Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM AND METHOD FOR A DIRECT DRIVE PUMP
FIELD OF INVENTION
[0001] The present invention relates to a system and method for a direct drive
pump to
be used for moving liquids and/or quasi-liquids. The present invention also
relates to a
system and method for the installation of a direct drive pump, for example,
for high
volume lifts from deep wells.
BACKGROUND
[0002] Current systems for deep well pumping involve electrical submersible
pumps
("ESPs") or geared centrifugal pumps ("GSPs"). Such pumps are the current,
principal
methods used as artificial lifts in high rate oil wells, where a multi-stage
centrifugal
pump is located downhole. For example, in an ESP system, a downhole electrical
motor directly drives the pump, with electric power supplied to the motor via
a cable
extending from the surface to the motor's location downhole. For example, in a
GSP
system, the pump is driven via a rotating rod string extending from the
surface to a
speed increasing transmission system located downhole. The speed increasing
transmission system is used to increase the relatively slow rotation of the
rod string to a
much faster rotation, as needed by the pump. In this example, the rod string
is driven
by a prime mover at the surface.
[0003] In current systems, the artificial lift system tends to be a bit
burdensome. For
example, in the installation of a current artificial lift system, a 300 to 400
foot artificial
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pump is installed in 10 foot sections in assembly form. Likewise, in the
maintenance of
a specific section of the pipe or tubing, the entire section of the pump must
be removed
all at once before any maintenance can be made.
[0004] Figs. 1A and 1B show example line shaft pumps. Fig. 1A shows a line
shaft
pump with water lubricated bearings. In Fig. 1A, the drive shaft is running
directly inside
the production tubing, or column pipe. Unlike the example shown in Fig. 1B,
this pump
does not use an oil pipe. Instead, in Fig. 1A, the drive shaft is centered
within the
column pipe by water lubricated bearings and bearing retainers attached to the
column
pipe. Such bearings are typically made of rubber, due to use in water. The
pump
thrust, as well as the weight of the drive shaft itself, are carried by a
thrust bearing
located at the surface.
[0005] Fig. 1B shows a line shaft pump with an oil pipe and oil lubricated
bearings. In
Fig. 1B, an oil lubricated drive shaft rotates inside the oil pipe, or oil
filled tubular
housing. The drive shaft is supported by shaft bearings, e.g., bronze
bushings,
attached fixedly to the oil pipe. The bushings are spaced, e.g., 5 feet to 10
feet, on yhr
oil pipe and along the drive shaft depending upon the intended rotational
speed of the
drive shaft. In this example, the steel pump shaft forms the journals for the
bronze
bushings. The pump thrust, as well as the weight of the drive shaft itself,
are carried by
a thrust bearing at the surface. Accordingly, the oil pipe can be centered
within the
column pipe by elastomer centralizers spaced evenly along its length as shown
in Fig.
1 B.
[0006] In both Figs. 1A and 1B, there is a required bearing spacing for
adequate
support of the drive shaft. Such spacing affects the configuration of the
tubulars used in
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installation. For example, in a water lubricated system shown in Fig. 1A, if
the drive
shaft bearings are required every 10 feet, then the column pipe is used in 10
foot
segments. The bearing retainers are fixed to the column pipe at the column
pipe
couplings. For example, in an oil lubricated system shown in Fig. 1B, if the
drive shaft
bearings are required every 10 feet, then the oil pipe is used in 10 foot
segments. The
bushings are fixed to the drive shaft housing at the housing couplings. In
both
examples, the pump systems can be installed in similar fashion. For example,
if the
bearing spacing is deemed to be 10 feet, then all of the components including
the
column pipe, oil pipe, and drive shaft, are in 10 foot length segments. Thus,
as the
pump is lowered into a well, each of the 10 foot segments of the drive shaft,
bearings
and column or oil pipe, must be installed in 10 foot segments.
[0007] Accordingly, a need exists for a less burdensome installation, de-
installation,
and maintenance of a pump system for both oil and water lubrication systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Fig. 1A shows a line shaft pump having water lubricated bearings.
[0009] Fig. 1B shows a line shaft pump with oil lubricated bearings.
[0010] Fig. 2 shows an exemplary embodiment of a direct drive pump according
to an
embodiment of the present invention.
[0011] Fig. 3 shows an exemplary embodiment of a drive rod with a drive tube
according to an embodiment of the present invention.
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[0012] Fig. 4 shows an exemplary embodiment of a drive rod without a drive
tube
according to an embodiment of the present invention.
