Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SURFACE-DRIVEN PUMPING SYSTEM
FIELD OF THE INVENTION
[0001] The present invention relates to the field of subsurface fluid recovery
and, in
particular, to surface-driven pump systems for oil production from subsurface
hydrocarbon
deposits.
BACKGROUND OF THE INVENTION
[0002] Producing subsurface hydrocarbon deposits requires that a system be
able to
efficiently recover typically viscous and abrasive fluids from such deposits,
typically
1,000 feet or greater below the surface, via a relatively small diameter
casing (e.g., 2 1/2" to
9.0" diameter). The challenges presented by such requirements has resulted in
the
development of a number of recovery systems. Of such systems, electric
submersible
pumping (ESP) has become one of the most widely applied systems for most field
applications due to its high volume producing capability. The ESP system
consists of a
multi-stage downhole centrifugal pump directly driven by a downhole electric
motor.
Although proven to be effective, operating and servicing the system's downhole
electric
motor can be complicated and cost prohibitive. Moreover, use of an electrical
pump
downhole, such electrical pump and electrical wires leading thereto are
potentially a source
of electrical sparking. In an sometimes explosive environment of hydrocarbon
and air as
typically occurs downhole in a well, this can be accordingly extremely
dangerous and thus
highly undesirable, resulting in inability in some downhole applications to
employ an ESP
pump.
[0003] Addressing some of the shortcomings of the ESP systems are progressive
cavity
pumping (PCP) systems. A PCP system consists of a downhole progressive cavity
pump
actuated by a rod string that is rotated by a surface drive, typically an
electric three phase
motor, that can be easily operated and accessed for servicing, which
progressive cavity
pumps are further well suited for producing hydrocarbons from downhole
explosive
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environments. Moreover, such downhole progressive cavity pumps, due to their
"auger"
design, are particularly suited to pump viscous, abrasive fluids found in
"heavy oil"
subsurface deposits. The performance of PCP systems, however, are known to be
limited
by speed and depth tolerance.
[0004] For efficient production, progressive cavity pumps typically require an
operating
speed of up to 1,200 rpm for best operation of the progressive cavity pump to
maintain
sufficient "head" to produce from depths at which viscous oil is typically
found in North
America, and in particular Alberta, in the Lloydminster, Alberta region.
[0005] Surface-driven rotation of the rod string does have vexing problems.
Specifically,
when a surface-driven PCP system is in operation, a significant quantity of
energy is stored
in the torsional strain of the rod string. The stored energy is released with
backspin of the
pump and/or rod string whenever the PCP system is shut down through routine
operator
intervention or automatic shut down, for example. When the power supply to the
drive is
lost or interrupted, the potential energy that remains in the system will
cause the surface
equipment and drive string to accelerate in the direction opposite its normal
operating
mode. Uncontrolled backspin can lead to surface equipment damage and backed-
off rod
strings or tubing. These conditions also pose a significant hazard to field
personnel
working on or near the surface equipment, and in some conditions, due to
significant back-
spin of a PCP drive unit at surface, have caused surface drive units to
overspeed and fail,
and in at least one instance fly apart and cause death to at least one
individual located in
proximity to the surface drive unit for a particular well. Thus, it is
essential that braking
mechanisms are provided to control the release of rod-string torque and
restrict rod recoil
to a safe speed. In many applications, if unrestrained by a braking mechanism,
backspin
speeds can increase to the point at which the drive fragments and radially
explodes
outward because of the high centrifugal forces generated.
[0006] United States Patent No. 5,573,063 discloses a surface-driven pumping
apparatus
that can efficiently recover fluids from a deep well. In particular, such
patent teaches a
geared centrifugal pumping system (GCP) consisting of an uphole electric motor
which
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uses flexible belts and pulleys 36, 40 at surface to reduce the driven speed
of the rod string,
which rod string downhole is connected to a downhole speed increasing gearbox
and
associated downhole pump assembly. The combination of the belts and pulleys at
surface to reduce the driven speed of the rod string several-fold, and the
speed-increasing
transmission located downhole to increase the rotational speed of the pump
several-fold in
relation to the rotational speed of the rod string allows the rotational speed
of the rod string
to thereby be lowered within the operation limits of the system while at the
same time
maintaining high rotational speed of the driven downhole pump to thereby
achieve the
desired necessary pressure, output, and efficiency from such downhole pump.
