Note: Descriptions are shown in the official language in which they were submitted.
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MODULAR DOWNHOLE MULTll'I-IASE PUMP
FIELD OF THE INVENTION
The present invention relates to a downhole pump for producing oil and gas
wells, and more
particularly to a modular downhole multiphase pump.
BACKUROUND OF THE INVENTION
Downhole pumps are used to provide artiricial lift in order to produce
petroleum products
from oil and gas wells. Conventional downhole pumps include pumpjack type
pumps, progressive
cavity pumps ("PC pumps") and electric submersible pumps (or "ES pumps").
ES pumps are downhole centrifugal pumps to which power is supplied by a cable
running
though the well bore from the surface. 'these pumps are well known and widely
used but suffer
from comparatively low ~ pumping efficiency and ,gin inability to handle
solids entrained in the
production :fluid.
PC pumps are well known and use a metal rotor rotating within an elastomeric
stator to lift
production fluids to the surface through the well's tubing string. PC pumps
may be powered from a
surface top drive through a sucker rod or by electric submersible motors
located below the pump at
the end of the tubing string. While an improvement over walking beam pumps,
conventional PC
pumps present many disadvantages. 'fhe abrasive downhole environment quickly
degrades the
c;lastomeric stator. Aromatic compounds may cause the stator to blister and
degrade. The frictional
contact between the rotor and stator also wears out both the rotor and the
stator. Replacing or
repairing a downhole PC pump involves expensive downtime For the well because
the entire tubing
string must be pulled up by a service rig.
As well, PC pumps are most efficient if they are pumping liquids only. They do
not function
well with multiphase operations with luigh gas content. Very often, gases and
solids are produced
with liquids and may cause rapid degradation and wt°ar in the I'C_'
pump.
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Another significant problem with PC pumps is the potential for backspinning
caused by
reverse flour of fluid through the pump. This situation may occur if an
electrically powered top
drive unit suffers a power failure. A typical well may have a PC' pump which
is hundreds of meters
underground. The column of production fluid within the tubing string will fall
back through the PC
pump, causing the pump, the sucker rod and associated surface machinery to
backspin at very high
rates. In some cases, the backspitunitng may cause components in the top drive
to fail
catastrophically, with the potential to injure personnel in the vicinity of
the top drive.
Therefore, there is a need in the art for a downhole pump which migrates the
disadvantages
of the prior art above.
~~UMMARV OF THE INVENTION
In general terms, the inventic.m comprises a modular pump for underground use
in
connection with an oil well having a drive source which mad be a surface drive
which rotates a
sucker rod or which may be a downhole motor. In onfa aspect of the invention,
the pump comprises:
a) a rotor module comprising:
a cylindrical housing having a bottom face, a top face, a cylindrical face, an
inlet, an
outlet and an internal rotor enclosure between said inlet and outlet;
ii) at least one pair of intertwined and counter-rotating rotors within the
internal
rotor enclosure;
iii) means for rotating the rotors; and
b) a gear module having means for connecting to the drive source and means for
outputting power to the rotor module.
The rotor module preferably comprises an upper and a lower pair of rotors
separated by an
intake plenum wherein the upper pair of rotors drives fluid upwards into an
outlet plenum and the
lower pair of rotors drives fluid downwards into a fluid passage which then
joins the outlet plenum.
The rotor module housing inlet preferably comprises an intake opeung in the
cylindrical face of the
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housing, which is in fluid communication with the intake plenum.
Alternatively, the rotor module
housing inlet comprises an opening defined in the bottom face of the housing
and a inlet passage
connecting the opening with the intake plenum.
In a. preferred embodiment, the pump comprises at least one rotor module
housing
(hereinafter referred to as a "volume module") having an inlet comprising an
intake opening around
t:he circumference of the housing, which is in fluid cc~mmunieation with the
intake plenum; and at
least one rotor module housing (hereinafter referred to as va "pressure
module") having an inlet
comprising .an opening defined in the bottom face of the housing and a inlet
passage connecting the
opening with the intake plenum, wherein the outlet of the volume module
connects with the inlet of
t:he pressure module. More preferably, the pump further comprises a plurality
of volume and
pressure modules connected in series wherein the pressure modules are arranged
in ascending order
of pressure capacity.
The gear module may be adapted For use with a sucker rod as a power source, in
which case
it preferably is a speed increaser, or tine gear module may be adapted for use
with a downhole
electrical motor as a power source. In addition, gear modules may be provided
to transfer power
from one rotor module to another.
