Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TOP HOLD DOWN ROD PUMP WITH HYDRAULICALLY
ACTIVATED DRAIN AND METHOD OF USE
FIELD OF THE INVENTION
[0001] The present invention relates to top hold-down pump systems having a
barrel
drain operatively connected to the pump positioned beneath a pump seating
nipple. The
design of the pump provides specific advantages over past systems by improving
the
efficiency of re-setting the barrel drain and the required work over costs
after the drain
has been activated.
BACKGROUND OF THE INVENTION
[0002] As is well known, oil is often pumped from a production well using
various
designs of reciprocating pump and pump jack. Generally, the pump jack includes
a
reciprocating rod (i.e. a polish rod) that passes through the wellhead that is
connected to a
series of sucker rods which provides the reciprocating pumping action to draw
oil from
the well. The down-hole pump is seated within a tubing string in the
production zone of
the well. The pump includes a pump barrel through which a pump piston operates
to lift
oil to the surface through the production tubing. This general style of pump
has been in
operation for over 100 years.
[0003] More specifically, the primary components of this type of pump consist
of a
pump barrel, a plunger and two valves; a traveling valve and a standing valve.
Sucker
rods which reciprocate within the tubing string of the well are connected to
the plunger
such that fluids are brought to the surface.
[0004] Over time, as various designs of pump have evolved, two hold down
positions of
rod pumps have been utilized; namely, the top hold down rod pump and the
bottom hold
down rod pump both of which are sealed within a seating nipple within the
production
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tubing. The top hold down rod pump (where the pump is below the seating
nipple) is
more commonly used as it is resistant to sand sticking and is typically easier
to remove
from the well when removal is required. The bottom hold down rod pump (where
the
pump is above the seating nipple) is less commonly used.
[0005] Similarly, top hold down insert progressive cavity pumps (PCPs) are
becoming
more available worldwide. A PCP includes a rotor and a stator and, as with
reciprocating
rod pumps, a pump barrel or stator is operatively sealed within a seating
nipple secured to
the production tubing. A rotor rotates within the stator within a helical
chamber so as to
positively lift fluids from the lower end of the stator into the production
tubing.
[0006] For both top and bottom hold down rod pumps and top hold down PCPs,
when
problems arise in the wellbore and the hydrostatic pressure above the pump is
desired to
be released for reasons such as to assist in killing a well or to avoid
pulling a wet tubing
string to the surface if the pump cannot be unseated, engineers may choose to
incorporate
a tubing drain. As a part of the tubing string, the tubing drain is located
towards the
bottom of the production tubing and slightly spaced above the pump seating
nipple. The
tubing drain will open at a threshold pressure and cause the discharged fluid
above the
pump to drain to the wellbore. As such, the pressure differential between the
inside of the
production tubing and the annulus between the well-bore and production tubing
will
equalize. The pressure equalization may then enable the tubing string to be
withdrawn
without the trapped fluid within the production tubing or alternatively may
enable the
pump to be unseated and withdrawn from within the production tubing to
surface.
Additionally, the tubing drain can be used as a safety feature to protect the
production
system from over-pressuring while in operation.
[0007] If the tubing drain (which in the past has always been located on the
production
tubing string above the pump) is opened, regardless of the problem being
solved or for
the reason the tubing drain was opened, the opened drain requires that the
production
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tubing string be returned to the surface in order to reset the tubing drain.
Self-resetting
tubing drains have not been employed due to the difficulty in automatically
resetting such
systems in the very dirty downhole environment. Withdrawing the entire tubing
string to
the surface is expensive and inefficient if the problem being solved does not
relate to the
tubing string.
[0008] More specifically, as the tubing drain is located slightly above the
hold down
seating nipple in the production tubing this means that when opened, the
tubing drain
allows the discharge fluid to drain to the annulus between the wellbore and
the
production tubing (usually by hydraulic over-pressure).
[00091 In summary therefore, there are many reasons for including a tubing
drain as part
of the production tubing with the top hold down rod pump. These include:
1) The tubing drain is a safety feature for preventing over pressuring of all
equipment downstream of the pump discharge;
2) The activation of the tubing drain can be invoked intentionally to assist
in
releasing a rod pump from the hold down seating nipple by removing both the
fluid within the production tubing and its hydrostatic head; or to avoid
pulling a
wet tubing string if the pump will not release from the seating nipple;
3) A tubing drain can also be activated in an effort to kill the surface
pressure on a
wellhead by pumping kill fluid down the tubing and entering the wellbore from
the bottom of the production string via the tubing drain and cycling to the
top.
