Note: Descriptions are shown in the official language in which they were submitted.
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
BIDIRECTIONAL PISTON SEALS WITH PRESSURE COMPENSATION
Related Applications
[001] The present application is a continuation-in-part of United States
Patent
Application Serial No. 14/075,656, entitled "Electric Submersible Motor Oil
Expansion
Compensator" filed November 8, 2013, the disclosure of which is herein
incorporated by
reference.
Field of the Invention
[002] This invention relates generally to the field of submersible pumping
systems, and
more particularly, but not by way of limitation, to a system for accommodating
the
expansion of motor lubricants in high-temperature environments.
Background
10031 Submersible pumping systems are often deployed into wells to recover
petroleum
fluids from subterranean reservoirs. Typically, the submersible pumping system
includes
a number of components, including one or more fluid filled electric motors
coupled to
one or more high performance pumps located above the motor. When energized,
the
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.
[004] Components commonly referred to as "seal sections" protect the electric
motors
and are typically positioned between the motor and the pump. In this position,
the seal
section provides several functions, including transmitting torque between the
motor and
pump, restricting the flow of wellbore fluids into the motor, protecting the
motor from
1
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
axial thrust imparted by the pump, and accommodating the expansion and
contraction of
motor lubricant as the motor moves through thermal cycles during operation.
Prior art
seal sections typically include a "clean side" in fluid communication with the
electric
motor and a "contaminated side" in fluid communication with the wellbore.
Bellows or
bags have been used to separate the clean side of the seal section from the
contaminated
side.
10051 Recently, manufacturers have employed polymer expansion bags within the
seal
section to accommodate the expansion and contraction of motor lubricants while
isolating
the lubricants from contaminants in the wellbore fluid. Although generally
effective at
lower temperatures, the currently available polymers become somewhat permeable
at
extremely elevated temperatures and allow the passage of moisture across the
membrane.
The moisture reduces the insulating properties of polyimide and other films
used to
electrically isolate components within the downhole pumping system. Although
piston-
based systems may provide an alternative to the use of polymer expansion bags,
prior art
piston-based seal assemblies are susceptible to failure from sand, scale or
other
particulates. Moreover, the sealing rings used in existing pistons may deform
under
differential pressures, apply unwanted pressure against the interior of the
seal section
housing and reduce the movement of the piston. There is, therefore, a need for
improved
designs that can be used to accommodate expansion of motor fluids in elevated
temperature applications. It is to this and other needs that the presently
described
embodiments are directed.
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
Summary of the Invention
[006] In one aspect, the exemplary embodiments include an electric submersible
pumping system for use in pumping fluids from a wellbore. The electric
submersible
pumping system includes a motor, a pump driven by the motor, and a fluid
expansion
module connected to the motor. The fluid expansion module includes a piston
seal
housing and a first piston assembly contained within the piston seal housing.
The first
piston assembly includes a piston body having an exterior surface, a plurality
of seals
connected to the exterior surface of the piston body and a pressure
equalization system.
The pressure equalization system reduces a pressure differential between fluid
in an
annular space between the plurality of seals and fluid surrounding the first
piston
assembly.
[007] In another aspect, the embodiments of the present invention include a
system for
accommodating the expansion of motor lubricant in a motor within an electric
submersible pump used for removing fluids from a wellbore. The system includes
a seal
section connected to a first end of the motor and a fluid expansion module
connected to
the second end of the motor. The fluid expansion module has a longitudinal
axis and at
least one piston assembly. The at least one piston assembly moves along the
longitudinal
axis of the fluid expansion module in response to an expansion of the motor
lubricant.
The at least one piston assembly includes a piston body having an exterior
surface, a
plurality of seals connected to the exterior surface of the piston body, and a
pressure
equalization system. The pressure equalization system reduces a pressure
differential
between fluid in the annular space between the plurality of seals and fluid
surrounding
the at least one piston assembly.
3
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
[008] In yet another aspect, the embodiments of the present invention include
a fluid
expansion module for use in an electric submersible pumping system that
includes a
pump driven by a fluid-filled motor. The fluid expansion module includes a
piston seal
housing in fluid communication with the fluid-filled motor and a first piston
assembly
contained within the piston seal housing. The first piston assembly includes a
piston
body having an exterior surface, a plurality of seals connected to the
exterior surface of
the piston body and a pressure equalization system. The space between the
plurality of
seals creates an annular space and the pressure equalization system reduces a
pressure
differential between fluid in the annular space and fluid in the piston seal
housing.
Brief Description of the Drawings
[009] FIG. 1 depicts a submersible pumping system constructed in accordance
with an
embodiment of the present invention.