[0013] Fig. 5A shows a cross-sectional view of a stabilizer embodiment for the
direct
drive pump according to an embodiment of the present invention.
[0014] Fig. 5B shows a top view of a stabilizer embodiment for the direct
drive pump
according to the embodiment of the present invention shown in Fig. 5A.
[0015] Fig. 50 shows a front view of a stabilizer embodiment for the direct
drive pump
according to the embodiment of the present invention shown in Fig. 5A.
[0016] Fig. 6A shows a cross-sectional view of a stabilizer embodiment for the
direct
drive pump according to an embodiment of the present invention.
[0017] Fig. 6B shows a top view of a stabilizer embodiment for the direct
drive pump
according to the embodiment of the present invention shown in Fig 6A.
[0018] Fig. 60 shows a front view of a stabilizer embodiment for the direct
drive pump
according to the embodiment of the present invention shown in Fig. 6A.
[0019] Fig. 7A shows a cross-sectional view of a stabilizer embodiment for the
direct
drive pump according to an embodiment of the present invention.
[0020] Fig. 7B shows a top view of a stabilizer embodiment for the direct
drive pump
according to the embodiment of the present invention shown in Fig. 7A.
[0021] Fig. 70 shows a front view of a stabilizer embodiment for the direct
drive pump
according to the embodiment of the present invention shown in Fig. 7A.
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[0022] Fig. 8A shows a cross-sectional view of a stabilizer embodiment for the
direct
drive pump according to an embodiment of the present invention.
[0023] Fig. 8B shows a top view of a stabilizer embodiment for the direct
drive pump
according to the embodiment of the present invention shown in Fig. 8A.
[0024] Fig. 80 shows a front view of a stabilizer embodiment for the direct
drive pump
according to the embodiment of the present invention shown in Fig. 8A.
[0025] Fig. 9A shows a cross-sectional view of a stabilizer embodiment for the
direct
drive pump according to an embodiment of the present invention.
[0026] Fig. 9B shows a top view of a stabilizer embodiment for the direct
drive pump
according to the embodiment of the present invention shown in Fig. 9A.
[0027] Fig. 90 shows a front view of a stabilizer embodiment for the direct
drive pump
according to the embodiment of the present invention shown in Fig. 9A.
[0028] Fig. 10 shows an embodiment of a direct drive pump bottom hole assembly
with a drive tube according to the present invention.
[0029] Fig. 11 shows an embodiment of a direct drive pump bottom hole assembly
without a drive tube according to the present invention.
[0030] Fig. 12 shows an embodiment of a top vented drive tube according to the
present invention.
[0031] Fig. 13 shows an embodiment method for installing a direct drive pump
according to the present invention.
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DETAILED DESCRIPTION
[0032] Embodiments of the present invention provide for a relatively easy to
install and
maintain artificial lift pump for use in oil and water pump systems. More
specifically,
embodiments of the present invention may be used for deep well pumping of oil,
water,
or other fluid / quasi-fluid.
[0033] Embodiments of the present invention provide for a deep well pump
system
which can be utilized at a greater depth and/or with a greater rotational
speed than
current pump systems allow. For example, water wells tend to be relatively
large in
diameter, e.g., 10 inches to more than 16 inches. Accordingly, available
agricultural
centrifugal pumps used in water wells require large diameter pump rotor which
produce
a large increase in pressure per stage. That is, pressure per stage is
proportional to the
square of the rotor diameter, and the square of the rotational speed. Given
the large
diameter and typically shallow depth of a water well, water well turbine pumps
typically
are operated at speeds between about 1200 RPM and 1800 RPM. Comparatively, oil
wells tend to use an about 5.5 inch or 7 inch production casing having an
inside
diameter of about 4.6 inches to 6 inches. Accordingly, available centrifugal
pumps
require a small diameter pump rotor, providing a small pressure increase per
stage.
This small pressure increase per stage results in the pump having to be
operated at a
high speed, e.g., about 3500 RPM. Even at such high speed, due to the small
pressure
increase per stage and the typically deep depth of oil wells, there can be as
many as
250 or more stages required to bring the produced fluid to the surface or
other desired
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location. If such pumps for oil production were operated at the typical speed
of an
agricultural pump (e.g., for a water well), about 1000 stages or more could be
required
to bring the produced fluid to the surface or other desired location, which
would be
prohibitively expensive and wearing on the system. In embodiments of the
present
invention, such restrictions and expense of the agricultural and oil pump
systems are
alleviated or diminished.
