U.S. patent application number 14/947839 was filed with the patent office on 2017-05-25 for operational control of wellsite pumping unit with continuous position sensing.
The applicant listed for this patent is WEATHERFORD TECHNOLOGY HOLDINGS, LLC. Invention is credited to Clark E. ROBISON, Benson THOMAS, James S. TRAPANI.
Application Number | 20170146006 14/947839 |
Document ID | / |
Family ID | 57348605 |
Filed Date | 2017-05-25 |
United States Patent
Application |
20170146006 |
Kind Code |
A1 |
ROBISON; Clark E. ; et
al. |
May 25, 2017 |
OPERATIONAL CONTROL OF WELLSITE PUMPING UNIT WITH CONTINUOUS
POSITION SENSING
Abstract
A well pumping system can include an actuator that reciprocably
displaces a rod string, a continuous position sensor that
continuously detects a position of a member of the actuator, and a
control system that modifies reciprocal displacement of the rod
string by the actuator, in response to an output of the continuous
position sensor. A well pumping method can include reciprocably
displacing a rod string, continuously detecting a velocity profile
with a continuous position sensor, and modifying the velocity
profile while the rod string reciprocably displaces, in response to
an output of the continuous position sensor.
Inventors: |
ROBISON; Clark E.; (Tomball,
TX) ; TRAPANI; James S.; (Houston, TX) ;
THOMAS; Benson; (Pearland, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WEATHERFORD TECHNOLOGY HOLDINGS, LLC |
Houston |
TX |
US |
|
|
Family ID: |
57348605 |
Appl. No.: |
14/947839 |
Filed: |
November 20, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04B 47/02 20130101;
E21B 43/126 20130101; F04B 49/22 20130101; F04B 9/103 20130101;
F04B 2203/0903 20130101; E21B 43/127 20130101; F04B 53/16 20130101;
F04B 19/22 20130101; F04B 49/20 20130101; F04B 2203/0409 20130101;
F04B 49/12 20130101 |
International
Class: |
F04B 49/12 20060101
F04B049/12; F04B 19/22 20060101 F04B019/22; F04B 9/103 20060101
F04B009/103; F04B 49/22 20060101 F04B049/22; F04B 53/16 20060101
F04B053/16; F04B 49/20 20060101 F04B049/20; E21B 43/12 20060101
E21B043/12; F04B 47/02 20060101 F04B047/02 |
Claims
1. A well pumping system, comprising: an actuator that reciprocably
displaces a rod string; a continuous position sensor that
continuously detects a position of a member of the actuator; and a
control system that modifies reciprocal displacement of the rod
string by the actuator, in response to an output of the continuous
position sensor.
2. The well pumping system of claim 1, wherein the control system
modifies the reciprocal displacement of the rod string, without
displacement of the continuous position sensor relative to the
actuator.
3. The well pumping system of claim 1, wherein the control system
modifies a stroke extent of the actuator member, in response to the
output of the continuous position sensor.
4. The well pumping system of claim 1, wherein the control system
modifies a stroke extent of the rod string at surface, in response
to the output of the continuous position sensor.
5. The well pumping system of claim 1, wherein the control system
modifies a stroke extent of the rod string proximate a downhole
pump, in response to the output of the continuous position
sensor.
6. The well pumping system of claim 1, wherein the control system
maintains a preselected velocity profile of the actuator member, in
response to the output of the continuous position sensor.
7. The well pumping system of claim 1, wherein the control system
maintains a preselected velocity profile of the rod string at
surface, in response to the output of the continuous position
sensor.
8. The well pumping system of claim 1, wherein the control system
maintains a preselected velocity profile of the rod string
proximate a downhole pump, in response to the output of the
continuous position sensor.
9. A well pumping method, comprising: reciprocably displacing a rod
string; continuously detecting a velocity profile with a continuous
position sensor; and modifying the velocity profile while the rod
string reciprocably displaces, in response to an output of the
continuous position sensor.
10. The well pumping method of claim 9, wherein the modifying
comprises changing a duration of the velocity profile.
11. The well pumping method of claim 10, wherein the changing is
performed while the rod string reciprocably displaces.
12. The well pumping method of claim 9, wherein the modifying
comprises changing a position at which an actuator member velocity
is zero, the position being detected by the continuous position
sensor.
13. The well pumping method of claim 12, wherein the changing is
performed while the rod string reciprocably displaces.
14. The well pumping method of claim 9, wherein the modifying
comprises changing a position at which the rod string velocity is
zero at a downhole pump.
15. The well pumping method of claim 14, wherein the changing
comprises solving a wave equation in the rod string.
16. The well pumping method of claim 9, wherein the modifying
comprises minimizing differences between the detected velocity
profile and a preselected velocity profile.
17. The well pumping method of claim 9, wherein the modifying
comprises maintaining acceleration of the rod string less than a
preselected level.
18. A well pumping method, comprising: reciprocably displacing a
rod string with an actuator; continuously detecting a position of a
member of the actuator with a continuous position sensor; and
modifying reciprocating displacement of the rod string by the
actuator, in response to an output of the continuous position
sensor.
19. The well pumping method of claim 18, wherein the modifying is
performed without displacing the continuous position sensor
relative to the actuator.
20. The well pumping method of claim 18, wherein the modifying
comprises varying a periodic energy input to the actuator relative
to the reciprocating displacement of the actuator member as
detected by the continuous position sensor.
21. The well pumping method of claim 20, wherein the varying
comprises varying a duration of the energy input, in response to
the output of the continuous position sensor.
22. The well pumping method of claim 20, wherein the varying
comprises varying a level of the energy input, in response to the
output of the continuous position sensor.
23. The well pumping method of claim 18, wherein the modifying
comprises varying a stroke extent of the actuator member, in
response to the output of the continuous position sensor.
24. The well pumping method of claim 23, wherein the varying
comprises displacing the stroke extent until either: a) the stroke
extent as detected by the continuous position sensor is positioned
at a preselected stroke extent, or b) the stroke extent has
displaced a preselected distance as detected by the continuous
position sensor.
