Note: Descriptions are shown in the official language in which they were submitted.
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METHOD, SYSTEM, AND MEDIUM FOR CONTROLLING RATE OF
PENETRATION OF A DRILL BIT
TECHNICAL FIELD
[0001] The present disclosure is directed at methods, systems, and
techniques for
controlling rate of penetration of a drill bit.
BACKGROUND
[0002] During oil and gas drilling, a drill bit located at the end of
a drill string is
rotated into and through a formation to drill a well. The rate of penetration
of the drill bit
through the formation reflects how quickly the well is being drilled.
Generally, it is
unadvisable to blindly increase drilling parameters such as weight-on-bit or
drill string
torque in an attempt to increase the rate of penetration; doing so may cause
the drilling
process to catastrophically fail.
[0003] To safely and efficiently drill wells, an automatic driller
may be used.
Automatic drillers attempt to control the rate of penetration of the drill bit
by taking into
account one or more drilling parameters.
SUMMARY
[0004] According to a first aspect, there is provided a method for
controlling rate
of penetration of a drill bit. The method comprises, for each of multiple
drilling
parameters, evaluating a control loop by (i) reading a drilling parameter
measurement;
(ii) determining an error measurement that represents a difference between a
drilling
parameter setpoint and the drilling parameter measurement; and (iii)
determining, from
the error measurement, an output signal proportional to the rate of
penetration of the drill
bit. The method further comprises selecting the output signal of one of the
control loops
to control the rate of penetration; and using the output signal that is
selected to control the
rate of penetration.
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=
[0005] Determining of the output signal may comprise adding a
proportional
component that varies proportionally with the error measurement and an
integral
component that varies with a sum of previous error measurements.
[0006] Selecting the output signal may comprise determining
which of the control
loops has the output signal of lowest magnitude, and selecting the output
signal of lowest
magnitude to control the rate of penetration.
[0007] Selecting the output signal may comprise determining
which of the control
loops has the error measurement that represents a lowest percentage error
relative to the
drilling parameter setpoint, and selecting the output signal of the control
loop that has the
lowest percentage error to control the rate of penetration.
[0008] Using the output signal that is selected to control the
rate of penetration of
the drill bit may comprise sending the output signal that is selected to a
variable
frequency drive that controls a drawworks of an oil rig.
[0009] Using the output signal that is selected to control the
rate of penetration of
the drill bit may comprise controlling a hydraulics system that controls the
height of a
traveling block, or a drawworks comprising brakes that are used to control the
descent of
the traveling block.
[0010] The method may further comprise, for each of the control
loops whose
output signal is not used to control the rate of penetration of the drill bit,
adjusting the
integral component used to determine the output signal such that the output
signal is
approximately equal to the output signal that is selected.
[0011] Determining the output signal may further comprise
adding a derivative
component to the proportional component and the integral component, and the
derivative
component may vary with a rate of change versus time of the error measurement.
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[0012] The drilling parameters may comprise at least one of weight-on-
bit,
differential pressure, torque applied to a drill string to which the drill bit
is coupled, and
traveling block velocity.
[0013] According to another aspect, there is provided a system for
controlling rate
of penetration of a drill bit. The system comprises a processor and a non-
transitory
computer readable medium communicatively coupled to the processor. The medium
has
stored thereon computer program code that is executable by the processor. The
computer
program code when executed by the processor causes the processor to, for each
of
multiple drilling parameters, evaluate a control loop by (1) reading a
drilling parameter
measurement; (2) determining an error measurement that represents a difference
between
a drilling parameter setpoint and the drilling parameter measurement; and (3)
determining, from the error measurement, an output signal proportional to the
rate of
penetration of the drill bit. The computer program code also causes the
processor to select
the output signal of one of the control loops to control the rate of
penetration; and use the
output signal that is selected to control the rate of penetration.
[0014] To determine the output signal, the processor adds a
proportional
component that varies proportionally with the error measurement and an
integral
component that varies with a sum of previous error measurements.
[0015] Selecting the output signal may comprise determining which of
the control
loops has the output signal of lowest magnitude, and selecting the output
signal of lowest
magnitude to control the rate of penetration.
