Note: Descriptions are shown in the official language in which they were submitted.
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ARTIFICIAL LIFT METHOD FOR LOW PRESSURE SAGD WELLS
Field of the Invention
[001] This invention relates generally to the field of submersible pumping
systems,
and more particularly, but not by way of limitation, to a hydraulically-driven
submersible pumping system configured for use in high-temperatures
applications.
Background
[002] Submersible pumping systems are often deployed into wells to recover
petroleum fluids from subterranean reservoirs. Historically, submersible
pumping
systems have included one or more fluid filled electric motors coupled to one
or more
high performance pumps located above the motor. When energized, the electric
motor provides torque to the pump, which pushes wellbore fluids to the surface
through production tubing. Each of the components in a submersible pumping
system
must be engineered to withstand the inhospitable downhole environment.
[003] Although widely accepted, the conductors and insulators within the
electric
motors may be inadequate for certain high-temperature downhole applications.
In
particular, motors employed in downhole applications where modern steam-
assisted
gravity drainage (SAGD) recovery methods are employed are be subjected to
elevated
temperatures. Electrical insulation materials often fail under these
elevated
temperatures or under prolonged exposure to wellbore fluids and contaminants.
If an
electrical insulator is compromised by these conditions, an electrical short
may occur
that causes the complete failure of the electric motor. There is, therefore, a
need for a
downhole pumping system that exhibits enhanced resistance to heat, corrosive
chemicals, mechanical wear and other aggravating factors experienced in modern
SAGD wells. It is to this and other deficiencies in the prior art that the
present
invention is directed.
Summary of the Invention
[004] In a preferred embodiment, a pumping system includes a hydraulic motor
assembly configured to drive a production pump. The hydraulic motor assembly
includes a master pump located on the surface and an electric motor configured
to
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controllably power the master pump. When moved by the electric motor, the
master
pump discharges a working fluid under pressure. The pressurized working fluid
is
transferred to a hydraulic turbine located in the wellbore. The hydraulic
turbine
converts the pressure of the working fluid into torque, which is transferred
through a
driveline to a production pump. The production pump pressurizes production
fluids,
which are carried under pressure to the surface.
Brief Description of the Drawings
[005] FIG. 1 depicts a submersible pumping system constructed in accordance
with
a preferred embodiment of the present invention.
[006] FIG. 2 is a partial cross-sectional view of the production pump of the
submersible pumping system of FIG. 1.
[007] FIG. 3 is a partial cross-sectional view of the hydraulic turbine of the
submersible pumping system of FIG. 1.
Detailed Description of the Preferred Embodiment
[008] In accordance with a preferred embodiment of the present invention, FIG.
1
shows an elevational view of a pumping system 100. The pumping system 100
generally includes a hydraulic motor assembly 102, a production pump 104 and
production tubing 106. The pumping system 100 is generally configured to pump
fluids through the production tubing 106 from a subterranean wellbore 108 to a
wellhead 110 located on the surface. The wellbore 108 is drilled for the
production of
a fluid such as water or petroleum. As used herein, the term "petroleum"
refers
broadly to all mineral hydrocarbons, such as crude oil, gas and combinations
of oil
and gas.
[009] Unlike convention submersible pumping systems, the pumping system 100
does not include an electric motor within the wellbore 108. In place of the
conventional electrical motor, the production pump 104 is driven by the
hydraulic
motor assembly 102. The hydraulic motor assembly 102 includes a master pump
112,
an electric motor 114 and a hydraulic turbine 116. The master pump 112 and
electric
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motor 114 are preferably located on the surface. The electric motor 114 is
connected
to, and drives, the master pump 112.
[010] The master pump 112 is connected to the hydraulic turbine 116 through a
feed
line 118 and a return line 120. The feed line 118 extends from the surface,
through
the wellbore 108 to the hydraulic turbine 116. The working fluid is returned
to the
surface from the hydraulic turbine 116 through the return line 120. In
preferred
embodiments, the hydraulic motor assembly 102 further includes a surface-
mounted
reservoir 122 that receives working fluid from the return line 120 and a
dedicated
suction line 124 extending from the reservoir 122 to the master pump 112. The
reservoir 122 provides a buffer and accumulator for the working fluid to
ensure that
the master pump 112 is provided with a constant, uninterrupted supply of
working
fluid. It will be appreciated that the feed line 118, return line 120 and
production
tubing 106 each preferably routed through the wellhead 110 so that the
internal
pressure of the wellbore 108 can be safely contained.
[011] The hydraulic turbine 116 is located in the wellbore 108 and is operably
connected to the production pump 104 through a series of connected shafts (not
shown in FIG. 1) to enable the transfer of torque and rotation from the
hydraulic
turbine 116 to the production pump 104. The pumping system 100 preferably
includes a seal section 126 and a thrust section 128 disposed between the
hydraulic
turbine 116 and the production pump 104. It will be appreciated that the seal
section
126 and thrust section 128 each include intermediate shafts that transfer
torque from
the hydraulic turbine 116 to the production pump 104.