25. The well pumping method of claim 18, wherein the modifying
comprises modifying a stroke extent of the rod string at surface,
in response to the output of the continuous position sensor.
26. The well pumping method of claim 18, wherein the modifying
comprises modifying a stroke extent of the rod string proximate a
downhole pump, in response to the output of the continuous position
sensor.
27. The well pumping method of claim 26, wherein modifying the
stroke extent of the rod string proximate the downhole pump
comprises solving a wave equation in the rod string.
28. The well pumping method of claim 18, wherein the modifying
comprises maintaining a preselected velocity profile of the
actuator member, in response to the output of the continuous
position sensor.
29. The well pumping method of claim 18, wherein the modifying
comprises maintaining a preselected velocity profile of the rod
string at surface, in response to the output of the continuous
position sensor.
30. The well pumping method of claim 18, wherein the modifying
comprises maintaining a preselected velocity profile of the rod
string proximate a downhole pump, in response to the output of the
continuous position sensor.
31. The well pumping method of claim 30, wherein maintaining the
preselected velocity profile of the rod string proximate the
downhole pump comprises solving a wave equation in the rod
string.
32. The well pumping method of claim 18, wherein the modifying
comprises maintaining a preselected velocity profile, during the
reciprocating displacement of the rod string, in response to the
output of the continuous position sensor.
Description
BACKGROUND
[0001] This disclosure relates generally to equipment utilized and
operations performed in conjunction with a subterranean well and,
in one example described below, more particularly provides a well
pumping system and associated method.
[0002] Reservoir fluids can sometimes flow to the earth's surface
when a well has been completed. However, with some wells, reservoir
pressure may be insufficient (at the time of well completion or
thereafter) to lift the fluids (in particular, liquids) to the
surface. In those circumstances, technology known as "artificial
lift" can be employed to bring the fluids to or near the surface
(such as a subsea production facility or pipeline, a floating rig,
etc.).
[0003] Various types of artificial lift technology are known to
those skilled in the art. In one type of artificial lift, a
downhole pump is operated by reciprocating a string of "sucker"
rods deployed in a well. An apparatus (such as, a walking beam-type
pump jack or a hydraulic actuator) located at the surface can be
used to reciprocate the rod string.
[0004] Therefore, it will be readily appreciated that improvements
are continually needed in the arts of constructing and operating
artificial lift systems. Such improvements may be useful for
lifting oil, water, gas condensate or other liquids from wells, may
be useful with various types of wells (such as, gas production
wells, oil production wells, water or steam flooded oil wells,
geothermal wells, etc.), and may be useful for any other
application where reciprocating motion is desired.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a representative partially cross-sectional view of
an example of a well pumping system and associated method which can
embody principles of this disclosure.
[0006] FIGS. 2-5 are representative views of actuator examples and
continuous position sensor examples.
[0007] FIGS. 5-9 are representative graphs of example velocity
profiles.
[0008] FIGS. 10 & 11 are representative flowcharts for
techniques of controlling operation of the well pumping system.
[0009] FIG. 12 is a representative example graph of position and
energy input versus time, with modifications thereof.
DETAILED DESCRIPTION
[0010] Representatively illustrated in FIG. 1 is a well pumping
system 10 and associated method for use with a subterranean well,
which system and method can embody principles of this disclosure.
However, it should be clearly understood that the well pumping
system 10 and method are merely one example of an application of
the principles of this disclosure in practice, and a wide variety
of other examples are possible. Therefore, the scope of this
disclosure is not limited at all to the details of the system 10
and method as described herein or depicted in the drawings.
[0011] In the FIG. 1 example, a power source 12 is used to supply
energy to an actuator 14 mounted on a wellhead 16. In response, the
actuator 14 reciprocates a rod string 18 extending into the well,
thereby operating a downhole pump 20.
[0012] The rod string 18 may be made up of individual sucker rods
connected to each other, although other types of rods or tubes may
be used, the rod string 18 may be continuous or segmented, a
material of the rod string 18 may comprise steel, composites or
other materials, and elements other than rods may be included in
the string. Thus, the scope of this disclosure is not limited to
use of any particular type of rod string, or to use of a rod string
at all. It is only necessary for purposes of this disclosure to
communicate reciprocating motion of the actuator 14 to the downhole
pump 20, and it is therefore within the scope of this disclosure to
use any structure capable of such transmission.
[0013] The downhole pump 20 is depicted in FIG. 1 as being of the
type having a stationary or "standing" valve 22 and a reciprocating
or "traveling" valve 24. The traveling valve 24 is connected to,
and reciprocates with, the rod string 18, so that fluid 26 is
pumped from a wellbore 28 into a production tubing string 30.
However, it should be clearly understood that the downhole pump 20
is merely one example of a wide variety of different types of pumps
that may be used with the well pumping system 10 and method of FIG.
1, and so the scope of this disclosure is not limited to any of the
details of the downhole pump described herein or depicted in the
drawings.
[0014] The wellbore 28 is depicted in FIG. 1 as being generally
vertical, and as being lined with casing 32 and cement 34. In other
examples, a section of the wellbore 28 in which the pump 20 is
disposed may be generally horizontal or otherwise inclined at any
angle relative to vertical, and the wellbore section may not be
cased or may not be cemented. Thus, the scope of this disclosure is
not limited to use of the well pumping system 10 and method with
any particular wellbore configuration.
[0015] In the FIG. 1 example, the fluid 26 originates from an earth
formation 36 penetrated by the wellbore 28. The fluid 26 flows into
the wellbore 28 via perforations 38 extending through the casing 32
and cement 34. The fluid 26 can be a liquid, such as oil, gas
condensate, water, etc. However, the scope of this disclosure is
not limited to use of the well pumping system 10 and method with
any particular type of fluid, or to any particular origin of the
fluid.