[0016] Selecting the output signal may comprise determining which of
the control
loops has the error measurement that represents a lowest percentage error
relative to the
drilling parameter setpoint, and selecting the output signal of the control
loop that has the
lowest percentage error to control the rate of penetration.
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[0017] The system may further comprise a drawworks communicatively
coupled
to the processor, and the output signal that is selected may be sent to the
drawworks to
adjust the rate of penetration of the drill bit.
[0018] The system may further comprise a hydraulics system
communicatively
coupled to the processor that controls the height of a traveling block, or a
drawworks
communicatively coupled to the processor that comprises brakes that are used
to control
the descent of the traveling block.
[0019] For each of the control loops whose output signal is not used
to control the
rate of penetration of the drill bit, the computer program code may cause the
processor to
adjust the integral component of the output signal such that the output signal
is
approximately equal to the output signal that is selected.
[0020] Determining the output signal may comprises adding a
derivative
component to the proportional component and the integral component, and the
derivative
component may vary with a rate of change versus time of the error measurement.
[0021] The system may further comprise a hookload sensor communicatively
coupled to the processor, wherein obtaining the drilling parameter measurement
for one
of the drilling parameters comprises reading a measurement from the weight-on-
bit
sensor; a standpipe sensor communicatively coupled to the processor, wherein
obtaining
the drilling parameter measurement for one of the drilling parameters
comprises reading a
measurement from the standpipe sensor; a torque sensor communicatively coupled
to the
processor, wherein obtaining the drilling parameter measurement for one of the
drilling
parameters comprises obtaining a torque measurement from the torque sensor;
and a
block height sensor communicatively coupled to the processor, wherein
obtaining the
drilling parameter measurement for one of the drilling parameters comprises
reading
block height measurements from the traveling block velocity sensor.
[0022] According to another aspect, there is provided a system for
controlling rate
of penetration of a drill bit. The system comprises drilling parameter
sensors; and an
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automatic driller communicatively coupled to each of the drilling parameter
sensors to
determine drilling parameter measurements from sensor readings. The automatic
driller is
configured to, for each of multiple drilling parameters corresponding to the
drilling
parameter measurements, evaluate a control loop by (1) reading a drilling
parameter
measurement; (2) determining an error measurement that represents a difference
between
a drilling parameter setpoint and the drilling parameter measurement; and (3)
determining, from the error measurement, an output signal proportional to the
rate of
penetration of the drill bit. The automatic driller is also configured to
select the output
signal of one of the control loops to control the rate of penetration; and use
the output
signal that is selected to control the rate of penetration.
[0023] 20. A non-transitory computer readable medium having
stored thereon
computer program code that is executable by a processor, and which when
executed by
the processor causes the processor to perform any of the foregoing aspects of
the method
and suitable combinations thereof.
[0024] This summary does not necessarily describe the entire scope of all
aspects.
Other aspects, features and advantages will be apparent to those of ordinary
skill in the
art upon review of the following description of specific embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] In the accompanying drawings, which illustrate one or more
example
embodiments:
[0026] FIG. 1 depicts an oil rig that is being used to drill a well
in conjunction
with an automatic driller, according to one example embodiment.
[0027] FIG. 2 depicts a block diagram of an embodiment of a system
for
controlling the rate of penetration of a drill bit and that comprises the
automatic driller of
FIG. 1.
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[0028] FIG. 3 depicts a block diagram of the automatic driller of
FIG. 1.
[0029] FIG. 4 depicts a block diagram of software modules running on
the
automatic driller of FIG. 1.
[0030] FIG. 5 depicts a method for controlling the rate of
penetration of a drill bit,
according to another example embodiment.
