U.S. patent application number 15/191072 was filed with the patent office on 2017-01-05 for detection and mitigation of detrimental operating conditions during pumpjack pumping.
This patent application is currently assigned to KLD Energy Nano-Grid System, Inc.. The applicant listed for this patent is KLD Energy Nano-Grind Systems, Inc.. Invention is credited to Victor Sauers, II, Bertrand Jeffery Williams.
Application Number | 20170002636 15/191072 |
Document ID | / |
Family ID | 57683383 |
Filed Date | 2017-01-05 |
United States Patent
Application |
20170002636 |
Kind Code |
A1 |
Williams; Bertrand Jeffery ;
et al. |
January 5, 2017 |
DETECTION AND MITIGATION OF DETRIMENTAL OPERATING CONDITIONS DURING
PUMPJACK PUMPING
Abstract
A motor-driven pumpjack is operated continuously while receiving
sensory feedback from one or more sensors. In response to feedback
indicating a detrimental operating condition, and while continuing
to operate the pumpjack, one or more speed adjustments are made to
specific control periods within the motor pumping cycle. The
automated control optimizes flow while reacting to detrimental and
changing conditions.
Inventors: |
Williams; Bertrand Jeffery;
(Austin, TX) ; Sauers, II; Victor; (Cedar Park,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KLD Energy Nano-Grind Systems, Inc. |
Austin |
TX |
US |
|
|
Assignee: |
KLD Energy Nano-Grid System,
Inc.
|
Family ID: |
57683383 |
Appl. No.: |
15/191072 |
Filed: |
June 23, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62187028 |
Jun 30, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04B 47/022 20130101;
F04B 49/20 20130101; F04B 47/00 20130101; E21B 47/009 20200501;
E21B 43/127 20130101 |
International
Class: |
E21B 43/12 20060101
E21B043/12 |
Claims
1. A method of operating a pumpjack continuously over a sequence of
pump stroke cycles, the method comprising: energizing an electric
motor to operate the pumpjack over a first pump stroke cycle,
according to a first motor speed profile comprising a plurality of
target motor speeds corresponding to each of a plurality of
discrete control periods within the first pump stroke cycle;
receiving sensory feedback during the first pump stroke cycle from
one or more sensors mounted to monitor at least one operating
condition of the pumpjack, the sensory feedback comprising data
collected during operation of the motor according to the first
motor speed profile; detecting, while continuing to operate the
pumpjack, a detrimental operating condition within the first pump
stroke cycle based on the sensory feedback; in response to
detecting the detrimental operating condition, determining one or
more speed adjustment values corresponding to a limited subset of
the plurality of discrete control periods; altering the first motor
speed profile based on the one or more adjustment values to provide
a second motor speed profile; and operating the electric motor over
a second pump stroke cycle, according to the second motor speed
profile.
2. The method of claim 1, wherein the first motor speed profile
comprises a predetermined default setting.
3. The method of claim 1, wherein the first motor speed profile
comprises an altered version of a motor speed profile utilized in a
previous pump stroke cycle of the sequence.
4. The method of claim 1, wherein the plurality of discrete control
periods of the first pump stroke cycle comprise at least 100
control periods.
5. The method of claim 1, wherein one or more of the plurality of
discrete control periods of the first pump stroke cycle comprise a
time duration of between about 5 and 100 milliseconds.
6. The method of claim 1, wherein each of the plurality of discrete
control periods of the first pump stroke comprise an identical time
duration.
7. The method of claim 1, wherein at least one of the sensors
comprises a load sensor.
8. The method of claim 7, wherein the load sensor is responsive to
load of a polish rod of the pumpjack.
9. The method of claim 1, wherein at least one of the sensors
comprises a crank rotation sensor.
10. The method of claim 1, wherein at least one of the sensors
comprises a motor shaft position sensor.
11. The method of claim 1, wherein at least one of the sensors
comprises a motor current sensor.
12. The method of claim 1, wherein detecting the detrimental
operating condition comprises constructing a data structure
relating position to load with respect to a polish rod of the
pumpjack over the first pump stroke cycle based on the sensory
feedback.
13. The method of claim 12, wherein detecting the detrimental
operating condition comprises comparing the data structure to one
or more predetermined load limits.
14. The method of claim 13, wherein at least one of the
predetermined load limits corresponds to structural integrity of
the polish rod.
15. The method of claim 12, wherein at least one of the
predetermined load limits corresponds to structural integrity of a
gear box coupled to the motor and the polish rod.
16. The method of claim 12, wherein detecting the detrimental
operating condition further comprises identifying an abrupt load
spike based on the data structure.
17. The method of claim 12, wherein the data structure comprises a
dynamometer surface card.
18. The method of claim 12, wherein the data structure comprises a
downhole pump card.
19. The method of claim 1, wherein determining the one or more
speed adjustment values comprises selecting a speed adjustment
value to increase the target motor speed at a control period within
the second pump stroke cycle preceding or subsequent to a different
control period where the detrimental operating condition is likely
to reoccur.
20. The method of claim 1, wherein determining the one or more
speed adjustment values comprises selecting a speed adjustment
value to decrease the target motor speed at a control period within
the second pump stroke cycle where the detrimental operating
condition is likely to reoccur.
21. The method of claim 1, wherein determining the one or more
speed adjustment values comprises selecting a speed adjustment
value to decrease the target motor speed at a control period within
the second pump stroke cycle preceding a different control period
where the detrimental operating condition is likely to reoccur.
22. The method of claim 1, wherein the electric motor comprises a
regenerative drive, and wherein the method further comprises
providing a breaking torque to control descent of a rod system of
the pumpjack during a downstroke of each of the pump stroke cycles,
while simultaneously converting kinetic energy of the rod system
into electrical power.
23. A method of operating a pumpjack, the method comprising:
operating an electric motor of a pumpjack to pump fluid, according
to a predetermined motor speed profile comprising a plurality of
target motor speeds corresponding to each of a plurality of
discrete control periods within a stroke cycle of the pumpjack,
while receiving sensory feedback comprising data collected from one
or more sensors mounted to monitor at least one operating condition
of the pumpjack, wherein the predetermined motor speed profile
corresponds to an optimized stroke timing curve determined during
one or more previous stroke cycles of the pumpjack; while
continuing to operate the electric motor to pump fluid, increasing
one or more of the plurality of target motor speeds over a
plurality of stroke cycles until a detrimental operating condition
is detected based on sensory feedback; and in response to detecting
the detrimental operating condition, and as the pumpjack continues
to pump fluid, decreasing a subset of the plurality of target motor
speeds selected based on a position of the detected detrimental
operating condition within the stroke cycle.
24. The method of claim 23, wherein the plurality of discrete
control periods comprises at least 100 control periods.
25. The method of claim 23, wherein one or more of the plurality of
discrete control periods comprise a time duration of between about
5 and 100 milliseconds.
26. The method of claim 23, wherein each of the plurality of
discrete control periods comprise an identical time duration.
27. The method of claim 23, wherein at least one of the sensors
comprises a load sensor.
28. The method of claim 27, wherein the load sensor is responsive
to load of a polish rod of the pumpjack.
29. The method of claim 23, wherein at least one of the sensors
comprises a crank rotation sensor.
30. The method of claim 23, wherein at least one of the sensors
comprises a motor shaft position sensor.
31. The method of claim 23, wherein at least one of the sensors
comprises a motor current sensor.
32. The method of claim 23, wherein incrementally increasing
selected ones of the plurality of target motor speeds comprises
incrementally increasing each of the plurality of target motor
speeds according to a predetermined adjustment schedule.
33. The method of claim 23, wherein the detrimental operating
condition is detected by: constructing a data structure relating
position to load with respect to a polish rod of the pumpjack over
the stroke cycle based on the sensory feedback; and comparing the
data structure to one or more predetermined load limits.
34. The method of claim 33, wherein at least one of the
predetermined load limits corresponds to structural integrity of
the polish rod.
35. The method of claim 33, wherein at least one of the
predetermined load limits corresponds to structural integrity of a
gear box coupled to the motor and the polish rod.
