Note: Descriptions are shown in the official language in which they were submitted.
CA 02716430 2010-10-04
50113-4D
PUMP DRIVE HEAD WITH STUFFING BOX
RELATED APPLICATIONS
The present application is a divisional application of Canadian patent
application
no. 2,350,047, filed June 11, 2001, and claims priority from therein.
FIELD OF THE INVENTION
The present invention relates generally to progressing cavity pump oil well
installations and, more specifically, to a drive head for use in progressing
cavity pump oil well
installations.
BACKGROUND OF THE INVENTION
Progressing cavity pump drives presently on the market have weaknesses with
respect to the stuffing box, backspin retarder and the power transmission
system. Oil
producing companies need a pump drive which requires little or no maintenance,
is very safe
for operating personnel and minimizes the chances of product leakage and
resultant
environmental damage. When maintenance is required on the pump drive, it must
be safe
and very fast and easy to do.
Due'the abrasive sand particles present in crude oil and poor alignment
between the
wellhead and stuffing box, leakage of crude oil from the stuffing box is
common in some
applications. This costs oil companies money in service time, down time and
environmental
clean up. It is especially a problem in heavy crude oil wells in which the oil
is often produced
from semi-consolidated sand formations since loose sand is readily transported
to the
stuffing box by the viscosity of the crude oil. Costs associated with stuffing
box failures are
one of the highest maintenance costs on many wells.
Servicing of stuffing boxes is time consuming and difficult. Existing stuffing
boxes are
mounted below the drive head. Stuffing boxes are typically separate from the
drive and are
mounted in a wellhead frame such that they can be serviced from below the
drive head
without removing it. This necessitates mounting the drive head higher,
constrains the design
and still means a difficult service job. Drive heads with integral stuffing
boxes mounted on
the bottom of the drive head have more recently entered the market. In order
to service the
stuffing box, the drive must be removed which necessitates using a rig with
two winch lines,
one to support the drive and the other to hold the polished rod. This is more
expensive and
makes servicing the stuffing box even more difficult. As a result, these
stuffing boxes are
typically exchanged in the field and the original stuffing box is sent back to
a service shop for
repair-still unsatisfactory.
Due to the energy stored in wind up of the sucker rods used to drive the
progressing
cavity pump and the fluid column on the pump, each time a well shuts down a
backspin
retarder brake is required to slow the backspin shaft speed to a safe level
and dissipate the
-1-
CA 02716430 2010-10-04
energy. Because sheaves and belts are used to transmit power from the electric
motor to
the pump drive head on all existing equipment in the field, there is always
the potential for
the brake to fail and the sheaves to spin out of control. If sheaves turn fast
enough, they will
explode due to tensile stresses which result due to centrifugal forces.
Exploding sheaves are
very dangerous to operating personnel.
SUMMARY OF THE INVENTION
The present invention seeks to address all these issues and combines all
functions
into a single drive head. The drive head of the present invention eliminates
the conventional
belts and sheaves that are used on all drives presently on the market, thus
eliminating belt
tensioning and replacement. Elimination of belts and sheaves removes a
significant safety
hazard that arises due to the release of energy stored in wind up of rods and
the fluid column
above the pump.
One aspect of the invention relates to a centrifugal backspin retarder, which
controls
backspin speed and is located on a drive head input shaft so that it is
considerably more
effective than a retarder located on the output shaft due to its mechanical
advantage and the
higher centrifugal forces resulting from higher speeds acting on the
centrifugal brake shoes.
A ball-type clutch mechanism is employed so that brake components are only
driven when
the drive is turning in the backspin direction, thus reducing heat buildup due
to viscous drag.
Another aspect of the present invention relates to the provision of an
integrated
rotating stuffing box mounted on the top side of the drive head, which is made
possible by
a unique standpipe arrangement. This makes the stuffing box easier to service
and allows
a pressurization system to be used such that any leakage past the rotating
seals or the
standpipe seals goes down the well bore rather than spilling onto the ground
or into a catch
tray and then onto the ground when that overflows.