DETAILED DESCRIPTION
[0031] During well drilling, multiple sensors may be used to monitor
various
drilling parameters, such as weight-on-bit ("WOB"), torque applied to the
drill string,
rate of penetration, and differential pressure. Those sensors may be
communicative with
an automatic driller that uses those sensor measurements to control the rate
of penetration
of the drill string. The embodiments described herein are directed at methods,
systems,
and techniques to control the rate of penetration of the drill string by
evaluating multiple
control loops, with each of the control loops corresponding to a particular
drilling
parameter. For example, in an embodiment in which one of the monitored
drilling
parameters is WOB, the control loop corresponding to WOB compares a setpoint
for
WOB to a measured WOB, and from the error between the setpoint and the
measured
WOB uses a proportional-integral ("PI") or proportional-integral-derivative
("PID")
control technique to determine an output signal that may be used to control
the rate of
penetration of the drill string. One of the output signals of the control
loops is selected
and used to control the rate of penetration. For example, in one embodiment
the different
output signals determined by the control loops corresponding to different
drilling
parameters are compared to each other, and the lowest output signal is used to
control the
rate of penetration. Operating in this manner helps to ensure that none of the
drilling
parameters substantially exceeds their setpoints.
[0032] In certain embodiments, when control of the rate of penetration is
transferred from one of the control loops to another, the transfer is done so
as to be
perceived to be smooth, or continuous, by a driller. For example, when the
output signal
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of one of the control loops is selected to be the signal that controls rate of
penetration, the
output signals of the remaining control loops may be adjusted to be
substantially identical
to the selected output signal; when PI or PID control loops are used, this may
be done by
adjusting the value of the integral component of those control loops.
[0033] Referring now to FIG. 1, there is shown an oil rig that is being
used to drill
a well in conjunction with an automatic driller 206, which comprises part of
an example
system for controlling the rate of penetration of a drill bit. The rig
comprises a derrick
102 from which downwardly extends into a formation 106 a drill string 110 at
the end of
which is a drill bit 112. Mounted to the derrick 102 are a crown block 132 and
a traveling
block 130 that is movable by means of a pulley system relative to the crown
block 132. A
top drive 128 is attached to the bottom of the traveling block 130 via a hook
and connects
the traveling block 130 to the drill string 110. The top drive 128 provides
the torque and
consequent rotary force used to rotate the drill string 110 through the
formation 106. A
drawworks 214 is at the base of the rig and comprises a pulley system that
connects the
drawworks 214 to the crown block 132 and that enables the drawworks 214 to
vertically
translate the traveling block 128 relative to the crown block 132. By
actuating its pulley,
the drawworks 214 is accordingly able to apply vertical forces to the drill
string 110 and
adjust its rate of penetration. While the drill string 110 in the depicted
embodiment is
rotatably powered by the top drive 128, in different embodiments (not
depicted) the top
drive 128 may be replaced with a swivel, rotary table and kelly. Rotation of
the drill bit
112 through the formation 106 drills a well 108.
[0034] A reservoir 120 for drilling fluid (hereinafter
interchangeably referred to
as a "mud tank 120" or "mud pit 120") stores drilling fluid for pumping into
the well 108
via the drill string 110. A volume meter 122 is affixed to the mud tank 120
and is used to
measure the total volume of the drilling fluid stored in the mud tank 120 at
any particular
time (this volume is hereinafter interchangeably referred to as "pit volume").
A closed
fluid circuit comprises the mud tank 120, a fluid input line 118a for sending
the drilling
fluid down the interior of the drill string 110 via the top drive 128 and
subsequently into
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=
the annulus between the drill string 110 and the annular surface of the well
108, and a
fluid return line 118b for returning the drilling fluid from that annulus to
the mud tank
120; the direction of drilling fluid flow along this closed fluid circuit is
shown by arrows
in FIG. 1. A mud pump 116 is fluidly coupled to and located along the fluid
input line
118a and is used to pump the drilling fluid from the mud tank 120 into the
drill string
110. An input flow meter 114a and a return flow meter 114b are fluidly coupled
to and
located along the fluid input line 118a and fluid return line 118b,
respectively, and are
used to monitor flow rates into and out of the well 108. A driller's cabin and
doghouse
are not shown in FIG. 1, but in certain embodiments are also present at the
rigsite and are
discussed in respect of FIG. 2, below.
[0035] As used herein, the rate of penetration of the drill
string 110, the drum
speed of the drawworks 214, and the speed of the traveling block 130 are all
directly
proportional to each other and are effectively used interchangeably for
simplicity.
[0036] The rig also comprises various sensors (depicted in FIG.
