U.S. patent application number 15/432542 was filed with the patent office on 2018-08-16 for linear pumping system and methods for controlling the same.
The applicant listed for this patent is Alkhorayef Petroleum Company Limited. Invention is credited to David S. Shanks.
Application Number | 20180230992 15/432542 |
Document ID | / |
Family ID | 63104610 |
Filed Date | 2018-08-16 |
United States Patent
Application |
20180230992 |
Kind Code |
A1 |
Shanks; David S. |
August 16, 2018 |
LINEAR PUMPING SYSTEM AND METHODS FOR CONTROLLING THE SAME
Abstract
An example linear pumping system suitable for small size and low
flow rate operation. The system includes a pump casing that
encloses a linear motor and one or two (an upper and lower) pumps.
The pump casing may include an upper fluid inlet port, a lower
fluid inlet port, and a fluid-outlet port. The linear motor
includes a stator and a mover, where the mover includes an upper
plunger portion and a lower plunger portion and is configured to
move alternately up and down relative to the stator. The upper and
lower pumps positioned on both sides of the mover may each include
a pump chamber, a fluid inlet valve, and a fluid outlet valve. In
operation, hydraulic pressure from the upper and lower pump outlet
valves causes fluid within an interior cavity of the pump casing to
be expelled through the fluid outlet port. The motion of the mover
can be controlled using pressure and/or plunger position
measurements.
Inventors: |
Shanks; David S.; (Aberdeen,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Alkhorayef Petroleum Company Limited |
Al-Khobar |
|
SA |
|
|
Family ID: |
63104610 |
Appl. No.: |
15/432542 |
Filed: |
February 14, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04B 17/03 20130101;
F04B 2207/046 20130101; F04B 53/18 20130101; F04B 2203/0405
20130101; F04B 2201/0201 20130101; F04B 1/12 20130101; E21B 43/128
20130101; F04B 47/06 20130101; F04B 49/06 20130101; F04B 49/12
20130101; F04B 17/044 20130101; F04B 2205/03 20130101; F04B 53/1002
20130101; F04B 19/22 20130101 |
International
Class: |
F04B 49/06 20060101
F04B049/06; E21B 43/12 20060101 E21B043/12; F04B 47/06 20060101
F04B047/06; F04B 19/22 20060101 F04B019/22; F04B 17/03 20060101
F04B017/03; F04B 1/12 20060101 F04B001/12; F04B 53/18 20060101
F04B053/18; F04B 53/10 20060101 F04B053/10 |
Claims
1. A linear pumping system, comprising: (a) a pump casing having an
interior cavity and at least one fluid inlet port receiving fluid
from outside the pump casing, and at least one fluid outlet port
expelling fluid from the interior cavity to the outside of the pump
casing; (b) a linear motor enclosed within the pump casing and
including a stator and a mover, the mover including a plunger and
being configured to move alternately up and down with respect to
the stator; and (c) a first pump enclosed within the pump casing
and including a first pump chamber, a first pump fluid inlet valve
configured to receive fluid into the first pump chamber from
outside the pump casing through the at least one fluid inlet port
of the pump casing, and a first pump fluid outlet valve configured
to expel fluid from the first pump chamber into the interior cavity
of the pump casing, wherein the first pump chamber is configured to
receive a top portion of the plunger of the linear motor mover, the
received top plunger portion causing fluid to be drawn into the
first pump chamber through the first pump inlet valve on a
downstroke of the linear motor mover, and causing fluid to be
expelled from the first pump chamber into the interior cavity of
the pump casing through the first pump outlet valve on an upstroke
of the linear motor mover; and wherein hydraulic pressure from the
first pump causes fluid within the interior cavity of the pump
casing to be expelled through the fluid outlet port of the pump
casing.
2. The linear pumping system of claim 1, further comprising (d) a
second pump enclosed within the pump casing and including a second
pump chamber, a second pump fluid inlet valve configured to receive
fluid into the second pump chamber from outside the pump casing
through the at least one fluid inlet port of the pump casing, and a
second pump fluid outlet valve configured to expel fluid from the
second pump chamber into the interior cavity of the pump casing,
wherein the second pump chamber is configured to receive a bottom
portion of the plunger of the linear motor mover, the received
bottom plunger portion causing fluid to be drawn into the second
pump chamber through the second pump inlet valve on an upstroke of
the linear motor mover, and causing fluid to be expelled from the
second pump chamber into the interior cavity of the pump casing
through the second pump outlet valve on a downstroke of the linear
motor mover; and wherein hydraulic pressure from the first pump and
the second pump causes fluid within the interior cavity of the pump
casing to be expelled through the fluid outlet port of the pump
casing.