36. The method of claim 23, wherein the detrimental operating
condition is detected by: constructing a data structure relating
position to load with respect to a polish rod of the pumpjack over
the stroke cycle based on the sensory feedback; and identifying an
abrupt load spike based on the data structure.
37. The method of claim 23, wherein decreasing a subset of the
plurality of target motor speeds comprises decreasing the target
motor speed at one or more control periods preceding a different
control period where the detrimental operating condition is likely
to reoccur.
38. The method of claim 23, wherein decreasing a subset of the
plurality of target motor speeds comprises decreasing the target
motor speed at the control period where the detrimental operating
condition is likely to reoccur.
39. The method of claim 23, wherein the electric motor comprises a
regenerative drive, and wherein the method further comprises
providing a breaking torque to control descent of a rod system of
the pumpjack during a downstroke of each of the pump stroke cycles
while simultaneously converting kinetic energy of the rod system
into electrical power.
40. A pumpjack motor system, comprising: an electric motor coupled
to a gear box of a pumpjack; one or more sensors mounted to monitor
at least one operating condition of the pumpjack; and a local
controller coupled to the electric motor and the one or more
sensors and operable, while the pumpjack continuously pumps fluid,
to: control the motor according to a first motor speed profile
comprising a plurality of target motor speeds corresponding to each
of a plurality of discrete control periods within a single stroke
cycle of the pumpjack; receive sensory feedback from the one or
more sensors, the sensory feedback comprising data, including load
data, collected during operation of the motor according to the
first motor speed profile; automatically increment a first set of
the target motor speeds corresponding to portions of the stroke
cycle outside of a predetermined load limit, based on the load
data; and automatically decrement a second set of the target motor
speeds corresponding to portions of the stroke cycle within the
predetermined load limit, thereby generating a second motor speed
profile; and to control the motor according to the second motor
speed profile.
41. The pumpjack motor system of claim 38, wherein at least one of
the sensors comprises a load sensor.
42. The pumpjack motor system of claim 41, wherein the load sensor
is responsive to load of a polish rod of the pumpjack.
43. The pumpjack motor system of claim 40, wherein at least one of
the sensors comprises a crank rotation sensor.
44. The pumpjack motor system of claim 41, wherein at least one of
the sensors comprises a motor shaft position sensor.
45. The pumpjack motor system of claim 40, wherein at least one of
the sensors comprises a motor current sensor.
46. The pumpjack motor system of claim 40, wherein the controller
is further configured to identify portions of the stroke cycle
outside of the predetermined load limit by: constructing a data
structure relating position to load with respect to a polish rod of
the pumpjack over the stroke cycle based on the sensory feedback;
and comparing the data structure to the predetermined load
limit.
47. The pumpjack motor system of claim 40, wherein the
predetermined load limit corresponds to structural integrity of the
polish rod.
48. The pumpjack motor system of claim 40, wherein the
predetermined load limit corresponds to structural integrity of a
gear box coupled to the motor and the polish rod.
49. The pumpjack motor system of claim 40, wherein the electric
motor comprises a regenerative drive configured to provide a
breaking torque to control the descent of a rod system of the
pumpjack during a downstroke of each stroke cycle, while
simultaneously converting kinetic energy of the rod system into
electrical power.
50. A pumpjack motor system, comprising: an electric motor coupled
to a gear box of a pumpjack; one or more sensors mounted to monitor
at least one operating condition of the pumpjack; and a local
controller coupled to the electric motor and the one or more
sensors and operable, while the pumpjack continuously pumps fluid
over two sequential pumping cycles, to: control the electric motor
through a first of the two sequential pumping cycles, according to
a first motor speed profile comprising a plurality of target motor
speeds corresponding to respective portions of the pumpjack stroke
cycle, while receiving sensory feedback from the one or more
sensors; detect a detrimental operating condition within the first
pump stroke cycle based on the sensory feedback; in response to the
detection, automatically adjust one or more of the target motor
speeds as a function of the sensory feedback, to generate an
adjusted motor speed profile; and to control the motor according to
the adjusted motor speed profile during a second of the two
sequential pumping cycles of the pumpjack.
51. The pumpjack motor system of claim 50, wherein the first motor
speed profile comprises a predetermined default setting.
52. The pumpjack motor system of claim 50, wherein the first motor
speed profile comprises an altered version of a motor speed profile
utilized in a previous pump stroke cycle of the sequence.
53. The pumpjack motor system of claim 50, wherein at least one of
the sensors comprises a load sensor.
54. The pumpjack motor system of claim 53, wherein the load sensor
is responsive to load of a polish rod of the pumpjack.
55. The pumpjack motor system of claim 50, wherein at least one of
the sensors comprises a crank rotation sensor.
56. The pumpjack motor system of claim 50, wherein at least one of
the sensors comprises a motor shaft position sensor.
57. The pumpjack motor system of claim 50, wherein at least one of
the sensors comprises a motor current sensor.
58. The pumpjack motor system of claim 50, wherein the local
controller is operable to detect the detrimental operating
condition by first constructing a data structure relating position
to load with respect to a polish rod of the pumpjack over the first
pump stroke cycle based on the sensory feedback.
59. The pumpjack motor system of claim 58, wherein the local
controller is operable to detect the detrimental operating
condition by also comparing the data structure to one or more
predetermined load limits.
60. The pumpjack motor system of claim 59, wherein at least one of
the predetermined load limits corresponds to structural integrity
of the polish rod.
61. The pumpjack motor system of claim 59, wherein at least one of
the predetermined load limits corresponds to structural integrity
of a gear box coupled to the motor and the polish rod.
62. The pumpjack motor system of claim 58, wherein the local
controller is operable to detect the detrimental operating
condition by identifying an abrupt load spike based on the data
structure.
63. The pumpjack motor system of claim 58, wherein the data
structure comprises a dynamometer surface card.
64. The pumpjack motor system of claim 58, wherein the data
structure comprises a downhole pump card.
65. The pumpjack motor system of claim 50, wherein the local
controller is operable to detect the detrimental operating
condition by selecting a speed adjustment value to increase the
target motor speed at a control period within the second pump
stroke cycle preceding or subsequent to a different control period
where the detrimental operating condition is likely to reoccur.
66. The pumpjack motor system of claim 50, wherein the controller
automatically adjusts one or more of the target motor speeds by
selecting a speed adjustment value to decrease the target motor
speed at a control period within the second pump stroke cycle where
the detrimental operating condition is likely to reoccur.
67. The pumpjack motor system of claim 50, wherein the controller
determines the one or more speed adjustment values by selecting a
speed adjustment value to decrease the target motor speed at a
control period within the second pump stroke cycle preceding a
different control period where the detrimental operating condition
is likely to reoccur.
68. The pumpjack motor system of claim 50, wherein the electric
motor comprises a regenerative drive configured to provide a
breaking torque to control the descent of a rod system of the
pumpjack during a downstroke of each of the stroke cycles, while
simultaneously converting kinetic energy of the rod system into
electrical power.
69. A method of pumping fluid, the method comprising: operating an
electric motor of a pumpjack to pump fluid, according to a
predetermined motor speed profile comprising a plurality of target
motor speeds corresponding to each of a plurality of discrete pump
stroke cycle segments, while receiving load data from one or more
sensors mounted to monitor at least one operating condition of the
pumpjack; storing and updating a pump stroke cycle load profile
based on the received load data over a period of several pump
stroke cycles; and in response to detecting load data deviating
from the load profile by more than a predetermined deviation
threshold, automatically decrementing a subset of the plurality of
target motor speeds selected based on a position of the deviating
load data within the stroke cycle.
70. The method of claim 69, wherein the detected load data
deviation is indicative of a rod load spike.
71. The method of claim 69, wherein the detected load data
deviation is indicative of a pump-off condition.
72. The method of claim 69, wherein the detected load data
deviation is indicative of a gearbox torque transfer anomaly.
73. The method of claim 69, wherein at least one of the sensors
comprises a load sensor.
74. The method of claim 73, wherein the load sensor is responsive
to load of a polish rod of the pumpjack.
75. The method of claim 69, wherein at least one of the sensors
comprises a crank rotation sensor.
76. The method of claim 69, wherein at least one of the sensors
comprises a motor shaft position sensor.