2), such as a
hookload sensor 222, standpipe pressure sensor 220, torque sensor 218, and
block height
sensor 216, as discussed in more detail below. As discussed in further detail
below,
sensor readings are sent to the automatic driller 206 and are used to
facilitate control of
the rate of penetration of the drill bit 112 by the automatic driller 206.
[0037] Referring now to FIG. 2, there is shown a hardware block
diagram 200 of
the embodiment of the system 100 of FIG. 1. An automatic driller 206, which is
shown in
more detail in FIG. 3, is present in the doghouse and is configured to perform
a method
for controlling the rate of penetration of a drill bit, as described in more
detail below. An
example automatic driller that may be modified to perform the method is the
Automatic
DrillerTM offered by Pason Systems Corp.TM The automatic driller 206 is
communicatively coupled to a doghouse computer 204 and a rig display 202 in a
driller's
cabin; the doghouse computer 204 and rig display 202 each permit a driller to
interface
with the automatic driller 206 by, for example, setting drilling parameter
setpoints and
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obtaining drilling parameter measurements. The rig display 202 may be, for
example, the
Rig DisplayI'm offered by Pason Systems Corp.TM
[0038] The automatic driller 206 is located within a doghouse and
transmits and
receives analog signals and indirectly transmits and receives digital signals.
The
automatic driller 206 is directly communicatively coupled to a hookload sensor
222 and a
standpipe pressure sensor 220, which the automatic driller 206 uses to obtain
WOB and
differential pressure measurements, respectively. Each of the hookload and
pressure
sensors 222,220 sends an analog signal directly to the automatic driller 206.
The
automatic driller 206 is indirectly communicatively coupled to a torque sensor
218 and a
block height sensor 216 that digitally transmit measurements indicating the
amount of
torque applied to a drill string 110 by, for example, the top drive 128, and
the height of
the traveling blocks. These digital measurements are sent to a programmable
logic
controller ("PLC") 210 in the doghouse. The automatic driller 206 is also
coupled via the
PLC 210 to a variable frequency drive ("VFD") 212, which is used to control
the drum
speed of a drawworks 214. The drawworks 214 is used to adjust the height of
the
traveling blocks of the rig. An example VFD is a YaskawaTM A1000 VFD, and an
example PLC is a SiemensTM SIMATICTm S7 series PLC. The PLC 210 transmits
those
signals to the automatic driller 206 via a gateway 208.
[0039] In other embodiments (not depicted), the automatic driller 206
may
communicate with equipment via only a digital interface, only an analog
interface, or
communicate with a different combination of analog and digital interfaces than
that
shown in FIG. 2. For example, in one different embodiment (not depicted) the
automatic
driller 206 communicates using an analog interface with all of the sensors
216,218,220,222. In another different embodiment (not depicted), the automatic
driller
206 communicates using a digital interface (e.g., via the PLC 210) to all of
the sensors
216,218,220,222. In another different embodiment (not depicted), the automatic
driller
206 may directly control the drawworks 214 or VFD 212 without using the PLC
210 as
an intermediary.
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[0040] Referring now to FIG. 3, there is shown a hardware block
diagram 300 of
the automatic driller 206 of FIG. 2. The automatic driller 206 comprises a
microcontroller
302 communicatively coupled to a field programmable gate array ("FPGA") 320.
The
depicted microcontroller 302 is an ARM based microcontroller, although in
different
embodiments (not depicted) the microcontroller 302 may use a different
architecture. The
microcontroller 302 is communicatively coupled to 32 kB of non-volatile random
access
memory ("RAM") in the form of ferroelectric RAM 304; 16 MB of flash memory
306; a
serial port 308 used for debugging purposes; LEDs 310, LCDs 312, and a keypad
314 to
permit a driller to interface with the automatic driller 206; and
communication ports in
the form of an Ethernet port 316 and RS-422 ports 318. While FIG. 3 shows the
microcontroller 302 in combination with the FPGA 320, in different embodiments
(not
depicted) different hardware may be used. For example, the microcontroller 302
may be
used to perform the functionality of both the FPGA 320 and microcontroller 302
in FIG.