In the present invention, only one winch line is required to support the
polish rod
because the drive does not have to be removed to service the stuffing box. In
order to
eliminate the need for a rig entirely, a still further aspect of the present
invention provides a
special clamp integrated with the drive head to support the polished rod and
prevent rotation
while the stuffing box is serviced. Preferably, blow out preventers are
integrated into the
clamping means and are therefore closed while the stuffing box is serviced,
thus preventing
any well fluids from escaping while the stuffing box is open.
According to the present invention then, there is provided a drive head
assembly for
use to fluid sealingly rotate a rod extending down a well, comprising a
rotatable sleeve
adapted to concentrically receive a portion of said rod therethrough; means
for drivingly
-2-
CA 02716430 2010-10-04
50113-4D
connecting said sleeve to the rod; and a prime mover drivingly connected to
said sleeve for
rotation thereof.
According to another aspect of the present invention then, there is also
provided in
a stuffing box for sealing the end of a rotatable rod extending from a well
bore, the
improvement comprising a first fluid passageway disposed concentrically around
at least a
portion of the rod passing through the stuffing box; a second fluid passageway
disposed
concentrically inside said first passageway, said second passageway being in
fluid
communication with wellhead pressure during normal operations; said first and
second
passageways being in fluid communication with one another and having seal
means
disposed therebetween to permit the maintenance of a pressure differential
between them;
and means to pressurize fluid in said first passageway to a pressure in excess
of wellhead
pressure to prevent the leakage of well fluids through the stuffing box.
According to another aspect of the present invention, then, there is also
provided a
drive head for use with a progressing cavity pump in an oil well, comprising a
drive head
housing; a drive shaft rotatably mounted in said housing for connection to a
drive motor; an
annular tubular sleeve rotatably mounted in said housing and drivingly
connected to said
drive shaft; a tubularstandpipe concentrically mounted within said sleeve in
annularlyspaced
relation thereto defining a first tubular fluid passageway for receiving fluid
at a first pressure
and operable to receive a polished rod therein in annularly spaced relation
defining a second
tubular fluid passageway exposed to oil well presure during normal operation;
seal means
disposed in said first fluid passageway; means for maintaining the fluid
pressure within said
first fluid passageway greater than the fluid pressure in said second fluid
passageway; and
means for releasably drivingly connecting said sleeve to a polished rod
mounted in said
standpipe.
According to another aspect of the present invention then, there is also
provided in
a drive head for rotating a rod extending down a well, the drive head having
an upper end
and a lower end, the improvement comprising a stuffing box for said rod
integrated into the
upper end of said drive head to enable said stuffing box to be serviced
without removing said
drive head from the well.
-3-
CA 02716430 2010-10-04
50113-4D
According to another aspect of the present invention, there is also
provided a blow out preventer for use on a well bore in a production oil,
water or gas
well installation, comprising: a housing having a bore for receiving a
cylindrical
member in spaced relation therethrough and opposed bores extending radially of
said bore of said housing; piston members in said housing, each said piston
member
being disposed in one of said radial bores, each piston member having an inner
end
and a concavely curved recess in said inner end for receiving said cylindrical
member; elastomeric seal means to provide a seal between a portion of the
length of
each said recess in each of said piston members and said cylindrical member,
and
between each said piston member and its associated radial bore to prevent well
fluid
from coming up said well bore and escaping to the exterior of said well bore
when
said piston members sealingly engage the cylindrical member; and manipulating
means secured to said housing and said piston members for moving said piston
members between a sealing position in which said piston members sealingly
engage
said cylindrical member and a retracted position in which said piston members
are
removed from said cylindrical member; wherein said elastomeric seal means are
mounted in grooves in said piston members; and wherein said elastomeric seal
means are deformable into said grooves when said piston members are in said
sealing position.
According to another aspect of the present invention, there is also
provided a blow out preventer seal for use on a blow out preventer mounted on
a
well bore in a production oil, water or gas well installation, wherein said
blowout
preventer includes radially opposed piston members, each piston member having
an inner end and a concavely curved recess in said inner end for receiving a
cylindrical member, and said piston members are moveable between a sealing
position in which said piston members sealingly engage said cylindrical member
and a retracted position in which said piston members are removed from said
cylindrical member; wherein said blow out preventer seal is comprised of an
elastomeric material, and is shaped to be mounted in a groove in one of said
piston members; and wherein said blow out preventer seal is deformable into
said
groove when said piston members are in said sealing position.