3. The linear pumping system of claim 1, wherein the linear motor
further includes an expandable diaphragm that seals oil within the
linear motor and is configured to allow the oil within the linear
motor to expand or contract with temperature.
4. The linear pumping system of claim 2, wherein the first and
second pump fluid inlet valves and first and second pump fluid
outlet valves are one-way valves that are configured to operate in
any orientation.
5. The linear pumping system of claim 4, wherein at least one of
the first and second pump fluid inlet valves and first and second
pump fluid outlet valves comprises a ball valve having a buoyant
ball.
6. The linear pumping system of claim 4, wherein at least one of
the first and second pump fluid inlet valves and the first and
second pump outlet valves comprises a ball valve having a metallic
ball and a magnetic valve seat.
7. The linear pumping system of claim 2, wherein the first and
second pump fluid inlet ports are configured to receive fluid in a
direction that is substantially perpendicular to a lengthwise
direction of the first and second pump chambers.
8. The linear pumping system of claim 2, further comprising one or
more pressure sensors configured to measure pressure within at
least one of the first and second pump chambers.
9. The linear pumping system of claim 8, further comprising a motor
controller that is configured to control movement of the linear
motor based at least in part on pressure measured by the one or
more pressure sensors.
10. The linear pumping system of claim 9, wherein the motor
controller is configured to control one or more motion parameters
of the linear motor dependent on the pressure measured within at
least one of the first or second pump chambers.
11. The linear pumping system of claim 2, further comprising one or
more sensors configured to determine a location of the mover in
relation to at least one of the first and second pump chambers.
12. The linear pumping system of claim 11, further comprising a
motor controller configured to control a stroke length of the
linear motor based at least in part on the position of the
mover.
13. The linear pumping system of claim 1, further comprising one or
more temperature sensors configured to measure an operating
temperature of the linear motor.
14. The linear pumping system of claim 13, further comprising a
motor controller that is configured to control one or more motion
parameters of the linear motor based at least in part on the
measured operating temperature of the linear motor.
15. The linear pumping system of claim 14, wherein the motor
controller is configured to stop movement of the linear motor if
the measured operating temperature of the linear motor reaches a
predetermined threshold.
16. A method of controlling operation of a linear pumping system
for use in an oil or gas well, the linear pumping system including
a linear motor and one or more pump chambers, comprising: measuring
pressure within the one or more pump chambers of the linear pumping
system; measuring a position of a plunger rod of the linear motor
in relation to the one or more pump chambers; and controlling
movement of the plunger rod within the one or more pump chambers
based at least in part on the measured pressure and position.
17. The method of claim 16, wherein a stroke length of the linear
motor is controlled based at least in part on the measured position
to cause a maximum penetration of the plunger rod within the one or
more pump chambers.
18. The method of claim 16, wherein movement of the linear motor is
stopped if the measured pressure exceeds a predetermined
threshold.
19. The method of claim 16, further comprising: measuring an
operational temperature of the linear motor; and controlling
movement of the linear motor based at least in part on the measured
operational temperature.
20. The method of claim 19, wherein movement of the linear motor is
stopped if the measured operational temperature exceeds a
predetermined threshold.
21. The method of claim 16, further comprising the step of using at
least one of (a) pressure measurements within the one or more pump
chambers and (b) linear motor temperature to provide an estimate of
the fluid/gas mixture in the portion of the oil or gas well where
the linear pumping system is located.
Description
FIELD
[0001] The technology described herein relates generally to a
linear pumping system, and more particularly to systems and methods
for pumping fluids from an oil or gas well.
BACKGROUND
[0002] The oil and gas industry relies heavily on pumping systems
with seventy percent or more of the world's oil wells requiring
some sort of a pump to produce fluids. Linear pump technology is
the most commonly used pump technology in the oil industry. More
specifically, the most common type of pumps used in wells having a
low flow rate or a small well bore size and also with gas wells is
the sucker rod driven linear pump. However, sucker rod driven
linear pumps are typically not efficient at low flow rates because
their slow operation and large pump size requires a very large
amount of force to lift fluid, even at a low flow rate. These pumps
may also have other disadvantages, such as a moving rod seal on the
well head that is prone to leaking, and operating poorly in the
presence of gas, as well as a pumping chamber that cannot be
stroked until empty because the plunger is on the end of a long rod
string, many thousands of feet long. There is therefore a need in
the industry for a system for pumping fluids from an oil or gas
well that operates efficiently at low flow rates and addresses
disadvantages associated with the prior art.