3; alternatively, a PLC may be used in place of one or both of the
microcontroller 302
and the FPGA 320.
[0041] The microcontroller 302 communicates with the hookload and
standpipe
pressure sensors 222,220 via the FPGA 320. More specifically, the FPGA 320
receives
signals from these sensors 222,220 as analog inputs 322; the FPGA 320 is also
able to
send analog signals using analog outputs 324. These inputs 322 and outputs 324
are
routed through intrinsic safety ("IS") barriers for safety purposes, and
through wiring
terminals 330. The microcontroller 302 communicates using the RS-422 ports 318
to the
gateway 208 and the PLC 210; accordingly, the microcontroller 302 receives
signals
from the block height and torque sensors 216,218 and sends signals to the VFD
212 via
the RS-422 ports 318.
[0042] The FPGA 320 is also communicatively coupled to a non-incendive
depth
input 332 and a non-incendive encoder input 334. In different embodiments (not
depicted), the automatic driller 206 may receive different sensor readings in
addition to or
as an alternative to the readings obtained using the depicted sensors
216,218,220,222.
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[0043] Referring now to FIG. 4, there is shown a block diagram of
software
modules, some of which comprise a software application 402, running on the
automatic
driller of FIG. 3. The application 402 comprises a data module 414 that is
communicative
with a PID module 416, a block velocity module 418, and a calibrations module
420. As
discussed in further detail below, the microcontroller 302 runs multiple PID
control loops
in order to determine the signal to send to the PLC 210 to control the VFD
212; the
microcontroller 302 does this in the PID module 416. The microcontroller 302
uses the
block velocity module 418 to determine the velocity of the traveling block 130
from the
traveling block height derived using measurements from the block height sensor
216. The
microcontroller 302 uses the calibrations module 420 to convert the electrical
signals
received from the sensors 216,218,220,222 into engineering units; for example,
to
convert a current signal from mA into kilopounds.
[0044] The data module 414 also communicates using an input/output
multiplexer, labeled "JO Mux" in FIG. 4. In one of the multiplexer states the
data module
414 communicates digitally via the Modbus protocol using the system modbus 412
module, which is communicative with a Modbus receive/transmit engine 408 and
the
UARTS 406. In another of the multiplexer states, the data module 414
communicates
analog data directly using the data acquisition in/out module 404. While in
FIG. 4 the
Modbus protocol is shown as being used, in different embodiments (not
depicted) a
different protocol may be used, such as another suitable industrial bus
communication
protocol.
[0045] Referring now to FIG. 5, there is shown a method 500 for
controlling the
rate of penetration of a drill bit, according to another example embodiment.
The method
500 may be encoded as computer program code and stored on to the flash memory
306.
The computer program code is executable by the microcontroller 302 and, when
executed
by the microcontroller 302, causes the microcontroller 302 and consequently
the
automatic driller 206 to perform the method 500 of FIG. 5.
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[0046] In FIG. 5, the microcontroller 302 receives a reading from the
hookload
sensor 222 from which it determines a WOB measurement; a reading from the
standpipe
pressure sensor 220 from which it determines a differential pressure (i.e., a
pressure
difference between the standpipe pressure and the standpipe pressure as
measured when
the drill bit 112 is off bottom) measurement; a reading from the torque sensor
218 from
which it determines a torque measurement of torque applied to the drill string
110 by the
top drive 128 or in one different embodiment a rotary table; and a reading
from the block
height sensor 216 from which it determines traveling block velocity. The
microcontroller
302 determines a traveling block velocity measurement by time indexing the
traveling
block height measurements and dividing changes in the block height
measurements over
time in the block velocity module 418. As discussed in further detail below,
by
performing the method 500 the microcontroller 302 is able to keep all of WOB,
torque,
traveling block velocity, and rate of penetration substantially at or below a
desired
setpoint. In the depicted embodiment, the microcontroller 302 operates four
PID control
loops (each a "control loop") using the PID module 416. Each of the control
loops
receives as input one of the drilling parameter measurements (e.g., the WOB
measurement, the differential pressure measurement, the torque measurement,
and the
traveling block velocity measurement) and outputs a signal that may be used to
adjust the
rate of penetration of the drill string 110. In the depicted embodiment, the
output signal
for any one of the control loops comprises the sum of a proportional
component, an
integral component, and a derivative component. The proportional component
comprises
the product of a proportional gain and an error measurement that represents a
difference
between a drilling parameter setpoint and the drilling parameter measurement;
the
integral component comprises the product of an integral gain and the sum of
previous
error measurements; and the derivative component comprises the product of a
derivative
gain and the rate of change of the error measurement. While in the depicted
embodiment
the control loops use all of the proportional, integral, and derivative
components, in
different embodiments (not depicted), any one or more of the control loops may
comprise
only the proportional and integral components, or be of a non-PI or PID type.
