Note: Descriptions are shown in the official language in which they were submitted.
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Universal Motor Head for Electrical Submersible Pump
This invention relates to an electrical submersible pump ("ESP") such as is
used in oil well
pumping operations. ESP systems consist, typically, of an assembled selection
of modular,
tandem pump and motor components from an inventory of components. The modular
tandem
motor components in the inventory, as supplied by international ESP
manufacturers today,
typically may include one or more of an Upper Tandem Motor ("UT"), a Centre
Tandem Motor
("CT"), and a Lower Tandem Motor ("LT"). The present invention provides a
Universal Motor
Head ("UMH") which facilitates a broader scope of use of the CT and LT
components.
Background of the Invention
An ESP is a pump that is designed to provide a pressure differential across
its length at
an optimized fluid flow rate. ESPs are designed and manufactured for
installation within narrow
diameter casings; generally pumps are between 3.38" and 10.5" in diameter and
motors are
between 3.75" and 7.38" in diameter. They are used to produce fluids such as
oil, water and
liquid gas and are predominantly applied to the international oil fields.
Presently, ESP manufacturers offer a wide variety of component products that
are
combined to make a working ESP system. An ESP will commonly consist of a
threaded pump
head for tubing connection, pump section (single or multiple tandems), intake
section, motor
protector / seal section, motor section (single or multiple tandems) and a
motor base (separately
mounted or factory installed) with an internal winding connector.
Power is supplied to the ESP motor through a cable that runs from the surface
power
supply facilities to the motor, where the power cable enters the motor through
a dedicated
connection port that is at the top of the upper motor. The end of the main
power cable has a
dedicated connector, commonly referred to as a 'pothead', and the dedicated
motor connection
port is commonly referred to as a 'pothole'. The pothole is generally of the
largest size possible
to fit within the constraints of the overall motor diameter and is normally
only suitable for the
specific type of motor being applied.
The reser~~oir characteristics and the volume of fluid being produced
determine the motor
horsepower requirements for ESP operation. In high pressure or high flow rate
pump
applications, horsepower requirements may exceed the amount available from a
single section
motor. Single section motor sizes are limited by their required relatively
small external diameter
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(to fit the drill hole) and the maximum transportable length of about 3 S feet
per section. Motors
are therefore designed to be connected together to increase the available
horsepower. Generally,
the individual motor sections are specified with the same horsepower, voltage
and current ratings.
For example, if a pump requires 300 hp to operate, then two sections of 150 hp
or three sections
of 100 hp motors would be assembled in series (or in tandem) to meet the
demand.
An ESP in use today may consist of a Single Section Motor ("STD" - for
"standard"),
which is made as a complete, stand alone unit for single motor applications,
or may consist of one
or more tandem motors. A tandem motor is made to be used in conjunction with
one or more
other tandem motors. The tandem motors currently available include the above-
noted UT, LT
and CT.
The UT has a wound stator, at its top an integral head with a flange for
connection to a
seal section / protector and an external cable entry port for a power cable
connection and at its
bottom an integral base with a flange connection with internal power
connection terminals for
connecting to the top of a CT or LT in multiple (tandem) motor applications.
If it is desired to
operate the UT as a single motor, then a universal motor base ("UMB") may be
used to close the
internal power connection terminals at the bottom of the UT. A UMB has power
connection
terminals at its top and forms a 3-phase Y-Point internally.
The CT has a wound stator, at its top an integral head with a flange with
internal power
connection terminals for connection to the bottom of another CT or to the
bottom of a UT, and
at its bottom an integral base with a connection flange with internal
electrical terminals for
connection to the top of another CT or to the top of an LT. A UMB may also be
connected to
the bottom of a CT if the CT is to be the bottom unit of a tandem motor unit,
i.e. if it is to be used
as if it were an LT. A CT type motor does not have an external cable entry
port and cannot
presently be used as the top unit of a tandem motor unit.
The LT has a wound stator, an integral head at its top with a flange with
internal power
connection terminals for connection to the bottom of a CT or UT, and has
internal factory
connected windings at the bottom to complete the three-phase power circuit and
end the tandem
unit. The LT can, therefore, presently only function as a lower unit of a
multiple motor unit.
It is apparent from the foregoing that, if a tandem, multiple section motor is
required, then
an UT motor must be used to facilitate connection of the main incoming power
cable.