77. The method of claim 69, wherein at least one of the sensors
comprises a motor current sensor.
78. The method of claim 69, wherein the pump stroke cycle load
profile comprises a data structure relating position to load with
respect to a polish rod of the pumpjack over one or more of the
pump stroke cycles based on the sensory feedback.
79. The method of claim 78, further comprising detecting the load
data deviation by comparing the data structure to one or more
predetermined load limits.
80. The method of claim 79, wherein at least one of the
predetermined load limits corresponds to structural integrity of
the polish rod.
81. The method of claim 79, wherein at least one of the
predetermined load limits corresponds to structural integrity of a
gear box coupled to the motor and the polish rod.
82. The method of claim 69, wherein the electric motor comprises a
regenerative drive, and wherein the method further comprises
providing a breaking torque to control the descent of a rod system
of the pumpjack during a downstroke of the pump stroke cycle, while
simultaneously converting kinetic energy of the rod system into
electrical power.
Description
TECHNICAL FIELD
[0001] This invention relates to detection and mitigation of
detrimental operating conditions during pumpjack operation.
BACKGROUND
[0002] Reciprocating oil pumps are traditionally provided in the
form of a beam-balanced pumpjack. Conventional pumpjacks provide a
sinusoidal characteristic of reciprocating pumping motion dictated
by geometry and power transmission from a fixed speed prime mover.
Other types of pumping units, such as long stroke or hydraulically
actuated pumping units, operate at a first constant speed during
upstroke motion and at a second constant speed during downstroke
motion. Some pumpjack systems are equipped with a complex sensor
suite including downhole fluid-level or pressure indicators, flow
and no-flow sensors, vibration sensors, motor current sensors,
and/or dynamometer card sensors (e.g., load cells) for detecting an
undesirable pump-off condition. A typical remedy for pump-off is to
decrease the pumping rate of the pumpjack (e.g., by adjustment of
the gear ratios to extend the stroke length) until the pump-off
condition disappears.
SUMMARY
[0003] This specification describes technologies related to systems
and methods for pumpjack fluid pumping.
[0004] One aspect of the invention features a method of operating a
pumpjack continuously over a sequence of two adjacent pump stroke
cycles. The method includes energizing an electric motor to operate
the pumpjack over a first pump stroke cycle (according to a first
motor speed profile including a plurality of target motor speeds
corresponding to each of a plurality of discrete control periods
within the first pump stroke cycle), receiving sensory feedback
during the first pump stroke cycle from one or more sensors mounted
to monitor at least one operating condition of the pumpjack (the
sensory feedback including data collected during operation of the
motor according to the first motor speed profile), and detecting,
while continuing to operate the pumpjack, a detrimental operating
condition within the first pump stroke cycle based on the sensory
feedback. In response to the detection, the method includes
determining one or more speed adjustment values corresponding to a
limited subset of the plurality of discrete control periods,
altering the first motor speed profile based on the one or more
adjustment values to provide a second motor speed profile, and
operating the electric motor over a second pump stroke cycle,
according to the second motor speed profile.
[0005] In some examples, the first motor speed profile is a
predetermined default setting. In some examples, the first motor
speed profile is an altered version of a motor speed profile
utilized in a previous pump stroke cycle of the sequence. The
plurality of discrete control periods of the first pump stroke
cycle preferably includes at least 100 control periods. In some
cases, one or more (or all) of the plurality of discrete control
periods of the first pump stroke cycle have a time duration of
between about 5 and 100 milliseconds. In some examples, each of the
discrete control periods have an identical time duration.
[0006] In some embodiments, at least one of the sensors is a load
sensor, such as a load cell sensor responsive to load of a rod
(e.g., a polish rod) of the pumpjack. In some examples, at least
one of the sensors is a crank rotation sensor, or a motor shaft
position sensor, or a motor current sensor.
[0007] In some examples, detecting the detrimental operating
condition includes constructing a data structure relating position
to load with respect to a polish rod of the pumpjack over the first
pump stroke cycle based on the sensory feedback. The the
detrimental operating condition may be detected by comparing the
data structure to one or more predetermined load limits, such as a
load limit corresponds to the structural integrity of the polish
rod, or to the structural integrity of a gear box coupled to the
motor and the polish rod, for example. In some examples, the
detrimental operating condition is identified by identifying an
abrupt load spike based on the data structure. The data structure
may include a dynamometer surface card and/or a downhole pump card,
for example.
[0008] In some examples, determining the one or more speed
adjustment values includes selecting a speed adjustment value to
increase the target motor speed at a control period within the
second pump stroke cycle preceding or subsequent to a different
control period where the detrimental operating condition is likely
to reoccur, or selecting a speed adjustment value to decrease the
target motor speed at a control period within the second pump
stroke cycle where the detrimental operating condition is likely to
reoccur, or selecting a speed adjustment value to decrease the
target motor speed at a control period within the second pump
stroke cycle preceding a different control period where the
detrimental operating condition is likely to reoccur.
[0009] The electric motor may include a regenerative drive, such
that the method further includes providing a breaking torque to
control the descent of a rod system of the pumpjack during a
downstroke of each of the pump stroke cycles, while simultaneously
converting kinetic energy of the rod system into electrical
power.
[0010] Another aspect of the invention features a method of
operating a pumpjack including operating an electric motor of a
pumpjack to pump fluid, according to a predetermined motor speed
profile including a plurality of target motor speeds corresponding
to each of a plurality of discrete control periods within a stroke
cycle of the pumpjack, while receiving sensory feedback including
data collected from one or more sensors mounted to monitor at least
one operating condition of the pumpjack. The predetermined motor
speed profile corresponds to an optimized stroke timing curve
determined during one or more previous stroke cycles of the
pumpjack. While continuing to operate the electric motor to pump
fluid, the method includes increasing one or more of the plurality
of target motor speeds over a plurality of stroke cycles until a
detrimental operating condition is detected based on sensory
feedback, and in response to detecting the detrimental operating
condition, and as the pumpjack continues to pump fluid, decreasing
a subset of the plurality of target motor speeds selected based on
a position of the detected detrimental operating condition within
the stroke cycle.
[0011] Various examples of the method according to this aspect of
the invention include one or more features discussed above with
respect to the first aspect.
[0012] In some embodiments, incrementally increasing selected ones
of the plurality of target motor speeds includes incrementally
increasing each of the plurality of target motor speeds according
to a predetermined adjustment schedule.
[0013] In some examples, the detrimental operating condition is
detected by constructing a data structure relating position to load
with respect to a polish rod of the pumpjack over the stroke cycle
based on the sensory feedback, and comparing the data structure to
one or more predetermined load limits, such as a load limit
corresponding to the structural integrity of the polish rod or of a
gear box coupled to the motor and the polish rod.
[0014] In some examples, the detrimental operating condition is
detected by constructing a data structure relating position to load
with respect to a polish rod of the pumpjack over the stroke cycle
based on the sensory feedback, and identifying an abrupt load spike
based on the data structure.
[0015] In some examples, decreasing the subset of the plurality of
target motor speeds includes decreasing the target motor speed at
one or more control periods preceding a different control period
where the detrimental operating condition is likely to reoccur, or
decreasing the target motor speed at the control period where the
detrimental operating condition is likely to reoccur.
[0016] Yet another aspect of the invention features a pumpjack
motor system including an electric motor coupled to a gear box of a
pumpjack, one or more sensors mounted to monitor at least one
operating condition of the pumpjack, and a local controller coupled
to the electric motor and the one or more sensors. The local
controller is operable, while the pumpjack continuously pumps
fluid, to control the motor according to a first motor speed
profile including a plurality of target motor speeds corresponding
to each of a plurality of discrete control periods within a single
stroke cycle of the pumpjack, receive sensory feedback from the one
or more sensors (the sensory feedback including data, including
load data, collected during operation of the motor according to the
first motor speed profile), automatically increment a first set of
the target motor speeds corresponding to portions of the stroke
cycle outside of a predetermined load limit, based on the load
data, and to automatically decrement a second set of the target
motor speeds corresponding to portions of the stroke cycle within
the predetermined load limit, thereby generating a second motor
speed profile, and to then control the motor according to the
second motor speed profile.