-3a-
CA 02716430 2010-10-04
50113-4D
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of preferred embodiments of the present
invention will become more apparent from the following description in which
reference is made to the appended drawings in which-
- 3b -
CA 02716430 2010-10-04
Figure 1 is a view of a progressing cavity pump oil well installation in an
earth
formation with a typical drive head, wellhead frame and stuffing box;
Figure 2 is a view similar to the upper end of Figure 1 but illustrating a
conventional
drive head with an integrated stuffing box extending from the bottom end of
the drive head;
Figure 3 is a cross-sectional view according to a preferred embodiment of the
present
invention;
Figure 4 is an enlarged, partially broken cross-sectional view of the drive
head of
Figure 3 including the main shaft and stuffing box thereof modified to include
an additional
pressure control system;
Figure 5 is an enlarged cross-sectional view of the pressure control system
shown
in Figure 4;
Figure 6 is a cross-sectional view of another preferred embodiment of the
drive head
including a floating labyrinth seal;
Figure 7 is an enlarged cross sectional view of the floating labyrinth seal
shown in
Figure 6;
Figure 8 is a cross sectional view of another embodiment of the drive head
including
a top mounted stuffing box which is not pressurized;
Figure 9 is a cross sectional view of another embodiment of the drive head
with a
hydraulic motor and another embodiment of the floating labyrinth seal;
Figure 10 is a side elevational cross-sectional view of a centrifugal backspin
retarder
according to a preferred embodiment of the present invention;
Figure 11 is a plan view of the centrifugal backspin retarder shown in Figure
10;
Figure 12 is a partially broken, cross-sectional view illustrating ball
actuating grooves
formed in the driving and driven hubs of the centrifugal backspin retarder
shown in Figure 10
when operating in the forward direction;
Figure 13 is similar to Figure 12 but illustrates the backspin retarder being
driven in
the backwards direction when the retarder brakes are engaged;
Figure 14 is a side elevational, cross-sectional view of one embodiment of a
polished
rod lock-out clamp according to the present invention;
Figure 15 is a top plan view of the clamp of Figure 14;
Figure 16 is a side elevational, cross-sectional view of another embodiment of
a
polished rod lock-out clamp according to the present invention;
Figure 17 is a top plan view of the clamp of Figure 16;
-4-
CA 02716430 2010-10-04
Figure 18 is a side elevational, cross-sectional view of another embodiment of
a
polished rod lock-out clamp according to the present invention;
Figure 19 is a top plan view of the clamp of Figure 18;
Figure 20 is a side elevational, cross-sectional view of one embodiment of a
blow-out
preventer having an integrated polished rod lock-out clamp according to the
present
invention; and
Figure 21 is a top plan view of the clamp of Figure 20.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
Figure 1 illustrates a known progressing cavity pump installation 10. The
installation
includes a typical progressing cavity pump drive head 12 , a wellhead frame 14
, a stuffing
box 16, an electric motor 18, and a belt and sheave drive system 20, all
mounted on a flow
tee 22 . The flow tee is shown with a blow out preventer 24 which is, in turn,
mounted on a
wellhead 25 . The drive head supports and drives a drive shaft 26 , generally
known as a
"polished rod". The polished rod is supported and rotated by means of a polish
rod clamp
28, which engages an output shaft 30 of the drive head by means of milled
slots (not shown)
in both parts. Wellhead frame 14 is open sided in order to expose polished rod
26 to allow
a service crew to install a safety clamp on the polished rod and then perform
maintenance
work on stuffing box 16 . Polished rod 26 rotationally drives a drive string
32, sometimes
referred to as "sucker rods", which, in turn, drives a progressing cavity pump
34 located at
the bottom of the installation to produce well fluids to the surface through
the wellhead.
Figure 2 illustrates a typical progressing cavity pump drive head 36 with an
integral
stuffing box 38 mounted on the bottom of the drive head and corresponding to
that portion
of the installation in Figure 1 which is above the dotted and dashed line 40.
