Note: Descriptions are shown in the official language in which they were submitted.
1
Description
FIELD OF THE INVENTION
The present invention relates to Progressive Cavity Pump (PCP) drive head
improvements on a backspin control braking system and a wellbore fluid sealing
system.
BACKGROUND OF THE INVENTION
In the past, many conventional wells were operated by a reciprocating drive
called
"pumpjack" to lift downhole fluid. Many of these pumpjacks have been replaced
by
rotary drive progressive cavity pumps to lift fluid. Such rotary pumps are
particularly
suited for heavy crude oil with sand and water. However, to turn a bottom hole
pump
through a rod string, surface drive head needs to apply a torque on top of the
rod string.
This causes a torsional energy storage between a surface drive head and a
bottom hole
pump. Whenever there is a power failure or a system needs to be shut down,
this
stored torsional energy, along with the energy created by the fluid head above
the
pump, must release itself. Without any control on the rate of backspin speed
of the rod
string, serious problems may occur, such as backspin speed exceeding safe
limits of
surface mechanical transmission. Damage the motor, and even cause it to
explode.
Top of the rod string extruded portion may bend or may be broken off then
flung away
due to a sudden centrifugal force.
Without a reliable braking system, the rod string could uncouple, and the
outcome
would be a high cost of fishing rod string job. Most important issue is the
field service
personal safety. There are three different backspin braking systems in the
market. First
is a caliper braking system which is a common braking system in the automobile
industry. Second is the use of centrifugal forces to trigger a brake mechanism
to brake
when back spinning and dis-engage when normal operation through an overrunning
clutch. Third is the use of over-running clutch to dis-engage hydraulic fluid
pump when
normal operation and to engage hydraulic fluid pump when back spinning to
control the
spinning speed. All three brake systems have a reliability issue and even
manufacturers
do not know when the braking system needs to be serviced. Fundamentally, all
three
braking systems have a worn-out issue because of utilizing contact friction as
a
controlling manner. Cost is for replacing an over-running clutch is high.
Although
manufacturers have a program to replace braking pads, it is time consuming and
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difficult in the field. Unfortunately, the over-running clutch replacement
must be
performed in a shop not in the field. This process adds more burden for oil
producers.
The second essential item in a PCP drive head is a well fluid seal assembly.
Generally
called a stuffing box. In the field operations, major drive head service is to
replace
stuffing box seals. Conventional stuffing boxes are mounted below the drive
head.
Conventional stuffing boxes are typically separated from the wellhead drive
and are
mounted in a wellhead frame such that they can be serviced from below the
wellhead
drive without removing it. A conventional stuffing box uses braided packing
that can be
replaced manually from side openings while the polished rod stays inside the
stuffing
box. Since the conventional stuffing boxes seal against the polished rod,
which is
subject to wear, and due to poor alignment of the polished rod to the stuffing
box,
leakage becomes somewhat inevitable. Replacing stuffing box seals from the
bottom of
drive head side openings is time consuming and difficult especially during
winter
operations. A drive head which has a built-in seal assembly inside the drive
head
bottom sub has been in the market for years. To replace a seal assembly, the
drive
head needs to be removed and then replace a stuffing box. Although some drive
head
seals can be replaced from top of the drive head opening without removal of
the drive
head to service the stuffing box, it is still time consuming and difficult to
replace
individual sealing elements and associated parts from a confined top annular
opening.
So, most companies are preferred to replace a complete drive head using a
lifting
device rather than servicing a stuffing box in the field. This operation adds
costs on oil
producers.
GENERAL DESCRIPTION OF THE INVENTION
One aspect of this invention is to provide a backspin control braking system
for use
with Progressive Cavity (PC) Pumping system. More precisely, this invention
provides a
braking mechanical system for avoiding a sudden release of torsional energy
stored in
a rod string between top of the rod string and a bottom hole pump, and the
fluid head
above the bottom hole pump on power failure and shut down. Top of the rod
string is
rotated by torque energy derived from a prime mover, and the bottom of the rod
string
rotates the bottom hole pump. The braking mechanism comprising:
a) a pinion shaft inserted in the mechanical transmission chain between a
drive
head main hollow shaft and a hydraulic fluid pump, such that the pinion shaft
rotates at
Date Recue/Date Received 2021-01-25
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a consistent speed ratio and direction with respect to the top end of the rod
string
through a second gear attached to the drive head main hollow shaft,
b) a hydraulic pump,
c) a clutch between the said pinion shaft and the said hydraulic pump, is
connected
such that when top end of the rod string rotates in the direction
corresponding to normal
operation of the downhole pump, the clutch is in non-contact position and does
not run
the hydraulic pump, but when top end of the rod string rotates in the
direction opposite
that corresponding to normal operation of the downhole pump, the clutch
engages and
drives the hydraulic pump,
d) a reservoir containing a fluid suitable for hydraulic pump,
e) an adjustable flow control valve which is connected to the fluid pump
output port
through a tubing, whereby the stored energy in the rod string, as energy is
released, is
made to do the work of pumping fluid through the said flow control valve, thus
dissipating the stored energy in a controlled manner.