There is, therefore, a need for a device which would expand the useful
capabilities of CT
and LT motors without the requirement for use of an UT motor to complete an
ESP of modular
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assembly. The prior art has not addressed this need, as is apparent from the
discussion below of
two United States patents relating to tandem motor assemblies.
United States Patent No. 3,255,367 discloses a multiple section motor assembly
which has
end termination units that cover the open ends of the assembly and contain
elements for improving
operation of the assembly. However, this patent discloses a fully integrated
motor assembly
which can only be assembled in a factory and is designed for application in a
specific layout with
no flexibility to change the assembly order of component parts. Thus, the
motor units and end
termination units are only modular parts in so far as final assembly must take
place at the well site.
They are not modular with respect to the interchangeability of the upper and
lower motor
sections. In this case the top section must always be a motor with a power
cable connection port.
Thus, these are not true modular components, for addition and removal
depending on needs at
the drill site, but rather are factory installed with a dedicated motor 'head'
using complex
components of an assembly intended to be shipped and used without modification
at the drill site.
For example, one end termination unit contains means for circulating a coolant
throughout the
assembly, a thrust bearing device for supporting the entire thrust load of the
assembly during its
operation, and a pressure balancing device. It is apparent that this patent
does not teach towards
a simple, modular device for easy installation and removal as an inventory
item of a modular
tandem motor system for making ESPs at a drill site.
United States Patent No. 3,384,769 is directed to a submersible pump assembly
including
a plurality of motor modules. The number of motor modules in an assembly may
be chosen to
provide the power out-put required. The motor modules are releasably connected
together at
their adjacent ends, via intermediate electrical connectors, so that the horse
power rating of the
assembly may be readily changed merely by adding or subtracting a standardized
motor module
without having to provide a different length of casing. The assembly includes
an "auxiliary
module" (in some respects similar to a modern day Protector / Seal Section), a
complex device
with several functions including equalizing pressure between the motor and the
annulus,
separation of the motor oil from the well (production) fluids; absorbing the
thrust loading from
the pump, and transfer of power generated by the motor to the pump. The
auxiliary module is
shown connected to a motor module by a connecting member, the latter being
permanently
attached at one connection to the auxiliary module but detachably connected
(with the auxiliary
module) to a motor module at another connection. The connecting member is
partly designed to
electrically connect the windings of the motor module to a three wire cable
which leads to a three
phase power supply for the entire assembly. It also accommodates a connection
between the
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drive shaft of a motor module and the auxiliary module. Since the connecting
member is a
permanent part ofthe somewhat complex auxiliary module, it is necessary for
the entire auxiliary
module to be used at the upper end of an assembly according to the teachings
of this patent.
Stockpiles of auxiliary modules would be costly to develop and would result in
similar problems
posed by the required use of UT units in tandem motor assemblies. Furthermore,
the auxiliary
module is not able to be connected in tandem with another auxiliary module,
for example to
increase the fluid pressure equalization facility, due to the permanently
attached connecting
member.
There is a need in the ESP art, therefore, for an element which will enable a
low cost
utilization of existing stockpiles of CT and LT units without having to use UT
units, or other
costly, complex units.
Summar~of the Invention
The invention provides a motor head for detachable attachment to a centre
tandem motor
or a lower tandem motor of a modular electrical submersible pump at a well
site. The motor head
comprises a first mechanical connector means configured for detachable
attachment of the motor
head at the well site to a top of a centre tandem motor or a top of a lower
tandem motor. There
is also a second mechanical connector means configured for detachable
attachment ofthe motor
head at the well site to a bottom of a protector / seal section. Preferably,
the first and second
mechanical connector means are flange-type connectors. There is also a
rotatable shaft configured
for power transfer from the centre tandem motor or the lower tandem motor to
the protector /
seal section. There is a first electrical connector for electrical connection
to an electrical power
source for the pump. Preferably, the first electrical connector is a plug
receptacle with side walls
at an angle from vertical of about 5° to 30°, more preferably
about 10° to 15° and most
preferably about 12° to 13 °. There is a second electrical
connector for electrical connection to
either the centre tandem motor or the lower tandem motor. There is, further,
an electrical conduit
to convey electrical power from the first electrical connector to the second
electrical connector.
The motor head also comprises a pressure-equalization fluid conduit for
between the centre
tandem motor or the lower tandem motor and the protector / seal section.