In
particular, the drive unit comprising the uphole speed reducing belts and
pulleys reduces
the motor RPM (typically up to 1,200 rpm) to a speed at which the rod string
can be stably
rotated (about 500 rpm) thus reducing wear on the rod string (both frictional
and fatigue
loading due to back and forth bending of such rod string during rotation
thereof) , and the
downhole geared transmission coupled at one end to the rod string and at
another end to
the downhole pump, is used to increase the speed of the rod string typically
to the 1200
rpm range to thereby reach the optimum rpm for best operation of the downhole
pump to
produce fluids from the well.
[0007] Advantageously, as noted in the specification of US 5,573,063 (ref.
col. 6, lines
63-65 thereof), the belt and pulley speed¨reduction system of US 5,573,063
provides
damping, via the belts, to avoid transitional high stresses being transmitted
from the rod
string to the pulleys and driving motor, and vice versa, which according to
the teaching of
such patent provides a clear advantage over direct gearing system being used
as the uphole
speed-reduction mechanism. Specifically, the above system of US 5,573,063
using belts
and pulleys to reduce speed at surface is particularly used to reduce high
cyclic stresses
between the rod string and the uphole motor and damp such high transitional
stresses
which would otherwise be directly transmitted via a gearbox to the rod string,
and vice
versa (ref. col. 6, lines 63-65).
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[0008] Undesirably, however, the belt and pulley speed- reduction system of US
5,573,063 poses a corresponding problem with regard to wear of the associated
semi-
elastic flexible belts due to imposed transitional tensional stresses imparted
thereon during
operation. Accordingly, the system of US 5,573,063 is often prone to failure
due to such
stresses being imposed on the belts and pulleys, resulting in the need to
frequently service
such systems and frequently stop operation of such system to replace belts.
[0009] Accordingly, a need still exists for a pumping system that can achieve
the
advantages of reduced rotational speed of the rod string yet still achieve
sufficient
downhole rotational speed of the downhole pump while further damping and/or
reducing
transmission of transitory high stresses between the rod string and the uphole
driving unit,
yet further be sufficiently robust to and avoid the need to frequently service
such uphole
drive systems.
[0010] This background information is provided for the purpose of making known
information believed by the applicant to be of possible relevance to the
present invention.
No admission is necessarily intended, nor should be construed, that any of the
preceding
information constitutes prior art against the present invention.
SUMMARY OF THE INVENTION
[0011] Disclosed herein are exemplary embodiments pertaining to a surface-
driven
pumping system which are able to achieve the advantages of reduced rotational
speed of
the rod string yet still provide sufficient downhole rotational speed of a
downhole pump,
and further be able to damp and/or reduce transmission of transitory high
stresses
between the rod string and the uphole driving unit and vice versa while still
providing a
robust and durable configuration which need not be serviced to replace worn
belts.
[0012] The surface-driven fluid recovery system according to the present
invention
comprises a surface drive system for generating rotational power that need not
use belts
and pulleys, and instead provides for a magnetic coupling that transmits the
generated
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rotational power of the prime mover to a high capacity pump submersed in a
subsurface
hydrocarbon deposit which provides a damping feature. In particular, the
system
comprises, in one embodiment thereof, a magnetic drive coupling that comprises
an outer
magnetic assembly mounted to the surface drive system and an inner magnetic
assembly
mounted to the shaft assembly/rod string to magnetically couple the shaft
assembly to the
surface drive system. The outer magnetic assembly is coupled to the inner
magnetic
assembly by a magnetic field, thereby allowing indirect transmission of the
rotational
power to the pump through the shaft assembly without direct coupling. The
magnetic
coupling of the present invention, in various embodiments thereof as set out
below,
provides many advantages to be realized. Importantly, however, in all
embodiments,
thereof, the magnetic drive coupling of the present invention does not allow
direct
coupling of the prime mover to the rod string and only allows indirect
coupling through a
magnetic field linking two components together. In such manner high transient
rotational
forces applied to the shaft assembly (rod string) caused by intermittent and
transient
variations in pump speed (due to receiving from time to time various "slugs"
of mixtures
of gas and oil) can thereby be damped and/or reduced in severity thereby
reducing
imparted cyclic stresses exerted on the system, thereby extending the life of
the
equipment, in particular the rod string, thereby reducing the number of times
the rod string
need be withdrawn from a well for servicing or replacement, thereby reducing
cost and
reducing consequential lost operating time of the well .
[0013] Due to the indirect manner of coupling provided by the magnetic
coupling of the
present invention, the degree of magnetic coupling may be controllable and is
limited.