[010] FIG. 2 provides a cross-sectional view of the motor, lower fluid
expansion
module and seal section of the submersible pumping system of FIG. 1.
[011] FIG. 3 presents a cross-sectional representation of the motor of the
pumping
system from FIG. 2.
[012] FIG. 4 presents a cross-sectional representation of the lower fluid
expansion
module of FIG. 2.
[013] FIG. 5 presents a cross-sectional view of a piston assembly constructed
in
accordance with a first embodiment.
[014] FIG. 6 presents a cross-sectional view of a piston assembly constructed
in
accordance with a second embodiment.
4
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
[015] FIG. 7 presents a perspective view of the sealing ring from the piston
assemblies
of FIGS. 5 and 6.
[016] FIG. 8 provides a cross-sectional view of the seal section and motor of
the
pumping system from FIG. 2.
[017] FIG. 9 provides a cross-sectional view of a mechanical seal from the
seal section
of FIG. 7.
Detailed Description
[018] FIG. 1 shows an elevational view of a pumping system 100 attached to
production
tubing 102. The pumping system 100 and production tubing 102 are disposed in a
wellbore 104, which 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.
[019] The pumping system 100 includes a pump 108, a motor 110, a seal section
112
and a fluid expansion module 114. The production tubing 102 connects the
pumping
system 100 to a wellhead 106 located on the surface. Although the pumping
system 100
is primarily designed to pump petroleum products, it will be understood that
the pumping
system 100 can also be used to move other fluids. It will also be understood
that,
although each of the components of the pumping system are primarily disclosed
in a
submersible application, some or all of these components can also be used in
surface
pumping operations.
[020] Generally, the motor 110 is configured to drive the pump 108. Power is
provided
to the motor 110 through a power cable 116. In some embodiments, the pump 108
is a
turbomachine that uses one or more impellers and diffusers to convert
mechanical energy
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
into pressure head. In other embodiments, the pump 108 is configured as a
positive
displacement pump. The pump 108 includes a pump intake 118 that allows fluids
from
the wellbore 104 to be drawn into the pump 108. The pump 108 forces the
wellbore
fluids to the surface through the production tubing 102.
[021] The seal section 112 is positioned above the motor 110 and below the
pump 108.
The fluid expansion module 114 is positioned below the motor 110. Although
only one
of each component is shown, it will be understood that more can be connected
when
appropriate, that other arrangements of the components are desirable and that
these
additional configurations are encompassed within the scope of exemplary
embodiments.
For example, in many applications, it is desirable to use tandem-motor
combinations, gas
separators, multiple seal sections, multiple pumps, sensor modules and other
downhole
components.
[022] It will be noted that although the pumping system 100 is depicted in a
vertical
deployment in FIG. 1, the pumping system 100 can also be used in non-vertical
applications, including in horizontal and deviated wellbores 104.
Accordingly,
references to "upper" and "lower" within this disclosure are merely used to
describe the
relative positions of components within the pumping system 100 and should not
be
construed as an indication that the pumping system 100 must be deployed in a
vertical
orientation.
1023] Referring now also to FIGS. 2 and 3, shown therein is a cross-sectional
view of
the seal section 112, motor 110 and fluid expansion module 114. As depicted in
the
close-up view of the motor 110 in FIG. 3, the motor 110 includes a motor
housing 120,
stator assembly 122, rotor assembly 124, rotor bearings 126 and a motor shaft
128. The
6
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
stator assembly 122 includes a series of stator coils (not separately
designated) that
correspond to the various phases of electricity supplied to the motor 110. The
rotor
assembly 124 is keyed to the motor shaft 128 and configured for rotation in
close
proximity to the stationary stator assembly 122. The size and configuration of
the stator
assembly 122 and rotor assembly 124 can be adjusted to accommodate application-
specific performance requirements of the motor 110. Sequentially energizing
the various
series of coils within the stator assembly 122 causes the rotor assembly 124
and motor
shaft 128 to rotate in accordance with well-known electromotive principles.
The motor
bearings 126 maintain the central position of the rotor assembly 124 within
the stator
assembly 122 and oppose radial and axial forces generated by the motor 110 on
the motor
shaft 128.
[024] The motor 110 is filled with non-conductive lubricating oil during
manufacture
that reduces frictional wear on the rotating components within the motor 110.
As the
motor 110 cycles during use and as the motor 110 is exposed to the elevated
temperatures
in the wellbore 104, the lubricating oil expands and contracts. It is
desirable to prevent
the clean motor oil from becoming contaminated with fluids and solids in the
wellbore.