The main
advantage of this type of drive head is that, since the main drive head shaft
is already
supported with bearings, stuffing box seals can be placed around the main
shaft, thus
improving alignment and eliminating contact between the stuffing box rotary
seals and the
polished rod. This style of drive head reduces the height of the installation
because there
is no wellhead frame and also reduces cost because there is no wellhead frame
and there
are fewer parts since the stuffing box is integrated with the drive head. The
main
disadvantage is that the drive head must be removed to do maintenance work on
the stuffing
box. This necessitates using a service rig with two lifting lines, one to
support the polished
rod and the other to support the drive head.
The drive head of the present invention is arranged to be connected directly
to and
between an electric or hydraulic drive motor and a conventional flow tee of an
oil well
-5-
CA 02716430 2010-10-04
installation to house drive means for rotatably driving a conventional
polished rod, and for not
only providing the function of stuffing box, but one which can be accessed
from the top of the
drive head to facilitate servicing of the drive head and stuffing box
components.
Another preferred aspect of the present invention is the provision of a
polished rod
lock-out clamp for use in clamping the polished rod during drive head
servicing operations.
The clamp can be integrated with the drive head or provided as a separate
assembly below
the drive head. Finally, the drive head may be provided with a backspin
retarder to control
backspin of the pump drive string following drive shut down.
Referring to Figures 3 and 4, the drive head assembly according to a preferred
embodiment of the present invention is generally designated by reference
numeral 5 and
comprises a drive head 50 and a prime mover such as electric motor 18 to
actuate drive
head 50 and rotate polished rod 26 as will be described below. The drive head
assembly
includes a housing 52 in which is mounted an input or drive shaft 54 connected
to motor 18
for rotation and, as part of the drive head 50, an output shaft assembly 56
drivingly
connected to a conventional polished rod 26. Drive shaft 54 is connected
directly to electric
drive motor 18, eliminating the conventional drive belts and sheaves and the
disadvantages
associated therewith. Output shaft assembly 56 provides a fluid seal between
the fluid in
drive head 50 and formation fluid in the well. The fluid pressure on the drive
head side of the
seal is above the wellhead pressure. The fluid seal provides the functions of
a conventional
stuffing box and, accordingly, not only eliminates the need for a separate
stuffing box, which
further reduces the height of the assembly above the flow tee, but is easily
serviceable from
the top of the drive head, as will be explained.
Electric motor 18 is secured to housing 52 by way of a motor mount housing 60
which
encloses the motor's drive shaft 62 which in turn is drivingly connected to
drive shaft 54 by
a releasable coupling 64 known in the art. Drive shaft 54 is rotatably mounted
in upper and
lower shaft bearing assemblies 66 and 68 , respectively, which are secured to
housing 52.
The lower end of drive shaft 54 is advantageously coupled to a centrifugal
backspin retarder
70 and to an oil pump 72. A drive gear 74 is mounted on drive shaft 54 and
meshes with a
driven gear 76 .
Driven gear 76 is drivingly connected to and mounted on a tubular sleeve 80
which
is part of tubular output shaft assembly 56 . Depending on the viscosity or
weight of the
fluids being produced from the well, the ratios between the drive and driven
gears can be
changed for improved operation. Part of assembly 56 functions as a rotating
stuffing box as
will now be described.
-6-
CA 02716430 2010-10-04
Sleeve 80 is mounted for rotation in upper and lower bearing cap assemblies 84
and
86, respectively, secured to housing 52 as seen most clearly in Figure 4.
Upper bearing cap
assembly 84 houses a roller bearing 88 and lower bearing cap 86 houses a
thrust roller
bearing 90 which vertically supports and locates sleeve 80 and driven gear 76
in the housing.
A standpipe 92 is concentrically mounted within the inner bore of sleeve 80 in
spaced
apart relation to define a first axially extending outer annular fluid passage
94 between the
standpipe's outer surface and sleeve 80's inner surface. Standpipe 92 is
arranged to
concentrically receive polished rod 26 therethrough in annularly spaced
relation to define a
second inner axially extending annular fluid passage 114 between the
standpipe's inner
surface and the polished rod's outer surface. Lower bearing cap assembly 86
includes a
downwardly depending tubular housing portion 96 with a bore 98 formed axially
therethrough
which communicates with inner fluid passage 114. The lower end of the
standpipe is seated
on an annular shoulder defined by a snap ring 102 mounted in a mating groove
in inner bore
98 of the lower bearing cap assembly. The standpipe is prevented from rotating
by, for
example, a pin 104 extending between the lower bearing cap assembly and the
standpipe.