In another aspect of the invention, the invention comprises a rotor module for
use in
a.ssernbling a modular pump for underground use in connection with an oil
well, said rotor module
comprising a cylindrical housing having an upper surface. a circumferential
surface, a bottom
surface and defining an internal rotor enclosure, said rotor module
characterized in that:
(a) the bottom surface defrues an fluid intake opening and a bypass opening;
(b) the circumferential surface defines a lateral intake opening; and
(c) the upper surface defines a bypass outlet opening;
wherein each of the openings communicates with the rotor enclosure and some of
the openings may
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be plugged while others are kept open to control the flowpath of fluid into
and out of the housing
such that two or more rotor modules rnay be connected in series to increase
the pressure and/or
volume capacity for the pump.
In another aspect of the invention, the invention comprises a modular pump for
underground use comprising at least one volume rotor module and at least one
pressure rotor
module connected in series wherein:
(a) the volume rotor module comprises a housing defining a rotor enclosure
including
an intake plenum, a flow inlet opening communicating with the intake plenum,
interleaved and counter rotating rotors within the rotor enclosure, and a flow
outlet
opening; and
(b) the pressure rotor module comprises a housing defining a rotor enclosure
including
an intake; plenum, a single inlet opening which communicates with the flow
outlet
opening of the volume rotor module and with the intake plenum, interleaved and
counter-rotating rotors within the rotor enclosure, and a flow outlet opening;
and
(c) means for rotating the rotors in each of the volume rotor module and the
pressure
rotor module.
In the preferred embodiment, the modular pump comprises a plurality of volume
rotor
modules and a plurality of pressure rotor modules connected in series and in
each such module, the
intake plenum is a substantially central portion of the rotor enclosure and
the rotors comprise an
upper and a lower rotor pair which pump fluid in opposite directions such that
each module is
hydraulically balanced.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be des<:ribed by way of exemplary embodiments with
reference to
the accomp~unying simplified,
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diagrammatic, not-to-scale drawings- In the drawings;
FIGURE 1 is a cross-sectional view of a preferred embodiment of a rotor
module.
FIGUR)H: 2 is a crass-sectional view of a preferred embodiment comprising two
rotor modules and a gear module.
FIGURE 3 is a cross-sectional view of the embodiment shown in FIGURE 2 along
a plane normal to the plane of view in. FIGiIRE 2.
FIGUR)H; 4 is a cross-sectional view along line 4-4 in FIGURES 2 and 3.
FIGUR>H; 5 is a cross-section of a prel:erred gear module of the present
invention.
FIGURE 6A is schematic representation of the bolting pattern of an alternative
embodiment.
FIGURE: 6B is a cross-section of the embodiment shown in FIGURE 6A.
FIGURE; 6C is a cross-section along a plane normal to the plane of view in
FIGUR>h, 6B.
FIGUR)E:S 6D and 6E ~~re transverse cross-sections along line 6D-6D and line
6E-
6E respectively in FIGURES 6A, 6B and 6C.
FIGURES 7A and 7B are schematic depictions of an alternative embodiment
comprising a plurality of preasure ~~nd volume modules along with an electric
submersible motor.
DETAILED DESCRIPTION OF THE 1 N V EN TION
The downhole pump assembly ( I l)? according to the 1~ figures comprises a
gear module ( I 2)
and a rotor module (I4). The following description will refer to the pump (
10) having a top end (8)
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amd a bottom end (9) as if the pump ( 10) is vertically oriented. It will be
understood that in certain
applications involving slant or horizontal wells, the pump (10) may be at an
angle or horizontally
oriented when installed ;end operated.
In a preferred embodiment the rotor module ( 14) comprises interleaved rotors
(16, 18)
which run axially within a rotor enclosure (19) formed by a rotor housing
(20). A pump drive (not
shown) is connected to the gear module ~ I 2) which in turn powers an input
shaft (22) which rotates
the first rotor (16). A drive gear (24) engages a second gear (26) to drive
the second rotor (18) at an
equal speed but in the opposite direction. The drim gears (24, 26) are timc;d
to prevent physical
contact between the rotors ( 16, 18) as they counter-rotate.
While the preferred embodiment illustrated and described herein is a twin-
rotor pump, it
will be understood by persons skilled in the art that three or more rotors may
be interleaved and
tamed in a similar fashion and such mufti-rotor pwnps shall fall within the
scope of the invention
claimed herein.
