Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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LINEAR ROD PUMP APPARATUS AND METHOD
FIELD OF THE INVENTION
[0002] This invention relates to pumping of fluids, such as water and/or
hydrocarbons,
from subterranean formations or reservoirs, and more particularly to a pumping
apparatus
and method for use in such pumping applications.
BACKGROUND OF THE INVENTION
[0003] For many years, the familiar "horse head", walking beam-type
mechanism has
been used for pumping fluids such as water and/or oil from subterranean
formations. An
example of such a walking beam apparatus 50, connected to a polished rod 52
extending
from a well head 54 of a well 56, is illustrated as prior art in the attached
FIG. I.
[0004] Conventional walking beam apparatuses have a number of
disadvantages, not the
least of which is their large size. In addition, performance of the walking
beam pump
apparatus is largely a function of the design and connection of a number of
mechanical
parts, which include massive counter-weights and complex drive mechanisms
which are
difficult to control for obtaining maximum pumping efficiency or to compensate
for
changes in condition of the well over time.
[0005] As shown in FIG. 1, because of their large size and weight, walking
beam-type
pumping mechanisms must typically be mounted on a heavy concrete foundation
58, which
may be poured in place or pre-cast, located adjacent the well head 54.
Construction of a
walking beam pumping mechanism, together with its foundation, typically
involves the
efforts of several construction workers, over a period which may be a week or
more, to
prepare the site, lay the foundation 58, and allow time for the foundation 58
to cure, in
addition to the time required for assembling the various components of the
walking beam
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mechanism 50 onto the foundation 58 and operatively connecting the mechanism
to the
polished rod 52. In general, because of the costs of transporting the
apparatus and the
concrete or pre-cast foundation to what may be a remote site and the
complexity of the site
preparation and assembly process, walking beam-type pumping mechanisms are
generally
only utilized in long-term pumping installations.
[0006] The large size and massive weight of the walking beam pumping
mechanism and
its foundation are also problematic when the well 56 is decommissioned.
Economic and
contractual obligations may require complete removal of the walking beam
mechanism and
its foundation. It is desirable, therefore, to provide an improved apparatus
and method for
operating the well 56, which eliminates, or at least greatly reduces, the
significant
expenditures in time, manpower, and money required to install and remove a
pumping
apparatus used for extracting fluid from the well 56.
[0007] Another disadvantage of walking beam-type pumping apparatuses is
that they
cannot typically operate at pumping speeds much below 5 strokes per minute. As
a result, it
has been necessary in the past, to only pump intermittently or to decommission
wells which
could not sustain pumping at rates of at least 5 strokes per minute, even
though such wells
would be capable of continued operation at lower pumping speeds. Intermittent
pumping
creates problems caused by varying levels of fluid in the well casing and
tubing and
collection of contaminants into the pump during "off" periods. As mentioned
above,
decommissioning a well equipped for pumping with a walking beam-type mechanism
is an
arduous and costly task. Further, government regulations frequently require
the costly
process of sealing the well 56 with cement or other sealing means when a well
is
decommissioned. It would be desirable, therefore, to provide an improved
apparatus and
method, for pumping fluid from the well 56, which could operate at
considerably slower
pumping rates than a walking beam-type mechanism, in a form that could be
connected to
the polished rod 52 in place of a walking beam mechanism 50, at an existing
well 56, to
thereby extend the useful life of the well 56 by operation at a pumping speed
lower than
could otherwise be accomplished by the walking beam-type apparatus. If such an
improved
pumping apparatus and method were available in a form that could be quickly
and simply
installed on an existing well 56, the necessity for, and cost related to,
decommissioning the
well, and in particular the cost related to sealing the well and removal of
the walking beam
mechanism and its foundation could be deferred, perhaps indefinitely, while
the well 56 is
operated at a low pumping rate.
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[0008] Because of their large size and complexity, walking beam-type
pumping
mechanisms typically need to be shut-down and repaired on site. Although there
have been
attempts in the past to develop portable walking beam apparatuses, such as
those described
in U.S. Patent No. 4,788,873, to Laney, such portable walking beam pumping
apparatuses
have not gained widespread acceptance in the art. It would be desirable,
therefore, to have
an improved pumping apparatus and method, in which the pumping apparatus could
be
readily transported to a well, and quickly installed in place of an existing
walking beam
apparatus, or another one of the improved pumping apparatuses previously
attached to the
well, to thereby substantially reduce downtime of the well during the process
of performing
maintenance and/or repairs of the pumping apparatus. It would also be
desirable for such an
improved pumping apparatus and method to allow for convenient installation
and/or
removal of the improved pumping apparatus, substantially in a completely
assembled form,
which could be initially assembled, or repaired, offline, at a location remote
from the well,
while the well was continuing to operate with another of the improved pumping
apparatuses.
[0009] Another problem inherent in the use of walking beam-type pumping
apparatuses
is that the apparatus must typically extend a substantial distance above
ground level in order
to achieve a desired pumping stroke length on the order of 3 to 6 feet. At
such substantial
heights it may be difficult, if not impossible, to operate irrigation
equipment, for example,
in close proximity to the walking beam pumping apparatus, where such
irrigation equipment
must pass over the top of the walking beam apparatus. U.S. Patent No.
6,015,271, to Boyer
et al. discloses a stowable walking beam pumping unit having a foldable
support structure to
allow storage of the pumping unit in a low profile position. A stowable
walking beam
pumping unit, as disclosed by Boyer, has not been shown to be commercially
viable,
however. It is desirable, therefore, for an improved pumping apparatus and
method to be
operable in a form having a low enough profile that other equipment, such as
irrigation
pipes mounted on rolling supports can safely pass above the pumping apparatus.
[0010] U.S. Patent No. 4,114,375, to Saruwatari discloses replacing the
conventional
walking beam pumping apparatus with a pump jack device including a double
acting piston
and cylinder motor, with the piston rod of the motor being adapted to be
connected to the
polished rod projecting upwardly from a well head. A variable displacement
hydraulic
pump, driven by a motor or engine, is included in a closed hydraulic loop
wherein conduits
are connected to a pair of output ports of the pump. A pump control means
controls the
direction and volume of flow in the loop so as to establish the stroke of the
piston rod. A
compressible fluid counter-balance is provided for accumulation of energy
during a down
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stroke of the piston rod so that the energy may be returned to the piston
during the upstroke.
The counter-balance cylinder may be mounted coaxially above the motor and an
additional
closed chamber may be provided in fluid communication with a charged chamber
of the
counter-balance.
[0011] To date, the apparatus of Saruwatari has not achieved commercial
success.
[0012] Regardless of the type of pumping apparatus utilized, controlling
and optimizing
the performance of a sucker-rod pumping apparatus involves inherent
difficulties. One
factor which must be taken into account is the stretching of the rod string,
which occurs
during the upward portion of each pump stroke, and the corresponding
contraction of the
rod string which occurs during the downward portion of each pump stroke. The
rod string,
which may be 1000 feet or more long, acts much like an extension spring, which
is
stretched during the portion of the pump stroke in which the rod string is
drawing the fluid
upward within the well, and which then contracts back to an essentially un-
stretched state as
the rod string moves downward during a return portion of the pump stroke. As a
result of
the rod stretch, an above-ground upward stroke of 32 inches, for a well
approximately 1300
feet deep, may only result in a down-hole stroke in the range of 24 to 26
inches, for
example. The difference between the magnitude and direction of movement of the
polished
rod at the top of the well and the corresponding reaction of the rod string
and down-hole
stroke of the pump involves other complicating factors, including inherent
damping within
the rod string, fluid damping which occurs during the pump stroke and
longitudinal
vibrations and natural frequencies of the rod string.
[0013] An additional difficulty occurs where the fluid being pumped upward
from the
well contains a significant amount of entrained gas. In such circumstances, a
suction effect
during the upward stroke of the rod string causes the entrained gas to bubble
out of the fluid
and form a foamy segment at the top of the column of fluid being pulled upward
toward the
surface through action of the down-hole components of the sucker-rod pump.
Specifically,
a typical down-hole pump portion of a sucker-rod pump, apparatus is located at
the bottom
of a length of tubing terminating in a fluid outlet above the surface of the
ground and
includes a standing valve, located at the lower end of the down-hole pump, and
a traveling
valve, which is attached to the bottom end of the rod string and is movable by
the rod string
within the down-hole pump above the standing valve. The standing valve
performs a
check-valve function which allows fluid to flow into the lower end of the down-
hole pump
when the pressure within the down-hole pump is lower than the pressure in the
well casing
outside of the down-hole pump. When pressure within the down-hole pump is
equal to, or
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greater than, the pressure outside of the down-hole pump, the check-valve
function of the
standing valve closes to preclude movement of fluid out of the down-hole pump
through the
standing valve. The traveling valve also includes a check-valve function,
which works
substantially oppositely to the check-valve function of the standing valve.
When the
pressure within the down-hole pump below the traveling valve is lower than the
pressure
within the tubing above the traveling valve, the traveling valve is closed.
Conversely, when
the pressure within the down-hole pump below the traveling valve is greater
than the
pressure within the tubing above the traveling valve, the traveling valve
opens and allows
fluid movement through the traveling valve, so that the traveling valve can
descend through
the fluid in the down-hole pump.