Typically, the degree of magnetic coupling is torque- limited due to limited
strength of
permanent magnets employed or where an electromagnet is provided to provide a
magnetic
field. This can be designed to be set to a desired maximum. Excess torque
being supplied
to such magnetic coupling causes partial decoupling may occur. Where a
magnetic field is
created through use of an electromagnet, partial de-actuation of the magnetic
field, as in
the case of a magnetic field which is created by the supply of electrical
power to an
electrical winding surrounding a ferro-magnetic material, which may be
instantly actuated
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and de-actuated, or partially de-actuated by a power control device , may be
used to
control the magnitude of electrical power provided to the electrical winding,
and thus the
extent of magnetic coupling or decoupling.
[0014] In addition, the present design incorporating a magnetic coupling
provides an
important further solution to a problem to which this speed-reduction and
speed increasing
design would otherwise uniquely suffer from, namely the problem of over-
torquing the rod
string and causing failure thereof.
[0015] Specifically, in the system of the present invention where a speed
¨reducing
gearbox is employed uphole, due to the same rotational energy being needed to
turn the
downhole pump via the speed-increasing gearbox, the torque being needed to be
transmitted to the shaft assembly (which in turn powers the speed-increasing
gearbox)
must necessarily be increased. However, when a pump seizure occurs, resulting
for
example from "sanding-in" of the pump during operation or in situations where
from time
to time various "slugs" of mixtures of gas and oil are temporarily encountered
by the
pump, due to the increased torque being supplied to the rod string via the
speed-reducing
transmission , very high torsional cyclic stresses can accordingly now be
imparted on the
rod string due to the rod string being unable to effectively release the
energy being
imparted thereto, Such a situation can easily thereby result in overstressing
(over-
torquing) of the rod string and failure thereof. However, with the present
system further
employing a magnetic coupling, due to the indirect manner of magnetically
coupling the
prime mover to the rod string, relative rotational movement can be designed to
be
permitted during times of overly high rotational forces being imparted, and
"slippage" of
the coupling being then allowed. Alternatively, when an electromagnetic
coupling system
is employed and such high transient stresses are imparted on the coupling,
current to the
electromagnet may be temporarily reduced to thereby allow the magnetic
coupling to
partially decouple and effectively operate as a clutch so as to thereby avoid
imparting a
high transient cyclic stress on the drive equipment, including and in
particular on the rod
string. This is particularly useful when the pump may become sanded-in, and
pump
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monitoring systems which monitor pump output and well production may not be
able to
sufficiently quickly register such reduced output and initiate stoppage of
supply of power
to the prime mover.
[0016] In certain additional embodiments of the present invention, the
magnetic drive
coupling comprises inner and outer magnetic assemblies that are
electromagnetically
coupled, wherein ceasing or reducing the electrical current supplied thereto
deactivates the
magnetic field and reduces or completely releases transmission of the
rotational power to
and from the rod string (shaft assembly).
[0017] The magnetic drive coupling of the surface-driven fluid recovery system
of the
present invention operates in combination with a speed-reduction transmission
to reduce
the rotational speed that is transmitted from the primary mover to the rod
string.
According to certain embodiments, the speed-reduction transmission is
integrated in the
surface drive system for controlling the rotational speed transmitted from the
primary
mover to the rod string (a.k.a. shaft assembly), and a downhole speed-
increasing
transmission is further used for increasing the rotational speed of the pump.
According to
particular embodiments, the uphole speed-reducing transmission and the
downhole speed-
increasing transmission may be identical, and simply reversed when employed in
the
system of the present invention. This advantageously allows for
interchangeability of
either transmission in the field, when only a single replacement transmission
may be
available, and thus allows for easier servicing of wells in remote locations
by allowing
changeout of either the uphole speed reducing transmission or the downholed
speed
increasing transmission where only one replacement transmission may otherwise
be on
hand.
[0018] According to particular embodiments, the uphole speed-reducing
transmission
and the downhole speed-increasing transmission may each comprise a planetary
gear
assembly configured to respectively reduce and increase the rotational speed.
According to
such embodiments, the rotational speed can be incrementally stepped down or
stepped up
by using a planetary gear assembly. In particular embodiments, for example,
the speed-
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reducing and speed-increasing transmissions can each comprise multi-stage
planetary gear
arrangements that can be successively combined to allow each speed
transmission to
produce a larger or smaller cumulative gear ratio. In this way, multi-stage
planetary gears
according to embodiments described herein and arranged in series can offer
variable
configurations for achieving variable desired gear ratios. In particular, such
planetary
gears assemblies can be arranged in stacked multi-stage configurations that
thereby
achieve the desired gear ratio.