The upper end of the standpipe is received in a static or ring seal carrier
110 which is
mounted in the upper end of sleeve 80.
A plurality of ring seals or packings 116 are provided at the upper end of
outer
annular fluid passage 94 between a widened portion of the inner bore of sleeve
80 and outer
surface of the standpipe 92, and between the underside of seal carrier 110 and
a
compression spring 118 which biases the packings against seal carrier 110, or
at least
towards the carrier if by chance wellhead pressure exceeds the force of the
spring and the
pressure in outer passage 94. A bushing or labyrinth seal 120 is provided
between the outer
surface of the lower end of sleeve 80 and an inner bore of lower bearing cap
assembly 86.
The upper end of inner fluid passage 114 communicates with the upper surface
of packings
116. As will be described below, pressurized fluid in outer fluid passage 94
and spring 118
act on the lower side of the packings, opposing the pressure exerted by the
well fluid in
passage 114 to prevent leakage.
The upper end of sleeve 80 is threadedly coupled to a drive cap 122 which in
turn is
.30 coupled to a polished rod drive clamp 124 which engages polished rod 26
for rotation. A
plurality of static seals 126 are mounted in static seal carrier 110 to seal
between the seal
carrier and the polished rod. 0-rings 236 seal the static seal carrier 110 to
the inside of
sleeve 80.
-7-
CA 02716430 2010-10-04
As there is clearance between the upper end of standpipe 92 and seal carrier
110 for
fluid communication between fluid passages 114 and 94, there is some
compliancy in the
standpipe's vertical orientation which allows it to adapt to less than perfect
alignment of the
polished rod.
A pressurization system is provided to pressurize outer annular fluid passage
94. To
that end, the lower bearing cap assembly includes a diametrically extending
oil passage 130.
One end of passage 130 in the lower bearing cap is connected to the high
pressure side of
oil pump 72 by a conduit (not shown) and communicates with the lower end of
outer annular
passage 94. The high pressure side of the pump is also connected to a pressure
relief valve
133 which, if the pressure delivered by the pump reaches a set point, will
open to allow oil
to flow into passage 132 in the upper bearing cap assembly by a conduit (not
shown) to
lubricate bearings 88. The other end of passage 132 in the upper bearing cap
assembly
communicates with a similar passage 134 in upper bearing cap 66 supporting
drive shaft 54.
The fluid pressure supplied to passage 130 from pump 72 is maintained above
the pressure
at the wellhead. A pressure differential in the order of 50 to 500 psi is
believed to be
adequate although greater or lesser differentials are contemplated.
An enhancement to automatically adjust stuffing box pressure in relation to
wellhead
pressure is illustrated in Figures 4 and 5. A valve spool or piston 140 is
mounted in a port
142 formed in the wall 144 of lower tubular portion 96 of lower bearing cap
assembly 86.
An access cap 146 is threaded into the outer end of the port. A spring 148
normally biases
spool 140 radially outwardly. As best shown in Figure 5, an axial fluid
passage 150
communicates pump pressure to the left side of valve spool 140. A second
passage 152
connects to upper bearing cap 84. The inner end of valve spool 140
communicates with
wellhead pressure in bore 98. The outer end of the spool communicates with
pump pressure
against the action of the spring and the wellhead pressure. The spool valve
serves to
maintain the fluid pressure applied to the first annular passage 94 greater
than the well
pressure in the second annular passage 114.
In operation, when electric motor 18 is powered, the motor drives shaft 54
which, in
turn, rotates drive gear 74 and driven gear 76. Driven gear rotates sleeve 80
and drive cap
122 to rotate polished rod 26 via rod clamp 124. Drive shaft 54 also operates
oil pump 72
which applies fluid to outer fluid passage 94 at a pressure which is greater
than the wellhead
pressure in inner fluid passage 114. This higher pressure is intended to
prevent oil well fluids
from leaking through the stuffing box and entering into drive head housing 52.
The pressure
applied to outer annular passage 94 can be set by adjusting pressure relief
valve 133 or in
-8-
CA 02716430 2010-10-04
the enhanced embodiment of Figure 4, the spool valve automatically adjusts the
pressure
applied to outer fluid passage 94 in response to wellhead pressure. Excess
flow which is not
required to the stuffing box can be released to the top bearings or gear mesh
for lubrication.