The universal motor head ("UMH") of the invention therefore may be used to
close the
internal power connection terminals at the upper end of a CT or LT. The
inventive UMH has
internal power connection terminals at the bottom, for connecting to the top
of a CT or LT, and
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port for external power cable connection at the top. An advantage of a UMH is
that a CT with
a UlV>TI can be used as if it were a UT, and an LT can be used as if it were a
single motor unit.
The greatly enhanced versatility of the CT and LT units obtained with the
UNB3, particularly CT
type motors in conjunction with UMB units, can lead to reduced motor stocks
and operating
costs.
Description of the Drawings
Figure 1 schematically illustrates ESP modular motor components available
currently from
international manufacturers;
Figure 2 schematically illustrates standard motor string configurations based
on the motor
components of Figure l;
Figure 3 schematically illustrates a UMI-I of the present invention and two
applications;
Figure 4 shows a cross-sectional view of a U1VBI of the present invention;
Figure S shows a cross-sectional view of the UMIi of Figure 4 including three
transverse
sectional views thereof; and
Figure 6 shows a three dimensional perspective view of the UMFI of Figure 4
Description of the Preferred Embodiments
The following description relates to one preferred embodiment of the present
invention
and is, therefore, not intended to be limiting of the scope of the invention
as defined in the claims
herein.
With reference to prior art Figure 1, there is shown a STD motor, a LJT motor,
a CT
motor and a LT motor. Beside each is shown the corresponding electrical wiring
configuration.
The STD motor is factory assembled as a complete unit for single motor
applications. It cannot
be used with other motors. It has a pothole in the head for power cable
connection and the
bottom windings are internally connected at the factory.
The UT motor is factory assembled with internal power connection terminals at
the
bottom. It has a pothole for power cable connection and, unless the present
invention is used,
must be used as the top motor when tandem motors are required. It can be used
as a complete
unit for single motor applications if a UMB is added.
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The LT motor is factory assembled with internal power connection terminals at
the top.
It does not have a pothole for power cable connection and must be used as the
bottom motor
when tandem motors are required. The bottom windings are internally connected
at the factory.
The CT motor is factory assembled with internal power connection terminals at
the top
and bottom. It must be used as the centre motor when tandem motors are
required. It can be
used as the lower tandem motor when a UMB is added.
The UMB attaches to the base of a motor and forms a three-phase Y-point.
Figure 2 illustrates conventional, i.e. prior art, string configurations using
the components
described above and shown in Figure 1. It is apparent that only a UT motor may
be used as the
top motor of any string.
Figure 3 illustrates application of the UMH of the invention in two
exemplified
configurations. The UMH is manufactured and factory assembled preferably with
internal power
connection terminals at the bottom. It preferably has a pothole for power
cable connection at the
top and is designed for connection to the top of a CT or LT motor.
With reference to Figure 4, in a preferred embodiment of the present invention
the
Universal Motor Head (UMH) consists ofthe main body 1 which has flange-type
connections and
'O' ring seals for attachment to a protector / seal section at the top 2 and a
tandem-type motor
at the bottom 3. The body 1 may be made of any of a wide variety of materials,
but preferably
may be made of carbon steel, stainless steel, or monel. A protector / seal
section is a separate
piece (not part of the present invention) which, absent the present invention,
attaches to the top
of a motor and contains an oil reservoir for the motor. As background, it is
noted that the
protector / seal section is designed to:
a) equalize pressure between the motor and the surrounding well bore (the
average oil well
pressure may be at 2500 psi, but the motor is assembled at surface pressure of
about 14 psi; it
cannot simply be sealed against invasion of well fluid under well pressure);
b) minimize contamination of the clean motor oil by the dirty well fluid by
using a
combination of Positive Seal (elastomer rubber bags that have motor oil inside
and well fluid
outside - separated by a non-return valve) and Labyrinth (a long convoluted
flow path that allows
well fluid / motor oil contact but that relies on different fluid gravities
for separation) sections; and
c) transfer power up to the pump sections through a central shaft; and
d) incorporate a thrust bearing to absorb the down thrust load generated by
the
differential pressure across the pump sections(s) above.
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All segments of ESP's currently are joined using bolted flanges. The number of
bolt holes
may vary, but the basic form is generally the same. The upper end of the UMI-I
preferably
therefore has a head that extends upwards to form a flange with as large an
outside diameter as
possible, and the inside diameter is determined by the O-ring seal that is
being used, and has a
smooth finish. The top of this flange preferably is drilled and tapped for the
bolts that will
typically be used to secure to the upper protector / seal section. The bottom
flange preferably is
machined with a protruding shoulder that fits inside the lower head, i.e.
inside the flange of the
upper end of the lower motor unit. This shoulder may be machined with one or
more grooves for
'O-ring' seals. The bottom flange has slightly larger holes drilled that will
line-up with the holes
drilled and tapped in the upper flange ofthe lower unit. The upper and lower
flanges each include
a central hole for accommodating passage of a drive shaft 4 from the motor up
to the driven
system.