[0017] In some examples, the controller is configured to identify
portions of the stroke cycle outside of the predetermined load
limit by constructing a data structure relating position to load
with respect to a polish rod of the pumpjack over the stroke cycle
based on the sensory feedback, and comparing the data structure to
the predetermined load limit. In some examples, the predetermined
load limit corresponds to the structural integrity of the polish
rod, or of a gear box coupled to the motor and the polish rod.
[0018] In some examples, the electric motor includes a regenerative
drive configured to provide a breaking torque to control the
descent of a rod system of the pumpjack during a downstroke of each
stroke cycle, while simultaneously converting kinetic energy of the
rod system into electrical power.
[0019] Yet another aspect of the invention features a pumpjack
motor system, including an electric motor coupled to a gear box of
a pumpjack, one or more sensors mounted to monitor at least one
operating condition of the pumpjack, and a local controller coupled
to the electric motor and the one or more sensors. The local
controller is operable, while the pumpjack continuously pumps fluid
over two sequential pumping cycles, to control the electric motor
through a first of the two sequential pumping cycles, according to
a first motor speed profile including a plurality of target motor
speeds corresponding to respective portions of the pumpjack stroke
cycle, and while receiving sensory feedback from the one or more
sensors. The local controller is also operable to detect a
detrimental operating condition within the first pump stroke cycle
based on the sensory feedback, and in response to the detection,
automatically adjust one or more of the target motor speeds as a
function of the sensory feedback, to generate an adjusted motor
speed profile. The local controller then controls the motor
according to the adjusted motor speed profile during the second of
the two sequential pumping cycles of the pumpjack.
[0020] In some examples, the first motor speed profile is a
predetermined default setting. In some examples, the first motor
speed profile is an altered version of a motor speed profile
utilized in a previous pump stroke cycle of the sequence.
[0021] Yet another aspect of the invention features a method of
pumping fluid. The method includes operating an electric motor of a
pumpjack to pump fluid, according to a predetermined motor speed
profile including a plurality of target motor speeds corresponding
to each of a plurality of discrete pump stroke cycle segments,
while receiving load data from one or more sensors mounted to
monitor at least one operating condition of the pumpjack. The
method also includes storing and updating a pump stroke cycle load
profile based on the received load data over a period of several
pump stroke cycles, and in response to detecting load data
deviating from the load profile by more than a predetermined
deviation threshold, automatically decrementing a subset of the
plurality of target motor speeds selected based on a position of
the deviating load data within the stroke cycle.
[0022] The detected load data deviation may be indicative of a rod
load spike, or of a pump-off condition, for example. The detected
load data deviation may also be indicative of a gearbox torque
transfer anomaly.
[0023] In some examples, the pump stroke cycle load profile is a
data structure relating position to load with respect to a polish
rod of the pumpjack over one or more of the pump stroke cycles
based on the sensory feedback. In some cases, the method includes
detecting the load data deviation by comparing the data structure
to one or more predetermined load limits, such as a load limit
corresponding to the structural integrity of the polish rod or of a
gear box coupled to the motor and the polish rod.
[0024] Various examples of methods or systems corresponding to one
or more of the described aspects of the invention discussed herein
may advantageously provide optimized pump operation by detecting
and automatically mitigating various detrimental operating
conditions, such as pump off, rod binding, acute rod stress or
excessive gearbox torque. Such conditions may be without user
interaction mitigated or prevented without user intervention, by
automatically adjusting the motor speed throughout the pump stroke
cycle. These detection and mitigation techniques may be conducted
by a local controller in essentially real time, without employing
computationally complex mathematical operations, resulting in
relatively quick responses times (e.g., within one cycle or less),
without interruption of the pumping process.
[0025] The details of one or more implementations of the subject
matter described in this specification are set forth in the
accompanying drawings and the description below. Other features,
aspects, and advantages of the subject matter will become apparent
from the description, the drawings, and the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a schematic view of a pumpjack in accordance with
one or more embodiments of the present disclosure.
[0027] FIG. 2 is a graph illustrating a default stroke cycle
compared to an adjusted stroke cycle.
[0028] FIG. 3 is diagram illustrating the modification of a default
motor speed profile to provide an adjusted motor speed profile.
[0029] FIG. 4 is a graph illustrating a technique of operating a
pumpjack that includes monitoring a surface dynamometer card and a
downhole pump card to detect a pump-off condition.
[0030] FIG. 5 is a graph illustrating a technique of operating a
pumpjack that includes monitoring a surface dynamometer card to
detect a rod binding.
[0031] FIG. 6 is a graph illustrating a technique of operating a
pumpjack that includes monitoring a surface dynamometer card to
detect a rod stress limit.
[0032] FIG. 7 is a graph illustrating a technique of operating a
pumpjack that includes monitoring a surface dynamometer card to
detect a gearbox torque limit.
[0033] FIG. 8 is a graph illustrating the progressive modification
of a pumpjack stroke cycle in response to varying motor speeds.
[0034] FIGS. 9A-9E are graphs illustrating the progressive
modification of pumpjack stroke cycle according to an iterative
tuning process.
[0035] FIG. 10 is a flow chart illustrating a first method of
operating a pumpjack in accordance with one or more embodiments of
the present disclosure.
[0036] FIG. 11 is a flow chart illustrating a second method of
operating a pumpjack in accordance with one or more embodiments of
the present disclosure.
[0037] FIG. 12 is a flow chart illustrating a third method of
operating a pumpjack in accordance with one or more embodiments of
the present disclosure.
[0038] FIG. 13 is a graph illustrating a varying voltage profile
determined based on a varying motor torque profile.
[0039] FIG. 14 is a flow chart illustrating a fourth method of
operating a pumpjack in accordance with one or more embodiments of
the present disclosure.
[0040] FIG. 15 is a graph illustrating a technique of operating a
pumpjack that includes monitoring a surface dynamometer card and
altering the stroke timing of the motor to increase fluid
production while avoiding gearbox torque limits.
[0041] Many of the features are exaggerated to better show the
features, process steps, and results.
DETAILED DESCRIPTION
[0042] One or more implementations of the present disclosure
include pumpjacks and pumpjack motor systems, as well as techniques
for operating the same, where the controller facilitates tuning and
adaptation of the stroke timing by dynamically (e.g., on a stroke
cycle interval basis) adjusting motor RPM to optimize a broad set
of configurable parameters, including overall system efficiency and
various stress conditions. In some examples, the controller can be
implemented by a moderately capable local processor, so as to avoid
exceedingly complex mathematical computations that may delay
adjustment of the stroke timing. In some examples, the controller
utilizes a combination of mathematically predictive and partially
predictive empirical (e.g., Perturb-now and Observe-later)
algorithms for dynamic stroke-timing modification.
[0043] Referring first to FIG. 1, a pumpjack 100 includes a frame
102 (sometimes referred to as a "Sampson post"), a walking beam
104, a horsehead 106, a polish rod 108, and a pump 110. The frame
102 is supported on a substantially flat base 112. The walking beam
104 is pivotally coupled (e.g., journaled) to the crest of the
frame 102. The horsehead 106 is coupled to a front end of the
walking beam 104, and therefore moves vertically upward and
downward as the walking beam 104 pivots about the frame 102. The
polish rod 108 is coupled to the horsehead 106 by a cable 114
(sometimes referred to as a "bridal") and extends downward
therefrom to project into the wellbore 10. The curved face of the
horsehead 106 ensures that the polish rod 108 is lowered and raised
in a straight line. The pump 110 is located towards the bottom of
the wellbore 10, coupled to the polish rod 108 by an intervening
sucker rod 116. Although depicted in FIG. 1 as a single component,
the sucker rod 116 may be provided as a string of multiple rod
segments coupled to one another in an end-to-end arrangement. In
some embodiments, the pump 110 includes two valves and a plunger
contained within a tubular pump barrel. During the "upstroke" of
the pump--that is, when the plunger is pulled upward by the sucker
rod 116--the top valve (sometimes referred to as the "riding
valve") closes and the bottom valve (sometimes referred to as the
"standing valve") opens. Fluid in the portion of the pump barrel
above the riding valve is drawn upward with the plunger, and the
bottom portion of the pump barrel is simultaneously filled with
fluid that enters the bottom of the wellbore 10 via perforations
that have made through the surrounding casing. During the
"downstroke" of the pump 110--that is, when the plunger is pushed
downward by the sucker rod 116--the riding valve opens and the
standing valve closes, which allows fluid from the bottom portion
of the pump barrel to flow through the riding valve. An
upstroke-downstroke pair is referred to as a "stroke cycle."