To permit the expansion and contraction of the lubricating oil under elevated
wellbore
temperatures, the seal section 112 and fluid expansion module 114 are
connected to the
motor 110 and placed in fluid communication with the motor oil.
[025] Continuing with FIG. 2 and referring now also to FIG. 4, shown therein
is a cross-
sectional view of the fluid expansion module 114. In the embodiment depicted
in FIG. 4,
the fluid expansion module 114 includes a piston seal housing 130, a bag seal
housing
132, one or more piston assemblies 134, a bag seal assembly 136 and a fluid
exchange
7
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
assembly 138. It will be appreciated, however, that in some embodiments, the
fluid
expansion module 114 may not include all of these components.
10261 As shown in FIG. 4, the fluid expansion module 114 includes a pair of
piston
assemblies 134a, 134b. The piston assemblies 134a, 134b are located in the
piston seal
housing 130 and are configured for axial movement within the fluid expansion
module
114 in response to a difference in pressure in the fluid surrounding the
piston assembly
134. Thus, if each piston assembly 134 is permitted to move freely within the
piston seal
housing 130, the piston assembly 134 will maintain a relatively minimal
pressure
differential across the piston assembly 134.
10271 In some embodiments, the inside surface of the piston seal housing 130
includes a
polymer liner 140 that reduces friction and stiction. The polymer liner 140
can be
manufactured from PTFE, PFA, PEEK and other high-temperature polymers.
Alternatively, the inside surface of the piston seal housing 130 can be
manufactured from
polished chrome, stainless steel or other durable metal. It will be noted that
piston
assembly 134a is constructed in accordance with a first embodiment and piston
assembly
134b is constructed in accordance with a second embodiment. The similarities
and
differences between the first and second embodiments of the piston assemblies
134a,
134b are described below.
10281 Turning to FIG. 5, shown therein is a cross-sectional view of the first
embodiment
of the piston assembly 134a within a portion of the piston seal housing 130.
The piston
assembly 134a includes a solid piston body 142 and a pair of seals 144. In
some
embodiments, the piston body 142 is manufactured from a highly-polished metal.
Suitable metals include chrome, stainless steel and related alloys.
Alternatively, the
8
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
piston body 142 can be manufactured from a high-temperature rated elastomer or
polymer. Polymers of the piston body 142 include polytetrafluoroethylene
(PTFE),
perfluoroalkoxy (PFA) and polyethether ketone (PEEK). The piston body 142 has
an
outside diameter that is only slightly smaller than the inside diameter of the
piston seal
housing 130. The seals 144 are positioned around the exterior of the piston
body 142 at
opposite ends of the piston body 142.
[029] Turning to FIG. 6, shown therein is a cross-sectional view of the second
embodiment of the piston assembly 134b within a portion of the piston seal
housing 130.
The piston assembly 134b includes a piston body 142 and pair of seals 144. The
seals
144 are positioned around the exterior of the piston body 142 at opposite ends
of the
piston body 142. The piston assembly 134b further includes a pressure
equalization
system 146 that is configured to reduce the pressure differential across the
seals 144 to
minimize the pressure-induced deformation of the seals 144. Reducing the
pressure
gradient across the seals 144 allows the piston assembly 134b to move more
easily within
the piston housing 130 while maintaining a positive barrier between the clean
motor fluid
above the piston assembly 134b and the wellbore fluid below the piston
assembly 134b.
[030] The pressure equalization system 146 includes an inlet check valve 148,
an
equalization chamber 150, one or more pressure ports 152 and a release check
valve 154.
The one or more pressure ports 152 extend from the equalization chamber 150
through
the piston body 142 to the annular space 158 between the piston body 142 and
the interior
wall of the piston seal housing 130 between the seals 144. In this way, the
equalization
chamber 150 is placed in fluid communication with the annular space 158.
9
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
[031] The inlet check valve 148 is a one-way valve that opens when a pressure
differential exceeds a predetermined threshold amount between the space above
the
piston assembly 134b and the equalization chamber 150. When the inlet check
valve 148
temporarily opens, clean motor lubricant passes through the inlet check valve
148 to
increase the pressure within the equalization chamber 150 and the annular
space 158 to
reduce the pressure gradient across the seals 144. The amount of differential
pressure
required to open the inlet check valve 148 can be set during manufacturing by
adjusting
the amount of closing force applied by a spring within the inlet check valve
148. In
exemplary embodiments, the inlet check valve 148 is configured to open under a
differential pressure that is greater than the amount of differential pressure
that is
anticipated to be present around the piston assembly 134b under normal
operating
conditions. In this way, the inlet check valve 148 will not open prematurely
and reduce
the movement of the piston seal assembly 134b under ordinary operating
conditions.