[0014] By virtue of this arrangement, as the rod string pulls the traveling
valve upward,
during the upward portion of the pump stroke, the traveling valve is closed,
and the upward
motion of the traveling valve within the tubing generates a suction in the
down-hole pump
below the traveling valve which causes the standing valve to open and allow
fluid to be
drawn upward into the portion of the down-hole pump between the standing and
traveling
valves. Where the sucker-rod pump is pumping a fluid with no entrained gas, as
soon as the
rod string begins the downward portion of its stroke, the standing valve
closes and the
stationary valve opens, to thereby trap fluid within the down-hole pump above
the standing
valve, and allow the traveling valve to move downward through the trapped
fluid within the
down-hole pump, toward the standing valve, to the bottom of the pump stroke,
where the
rod string reverses direction and begins to pull the traveling valve upward at
the start of the
next pump stroke.
[0015] For the above-mentioned exemplary well, pumping water for dewatering
coal
bed methane and having a depth of approximately 1300 feet, the fluid load
being moved
upward by each stroke of the pump once the entire length of tubing has been
filled, for
example, would be 5400 pounds, and the weight of the rod string would be
approximately
1800 pounds. As a result, during each stroke of the pump, the load on the rod
string varies
approximately by the 5400 pound fluid load, which causes a significant change
in the length
of the rod string, as the rod string stretches and contracts during each pump
stroke. Fluid
damping effects which occur as a result of the movement of the traveling valve
upward and
downward through fluid within the tubing and viscous effects related to the
flow of the fluid
upward within the tubing also affect the dynamic performance of the rod
string.
[0016] Other complications also occur in wells having a fluid in the form
of a liquid
having entrained gas. In these wells, the traveling valve does not open
immediately as it
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begins the downward portion of its movement within the down-hole pump, due to
the
presence of the foamy portion of the fluid column existing between the
traveling valve and
the liquid portion of the fluid column. The traveling valve must travel
downward in the
down-hole pump some distance while compressing the gas which has foamed out of
the
fluid before the suction effect dissipates to the point where the pressure
difference across
the traveling valve is such that the traveling valve can open.
[0017] As will be readily understood by those having skill in the art,
accurately
predicting the down-hole performance of the sucker-rod pump for a given input
at the
polished rod above the surface of the ground is a challenging design problem,
with the
specific difficulties discussed briefly above being far from totally
inclusive.
[0018] The problems of effectively and efficiently operating a sucker-rod
pump
apparatus are addressed in significantly greater detail in a commonly assigned
U.S. Patent,
No. 7,168,924 B2, to Beck et al., titled "Rod Pump Control System Including
Parameter
Estimator." The Beck et al. patent also discloses a rod pump control system,
which includes
a parameter estimator that determines, from motor data, parameters relating to
operation of
the rod pump and/or generating a down-hole dynamometer card, without the need
for
external instrumentation such as down-hole sensors, rod load sensors, flow
sensors, acoustic
fluid level sensors, etc. In some embodiments disclosed by Beck et al., having
a pumping
apparatus driven by an electric motor, instantaneous current and voltage,
together with
pump parameters estimated through the use of a computer model of the sucker-
rod pump,
are used in determining rod position and load. The rod position and load are
used to control
the operation of the rod pump to optimize operation of the pump. Beck et al.
also discloses
a pump-stroke amplifier that is capable of increasing pump stroke without
changing the
overall pumping speed, or in the alternative, maintaining the well output with
decreased
overall pumping speed.
[0019] The commonly assigned Beck et al. patent, also provides a detailed
description
of the considerable additional complexity involved in operating a sucker-rod
pump with a
walking beam pumping apparatus, or with prior belt driven pumping units, and
further
provides a method and apparatus for efficiently and effectively controlling a
sucker-rod
pumping apparatus having a rod string driven by a walking beam pumping
apparatus, or
other types of previously-known pumping apparatuses.
[0020] With regard to the present invention, the detailed descriptions
within Beck et al.,
of the manner in which the inherent difficulties of operating a sucker-rod
pump apparatus
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are compounded by a complex pumping apparatus such as the typical walking-beam-
type
apparatus serve as ample evidence of the desirability of providing a new and
improved
pumping apparatus for use with a sucker-rod pump, which is not subject to the
multitude of
complexities involved in controlling prior pumping apparatuses such as the
typical walking-
beam-type pumping apparatus.
[0021] Even though the performance of walking-beam pump and other types of
prior
pumping apparatuses can be substantially improved through practicing the
teachings of
Beck et al., it is, therefore, still highly desirable to provide an improved
apparatus and
method for use in pumping fluids such as water and/or hydrocarbons from
subterranean
formations and reservoirs in a form overcoming problems such as, and in
addition to, those
discussed above. It is further desirable that such improvements be provided in
a form which
is considerably smaller in physical size than conventional walking beam
apparatuses and
also in a form which is less complex and more readily controllable and/or
adjustable than
prior conventional walking beam-type apparatuses. It is further desirable that
such an
improved apparatus and method provide advancements over the pump jack device
of
Saruwatari, in a form that is commercially viable.
BRIEF SUMMARY OF THE INVENTION
[0022] The invention provides an improved apparatus and method for pumping
fluids,
such as water and/or hydrocarbons, from a subterranean formation or reservoir,
through use
of a linear rod pumping apparatus having a linear mechanical actuator
arrangement and a
reversible motor operatively connected for imparting reciprocating,
substantially vertical
motion to a rod string of a sucker-rod pump. The linear mechanical actuator
arrangement
has a substantially vertically movable member attached to the polished rod of
the sucker-rod
pump for imparting and controlling vertical motion of the rod string of the
sucker-rod pump.
The reversible motor has a reversibly rotatable element thereof operatively
connected to the
substantially vertically movable member of the linear mechanical actuator
arrangement in a
manner establishing a fixed relationship between the rotational position of
the motor and the
linear position of the vertically movable member.
[0023] Apparatus and methods, in accordance with the present invention,
have
demonstrated their commercial viability, and the considerable advantages that
can be
obtained through practice of the invention, during operational field testing
on actual
hydrocarbon wells.
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[0024] In some forms of the invention, a linear rod pumping apparatus
includes a
mechanical rack and pinion drive arrangement adapted for attachment to a
pumping
mechanism, such as the polished rod at the top of a rod string in a
hydrocarbon well. The
rack gear of the rack and pinion drive arrangement is adapted for connection
to, and
translating movement with, the polished rod. The pinion gear does not
translate with the
rack gear, and is driven by a reversible motor for effecting up and down
reciprocating
motion of the rack gear and pumping mechanism.
[0025] In some forms of the invention, a compressible gas cylinder is
utilized to provide
a counter-balancing force which counteracts generally downwardly directed
forces which
are inherently applied to the reciprocating pumping mechanism by the rod
string.
[0026] In other forms of the invention, a linear rod pump apparatus,
according to the
invention, is utilized without a pressurized gas counter-balance cylinder.
[0027] In some forms of the invention, the pinion gear is driven by a
reversible electric
motor. The electric motor may be driven by an electronic drive, having a
configuration in
accordance with the invention, with the drive being controlled by a controller
configured
according to the invention.
[0028] A drive and/or controller, according to the invention, may provide
energy
storage and/or dynamic braking to accommodate energy generation within the
drive circuit,
resulting from reversals in direction of rotation of the drive motor and/or
inherent cyclical
fluctuations on the electrical buses of the drive mechanism, particularly
during the
downward stroke of the pump mechanism, when gravitational force is essentially
driving
the motor as a generator.
[0029] In various embodiments of the invention, energy generated during the
pumping
process may be stored within a capacitor baffl( section of the drive and used
on a subsequent
upstroke of the pump for enhancing overall pumping efficiency of a linear rod
pump
apparatus and/or method, according to the invention. Alternatively, in some
forms of the
invention, the drive includes a regenerative control section, which modulates
energy
generated during the pumping cycle in such a manner that it can be transferred
back to the
source of electrical power supplying power through the drive to the motor. In
yet other
forms of the invention, the drive may include a dynamic braking section, in
which electrical
energy developed during the pumping process is dissipated across a dynamic
braking
resistor, of the drive, according to the invention.
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[0030] A given embodiment of a drive and controller, according to the
invention, may
include any one or all of the aforementioned: capacitor baffl( section;
regenerative control
section; and/or dynamic braking section. In some forms of the invention, all
three sections
will be provided within the drive, to allow for adaptation of the drive for
operation in
various installations. Where it is not desirable, or practical, to transfer
power back to the
source of electrical power to the drive, such as might be the case in an
installation having an
engine driven electrical generator, the invention may utilize only one or both
of the
capacitor bank section or dynamic brake section of the drive. Should
circumstances change,
such as electrical power from a power grid becoming available at the well
site, so that the
engine driven generator can be eliminated, the drive can then be simply
reconfigured to
make use of the regenerative control section.
[0031] A linear mechanical actuator arrangement, according to the
invention, may
include a rack and pinion gearing arrangement, with the rack being disposed
for operation in
a substantially vertical direction, for reciprocating motion along a pumping
axis. The rack
may be operatively connected in gear mesh relationship with the pinion, and
the pinion may
be operatively connected to the rotating output of the reversible motor, such
that rotation of
the motor in a first direction is accompanied by a substantially vertically
upward motion of
the rack along the pumping axis, and such that a substantially vertically
downward motion
of the rack along the pumping axis is accompanied by rotation of the motor
rotatable
element in a second direction opposite the first direction. The rack may also
be operatively
connected to the rod of the sucker-rod pump for imparting vertically upward
motion to the
rod of the sucker-rod pump along the pumping axis when the rack is moving
upward. The
rack may be further operatively coupled to the rod of the sucker-rod pump such
that the rod
exerts a substantially vertically downward directed force on the rack while
the rack is
moving downward, acting substantially along the pumping axis, during a portion
of the
pump stroke.
[0032] In some forms of the invention, the rack of a rack and pinion
gearing
arrangement has a longitudinally directed opening therein, extending along the
pump axis
from a bottom end of the rack to the top end of the rack when the linear
mechanical actuator
is operatively disposed above the sucker-rod pump. The rack may further have
an upper
end thereof adapted for operative attachment of the rod thereto.