Definitions
[0019] Unless defined otherwise, all technical and scientific terms used
herein have the
same meaning as commonly understood by one of ordinary skill in the art to
which this
invention belongs.
[0020] As used herein, the term "about" refers to an approximately +/-10%
variation
from a given value. It is to be understood that such a variation is always
included in any
given value provided herein, whether or not it is specifically referred to.
[0021] Accordingly, in a first broad embodiment of the present invention, such
invention
comprises a surface-driven fluid recovery system for producing viscous fluids
from a
subsurface hydrocarbon deposit, comprising:
a downhole pump situated downhole in a wellbore, and actuable by rotation;
an elongate shaft assembly extending from surface downhole is said wellbore,
having a first uphole end and a second downhole end;
a speed-increasing transmission, interconnecting said second downhole end of
the
shaft assembly and said downhole pump, to increase rotational speed of said
downhole
pump;
a surface drive system, situated as said surface, for providing rotational
energy to
said first uphole end of said elongate shaft assembly, comprising:
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(A) a primary mover for generating rotational power;
(B) a speed reduction transmission for reducing rotational speed
supplied by said primary mover directly or indirectly to said first end of
said shaft; and
(C) a magnetic drive coupling, having an outer magnetic assembly
and an inner magnetic assembly, each of which is magnetized or
magnetizable;
wherein :
(i) said magnetic drive coupling is situated intermediate said primary
mover and said speed reduction transmission, and :
(a) said outer magnetic assembly is coupled to an input end of
the speed reduction transmission and said inner magnetic assembly
is coupled to said primary mover; or
(b) said outer magnetic assembly is coupled to said primary mover
and said inner magnetic assembly is coupled to said input
end of the speed reduction transmission;
or
(ii) said magnetic drive coupling is situated intermediate said speed
reduction transmission and said first uphole end of said shaft assembly, and:
(a) the outer magnetic assembly is coupled to an output end
of the speed reduction transmission and said inner magnetic
assembly is coupled to said first uphole end of said shaft assembly;
or
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(b) said outer magnetic assembly is coupled to said first uphole end
of said shaft assembly and said inner magnetic assembly is coupled
to said output end of the speed- reduction transmission.
[0022] In a
preferred embodiment, either the outer magnetic assembly or the inner
magnetic assembly comprises an electromagnet and said electromagnet may de-
actuated
or partially de-actuated when desired, and wherein said de-actuation or
partial de-
actuation thereof causes the inner and outer magnetic assemblies to cease or
reduce
transmission of rotational energy between the surface drive system and the
shaft
assembly, particularly , but not limited to, instances when excessive
rotational stresses
being applied to said shaft assembly.
[0023]
Specifically, in one refinement the outer magnetic assembly comprises an
electromagnet and said inner magnetic assembly comprises a material capable of
being
magnetized by said electromagnet when an electrical current is supplied to
said
electromagnet, wherein when said electrical current is supplied to said
electromagnet said
outer magnetic assembly reduces or prevents relative rotational movement
between said
outer magnetic assembly relative to said inner magnetic assembly.
[0024] Alternatively, in another refinement the inner magnetic assembly
comprises an
electromagnet, and said outer magnetic assembly comprises a material capable
of being
magnetized by said electromagnet when an electrical current is supplied to
said
electromagnet, wherein when said electrical current is supplied to said
electromagnet said
inner magnetic assembly reduces or prevents relative rotational movement
between said
inner magnetic assembly relative to said outer magnetic assembly.
[0025] Power control means may further be incorporated in the above system, to
variably regulate the amount of electrical current supplied to said
electromagnet.
[0026] In top drive systems, "back spin" of the shaft assembly potentially
results due to
the "rubber band" effect of energy storage in the shaft assembly, which occurs
when a
torque is applied at one end of a long shaft to rotate a downhole pump
situated at its other
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end. Back spin can be dangerous and cause damage to equipment, if for example
sudden
loss of power was to result and the prime mover, typically an electric motor,
be free to
rotate in an opposite direction to the normal driving direction, or in an
instance where the
downhole pump becomes "sanded-in" and thus lodged, and the rod string as a
result
becomes overtorqued and fails, resulting in immediate release of rotational
energy and
typically overspeed of transmissions/gearboxes and possibly "whippstocking" of
the rod
string at such time due to "over design" rotational speeds thereof being
experienced.