The UNIFI of the present invention, which intervenes between a protector /
seal section
and a motor, has the central shaft 4 for power transfer through the head. The
central shaft is
configured, e.g. with spline or key, for coupling to a shaft of the motor
below and a shaft
extending to a system to be driven above. The shaft 4 preferably is supported
by shaft bearings
or bushings 5 and isolated from the internal wiring by a guard tube 6. The
shaft bearings or
bushings 5 are in direct contact with the motor fluid and are both cooled and
lubricated by such
fluid. The UMFI includes an internal flow path (not shown), e.g. formed by
drilling one or more
through holes from top to bottom, for motor fluid from the motor unit below to
the protector /
seal section above. This ensures free movement of motor fluid in response to
changing pressure.
In a typical ESP, the protector / seal section includes a thrust bearing to
take the thrust
loads transferred downwards from the pump shaft. Thus the UMfI does not
require a thrust
bearing. The only load on the UMI-I is that from the mass of the shaft; the
differential pressure
between the two ends of the shaft being nominal. The underlying motor assembly
is supported
by the bearing at the top of the motor, thus the weight of the UMI-I shaft
will ride on the motor
bearing.
The UNIFi has a pothead attachment port 7 (or "pothole") for connection of a
main
incoming power cable, and internal cabling 8 to facilitate transfer of power
from the pothead to
preferably internal motor connectors 9 of which one generic phase (of three)
is shown in Figure
4. The actual size of the pothole may vary. Preferably, the port 7 has side
walls angled from
vertical at from about 5° to 30°, more preferably about
12° to 18 °and most preferably about
15 °, and has a lower face at right angles to the side walls. Sealing
of a pothead in the porthole
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may be by use of an 'O' ring and a dedicated 'O' ring groove on the outside
diameter of an
extended pothead face. The UMH can be adapted to work with "tape-in" or "plug-
in"
connectors. Both types fit within the recess in the UMH without protruding
past the the outside
diameter of the motor. As these each typically include three connectors for
three phase power,
these are preferably connected in use to a low profile parallel conductor (a
flat cable to fit between
the ESP and the side of the bore hole) that runs up to the main power cable.
The field attachable UMH of the present invention is unique in that:
(a) The UMH allows a CT or LT type motor to be connected, as the top motor
section, to a protector / seal section. Such was not possible prior to the
present invention as CT
and LT type motors do not have a power connection port for main power cable
connection;
(b) When attached to a CT or LT type motor the UMH will convert the function
of
the assembled unit to that of an UT or Single Section STD type motor
respectively;
(c) The UMH has an integral connection port (pothole) for attachment of a
power
cable pothead, which enables main power cable connection. Prior to the present
invention this
type of connection port was only available on UT type motors, which had to be
used as the top
motor component;
(d) The UMH is a separate component part that can be attached to a CT or LT
motor
either during manufacture, maintenance in a workshop or during final assembly
at the well site
(field);
(e) The UMH readily allows the end user to combine motors and protector / seal
sections from different manufacturers, which is normally not possible due to
flange size and bolt
pattern, 'O' ring seal size and type, electrical connection layout and
termination type and shaft size
and spine type incompatibilities.
The UMH allows ESP operators to meet their needs by stocking a relatively
small number
ofuniversally applicable CT motors, UMHs and UMBs. It also allows ESP users to
standardize
their motor types and sizes and significantly to reduce overhead associated
with running and
stocking ESP equipment. A stock of CT motors, in which each CT motor
effectively is a
"universal motor" that has the flexibility of being used as a UT, CT or LT
motor, thus eliminates
the need to purchase dedicated motor types.
The UMH is preferably designed to be compatible with all ESP designs for
connection
flange types and configurations, electrical connection and shaft connection
types and sizes. The
UMH preferably is therefore capable of adapting from any type of ESP motor to
any type of
protector / seal section, regardless of manufacturer. It follows that the UMH
allows ESP
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operators the option of mixing different manufacturers' equipment, thereby
increasing the
flexibility of ESP stocks.