SUMMARY
[0003] An example linear pumping system and methods of operation
are provided. An example linear pumping system may include a pump
casing that encloses a linear motor and one or preferably two pumps
designated herein for convenience upper and lower pump. In an
embodiment, the pump casing includes an upper fluid inlet port, a
lower fluid inlet port, and a fluid-outlet port. The linear motor
includes a stator and a mover, where the mover may include an upper
plunger portion and a lower plunger portion and is configured to
move alternately up and down relative to the stator when the motor
is powered up. In embodiments, the upper pump may include an upper
pump chamber, an upper pump fluid inlet valve, and an upper pump
fluid outlet valve, and the lower pump may include a lower pump
chamber, a lower pump fluid inlet valve, and a lower pump fluid
outlet valve. In operation, hydraulic pressure from the upper and
lower pump outlet valves causes fluid within an interior cavity of
the pump casing to be expelled through the fluid outlet port of the
pump casing.
[0004] In embodiments, an upper pump fluid inlet valve may be
provided between the upper pump chamber and the upper fluid inlet
port and is configured to receive fluid into the upper pump chamber
from outside of the pump casing. An upper pump fluid outlet valve
may be provided between the upper pump chamber and an interior
cavity of the pump casing and is configured to expel fluid from the
upper pump chamber into the interior cavity of the pump casing. The
upper pump chamber may be configured to receive the upper plunger
portion of the linear motor mover, where the upper plunger portion
causes fluid to be drawn into the upper pump chamber through the
upper pump inlet valve on a downstroke of the linear motor mover
and causes fluid to be expelled from the upper pump chamber through
the upper pump outlet valve on an upstroke of the linear motor
mover.
[0005] In embodiments, a lower pump fluid inlet valve may be
provided between the lower pump chamber and the lower fluid inlet
port and is configured to receive fluid into the lower pump chamber
from outside of the pump casing. A lower pump fluid outlet valve
may be provided between the lower pump chamber and the interior
cavity of the pump casing and configured to expel fluid from the
lower pump chamber into the interior cavity of the pump casing. The
lower pump chamber may be configured to receive the lower plunger
portion of the linear motor mover, where the lower plunger portion
causes fluid to be drawn into the lower pump chamber through the
lower pump inlet valve on the upstroke of the linear motor mover
and causes fluid to be expelled from the lower pump chamber through
the lower pump outlet valve on the downstroke of the linear motor
mover.
[0006] An example method of controlling operation of a linear
pumping system for use in an oil or gas well, where the linear
pumping system includes a linear motor and one or more pump
chambers, may include the steps of: measuring pressure within the
one or more pump chambers of the linear pumping system; measuring a
position of a plunger rod of the linear motor in relation to the
one or more pump chambers; and controlling movement of the plunger
rod within the one or more pump chambers based at least in part on
the measured pressure and/or position. In embodiments, a stroke
length of the linear motor may be controlled based at least in part
on the measured position of the plunger rod to cause a maximum
penetration of the plunger rod within the one or more pump
chambers. In embodiments, movement of the linear motor may be
stopped if the measured pressure exceeds a predetermined threshold.
Example methods of controlling operation of a linear pumping system
for use in an oil or gas well may further include the steps of
measuring an operational temperature of the linear motor; and
controlling movement of the linear motor based at least in part on
the measured operational temperature. In embodiments, movement of
the linear motor may be stopped if the measured operational
temperature exceeds a predetermined threshold.
[0007] The invention is described as advantageously having two
pumping chambers, one on either end of the linear motor. This
arrangement provides several advantages over other arrangements,
principally balanced forces on the motor and near continuous
pumping. However it should be noted that this pump arrangement also
provides redundancy, and that if one pumping chamber fails the
second one may continue to operate, providing some failure
tolerance. It is also true that in a vertical well bore one can
observe what is known as a pump-off. Pump-off is a phenomenon
occurring when pumping action draws the fluid column down below the
pump intake. A pump-off situation will significantly increase the
gas intake, reducing the pump efficiency. Thus, if the surrounding
fluid level gradually drops (pumping off) the upper chamber will
draw gas (or gassy fluids) before the lower chamber, and so the
pump described herein should not pump off suddenly. This asymmetric
behavior of the pump will be an indication to the control system of
a pump off condition, and will provide the mechanism to control
pumping under such common conditions. This is an additional
advantage of the pump design disclosed herein. It is also obvious
that when one pump fails or operates in a pump-off condition, the
pump in this disclosure will advantageously function as a simplex
pump, with either only the upper or lower pump chambers pumping
fluid.
