing a feedback
pressure signal or a piping vibration signal. Alternatively or
additionally, the control algorithm includes avoiding an acoustic
resonance in the piping by avoiding running the pumps at certain
speeds.
[0073] In some circumstances, a lower pressure pulsation may be
experienced if the pump rates are selected to avoid acoustic
frequencies in the piping. However, acoustic frequencies in
discharge piping are dependent on the rig up which changes from job
to job. A diagnostic capability may be implemented at the start of
the job to sweep one or more pumps in all the gears and use the
pressure pulsation data to determine the resonance frequencies of
the pumping system. This information may be used to alert the pump
operator of these "hot spots" or automated in the pump controls
software to avoid pump speeds that excite those resonant
frequencies."
[0074] Embodiments may also include a feedback loop control that
uses artificial intelligence to modulate the pump rates during a
job to achieve a local minima of discharge pressure fluctuations or
treating iron vibration.
[0075] Random walk of the pumps speed on the job may be combined
with other search methods and artificial intelligence such as
genetic algorithm (GA) to obtain the best possible combination of
pumps speed to obtain least discharge line harmonics. Such a method
may allow continuous searching for a better combination of pump
speeds independent of job layout and pumped fluid properties. In a
simple form, GA may have three operators--Selection, Crossover,
and/or Mutation. A set of rules may be constructed to perform these
operations on the pumps and measure the "fitness" of the new
combination. For example, if out of 10 pumps on location, Pump 3
and 8 are selected either randomly or due to their high sensitivity
to fitness function (which would be the discharge line harmonics),
their speeds may be swapped to obtain a new combination without
changing the overall pump rate. If the resulting combination
reduces the harmonics, maintain such and perform next round of
processing, otherwise discard this combination and restart with the
last set. In such a system, an expectation is that the average
fitness of the pumping system will improve over time, and so by
repeating this process for tens of rounds, an optimal combination
of pump speeds can be discovered that may help maintain low
pressure fluctuations.
[0076] While the invention has been illustrated and described in
detail in the drawings and foregoing description, the same is to be
considered as illustrative and not restrictive in character, it
being understood that only certain exemplary embodiments have been
shown and described and that all changes and modifications that
come within the spirit of the inventions are desired to be
protected. In reading the claims, it is intended that when words
such as "a," "an," "at least one," or "at least one portion" are
used there is no intention to limit the claim to only one item
unless specifically stated to the contrary in the claim. When the
language "at least a portion" and/or "a portion" is used the item
can include a portion and/or the entire item unless specifically
stated to the contrary.
* * * * *