[0027] Accordingly, in a further refinement of the present invention, such
invention
provides for a means of reducing the danger of overspeed during backspin, to
reduce the
overspeed and possible resulting damage to the recovery equipment. Thus in a
further
embodiment, wherein one of said outer magnetic assembly or said inner magnetic
assembly comprises an electromagnet, the fluid recovery system of the present
invention
further comprises a selectively-actuable direct coupling means between said
outer
magnetic assembly and said inner magnetic assembly.
[0028] Such selectively-actuable direct coupling may comprise a spring-biased
electrically-actuated solenoid, which in the normal operating condition a
solenoid
compresses a moveable pin member against a spring, to disengage from direct
coupling the
outer magnetic assembly from the inner magnetic assembly. Upon, for example,
failure of
electric current to be provided to the solenoid, the spring forces the pin
member to extend
so as to directly couple the outer magnetic assembly to the inner magnetic
assembly.
Many other ways, means, and configurations for providing a selectively-
actuable direct
coupling between the outer magnetic coupling and the inner magnetic coupling
will now
occur to those of skill in the art, and the invention is not to be limited to
the single
embodiment disclosed herein.
[0029] In such embodiment, in the event of failure of supply of electrical
current to said
electromagnet and said primary mover, the selectively-actuable direct
coupling, namely in
one embodiment the spring-biased pin which becomes released by the de-actuated
solenoid
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and via the spring is biased into and provides direct coupling so as to
directly couple the
outer magnetic assembly to said inner magnetic assembly.
[0030] This aforesaid selectively-acutable direct coupling feature is
particularly useful
where the primary mover is an electric motor, and in the event of cessation of
electrical
power being provided to such electrical motor the electrical windings of such
motor are
electrically connected ("shunted") thereby allowing the motor to serve as a
brake. In such
a surface-drive system, further having the selectively-acutable direct
coupling feature, the
solenoid (which in such embodiment is now no longer being provided with
electrical
power) then causes the outer magnetic assembly to be directly mechanically
coupled to
inner magnetic assembly, to thereby directly connect the electrical driving
motor to the rod
shaft and thereby, through the braking provided by the motor, prevent the
uncontrolled
back-spin and possible damage through overspeed of the shaft assembly.
[0031] In one embodiment of the surface drive system of the present invention,
the
magnetic drive coupling is situated intermediate said speed reduction
transmission and
said first end of said shaft assembly (rod string) , and:
(i) the outer magnetic assembly thereof is coupled to said first end of the
speed
reduction transmission and said inner magnetic assembly thereof is coupled to
said
first end of said shaft assembly; or
(ii) said outer magnetic assembly thereof is coupled to said first end of said
shaft
assembly and said inner magnetic assembly is coupled to said first end of the
speed reduction transmission
Tin the event of loss of electric current to the electric motor (prime mover)
(where no
electrical shunting is employed on the electric motor to act as a brake), such
embodiment
has the advantage of avoiding "back spin" of the rod string and possible
overspeed of the
speed-reducing transmission, due to the rod string in such circumstances being
disconnected from being coupled to the speed reducing transmission due to loss
of
coupling by the (electromagnetic) coupling device. In absence of such feature,
possible
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overspeed of the speed-reducing transmission due to back-spin might have
resulted causing
possible failure thereof.