In another aspect, the present invention provides a seal assembly to seal
wellbore fluid
for a drive head during operation. The downhole pump implementation comprises
a
drive head, a PC pump, and a drive string, also a drive head comprising an
insertable
seal assembly. The insertable seal assembly comprises stationary seal housing
assembly, and a sealing sleeve, wherein the said sealing sleeve rotates with
the drive
string.
In another respect, the present invention provides a method of replacing an
insertable
seal assembly. The method includes providing a wellhead and a drive system,
wherein
the drive system comprises a drive head, an insertable sealing assembly, a
driving
clamp. The method also includes providing a safety clamp (not shown) for
securing the
weight of the rod string which is mounted under the drive head wellhead
flange. The
method also includes shutting down the well, securing the weight of the drive
rod string
by placing the safety clamp below the insertable seal assembly at the surface
and
holding the drive unit stationary. The method also includes pulling insertable
seal
assembly upwards relative to the drive unit. After removing the top driving
clamp, lifting
the insertable seal assembly upwards and removing the insertable seal assembly
from
the drive head top annular opening.
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BRIEF DESCRIPTION OF THE DRAWINGS
According to the features recited above, the advantages and objects for the
present
invention can be more fully understood, certain embodiments of the invention
are
illustrated in the appended drawings.
FIG.1 is an overall system layout illustrating a drive unit, a rod string, a
well head, and a
bottom hole pump.
FIG.2 is a drive head.
FIG.3 is a cross-sectional view of a drive head including a wellbore fluid
seal assembly,
a clutch, a motor support frame, a prime mover, and a drive unit bottom
flange.
FIG.4 is a detailed cross-sectional view of a flow control valve.
FIG. 5 is a detailed cross-sectional view of fluid pump pressure port output,
a tubing,
and a flow control valve.
FIG. 6 is a sectional detail view of a clutch mechanism.
FIG. 7 is a detailed view of a clutch at a dis-engaged position.
FIG. 8 is a detailed view of a clutch at an engaged position.
FIG. 9 is an exploded view of a clutch.
FIG. 10 a mounting relationship between a top mounted seal assembly and a
drive
head.
FIG. 11 a view top of seal assembly mounted on a main hollow shaft.
FIG. 12 a detailed view of the top of seal assembly mounted on a main hollow
shaft.
FIG.13 is a driving connector bottom end flat.
FIG. 14 a detail sectional view of a top mounted seal assembly.
FIG. 15 is a view of sealing sleeve flat.
FIG. 16 is a cross sectional view of a drive head.
FIG. 17 is a cross sectional view of a bottom mounted seal assembly.
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FIG.18 is a detailed cross-sectional view of the installation relationship
between drive
head and the bottom mounted seal assembly.
DETAILED DESCRIPTION OF THE DRAWINGS
The apparatus and methods of the present invention, in the context of downhole
pump
implementations, provides a sealing of production fluid from the environment
using a
top or bottom mounted seal assembly and a clutch for a reliable backspin
control
braking mechanism for safety operation.
The discussion below focuses mainly on a clutch. The clutch has a reliable
safety
mechanism compared with friction types of clutches due to non-friction
transmission
features when in normal operation.
FIG. 1 illustrates a known progressive cavity pump installation 10 in
accordance with
one embodiment of the present invention. The installation includes a typical
progressive
cavity pump drive head 12, a wellhead 18, a bottom hole pump rotor 28, a
stator 25,
and a drive rod string 20. The bottom of drive rod 20 is connected to the top
of rotor 28
and the top of drive rod (most time called polish rod) 35 is clamped on top of
the drive
unit using rod clamp 30. A safeguard 40 is installed on top of clamp 30. The
drive head
supports and drives a drive shaft 54. The polish rod 35 is supported and
rotated by
means of a polish rod clamp 30, which engages an output shaft 54 of the drive
head by
a driving connector through milled slots and bosses in both parts. The polish
rod 35
rotationally drives a drive string 20, sometimes referred to as "drive rods",
which, in turn,
drives a progressing cavity pump rotor 28 located at the bottom of the
installation to
produce well fluids to the surface through the wellhead.