Sleeve 80, packings 116, spring 118, static seals 126 and seal carrier 110 all
rotate or are
adapted to rotate relative to standpipe 92.
The labyrinth seal 120 between sleeve 80 and the main bearing cap 86 as shown
in
Figure 3 is used in the present invention so that there is no contact and thus
no wear
between these parts in normal operation. However, it is difficult to
manufacture a close fitting
labyrinth due to run out which is common in all manufactured parts. Due to the
difficulty of
manufacture, a preferred embodiment of the labyrinth seal is a floating seal
229 which is
compliantly mounted to main bearing cap 86 by studs 230 and locknuts 231 as
shown in
Figure 6 and in greater detail in Figure 7. In this embodiment, sleeve 80 is
shortened to
provide clearance for the seal. Labyrinth seal 229 has clearance holes to
receive studs 230
to allow movement of the seal in the horizontal plane. Lock nuts 231 are
adjusted to provide
a sliding clearance between seal 229 and the top surface of bottom bearing cap
86. An 0-
ring 232 prevents the flow of oil between the labyrinth seal and the bottom
bearing cap. The
O-ring preferably has a diameter nearly equal to that of the labyrinth seal
since this balances
the hydraulic load on the labyrinth seal, reduces force on the lock nuts and
allows the
labyrinth seal to move and align itself more easily within rotating driven
gear 76. Due to
typical diametral clearances of 0.002 to 0.005 inches between the stationary
labyrinth seal
and the rotating driven gear, leakage occurs. Due to hydrodynamic forces
generated within
the leaked oil by the rotation of the rotating member, similar to the
principle of a journal
bearing, the labyrinth seal tends to align itself in the center of the
rotating component. The
rotating component can be the driven gear as shown in Figure 6, the main
bearing inner race
as shown in Figure 9, sleeve 80 or a bushing fixed to the sleeve.
In some cases, pressurization of the stuffing box is not worthwhile
economically but
having the stuffing box mounted on the top of the drive head remains a service
benefit.
Figure 8 shows a preferred embodiment of a stuffing box which can be serviced
from the top
of the drive but does not have outer annular passage 94 pressurized. In this
embodiment,
wellhead pressure is applied to inner annular passage 114. Stuffing box spring
118 is placed
between packing rings 116 and static seal carrier 110 eliminating the need for
adjustment
of the packing rings. Static seals 126 prevent escape of well fluids between
polished rod 26
and static seal carrier 110. O-rings 236 prevent escape of well fluids between
static seal
carrier 110 and the inner bore of sleeve 80. Drive cap 122 is threaded onto
sleeve 80 and
transmits torque to polished rod clamp 124 to rotate polished rod 26. Leakage
past packing
-9-
CA 02716430 2010-10-04
rings 116 flows into a lantern ring 239 which has radial holes 242 to
communicate with radial
holes 238 in sleeve 80 to drain the fluid for collection in the housing.
Leakage of well fluids
from the drive head is prevented by static O-rings 241 between the lantern
ring and sleeve
80 and by dynamic lip seals 240 between lantern ring 239 and standpipe 92.
In some cases, progressing cavity pump drives use a hydraulic motor rather
than an
electric motor. Use of hydraulic power provides an opportunity to simplify the
drive system
and the stuffing box pressurization which will be explained with reference to
Figure 9,
showing a preferred embodiment of a drive head driven by a hydraulic motor
233. The drive
head assembly 234 shown in this figure with hydraulic drive does not have a
backspin
retarder braking system since the braking action can be achieved by
restricting the flow of
hydraulic oil in the backspin direction. Additionally, the pressure from the
hydraulic system
can be used to pressurize the stuffing box, thus eliminating the need for oil
pump 72. Both
simplifications affect the drive shaft from the motor since the braking system
and the oil
pump can be left out of the design thus reducing cost, size and complexity. In
hydraulic drive
head assembly 234, hydraulic pressure on the input port of hydraulic motor 233
is diverted
though a channel (not shown) to a pressure reducing valve 235. The reduced
pressure fluid
is supplied to oil passage 130 in the lower bearing assembly to pressurize
outer fluid
passage 94. The pressure reducing valve is set higher than the wellhead
pressure in inner
fluid passage 114 as in other embodiments.