[0033] The upper end of the rack may define a hole extending therethrough,
and an
upper load bearing surface. The hole in the upper end may be configured such
that the
upper end of the rod may slideably extend through the hole. The linear
mechanical actuator
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arrangement may further include a rod securing clamp or collar fixedly
attached to the
upper end of the rod above the upper end of the rack. Such a rod securing
clamp or collar
may have a lower load bearing surface thereof adapted for bearing contact with
the upper
load bearing surface of the upper end of the rack for transferring force
between the rod and
the upper end of the rack when the lower load bearing surface of the collar is
in contact with
the upper load bearing surface of the upper end of the rack.
[0034] In some forms of the invention, a rack, of a rack and pinion gearing
arrangement,
may be configured to have a substantially U-shaped cross-section, with first
and second legs
of the U extending from a bight section thereof, in such a manner that the
legs and bight
define a longitudinally extending opening in the rack having the form of an
open channel
disposed about the pumping axis, with an outer surface of the bight that faces
substantially
oppositely from the legs including gear teeth of the rack, configured for
engagement with
corresponding gear teeth of the pinion.
[0035] A linear rod pumping apparatus, according to the invention, may
further include
one or more guide rollers, disposed to bear against the longitudinally
extending distal edges
of the legs of the rack at a point or points substantially opposite the
pinion, for urging the
rack into gear mesh relationship with the pinion. An apparatus, according to
the invention,
may further include a pair of guide bars bearing against the legs of the rack,
substantially
opposite from one another, for urging the rack into axial gear mesh
relationship with the
pinion.
[0036] An apparatus, according to the invention, may also include a pinion
housing
having a longitudinally extending opening therein, disposed about the pumping
axis, for
passage therethrough of the rack, and defining a rotational axis of the
pinion. The rotational
axis of the pinion may be laterally offset from, and extend substantially
perpendicularly to,
the pumping axis. A first anti-drive end of the pinion may be journaled in a
pinion bearing
disposed in and mounted to the pinion housing. A second drive-end of the
pinion may be
adapted for connection to an output element of a drive mechanism such as a
motor or
gearbox, and for being supported by an output bearing of the drive mechanism.
[0037] Some forms of an apparatus, according to the invention, may include
a gearbox
operatively connected between the motor and the linear mechanical actuator
apparatus. The
gearbox may have an input element thereof operatively attached to the
rotatable element of
the motor for rotation therewith. The gearbox may also have an output element
thereof
operatively attached to the pinion for rotation therewith. In some forms of
the invention, the
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input and output elements of the gearbox may be arranged substantially at a
right angle to
one another, with the output element being oriented for alignment with and
rotation
substantially about the pinion axis, and with the input element of the gearbox
and the
rotatable element of the motor being oriented substantially parallel to the
pumping axis.
[0038] Some forms of the invention also include a control arrangement,
operatively
connected to the motor, for controlling the motor. The control arrangement may
operate the
motor in a driving mode to urge upward movement of the rack on a lifting
portion of the
stroke of the pump rod. The control arrangement may also operate the motor in
a braking
mode, during downward movement of the rack, on a return/fill portion of the
stroke of the
pump rod.
[0039] In some forms of the invention, the control arrangement may include
an energy
storage element for storing energy generated during the braking mode of
operation of the
motor. In other forms of the invention, the control arrangement may be
configured for
utilizing the stored energy in the energy storage element to assist in driving
the motor
during the driving mode. In some forms of the invention, the control
arrangement may
include an energy dissipation element for dissipating energy generated during
the braking
mode of operation of the motor. In some forms of the invention, a control
arrangement may
be selectively configurable for operation of one or the other of the energy
storage and
energy dissipation modes. A control arrangement, according to the invention,
may further
include sensing arrangements for sensing one or more parameters of the group
of
parameters consisting of: linear position of the rack along the pumping axis;
rotational
position of the pinion about the pinion axis; motor torque; motor speed; motor
acceleration;
and motor input power.
[0040] A control arrangement, according to the invention, may include a
pump rod
dynamics model, for use in controlling operation of the motor. In forms of the
invention
having a sensing arrangement, the sensing arrangement may determine linear
position of the
rack twice during each pump cycle, once on the upstroke and once on the
downstroke.
[0041] A control arrangement, according to the invention, may be configured
for
detecting fault conditions and applying corrective action to modify operation
of the motor.
Fault conditions which may be detected, in accordance with the invention, may
include, but
are not limited to: loss of power to the motor; invalid or missed position
reference; non-
filling of the pump; and motor overheating. Corrective actions may include,
but are not be
limited to, applying braking force through the motor, or actuation of brake
mechanisms
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external to the linear rod pumping arrangement; changing stroke length and/or
frequency;
dwelling for a period of time in an off position; or operating the motor to
slowly lower the
rack to the lower mechanical limit of travel.
[0042] The invention may be practiced with a variety of different types of
motors,
including, electrical, hydraulic, and pneumatic.
[0043] An apparatus, according to the invention, may also include a
pneumatic energy
storage element operatively connected for storing energy generated during
downward
movement of the vertically movable element, and utilizing the stored energy
for aiding
upward vertical movement of the vertically movable element. In forms of the
invention
including a rack and pinion, the pneumatic energy storage element may be
operatively
connected for storing energy generated during the downward movement of the
rack, and
releasing the stored energy for aiding upward movement of the rack.
[0044] In some forms of the invention, a spring member is operatively
positioned below
the lower end of the rack and configured for engaging and applying an upwardly
directed
force to the lower end of the rack when the lower end of the rack has moved
beyond a
normal lower position of the rack during a pump stroke. In some forms of the
invention, a
spring member operatively positioned below the lower end of the rack may be
positioned
and configured for engaging and applying an upwardly directed force to the
lower end of
the rack during a portion of each pump stroke.
[0045] Some forms of the invention include an oil sump disposed around the
lower end
of the rack and configured for containing a volume of lubricant therein and
for receiving a
portion of the rack adjacent the lower end of the rack to thereby apply the
lubricant to the
rack. The sump and the volume of lubricant therein may be configured and
positioned such
that the portion of the rack is immersed into the lubricant during at least a
portion of each
stroke of the pump. The sump may include an inner and outer longitudinally
extending,
radially spaced tubular wall, sealingly connected at lower ends thereof to
define an annular-
shaped cavity therebetween, for receipt within the cavity of the volume of
lubricant, and
terminating in an annular-shaped opening between the upper ends of the inner
and outer
tubular walls. The inner tubular wall of the sump may have, an inner periphery
thereof
disposed about the pump rod, and an outer periphery thereof disposed within
the opening in
the rack. The outer tubular wall of the sump may have an inner periphery
thereof disposed
about the rack.
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[0046] In an apparatus having a sump, according to the invention, the
apparatus may
further include a spring member operatively positioned within the cavity in
the sump below
the lower end of the rack and configured for engaging and applying an upwardly
directed
forced to the lower end of the rack when the lower end of the rack has moved
beyond a
normal position of the rack during a pump stroke. In some forms of the
invention, such a
spring member, operatively positioned within the cavity of the sump below the
lower end of
the rack, may be configured for engaging and applying an upwardly directed
force to the
lower end of the rack during a portion of each pump stroke.
[0047] Some forms of the invention include a position sensing arrangement
for sensing
a position of the rack along the pump axis. The position sensing arrangement
may include a
stationary position sensor and a sensor flag. The stationary position sensor
is disposed
adjacent the rack substantially at a mid-stroke position along the pumping
axis. The sensor
flag is attached to the rack and disposed such that the flag is juxtaposed
with, and sensed by,
the sensor during each pumping stroke.
[0048] In some forms of sensing arrangements, according to the invention,
an upper
sensor flag and a lower sensor flag are axially spaced from one another along
the rack, to
form a gap between the upper and lower flags, with the gap being substantially
centrally
disposed along the rack. The upper sensor flag extends substantially from the
upper end of
the rack to a lower edge of the upper sensor flag defining an upper end of the
gap between
the upper and lower sensor flags, and the lower sensor flag extends
substantially from the
lower end of the rack to an upper edge of the lower sensor flag defining the
lower end of the
gap between the upper and lower sensor flags. With such an arrangement, the
sensor may
produce an output having a substantially square-wave shape, with a step change
from a first
state, whereat one or the other of the flags is juxtaposed with the sensor, to
a second state
whereat the gap is juxtaposed with the sensor.
[0049] The invention may also be practiced in the form of a method for
constructing,
operating, maintaining, or replacing a linear rod pumping apparatus according
to the
invention.
[0050] In one form of the invention, a method is provided for operating a
linear rod
pumping apparatus including a linear mechanical actuator arrangement and a
reversible
motor, where the linear mechanical actuator has a substantially vertically
movable member
adapted for attachment thereto of the rod of a sucker-rod pump, for parting
and controlling
vertical motion of the rod of the sucker-rod pump. The reversible motor has a
reversibly
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rotatable element thereof, operatively connected to the substantially vertical
member of the
linear mechanical actuator arrangement in a manner establishing a fixed
relationship
between the rotational position of the rotatable element of the motor and the
vertical
position of the vertically movable member, with the method including,
operating the motor
in a manner imparting reciprocating substantially vertical motion to the
vertically movable
member. The method may further include determining dynamic operation of the
pump rod,
and controlling the motor in accordance with the dynamic operation of the pump
rod.