[0034] Embodiments of the present invention provide for a pump installation in
which
larger sections of the pump may be installed than current pump systems allow.
For
example, in agricultural and oil pumps, the drive shaft is stabilized by
bearings that are
fixed to either the tubular drive shaft housing, i.e., the oil pipe, or the
column pipe. Each
of these segments are made to be all the same length so that the bearings can
be fixed
to the column pipe or oil pipe at the junction of the segments of pipe as the
pump is
being installed into the well. In an oil lubricated bearing system, bronze
bushings are
attached to the oil pipes, with a steel drive shaft forming the journal. In a
water
lubricated bearing system, the rubber bearing is held in the center of the
column pipe by
the bearing retainers. The drive shaft runs through the rubber bearing and is
fitted with
a stainless steel sleeve serving as journal. In both the agricultural (e.g.,
water) and oil
pump systems, the bearing is affixed to the column pipe or oil pipe,
respectively.
Accordingly, as discussed above, the installation of such available systems
require
assembly of each 10 feet of pump system segments. Embodiments of the present
invention provide for installations of larger pump system segments, e.g., 25
foot
sections, 60 foot sections, and more.
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[0035] Embodiments of the present invention provide for a high volume
artificial lift
system, i.e., a direct drive pump ("DDP"), in which a multi-stage downhole
centrifugal
pump is driven by a rod string extending from the surface to the downhole
pump. The
rod string is driven at the surface, e.g., ground level, by a prime mover,
e.g., an electric
motor. For example, the motor may drive the rod string at a 3500 RPM pump
operational speed. This speed can be decreased or increased, depending upon
the
situation needed, in embodiments of the present invention.
[0036] Embodiments of the present invention provide for closely spaced
bearings to
provide rotational stability of the drive string. In an embodiment, the
individual bearings
are attached to the drive string, and are not fixed to the production casing
or drive tube.
[0037] Fig. 2 shows an embodiment of a direct drive pumping system 220
according to
the present invention. In Fig. 2, a motor 200 is shown connected to the
remaining
elements of the pump via tubing hangers and at least one thrust bearing 201.
In an
embodiment, the motor 200 is an electric motor which drives the rod string at
full pump
speed. Alternatively, the motor 200 is a direct drive motor, e.g., turning at
3500 RPM.
Alternatively, the motor 200 has a low output RPM, i.e., lower than 3500 RPM,
but with
speed increasing capability gearing. In this embodiment, the pressure of the
pump
system is monitored by a pressure regulator 202 situated between the pump and
the
flow line 203 to the pump. The pressure regulator 202 opens when the pressure
differential between the drive tube and the production tubing exceeds a
predetermined,
set value. A wellhead 204 couples the well casing to the upper portion of the
pump
system which includes the motor 200 and the flow line pipe 203. Inside the
protective
well casing 205, a production tubing or pipe 207 is situated and houses a
drive rod
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string 206. The lower portion of the pump system includes a receiver and
thrust
bearing(s) 208. In an embodiment, the thrust bearing 208 carrying the weight
of the
drive rods is located in the surface drive head. Due to the high rotational
speed, the rod
string 206 is equipped with stabilizers or bearings closely spaced along the
entire length
of the rod string to assure stable rotation. Some example embodiments of such
stabilizers are shown herein. Perforations 209 in the well casing in the pay
zone 212
area, i.e., where the water or oil or other liquid/quasi-liquid is located,
allow for entry of
the liquid or quasi-liquid into the well casing for pumping via the pump 210
having a
pump inlet 211, up to the surface or other desired location.
[0038] Fig. 3 shows an embodiment of a drive rod 304 having a drive tube 301
according to an embodiment of the present invention. For example, in larger
sizes of
production tubing, the drive rod string 304 and stabilizers 305 rotate within
a small
diameter tubular housing called a drive tube 301. The drive tube 301 runs
inside the
production tubing 302. In order to stabilize the drive tube 301, drive tube
stabilizers 303
are spaced between the production tubing 302 and the drive tube 301. Within
the drive
tube 301 itself, the drive rod string 304 is supported by drive rod
stabilizers 305 to the
drive tube 301.
[0039] Fig. 4 shows an embodiment of a drive rod string 402 being encased
directly in
production tubing 401. In such case, the drive rod string 402 is supported by
drive rod
stabilizers 403 to the production tubing 401. Such an embodiment may be used
in the
situation of a relatively small diameter production tubing, where there is
insufficient
and/or no need for a drive tube.