As mentioned above, backspin from the windup in sucker rods 34 can reach
destructive levels. The present drive head assembly can therefore
advantageously
incorporate a braking assembly to retard backspin, as will now be described in
greater detail.
Referring to Figures 10 - 13, a centrifugal brake assembly 70 is comprised of
a
driving hub 190 and a driven hub 192. Driving hub 190 is connected to the
drive shaft 54 for
rotation therewith. Driven hub 192 is mounted to freewheel around shaft 54
using an upper
roller bearing 194 and a lower thrust bearing assembly 196. One end of each of
a pair of
brake shoes 198 is pivotally connected to a respective driven hub by a pivot
pin 200. A pin
202 on the other end of each of the brake shoes is connected to an adjacent
pivot pin 200
on the other respective brake shoe by a helical tension spring 204 so as to
bias the brake
shoes inwardly toward respective non-braking positions. Brake linings 206 are
secured to
the outer arcuate sides of the brake shoes for frictional engagement with the
inner surface
208 of an encircling portion of drive head housing 52. One end of each brake
shoe is fixed
to the driven hub by means of one of the pivot pins 200. The other end of each
shoe is free
to move inwardly under the influence of springs 204, or outwardly due to
centrifugal force.
-10-
CA 02716430 2010-10-04
Referring to Figures 12 and 13, the driving and driven hubs 190 and 192 are
formed
with respective grooves 210 and 212, respectively, in adjacent surfaces 214
and 216, for
receiving drive balls 218, of which only one is shown. Groove 210 in driving
hub 190 is
formed with a ramp or sloped surface 220 which terminates in a ball chamber
222 where it
is intersected by a radial hole 209 in which the edge of the ball is located
when drive shaft
54 rotates in a forward direction. Centrifugal force holds the ball radially
outwards and
upwards in the ball chamber by pressing it against radial hole 209 so there is
no ball motion
or contact with freewheeling driven hub 192 while rotation is in the forward
direction. When
the drive shaft rotates in the reverse direction, the ball moves downward to a
position in
which it engages and locks both hubs together.
When the drive head starts to turn in the forward direction, the ball 218
rests on
driven hub 192. The edge 211 of ball chamber 222 pushes the ball to the right
and causes
it to ride up ramped surface 215. As the speed increases, the ball jumps
slightly above the
ramp and is thrown up into ball chamber 222, where it is held by centrifugal
force as shown
in Figure 12.
When the electric motor turning the drive head is shut off, the drive head
stops and
ball 218 drops back onto driven hub 192 as windup in the sucker rod begins to
counter or
reverse rotate the drive head, which transmits the reverse rotation to drive
shaft 54 through
sleeve 80 and driven gear 76. More specifically, sloped surface 220 of driving
hub 190
pushes the ball to the left until it falls into groove 212 of the driven hub.
The ball continues
to be pushed to the left until it becomes wedged between the spherical surface
213 of the
driving hub and the spherical surface 217 of the driven hub thus starting the
driven hub and
thereby the brake shoes turning. This position is illustrated in Figure 13.
The reverse ramp
220 of driving hub 190 serves an important function associated with the
centrifugal brake.
The centrifugal brake has no friction against housing surface 208 until the
brake turns fast
enough to overcome brake retraction springs 204. If the driving hub generates
a sufficient
impact against driven hub 192 during engagement, the driven hub can accelerate
away from
the driving hub. If the driving hub is itself turning fast enough, the ball
can rise up into ball
chamber 222 and stay there. By adding reverse ramp 220, the ball cannot rise
up during
impact and since the ramp is relatively long, it allows driving hub 190 to
catch up to driven
hub 192 and keep the ball down where it can wedge between the driving and
driven hubs.
Brake assembly 70 is preferably but not necessarily an oil brake with surface
208
(which acts as a brake drum) having, for example, parts for oil to enter or
fall into the brake
to reduce wear.
-11-
CA 02716430 2010-10-04
As will be appreciated, energy from the recoiling sucker rod is transmitted to
brake
70 to safely dissipate that energy non-destructively.