[0032] In an alternate embodiment the magnetic drive coupling is situated
intermediate
said primary mover and said speed-reducing transmission, and:
(a) said outer magnetic assembly is coupled to said input end of
the speed-reducing transmission and said inner magnetic assembly
is coupled to said primary mover; or
(b) said outer magnetic assembly is coupled to said primary mover
and said inner magnetic assembly is coupled to said input
end of the speed reduction transmission;
[0033] Such alternate embodiment has the advantage that in the event of
failure of the
magnetic coupling, any backspin of the shaft at the upper end thereof will
necessarily be
directed through the uphole speed-reduction transmission, the inertia of which
will thereby
resulting in a more gradual dissipation of the back-spin energy built up in
the rod string
than would be the case if the magnetic drive was directly coupled to the rod
string without
the uphole speed reduction transmission being situated therebetween and such
magenetic
drive was to fail.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] These and other features of the invention will become more apparent in
the
following detailed description in which reference is made to the appended
drawings,
depicting exemplary embodiments of the invention, in which:
[0035] Figures 1A and 1B are side elevational views of a surface-driven fluid
recovery
system having a single motor, according to one embodiment of the present
invention;
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[0036] Figures 2A and 2B are side elevational views of a surface-driven fluid
recovery
system having two motors, according to another embodiment of the present
invention;
[0037] Figure 3 is a side elevational view of a surface-driven fluid recovery
system
having three motors, according to another embodiment of the present invention;
[0038] Figure 4 is a side elevational view of an exemplary magnetic coupling
drive of
the surface-driven fluid recovery system shown in Figures 1 to 3, according to
the present
invention;
[0039] Figures 5A and 5B are schematic views of exemplary planetary gear
assemblies
of the surface-driven fluid recovery system shown in Figures 1 to 3, according
to
embodiments of the present invention, producing gear ratios of 2:1 (Figure 5A)
and 3:1
(Figure 5B);
[0040] Figures 6A, 6B, and 6C are schematic views of exemplary multi-stage
configurations of the planetary gear assemblies, according to embodiments of
the present
invention;. and
[0041] Figures 7A, 7B show a modified magnetic coupling, further having a
selectively-
actuable direct coupling in the form of a solenoid and pin assembly, for
selectively directly
coupling the outer magnetic assembly with the inner magnetic assembly, with
Fig. 7A
showing the outer magnetic assembly directly coupled to the inner magnetic
assembly,
with Fig. 7B showing the solenoid having caused the outer magnetic assembly to
no longer
be directly coupled to the inner magnetic assembly.
DETAILED DESCRIPTION OF THE INVENTION
[0042] Embodiments of the present disclosure will now be described by
reference to
Figs. 1 to 6, which show exemplary embodiments of the surface-driven fluid
recovery
system according to the present invention.
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[0043] Referring now to Figs. 1 to 3, a surface-driven fluid recovery system
10 for
producing viscous fluids from a subsurface hydrocarbon deposit is illustrated
in various
embodiments. The surface-driven fluid recovery system 10 of the present
disclosure
includes a surface drive system comprising a primary mover 15, 20, 25 for
generating
sufficient rotational power to rotate the shaft assembly 50. Primary movers
typically used
with surface-driven systems are well known in the art and include without
limitation, for
example, electric motors and internal combustion engines as well as
hydraulically powered
motors. The surface-driven fluid recovery system 10 of the present disclosure
can include
a variety of prime mover 15, 20, 25 arrangements in order to achieve
sufficient generation
of rotational power. According to embodiments, the primary mover can include
at least
one motor (Figs. 1A and 1B). According to other embodiments, the primary mover
can
include two motors (Figs. 2A and 2B) in various arrangements. According to
further
embodiments, the primary mover can include three motors (Fig. 3) in various
arrangements.
[0044] The rotational power generated by the primary mover 15, 20, 25 is
transmitted
through a shaft assembly 50 to a high capacity pump 80, typically a
progressive cavity
pump comprising an inner helical rotatable rotor( not shown) rotatably
inserted in a
stationary outer stator (not shown), which pump 80 is submersed in a
subsurface
hydrocarbon deposit. The shaft assembly / rod string 50 is typically comprised
of a series
of sections of solid rod or pipe that are connected together, typically
threadably, to make
up the needed length to reach the particular depth of the deposit. The shaft
assembly 50
alternatively may comprise continuous hollow tubing. The shaft assembly 50 is
typically
encased in a tubular well casing 60 of relatively small diameter. For example,
it is not
uncommon for a well casing to have an interior diameter of from about 2 'A" to
about 9".
As a result, the shaft assembly 50 is vulnerable to wear and torsional
fracture at rotational
speeds of greater than about 1,000 rpm. It is necessary, therefore, to be able
to control the
rotational speed generated by the primary mover 15, 20, 25, which typically
generates
rotational power at speeds greater than 500 rpm, for example about 1,200 rpm.
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[0045] According to embodiments, the surface-driven fluid recovery system 10
of the
present disclosure includes a rotational power transmission system that
comprises an
uphole speed-reducing transmission or gearbox 30, which in the embodiment
shown is
integrated in the surface drive system 10 for reducing the rotational speed of
shaft
assembly 50 as " powered by the primary mover 15, 20, 25. The speed-reducing
transmission 30 is configured to effect a reduction in the speed of the
rotational speed
generated by the primary mover 15, 20, 25 to ensure that the rotational speed
transmitted to
the shaft assembly 50 remains within the rotational speed limits of the shaft
assembly 50.