FIG.2 is a belt transmission drive head. It may also be a gear transmission
drive head.
FIG. 3 is a sectional view of the drive head. A braking mechanism is
illustrated,
including a first pinion shaft 107, carrying a clutch below which are
108,109,110 and
115 in accordance with one embodiment of the present invention. The pinion
shaft 107
is an elongate shaft parallel with the main hollow shaft 54 and extends
through the
interior of a reservoir 119. The reservoir has four side walls and a bottom
wall. The
reservoir is completely sealed by a top cap and filled lubricant oil which
completely
merges the clutch. A second pinion shaft 112 is parallel with the first pinion
107, and it
is connected to a hydraulic braking pump 120.
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Within the interior of the reservoir 119, the first pinion shaft 107 and the
main drive head
hollow shaft 54 are interconnected through a second gear 105. In one variant,
the first
pinion 107 and the second gear 105 may mesh in such a way that the ratio of
rotation
between the shafts 107 and 54 remains constant but 107 pinion gear rotating
direction
is opposite. On the first pinion shaft 107, there may be a perpendicular
cylindrical hole
which accommodates a drive pin 109. The drive pin 109 may be positioned in the
center of the perpendicular cylindrical hole by a set screw 255. The first
half clutch 108
which has a cylindrical sleeve with helical open slots at a given helical
rate, moves up
and down driven by the driving pin as pinion shaft 107 rotates clockwise or
anti-
clockwise.
Further, the first half clutch 108 may have evenly disposed teeth. At least
two
propellers 110 are interconnected to the first half clutch 108 external
surfaces at a given
angle. As pinion shaft 107 rotates, the drive pin 109 rotates at the same rate
and
direction of the pinion shaft 107. The drive pin 109 drives the first half
clutch 108 move
up and down along opened helical slots due to hydraulic force generated on the
propeller surfaces. The up and down movements result in engaging and dis-
engaging
teeth 113 and 114.
A second half clutch comprising a third gear 115 and at least two evenly
positioned
clutch teeth, is positioned along pinion shaft axial direction and free
rotating relative to
pinion shaft 107. The second pinion shaft 112 and the third gear 115 may mesh
in such
a way that the ratio of rotation between the second pinion shaft 112 and the
third gear
115 remains constant but rotating direction is opposite. The second pinion
shaft 112 is
interconnected to hydraulic braking pump 120.
As explained above, the braking drive chain, in operation, whenever downhole
pump is
being operated normally, the direction of rotation of the pinion shaft 107 is
such that the
clutch is in non-contact position and no rotation is transmitted through
clutch to the
second pinion 112, and therefore no hydraulic fluid is pumped.
However, when the entire pumping system shuts down for any reasons, the rod
string
20 may attempt to spin backwards, as the stored torsional energy is released,
this may
cause rotation of the main shaft 54, which in turn may rotate the shaft 107
through the
second gear 105. During this backspin of the rod string 20, the rotational
direction of the
shaft 107 is such as to power the hydraulic braking pump 120 through clutch
and
Date Recue/Date Received 2021-01-25
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meshed gear 112, 115, thus causing reservoir oil to be drawn through pump
intake (not
shown) and discharge pressurized oil to a flow control valve 250 through
pressure tube
205.
FIG. 4 and 5, In operation on flow control valve, if a rod string 20 is
turning too fast or
too slow, then by turning flow control valve handle 223 clockwise or
counterclockwise to
adjust an orifice 227 in accordance with one embodiment of the present
invention.
There is a thread engagement between flow control valve housing 229 and flow
control
valve stem 219. As the turning handle 223, stem 219 moves forwards or
backwards
relative to flow control valve housing 229. The pressurised fluid from pump
120 out port
203 is regulated through the orifice 227 and discharged through side ports 213
to
reservoir 118. This results in controlling the pump rotating speed.
Furthermore, the rate
of rod string backspin speed is controlled. The pressurised fluid is sealed
through seals
215, 217 and flow control valve is held by 231, 233, which relates to the
reservoir
housing 118.