[0051] A method, according to the invention, may include operating the
motor in a
driving mode, for applying torque to the rotatable element of the motor in a
first direction to
urge rotation of the rotatable element in the first direction and upward
movement of the
vertically movable member on an upward portion of a stroke of the pump rod. A
method,
according to the invention, may further include operating the motor in a
braking mode, for
applying a net torque to the rotatable element in the first direction, for
resisting rotation of
the rotatable element in the opposite direction during downward movement of
the vertically
movable member on a downward portion of the stroke of the pump rod.
[0052] In some forms of the invention, the motor generates energy during
the braking
mode, and a method, according to the invention, may further include extracting
at least a
portion of the generated energy during the braking mode of operation. The
extracted energy
may be utilized, in some forms of the invention, to assist in driving the
motor during at least
one of the driving and braking modes. Alternatively, the energy generated
during the
braking mode of operation of the motor may be dissipated.
[0053] The invention may also include controlling the motor in accordance
with sensed
values of one or more parameters selected from the group of parameters
consisting of, linear
position of the vertically movable member, rotational position of the
rotatable element of
the motor, motor torque, motor speed, motor acceleration, and motor input
power. In some
forms of the invention, one or more of the sensed values of parameters used
for controlling
the motor are sensed above-ground, rather than through the use of down-hole
sensors. In
some forms of the invention, all sensed values of the parameters used for
controlling the
motor are sensed above-ground.
[0054] Some forms of the invention may include detecting a fault condition,
and taking
corrective action. Some forms of the invention may include detecting a fault
condition from
the group of faults consisting of, loss of power to the motor, invalid or
missed position
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reference, loss of control of the motor, non-filling of the pump, breakage
and/or separation
of the pump rod, and overheating of the motor.
[0055] In some forms of the invention, the corrective action taken may be
one of a
group of corrective actions from the group consisting of, applying braking,
changing pump
stroke length, changing pump stroke frequency, dwelling in a non-pumping
state, operating
the motor to slowly lower the rack to the lower mechanical limit of travel,
and entering a
start-up mode of operation.
[0056] In some forms of the invention, where a linear rod pumping
apparatus, according
to the invention, includes a position sensing arrangement having a stationary
position sensor
disposed adjacent the vertically movable member, approximately at a mid-stroke
position
thereof along the pumping axis, and a sensor flag attached to the vertically
movable member
and disposed such that the flag is juxtaposed with, and sensed by, the sensor
during each
pumping stroke, a method, according to the invention, may include detecting
the vertical
position of the vertically movable member by detecting juxtaposition of the
flag with the
sensor during each pump stroke.
[0057] In some forms of the invention, a sensing arrangement includes an
upper sensor
flag and a lower sensor flag, axially spaced from one another along the rack,
to form a gap
between the upper and lower flags, with the gap being substantially centrally
longitudinally
disposed along the rack. The upper sensor flag may extend substantially from
the upper end
of the rack to a lower edge of the upper sensor flag, defining an upper end of
the gap
between the upper and lower flags. In similar fashion, the lower sensor flag
may extend
substantially from the lower end of the rack to an upper edge of the lower
sensor flag, to
thereby define the lower end of the gap between the upper and lower sensor
flags. Where
such an arrangement is provided, a method, according to the invention, may
include
detecting the vertical position of the vertically movable member by detecting
juxtaposition
of the sensor with at least one of the upper and lower sensor flags during
each pump stroke.
A method may further include detecting an output of the sensor having a
substantially
square-wave shape, with a step change form a first state while one or the
other of the lower
flags is juxtapose with the sensor, to a second state when the gap is
juxtapose with the
sensor.
[0058] In one form of the invention, a method is provided for extending the
operating
life of a hydrocarbon well where the well has a walking beam apparatus
operatively
connected to the well for imparting reciprocating substantially vertical
motion to a rod of a
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sucker-rod pump stroke. The method may include disconnecting the rod from the
walking
beam apparatus, and operatively connecting the rod to a linear rod pumping
apparatus
including a linear mechanical actuator arrangement and a reversible motor,
according to the
invention. The linear mechanical actuator arrangement may include a
substantially
vertically movable member configured for attachment to the rod of the sucker-
rod pump for
imparting and controlling vertical motion of the rod of the sucker-rod pump.
The motor
may include a reversibly rotatable element thereof, operatively connected to
the
substantially vertically movable member of the linear mechanical actuator
arrangement in a
manner establishing a fixed relationship between the rotational position of
the motor and the
linear position of the vertically movable member.
[0059] A method for extending the operating life of a hydrocarbon well may
further
include mounting the linear rod pumping apparatus directly on the well head of
the well, to
thereby preclude the need for a separate mounting structure for the linear rod
pumping
apparatus. In some forms of a method, according to the invention, the walking
beam
apparatus is left in place adjacent the well. Some forms of a method,
according to the
invention, may include removal of the walking beam pump, while operating the
well with
the linear rod pumping apparatus.
[0060] A method for operating a hydrocarbon well, in accordance with the
invention,
may include the steps of: installing a first linear rod pumping apparatus on a
well head of
the well; operating the well for a period of time with the first linear rod
pumping apparatus;
removing the first linear rod pumping apparatus from the well head,
substantially without
disassembly of the first linear rod pumping apparatus; and replacing the first
linear rod
pumping apparatus with a second substantially assembled linear pumping rod
apparatus;
and operating the well with the second linear rod pumping apparatus. The
method may
further include disposing of the first linear rod pumping rod apparatus.
Alternatively, a
method may include repairing and/or refurbishing of the first linear rod
pumping apparatus
offline, while the well is being operated with the second linear pumping rod
apparatus.
[0061] Other aspects, objects and advantages of the invention will be
apparent from the
following detailed description and accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0062] FIG. 1, labeled as prior art, is a schematic illustration of a
typical walking-beam-
type pumping mechanism, mounted on a foundation located adjacent a well head
of a
hydrocarbon well, and attached to pump fluid from the hydrocarbon well.
[0063] FIG. 2 is a schematic illustration of a first exemplary embodiment
of a linear rod
pumping apparatus, according to the invention, mounted on the well head of a
hydrocarbon
well.
[0064] FIG. 3 is a schematic illustration of a second exemplary embodiment
of a linear
rod pumping apparatus, according to the invention, mounted on the well head of
the well
shown in FIG. 1, and operatively connected for pumping fluid from the well,
instead of the
walking beam apparatus, with the linear rod pumping apparatus and walking beam
pumping
apparatus being drawn to the same scale, to illustrate the substantial
reduction in size and
complexity of the linear rod pumping apparatus, according to the invention, as
compared to
a walking beam apparatus which was providing similar pumping output as the
second
exemplary embodiment of the linear rod pumping apparatus, according to the
invention.
[0065] FIG. 4 is an external perspective view of the second exemplary
embodiment of
the linear pumping apparatus, according to the invention, shown in FIG. 3.
[0066] FIG. 5 is a partially cut-away perspective illustration of the
second exemplary
embodiment of a linear pumping apparatus, according to the invention, shown in
FIG. 4.
[0067] FIG. 6 is an exterior orthographic illustration of the second
exemplary
embodiment of the linear pumping apparatus, according to the invention, shown
in FIGS. 3-
5.
[0068] FIG. 7 is a partial cross-sectional illustration of the second
exemplary
embodiment of the linear rod pumping apparatus, according to the invention,
shown in FIG.
6.
[0069] FIG. 8 is a schematic cross-section view of the second exemplary
embodiment of
the linear pumping apparatus, according to the invention, shown in FIGS. 3-7.
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[0070] FIG. 9 is an enlarged, partial cross-sectional, schematic
illustration of a variation
of the second exemplary embodiment having a tubular-shaped spacer disposed
between a
rod clamp and the upper end of a rack of a rack and pinion arrangement of the
second
exemplary embodiment of the invention.
[0071] FIG. 10 is a schematic cross-sectional illustration, taken along
line 10-10 in FIG.
8.
[0072] FIG. 11 is a graphical illustration of an exemplary substantially
square-wave
output produced by a sensing mechanism, according to the invention, of the
second
exemplary embodiment of the linear rod pumping apparatus, according to the
invention, as
shown in FIGS. 8 and 10.
[0073] FIG. 12 is a schematic cross-section of a third exemplary embodiment
of a linear
rod pumping apparatus, according to the invention.
[0074] FIG. 13 is a schematic cross-sectional illustration of a fourth
exemplary
embodiment of a linear rod pumping apparatus, according to the invention,
which includes a
pneumatic storage apparatus and regulator, for supply a counter-balance force
to elements
of the linear rod pumping apparatus.
[0075] FIG. 14 shows a first exemplary embodiment of a motor drive, for use
in a
control arrangement in embodiments of the invention having an electric motor.
[0076] FIG. 15 shows a second exemplary embodiment of a motor drive, for
use with an
electric motor in practicing the invention.
[00771 While the invention will be described in connection with certain
preferred
embodiments, there is no intent to limit it to those embodiments. On the
contrary, the intent
is to cover all alternatives, modifications and equivalents as included within
the scope of the
invention defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
[0078] FIG. 2 is a schematic illustration of a first exemplary embodiment
of a linear rod
pumping apparatus 100 mounted on the well head 54 of a hydrocarbon well 56.
The well
includes a casing 60 which extends downward into the ground through a
subterranean
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formation 62 to a depth sufficient to reach an oil reservoir 64. The casing 60
includes a
series of perforations 66, through which fluid from the hydrocarbon reservoir
enter into the
casing 60, to thereby provide a source of fluid for a down-hole pumping
apparatus 68,
installed at the bottom of a length of tubing 70 which terminates in an fluid
outlet 72 at a
point above the surface 74 of the ground. The casing 60 terminates in a gas
outlet 76 above
the surface of the ground 74.