[0016] As depicted in FIG. 1, the casing 32 and the production
tubing string 30 extend upward to the wellhead 16 at or near the
earth's surface 40 (such as, at a land-based wellsite, a subsea
production facility, a floating rig, etc.). The production tubing
string 30 can be hung off in the wellhead 16, for example, using a
tubing hanger (not shown). Although only a single string of the
casing 32 is illustrated in FIG. 1 for clarity, in practice
multiple casing strings and optionally one or more liner strings (a
liner string being a pipe that extends from a selected depth in the
wellbore 28 to a shallower depth, typically sealingly "hung off"
inside another pipe or casing) may be installed in the well.
[0017] In the FIG. 1 example, a rod blowout preventer stack 42 and
a stuffing box 44 are connected between the actuator 14 and the
wellhead 16. The rod blowout preventer stack 42 includes various
types of blowout preventers (BOP's) configured for use with the rod
string 18. For example, one blowout preventer can prevent flow
through the blowout preventer stack 42 when the rod string 18 is
not present therein, and another blowout preventer can prevent flow
through the blowout preventer stack 42 when the rod string 18 is
present therein. However, the scope of this disclosure is not
limited to use of any particular type or configuration of blowout
preventer stack with the well pumping system 10 and method of FIG.
1.
[0018] The stuffing box 44 includes an annular seal (not visible in
FIG. 1) about an upper end of the rod string 18. A reciprocating
rod member 50 of the actuator 14 connects to the rod string 18
above the annular seal, although in other examples a connection
between the rod member 50 and the rod string 18 may be otherwise
positioned.
[0019] The power source 12 may be connected directly to the
actuator 14, or it may be positioned remotely from the actuator 14
and connected with, for example, suitable electrical cables,
mechanical linkages, hydraulic hoses or pipes. Operation of the
power source 12 is controlled by a control system 46.
[0020] The control system 46 may allow for manual or automatic
operation of the actuator 14 via the power source 12, based on
operator inputs and measurements taken by various sensors. The
control system 46 may be separate from, or incorporated into, the
actuator 14 or the power source 12. In one example, at least part
of the control system 46 could be remotely located or web-based,
with two-way communication between the actuator 14, the power
source 12 and the control system 46 being via, for example,
satellite, wireless or wired transmission.
[0021] The control system 46 can include various components, such
as a programmable controller, input devices (e.g., a keyboard, a
touchpad, a data port, etc.), output devices (e.g., a monitor, a
printer, a recorder, a data port, indicator lights, alert or alarm
devices, etc.), a processor, software (e.g., an automation program,
customized programs or routines, etc.) or any other components
suitable for use in controlling operation of the actuator 14 and
the power source 12. The scope of this disclosure is not limited to
any particular type or configuration of a control system.
[0022] In operation of the well pumping system 10 of FIG. 1, the
control system 46 causes the power source 12 to increase energy
input to the actuator 14, in order to raise the rod string 18.
Conversely, the energy input to the actuator 14 is reduced or
removed, in order to allow the rod string 18 to descend. Thus, by
alternately increasing and decreasing energy input to the actuator
14, the rod string 18 is reciprocated, the downhole pump 20 is
actuated and the fluid 26 is pumped out of the well.
[0023] Note that, when energy input to the actuator 14 is decreased
to allow the rod string 18 to displace downward (as viewed in FIG.
1), the energy input may not be decreased to zero. Instead, a
"balance" energy level may be maintained in the actuator 14 to
nominally offset a load due to the rod string 18 being suspended in
the well (e.g., a weight of the rod string, taking account of
buoyancy, inclination of the wellbore 28, friction, well pressure,
etc.).
[0024] In this manner, the power source 12 is not required to
increase energy input to the actuator 14 from zero to that
necessary to displace the rod string 18 upwardly (along with the
displaced fluid 26), and then reduce the energy input back to zero,
for each reciprocation of the rod string 18. Instead, the power
source 12 only has to increase energy input to the actuator 14
sufficiently greater than the balance energy level to displace the
rod string 18 to its upper stroke extent, and then reduce the
energy input to the actuator 14 back to the balance energy level to
allow the rod string 18 to displace back to its lower stroke
extent.
[0025] Note that it is not necessary for the balance energy level
in the actuator 14 to exactly offset the load exerted by the rod
string 18. In some examples, it may be advantageous for the balance
energy level to be somewhat less than that needed to offset the
load exerted by the rod string 18. In addition, it can be
advantageous in some examples for the balance energy level to
change over time. Thus, the scope of this disclosure is not limited
to use of any particular or fixed balance energy level, or to any
particular relationship between the balance energy level, any other
force or energy level and/or time.
[0026] A reciprocation speed of the rod string 18 will affect a
flow rate of the fluid 26. Generally speaking, the faster the
reciprocation speed at a given length of stroke of the rod string
18, the greater the flow rate of the fluid 26 from the well (to a
point).
[0027] It can be advantageous to control the reciprocation speed,
instead of reciprocating the rod string 18 as fast as possible. For
example, a fluid interface 48 in the wellbore 28 can be affected by
the flow rate of the fluid 26 from the well. The fluid interface 48
could be an interface between oil and water, gas and water, gas and
gas condensate, gas and oil, steam and water, or any other fluids
or combination of fluids.
[0028] If the flow rate is too great, the fluid interface 48 may
descend in the wellbore 28, so that eventually the pump 20 will no
longer be able to pump the fluid 26 (a condition known to those
skilled in the art as "pump-off"). On the other hand, it is
typically desirable for the flow rate of the fluid 26 to be at a
maximum level that does not result in pump-off. In addition, a
desired flow rate of the fluid 26 may change over time (for
example, due to depletion of a reservoir, changed offset well
conditions, water or steam flooding characteristics, etc.).
[0029] A "gas-locked" downhole pump 20 can result from a pump-off
condition, whereby gas is received into the downhole pump 20. The
gas is alternately expanded and compressed in the downhole pump 20
as the traveling valve 24 reciprocates, but the fluid 26 cannot
flow into the downhole pump 20, due to the gas therein.