[032] The release check valve 154 is calibrated to temporarily open if the
pressure
within the equalization chamber 150 exceeds the pressure below the piston
assembly
134b by a predetermined threshold amount. This relieves the elevated pressure
within the
piston assembly 134b to reduce any pressure gradient across the seals 144.
Once the
elevated internal pressure has been relieved, the release check valve 154
closes to prevent
any fluids from passing into the equalization chamber 150.
1033] Thus, the pressure equalization system 146 ensures the optimal
performance of
the seals 144 by reducing the deformation-based friction between the piston
assembly
134b and the piston seal housing 130. This allows the piston assembly 134b to
respond
quickly to slight pressure imbalances within the piston seal housing 130. For
example, if
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
the pressure below the piston assembly 134b increases during the installation
of the
pumping system 100 in the wellbore 104, the piston assembly 134b may be forced
upward to increase and balance the pressure above the piston assembly 134b. If
the
increased pressure above the piston assembly 134b is sufficiently greater than
the
pressure within the equalization chamber 150, the inlet check valve 148 will
temporarily
open to equalize the pressure around the seals 144.
[0341 FIG. 7 presents a cross-sectional view of the seal 144. The seal 144
includes a
body 160 and an interior spring 162. The body 160 is manufactured from a
durable,
high-temperature and wear-resistant elastomer or polymer, such as
polytetrafluoroethylene (PTFE), perfluoroalkoxy (PEN), polyethether ketone
(PEEK) and
perfluoroelastomer. The interior spring 162 is configured to exert force
against the body
160 in an outward radial direction. In this way, the sprint., 162 presses the
body 160
against the inside surface of the piston seal housing 130. The interior spring
162 can be
configured as a coiled ring, or finger springs.
10351 Turning to back FIG. 4, the bag seal assembly 136 is contained within
the bag
seal housing 132. The bat., seal assembly 136 includes a bag support 164, a
bladder 166,
inlet ports 168 and discharge valves 170. The bag support 164 is rigidly
attached to the
inside surface of the bag seal housing 132. The bladder 166 is secured to the
bag support
164 with compression flanges 172. Alternatively, the bladder 166 can be
secured to the
bag support 164 with grips or hose clamps. The inlet ports 168 provide a path
of fluid
communication from the piston seal housing 130 into the inside of the bladder
166 and
bag support 164. Importantly, the bag support 164 permits the passage of
fluids between
the piston seal housing 130 and bag seal housing 132 only through the inlet
ports 168.
11
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
Fluids external to the bladder 166 are not allowed to pass directly into the
piston seal
housing 130.
10361 The discharge valves 170 are one-way relief valves that are configured
to open at
a predetermined threshold pressure that exceeds the exterior wellbore
pressure. In this
way, if the fluid pressure inside the bladder 166 exceeds the set-point
pressure, the
discharge valves 170 open and relieve the pressure inside the bladder 166 by
discharging
a small volume of fluid into the wellbore 104. The bladder 166 can be
manufactured
from a high-temperature polymer or elastomer. Suitable polymers and elastomers
include
polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA) and polyethether ketone
(PEEK).
[037] The bag seal housing 132 also includes the fluid exchange assembly 138.
The
fluid exchange assembly 138 optionally includes a solids screen 174 and a
plurality of
exchange ports 176. The exchange ports 176 allow fluids to pass from the
wellbore 104
through the solids screen 174 into the bag seal housing 132 around the
exterior of the
bladder 166. The solids screen 174 reduces the presence of particulates in the
bag seal
housing 132. The solids screen 174 is manufactured from a metal or polymer
fabric
mesh.
[038] During manufacture, the fluid expansion module 114 is filled with clean
motor
lubricant. The piston assemblies 134a, 134b are then placed into the piston
seal housing
130. As the fluid in the motor 110 expands during operation, the increased
volume exerts
pressure on the upper side of the piston assembly 134b. In response, piston
assembly
134b moves downward toward piston assembly 134a. When the volume between the
piston assemblies 134a, 134b decreases, the increased pressure on piston
assembly 134a
forces it downward toward the bag seal housing 132. As piston assembly 134a
moves
12
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
downward it pushes clean motor lubricant through the inlet ports 168, through
the bag
support 152 and into the bladder 166. The bladder 166 expands to accommodate
introduction of fluid from the piston seal housing 130. As the bladder 166
expands, fluid
external to the bladder 166 is expelled through the exchange ports 176 and
solids screen
160. If the pressure inside the bladder 166 exceeds the threshold pressure
limit of the
discharge valves 170, the discharge valves 170 open and vent a portion of
fluid into the
wellbore 104.