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[0040] Figs. 5, 6, and 7, show embodiments of bearing assemblies or
stabilizers for a
direct drive pump embodiment which does not utilize a drive tube according to
the
present invention. In each of these embodiments, the bearing assembly includes
a
bushing attached to a rod body, with a bearing mounted in a housing, e.g., a
plastic or
other type housing, that closely fits the internal diameter of the production
tubing. The
housing, and thus, the bearing, remain fixed relative to the tubing with the
rod string
rotating within the bearing. Fig. 5 shows a ceramic-polymer alloy bearing
example
embodiment. In Fig. 5A, a polymer housing and bearing 500 are situated near a
ceramic bushing 501, the ceramic bushing 501 being situated on the drive rod
502. In
Fig. 5B, the polymer housing and bearing 500 surrounding the ceramic bushing
501 are
shown. A resulting flow area is available outside of the polymer housing 500.
In Fig.
5C, a front view of the assembly is shown in which inside the production
tubing 503, a
retention band 504 is used to hold the housing 500 which surrounds a portion
of the
drive rod 502.
[0041] Fig. 6 shows a non-corrosive bearing example embodiment. In Fig. 6A, a
polymer housing and bearing 600 are situated near a molded stop 601, e.g., a
molded
plastic stop, the molded stop 601 being situated on the drive rod 602. In Fig.
6B, the
polymer housing and bearing 600 surrounding the drive rod 602 are shown. A
resulting
flow area is available outside of the polymer housing 600. In Fig. 60, a front
view of the
assembly is shown in which inside the production tubing 603, a retention band
604 is
used to hold the housing 600 which surrounds a portion of the drive rod 602.
[0042] Fig. 7 shows a ceramic bearing example embodiment. In Fig. 7A, a
plastic
housing and bearing 700 are situated near a ceramic bushing 701, the ceramic
bushing
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701 being situated on the drive rod 702. In Fig. 7B, the plastic housing and
bearing 700
surrounding the ceramic bushing 701 are shown. A resulting flow area is
available
outside of the plastic housing 700. In Fig. 70, a front view of the assembly
is shown in
which inside the production tubing 703, a retention band 704 is used to hold
the housing
700 which surrounds a portion of the drive rod 702.
[0043] In embodiments of the present invention, the bearing material to be
used
depends upon the wear and lateral load expected at the bearing's location
within the
well. For example, where high lateral loading is expected due to bore hole
deviations,
ceramic or even carbide bearings can be used. Or, for example, where not much
side
loading is expected, simpler and less expensive polymer alloy bearings can be
used.
The bearing housing material can be plastic, nylon, polymer alloy, or some
other strong,
chemically inert material.
[0044] In embodiments of the present invention, various types of bearings can
be
used. Determining which bearing type to use can depend upon the expected load,
depth of the pump, use of a drive tube, and other considerations. In Figs. 5
to 9, the
bearings differ in the provision for fluid flow around the bearing housing.
For example,
when a drive tube is not used, the bearings are exposed to the production
fluid flow,
thus the area open to flow between the bearing housing and the inside of the
production
tubing should be maximized to reduce pressure losses as the fluid flows past
the
bearings. See, e.g., Figs. 5 to 7. Or, for example, when a drive tube is used,
the fluid in
the tube is virtually stagnant, and the bearing housings need only be fluted
enough to
allow for a low rate flow communication throughout the drive string. See,
e.g., Figs. 8
and 9.
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[0045] Figs. 8 and 9 show embodiments of bearing assemblies or stabilizers for
a
direct drive pump embodiment having a drive tube according to the present
invention.
In each of these embodiments, the bearing assembly includes a bushing attached
to a
rod body, with a bearing mounted in a housing, e.g., a plastic or other type
housing, that
closely fits the internal diameter of the drive tube housing. The housing, and
thus, the
bearing, are situated to remain fixed relative to the drive tube housing with
the rod string
rotating within the bearing.
[0046] Fig. 8 shows a ceramic-polymer alloy bearing example embodiment. In
Fig. 8A,
a polymer housing and bearing 800 are situated near a ceramic bushing 801, the
ceramic bushing 801 being situated on the drive rod 802. A drive tube 805
surrounds
this assembly. In Fig. 8B, the production tubing 803 surrounds the drive tube
805 which
surrounds the bearing assembly. In Fig. 80, a front view of the assembly is
shown in
which within the drive tube 805, a retention band 804 is used to hold the
housing 800
which surrounds a portion of the drive rod 802.