By having a lower rotational speed the number of cycles of alternating
stresses, particularly
where the rod string may not be perfectly straight and a whipping action
results, is thereby
reduced resulting in longer life of the rod string/ shaft assembly 50.
According to
embodiments, the speed-reducing transmission 30 is configured to reduce the
rotational
speed to less than 1,000 rpm. According to other embodiments, the speed-
reducing
transmission 30 is configured to reduce the rotational speed to about 500 rpm
or less.
[0046] In order to operate the pump 80 submersed in the subsurface deposit,
however,
the rotational power transmitted from the shaft assembly 50 must be increased
to operating
speeds of up to about 1,200 rpm. To achieve this, the rotational power
transmission
system of the surface-driven fluid recovery system 10 further comprises a
speed-increasing
transmission 70 which interconnects the downhole end of the shaft assembly 50
to the
pump 80. According to embodiments, the speed-increasing transmission 70 is
disposed in
close proximity, or even connected to, the pump 80 in order to minimize impact
of the
increased rotational speed on the shaft assembly 50. According to embodiments,
the -
increasing transmission 70 is configured to increase the rotational speed up
to about 1,200
rpm.
[0047] In addition to controlling the rotational speed of the shaft assembly
50, a certain
level of vibration dampening is further achieved by a magnetic drive coupling
40
interconnecting the shaft assembly 50 to the surface-drive assembly. Referring
to Fig. 4,
the magnetic drive coupling 40 comprises an outer magnetic assembly 100
mounted to the
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surface drive system which provides a driving force, and a driven inner
magnetic assembly
110 mounted to the shaft assembly 50. The inner 110 and outer 100 magnetic
assemblies
magnetically couple to connect the shaft assembly 50 to the surface drive
system without
physical contact, thereby, effecting a dampening effect. The outer magnet
assembly 100
further moves the inner magnet assembly 110 by a rotating magnetic field which
in turn
ultimately allows transmission of the rotational power to the pump.
[0048] In one exemplary embodiment of the invention, the surface-driven fluid
recovery
system 10 comprises a high capacity pump 80. Typical of hydrocarbon
production, high
capacity pumps 80 can include multi-stage pumps, centrifugal pumps, and
progressive
cavity pumps (PCP). , According to certain embodiments, the surface-driven
fluid recovery
system 10 comprises a progressive cavity pump (PCP).
Magnetic Drive Coupling
[0049] The inner magnetic assembly 110 and the outer magnetic assembly 100 may
each
possess permanent magnets, so as to permit, when coupled together , a coupling
force
which prevents relative motion of inner magnetic assembly 110 relative to the
outer
magnetic assembly 100, at least up to a pre-determined maximum rotational
force being
applied thereto. Where excess of such maximum rotational coupling force being
provided
thereto, relative "slippage" will advantageously occur between such two
components 110,
100.
[0050] Alternatively, an electromagnet or electromagnets may be employed in
one or
both of said inner 110 and outer magnetic assembly 100 to achieve the required
rotational
coupling force between such two components. Thus in one embodiment thereof,
outer
magnetic assembly 100 may comprise an electromagnet, in the form of a
ferromagnetic
material surrounded by electrical windings (not shown), and inner magnetic
assembly 110
merely comprise a ferromagnetic material.
[0051] In an alternative embodiment thereof, outer magnetic assembly 100 may
comprise
a ferromagnetic material, and inner magnetic assembly 110 may comprise an
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electromagnet, in the form of a ferromagnetic material surrounded by
electrical windings
(not shown).
[0052] In a further embodiment, both outer magnetic assembly 100 and inner
magnetic
assembly 110 may both comprise an electromagnet, in the form of a
ferromagnetic material
surrounded by electrical windings (not shown).
[0053] Fig.s 7A and 7B show a modification of the magnetic coupling 40 of the
present
invention, further being provided with a a selectively-actuable direct
coupling.
[0054] In the embodiment thereof shown in Fig.s 7A, 7B, the selectively-
actuable direct
coupling takes the form of a solenoid assembly 200, having a ferro-magnetic
pin member
201 slidably moveable within windings 205 of solenoid assembly 200 for
selectively
directly coupling the outer magnetic assembly 100 with the inner magnetic
assembly 110,
when loss of electrical power occurs. Individual slip rings 203 are positioned
on the
exterior of outer magnetic assembly (which rotates), in order to allow supply
of electrical
current via slip rings 203 to solenoid windings 205. A compressible spring
member (not
shown) may be positioned within solenoid assembly 200 to force pin member 201
into
engagement with inner magnetic assembly 110 to thereby couple outer magnetic
assembly
100 with the inner magnetic assembly 110. Fig. 7A shows the outer magnetic
assembly
100 directly coupled to the inner magnetic assembly110. Fig. 7B
shows the solenoid
assembly 200 having caused pin member to be withdrawn from engagement with
inner
magnetic assembly110, thereby having caused the outer magnetic assembly100 to
no
longer be directly coupled to the inner magnetic assembly 110.