[0008] The proposed duplex pump design in which two pumps are
arranged on either side of the motor is also believed preferable to
alternate designs in which the duplex pumps are mounted either
completely above or completely below the motor. While such
arrangements may potentially provide a simpler mechanical interface
between the motor and the pump, this is offset due to a more
complicated design of the pumping chambers and the considerable
complexity required in the design of flowing fluid paths to achieve
full duplex pumping.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 depicts an example linear pumping system for pumping
fluids from an oil or gas well in accordance with this
disclosure.
[0010] FIGS. 2A, 2B, 2C, and 2D depict an example of the fluid
pumping action of the linear pumping system shown in FIG. 1.
[0011] FIG. 3 is a stroke-pressure diagram illustrating an example
method of operating a linear pumping system to regulate pressure
buildup within the pump chambers.
[0012] FIGS. 4A, 4B, and 4C are diagrams illustrating different
types of linear motors that can be used in different
embodiments.
[0013] FIGS. 5A and 5B illustrate an embodiment of a linear motor
with a mover and stator, and the mechanism to control the motion of
a mover relative to the stator.
[0014] FIGS. 6A, 6B, 6C, and 6D are a series of diagrams
illustrating how the pump behavior can be determined from the
piston pressure.
DETAILED DESCRIPTION
[0015] FIG. 1 depicts an example linear pumping system for pumping
fluids from an oil or gas well. The left-hand portion 14 of FIG. 1
shows separate components of a partially disassembled linear
pumping system, and the right-hand portion 16 of FIG. 1 depicts a
fully assembled pumping system.
[0016] The example linear pumping system depicted in FIG. 1
includes a pump casing 11 that encloses a linear motor comprising
stator 5 and mover 15, an upper pump 12 and a lower pump 6, such
that the linear motor (including stator 5 and mover 15) is
integrated into the pump assembly. The pump casing 11 includes an
upper fluid inlet port 22, a lower fluid inlet port 23, and a fluid
outlet port 1.
[0017] As noted, the linear motor includes a stator 5 and a mover
15. The linear motor mover 15 includes a plunger rod made of
mechanically strong material that is surrounded by permanent
magnets 9 at a center portion of the rod, defining an upper plunger
portion 8 extending above the permanent magnets 9 and a lower
plunger portion 19 extending below the permanent magnets 9. In
embodiments, the plunger rod of the linear motor may have a small
diameter (e.g., less than one inch) to provide a pump system that
is suitable for use in deep wells at low flow rates and also
pumping fluid from a small diameter oil or gas well. A person of
skill in the art will appreciate that the primary advantage of a
small pump is that it reduces the force the linear motor has to
generate to move the pump plunger, which in turn makes the pump
small and cheaper to build. In operation, the linear motor mover 15
is caused to move alternately up and down within the motor assembly
when the stator 5 is coupled to a power source. The up and down
movement of the linear motor mover 15 within the linear motor
assembly is respectively referred to herein as the upstroke and
downstroke of the linear motor.
[0018] In an embodiment, the linear motor may be an oil-filled
motor assembly to improve longevity and provide a highly efficient
motor with close tolerances between the mover 15 and stator 5. Oil
may be contained in the motor assembly using pressure balancing
diaphragms made from a soft material, such as silicone or an
elastomer, to allow the oil to expand and contract with
temperature. In the example illustrated in FIG. 1, oil is sealed
within the motor assembly by moving seals 3, 17 that provide seals
between the mover 15 and the upper and lower pump chambers 2, 13.
The illustrated example further includes bellows 4, 18 that allow
the oil to expand and contract with temperature within the motor
chamber.