[0044] The rod system (e.g., the polish rod 108 and the sucker rod
116) carries a continuously varying load due to the reciprocating
motion of the horsehead 106 and the associated fluid movement of
the pump 110. The maximum load occurs shortly after the beginning
of the upstroke, when the riding valve closes. The polish rod 108
must carry the full weight of the fluids, the rod system, and the
added inertial effects that occur as the motion of the rods is
reversed. The minimum load occurs shortly after the beginning of
the downstroke, as the riding valve opens. At that point, the rod
system no longer carries the fluid load and the inertial effects
are reversed, thereby reducing the total rod load below the weight
of the rods and the produced fluids. The rod system continuously
stretches and contracts in response to the varying load. In
addition, because of the elasticity of the sucker rod 116, which is
usually of substantial length (e.g., over 5,000 ft.), large stress
waves run up and down the rod in response to the various applied
forces (e.g., the above described loads, as well as mechanical and
fluid friction). These stress waves may cause the sucker rod 116 to
break if they become excessive.
[0045] The walking beam 104 is driven by powertrain assembly
including a prime mover 118, a reduction gearbox 120, and a
piloting shaft 122 (sometimes referred to as a "Pitman arm"). The
prime mover 118 drives the gearbox 120 through a belt system (not
shown). The gearbox 120 imparts rotary motion into the proximal end
of the piloting shaft 122 via a rotating crank 123. The distal end
of the piloting shaft 122 is coupled to a rear end of the walking
beam 104, and rocks the walking beam 104 back and forth in a
pivoting motion about the frame 102, thus moving the horsehead 106
up and down as described above. In this example, the free end of
the rotating crank 123 carries a counterweight 124, which at least
partially offsets the weight of the rods (e.g., the polish rod 108
and sucker rod 116) and fluid to assist the prime mover 118 during
the upstroke of the pump 110, and provides substantial resistance
against the prime mover 118 to inhibit freefall of the rod system
and pump 110 during the downstroke.
[0046] In this example, the prime mover 118 is provided in the form
of an electrical induction motor (e.g., a high efficiency Nema B
motor) operated by a variable frequency drive ("VFD") 126. The VFD
126 regulates the speed and torque output of the prime mover 118 by
varying input frequency and voltage. In some embodiments, the VFD
126 includes appropriate hardware and circuitry (e.g., processors,
memory, and I/O components) to regulate the speed and torque output
based on one or more setpoint values. A controller 128
communicatively coupled to the VFD 126 includes appropriate
hardware and circuitry (e.g., processors, memory, and I/O
components) so as to achieve any of the control operations
described herein. For example, the controller 128 may be configured
to provide a target motor speed and/or a target motor torque
setpoint to the VFD 126. In some implementations, the controller
128 may be implemented locally with the VFD 126 (e.g., fully or
partially integrated therewith) or located at a remote location
with communication between the components being conducted across a
wired or wireless link (e.g., wired radio, the Internet, wireless
cellular network, telephone network or satellite communication). In
some examples, the prime mover 118 is further equipped with a
regenerative drive provided for the dual purpose of providing a
braking (or negative) torque to control the descent of the rod
system and simultaneously converting the kinetic energy of the
downward moving rod system into electrical power. Thus, the
pumpjack is able to recapture at least a portion of its power draw
from the grid as it operates according to the various tuning and
monitoring techniques described in the present disclosure.
[0047] One or more aspects of the present disclosure are based on a
realization that the timing of the stroke cycle of the pump 110 can
be dynamically adjusted via the controller 128 without physically
altering the pumpjack components discussed above (e.g., the gearbox
120, the piloting shaft 122, and the crank 123). For example, the
controller 128 can provide a motor speed profile to the VFD 126
that includes a plurality of varying target motor speeds
corresponding to each of a plurality of discrete control periods
within a pump stroke cycle. In some embodiments, the motor speed
profile may be determined by the controller 128 so as to improve
the production of fluid from the pump 110. In some embodiments, the
motor speed profile may be determined by the controller 128 so as
to mitigate or decrease the risk of pump-off (a condition where the
lower portion of the pump barrel is not filled with fluid during
the upstroke, causing the plunger to pound into the fluid during
the downstroke, which sends a damaging shockwave through the rod
system), high stress or fatigue load limits in the rod system
(e.g., the polish and sucker rods), and/or high torque in the
gearbox.
[0048] In some embodiments, the controller 128 determines an
appropriate motor speed profile in response to feedback received
during a previous stroke cycle of the pump 110 from one or more
sensors distributed across the pumpjack 100. In this example, the
pumpjack 100 includes a load cell sensor 130, a crank rotation
sensor 132, and a motor shaft position sensor 134 (each of which is
depicted schematically in FIG. 1). The load cell sensor 130 (e.g.,
a strain gauge) provides a feedback signal proportional to the load
carried by the polish rod 108. The crank rotation sensor 132
provides a feedback signal corresponding to the angular position of
the crank 123 coupling the gearbox 120 to the piloting shaft 122.
In some embodiments, the crank rotation sensor 132 includes a
traveling magnet attached to the counterweight 124 carried by the
crank 123 and a stationary transducer mounted to the gearbox 120 or
the base 112. The transducer is responsive to the lines of magnetic
flux effected by the traveling magnet, so that a signal is
generated at each full 360.degree. rotation of the counterweight
124.
[0049] FIG. 2 illustrates a graph 200 plotting polish rod position
versus time illustrates a default stroke timing curve 202 and an
adjusted stroke timing curve 204. The polish rod position data may
be captured directly by a polish rod displacement sensor, or
calculated based on feedback from the motor shaft position sensor
134 for the given geometry of the gearbox 120, crank 123 and other
pumpjack components. The default stroke timing curve 202 is
representative of a pumpjack where the prime mover is operated at
constant speed. The default stroke timing curve 202 resembles a
sinusoidal wave pattern, exhibiting a smooth repetitive oscillation
between the upstroke and the downstroke, which are equal in
duration. The adjusted stroke timing curve 204 is a modified
version of the default stroke timing curve 202, and is
representative of a pumpjack in accordance with one or more
embodiments of the present disclosure, where the prime mover is
controlled according to a motor speed profile including a plurality
of varying target motor speeds within the stroke cycle. In this
example, the adjusted stroke timing curve 204 demonstrates that
that the prime mover is slowed down during the upstroke and sped up
during the downstroke. As illustrated in the graph 200, the result,
relative to the default stroke timing curve 202, is an increased
upstroke time and a decreased downstroke time. The increased
upstroke time increases the volumetric efficiency of the pump,
because there is more time for the pump barrel to refill with fluid
from the reservoir. Furthermore, slowing the prime mover, and
therefore the pump plunger, during the upstroke may also increase
the stroke length of the pump by allowing the elastic sucker rod to
recover from stretching during the downstroke and potentially
contract near the top of the upstroke. The amount of time added to
the upstroke is compensated for by the decreased downstroke
time.
[0050] As illustrated in the graph 200, the adjusted stroke timing
curve 204 has the same duration as the default stroke timing curve
202. Thus, the adjusted stroke timing curve 204 provides an
increase in pumping efficiency without affecting the overall
"pumping rate" (by "pumping rate" we refer to the number of pump
stroke cycles executed in a given time period--e.g., strokes per
minute (SPM)). The increase in pump efficiency and pump stroke
length combined with a constant pumping rate results in an
increased fluid production rate. The fluid production rate is
typically measured in units of barrels of fluid per day (BFPD). In
some embodiments, such as described below, the downstroke time may
be even further decreased to increase the pumping rate relative to
the default stroke timing curve and further increase the fluid
production rate.