[0030] In the FIG. 1 well pumping system 10 and method, the control
system 46 can automatically control operation of the actuator 14
via the power source 12 to regulate the reciprocation speed, so
that pump-off is avoided, while achieving any of various desirable
objectives. Those objectives may include maximum flow rate of the
fluid 26, optimized rate of electrical power consumption, reduction
of peak electrical loading, etc. However, it should be clearly
understood that the scope of this disclosure is not limited to
pursuing or achieving any particular objective or combination of
objectives via automatic reciprocation speed regulation by the
control system 46.
[0031] As mentioned above, the power source 12 is used to variably
supply energy to the actuator 14, so that the rod string 18 is
displaced alternately to its upper and lower stroke extents. These
extents do not necessarily correspond to maximum possible upper and
lower displacement limits of the rod string 18 or the pump 20.
[0032] For example, it is typically undesirable for a valve rod
bushing 25 above the traveling valve 24 to impact a valve rod guide
23 above the standing valve 22 when the rod string 18 displaces
downward (a condition known to those skilled in the art as
"pump-pound"). Thus, it is preferred that the rod string 18 be
displaced downward only until the valve rod bushing 25 is near its
maximum possible lower displacement limit, so that it does not
impact the valve rod guide 23.
[0033] On the other hand, the longer the stroke distance (without
impact), the greater the productivity and efficiency of the pumping
operation (within practical limits), and the greater the
compression of fluid between the standing and traveling valves 22,
24 (e.g., to avoid gas-lock). In addition, a desired stroke of the
rod string 18 may change over time (for example, due to gradual
lengthening of the rod string 18 as a result of lowering of a
liquid level (such as at fluid interface 48) in the well,
etc.).
[0034] In the FIG. 1 well pumping system 10 and method, the control
system 46 can automatically control operation of the power source
12 to regulate the upper and lower stroke extents of the rod string
18, so that pump-pound is avoided, while achieving any of various
desirable objectives. Those objectives may include maximizing rod
string 18 stroke length, maximizing production, minimizing
electrical power consumption rate, minimizing peak electrical
loading, etc. However, it should be clearly understood that the
scope of this disclosure is not limited to pursuing or achieving
any particular objective or combination of objectives via automatic
stroke extent regulation by the control system 46.
[0035] In the FIG. 1 example, the system 10 includes a continuous
position sensor 52 in communication with the control system 46. The
continuous position sensor 52 is capable of continuously detecting
a position of a reciprocating member of the actuator 14 (such as
the rod member 50 or another member).
[0036] An output of the continuous position sensor 52 can be useful
to achieve a variety of objectives, such as, controlling stroke
distance, speed and extents to maximize production and efficiency,
minimize electrical power consumption and/or peak electrical
loading, maximize useful life of the rod string 18, etc. However,
the scope of this disclosure is not limited to pursuing or
achieving any particular objective or combination of objectives via
use of a continuous position sensor.
[0037] As used herein, the term "continuous" is used to refer to a
substantially uninterrupted sensing of position by the sensor 52.
For example, when used to continuously detect the position of the
rod member 50, the sensor 52 can detect the member's position
during all portions of its reciprocating motion, and not just at
certain discrete points (such as, at the upper and lower stroke
extents).
[0038] However, a continuous position sensor may have a particular
resolution (e.g., 0.001-0.1 mm) at which it can detect the position
of a member. Accordingly, the term "continuous" does not require an
infinitely small resolution.
[0039] Using the continuous position sensor 52, the control system
46 can be provided with an accurate measurement of an actuator 14
member position at any point in the member's reciprocation, thereby
dispensing with any need to perform calculations based on discrete
detections of position. It will be appreciated by those skilled in
the art that actual continuous position detection can be more
precise than such calculations of position, since various factors
(including known and unknown factors, such as, temperature, fluid
compressibility, fluid leakage, etc.) can affect the
calculations.
[0040] By continuously sensing the position of a member of the
actuator 14 at or near a top of the rod string 18, characteristics
of the rod string's reciprocating displacement are communicated to
the control system 46 at each point in the rod string's
reciprocating displacement. The control system 46 can, thus,
determine whether the rod string's 18 position, speed and
acceleration correspond to desired preselected values.
[0041] If there is a discrepancy between the desired preselected
values and the rod string's reciprocating displacement as detected
by the sensor 52, the control system 46 can change how energy is
supplied to the actuator 14 by the power source 12, so that the
reciprocating displacement will conform to the desired preselected
values. For example, the control system 46 may change a level,
timing, frequency, duration, etc., of the energy input to the
actuator 14, in order to change the rod string's upper or lower
stroke extent, or velocity or acceleration at any point in the rod
string's reciprocating displacement.
[0042] Note that the desired preselected values may change over
time. As mentioned above, it may be desirable to change the upper
or lower stroke extent, or the pumping rate, during the pumping
operation, for example, due to the level of the fluid interface 48
changing, reservoir depletion over time, detection of a pump-off,
pump-pound or gas-lock condition, etc.
[0043] Referring additionally now to FIGS. 2-5, examples of
different actuators 14 that may be used with the system 10 and
method are representatively illustrated.
[0044] These examples are not limiting of the scope of this
disclosure, but are instead provided to demonstrate that the
principles disclosed herein are applicable to a wide variety of
different actuator configurations.
[0045] In FIG. 2, the actuator 14 includes a piston member 54
sealingly and reciprocably disposed in a generally cylindrical
housing 56. The rod member 50 is connected to the piston member 54
and extends downwardly through a lower end of the housing 56.
[0046] The power source 12 in this example comprises a hydraulic
pressure source (such as, a hydraulic pump and associated
equipment) for supplying energy in the form of fluid pressure to a
chamber 58 in the housing 56 below the piston member 54. To raise
the piston member 54, the rod member 50 and the rod string 18,
hydraulic fluid at increased pressure is supplied to the chamber 58
from the power source 12. To cause the piston member 54, rod member
50 and rod string 18 to descend, the pressure in the chamber 58 is
reduced (with hydraulic fluid being returned from the chamber to
the power source 12).
[0047] In this example, the sensor 52 is attached externally to the
housing 56. In other examples, the sensor 52 could be positioned
internal to, or in a wall of, the housing 56. The scope of this
disclosure is not limited to any particular position or orientation
of the sensor 52.