The rotor module (141 further comprises se~~l housings (28. 30) at either end
of the main
rotor housing (20) and a gear housing (29) at the lower, end of the rotor
module (14). The seal
housings (28, 30) contain mechanical seals (32) for maintaining a fluid-tight
seal around the rotor
enclosure (19). Ball or roller bearings ( 34) support the rotor shafts at
either end of the rotor module
(14) and needle bearings (36) are provided in the intake plenum (38) between
the upper rotor pair
(165, 185) and the lower rotor pair ( lbb. 18b;1.
In the preferred embodiment. the rotor module (14) may be configured as a
volume
increasing module (14V) or a pressure increasing module ( 14P). h~ a pump
configuration where
only one rotor module is provided, it is unimportant which rotor module
configuration is used,
however, it will be preferred to use a volume module as depicted in Figure 6.
'The present invention
provides a pump (10) where two or more rotor modules (14) of either variey may
be connected in
series to increase the volume and pressure capabilities of the pump (10).
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A volume rotor module (14V) preferably has a single fluid intake opening
around the
circumference of the rotor housing (20) such that fluid is drawn directly into
the intake plenum
(38). Alternatively, an intake opening (~2) may be provided on the bottom of
the rotor module, as is
shown in Figure 3. The upper rotor pair ( 165, 185) drives a portion of this
fluid upwards directly
into an outlet plenum (40). The lower rotor pair ( 16b. 18b) drives a portion
of the fluid downwards.
This fluid is then redirected by a fluid passage (42) in the rotor housing to
the outlet plenum (40)
where the two fluid streams are rejoined and pass to the, outlet (46). Because
the fluid is split into
two streams. and pumped into opposite directions in the preferred embodiment,
the rotor module
(14) is hydraulically balanced. It is possible to use a single rotor pair
driving the fluid in one
direction only. Although such an embodiment is ncjt preferred, it is still
within the scope of this
i nvention.
A pressure rotor module ( I4P) preferably has a single intake opening (48)
which is provided
in the bottom gear housing (29) and which leads to an intake fluid passage (51
) in the rotor housing
(20) which leads to the intake plenum (s8). 'there t:he fluid stream is split
between the two rotor
pairs (16a, 18a and 16b, 18b) in the same manner as in the volume rotor module
(14V) and
discharged through the outlet plenum (40) and outlet (46>.
Preferably, the housings (20) tire hardened and coated with titanium nitride,
as is well
known in the art, to withstand abrasion and the stress of processing solids
such as sand- The rotors
are coated with titanium carbonitride, as is also wt;ll known in the art, to
achieve a hardness in
excess of 3000 Vickers. It is preferred to coat the rotors in order to deal
with the sand which is
produced in many oil wells without premature wear-. Without protective
coatings, the rotors (16, 18)
rnay quickl~~ wear from the abrasion caused by sand and other solids which may
be present in the
production fluid.
The gear module (12) is adapted to receive rotational energy from a surface
driven sucker
rod. The ge;~r module (12) is positioned above the pump module or modules as
is shown in Figure
2. The gear module (12;1 comprises a gear housing (.i0). a power shaft (_52),
and an arrangement of
gears (54) v~~hich are designed to multiply the rotational speed of the power
shaft and drive the
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output shaft (56). The output shaft (~6) connects with and drives the rotor
shaft (22) of the rotor
module (14).
Additional gear modules (44) may be provided between rotor modules (14) to
transfer
power between the rotor modules, as is shown in Figuzre ?.
A preferred embodiment of the pump (10) is shown in Figures 6A, 6B and 6C. In
this
configuration, the gear module (12) connects to a drive shaft module (60 )
which comprises an
elongate housing (62) and a drive shaft (64) which accepts a male splined
driver (not shown) at its
top end (65) and connects to the gear housing (50) at its bottom end. It is
important to have an
extended drive shaft and an extended male spline driver' because of the
shortening effect on sucker
rods when they are rotated. Essentially, the sucker rod will become twisted as
it is rotated which
will shorten its length. This effect becomes more pronounced as the sucker rod
becomes longer and
a.s it is rotated faster. To prevent the m,:ale splined driver from
disengaging the drive shaft (64) as a
result of a shortened sucker rod. it is necessary to significantly overlap the
two.
Also shown in Figure 6A is a preferred bolting pattern using intermediate
housings (70 ).
7.'he bottom intermediate housing (70>) spaces the rotor module (14) apart
from the gear housing
(50) while tine others (70b, 70c) separate the gear housing (50) from the
drive shaft module housing
(62). The purpose of the; intermediate housings (70) is simply to allow the
use of shorter bolts (73)
in assembling the pump ( 10). Each intermediate housing (70) has opposing
recesses (72) to expose
the bolt heads or nuts (73~) used to fasten the various housings and modules
together as is shown in
Figure 6A and 6D. A fluid passage ('~74) is provided to handle the fluid
stream from the pump
module- An intermediate drive shaft (76) connects the gear module (12) to the
rotor shaft (22).