[0051] Referring next to FIG. 3, a sequential diagram 300
(illustrated graphically at FIGS. 9A-9C) demonstrates that a
default motor speed profile 302 can be adapted by a motor speed
adjustment table 304 to provide an adjusted motor speed profile
306. As described above, a motor speed profile includes a plurality
of target motor speeds corresponding to each of a plurality of
discrete control periods within a pump stroke cycle. In this
example, the motor speed profiles include one-hundred control
periods, each of which represents between about 5 and 100
milliseconds (e.g., between about 10 and 70 milliseconds, such as
about 30 milliseconds or about 50 milliseconds) of the stroke
cycle. However, other suitable configurations are also envisioned
within the scope of the present disclosure (e.g., the number of
control periods per cycle may be greater than or less than
one-hundred, the number of control periods and/or the time duration
of each control period may vary between cycles, etc.). The default
motor speed profile 302 is representative of a pumpjack where the
prime mover that is operated at constant speed of about 1,100 RPM.
Thus, the target motor speed for each of the control periods of the
default motor speed profile 302 is set to 1,100 RPM. In contrast to
the default motor speed profile 302, the adjusted motor speed
profile 306 includes a varying array of target motor speeds,
ranging from 1,060 RPM to 1,170 RPM, distributed over the
respective one-hundred control periods. The varying target motor
speeds of the adjusted motor speed profile 306 are determined by
modifying the default motor speed profile 302 according to the RPM
adjustment values of the motor speed adjustment table 304. In this
example, the RPM adjustment values are provided in the form of an
array of increment (e.g., +0 to 70), decrement (e.g., -0 to -40)
and null or zero (i.e., +0) values, each of which corresponds to a
respective control period of the stroke cycle. Note that the target
motor speeds and motor speed adjustment values discussed here with
reference to the example of FIG. 3 are provided for illustrative
purposes, and are not meant to limit the present disclosure.
Various techniques within the scope of the present disclosure may
produce significantly different results in this regard.
[0052] In some embodiments, the RPM adjustment values are
determined according to a pumpjack optimization algorithm
implemented by the controller 128. The pumpjack optimization
algorithm may include a tuning mode and a monitoring mode. While
operating in the tuning mode, the algorithm may determine one or
more RPM adjustment values that will improve fluid production.
While operating in the monitoring mode, the algorithm may determine
one or more RPM adjustment values that will relieve one or more
detrimental operating conditions (e.g., the onset of pump-off, high
stress on the rod system, and/or high torque at the gearbox)
detected based on sensory feedback.
[0053] As discussed above with reference to FIG. 2, the fluid
production rate achieved by the pumpjack can be increased relative
to a constant RPM prime mover by increasing the upstroke time, and
decreasing the downstroke time. Thus, in some examples, the
pumpjack optimization algorithm, while operating in the tuning
mode, may derive a motor speed adjustment table 304 including RPM
adjustment values that decrease one or more target motor speeds on
the upstroke and increase one or more target motor speeds on the
downstroke. In some examples, the pumpjack optimization algorithm
may be designed to increase fluid production by increasing the
pumping rate--i.e., reducing the duration of the total stroke cycle
(upstroke plus downstroke) to achieve a higher SPM level. Thus, in
some examples, the algorithm may derive a motor speed adjustment
table 304 including RPM adjustment values that increase the target
motor speeds on both the upstroke and the downstroke to increase
the number of SPM. In such examples, any loss of pump efficiency
and/or pump stroke length from decreasing the upstroke time is more
than overcome by the increased pumping rate, the net result of
which is an increased the fluid production rate.
[0054] In some embodiments, one or more of the RPM adjustment
values is determined based on sensory feedback, such as may be
received by the controller 128 from the load cell sensor 130, the
crank rotation sensor 132, and/or the motor shaft position sensor
134 can be used to determine suitable RPM adjustment values. As
noted above, the feedback from the crank rotation sensor 132 and
the motor shaft position sensor 134 can be used to determine the
position of the polish rod 108, and feedback from the load cell
sensor 130 is proportional to the load carried by the polish rod
108. This position and load data can be used to construct a
synthetic surface dynamometer card (e.g., using techniques
described in U.S. Pat. No. 4,490,094) representative of loading at
the polish rod 108 during a stroke cycle. The surface dynamometer
card can then be transformed using techniques known to those of
skill in the art (such as described in U.S. Pat. No. 3,343,409)
into a downhole pump card representative of loading at the pump 110
during a stroke cycle. The surface dynamometer card and the
downhole pump card can be used to detect or predict the conditions
that are detrimental to pumpjack fluid production, such as the
onset of pump-off, high stress on the rod system, and high torque
at the gearbox. Thus, in some examples, the pumpjack optimization
algorithm may conduct this type of analysis and appropriately
respond by deriving an appropriate motor speed adjustment table 304
to relieve the detrimental condition by: (1) implementing a limited
increment amount of one or more RPM adjustment values; (2)
implementing one or more null or zero RPM adjustment values; and/or
(3) implementing a decrement for one or more RPM adjustment
values.
[0055] The graph 400 of FIG. 4 demonstrates how a surface
dynamometer card 402 and/or a downhole pump card 404 can be used to
detect the onset of a pump-off during a pump stroke cycle. As
shown, each of the cards 402 and 404 reflects a noticeable inward
curvature 406a, 406b (sometimes referred to as a "compression
curve") when a significant amount of gas is compressed during the
upstroke. The detection of gas compression in the downstroke means
that the pump barrel is not completely filling with fluid during
the upstroke. A slight compression curve (406a) may suggest that
pump-off is imminent, and a severe compression curve (406b) may
suggest that pump-off is presently occurring. Pump-off generally
occurs when the upstroke timing is too fast, preventing the pump
barrel from refilling to an acceptable level and causing the
plunger to pound into the fluid column on the downstroke. Pump-off
may be relieved by implementing a decrement for one or more RPM
adjustment values during the upstroke to slow down the prime-mover
RPM and increase the upstroke time. One or more increment RPM
adjustment values may be used on the downstroke to compensate for
the increase in upstroke time.
[0056] The graph 500 of FIG. 5 demonstrates how a surface
dynamometer card 502 can be used to detect a "binding" (e.g., a
point at which the sucker rod is encountering interference from
pipe or casing joints within the wellbore) in the rod system during
a pump stroke cycle. A binding of the rod system may be exhibited
on the surface dynamometer card 502 as a sharp increase in rod load
504a along the upstroke and a sharp decrease in rod load 504b along
the downstroke of the stroke cycle. Similar to a fluid pounding
event experienced during a pump-off condition, a rod binding may
cause damage to the rod system over time. In some examples, a rod
binding may be relieved by appropriately adjusting the stroke
timing of the pumpjack. For example, one or more RPM adjustment
values may be determined to slow down the sucker rod speed or lower
its acceleration at or near the point within the wellbore where the
binding has occurred. Such modifications to the stroke timing may
be implemented immediately during the stroke cycle following
detection or progressively over a serious of subsequent stroke
cycles.
[0057] The graph 600 of FIG. 6 demonstrates how a surface
dynamometer card 602a-d can be used to detect that the sucker rod
is being subjected to loads approaching one or more predetermined
load and/or stress limits during a pump stroke cycle.
Interpretation of the surface dynamometer card 602a-d for rod
loading may include identification of the peak maximum rod load
604, the peak minimum rod load 606, and the difference 608 between
these values. The peak maximum rod load 604 is observed near the
beginning of the upstroke. The peak maximum rod load 604 can be
compared to a predetermined maximum allowable rod load to identify
an existing or imminent overloading event (see card 602d) that may
cause the rod system to experience tensile failure (e.g.,
fracturing). The peak minimum rod load 606 is observed near the
beginning of the downstroke. The peak minimum rod load 608 may be
monitored with respect to the zero load level, at which point the
rod system is essentially in freefall (see card 602d), and
therefore susceptible to buckling. The difference 608 between the
peak maximum rod load 604 and the peak minimum rod load 606 is
proportional to the rod fatigue stress. Fatigue failures are
progressive and begin as small stress cracks that grow under the
action of cyclic stresses. Thus, the rod fatigue stress can also be
monitored with respect to a predetermined limit value. Overloading
and freefall can be relieved by implementing a decrement for one or
more RPM adjustment values during the upstroke and/or the
downstroke.