[0079] The down-hole pumping apparatus 68 includes a stationary valve 78,
and a
traveling valve 80. The traveling valve 80 is attached to a rod string 82
extending upward
through the tubing 70 and exiting the well head 54 at the polished rod 52.
Those having
skill in the art will recognize that the down-hole pumping apparatus 68, in
the exemplary
embodiment of the invention, forms a traditional sucker-rod pump arrangement
for lifting
fluid from the bottom of the well 56 as the polished rod 52 imparts reciprocal
motion to rod
string 82 and the rod string 82 in turn causes reciprocal motion of the
traveling valve 80
through a pump stroke 84. In a typical hydrocarbon well, the rod string 82 may
be several
thousand feet long and the pump stroke 84 may be several feet long.
[0080] As shown in FIG. 2, the first exemplary embodiment of a linear rod
pump
apparatus 100, according to the invention, includes a linear mechanical
actuator
arrangement 102, a reversible motor 104, and a control arrangement 106, with
the control
arrangement 106 including a controller 108 and a motor drive 110. In all forms
of the
invention, the linear mechanical actuator arrangement 102 includes a
substantially vertically
movable member attached to the polished rod 52 for imparting and controlling
vertical
motion of the rod string 82 and the sucker-rod pump 68. The reversible motor
of a linear
rod pump apparatus, according to the invention, includes a reversibly
rotatable element
thereof, operatively connected to the substantially vertically movable member
of the linear
mechanical actuator arrangement 102 in a manner establishing a fixed
relationship between
the rotational position of the motor 104 and the vertical position of the rack
206. As will be
understood, by those having skill in the art, having a fixed relationship
between the
rotational position of the motor 104 and the vertical position of the polished
rod 52 provides
a number of significant advantages in the construction and operation of a
sucker-rod pump
apparatus, according to the invention.
[0081] FIG. 3 shows a second exemplary embodiment of a linear rod pumping
apparatus 200, according to the invention, mounted on a standoff 202 to the
well head 54,
and operatively connected for driving the polished rod 52. In FIG. 3, the
second exemplary
embodiment of the linear rod pumping apparatus 200 is illustrated to scale,
adjacent to the
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walking beam pumping apparatus 50, to show the substantial reduction in size,
weight, and
complexity afforded through practice of the invention, as compared to prior
approaches
utilizing walking beam apparatuses 50.
[0082] It will be noted that an arrangement such as the one illustrated in
FIG. 3, in
which a linear rod pumping apparatus 200 is mounted adjacent a walking beam
apparatus
50, might actually be observed in practicing the invention where the walking
beam
apparatus 50 is disconnected from the polished rod 52 and replaced by the
linear rod
pumping apparatus 200 to extend the life of the well 56 by utilizing the
linear rod pumping
apparatus 200 to pump at a slower rate than is possible through use of the
walking beam
apparatus 50.
[0083] It will be appreciated by those having skill in the art, that where
a linear rod
pumping apparatus 200 is used to replace a walking beam apparatus, or a
previously
installed embodiment of a linear rod pumping apparatus according to the
invention, the
replacement linear rod pumping apparatus 200 can be installed in a fully
assembled form, or
in a substantially fully assembled form, with only a minimal number of
components, such as
the upper section 214 of a housing, for example, being installed after the
linear rod pumping
apparatus 200 is installed on the well head 54. As will also be understood
from the
following description and inspection of the drawings, it may be desirable, in
practicing the
invention, to ship an otherwise substantially fully assembled linear rod
pumping apparatus,
according to the invention, with components such as the upper housing section
214 not
installed, to thereby reduce the physical size of the linear rod pump 200 in a
manner that is
more compact to facilitate shipping and handling. As will be further
understood, the
compact size of a linear rod pumping apparatus according to the invention
allows the linear
rod pumping apparatus that is being replaced to be conveniently removed in a
fully
assembled or a substantially fully assembled form.
[0084] As shown in FIGS. 3-8, the second exemplary embodiment of the linear
rod
pumping apparatus 200, according to the invention, includes a linear
mechanical actuator
arrangement 204 which, in turn, includes a rack and pinion gearing arrangement
having a
rack 206 and a pinion 208 operatively connected through a gearbox 210 to be
driven by a
reversible electric motor 212 in a manner described in more detail below.
[0085] As shown schematically in FIG. 8, the linear mechanical actuator
arrangement
204 of the second exemplary embodiment of the linear rod pumping apparatus 200
includes
a rack and pinion gearing arrangement 206, 208 with the rack 206 being
disposed for
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operation in a substantially vertical direction for reciprocating motion
within a three piece
housing having an upper, middle and lower section 214, 216, 218 along a
substantially
vertically oriented pumping axis 220. The rack 206 is operatively connected in
gear mesh
relationship with pinion 208 and the pinion 208 is operatively connected to a
rotating output
shaft 222 of the motor 212 (see FIG. 7) such that rotation of the motor output
shaft in a first
direction is accompanied by a substantially vertically upward motion of the
rack 206 along
the pumping axis 220, and such that a substantially vertically downward motion
of the rack
206 along the pumping axis 220 is accompanied by rotation of the motor output
shaft 222 in
a second direction opposite the first direction. The rack 206 is also
operatively connected to
the polished rod 52 of the sucker-rod pump 68, such that the rack 206 cannot
exert a
substantially vertically downward directed force on the polished rod 52.
[0086] As shown in FIG. 9, which is a section view taken along line 9-9 in
FIG. 8, the
rack 206 of the exemplary embodiment 200 has a substantially U-shaped cross-
section, with
first and second legs 224, 226 extending from a bight section 228 in such a
manner that the
legs and bight 224, 226, 228 define a longitudinally extending opening in the
rack 206 in
the form of an open channel 230 disposed about the pumping axis 220. An outer
surface
232 of the bight 228, facing substantially oppositely from the legs 226, 228
of the rack 206,
is configured to form gear teeth of the rack 206 for engagement with
corresponding gear
teeth in the pinion 208.
[0087] The longitudinally directed channel 230 in the rack 206 extends
along the
pumping axis 220 from a bottom end 234 of the rack 206 to a top end 236 of the
rack 206,
with the upper end 236 of the rack 206 being adapted for operative attachment
thereto of the
polished rod 52. Specifically, as shown in FIG. 8, the upper end 236 of the
rack 206
includes a top plate 238 having a hole 240 extending therethrough and defining
an upper
load bearing surface 241 of the upper end 236 of the rack 206.
[0088] The linear mechanical actuator apparatus 204, of the second
exemplary
embodiment of the linear rod pumping apparatus 200, also includes an actuator
rod 242,
having a lower end 244 thereof fixedly attached to the top end of the polished
rod 52 by a
threaded joint or other appropriate type of coupling. The actuator rod 242
extends upward
from the lower end 244, through the channel 230 in the rack 206 and the hole
240 in the top
plate 238 of the rack 206, and terminates at and upper end 246 of the actuator
rod 242 which
is disposed above the bearing surface 241 on the upper surface of the top
plate 238 of the
rack 236. A rod clamp 248 is fixedly attached below the upper end 246 of the
actuator rod
242 and above the upper end 236 of the rack 206. The clamp 248 has a lower
load bearing
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surface thereof adapted for bearing contact with the upper load bearing
surface 241 of the
upper end 236 of the rack 206, for transferring force between the actuator rod
242 and the
upper end 236 of the rack 206 when the lower load bearing surface of the clamp
248 is in
contact with the upper load bearing surface 241 on the upper end 236 of the
rack 206.
[0089] The clamp 248, of the exemplary embodiment 200 forms an expanded
upper end
of the actuator rod 242 having a configuration that is incapable of entry into
or passage
through the hole 240 in the upper end 236 of the rack 206. It will be further
appreciated
that, to facilitate installation of the linear rod pumping apparatus 200 on
the well head 54,
the actuator rod 242 may be allowed to extend some distance beyond the collar
248, to
thereby provide some measure of adjustment to accommodate variations in the
positioning
of the upper end of the polished rod 52, with respect to the lower end of the
lower section
218 of the housing of the linear mechanical actuator arrangement 204. The
upper section
214, of the housing of the linear mechanical actuator arrangement 204 includes
sufficient
head space to accommodate a portion of the actuator rod 242 extending above
the clamp
248. It will be appreciated that, in some embodiments of the invention, a
linear rod
pumping apparatus 200 may be formed without the actuator rod 242 such that the
polished
rod 52, or an extension thereof, may be fed longitudinally entirely through
the rack 206 and
clamped above the upper end 236 of the rack 206 with a clamp 248. It is
contemplated,
however, that the addition of the actuator rod 242 will substantially
facilitate installation of
a linear rod pumping apparatus according to the invention.
[0090] As shown in FIG. 9, some forms of the second exemplary embodiment
200 of
the invention may also include a tubular-shaped spacer 249 disposed about the
actuator 242
between the clamp 248 and the top plate 238 of the rack 206. Such a spacer 249
may be
utilized when practicing the invention with a clamp 248 having a peripheral
dimension
which is larger than an opening 217 in the center section 216 of the housing.
[0091] As shown in FIGS. 7, 8 and 10, the linear mechanical actuator
arrangement 204
of the second exemplary embodiment 200 of the invention includes four guide
rollers 250
arranged in two pairs, attached to the center section 216 of the housing
substantially
opposite the pinion 208, and configured to bear against the longitudinally
extending distal
edges of the legs 226, 228 of the rack 206 for urging the rack 206 into a gear
mesh
relationship with the pinion 208. Two guide bars 252, operatively extending
from the
middle section 216 of the housing and substantially opposite from one another,
are provided
for urging the rack 206 into alignment with the pinion 208.