FIG.6, FIG.7, FIG.8, and FIG.9 present details of clutch mechanism in
accordance with
preferred embodiment of the present invention. The pinion shaft 107 is
supported by
two upper and lower bearings 121. Whenever pinion shaft gear 107 driven by the
main
shaft gear 105 rotates at counterclockwise direction 268, cross pin 109
rotates at the
same rate of speed and direction. Due to the hydraulic force generated on
propeller 110
surfaces, the hydraulic force keeps the first half clutch away from the second
half clutch
along opened pin helical slots 265 and the pin stops at the lowest slot pin
hole. Note
that the front tooth angle on the first half clutch formed between surface 258
and
surface 285 may be less than 90 and the rear tooth angle on the first half
clutch
formed between surface 258 and surface 290 may be larger than 90 . This
results in
upper clutch teeth slide off and the first half clutch may be lifted by
hydraulic force
generated on propeller surfaces.
Whenever the pinion gear 107 driven by the main shaft gear 105 rotates at
clockwise
direction 270, the cross pin 109 rotates the same rate of speed and direction.
Due to
the hydraulic force generated on the propeller 110 surfaces, the force keeps
the first
half clutch towards the second half clutch along opened pin helical slots 265
and the pin
stops at the top of the slot pin hole. Note that the tooth front angle on the
second half
clutch formed between surface 278 and surface 280 may be smaller than 90 and
the
tooth rear angle on the second half clutch formed between surface 278 and
surface 275
Date Recue/Date Received 2021-01-25
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may be bigger than 900. The first half clutch and the second half clutch front
teeth
angles are the same so that they are fully contact when engaged to transfer
the torque.
Once fluid pump 120 starts pumping pressure fluid, torque may be transferred
through
the clutch teeth engagement and the cross-driving pin 109.
The discussion below focuses mainly on a top or bottom mounted seal assembly.
The
principles of present invention also allow for a quick installation or a quick
removal of
the seal assembly without the need to remove a drive head.
Center of FIG.3 presents a cross-sectional view of a drive head 100 wellbore
fluid seal
assembly 300 in accordance with one embodiment of the present invention. The
seal
assembly 300 is installed at the top of the main hollow shaft internal upper
location. A
driven sheave 52 is coupled with the main hollow shaft 54 slot 133 to transfer
the
torque. The main shaft slot 133 allows for torque supplied by prime mover 15
mounted
on frame 130 and transfers the torque to the main hollow shaft 54. Note that
the main
hollow shaft 54 internal diameter is bigger than the seal assembly's biggest
external
diameter and the bottom of seal housing center tube 145 largest diameter. The
bottom
of the center tube 145 is slid into the bottom flange 128 top internal
cylindrical surface,
and the bottom of the center tube 145 is locked by the side locking bolts 125.
At least
two side locking bolts lock the center tube to prevent from rotating and
moving up and
down. Locking bolts are engaged with holding plates 141 through thread 139.
Seal ring
135 seals well bore fluid from leaking to atmosphere.
In removing the seal assembly operation, retract two side clamping bolts by
turning
125, the bolts 125 comes out of center tube groove 127, then the center tube
145 with
top seal assembly can be pulled out of the drive head main shaft through the
main shaft
top annular opening which formed between the main hollow shaft internal
cylindrical
surface and the polish rod external cylindrical surface.
FIG. 10, FIG.11 and FIG.12 present the interference between the top mounted
seal
assembly and top of the hollow shaft annular opening in accordance with one
embodiment of the present invention. A polish rod clamp 30 clamps polish rod
35
through polish rod clamp bolts 316. Clamp slots 311 mates with a driving
connector 319
upper boss 317. The driving connector bottom side bosses 321 mate with the
main
shaft top opening slots 325.
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FIG 13, FIG. 14, and FIG.15 present more details of the internal sealing
assembly part
relationship. There is a flat 433 on the sealing sleeve 415, it mates with an
internal flat
438 in the bottom side of driving connector 319. These two mated flats are for
transferring torque. The sealing sleeve rotates with the driving connector
319, and the
sealing sleeve axial movement is stopped by snap ring 413.