[0058] The graph 700 of FIG. 7 demonstrates how a surface
dynamometer card 702a-c can be used to detect that the gearbox is
being subjected to loads approaching one or more predetermined
torque limits during a pump stroke cycle. Interpretation of the
surface dynamometer card 702a-c for gearbox torque may include
monitoring the rod load with respect to an upstroke torque limit
curve 704 and a downstroke torque limit curve 706. The torque limit
curves 704 and 706 represent the rod loads plotted as a function of
rod position that causes the net torque at the gearbox (which may
be considered as the torque caused by the well loads acting on the
polish rod discounted by the torque caused by the counterweight
acting on the crank) to exceed a predetermined maximum limit.
Overtorquing the gearbox can be relieved by implementing a
decrement for one or more RPM adjustment values during the upstroke
and/or the downstroke.
[0059] In some embodiments, the tuning mode and/or the monitoring
mode of the pumpjack optimization algorithm may include an
iterative process for progressively improving pumpjack performance.
In some examples, the iterative process may proceed continuously
over a sequence of two or more adjacent pump stroke cycles. So, one
or more of the above-described techniques may be repeated through
multiple iterations to gradually increase fluid production. FIG. 8
illustrates a graph 800 including a motor RPM curve 802, a rod load
curve 804, and a stroke timing curve 806, which demonstrates an
interactive tuning process such as may be implemented by the
pumpjack optimization algorithm. In particular, the graph 800 is
illustrative of how the operations of a pumpjack can be
progressively tuned through successive adjustments of the motor
speed profile applied to the prime mover. In Stroke Cycle 1, the
prime mover is operated according to a default motor speed profile
having constant speed. In Stroke Cycle 2, the motor speed profile
is adjusted to increase and decrease motor RPM at specific points
of the upstroke and downstroke. The RPM adjustments applied during
Stroke Cycle 2 may be derived at least partially based on sensory
feedback received during Stroke Cycle 1. In Stroke Cycle 3, the
motor speed profile is modified yet again based at least in part on
sensory feedback received during the previous stroke cycles. As
discussed above, sensory feedback can be used to detect or predict
detrimental operating conditions that may be relieved or inhibited
by appropriate RPM adjustments in the subsequent motor speed
profile. However, sensory feedback may also be used facilitate the
derivation of RPM adjustment values that are likely to increase
fluid production. For example, the surface dynamometer card and the
downhole pump card can be monitored during the tuning process to
identify specific control periods within the motor speed profile
where an appropriate RPM adjustment (e.g., a decrement or
increment) is likely to result in increased pump efficiency and/or
increased pump stroke length. In some embodiments, the RPM
adjustments may be determined based on historical data from
previous operations of the current pumpjack or a similarly designed
pumpjack. Such historical data may outline the general profile of a
previously identified high-production and stable motor speed
profile. Thus, the pumpjack optimization algorithm may initially
implement suitable RPM adjustments to approach the historical motor
speed profile. Deviations from the historical motor speed profile
may occur over time based on current sensory feedback.
[0060] In some embodiments, iterative tuning of the pumpjack may
take place over several stroke cycles. In some examples, RPM
adjustments to the motor speed profile may be conducted in
successive cycles of the tuning process, such as shown in the graph
800 of FIG. 8. Such RPM adjustments may be relatively small (e.g.,
within the range of +10 RPM and -10 RPM) in some cases, so as to
maintain system stability and prevent damage from unforeseen
detrimental operating conditions. In some examples, RPM adjustments
to the motor speed profile may be conducted piecemeal, with one or
more intervening stroke cycles occurring therebetween. For example,
RPM adjustments to increase fluid production may be implemented
according to predetermined intervals (e.g., every 10 stroke
cycles). The intervening stroke cycles can be monitored to detect
the onset of any potential adverse operating conditions. In any
event, the controller 128 may cease the iterative tuning process
when it is determined that the motor speed profile has been
optimized. For example, the controller 128 may determine that the
motor speed profile has been optimized when subsequent adjustments
no longer provide significant improvements in fluid production
and/or when subsequent adjustments cannot be implemented without
introducing an adverse operating condition (e.g., when further
incrementing RPM adjustments will result in overtorquing of the
gearbox).
[0061] The graphs of FIGS. 9A-9E provide yet another illustration
of an iterative tuning process that may take place over multiple
cycles of a pumpjack. In this example, the tuning process may be
conducted according to the technique described above with reference
to FIG. 3, where a motor speed profile can be adjusted based on a
motor speed adjustment table. Accordingly, the graph 900a
illustrates a default motor speed curve 902 where the target motor
speed for each control period of the cycle is set to a constant
speed of 1,100 RPM. The graph 900b illustrates a first motor speed
adjustment curve 904 representative of a varying array of increment
(e.g., +0 to 70), decrement (e.g., -0 to -40) and null (i.e., +0)
values, each of which corresponds to a respective control period of
the cycle. The graph 900c illustrates a first adjusted motor speed
curve 906 overlaying the default motor speed curve 902. As shown,
the first adjusted motor speed curve 906 represents a varying array
of target motor speeds, ranging from 1,060 RPM to 1,170 RPM,
distributed over the respective the control periods of the cycle.
As discussed above, the first adjusted motor speed curve 906 is
provided by applying the increment, decrement, and null values of
the first motor speed adjustment curve 904 to the default motor
speed curve 902. Thus, the first adjusted motor speed curve 906
features one or more target motor speeds greater than the default
1,100 RPM and one or more target speeds less than the default. The
graph 900d illustrates a second motor speed adjustment curve 908
having increment and decrement values that range between +25 RPM
and -20 RPM. And the graph 900e illustrates a second adjusted motor
speed curve 910 representing a varying array of target motor speeds
ranging from 1,065 RPM to 1,191 RPM. The second adjusted motor
speed curve 910 is provided by applying the respective adjustment
values from the second motor speed adjustment curve 908 to the
first adjusted motor speed curve 906. Thus, the second adjusted
motor speed curve 910 is a second order iteration of the default
motor speed curve 902.
[0062] This iterative tuning process, while demonstrated across two
pump stroke cycles in this example, may be repeated any number of
times to achieve an optimized motor speed profile. As noted above,
such adjustments of the motor speed profile may be conducted across
successive cycles or between one or more intervening cycles. The
first and second motor speed adjustment curves 902 and 908 may be
derived according to any suitable algorithm for improving fluid
production, such as those described above involving increased pump
efficiency, increased pumping rate, as well as preventing,
relieving or mitigating detrimental operating conditions using
sensory feedback. Furthermore, a similar process may be performed
to adjust the motor speed profile during a monitoring mode. For
example, the controller may detect one or more detrimental
operating conditions based on sensory feedback and derive an
appropriate motor speed adjustment curve to relieve the condition.
In some embodiments, after a detrimental condition detected during
the monitoring mode has been relieved, the pumpjack controller may
re-enter the tuning mode in an attempt to improve fluid
production.
[0063] FIGS. 10-12 and 14 illustrate processes 1000, 1100, 1200 and
1400 for operating a pumpjack. These processes can be implemented,
for example, in connection with one or more components of the
pumpjack 100, particularly the controller 128 and/or the VFD 126.
Further, the operations of the processes do not require the any
particular order to achieve desirable results. In addition, other
operations may be provided, or operations may be eliminated, from
the described processes without departing from the scope of the
present disclosure.