[012] During operation, the electric motor 114 is selectively energized with a
motor
controller. The electric motor 114 then transfers torque through a shaft or
coupling to
the master pump 112. The master pump 112 pressurizes a working fluid that is
discharged from the master pump 112 through the feed line 118. The feed line
118
provides the pressurized working fluid to the hydraulic turbine 116. The
hydraulic
turbine rotates in response to the application of pressurized working fluid
and thereby
converts a portion of the energy stored as working fluid pressure into torque.
[013] The hydraulic turbine 116 transfers the torque to the production pump
104
through a driveline 130. The driveline 130 preferably includes a series of
connected
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shafts 132 that extend from the hydraulic turbine 116, through the seal
section 126,
the thrust section 128 and into the production pump 104. The seal section 126
isolates
the hydraulic turbine 116 from the production fluids and contaminants found in
the
wellbore 108 and production pump 104. The seal section 126 preferably includes
a
series of mechanical seals, bellows or seal bags to prevent the contamination
of the
clean working fluid found in the hydraulic turbine 116. The thrust section 128
includes a series of thrust bearings that oppose the axial movement of the
driveline
130. Reducing the axial movement of the driveline 130 reduces wear on the
internal
components connected to the shafts 132.
[014] Once driven by the hydraulic turbine 116, the production pump 104 pushes
production fluids from the wellbore 108 to the surface through the production
tubing
106. The working fluid is returned from the hydraulic turbine 116 under lower
pressure to the reservoir 122, before being drawn back into the master pump
112. The
speed and other operational characteristics of the production pump 104 can be
adjusted by controlling the output of the master pump 112. In this way, the
production pump 104 can be driven without the placement of an electrical motor
in
the wellbore 104. In high-temperatures applications, the ability to remove
sensitive
electrical components from the wellbore 108 presents a significant advancement
in
the art.
[015] Turning to FIG. 2, shown therein is a partial cross-sectional view of
the
production pump 104. The production pump 104 preferably includes a production
pump housing 134, a plurality of production pump stages 136, a production pump
intake 138 and a production pump discharge 140.
[016] Each production pump stage 136 includes a production pump diffuser 142
and
a production pump impeller 144. The production pump impellers 144 are each
connected for rotation with the shaft 132. As the production pump impellers
114
rotate, they impart kinetic energy into the production fluid. A portion of the
kinetic
energy is then converted into pressure as the production fluid passes through
the
corresponding production pump diffuser 144. It will be appreciated that
production
fluid is drawn into the production pump 104 through the production pump intake
138
and discharged under higher pressure through the production pump discharge
140.
Although the production pump 104 has been disclosed in preferred embodiments
as a
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turbomachine, it will be appreciated that the production pump 104 could
alternatively
be configured as a positive displacement pump that incorporates screws or
spiraled
flights to impart motion to the production fluid.
[017] Turning to FIG. 3, shown therein is a partial cross-sectional view of a
preferred embodiment of the hydraulic turbine 116. The hydraulic turbine 116
is
preferably configured as a conventional turbomachine turned upside-down. In
this
configuration, the hydraulic turbine 116 converts a portion of the energy from
the
pressurized working fluid into torque. The torque is then transferred through
the
driveline 130 into the production pump 104.
[018] The hydraulic turbine 116 preferably includes a turbine housing 146, one
or
more turbine stages 148, a turbine intake 150 and a turbine discharge 152.
Pressurized working fluid is introduced to the hydraulic turbine 116 from the
feed line
118 through the turbine intake 150. As noted in FIG. 3, the turbine diffusers
156 and
turbine impellers 154 are provided in a "reverse orientation" to the "standard
orientation" of the production pump diffusers 144 and production pump
impellers
142. As pressurized working fluid is forced through the hydraulic turbine 116,
the
turbine impellers 154 rotate in response to the pressurized fluid. The
pressurized fluid
exits from the hydraulic turbine 116 into the return line through the turbine
discharge
152.
[019] In a presently preferred embodiment, the hydraulic turbine 116 and
production
pump 104 are sized and configured to produce offsetting thrust forces. The
hydraulic
turbine produces an upward thrust along the driveline 130, while the
production pump
104 produces a downward thrust. In a particularly preferred embodiment, the
production pump 104, the hydraulic turbine 116 and the master pump 112 are
collectively configured to minimize the amount of differential thrust
transferred
across the driveline 130. By limiting the amount of differential thrust, the
size of the
thrust section 128 can be reduced.
[020] In a particularly preferred embodiment, portions of the pumping system
100
are preassembled before being introduced into the well. For example, the
thrust
section 128 can be oil serviced before connection to the seal section 126 and
production pump 104. The feed line 118 and return line 120 can be connected to
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hydraulic turbine 116 before deployment. In an alternate preferred embodiment,
the
feed line 118 and return line 120 can be ganged or collected together within a
single
housing. In yet another preferred embodiment, the feed line 118, return line
120 and
production tubing 106 are located within a common housing.
[021] It is to be understood that even though numerous characteristics and
advantages of various embodiments of the present invention have been set forth
in the
foregoing description, together with details of the structure and functions of
various
embodiments of the invention, this disclosure is illustrative only, and
changes may be
made in detail, especially in matters of structure and arrangement of parts
within the
principles of the present invention to the full extent indicated by the broad
general
meaning of the terms in which the appended claims are expressed. It will be
appreciated by those skilled in the art that the teachings of the present
invention can
be applied to other systems without departing from the scope and spirit of the
present
invention.
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