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[0047] In
the method 500 of FIG. 5, the microcontroller 302 evaluates each of the
control loops once and in sequence for each of the drilling parameters before
deciding
whether to adjust the output signal sent to the VFD 212. Accordingly, the
microcontroller
302 at block 504 determines if, for a particular iteration of the method 500,
the control
loops corresponding to each of WOB, differential pressure, traveling block
velocity, and
torque have been evaluated. If not, the microcontroller 302 proceeds to block
506 where
it begins to evaluate one of the control loops.
[0048] At
block 506, the microcontroller 302 obtains a drilling parameter
measurement of the drilling parameter associated with the control loop being
evaluated.
For example, if the microcontroller 302 is evaluating the control loop for
WOB, the
microcontroller 302 reads the hookload sensor 222 and from it determines the
WOB
measurement. After reading the drilling parameter measurement at block 506,
the
microcontroller 302 proceeds to block 508 where it determines an error
measurement that
represents a difference between a drilling parameter setpoint and the drilling
parameter
measurement. After determining the error measurement, the microcontroller 302
evaluates the control loop to determine the control loop's output signal. The
microcontroller 302 does this by evaluating Equation (1):
rt de (t)
Output Signal = Kpe(t) + Ki e(r)d-r. + Kd ________________________________
(1)
0 dt
[0049]
Equation (1) is an equation for evaluating a PID control loop in a
continuous time domain; alternatively, the microcontroller 302 may evaluate
any one or
more of the control loops, or any one or more terms of any one or more of the
control
loops, in the discrete time domain.
[0050]
Once the microcontroller 302 determines the output signal for the control
loop at block 510, it returns to block 504. If any control loops remain
unevaluated for the
current iteration of the method 500, the microcontroller 302 performs blocks
506, 508,
and 510 again to evaluate one of the unevaluated control loops. If the
microcontroller 302
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has evaluated all of the control loops for the current iteration of the method
500, the
microcontroller 302 proceeds to block 512.
[0051] In FIG. 5, for any particular iteration of the method 500 the
microcontroller 302 evaluates each of the control loops once and in sequence.
In different
embodiments (not depicted), however, the microcontroller 302 may evaluate the
control
loops differently. For example, the microcontroller 302 may evaluate any one
or more of
the control loops in parallel before proceeding to block 512. Additionally or
alternatively,
the microcontroller 302 may evaluate any one or more of the control loops in a
separate
thread and rely on interrupts to determine when to perform blocks 512 to 516.
[0052] When the microcontroller 302 arrives at block 512, it selects which
of the
control loops to use to control the rate of penetration of the drill bit 112.
In the depicted
embodiment, the microcontroller 302 does this by sending the output signal of
lowest
magnitude to the PLC 210 via the gateway 208, and the PLC 210 relays the
output signal
to the VFD 212. The VFD 212 in turn adjusts the drawworks 214, which raises
and
lowers the traveling block and consequently the drill string 110. In different
embodiments
(not depicted), however, the microcontroller 302 may be used to control rigs
that adjust
the drill string 110 using equipment other than the drawworks 214 and VFD 212.
For
example, the drawworks 214 and VFD 212 may be replaced with alternative
equipment
such as a hydraulics system to raise and lower the traveling block 130 and a
drawworks
with brakes, such as band or disc brakes, with the brakes being used to
control the
downward movement of the traveling block 130. In the depicted embodiment the
output
signal may vary, for example, between 0 mA and 20 mA, with 0 mA corresponding
to a
rate of penetration of 0 m/hr and 20 mA corresponding to a rate of penetration
of 400 to
500 m/hr.