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[0092] The middle section 216 of the housing functions as a pinion housing,
having a
longitudinally extending opening 254 (see FIG. 10) disposed about the pumping
axis 220
for passage therethrough of the rack 206, and defining a rotational axis 256
of the pinion
208, with the pinion axis 256 being laterally offset from, and extending
substantially
perpendicularly to, the pumping axis 220.
[0093] A first, anti-drive end of the pinion 208 is journaled in a pinion
bearing 258
disposed in, and mounted to, the pinion housing 216. The second, drive end 260
of the
pinion 208, in the linear mechanical actuator 204 of the second exemplary
embodiment 200,
is adapted for connection to an output element 262 of the gearbox 210 and is
supported by
an output bearing 264 of the gearbox 210. By virtue of this arrangement, the
output bearing
264 of the gearbox 210 serves two functions and provides a more compact
assembly than
would be achievable in an embodiment of the invention having an additional
bearing
attached to the middle housing 216 for supporting the drive end 260 of the
pinion 208. In
other embodiments of the invention, however, an additional bearing may be
provided for
supporting the drive end 260 of the pinion 208.
[0094] To further reduce the size of the second exemplary embodiment of the
linear rod
pumping apparatus 200, the gearbox 210 is a right angle gear box having input
and output
elements 266, 262 (see FIGS. 7 and 10) arranged substantially at a right angle
to one
another, with the output element 262 being oriented for alignment with, and
rotation
substantially about, the pinion axis 256, and the input element 266 of the
gearbox 210 and
the rotatable shaft 222 of the motor 212 being oriented substantially parallel
to the pumping
axis 220. It will be understood that, in other embodiments of the invention, a
motor 212
may be operatively attached to the pinion 208 by a variety of other means and
in other
relative orientations.
[0095] As best seen in FIG. 8, the linear mechanical actuator arrangement
204, of the
second exemplary embodiment 200 of the invention, also includes an oil sump,
formed by
the lower section 218 of the housing, and configured for containing a
sufficient volume of
lubricant therein, such that a lower portion of the rack 206 is immersed into
the lubricant
during at least a portion of each stroke 84 of the pump 68 (FIG. 2). The sump
includes
inner and outer longitudinally extending radially spaced tubular walls 270,
272 sealingly
connected at lower ends thereof by the bottom end of the lower section 218 of
the housing,
to thereby define an annular-shaped cavity therebetween, for receipt within
the cavity of the
volume of the lubricant, and terminating in an annular-shaped opening between
upper ends
of the inner and outer tubular walls 270, 272. As will be understood from an
examination of
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FIGS. 8 and 9, the inner tubular wall 270 of the sump 268 has an inner
periphery thereof
disposed about the actuator rod 242, and an outer periphery thereof disposed
within the
channel 230 in the rack 206. The outer tubular wall 272 of the sump 268 has an
inner
periphery thereof disposed about the rack 206.
[0096] As shown in FIG. 8, the inner tubular wall 270 extends substantially
above a
fluid level 274 of the lubricant within the sump 268, even when the rack 206
is positioned in
a maximum downward location thereof, so that the lubricant is precluded from
flowing over
the top end 275 of the inner tubular wall 270. By virtue of this arrangement,
it is not
necessary, in the exemplary embodiment 204 of the linear actuator arrangement
of the
second exemplary embodiment 200 of the invention, to provide any sort of
packing between
the lower end of the lower section 218 of the housing and the polished rod 52,
or the
actuator rod 242. It will be noted, however, that in other embodiments of the
invention,
other arrangements for providing lubrication of the rack in a sump may be
utilized, wherein
it would be desirable to provide a packing between the rod 52, 242 and the
lower end of the
lower section 218 of the housing of the linear mechanical actuator arrangement
204.
[0097] With reference to FIG. 7, it is further contemplated that, in some
embodiments
of the invention, it may be desirable to have the cross-sectional area of the
sump 268 match
the cross-sectional area of the rack 206, or a lower end plate 276 (see FIG.
8) closely
enough so that immersion of the rack into the sump 268 generates hydraulic
damping of the
movement of the rack 206.
[0098] As shown in FIGS. 7 and 8, the linear mechanical actuator
arrangement, in the
second exemplary embodiment of a linear pumping apparatus 200 according to the
invention, includes a pair of nested helical compression springs 278, 280,
operatively
positioned within the annular cavity in the bottom of the sump 268, below the
lower end
234 of the rack 206, and configured for engaging and applying an upwardly
directed force
to the lower plate 276 on the lower end 234 of the rack 206, when the lower
end plate 276
comes into contact with a longitudinally movable spring contact plate 282
configured to rest
on an upper end of the springs 278, 280 and move longitudinally along the
inner tubular
wall 270 as the springs 278, 280 act on the lower end 234 of the rack 206.
[0099] In the exemplary embodiment 200, the springs 278, 280 are configured
for
engaging and applying an upwardly directed force to the lower end 236 of the
rack 206 only
when the lower end 234 of the rack 206 has moved beyond a normal lower
position of the
rack 206 during a pump stroke. Such an arrangement provides a safety cushion
to safely
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bring the rack and rod string slowly to a halt in the event that a fault
condition should result
in the rack 206 moving downward to a longitudinal position lower than would be
attained
during a normal pump stroke. By virtue of this arrangement, a potentially
damaging impact
between components of the linear mechanical actuator arrangement and/or
between the
stationary and traveling members of the pump 68 is precluded.
[0100] In other embodiments of the invention, however, the springs 278, 280
may be
configured in such a manner that they engage and apply an upwardly directed
force to the
lower end of the rack during a portion of each pump stroke, to thereby recover
a portion of
the kinetic energy generated by the weight of the rod string and pump during
the downward
portion of the pump stroke under the force of gravity and utilize that stored
energy in the
springs 278, 280 for aiding the action of the linear rod pumping apparatus
during the
upward portion of the stroke, in addition to precluding mechanical damage the
rack 206 or
other components at the bottom of each pumping stroke.
[0101] As best seen in FIGS. 8 and 10, the second exemplary embodiment of a
linear
rod pumping apparatus 200 also includes a position sensing arrangement for
sensing a
position of the rack 206 along the pump axis 220. Specifically, the position
sensing
arrangement of the second exemplary embodiment 200 includes a stationary
position sensor
284 disposed adjacent the rack 206 at a mid-stroke position along the pumping
axis 220 in
combination with upper and a lower sensor flags 286, 288 attached to the rack
206,
respectively, at the upper and lower ends 236, 234 of the rack 206. The first
and second
sensor flags 286, 288 are positioned along the first leg 244 of the rack 206
in such a manner
that the flags 286, 288 are brought into juxtaposition with, and sensed by,
the sensor 284
during each complete pumping stroke.
[0102] The upper sensor flag 286 and lower sensor flag 288 are axially
spaced from one
another along the rack 286 to form a gap between the upper and lower flags
286, 288 with
the gap being substantially centrally longitudinally disposed along the rack
206. The upper
sensor flag 286 extends substantially from the upper end 236 of the rack 206
to a lower edge
290 of the upper sensor flag 286, which defines an upper end of the gap
between the upper
and lower sensor flags 286, 288. The lower sensor flag 288 extends
substantially from the
lower end of the rack 206 to an upper edge 292 of the lower sensor flag 288,
to thereby
define the lower end of the gap between the upper and lower sensor flags 286,
288.
[0103] By virtue of this arrangement, the sensor 284 produces an output, as
shown in
FIG. 11, having a substantially square wave 294 shape, with a step change from
a first state
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296, while one or the other of the flags 286, 288 is juxtapose with the sensor
284, to a
second state 298, when the gap is juxtapose with the sensor 284.
[0104] The sensing arrangement described above, in relation to the second
exemplary
embodiment 200 of the invention, can be used with great efficacy in
combination with
control apparatuses and methods of the type described in commonly assigned
U.S. Patent
No. 7,168,924 B2, to provide a highly precise, accurate, effective and
efficient calculation
of the polished rod position and control of the linear rod pumping apparatus
200. The
exemplary embodiment of the sensing arrangement described above can also be
utilized to
control the motor 212 in such a manner that downward motion of the rack 206 is
slowed as
the bottom of the pump stroke is approached through braking action of the
motor 212, to
thereby provide an electrically controlled velocity profile, which may be used
in addition to,
or in place of, the springs 278, 280 of the second exemplary embodiment of a
linear rod
pumping apparatus 200.
[0105] FIG. 12 shows a third exemplary embodiment of a linear rod pumping
apparatus,
according to the invention, having a linear mechanical actuator apparatus 302,
including a
rack 304 and pinion 306 gear train arrangement, similar to the rack and pinion
arrangement
of the second exemplary embodiment 200 described above. The linear mechanical
actuator
302, of the third exemplary embodiment 300, as shown in FIG. 11, is mounted
directly to
the well head 54, through a standoff arrangement 308.
[0106] The third exemplary embodiment of a linear rod pumping apparatus
300,
according to the invention, is similar in many respects to the second
exemplary embodiment
200, described above, with several exceptions. In the third exemplary
embodiment 300, the
polished rod 52 is shown as extending completely through the rack 304 along
the pumping
axis 220, and is secured at both the upper and lower ends of the rack 304 by
upper and
lower end plate and clamp arrangements 310, 312. A stop block 314 is fixedly
attached to
the middle section 316 of the housing, in such a manner that the end plate and
clamping
arrangements 310, 312 will contact the stop block 314, and arrest further
movement of the
rack 304, to preclude having the rack 304 run off of the pinion 306.
[0107] The third exemplary embodiment of the linear pumping rod apparatus
300 also
includes only a single pair of guide rollers 318, disposed for urging the rack
304 into a gear
mesh arrangement with the pinion 306.