[0048] A magnet 60 is attached to, and displaces with, the piston
member 54. A position of the magnet 60 (and, thus, of the piston
member 54) is continuously sensed by the sensor 52 during
reciprocating displacement of the piston member. A suitable magnet
for use in the actuator 14 is a neodymium magnet (such as, a
neodymium-iron-boron magnet) in ring form. However, other types and
shapes of magnets may be used in keeping with the principles of
this disclosure.
[0049] A suitable linear position sensor (or linear variable
displacement transducer) for use as the sensor 52 in the system 10
is available from Rota Engineering Ltd. of Manchester, United
Kingdom. Other suitable position sensors are available from Hans
Turck GmbH & Co. KG of Germany, and from Balluff GmbH of
Germany. However, the scope of this disclosure is not limited to
use of any particular sensor with the system 10.
[0050] In the FIG. 3 example, the sensor 52 is not mounted external
to the housing 56, but is instead positioned internal to another
housing 62 at a lower end of the actuator 14. In this manner, the
sensor 52 does not have to detect the position of the magnet 60
through a wall of the housing 62, and can be in closer proximity to
the magnet.
[0051] In addition, the magnet 60 in the FIG. 3 example is mounted
to the rod member 50, instead of to the piston member 54. Thus, the
position of any reciprocating member of the actuator 14 can be
continuously detected using an appropriately configured sensor 52.
Note that the actuator 14 in the FIG. 3 example is not necessarily
a hydraulic actuator.
[0052] In the FIG. 4 example, the actuator 14 comprises a cable,
ribbon, tape, belt or other flexible member 64 stored on a spool
66. The flexible member 64 extends upwardly about a sheave member
68 and downwardly to a connection with the rod member 50.
[0053] The spool 66 is driven by an electric motor 70 of the power
source 12, so that the flexible member 64 is alternately wound and
unwound about the spool, to thereby alternately raise and lower the
rod member 50. In this example, the power source 12 and the
actuator 14 may be conveniently combined, with the control system
46 controlling operation of the motor 70 to achieve a desired
reciprocating displacement of the rod member 50 and rod string 18
connected thereto (see FIG. 1).
[0054] The sensor 52 in the FIG. 4 example comprises a rotary
encoder capable of continuously detecting a rotational position of
the sheave member 68. In this manner, the position, velocity and
acceleration of the sheave member 68, the flexible member 64 and
the rod member 50 (and the upper end of the rod string 18) can be
continuously known.
[0055] The FIG. 5 example is similar in some respects to the FIG. 4
example, but the actuator 14 in the FIG. 5 example comprises a
hydraulic cylinder 72 for alternately raising and lowering the
sheave member 68 to thereby alternately raise and lower the rod
member 50. Similar to the FIG. 2 example, the FIG. 5 power source
12 comprises a hydraulic pressure source to alternately increase
and decrease fluid pressure applied to the cylinder 72.
[0056] The sensor 52 in the FIG. 5 example can comprise an infrared
or ultrasonic sensor for sensing the position of the sheave member
68 as it reciprocates upward and downward. Alternatively, the
sensor 52 could sense the position of another member of the
actuator 14 as it reciprocably displaces.
[0057] Referring additionally now to FIGS. 6-9, examples of
velocity profiles 74 that may be used with the system 10 and method
are representatively illustrated as graphs of velocity versus
position. The velocity profiles 74 may be used with other systems
and methods, in keeping with the scope of this disclosure.
[0058] Since the position of a reciprocating member of the actuator
14 (or an upper end of the rod string 18) can be detected at any
point in the displacement of the member, the control system 46 can
readily determine the velocity of the member at any point in the
displacement of the member (velocity equals the derivative of
position over time). This determination of velocity may be made by
the control system 46, or in some examples the sensor 52 may
provide an output of instantaneous velocity, as well as position.
In other examples, acceleration (equal to the derivative of
velocity over time) may also be determined by the control system
46, or may be provided as an output of the sensor 52.
[0059] In the FIG. 6 example, an upstroke begins at zero velocity
and at a lower stroke extent 76. The velocity rapidly increases,
and then levels off once the rod string 18 is displacing upward at
a desired rate. Note that the entire rod string 18 does not
displace as an infinitely rigid member. Instead, the rod string 18
has some elasticity and there are dampening effects present (such
as, friction between the rod string 18 and the tubing string 30,
etc.), so that the reciprocating displacement of a lower end of the
rod string at the downhole pump 20 is not the same as the
reciprocating displacement of the upper end of the rod string at
the surface.
[0060] Accordingly, a wave equation in the rod string 18 can be
solved, so that the velocity profile 74 to be maintained at the
surface corresponds to a desired velocity profile at the downhole
pump 20. The Everitt-Jennings algorithm may be used to solve the
wave equation (see Everitt, T. A. and Jennings, J. W., An Improved
Finite-Difference Calculation of Downhole Dynamometer Cards for
Sucker-Rod Pumps, SPE 18189, February 1992). Although the full
Everitt-Jennings algorithm produces a calculation of load versus
position, the algorithm can be used to calculate velocity (and
acceleration) as an intermediate step.
[0061] Thus, working "backward" from a desired velocity profile at
the downhole pump 20, solution of the wave equation produces a
corresponding desired velocity profile at the surface (e.g., at a
reciprocating member of the actuator 14, or an upper end of the rod
string 18). The desired velocity profile (either the desired
velocity profile at the surface, or the desired velocity profile at
the downhole pump 20 if the wave equation is to be solved by the
control system 46) may be input to the control system, and the
control system can then operate the power source 12 and the
actuator 14, so that any deviation of the velocity profile as
detected by the sensor 52 from the desired velocity profile is
minimized.
[0062] Referring again to the velocity profile 74 of FIG. 6, it
will be appreciated that, when the velocity increases rapidly from
the lower stroke extent 76, the upper end of the rod string 18 will
begin displacing before the lower end of the rod string. Thus, the
rapid velocity increase can be used to obtain displacement of the
lower end of the rod string 18 relatively quickly, and then the
velocity can level off once the entire rod string is
displacing.