[0047] Fig. 9 shows a ceramic bearing example embodiment. In Fig. 9A, a
plastic
housing and bearing 900 are situated near a ceramic bushing 901, the ceramic
bushing
or bearing 901 being situated on the drive rod 902. A drive tube 905 surrounds
this
bearing assembly. In Fig. 9B, the production tubing 903 is shown surrounding
the drive
tube 905 which surrounds the bearing assembly. In Fig. 90, a front view of the
assembly is shown in which inside the drive tube 905, a retention band 904 is
used to
hold the housing 900 which surrounds a portion of the drive rod 902.
[0048] In embodiments of the present invention, the bearing assembly, or
configuration, provides that the tubulars and the drive string can be run
separately and
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sequentially, rather than simultaneously as done in currently available pump
systems.
In embodiments of the present invention, the bearing assembly allows for
individual
segments of pipe and drive string to be much longer since the bearings are not
attached
to the tubulars' couplings. Thus, the couplings can be spaced much more
widely,
without having to adjust for the earlier necessary placement of bearings.
Accordingly,
this allows for relatively easier service and maintenance of the pump system.
For
example, when the pump requires service, the drive rods and/or tubulars can be
pulled
from and subsequently rerun into the well in large lengths, e.g. several feet,
100 foot
lengths, etc., at a time. Further, in an embodiment, the tubing couplings are
threaded,
instead of having flange couplings, e.g., as shown in Figs. 1A and 1B, thus
greatly
improving seal integrity and speed of installation.
[0049] In an embodiment of the present invention, mounting such bearing
assemblies
on a drive rod allows the bearings to be located optimally as required by the
conditions
in the well. For example, such conditions may include rod tension and
potential side
loads in the well due to, e.g., borehole deviation. In an example, the
rotational stability
of a drive string is a function of rod tension. That is, the higher the
tension, the more
stably the rod will rotate. However, at the bottom of the hole, near the pump,
the rod
may have little tension. Thus, at this location of the pump in the well, the
bearing
spacing needs to be the closer in space in order to assure stable rotation.
Likewise,
proceeding up the hole toward the surface, the tension of the rod increases as
the
weight of the rod hanging below effectively is increased. Thus, the spacing of
the
bearings can be increased in this area. That is, where the rod tension is
greatest, the
relative bearing spacing along the drive rod may be the widest and still be
adequately
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effective. In an embodiment of the present invention, an optimized drive rod
string has
bearings spaced according to the requirements dictated by the rod tension.
[0050] In a practical situation, wells ¨ oil or water ¨ are frequently neither
perfectly
straight nor vertical. Thus, a drive rod rotating within tubing with a small
diameter may
be forced to the side by deviations of the direction of the well, causing
lateral loads on
the bearings situated in and/or near the area of the deviation. The drive rod
bearings
are principally designed to keep the rod string rotating stably, and are
normally
expected to exposed to only small lateral loads. However, if side loads are
expected to
be unusually high due to borehole deviations, special bearings designed for
side-load
resistance can be installed in those areas where high lateral load is
expected, e.g., the
ceramic bearings as shown in Figs. 5 to 9.
[0051] In embodiments of the present invention, relatively easy maintenance is
needed due to the structure of the pump system. In an embodiment, the drive
rod(s)
can be removed without having to remove the other components. Such allows for
relatively easy "tuning" or adjustment of the pump system for changing /
changed
operational conditions, or for normal maintenance. For example, if an
operation
condition such as pump speed is changed, the drive rod(s) can be replaced with
other
drive rod(s) having a more useful bearing type, configuration, and/or
distribution. For
example, if the pump speed is increased in order to increase liquid
production, the drive
rods can be easily replaced with one with a different distribution of bearings
that is
designed for the higher rotational speed. Likewise, if there is a failure in
one or more of
the drive rods, a replacement drive rod(s) can be quickly run downhole thus
minimizing
downtime.
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[0052] Embodiments of the present invention provide for pumping at greater
depths.
Presently available line shaft pump systems typically have a head capacity of
less than
1500 feet, and are run to depths of less than 1000 feet. The relatively short
length of
the pipes and drive shaft results in a small amount of stretch by the
components due to,
e.g., water column weight and/or pump thrust, during operation. Such stretch
allows the
supporting thrust bearing for the drive shaft to be located at the surface.
See, e.g., Figs.