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[0108] In the form illustrated in FIG. 12, the linear mechanical actuator
arrangement
302 of the third exemplary embodiment of the linear rod pumping apparatus 300
further,
does not include the oil sump 268 or the springs 278, 280 of the second
exemplary
embodiment. It will be understood, however, that in alternate embodiments of
the
invention, various features of the exemplary embodiment shown herein can be
used,
omitted, or combined together in forms other than the exemplary embodiments of
the
invention shown in the drawings and specifically described herein.
[0109] FIG. 13 shows a fourth exemplary embodiment of a linear rod pumping
apparatus 400, according to the invention, in which a linear mechanical
actuator
arrangement 402 that is substantially identical to the linear mechanical
actuator arrangement
302 of the third exemplary embodiment 300 of the invention described above,
includes a
piston plate 404 attached to the lower end of the rack 406 of the rack 406 and
pinion 408
arrangement, and the lower end of the lower section 410 of the housing is
cooperatively
configured with the piston plate 404 in such a manner that a gas tight
cylinder is provided,
below the piston plate 404. A pneumatic storage apparatus 414, such as an
accumulator, is
connected to the pneumatic cylinder chamber 412 through a conduit 416, and a
regulator
418 is disposed between the accumulator 414 and the cylinder 412 for
regulating pressure
and volume of the gas stored in the pneumatic cylinder and accumulator 412,
414.
[0110] By virtue of this arrangement, a counter-balance force may be
applied to the
lower end of the rack 406. Although only a singular accumulator 414 and
regulating valve
418 are illustrated in FIG. 12, in some embodiments of the invention it may be
desirable to
have multiple accumulators and/or regulating valves 414, 416, to aid in
adjusting the
counter-balance force applied to the lower end of the rack. Some embodiments
of the
invention may also include venting part, or all of the pressure generated in
the pneumatic
cylinder cavity 412 on the downstroke. In the exemplary embodiment shown in
FIG. 13,
the interior of the lower section 410 of the housing is vented to atmosphere
above the
highest level of travel of the piston plate 404.
[0111] It will be understood, that the pneumatic counter-balancing
arrangement of the
fourth exemplary embodiment 400 of the invention may also be incorporated into
other
embodiments of the invention, including some or all of the features of the
first and second
exemplary embodiments 100, 200 of the invention described above.
[0112] FIG. 14 shows a first exemplary embodiment of a motor drive 500 for
use in a
control arrangement in embodiments of the invention having an electric motor.
The motor
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drive 500 includes a rectifier bus charging section 502, a capacitor bank
section 504, a
dynamic braking section 506, and an inverter motor output section 508
connected along
common bus rails 510, 512, for connecting a three phase power input R, S, T to
a three
phase output U, V, W, provided to the motor.
[0113] When the motor is drawing power, diodes in the charging section 502
charge the
capacitor bank 504 and an IGBT bridge arrangement in the inverter motor output
section
508 modulates capacitor voltage to control current in the motor windings.
[0114] When the motor is regenerating power, due to braking action, as the
rod string
pulls the rack downward on the return/fill portion of the pump stroke, for
example, diodes in
the inverter motor output section 508 transfer power to the capacitor bank
504, causing
capacitor bank voltage to rise. The first exemplary embodiment of the motor
drive 500
provides two options for dealing with the energy that is transferred to the
capacitor bank
during braking. In some forms of the invention, the capacitor bank 504
includes sufficient
capacitance to store the energy generated during braking action, without
exceeding voltage
limits on the rails 510, 512. Alternatively, a dynamic braking IGBT 514 in the
dynamic
braking section 506 may be turned on to allow the energy generated during
braking action
to be dissipated across a dynamic braking resistor 516 of the dynamic braking
section 506.
[0115] FIG. 15 shows a second exemplary embodiment of a motor drive 600 for
use
with an electric motor in practicing the invention. The second exemplary
embodiment of
the motor drive 600 is substantially identical to the first exemplary
embodiment of the
motor drive 500, as described above, except that an IGBT switching bridge is
provided in
parallel with the diodes in the rectifier section to provide a regenerative
bus charging
section 602, a capacitor bank section 604, a dynamic braking section 606 and
an inverter
motor output section 608 disposed across a pair of common rails 610, 612 for
connecting a
three phase R, S, T input to the motor drive to a three phase U, V, W
connection to the
motor.
[0116] In the second exemplary embodiment of the motor drive 600, when the
motor is
drawing power the diodes in the regenerative bus charging section 602 charge
capacitors in
the capacitor bank 604 and an IGBT bridge in the inverter motor output section
608
modulates capacitor voltage in the capacitor bank section 604 to control
current in the motor
windings.
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[0117] In the second exemplary embodiment of the motor drive 600, when the
motor
regenerates power due to braking action, diodes in the inverter motor output
section transfer
power to the capacitor bank 604, causing capacitor bank voltage to rise. The
second
exemplary embodiment of the motor drive 600 provides three options for dealing
with the
energy being transferred to the capacitor bank.
[0118] In one option, the capacitor bank section 604 has sufficient
capacitance to store
the energy generated during braking, without exceeding voltage limits.
[0119] With the second option, a dynamic braking IGBT 614 of the dynamic
braking
section 606 is turned on, and all, or a portion of the energy generated during
braking, is
dissipated across a dynamic braking resistor 616 of the dynamic braking
section 606.
[0120] In the third optional mode of operation, the IGBTs in the
regenerative bus
charging section are switched to modulate the capacitor voltage of the
capacitor bank
section in such a manner as to allow a transfer of the power generated during
braking back
to the incoming three phase R, S, T source.
[0121] Those having skill in the art will recognize that, through practice
of the
invention, significant advantages are provided as compared to prior pumping
apparatuses
and methods, such as the control of a walking-beam-type, or a belt-driven,
pumping
apparatus controlled by a rod pump control system as disclosed in the above-
referenced,
commonly assigned, U.S. Patent No. 7,168,924 B2, to Beck et al., titled "Rod
Pump Control
System Including Parameter Estimator." It will be further recognized that a
rod pump
control system, including parameter estimation, of the type disclosed in Beck
et al., U.S.
7,168,924 B2, may be used with considerable efficacy in combination with a
linear rod
pumping apparatus, according to the present invention. The disclosure and
teachings of
Beck et al. may be referred to for further details.
[0122] For example, it will be readily appreciated that in a linear rod
pumping
apparatus, according to the invention, the surface position of the pump rod,
and the current
load on the pump rod above the surface of the ground may be readily
determined, without
the need for down-hole sensors, by virtue of the elegantly simple construction
of the linear
mechanical actuator arrangement and the direct relationship that exists
between the vertical
position of the vertically movably member of the linear mechanical actuator
arrangement
and the rotatable element of the motor. Where the motor is an electric motor,
for example,
the vertical position of the vertically movable member can be directly
determined from the
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angular rotational position of the motor shaft, and the load on the rod above
the surface of
the ground can be readily determined from motor current and voltage, in
accordance with
the apparatuses and methods of a rod pump control system including parameter
estimation,
as taught by Beck et al., or through the use of other applicable methods and
apparatuses in
accordance with the teachings with the present invention. Other parameters
useful for
controlling a linear rod pumping apparatus, in accordance with the invention,
such as
direction and speed of the vertical member and/or the motor shaft, and the
magnitude and
direction of motor torque can also readily be obtained through use of a rod
pump control
system according to Beck et al., or any other appropriate apparatus and method
in
accordance with the presence invention.
[0123] Once the above-ground parameters, such as surface rod position and
load are
determined for a linear rod pumping apparatus, according to the invention, a
model of
dynamic rod performance, of the type disclosed in Beck et al., or any other
appropriate
apparatus or method for modeling the dynamic performance of the pump rod, may
be
utilized to determine a down-hole pump position and load. The pump dynamic
model may
then also be utilized to determine pump "fillage" as a percentage of the total
capacity of the
sucker-rod pump, in real time.
[0124] Operation of the linear rod pumping apparatus can then be controlled
and
adjusted to provide a vertical stroke length and speed of the vertically
movable member of
the linear rod pumping apparatus, according to the invention, to achieve a
target desired
pump fillage percentage. Practice of the invention also contemplates
controlling the linear
rod pumping apparatus in a manner consistent with optimizing other performance
parameters of a particular well installation, such as minimizing power
consumption by the
motor for a given volume of pumped fluid, or minimizing variation in the level
of input
power draw in a manner which might be desirable in hydrocarbon well
installations wherein
the motor of the linear rod pumping apparatus receives input power from an
engine-driven
generator.
[0125] Those having skill in the art will readily recognize that the
elegantly simple
construction of a linear rod pumping apparatus, according to the invention,
results in the
operating members having very low inertias, as compared to prior pumping
apparatuses.
[0126] Those having skill in the art will further recognize that the
elegant simplicity of
construction and operation of a linear rod pumping apparatus, according to the
invention, is
inherently much more readily controllable than walking-beam-type apparatuses
in which
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complex kinematic motions and large inertias of multiple interconnected parts
must be
taken into consideration, in the manner disclosed, for example, in the Beck et
al. U.S. Patent
No. 7,168,924 B2, in order to determine the present position and loading on
the pumping
apparatus and control the input being provided by the pumping apparatus to the
pump rod.
The complexities, and in particular the high inertias, of prior pumping
apparatuses also
make it difficult to efficiently and effectively provide control inputs for
modifying
performance of the down-hole pump in real time.