[0019] The upper and lower pumps (12 and 6, respectively) each
include a fluid inlet valve 7, 10 and a fluid outlet valve 21, 20
respectively, and each define a pump chamber 2 (upper) and 13
(lower) for receiving the upper and lower plunger rod portions 8,
19 of the linear motor mover 15. Specifically, the upper pump
chamber 2 is configured to receive the upper plunger portion 8 and
the lower pump chamber 13 is configured to receive the lower
plunger portion 19, as illustrated by the fully assembled pump
shown on the right-hand side 16 of FIG. 1. In this way, a duplex
pump is formed with minimal complexity and size from two simplex
pumps mounted on either end of the linear motor (stator 5 and mover
15), allowing fluid to be pumped in both stroking directions.
[0020] The fluid inlet (7, 10) and outlet (21, 20) valves to the
upper and lower pump chambers 2, 13 are one-way valves (i.e.,
non-return valves), and are preferably configured to allow the
linear pumping system to operate in any orientation without being
dependent on gravity. Specifically, the fluid inlet valves 7, 10
are one-way valves that are respectively coupled between the upper
and lower pump chambers 2, 13 and the upper and lower fluid inlet
ports at 22, 23, and are configured to receive fluid into the pump
chambers 2, 13 from outside of the pump casing 11. The fluid inlet
valves 7, 10 may preferably be coupled to fluid inlet ports 22, 23
that are oriented such that the fluid inlets are not in line with
the length of the pumping chamber, as shown in the illustrated
embodiment. The fluid outlet valves 21, 20 are one-way valves that
are respectively coupled between the upper and lower pump chambers
2, 13 and an interior cavity 24 of the pump casing 11, and are
configured to expel fluid from the pump chambers 2, 13 into the
interior cavity 24 of the pump casing. In an embodiment, the
one-way inlet (7, 10) and outlet (21, 20) valves may comprise
buoyant balls in ball valves that are configured to move with the
fluid without being dependent on gravity. The buoyant ball valves
may, for example, utilize a retaining spring force provided by a
spring return mechanism. In another example, the buoyant ball
valves may include buoyant metallic balls (e.g., hollow metal
balls) and magnets in the ball seats to attract the balls back into
the valve seat. Other one-way valves known in the art may also be
used, as appropriate.
[0021] In operation, on an upstroke of the linear motor mover 15,
fluid is drawn into the lower pump chamber 13 and expelled from the
upper pump chamber 2, and on a downstroke of the linear motor mover
15, fluid is drawn into the upper pump chamber 2 and expelled from
the lower pump chamber 13. Fluid from both pump chambers 2, 13 is
expelled into the interior cavity 24 of the pump casing 11, and the
resulting hydraulic pressure causes the fluid to be expelled
through the fluid outlet port 1 of the casing, for example into a
fluid pipeline. The linear pump system may preferably be configured
to operate in an oil or gas well at a minimum of 20 strokes per
minute and a maximum of 1200 strokes per minute, such that the pump
system may achieve reasonable flow rates with small diameter
pumping chambers. An example of the fluid pumping action of the
linear pumping system is shown in the diagrams of FIG. 2.
[0022] The example illustrated in FIGS. 2A-2D depicts the operation
of a linear pumping system in four stages, where certain reference
numerals used in FIG. 1 have been omitted for clarity. The linear
pumping system in the illustrated example is submersed within a
fluid 25, such as oil. In the first stage (FIGS. 2A to 2B) of
operation, a down stroke of the linear motor causes a suction
within the upper pump chamber 2 that draws fluid into the upper
pump chamber 2 through the upper fluid inlet port 22. In the second
stage (FIGS. 2B to 2C) of operation, an upstroke of the linear
motor causes the fluid to be expelled from the upper pump chamber 2
through the one-way fluid outlet valve 21 into an interior cavity
24 of the pump casing. On the same upstroke of the linear motor in
the second stage (FIGS. 2B to 2C) of operation, a suction is
created in the lower pump chamber 13, drawing fluid into the lower
pump chamber 13 through the lower fluid inlet port 23.
[0023] In the third stage of operation (FIGS. 2C to 2D), the next
down stroke of the linear motor causes fluid to refill the upper
pump chamber 2 and fluid to be expelled from the lower pump chamber
13 through the one-way fluid outlet valve 20 and into the interior
cavity 24 of the pump casing. At the third stage of operation,
fluid expelled from both the upper and lower pump chambers 2, 13
has intermixed within the interior cavity 24 of the pump casing,
and the resulting hydraulic pressure causes fluid to exit the pump
casing through the fluid outlet port 1. Similarly, in the fourth
stage of operation (FIGS. 2C to 2D), the next upstroke of the
linear motor causes fluid to refill the lower pump chamber 13,
fluid to be expelled from the upper pump chamber 2 into the
interior cavity of the pump casing 24, and fluid to exit the pump
casing through the fluid outlet port 1. The linear pumping system
then continues to cycle between the third and fourth operational
stages (FIGS. 2C, 2D), pumping fluid out of the pump casing from
the fluid outlet port 1 on each upstroke and down stroke of the
linear motor.