[0063] Near an end of the upstroke, the velocity rapidly decreases
to zero velocity at the upper stroke extent 78. Note that there is
desirably a slope to the profile 74 prior to the upper stoke extent
78, instead of an abrupt reversal of direction, which would be
inefficient and possibly damaging to system components. Similarly,
although the profile 74 is depicted as being composed of straight
line segments, in practice the profile would have smoother
transitions.
[0064] The downstroke in the FIG. 6 example is a mirror image of
the upstroke. However, it is not necessary for this to be the case
and, as discussed more fully below, it can be beneficial for there
to be differences in the velocity profile 74 between the upstroke
and the downstroke.
[0065] In the FIG. 7 example, a slope of the velocity profile 74
changes multiple times on the upstroke after the lower stroke
extent 76 and prior to the upper stroke extent 78. The downstroke
is again a mirror image of the upstroke, and so the velocity
profile slope changes multiple times on the downstroke after the
upper stroke extent 78 and prior to the lower stroke extent 76.
[0066] Such changes in the velocity profile 74 may be used to
account for the fact that progressively more of the rod string 20
is being displaced over time after the upper and lower stroke
extents 78, 76, and that progressively more of the rod string is
being slowed to zero velocity prior to the upper and lower stroke
extents.
[0067] In the FIG. 8 example, the downstroke is a reversed mirror
image of the upstroke, with multiple velocity profile slope changes
after each of the lower and upper stroke extents 76, 78, and with a
single velocity slope change prior to each of the lower and upper
stroke extents. This example demonstrates that a wide variety of
different shapes are possible for the velocity profile 74.
[0068] In the FIG. 9 example, a maximum velocity (absolute value)
on the downstroke is much less than a maximum velocity on the
upstroke. This velocity profile 74 can be beneficial in avoiding a
gas-lock condition, since the reduced downstroke velocity can
provide more time for the downhole pump 20 to fill, as well as
provide more precise control over the lower stroke extent at the
downhole pump (momentum effects on the downward moving rod string
18 are more controllable and predictable, as compared to the
upstroke). In other examples, a reduced velocity may be provided on
the upstroke to reduce stresses in the rod string 18. Thus, the
scope of this disclosure is not limited to any particular velocity
profile, or to any particular relationship between upstroke and
downstroke velocity profiles.
[0069] Since the control system 46 knows the velocity at any point
during reciprocating displacement (the velocity being provided by
the continuous position sensor 52 output, or being calculated by
the control system based on the sensor output), the control system
can at any point during the reciprocating displacement compare the
detected velocity to the desired velocity, and vary operation of
the power source 12 and the actuator 14 as needed to minimize any
discrepancies. In this manner, the control system 46 can maintain a
preselected desired velocity profile at a member of the actuator
14, the rod string 18 at the surface, and the rod string at the
downhole pump 20.
[0070] In addition, the velocity profile 74 can be changed as
needed to achieve other objectives. For example, if it is desired
to change the position of the lower and/or upper stroke extents 76,
78, the velocity profile 74 can be appropriately changed, and the
control system 46 will accordingly change its operation of the
power source 12 and the actuator 14. Similarly, the velocity
profile 74 can be changed, if desired, to achieve increased
efficiency, increased production, reduced rod string wear,
increased rod string usable life, reduced electricity consumption
or peak load, or in response to changed conditions (such as,
depletion of a reservoir, pump-off, pump-pound, gas-lock,
etc.).
[0071] Referring additionally now to FIGS. 10 & 11, an example
technique or method 80 for controlling operation of the well
pumping system 10 is representatively illustrated in flowchart
form. In this method 80, it is desired to change one or both of the
lower and upper stroke extents 76, 78 at the surface, in order to
achieve a corresponding (although not necessarily equal) change in
stroke extent(s) of the rod string 18 at the downhole pump 20.
[0072] Similar methods or techniques may be used to achieve other
changes in the reciprocating displacement of the rod string 18 at
the downhole pump 20. For example, similar methods may be used to
change velocity, acceleration or stroke length of the rod string 18
at the downhole pump 20. Thus, the scope of this disclosure is not
limited to any particular change made in the reciprocating
displacement of the rod string 18.
[0073] In step 82 of the method 80, the stroke extents 76, 78 are
detected at the surface using the continuous position sensor 52.
The stroke extents 76, 78 correspond to minimum and maximum
displacement values detected by the sensor 52, and to positions at
which the velocity is zero.
[0074] The continuous position sensor 52 may detect the position of
a member of the actuator 14 (such as, the rod member 50, the piston
member 54, the sheave member 68 or another member), or the upper
end of the rod string 18 (for example, by positioning the sensor 52
in or on the stuffing box 44). The scope of this disclosure is not
limited to the position of any particular component being detected
by the continuous position sensor 52.
[0075] In step 84, a desired change to one or both of the stroke
extents 76, 78 is determined. For example, it may be desired to
increase a stroke distance by changing one or both of the stroke
extents 76, 78, in order to increase the pumping rate. As another
example, it may be desired to raise the lower stroke extent at the
downhole pump 20, in order to alleviate a pump-pound condition. As
yet another example, it may be desired to change one or both of the
stroke extents at the downhole pump 20, in order to increase a work
output of the system 10.
[0076] The determination of the desired change to one or both of
the stroke extents 76, 78 may be made automatically by the control
system 46 (for example, in response to detection of a pump-pound
condition, detection of a pump-off condition, detection of a
reduction in work output, etc.), or as part of a pre-programmed
routine (for example, to periodically adjust the lower stroke
extent, so that maximum compression is achieved on the downstroke
to avoid gas-lock). Alternatively, the determination may be made
elsewhere and then input to the control system 46 by a user.
[0077] In step 86, the control system 46 modifies the operation of
the power source 12 and actuator 14 as needed to achieve the
desired change. Since the continuous position sensor 52 provides to
the control system 46 a continuous output of position during the
reciprocating displacement, the control system can make any
appropriate changes in operation while the reciprocating
displacement continues, and without any need to change the sensor's
position relative to the actuator 14 or any other component of the
system 10.