In operation, torque is transferred from the driven sheave 52 to main shaft
54. With the
engagement between shaft slots 325 and driving connector boss 321, and the
engagement between the driving connector boss 317 and the polish rod clamp
slot 311,
the torque is transferred to the top of rod string from main shaft 54. As the
center tube
145 is locked on to bottom flange 128, and the top of center tube is connected
to seal
housing 430 through thread connection 432, the seal housing keeps stationary
relative
to the rotating sealing sleeve. Collar 427, and collar 425 are two lip seal
421 holding
collars. Further, collar 427, collar 421, and backup nut 419 position at least
two lip seals
on axial direction held by thread connection 435 and locked by locking thread
bolt 417
and prevent the sealing sleeve from running out on radial direction. This
results in
loaded internal seal lips resting against on sealing sleeve 415 external
cylindrical
hardened surface 434. Wellbore fluid 431 is sealed against the sealing sleeve
external
surface. If the first lip seal 421 leaked, the wellbore fluid is contained by
the second lip
seal and seal ring 420.
As mentioned above, the polish rod is clamped by a rod clamp 30 and positioned
radially by the centralizing collar 404. There is internal seal ring 405 and
external seal
ring 407 among polish rod centralizing collar 404 internal, external
cylindrical surfaces,
and the polish rod external cylindrical surface. centralizing collar 404 keeps
polish rod
centered to avoid radial runout. It seals wellbore fluid 431 from leaking to
the
atmosphere.
In the operation of removing the top mounted seal assembly, first step may
clamp
bottom drive head secure clamp which is not shown herein to hold the weight of
the rod
string and remove the polish rod clamp, unthread the top holding cap 315
thread. Then
the driving connector and the seal sleeve may pull upwards from top annular
opening.
Second step is to unlock the bottom flange locking bolt 125
out of groove 127, then using a pulling tool (not shown) to engage with top of
the seal
housing J groove 316 (in FIG.12 detail B) to pull upwards the entire assembly.
Another
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option may unscrew thread 430 using a pulling tool and pull upwards. Only the
seal
housing assembly top portion may be pulled out without the center tube.
Installation
process is opposite to the steps described above.
FIG.16, FIG.17, and FIG.18 present a bottom mount seal assembly in accordance
with
one embodiment of the present invention. Note that most parts are the same
compared
with the top mounted seal assembly. The sealing sleeve 530 may have the same
connection with the driving connector 319 compared with the top mounted seal
assembly. There is an external tube 535 which the external tube bottom is
connected to
backup nut 545 through thread connection 540. At least two lip seals are
accommodated inside lip seal holder 425 and 427. Top backup nut 545 threaded
into
seal housing 555, rests against lip seal holder 425 and 427 to prevent lip
seals from
moving axial direction and locked by set screw 419. Internal cylindrical
surfaces of lip
seal holders 425, 427 and top backup nut 545, may constrain the sealing sleeve
external cylindrical surface to prevent radial runout so that wellbore fluid
is sealed
during the sealing sleeve is rotating. There is a stop ring 560 at the bottom
of the
sealing sleeve 530 and locked by snap locking ring 565. The stop ring prevents
seal
housing assembly from sliding down during installation and contacts against
the bottom
of seal housing surface 557 when pulling upwards from the top annular opening.
There
may be a gap between the top of external tube 525 and the bottom of the
driving
connector 520 surface. The gap eliminates interference between these two
surfaces
during system running. This gap is set during installation by adding a spacer
515.
In the seal assembly removable operation, first step may clamp secure clamps
below
the drive head to hold the weight of the drive rod string and remove the
polish rod
clamp 30, un-lock locking bolts 125 (See FIG. 18), and un-thread top cap 410.
With a
tool help (not shown), pull connector 319 upward, the entire seal assembly is
pulled out
from the top annular opening which is formed between the main shaft internal
cylindrical
surface and the external polish rod cylindrical surface.
In the installation operation, whenever pushing the seal assembly into the
bottom
flange, the gap between two surface 520 and 525 is eliminated due to free
sliding of the
seal housing assembly relative to the sealing sleeve, and a resistance between
the
external seal housing surface and the bottom flange internal mating surface.
As the seal
assembly is pushed in and reaches the pre-calculated depth, lock the seal
housing by
locking bolts 125. Locking bolts are located right above top of the seal
housing surface
Date Recue/Date Received 2021-01-25
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570. Once finished locking the seal housing, pull upwards the driving
connector 319
and add cylindrical spacer 515, then lower the driving connector on the
spacer. Noted
that two driving connector bosses 321 have engaged in shaft slots 325 (FIG.12
detail
B). Install top cap 315 by threading it onto top of the hollow shaft 54. The
last step
Installation is finished by installing rod clamp 30.
Date Recue/Date Received 2021-01-25