1A and 1B, described above. This allows for small manual adjustments to the
relative
length of those components so that the pump impellers ¨ which are fixedly
attached
both torsionally and axially to the drive shaft ¨ turn freely. In embodiments
of the
present invention, however, given the greater depth of the components allowed,
and
consequently the greater hydrostatic forces, there is a much greater relative
movement
between the production tubing to which the pump is attached and the drive rods
and/or
drive tube, allowing for a more flexible range of manual adjustment.
[0053] In Fig. 10, an embodiment of the direct drive pump hole assembly having
a
drive tube according to the present invention is shown. In such an embodiment,
the
pump drive shaft thrust bearing can be placed immediately above or below the
pump.
The pump drive shaft and rotors are driven by the drive rod(s) 1000 via a
spline
coupling or spline rod connector 1005 that allows for significant relative
vertical
movement of production tubing and the drive rod(s) 1000 while allowing the
pump drive
shaft and rotors to remain axially fixed relative to the pump body. In an
embodiment,
there is an additional thrust bearing located at the surface to handle the
weight of the
drive string. See, e.g., Fig. 2. In Fig. 10, the production tubing 1003
surrounds the
drive tube 1001 which surrounds the drive rod 1000. Stabilizers 1002 are
located on
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and spaced to support the drive rod 1000. Within the drive tube 1001 itself,
is a bottom
drive tube vent 1004. Fig. 10 further shows the relationship and relative
locations of a
seal bore drive tube connection 1006, stab-in receiver 1007, stab-in receiver
vent 1008,
thrust bearing 1009, pump 1010, and pump intake 1011.
[0054] Fig. 11 shows an embodiment of the present invention similar to that
shown in
Fig. 10, except without a drive tube 1001. In this embodiment, a spline
coupling 1105 is
still employed. Further, use of a thrust bearing 1101, e.g., a polycrystalline
diamond
(POD) thrust bearing, is shown situated below the pump and above the pump
intake.
[0055] Fig. 12 shows an embodiment of the present invention having a top
vented
drive tube. Fig. 12 shows an enlarged section of the pump system just below
the
wellhead 1201. A well casing 1208 surrounds the production tubing 1200, the
production tubing 1200 surrounding the drive tube 1203. The drive tube 1203 is
shown
having vents 1202 in its upper area to allow for fluid flow. As the drive rod
1204 located
within the drive tube 1203 moves in operation, the drive rod stabilizers 1205
are located
on and support the rod. In operation of the embodiment, fluid flow in the
production
tubing 1200, within the drive tube 1203, and from the drive tube 1203 moves
upward
toward the surface.
[0056] In embodiments of the present invention, various lubricants can be used
for the
bearings. For example, in an embodiment having a large production housing or
tubing,
a drive tube having a smaller diameter can be utilized to encase the drive
rod. The
drive tube may be centralized within the production tubing, and be used to
essentially
protect the drive rod from corrosion and scale deposition that might occur in
the flow
stream of a produced fluid. In such an embodiment, lubrication of the bearings
must be
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chosen so as to not negatively affect other parts of the system, e.g., sealing
between
components, etc. For example, in some systems, oil is used as a lubricant. In
such
systems, an oil lubricant can be useful at relatively shallow depths. However,
using an
oil lubricant at relatively greater depths can cause sealing issues between
the produced
fluid in the production tubing and the oil in the drive tube. Such issues can
occur
because of the difference in the density of the lubricating oil and the
produced well fluid,
e.g., typically water. For example, at deep depths, e.g., 6000 feet, the
pressure
difference between a column of lubricating oil with a specific gravity of 0.9,
and water,
with a specific gravity of 1.0, is nearly 260 psi at 6000 foot depth. And, in
a pumping
system, if the produced fluid and the lubricating oil are to be kept separate,
the seals at
the bottom of the oil filled drive tube must seal against this 260 psi
pressure differential
at 3500 RPM. This pressure situation can presents potential operational
difficulties. In
the alternative, one can pressure up the oil column at the surface to 260 psi
so that the
bottom hole pressures of the oil column and the produced fluid column are
equal, or
nearly so, relieving the pressure differential across the seals. This
alternative also
present operational difficulties. For example, if there are any changes in
surface
producing pressures, and during well shut-downs and start-ups, the surface
pressure in
the drive tube will need to be adjusted to the expected changes in bottom hole
producing pressure. In another alternative, an oil lubricant having a similar
density to
that of water can be used so that the hydrostatic pressure in both columns is
about
equal at the bottom of the hole. This too presents difficulties in that such
oils are
synthetic, and thus, cost prohibitive. In embodiments of the present
invention, these
difficulties are overcome. For example, a water lubricated drive shaft in an
embodiment
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of the present invention provides the benefits of the oil lubricated system
without the
operation difficulties, lubricant costs, and/or pressure balancing issues. The
water
lubricated system involves the drive shaft turning within a small diameter
drive tube, and
equipped with closely spaced bearings to provide rotational stability, as
discussed
herein. In an embodiment, the drive tube is not sealed off from the produced
fluid. The
produced fluid fills the drive tube and serves as the bearing lubricant. In
such an
embodiment using water as a lubricant, bearings designed for water lubrication
can be
used. Such bearings can designed using ceramic, carbide, or polymer alloy
bearings,
depending upon the load and wear requirements, as discussed herein. As shown
in
Fig. 12, the drive tube is vented to the production flow line at the surface
to expel oil or
gas that collects in the tub, and to allow the rate of flow up the drive tube
to be
controlled. In an embodiment, the drive tube is vented into the production
tubing below
the wellhead, allowing produced fluid to flow continuously up the drive tube.