[0078] The control system 46 can change operation of the power
source 12 and actuator 14, for example, by varying a duration,
level, relative timing, frequency, etc., of energy supplied to the
actuator from the power supply 12. An example is described more
fully below in relation to the graph illustrated in FIG. 12.
[0079] In FIG. 11, the step 84 of determining the desired change to
the stroke extent(s) at the surface is more particularly expanded
for a situation where it is desired to increase a work output at
the downhole pump 20. For example, work output at the downhole pump
20 may be monitored over time, and a decrease in work output can be
indicative of a pump-pound condition. Thus, if a decrease in work
output at the downhole pump 20 is detected, the method 80 can be
used to change the stroke extent(s) as needed to alleviate the
pump-pound condition and thereby increase the work output.
[0080] As mentioned above, the Elliott-Jennings algorithm may be
used to solve the wave equation in the rod string 18 and determine
load (force) versus position (displacement) at the downhole pump
20. Since work equals force applied over a distance, a force versus
displacement curve at the downhole pump 20 (also known to those
skilled in the art as a "downhole card") can be integrated to
determine work output.
[0081] In one technique, the lower stroke extent of the rod string
18 at the downhole pump 20 can be incrementally raised by the
control system 46 to thereby alleviate the pump-pound condition and
increase the work output. Steps 88-92 can be repeated for each
increment, until the work output is sufficiently increased.
[0082] For example, the control system 46 can monitor the work
output in step 88. In step 90, a desired change in the lower stroke
extent (the amount of the incremental raising) at the downhole pump
20 is determined. This desired change in the lower stroke extent at
the downhole pump 20 may be determined separately for each
occurrence of a pump-pound condition, or it may be preselected (for
example, by user input or initial programming of the control system
46).
[0083] In step 92, a desired change in the lower stroke extent at
the surface corresponding to the desired change in the lower stroke
extent at the downhole pump 20 is determined. Again, the solution
to the wave equation in the rod string 18 can be used to relate
reciprocating displacement at the downhole pump 20 to reciprocating
displacement at the surface (for example, using the
Elliott-Jennings algorithm or another suitable algorithm), in order
to determine the desired change in the lower stroke extent at the
surface.
[0084] The control system 46 can then modify operation of the power
source 12 and actuator 14 as needed to achieve the desired change
(as in step 86). The continuous position sensor 52 output will
confirm whether the modified operation in fact achieves the desired
change, and the control system 46 will make further modifications
as needed to minimize any discrepancies between the detected change
and the desired change in lower stroke extent at the surface.
[0085] Referring additionally now to FIG. 12, an example graph of
position and energy input versus time is representatively
illustrated. The graph demonstrates how characteristics of the
reciprocating displacement can be varied by modifying the energy
input to the actuator 14 from the power source 12.
[0086] As discussed above, the control system 46 can control the
energy input to the actuator 14 to achieve various objectives. In
the FIG. 12 example, an upper stroke extent (e.g., of an actuator
member, or the rod string 18 at the surface or at the downhole
pump) is desired to be raised, and two different ways of achieving
this objective are depicted in FIG. 12.
[0087] In a solid line, the position (for example, as detected by
the continuous position sensor 52 and optionally resulting from a
solution of the wave equation in the rod string 18) is depicted
over time prior to modification of the energy input to the actuator
14. The energy input over time is also depicted as a solid line
prior to modification.
[0088] Note that the upper stroke extent 78 occurs after the energy
input periodically decreases to a minimum level, and the lower
stroke extent 76 occurs after the energy input periodically
increases to a maximum level. This is due to inertia and friction
effects on the rod string 18, so that the rod string does not
immediately begin to displace upward when the energy input is
increased, and the rod string does not immediately begin to
displace downward when the energy input is decreased.
[0089] One technique of raising the upper stroke extent 78 is
depicted in relatively long dashed lines in FIG. 12. In this
technique, a duration of the maximum energy input level is
increased, so that the rod string 18 displaces upward over a
correspondingly increased duration. Since the rod string 18
displaces upward longer, the upper stroke extent 78 is raised.
[0090] Another technique of raising the upper stroke extent 78 is
depicted in relatively short dashed lines in FIG. 12. In this
technique, the maximum energy input level is increased, so that the
acceleration and velocity of the rod string 18 on the upstroke is
correspondingly increased. Since the rod string 18 displaces faster
upward, the upper stroke extent 78 is raised.
[0091] The example of FIG. 12 demonstrates that a variety of
different techniques and combinations of techniques may be used by
the control system 46 to modify the reciprocating displacement
characteristics of the rod string 18. Such techniques may be used
to modify the velocity (including upstroke and downstroke velocity
profiles), acceleration (including upstroke and downstroke
acceleration profiles), lower and upper stroke extents, and stroke
length of the rod string 18 at surface and at the downhole pump
20.
[0092] It may now be fully appreciated that the above disclosure
provides significant advancements to the arts of monitoring and
controlling operation of a well pumping system. In examples
described above, the well pumping system 10 can be precisely
controlled, in part by utilizing the continuous position sensor 52
to provide substantially continuous output of position to the
control system 46 as the actuator 14 reciprocates the rod string
18.
[0093] The above disclosure provides to the art a well pumping
system 10. In one example, the well pumping system 10 can include
an actuator 14 that reciprocably displaces a rod string 18, a
continuous position sensor 52 that continuously detects a position
of a member (such as, the rod member 50, the piston member 54 or
the sheave member 68) of the actuator 14, and a control system 46
that modifies reciprocal displacement of the rod string 18 by the
actuator 14, in response to an output of the continuous position
sensor 52.
[0094] The control system 46 can modify the reciprocal displacement
of the rod string 18, without displacement of the continuous
position sensor 52 relative to the actuator 14.
[0095] The control system 46 can modify a stroke extent 76, 78 of
the actuator 14 member, in response to the output of the continuous
position sensor 52.