[0024] In embodiments of the disclosure, the linear pumping system
includes one or more sensors (not shown here) that are configured
to measure the location of the motor mover 15 within the motor
assembly. In embodiments, the linear pumping system may further
include a motor controller (not illustrated) that is configured to
regulate the movement and stroke of the pumping system based at
least in part on the measured location of the motor mover 15. In
this way, the upper and lower plunger rod portions 8, 19 may be
cycled to the end of their respective pump chambers 2, 13,
providing a maximum compression ratio for the pump.
[0025] In specific embodiments of the disclosure, the linear
pumping system may include one or more sensors (not shown) that are
configured to measure the pressure and/or temperature within the
pump chambers 2, 13. In embodiments, the linear pumping system may
further include a motor controller (not shown) that is configured
to regulate the movement and stroke of the pumping system based at
least in part on the measured pressure within the pump chambers 2,
13 in order to regulate pressure, e.g., to prevent the pump from
becoming hydraulically locked. In this way, the linear pumping
system may provide full compression on gassy fluids and reduced
compression on fluids.
[0026] FIG. 3 is a stroke-pressure diagram illustrating an example
of how a linear pumping system may be controlled to regulate
pressure buildup within the pump chambers. The diagram in FIG. 3
includes an example plot of measured pressure within a pump chamber
during a cycle (i.e., upstroke and downstroke) of the linear motor.
The plotted solid line is an example of a normal pump cycle that
includes a ramping portion 31 where pressure is building within the
chamber, followed by a flowing portion 33 (i.e., the horizontal
flat portion) where fluid is pumped out of the chamber. If a pump
outlet becomes blocked, however, then pressure will continue to
build within the pump chamber, as illustrated in FIG. 3 by the
continuation of the ramping pressure shown by the dotted line 32.
By monitoring the pressure within the pump chamber, the pump
movement may be regulated to stop movement of the pump when the
pressure reaches a predetermined threshold. In the illustrated
example, pump movement is stopped at position 34 to prevent any
further increase in pressure. The pump may, for example, be
regulated to stroke only to position 34 to maintain the maximum
possible pressure, or to stop under control of the motor
controller. Details of the implementation control following this
processing operation are familiar to those of skill in the art and
need not be described in detail.
[0027] In another example, a feedback system similar to that shown
in FIG. 3 may be used to monitor and control the motor stator
temperature. The linear motor may, for example, be stopped if the
stator temperature reaches a predetermined threshold, or may be
regulated to slow the motor or cause the motor to operate with a
reduced stroke to maintain the stator temperature below the
predetermined threshold (i.e., the maximum operating temperature.)
Again, details of the practical implementation of such control need
not be described in detail.
[0028] In yet additional embodiments, the linear pumping system may
be further configured to measure or compute the amount of gas in
the pump based on the motor current and chamber pressures. In this
way, the stroke length of the linear motor may be altered to better
suit the fluid being pumped, allowing the linear pumping system to
operate effectively with fluids of different viscosities and with
varying amounts of intermixed gas.
[0029] Linear motors can be implemented with a simple coils and
metal structure where the induction of large currents in the mover
creates movement, a linear induction motor. A linear motor can also
be implemented with a reluctance linear motor with several windings
and an alternating magnetic mover so that moving the field along
the length of the motor provides movement of the mover. This
implementation is a synchronous linear reluctance motor. The third
possibility is to incorporate permanent magnets into the mover
and/or stator increasing the flux density and energy density of the
motor, which is a synchronous permanent magnet linear motor. FIGS.
4A-4C illustrate this principle.
[0030] In FIG. 4A, a linear induction motor is shown with active
windings in the stator 42 and a cylindrical solid metal mover 41.