A further aspect of the present invention is the provision of a polished rod
lock out
clamp 160 for use in securing the polished rod when it is desired to service
the drive head.
The clamp may be integrated into the drive head or may be provided as a
separate
assembly, which is secured to and between the drive. head and a flow tee.
Figures 14-17
illustrate two embodiments of a lock-out clamp.
As shown, in each embodiment, the clamp includes a tubular clamp body 162
having
a bore 164 for receiving polished rod 26 in annularly spaced relation
therethrough. A bushing
166 is mounted on an annular shoulder 168 formed at the bottom end of bore 164
for
centering the polished rod in the housing. Flanges 167 or threaded connections
depending
on the application are formed at the upper and lower ends of the housing for
bolting or
otherwise securing the housing to the underside of the drive head and to the
upper end of
the flow tee. The clamp includes two or more equally angularly spaced clamp
members or
shoes 170 about the axis of the housing/polished rod. The clamp shoes are
generally in the
form of a segment of a cylinder with an arcuate inner surface 172 dimensioned
to correspond
to the curvature of the surface of the polished rod. Arcuate inner surfaces
172 should be
undersize relative to the polished rod's diameter to enhance gripping force.
In the
embodiment of Figures 14 and 15, spring means 174 are provided to normally
bias the
clamp members into an un-clamped position. In the embodiment of Figures 16 and
17, the
ends of bolts 176 are generally T-shaped to hook into correspondingly shaped
slots 171 in
shoes 170 to positively retract the shoes without the need for springs 174.
Clamp shoes 170 are actuated by radial bolts 176, for example, to clamp the
polished
rod such that it cannot turn or be displaced axially. The lock out clamp may
be located
between the flow tee and the bottom of the drive head. Alternately, it can be
built into the
lower bearing cap 86 of the drive head.
In some applications it is preferable not to restrict the diameter through the
bore 164
of the lock out clamp so that the sucker rods can be pulled through the clamp
160. In this
embodiment of the polish rod clamp as shown in Figure 18 and 19, where like
numerals
identify like elements, two opposing radial pistons 182 are actuated by bolts
184 to force the
pistons together and around polish rod 26. The polish rod is gripped by
arcuate recesses
186, which are preferably made undersize relative to the polished rod to
enhance gripping
force.
In a further embodiment of the polished rod lock out clamp, the clamping means
are
integrated with a blow out preventer 180, shown in Figures 20 and 21. Blow out
preventers
-12-
CA 02716430 2010-10-04
are required on most oil wells. They traditionally have two opposing radial
pistons 182
actuated by bolts 184 to force the pistons together and around the polish rod
to effect a seal.
The pistons are generally made of elastomer or provided with an elastomeric
liner such that
when the pistons are forced together by the bolts, a seal is formed between
the pistons,
between the pistons and the polish rod and between the pistons and the piston
bores.
Actuation thus serves as a means to prevent well fluids from escaping from the
well.
In accordance with the present invention, an improved blow out preventer
serves as
a lock out clamp for well servicing. In order to serve this purpose, the
pistons must be
substantially of metal which can be forced against the polished rod to prevent
axial or
rotational motion thereof. The inner end of the pistons is formed with an
arcuate recess 186
with curvature corresponding substantially to that of the polished rod.
Enhanced gripping
force can be achieved if the arcuate recess diameter is undersize relative to
the polished rod.
The sealing function of the blow out preventer must still be accomplished.
This can be done
by providing a narrow elastomeric seal 188 which runs across the vertical flat
face of the
piston, along the arcuate recess, along the mid height of the piston and then
circumferentially
around the piston. Seal 188 seals between the pistons, between the pistons and
the polish
rod and between the pistons and the piston bores. Thus, well fluid is
prevented from coming
up the well bore and escaping while the well is being serviced, as might be
the case while
the stuffing box is being repaired. By including the sealing function of the
BOP with clamping
means, one set of pistons can accomplish both functions, enhancing safety and
convenience
without increasing cost or size.
The above-described embodiments of the present invention are meant to be
illustrative of preferred embodiments and are not intended to limit the scope
of the present
invention. Various modifications, which would be readily apparent to one
skilled in the art,
are intended to be within the scope of the present invention. The only
limitations to the scope
of the present invention are set forth in the following claims appended
hereto.
-13-