[0053] As described above, the microcontroller 302 selects the output
signal of
lowest magnitude to control the rate of penetration. However, in different
embodiments
the microcontroller 302 may select the output signal by applying a different
rule or set of
rules. For example, in one different embodiment the microcontroller 302
determines
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which of the control loops has the error measurement that is the lowest
percentage error
relative to the drilling parameter setpoint for that control loop, and then
uses the output
signal for that control loop to control the rate of penetration. In another
different
embodiment, a combination of multiple selection methods may be used to select
the
output signal that is used.
[0054] The microcontroller 302 subsequently proceeds to block 516
where it
adjusts the integral component of the output signals of the control loops that
are not used
to adjust the drill string's 110 ROP so that those output signals are
approximately, and in
certain embodiments exactly, equal to the output signal of lowest magnitude
used to
adjust the ROP. For example, if the output of the WOB control loop is the
lowest of the
outputs of the control loops and is sent to the PLC 210 and subsequently to
the VFD 212
at block 514, at block 516 the microcontroller 302 adjusts the integral
component of each
of the differential pressure, torque, and traveling block velocity control
loops such that
their outputs equals the output of the WOB control loop. In certain
embodiments, the
integral component may be negative to account for a relatively high
proportional
component, derivative component, or both. Adjusting the integral component in
this
fashion facilitates a relatively continuous transfer of control from one
control loop to
another.
[0055] While the microcontroller 302 is used in the foregoing
embodiments, in
different embodiments (not depicted) the microcontroller 302 may instead be,
for
example, a microprocessor, processor, controller, programmable logic
controller, field
programmable gate array, or an application-specific integrated circuit.
Examples of
computer readable media are non-transitory and include disc-based media such
as CD-
ROMs and DVDs, magnetic media such as hard drives and other forms of magnetic
disk
storage, and semiconductor based media such as flash media, SSDs, random
access
memory, and read only memory. Additionally, for the sake of convenience, the
example
embodiments above are described as various interconnected functional blocks.
This is not
necessary, however, and there may be cases where these functional blocks are
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CA 02930320 2016-05-13
equivalently aggregated into a single logic device, program or operation with
unclear
boundaries. In any event, the functional blocks can be implemented by
themselves, or in
combination with other pieces of hardware or software.
[0056] FIG. 5 is a flowchart of an example embodiment of a method.
Some of the
blocks illustrated in the flowchart may be performed in an order other than
that which is
described. Also, it should be appreciated that not all of the blocks described
in the
flowchart are required to be performed, that additional blocks may be added,
and that
some of the illustrated blocks may be substituted with other blocks.
[0057] As used herein, the terms "approximately" and "about" when
used in
conjunction with a value mean +1- 20 % of that value.
[0058] Directional terms such as "top", "bottom", "upwards",
"downwards",
"vertically", and "laterally" are used in this disclosure for the purpose of
providing
relative reference only, and are not intended to suggest any limitations on
how any article
is to be positioned during use, or to be mounted in an assembly or relative to
an
environment. Additionally, the term "couple" and variants of it such as
"coupled",
"couples", and "coupling" as used in this disclosure are intended to include
indirect and
direct connections unless otherwise indicated. For example, if a first article
is coupled to
a second article, that coupling may be through a direct connection or through
an indirect
connection via another article. As another example, when two articles are
"communicatively coupled" to each other, they may communicate with each other
directly or indirectly via another article. Furthermore, the singular forms
"a", "an", and
"the" as used in this disclosure are intended to include the plural forms as
well, unless the
context clearly indicates otherwise.
[0059] It is contemplated that any part of any aspect or embodiment
discussed in
this specification can be implemented or combined with any part of any other
aspect or
embodiment discussed in this specification.
=
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CA 02930320 2016-05-13
[0060]
While particular embodiments have been described in the foregoing, it is
to be understood that other embodiments are possible and are intended to be
included
herein. It will be clear to any person skilled in the art that modifications
of and
adjustments to the foregoing embodiments, not shown, are possible.
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