The motor is an induction motor inducing high currents in the solid
mover. In FIG. 4B the motor consists of a stator 44 with
alternating magnetic properties and a stator 43 with alternating
field coils. The field in the stator coils is alternated to create
a moving magnetic force which can be alternated to create linear
motion, as illustrated in more detail in the following FIG. 5B. The
control and switching of the stator windings has to be synchronized
to the position of the mover, hence the term synchronous motor can
be used.
[0031] In FIG. 4C, the motor consists of a stator 46 with
alternating magnetic properties (and in one embodiment permanent
magnets) and a stator 45 with alternating field coils, and
permanent magnets. The field in the stator coils is alternated to
create a moving magnetic force which can be alternated to create
linear motion. The control and switching of the stator windings has
to be synchronized to the position of the mover, hence the term
synchronous permanent magnet motor can be used.
[0032] The issue of the manner in which motion can be controlled in
a linear oscillating motor as shown above has several important
aspects. The main areas of concern in controlling the motor motion
is starting and controlling the stops and starts at the ends of the
motion range.
[0033] FIG. 5A illustrates again a mover 15 and stator 5 in a
specific embodiment. FIG. 5B provides a closer look at the magnetic
system. In particular, as shown, the mover has several pairs of
alternating magnetic elements 52 and 53 that make up the complete
mover, while the stator has several alternating windings 50 and 51.
It will be appreciated that in the above arrangement reversing the
electrical field in windings 50 and 51 (and all the other stator
windings) in anti-phase results in moving the mover in one
direction or the other. To create continuous movement, the fields
in windings 50 and 51 must remain in one polarity until a pair of
magnetic elements in the mover moves over the windings pair. Once
the pair of magnetic elements in the mover moves past the pair of
windings, the fields in the stator windings must be reversed to
then continue the movement to the next pair of stator field coils.
Reversing the fields again continues the movement of the mover
15.
[0034] This principle of operation requires the stator fields to be
reversed at a frequency dependent on the distance between the
magnetic components and the linear speed of the motor. Accordingly,
for this motor to operate, the stator field coils must be switched
at the correct point to create a moving field which is always
creating motion in one direction. When the mover approaches the end
of its stroke, the rate of field switching should preferably be
slowed to slow down the motion of the mover, and also finally be
applied out of phase to stop the motion. Preferably, the system
will ramp down the linear mover velocity toward the end of the
stroke, bringing the mover to a halt a very small distance away
from the end of the mechanical travel, without making contact with
the end of the pump chamber. Such operation requires sensing of the
position of the mover and in particular determining how close the
mover is to the end of the stroke.
[0035] Sensing of the mover position is therefore important in the
control of a linear synchronous motor. There are several methods of
control that can be used in different embodiments. One simple
control mechanism in applications where the motor will operate a
long way from the power supply in a deep well, is to sense the
current drawn by the stator coils. This current is proportional to
the relative position of the mover magnetic circuit (whether
passive, as in a reluctance motor or active with a permanent magnet
motor). Thus, by sensing the current drawn by the stator it is
possible to establish where the mover is relative to the stator. It
is, however, problematic to determine how close the mover is to the
end of travel. One possible method of establishing this end of
travel position is to switch fields slowly at start up until the
mover comes in contact with the end of the pump chamber, at which
point the stator coil current will increase rapidly, and the mover
will not move. Once the end position is known, the controller can
simply count the stator current changes as the mover moves through
the stator windings. Since the size of the motor is known and the
number of coils is known, counting the current changes can be used
as a position sensor.
[0036] In alternative embodiments, electronic position sensors may
be fitted to the motor so that its absolute position and velocity
can be sensed real time. This approach provides more accurate and
direct feedback for controlling the motion of the mover. A person
of skill in the art will appreciate details of the implementation
of such control mechanisms, which are thus not discussed in further
detail.
[0037] Controlling the motion of the mover in the manner described
above is another aspect of this invention. In particular, in this
aspect the general control mechanism which in its simplest form is
used to create linear oscillating motion of the mover relative to
the stator, is also further controlled to adapt the pump behavior
to respond more appropriately to changing fluid conditions in the
pump. The main additional aspects of control include prevention of
over pressure, adapting the motor speed to react to motor winding
over temperature, and dealing with gassy fluids and gases.
[0038] Over pressure can happen because of stuck valves, or heavy
fluids, deep wells, etc. To address such conditions, in a specific
embodiment a pressure sensor can be fitted to one or both of the
pumping chambers. Data from this pressure sensor(s) can be used to
regulate the motor velocity and stop the motor short of the end
position to prevent over pressure. Mechanisms to take into account
pressure sensor data to control the mover are described in more
detail below.