[039] Conversely, during a cooling cycle, the fluid in the motor 110 contracts
and the
movement of the components within the fluid expansion module 114 reverses. As
the
pistons 134a, 134b are drawn upward, fluid is pulled out of the bladder 166.
As the
volume and pressure inside the bladder 166 decreases, fluid from the wellbore
is pulled
into the bag seal housing 132 through the solids screen 174 and exchange ports
176. The
fluid expansion module 114 provides a robust mechanism for allowing expansion
and
contraction of lubricants from the motor 110 while maintaining an isolation
barrier
between the clean motor lubricants and the contaminated fluids from the
wellbore 104.
Notably, the use of piston assemblies 134 provide redundant barriers to the
bladder 166
that are not susceptible to the increased permeability found in even high-
temperature
bladders. Accordingly, even if the bladder 166 is exposed to extremely high
temperatures and permits the passage of some moisture from the wellbore 104
into the
piston seal housing 130, the moisture is isolated from the motor 110 by the
redundant
piston assemblies 134.
[040] It will be appreciated that the fluid expansion module 114 can include
one or
more piston assemblies 134 that may include the first embodiment of the piston
assembly
13
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
134a, the second embodiment of the piston assembly 134b, or a combination of
the first
and second embodiments of the piston assemblies 134a, 134b (as shown in FIG.
4).
Additionally, it will be appreciated that in some embodiments, the piston
assemblies 134
may be used without the use of the bag seal assembly 136. In certain
applications, it may
be desirable to place the pump 108 below the motor 110. In those applications,
the fluid
expansion module 114 will be positioned above the motor 110 and the seal
section 112
will be placed between the motor 110 and the pump 108. In these alternative
embodiments, the bag seal housing 132 will be positioned above the piston seal
housing
130.
[041] Turning to FIG. 8, shown therein is a cross-sectional view of the motor
110 and
seal section 112. The seal section 112 is attached to the upper end of the
motor 110 and
provides a second system for accommodating the sealing of the rotating shaft
128 to the
equipment and support the thrust load of the pump 108. The seal section 112
includes a
seal section shaft 178, a thrust bearing assembly 180, one or more mechanical
seals 182
and one or more relief valves 184. During manufacture, the seal section 112 is
filled with
clean motor lubricant oil.
[042] The seal section shaft 178 is coupled to the motor shaft 128, or formed
as a
unitary shaft with the motor shaft 128, and transfers torque from the motor
110 to the
pump 108. The thrust bearing assembly 180 includes a pair of stationary
bearings 186
and a thrust runner 188 attached to the seal section shaft 178. The thrust
runner 188 is
captured between the stationary bearings 186, which limit the axial
displacement of the
runner 188 and the motor shaft 128 and seal section shaft 178.
14
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
[043] As shown in FIG. 8, the seal section 112 includes a plurality of
mechanical seals
182. As best illustrated in the close-up view of the mechanical seal 182 in
FIG. 9, the
mechanical seals 182 each include bellows 190, a coiled spring 192, a runner
194 and a
stationary ring 196. These components cooperate to prevent the migration of
fluid along
the seal section shaft 178. The stationary ring 196 has an internal diameter
sized to
permit the free rotation of the seal section shaft 178. In contrast, the
bellows 190, spring
192 and runner 194 rotate with the seal section shaft 178. The rotating runner
194 is held
in place against the stationary ring 196 by the spring-loaded bellows 190. The
bellows
190 includes a series of folds that allow its length to adjust to keep the
runner 194 in
contact with the stationary ring 196 if the seal section shaft 178 should
experience axial
displacement. The bellows 190 may be manufactured from thin corrugated metal
or from
elastomers and polymers, including AFLAS, perfluoroelastomer,
polytetrafluoroethylene
(PTFE), perfluoroalkoxy (PFA) and polyethether ketone (PEEK).
[0441 The exemplary embodiments include a method of accommodating the
expansion
of motor lubricant with a fluid expansion module. The method includes the
steps of
providing a fluid expansion module that includes a piston seal housing and one
or more
pistons that have a pressure equalization system. The method further includes
the step of
connecting the fluid expansion module to a first end of the motor such that
the lubricant
in the motor is in fluid communication with the fluid expansion module. The
method
may also include the step of connecting a seal section to the second end of
the motor.
[045] 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
CA 03068438 2019-12-23
WO 2018/236515
PCT/US2018/033762
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.
16