Surface-Driven Rotational Power ¨ Staged Gearbox Assembly
[0055] As described above, effective transmission of rotational power through
the
surface-driven fluid recovery system 10 is achieved by the rotational power
transmission
system comprising a speed-reducing transmission 30 integrated in the surface
drive system
10, configured to reduce the rotational speed generated by the surface drive
system 10, and
a speed-increasing transmission 70 interconnecting the downhole end of the
shaft
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assembly 50 to the pump 80 and configured when supplied by rotation energy
from the
shaft assembly 50 to increase the rotational speed of the pump 80.
[0056] According to preferred embodiments, the speed-reducing transmission 30
and/or
the speed-increasing transmission 70 are planetary gear assemblies as
exemplified in Figs.
5A and 5B. In such embodiments, one or more planet gears 150 rotate around a
central sun
gear 130. Typically, a planet carrier is driven by the input torque which
rotates the planet
gears 150 around a fixed outer ring 140. This in turn drives the sun gear 130
which then
provides the output torque. By manipulating the configuration of the gears,
according to
known methods, gear ratios can be created that reduce or increase the
rotational speed of
the interconnected shaft assembly 50 to the desired level. According to
embodiments, the
planetary gear assembly is configured to have a reduction ratio ranging from
about 1.5:1 to
about 3:1. According to other embodiments, the planetary gear assembly is
configured to
have a reduction ratio of about 3:1. According to embodiments, the planetary
gear
assembly is configured to have a step-up ratio ranging from about 1:1.5 to
about 1:3.
According to other embodiments, the planetary gear assembly is configured to
have a step-
up ratio of about 1:3.
[0057] The compact design of a planetary gear assembly lends itself well to
the small
internal diameters found with typical well casings used in hydrocarbon
recovery systems.
According to embodiments, a planetary gear assembly of the present disclosure
will have a
length of up to about 3'. According to other embodiments, a planetary gear
assembly of
the present disclosure will have a length of up to about 2'. In this way, the
transmissions
30, 70 can be made very compact yet provide the necessary substantial
reduction and
increase in rotational speed.
[0058] Moreover, as illustrated in Figs. 6A, 6B, and 6C, the planetary gear
assemblies
can further be configured in multiple stages by coupling them to each other in
series,
whereby rotational speed can thereby be incrementally and sequentially stepped
down or
stepped up. In particular embodiments, for example, the speed-reducing
transmission 30
and/or the speed-increasing transmission 70 can comprise multi-stage planetary
gear
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assemblies 120 that can be combined to allow each stage of planetary gears to
produce a
larger or smaller cumulative gear ratio. According to embodiments, the multi-
stage
configuration 160 comprises up to ten stages of planetary gear assemblies 120.
According
to other embodiments, the multi-stage configuration 160 comprises up to eight
stages of
planetary gear assemblies 120. According to further embodiments, the multi-
stage
configuration 160 comprises up to six stages of planetary gear assemblies 120.
According
to other embodiments, the multi-stage configuration 160 comprises up to four
stages of
planetary gear assemblies 120. According to further embodiments, the multi-
stage
configuration 160 comprises up to two stages of planetary gear assemblies 120.
As
illustrated in Figs. 6A, 6B, and 6C each stage of planetary gears 120 in the
configuration
will increase or reduce the gear ratio of the preceding stage to produce the
cumulative gear
ratio.
[0059] Use of examples in the specification, including examples of terms, is
for
illustrative purposes only and is not intended to limit the scope and meaning
of the
embodiments of the invention set out and described in the disclosure. In the
specification,
the word "comprising" is used as an open-ended term, substantially equivalent
to the
phrase "including, but not limited to," and the word "comprises" has a
corresponding
meaning.
[0060] The scope of the claims should not be limited by the preferred
embodiments set
forth in the foregoing examples, but should be given the broadest
interpretation consistent
with the description as a whole, and the claims are not to be limited to the
preferred or
exemplified embodiments of the invention.
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