Sucker rods are typically rotated in the range of 50 to 600 rpm. 7,he rotor
modules (14) may
be configured for efficient operation in a range of 400 to 16()0 rpm for
fluids having a viscosity
equivalent to API 11 or 12 for crude oil. In such a case, the gear module (12)
may be geared
appropriately. For example, if the gear module (12) increases the speed three-
:fold,
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:hen the sucker rod ma.y be turned at about .350 rpm resulting in a rotor
speed of 1050 rpm. For
lighter, less viscous fluids, the rotors may turn at a much higher rate as a
result of higher gearing in
the gear module ( 12) or faster sucker rod speeds.
If it is desired to use a downhole elcetrical motor drive, the electric motor
(30) may be
positioned below the rotor module, as is shown in Figures 7A and 7Ei. In this
case, the gear module
( 12) is adapted for use with electric mc,~tors which are capable of speeds
well in excess of the speed
capacity of the pump ( 10). Therefore, no speed increasi~~g gear arrangement
is necessary. However,
some simple seats to centralize the rotor shaft to the electric motor shaft
(not shown) may be
necessary.
The intake opening of a pressure rotor module (14P) is adapted tc> cooperate
with the outlet
of either another pressure rotor module (14P) or with the outlet of a volume
module (14V).
Therefore, a ptunp of the present invention may have a plurality of pressure
and/or voltune modules
connected in series to boost the volume and/or pressure capacity c.~f the pump
(10), as is
schematically shown in Figures '7A and. 7B. As shov~n is Figures 7A and 7H.
two volume modules
(114V) are combined to form a single unit. In this embodiment, each volume
module (114V) not
only has a plurality of intake openings ( I I 6) ~~round the circtunference,
but also an intake opening
(118) in the bottom of the housing (120) which permits the module (114) to
receive the output from
another volume module (114V). This intake opening (118) may be blocked with a
plug on the
bottom most volume module (I 14V) or if~only one volume module is provided.
The two volume modules (114) are connected to two twinned pressure modules
(214) as is
shown in Figures 7A and 713. 'fhe first pair of pressure modules (? 14)
accepts the output flow ( 122)
of the volume modules through an intake ( 124). A ti rst portion ( 1.10) of
the flow enters the intake
plenum of the first pressure module (2145 ). This fluid ( 130) is pressurized
and is pumped to a flow
receptor (132) in the second pressure module (214b). A second portion (140) of
the flow passes
through the first pressure module (2145 ) and enters the second pressure
module (214b) through the
intake (124). This second portion (140) is pressurized arid pumped where it
joins the output (130)
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1 ~i
of the first module (2145) as is depicted in the schematic flow diagram of
Figure 7B. The first pair
of pressure modules then outputs the recombined flow ( 150) to the intake
(124) of the second pair
of pressure modules (214), where the same flow is repeated to further boost
the pressure of the
pump ( 10).
The clearance between the rotors ( 16, 18) arid between the rotors and the
rotor housing is
preferably different for the different rotor modules. As the input pressure
increases and the desired
pressure boost increases, the clearances are preferably tighter. Generally.
the volume modules have
the largest clearances and the highest capacity pressure modules have the
smallest clearances. In the
example shown in Figures 7A and 7I3, the two volume modules ( 114) each
produce approximately
~t00 barrels per day at approximately 60 bar. 'fhe first pair ot~ pressure
modules (214) boosts the
pressure to about 180 bar and the second pair of pressure modules (214) boosts
the pressure to
about 400 bar. As may be appreciated by a person skilled in the art, further
or different flow rates
and pressures may easily be achieved by varying the number of the different
modules, the rotor
clearances and the screw pitch or number of threads in each of the modules.
It is convenient to fabricate the various rotor modules in an identical
fashion, each having
the bottom intake (124) and flow receptor ( 132), the aircumierential intake (
1 16), and a flow bypass
and a output. Each such rotor module rnay then be modified by plugging the
appropriate opening or
output to create a volurz~e module, a pressure moaule or to create twinned
volume or pressure
modules as shown in Figure 713.
As will be apparent to those skilled in the art, various modifications,
adaptations and
variations of the foregoing specific disclosure can be made without departing
from the teachings of
the present invention.