[0064] According to the process 1000 of FIG. 10, an electric motor
driving the pumpjack is operated (1002) in a first pump stroke
cycle according to a first motor speed profile. The first motor
speed profile includes a plurality of target motor speeds, each of
which corresponds to a respective discrete control period within
the first pump stroke cycle. In some embodiments, the first motor
speed profile may be a predetermined default setting (e.g., a
constant RPM pattern), or an altered version of a motor speed
profile utilized in a previous pump stroke cycle. Sensory feedback
is received (1004) during the first pump cycle from one or more
sensors mounted to monitor the operations of the pumpjack. The
sensory feedback includes data collected during operation of the
motor according to the first motor speed profile. In some
embodiments, the sensory feedback may be received from one or more
of a load cell sensor, a crank rotation sensor, and a motor shaft
position sensor. One or more speed adjustment values corresponding
to a limited subset of the plurality of control periods are
determined (1006) in response to receiving the sensory feedback,
and while continuing to operate the pumpjack. In some embodiments,
the speed adjustment values may be determined by constructing a
data structure relating position to load with respect to the rod
system of the pumpjack (e.g., a surface dynamometer card and/or a
downhole pump card), and comparing the data structure to one or
more predetermined load limits (e.g., a maximum rod load, a minimum
rod load, an upstroke torque load limit, and a downstroke torque
load limit) to identify an adverse operating condition (e.g., the
onset of pump-off, high stress on the rod system, and high torque
at the gearbox). In some embodiments, the speed adjustment values
may be determined by identifying an abrupt load spike indicative of
a rod binding. In some embodiments, the speed adjustment values may
include a decrement to decrease the target motor speed at a control
period where an adverse operating condition is likely to reoccur,
or at an earlier control period. Decreasing motor speed at or
before the control period where the adverse operating condition is
likely to reoccur may relieve the condition. In some embodiments,
the speed adjustment values may include an increment to increase
the target motor speed at a control period where an adverse
operating condition is not likely to reoccur. Increasing motor
speed at a different point in the stroke cycle may increase the
pumping rate, without aggravating or re-initiating the adverse
operating condition. The first motor speed profile is adjusted
(1008) based on the one or more speed adjustment values to provide
a second motor speed profile. And the electric motor is operated
(1010) over a second pump stroke cycle, which is immediately
subsequent to the first pump stroke cycle, in accordance with the
second motor speed profile.
[0065] According to the process 1100 or FIG. 11, an electric motor
driving the pumpjack is operated (1102) according to a
predetermined motor speed profile. The motor speed profile includes
a plurality of target motor speeds, each of which corresponds to a
respective control period within a stroke cycle of the pumpjack.
Sensory feedback is received (1104) as the motor is operated during
the stroke cycle from one or more sensors mounted to monitor the
operations of the pumpjack (e.g., a load cell sensor, a crank
rotation sensor, and/or a motor shaft position sensor). While
continuing to operate (1102) the electric motor and receive (1104)
sensory feedback, selected target motor speeds are incrementally
increased (1106) over a plurality of sequential stroke cycles until
an adverse operating condition (e.g., the onset of pump-off, high
stress on the rod system, and high torque at the gearbox) is
detected (1108) based on the sensory feedback. In response to
detecting (1108) the adverse operating condition, a select subset
of the plurality of target motor speeds are decreased (1110) based
on a position of the detected adverse operating condition within
the stroke cycle. In some embodiments, the select subset of the
plurality of target motor speeds may include one or more target
motor speeds at or before the control where the adverse operating
condition is likely to reoccur.
[0066] According to the process 1200 of FIG. 12, an electric motor
driving the pumpjack is operated (1202) according to a
predetermined motor speed profile. The motor speed profile includes
a plurality of target motor speeds corresponding to each of a
plurality of discrete pump stroke cycle segments (e.g., discrete
control periods). Load data is received (1204) from one or more
sensors (e.g., a load cell sensor) mounted to monitor operations of
the pumpjack. A pump cycle load profile is stored (1206) in
computer memory and updated (1208) over a period of several pump
stroke cycles based on the received load data. And, in response to
detecting (1210) that current load data has deviated from the
historical load profile by more than a predetermined deviation
threshold, a subset of the plurality of the target motor speeds are
automatically decremented (1212). The target motor speeds to be
decremented are selected based on the position of the deviating
load data within the stroke cycle. The detected load data deviation
may be indicative of an adverse operating conditions such as a rod
binding, pump-off, high stress on the rod system, and high torque
at the gearbox.
[0067] As described in detail above, the prime mover of a pumpjack
may be operated according to varying motor speed profile to improve
fluid production and prevent or inhibit certain adverse operating
conditions. The motor speed profile includes a plurality of target
motor speeds corresponding to each of a plurality of discrete
control periods within the stroke cycle. The VFD regulates the
speed and torque output of the pumpjack motor by varying input
frequency and voltage. In some embodiments, a controller coupled to
the VFD can be configured (e.g., appropriately programmed) to
implement a dynamic torque control technique where the torque of
the motor is adapted to meet, but not exceed (at least beyond a
predetermined safety margin), the load requirements for operation
at the prescribed motor speed for each control period of the
current stroke cycle. The voltage applied creates the potential for
torque within the motor. Thus, the applied voltage may be reduced
according to a reduction in torque required by the motor. In some
examples, the voltage required may be accurately predicted and
regulated based upon historical pump cycle data, allowing for
prevention of stall conditions (i.e., where the motor is starved of
torque) and optimization of the efficiency of the motor by applying
only the voltage required to deliver that torque. Accordingly,
decreased energy consumption may be achieved by using dynamic
torque control. The graph 1300 of FIG. 13 illustrates a dynamic
motor torque curve 1302 and a motor voltage curve 1304 applied to
provide the required torque at each point in the stroke cycle.
[0068] According to the process 1400 of FIG. 14, an electric motor
driving the pumpjack is operated (1402) according to a varying
motor speed profile. The motor speed profile includes a plurality
of target motor speeds corresponding to each of a plurality of
discrete pump stroke cycle segments (e.g., discrete control
periods). Load data is received (1404) from one or more sensors
(e.g., a load cell sensor) mounted to monitor operations of the
pumpjack. A pump cycle load profile is stored (1406) in computer
memory based on the received load data. A varying voltage profile
is automatically determined (1408) to drive the electric motor
according to the plurality of target motor speeds and the pump
cycle load profile. And the varying voltage profile is subsequently
applied (1410) to the motor. Further, in some embodiments, a
dynamic torque control technique may be conducted predictively on a
cycle-by-cycle bases. That is, the pump cycle load profile (e.g.,
the dynamic motor torque curve) can be mathematically predicted
based on an altered motor speed profile to be implemented during
the upcoming pump stroke cycle. The predicted pump cycle load
profile can then be used to determine a predicted varying voltage
profile. The altered motor speed profile and the predicted varying
voltage profile can be simultaneously implemented during the next
pump stroke cycle. This predictive technique would normally be
dangerous to implement in a highly variable torque environment,
because a large increase in the torque requirement on the motor
cannot be predicted by a conventional control system. However, in
one or more embodiments of the present disclosure, the pump cycle
load profile can be accurately determined (e.g., mathematically
predicted) based at least in part on historical sensory feedback
data and/or adjustments between the current motor speed profile and
one or more stroke timing curves implemented during one or more
previous cycles.
[0069] The graph 1500 of FIG. 15 demonstrates how a surface
dynamometer card 1502a can be adjusted over one or more pump stroke
cycles to increase fluid production while avoiding the
predetermined gearbox torque limits 1504 and 1506. As discussed
above with reference to FIG. 7, overtorquing the gearbox can be
prevented or relieved by implementing a decrement for one or more
RPM adjustment values during the upstroke and/or the downstroke.
However, decreasing the motor RPM to remedy or prevent damage to
the gearbox can have a detrimental effect on the fluid production
rate. Thus, in order to maintain (or even increase) the rate of
fluid production, one or more increments RPM adjustment values may
be implemented at other regions of the stroke cycle that are not
structurally limited by the torque limits. The surface dynamometer
card 1502b illustrates two regions of the stroke cycle 1508a, 1508b
where the motor RPM is decreased to avoid the torque limits, and
two other regions 1508c, 1508d where the motor RPM is increased to
make up for the motor speed decrease. In this way, the stroke cycle
can be further optimized via a strategically alteration of the
surface dynamometer card to effectively redistribute the gearbox
torque. Similar techniques for altering the surface dynamometer
card can be implemented with respect to the peak maximum and peak
minimum rod loads described above with reference to FIG. 6 and/or
the detection of a rod binding described above with reference to
FIG. 5, with the effect of preventing or curing a rod stress
condition while increasing fluid production.
[0070] A number of embodiments of the invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the inventions.
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