This can
improve lubrication and/or improve the cooling of the bearings. In an
embodiment,
using a produced fluid filled drive tube can provide both cost and reliability
benefits. In
this embodiment, the drive shaft seals at the pump assembly are not needed.
Instead,
a bushing, e.g., carbide, is used to center the shaft at the bottom of the
drive tube. The
drive tube is vented at the bottom to allow the free movement of produced
fluid into the
drive tube, assuring that the drive shaft bearings are always immersed in
fluid. In an
embodiment, if the produced fluid is either corrosive or prone to scale
deposition, the
production line vented option can be used, as the flow rate up the drive tube
could be
closely controlled so that the fluid in the drive tube would be essentially
stagnant. Thus,
any potential for corrosion or scale formation on the drive string and/or
bearings is
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greatly reduced. In such an embodiment, any remaining scale and corrosive
components in the resulting stagnant column of water would have minimal effect
given
the lack of continuous movement.
[0057] In an embodiment, the drive tube is open to the pump outlet, thus, when
it is
completely filled with liquid, the pressure in the tube at the surface will be
equal to the
pump outlet pressure less the hydrostatic pressure exerted by a static liquid
column.
The pressure at the production tubing outlet at the surface will be equal to
the pump
outlet pressure less the hydrostatic pressure exerted by a static liquid
column less the
frictional pressure drop due to fluid flow in the production tubing. Thus, as
long as there
is flow in the tubing, the pressure at the top of the drive tube will be
greater than the
surface production tubing pressure, the difference being the pressure drop due
to
flowing friction. This difference can be used to purge the gas that will
naturally
accumulate at the top of the drive tube. Since the drive tube is open to the
well's
production fluid, some gas and/or oil may migrate up the drive tube during
production.
Eventually, the oil and/or gas will completely displace the water in the drive
tube. The
situation is more serious if gas fills even a portion of the tube since the
upper bearings
can become starved of liquid lubricant, resulting in eventual bearing failure.
[0058] In an embodiment, a drive tube can be fitted with vent line to the
production
tubing outlet, and the line can be equipped with a pressure regulator that
opens when
the pressure differential between the drive tube and the production tubing
exceeds a set
value. In the situation of possible accumulation of oil and/or gas in the
drive tube, the
pressure setting for the pressure regulator may need to be set after taking
into account
a higher than the expected friction loss pressure drop, so that the valve
opens only after
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such accumulations occur. Thus, as oil and gas accumulate at the top of the
drive tube,
the pressure-regulated valve can be set to open periodically to vent some of
the oil and
gas from the tube, keeping a constant amount of water in the drive tube so
that the
bearings are always lubricated.
[0059] In an embodiment where neither corrosion nor scale deposition is of
great
concern, then the drive tube-venting embodiment can be used. In this
embodiment, the
drive tube is vented at the bottom, but there is an additional drive tube vent
into the
production tubing just below the wellhead as shown in Fig. 12. During
production
operations, there may be a significant frictional pressure drop in the
production tubing
between the bottom hole and the surface, due to the high rate of flow in the
production
tubing. Consequently, there is a greater fluid pressure inside the drive tube
at the
surface than in the adjacent production tubing. This differential can be used
to force a
low rate fluid to flow up the drive tube and out the top vent, resulting in a
continual
circulation of produced fluid up the drive tube, lubricating and cooling the
bearings. Any
oil and/or gas entering the drive tube would also pass through the top vent,
eliminating
the chance of gas accumulation causing lack of adequate lubricant, as
described above.