[0039] In alternative embodiments, if the motor winding temperature
is measured or computed, this temperature can be regulated by
simply shutting the motor off if it gets too hot, or slowed down to
reduce the power consumption to a level where the temperature rise
becomes stable.
[0040] Additionally, it will be appreciated that gassy fluids will
cause reduced pressure build up as the gas compresses with the
stroking of the pump. This means that the pump and motor can move a
lot faster during the compression stroke and only slow down again
as the gas reaches the opening pressure of the non-return valve.
With this understanding, in accordance with another embodiment the
velocity profile of the pump can be changed to make it pump gassy
fluids more effectively. Such a change can be implemented in
practice by measuring the pressure in the pumping chamber or, where
no pressure sensor is available, the current drawn by the motor. At
any given depth this current will be proportional to the force
developed, and so the force required to stroke the pump can be
calculated from the motor current. It will also be appreciated that
the motor current is also proportional to the depth of the pump and
the friction in the seals, which can also be taken into account for
more accurate control.
[0041] Implementation details of these and other control mechanisms
will be appreciated by those of skill in the art, and employed in
practical implementations without departing from the principles of
this invention. The following description is intended to provide
additional detail and illustration.
[0042] FIG. 6A shows one of the two identical pumping sections in
FIG. 1, illustrating that the pressure at the fluid inlet port 22
may be measured using a sensor 70. Pressure in the piston chamber 2
may also be measured using a second sensor. In different
embodiments, the position of the mover 8 can be measured using an
additional down hole sensor 63, or computed at the surface.
[0043] FIG. 6B shows the pressure build up in the chamber with the
piston moving during one stroke of the piston. In an upstroke of
the piston, the fluid in the chamber is compressed, with the
pressure building as the velocity of the motor increases and the
pressure rises to overcome the tubing pressure, opening the upper
valve. This portion of the diagram is illustrated by line 64. Then,
as the valve opens, the pressure becomes steady at constant
velocity, as illustrated by line 65. The pressure is directly
proportional to force and so the motor current will also provide a
measure of cylinder pressure, albeit also related to several other
factors like friction and pump mover inertia. Accordingly, one can
measure the activity in the pump chamber either directly with
pressure sensors (such as 70), or indirectly via the motor
current.
[0044] FIG. 6C illustrates a pump chamber with some fluid and some
gas in it. This combination leads to a complex pressure stroke
diagram with different segments, such as 66, 67 and 68 illustrated
in FIG. 6C, corresponding to different stages in the mover stroke
and fluid-gas combinations. In particular, the initial pressure
rise will be slow and the piston will initially compress the gas,
leading to a stroking pressure with the gas in compression and the
incompressible fluid flowing. In the case of a complex fluid-gas
mixture, the pressure stroke overall diagram is likely to be
complex as gas under pressure will likely release rapidly through
the exit valve.
[0045] FIG. 6D illustrates a chamber filled with gas, which will
restrict the pressure achievable as the pump compresses the gas it
may never generate enough pressure as shown by line 69 in FIG. 6D
to open the valve, or it may in the final portion of the pump
stroke compress the gas sufficiently to open the exit valve.
[0046] It is an intention of this invention that either using
pressure sensors and/or current measurement one can measure the
pressure behavior in the pump chambers and determine the fluid and
gas mix the pump is working with. Importantly, in accordance with
an aspect of the invention, information about the fluid mix in the
chamber can be used to adjust the pump control, so the piston
movement suits the property of the mix.
[0047] Note that in the event the pump is immersed in gas only,
this will alter the pressure and current behavior as indicated
above, but also reduce the cooling available to the motor, and
accordingly would also result in increased motor winding
temperatures. The measurement of motor temperature is therefore a
useful measurement, as well as the pressure to determine what fluid
or gas mixture the pump is working in.
[0048] This application uses examples to illustrate the invention,
the scope of which is determined by the attached claims. Other
examples falling within the scope of the invention may be apparent
to those of skill in the art. It is noted that the figures
described herein are not necessarily to scale. Certain features of
the instant disclosure may be shown exaggerated in scale or in
somewhat schematic form, and some details of conventional elements
may not be shown in the interest of clarity and conciseness. It is
to be recognized that the different teachings of the embodiments
discussed herein may be employed separately or in any suitable
combination to produce the desired results.
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