[0096] The control system 46 can modify a stroke extent 76, 78 of
the rod string 18 at surface, in response to the output of the
continuous position sensor 52.
[0097] The control system 46 can modify a stroke extent 76, 78 of
the rod string 18 proximate a downhole pump 20, in response to the
output of the continuous position sensor 52.
[0098] The control system 46 can maintain a preselected velocity
profile 74 of the actuator 14 member, in response to the output of
the continuous position sensor 52.
[0099] The control system 46 can maintain a preselected velocity
profile 74 of the rod string 18 at surface or proximate a downhole
pump 20, in response to the output of the continuous position
sensor 52.
[0100] A well pumping method is also provided to the art by the
above disclosure. In one example, the method can comprise:
reciprocably displacing a rod string 18; continuously detecting a
velocity profile with a continuous position sensor 52; and
modifying the velocity profile while the rod string 18 reciprocably
displaces, in response to an output of the continuous position
sensor 52.
[0101] The modifying step can include changing a duration of the
velocity profile (e.g., between the lower and upper stroke extents
76, 78). The changing step may be performed while the rod string 18
reciprocably displaces.
[0102] The modifying step can include changing a position at which
an actuator 14 member (such as, the rod member 50, the piston
member 54 or the sheave member 68) velocity is zero, with the
position being detected by the continuous position sensor 52. The
changing step may be performed while the rod string 18 reciprocably
displaces.
[0103] The modifying step can include changing a position at which
the rod string 18 velocity is zero at a downhole pump 20 (e.g., the
lower or upper stroke extent 76, 78). The changing step may include
solving a wave equation in the rod string 18.
[0104] The modifying step may include minimizing differences
between the detected velocity profile and a preselected velocity
profile 74. The modifying step may include maintaining acceleration
of the rod string 18 less than a preselected level (e.g., to limit
stresses in the rod string 18).
[0105] Another example of a well pumping method described above can
comprise: reciprocably displacing a rod string 18 with an actuator
14; continuously detecting a position of a member (such as, the rod
member 50, the piston member 54 or the sheave member 68) of the
actuator 14 with a continuous position sensor 52; and modifying
reciprocating displacement of the rod string 18 by the actuator 14,
in response to an output of the continuous position sensor 52.
[0106] The modifying step may be performed without displacing the
continuous position sensor 52 relative to the actuator 14.
[0107] The modifying step may comprise varying a periodic energy
input to the actuator 14 relative to the reciprocating displacement
of the actuator 14 member as detected by the continuous position
sensor 52. The varying step can include varying a duration and/or
level of the energy input, in response to the output of the
continuous position sensor 52.
[0108] The modifying step may include varying a stroke extent 76,
78 of the actuator 14 member, in response to the output of the
continuous position sensor 52. The varying step can comprise
displacing the stroke extent 76, 78 until either: a) the stroke
extent as detected by the continuous position sensor 52 is
positioned at a preselected stroke extent, or b) the stroke extent
has displaced a preselected distance as detected by the continuous
position sensor 52.
[0109] The modifying step may include modifying a stroke extent 76,
78 of the rod string 18 at surface, and/or proximate a downhole
pump 20, in response to the output of the continuous position
sensor 52. Modifying the stroke extent 76, 78 of the rod string 18
proximate the downhole pump 20 can comprise solving a wave equation
in the rod string 18.
[0110] The modifying step may include maintaining a preselected
velocity profile 74 of the actuator 14 member, and/or the rod
string 18 at surface, in response to the output of the continuous
position sensor 52.
[0111] The modifying step may include maintaining a preselected
velocity profile 74 of the rod string 18 proximate a downhole pump
20, in response to the output of the continuous position sensor 52.
The step of maintaining the preselected velocity profile 74 of the
rod string 18 proximate the downhole pump 20 may include solving a
wave equation in the rod string 18.
[0112] The modifying step may include maintaining a preselected
velocity profile 74, during the reciprocating displacement of the
rod string 18, in response to the output of the continuous position
sensor 52.
[0113] Although various examples have been described above, with
each example having certain features, it should be understood that
it is not necessary for a particular feature of one example to be
used exclusively with that example. Instead, any of the features
described above and/or depicted in the drawings can be combined
with any of the examples, in addition to or in substitution for any
of the other features of those examples. One example's features are
not mutually exclusive to another example's features. Instead, the
scope of this disclosure encompasses any combination of any of the
features.
[0114] Although each example described above includes a certain
combination of features, it should be understood that it is not
necessary for all features of an example to be used. Instead, any
of the features described above can be used, without any other
particular feature or features also being used.
[0115] It should be understood that the various embodiments
described herein may be utilized in various orientations, such as
inclined, inverted, horizontal, vertical, etc., and in various
configurations, without departing from the principles of this
disclosure. The embodiments are described merely as examples of
useful applications of the principles of the disclosure, which is
not limited to any specific details of these embodiments.
[0116] In the above description of the representative examples,
directional terms (such as "above," "below," "upper," "lower,"
"raised," "lowered," etc.) are used for convenience in referring to
the accompanying drawings. However, it should be clearly understood
that the scope of this disclosure is not limited to any particular
directions described herein.
[0117] The terms "including," "includes," "comprising,"
"comprises," and similar terms are used in a non-limiting sense in
this specification. For example, if a system, method, apparatus,
device, etc., is described as "including" a certain feature or
element, the system, method, apparatus, device, etc., can include
that feature or element, and can also include other features or
elements. Similarly, the term "comprises" is considered to mean
"comprises, but is not limited to."
[0118] Of course, a person skilled in the art would, upon a careful
consideration of the above description of representative
embodiments of the disclosure, readily appreciate that many
modifications, additions, substitutions, deletions, and other
changes may be made to the specific embodiments, and such changes
are contemplated by the principles of this disclosure. For example,
structures disclosed as being separately formed can, in other
examples, be integrally formed and vice versa. Accordingly, the
foregoing detailed description is to be clearly understood as being
given by way of illustration and example only, the spirit and scope
of the invention being limited solely by the appended claims and
their equivalents.
* * * * *