[0060] In the embodiments, an effective cooling and lubrication of the
stabilizer
bearings is provided by the constant flow of water. See, e.g., Fig. 12. Such
cooling and
lubrication may be critical in deviated well situations, since the stabilizer
bearings
experience heavier side loads due to the bending of the drive string. In an
embodiment,
the production line venting also can provide continuous flow of produced fluid
up the
drive tube to both cool the bearings situated in that area. Further the
production line
venting can provide for continuous purging of any oil and/or gas that
accumulates in the
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drive tube by merely opening a control valve to allow the desired amount of
liquid to
continuously flow up the drive tube and into the production flowline.
[0061] Embodiments of the present invention facilitate easier installation of
a well
pump. Fig. 13 shows an example method for installing a direct drive pump, the
direct
drive pump having a drive tube and a drive rod such as the embodiments
illustrated in
Figs. 2 and 7. Generally, in an oilfield operation, a pump assembly is
installed in a well
using a well service rig. The well service rig has a derrick, draw works, and
accessory
equipment that allows the running in and pulling out of tubulars and other
equipment for
use in a well. The bottom hole assembly, including a multi-stage pump, thrust
bearing,
and drive rod and drive tube receiver, is attached via a connection, e.g., a
threaded
connection, to a length of production tubing 1301. The length of production
tubing
typically includes two joints of tubing, each 30 feet in length, and connected
together
via, e.g., a threaded connection, thus forming a stand of tubing that is about
60 feet
long. The pump assembly and single stand of tubing are lowered into the well
1302 via
the well service rig for about 60 feet, and the tubing is secured in the
wellhead 1303.
Another 60 foot stand of tubing is attached 1304, via, e.g., a threaded
connection, to the
stand that is secured in the wellhead and which is attached to the bottom hole
assembly. The entire assembly is lowered 1305 a further 60 feet and another
stand is
attached to the production tubing. This process is continued until the bottom
hole
assembly is located at the desired depth in the well 1306, and the production
tubing is
secured in the well head. Next, the drive tube, which consists of 60 foot
stands (two 30
foot joints joined via a threaded connection) of smaller diameter tubing is
inserted into
the production tubing 1307, and run to bottom in a similar fashion as the
production
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tubing and bottom hole assembly was run and secured in the wellhead 1308. The
drive
string tube is equipped with centralizers to locate it concentrically inside
the production
tubing See, e.g., Figs. 2, 3. The drive string is also equipped with a close
fitting male
stab-in member at the bottom, which fits into the drive tube seal bore
receiver in the
bottom hole assembly. This seal bore assembly locates the drive tube so that
it is
centered around the drive rod receiver within the bottom hole assembly (see,
e.g., Fig.
10), while also allowing relative vertical movement between the drive tube and
bottom
hole assembly. The drive rods with stabilizers, in 50 to 75 foot stands, are
then run
inside of the drive tube, in a manner similar to how the drive tube was run
1309. The
drive rods are typically 25 feet or 30 feet in length, and are attached to one
another via
threaded connections. The drive rod string is run to bottom and the splined
rod
connector is stabbed into the drive rod stab-in receiver in the bottom hole
assembly.
See, e.g., Fig. 10. This splined connection allows the rod to rotationally
drive the
centrifugal pump but provide for relative vertical movement between the drive
rods and
the bottom hole assembly. The direct drive pump which does not use a drive
tube is
installed in the same manner. The difference being that no drive tube is
installed in the
direct drive pump. Instead, the drive rod string is run directly after the
bottom hole
assembly and production tubing string are run to the proper depth and secured
in the
well head. The drive head is then installed such that the drive rod can be
turned by the
electric motor (see, e.g., Fig.2), thus driving the multi-stage centrifugal
pump in the
bottom hole assembly 1310. The surface flow line is attached to the well head
1311
and the pump is ready for operation. The surface flow line can then be used to
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transport well fluids lifted by the pump to any desired location, e.g., nearby
storage
container, etc.
[0062] It should be understood that there exist implementations of other
variations and
modifications of the invention and its various aspects, as may be readily
apparent to
those of ordinary skill in the art, and that the invention is not limited by
specific
embodiments described herein. Features and embodiments described above may be
combined with and without each other. It is therefore contemplated to cover
any and all
modifications, variations, combinations or equivalents that fall within the
scope of the
basic underlying principals disclosed and claimed herein.
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