[0127] The low inertia of a linear rod pumping apparatus, according to the
invention,
provides particular advantages in affecting real time control of the pumping
apparatus, in a
manner consistent with achieving a desired performance from the sucker-rod
pump. In
some modes of operation, however, the low inertia of a linear rod pumping
apparatus,
according to the invention, must be taken into account and compensated for, to
preclude
having the weight of the rod string and fluid load accelerate the vertically
movable member
of the linear rod pump downward more rapidly than is desirable during the
downward
portion of the pump stroke under conditions such as a loss of power to the
motor, for
example, or periods of operation in which the traveling valve of the sucker-
rod pump is not
immersed in fluid having sufficient viscosity to provide hydraulic damping of
the
downward movement of the traveling valve and rod string. Under such operating
conditions, the controlled stop provisions at the bottom of the motion of the
apparatus, as
described above, as provided mechanically through spring elements, or
electrically through
braking of the motor are provided by the present invention, for use in
combination with a
rod pump control system such as the one described in Beck et al., or another
appropriate
control system to preclude having the rod string drive the vertically movable
member of a
linear rod pumping apparatus, according to the invention, at an undesirably
high speed
and/or acceleration rate, and to preclude damaging of the down-hole pump
components by
preventing "tagging" of the standing valve by the traveling valve.
[0128] With specific reference to the second exemplary embodiment of a
linear
pumping rod apparatus 200, according to the invention, as described above, a
method of
operating a linear rod pumping apparatus, according to the invention, might
include the
following eight steps. During all eight steps, the instantaneous vertical
velocity of the rack
206 is calculated from the instantaneous angular velocity of the motor shaft
222, and the
position of the actuator rod 242 is calculated by integration using the
instantaneous vertical
velocity of the actuator rod 242.
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[0129] Step 1. Begin with the actuator rod 242, in a fully lowered
position, and
attached to the upper end of the polished rod 52
[0130] Step 2. The motor 212 is then energized to accelerate the rod to a
predetermined
"UP SPEED."
[0131] Step 3. As the motor 212 drives the rack 206 upward, to thereby
accelerate the
actuator rod 242 to UP SPEED, the output signal 294 (see FIG. 10) of the
stationary
position sensor 284 is monitored to detect the rising edge of the square-wave
294 caused by
the upper edge 292 of the lower reference flag 288 coming into juxtaposition
with the
position sensor 284.
[0132] If the upper edge 292 is detected before the rod 242 reaches a
calculated vertical
rod position, corresponding to a desired pump stroke, where the upper edge 292
is within a
predetermined reference position window, or where the upper edge 292 is not
detected
within a predetermined period of time or a predetermined angular rotation of
the motor shaft
222, a fault condition is identified and the motor 212 is operated in such a
manner that the
rack 206 and actuator rod 242 are lowered to the fully lowered position at a
very slow
speed. Once the fully lowered position is achieved, the method may begin again
by
returning to step 1.
[0133] If the upper edge 292 of the lower reference flag 288 is detected,
however, while
the calculated rod position is within the predetermined raised rod reference
position
window, the calculated rod position is set to the raised rod reference
position value, and the
instantaneous vertical position of the actuator rod 242 is calculated by
integration using the
upward velocity of the actuator rod 242.
[0134] Step 4. As the actuator rod 242 approaches a desired top of stroke
position, the
motor 212 is operated in such a manner that the upward speed of the rod 242
decelerates so
that the upward velocity is reduced to substantially zero at the desired top
of stroke position.
[0135] Step 5. From the top of stroke position, the motor 212 is operated
in such a
manner that the actuator rod 242 accelerates to a "DOWN SLOW SPEED." From the
foregoing description of exemplary embodiments, it will be understood that
during
downward motion of the actuator rod 242, the motor 212 is operated in a
braking mode, by
commanding the motor 212 to drive the pinion 208 at a slower rotational speed
than the
pinion 208 would otherwise achieve due to the downward forces on the rack 206
caused by
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the weight of the rod string and any fluid loads acting on the sucker-pump
apparatus, so that
a net braking torque is applied to the pinion 208.
[0136] Step 6. As the rod 242 moves downward, at DOWN SLOW SPEED, the
output
of the position sensor 282 is monitored to detect a rising edge of the
reference signal 294
caused by the lower end 290 of the upper reference flag 286 coming into
juxtaposition with
the position sensor 282. If this edge 290 is detected before a predetermined
calculated rod
position whereat the rod 242 is within a lowered rod reference position
window, or is not
detected, a fault condition is identified and the motor 212 is operated in
such a manner that
the actuator rod 242 is lowered to the fully lowered position at a very low
speed. Once the
actuator rod 242 has reached the fully lowered position, the method may then
return to step
1 above. If, however, the lower edge 290 of the upper reference flag 286 is
detected, while
the calculated rod position is within a desired lower rod reference position
window, the
calculated rod position is reset to the measured lowered rod reference
position value, and
the rod 242 is allowed to continue downward, while rod position is calculated
by integration
of the downward velocity of the rod 242.
[0137] As the actuator rod 242 is lowered, load on the down-hole pump is
determined,
by monitoring motor torque, for example. When the load on the down-hole pump
drops to a
very low level, i.e. drops below a predetermined threshold indicating that the
traveling valve
has opened, the motor 212 is operated such that the actuator rod 242 can
accelerate to a
"DOWN FAST SPEED."
[0138] Step 7. As the actuator rod 242 continues downward at DOWN FAST
SPEED,
the vertical position of the actuator rod 242 is monitored, and the down-hole
position of the
traveling valve is calculated. As the actuator rod 242 approaches a
predetermined bottom of
stroke position, which may be vertically above the fully lowered position of
the actuator rod
242, the motor 212 is operated in a braking mode, to provide a velocity
profile, such that the
actuator rod 242 is decelerated to substantially zero velocity at the desired
bottom of stroke
position.
[0139] Step 8. Once the actuator rod 242 has reached the desired bottom of
stroke
position, operation of the linear rod pumping apparatus 200 is continued by
returning to step
2 above, and repeating steps 2-8 for each pump stroke.
[0140] With reference to FIGS. 2 and 13, operation, according to the
invention, of a
linear pumping apparatus having an electric motor driven by a motor drive 110,
500
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controlled by a controller 108 will be described, for a "power loss" fault
condition, wherein
the method may include the following four steps:
[0141] Step A. The controller 108 detects a loss of line power whenever
voltage across
the common power busses 510, 512 drops below a predetermined minimum threshold
value.
[0142] Step B. If the actuator rod 242 is moving upward, at the time that a
line power
loss is detected, the controller 108 commands the motor 104, 212 to enter a
reverse braking
mode in which the motor 104, 212 acts as a generator as the rack 206 continues
to move
upward, due to inertia in the linear rod pumping apparatus, to keep the
voltage across the
busses 510, 512 at a level which would allow the motor drive 110, 500 to
continue to
control the motor 104, 212.
[0143] Step C. If the actuator rod 242 is moving downward, at the time that
a line
power loss is detected or after braking action of Step B has caused the
actuator rod 242 to
begin downward motion, the controller 108 commands the motor 212 to operate in
a
braking mode, to limit the lowering speed of the actuator rod 242 in such a
manner that
impact forces are reduced when the rack 206 contacts the springs 278, 280, and
also causing
the motor 104, 212 to act as a generator and keep the voltage across the
busses 310, 312 at a
level which allows the motor drive 110, 500 to continue to control the motor
104, 212.
[0144] Step D. When the actuator rod 242 has reached a fully lowered
position, the
voltage across the busses 310, 312 will decay and the motor drive 110, 500 is
turned off
until line power is restored.
[0145] Those having skill in the art will recognize, that the above-
described exemplary
embodiments of normal operation and various fault conditions, for exemplary
embodiments
of the invention, are provided solely for the purpose of helping the reader to
more fully
understand the invention, and are by no means intended to limit the scope of
the invention.
It will be further understood, that the invention may be practiced in a wide
array of other
forms, within the scope of the invention.
[0146] Those having skill in the art will also appreciate, that a linear
rod pump
apparatus and/or method, according to the invention, provides significant
advantages, in
addition to being physically smaller, in comparison to both a conventional
walking beam
pumping apparatus, and other prior pumping apparatuses, such as the hydraulic
motor
driven pump jack device of Saruwatari.
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[0147] The use of the terms "a" and "an" and "the" and similar referents in
the context
of describing the invention (especially in the context of the following
claims) is to be
construed to cover both the singular and the plural, unless otherwise
indicated herein or
clearly contradicted by context. The terms "comprising," "having,"
"including," and
"containing" are to be construed as open-ended terms (i.e., meaning
"including, but not
limited to,") unless otherwise noted. Recitation of ranges of values herein
are merely
intended to serve as a shorthand method of referring individually to each
separate value
falling within the range, unless otherwise indicated herein, and each separate
value is
incorporated into the specification as if it were individually recited herein.
All methods
described herein can be performed in any suitable order unless otherwise
indicated herein or
otherwise clearly contradicted by context. The use of any and all examples, or
exemplary
language (e.g., "such as") provided herein, is intended merely to better
illuminate the
invention and does not pose a limitation on the scope of the invention unless
otherwise
claimed. No language in the specification should be construed as indicating
any non-
claimed element as essential to the practice of the invention.
[0148] Preferred embodiments of this invention are described herein,
including the best
mode known to the inventors for carrying out the invention. Variations of
those preferred
embodiments may become apparent to those of ordinary skill in the art upon
reading the
foregoing description. The inventors expect skilled artisans to employ such
variations as
appropriate, and the inventors intend for the invention to be practiced
otherwise than as
specifically described herein. Accordingly, this invention includes all
modifications and
equivalents of the subject matter recited in the claims appended hereto as
permitted by
applicable law. Moreover, any combination of the above-described elements in
all possible
variations thereof is encompassed by the invention unless otherwise indicated
herein or
otherwise clearly contradicted by context.