[0010] However, in each case when the tubing drain of these past systems is
activated,
the production tubing must be removed from the wellbore to replace/reset the
opened
tubing drain and then returned downhole in order to resume production. This
will result
in significant cost increases, as service equipment and time is required to
complete the
work over.
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[0011] Accordingly, there has been a need for a pump system that does not
require that
the production tubing be removed from the well in the event that it is
required that the
hydrostatic pressure within the production tubing is released.
[0012] A review of the prior art reveals that while limited hydraulic drain
systems and
various mechanically operated drains have been incorporated into various
downhole
pump designs, no such solution has been provided to a top hold down rod pump.
[0013] For example, US Patent 3,994,338 discloses a hydrostatic pressure
release for
bottom hold down rod pumps. This system provides a sub-joint having a release
port that
will drain oil from the production tubing into the borehole. The sub-joint is
located
between the standing valve and bottom hold down seal assembly on the pump.
This
system is limited by virtue of the bottom hold down drain being located in an
area where
sand commonly bridges off in the static fluid area adjacent the exterior of
the pump
barrel. As a result, the normal settling of sand in many wells would make this
drain
inoperable in many wells. Moreover, trapped sand commonly causes the pump to
become
stuck in the pump seating nipple.
[0014] US Patent 3,150,605 describes a casing pump drain incorporating a
pressure
release valve beneath the casing seal that incorporates channels and a
mechanical valve
system to convey liquid from above the pump seal to below the pump seal.
[0015] Other examples of various pump systems include US Patent 6,857,477
which
discloses a reciprocating pump vent-dump valve using a mechanical valve
system; US
Publication 2004/0055743 which discloses a reciprocating pump dump valve using
a
mechanical dumping system; US Publication 2004/0216867 and US Patent 6,752,212
which disclose dump valves for use with tubing; US Patent 4,273,520 which
discloses a
deep well pump incorporating a mechanical valve system; US Patent 4,909,326
which
discloses a tubing unloader incorporating a mechanical valve system and seals;
US Patent
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4,166,715 which discloses a tubing drain device that is mechanically operated;
US Patent
4,157,117 which discloses a tube draining system that is mechanically
operated; and, US
Patent 5,005,651 which discloses a downhole pump unseating apparatus.
SUMMARY OF THE INVENTION
[0016] The present invention provides a pump system that overcomes the primary
shortcomings of prior art in not requiring the withdrawal of production tubing
from the
wellbore in the event of releasing the hydrostatic pressure within the
production tubing.
100171 More specifically, the invention utilizes the discharged fluid space
within the
interior of a top hold down pump body as a conduit for the discharge fluid
within the
tubing string to reverse flow through a pressure activated barrel drain
integral to the
pump body. The fluid drain path continues through the micro-annulus between
the
exterior of the barrel and inner tubing below the seating nipple. The barrel
drain
duplicates every function of a past tubing drain, but with the significant
advantage of not
requiring the withdrawal of the production tubing from the wellbore.
[0018] More specifically, the invention provides in a top hold-down pump for
pumping
fluids from a well to the surface through production tubing, the top hold-down
pump
having an upper end for sealing engagement with a seating nipple within the
production
tubing and a positive displacement pumping system operatively retained within
a barrel
for allowing fluid within the barrel to be displaced to the surface by a
reciprocating or
rotating rod operatively connected to the positive displacement pumping
system, the
improvement comprising a barrel drain between the upper end and the lower end
for
draining fluid from the production tubing to the exterior of the barrel
beneath the seating
nipple.
[0019] In a further embodiment, the invention provides a top hold-down pump
comprising:
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a barrel having a top section for sealing engagement with a seating nipple
within
the production tubing and a bottom section operatively retaining positive
displacement pumping equipment;
a barrel drain operatively connected to the barrel between the top section and
the
bottom section for releasing hydrostatic fluid pressure from the production
tubing
to the exterior of the barrel beneath the seating nipple.
[0020] In a further embodiment, the barrel drain includes at least one barrel
drain port
and a barrel sleeve operatively retaining a drain sleeve between a closed
position where
the at least one barrel drain port is closed and an open position where the at
least one
barrel drain port is open, the drain sleeve and barrel sleeve retaining a
shear pin for
holding the drain sleeve in the closed position wherein an increase in
hydraulic pressure
on the interior of the barrel drain will cause the shear pin to shear at a
threshold pressure
causing the drain sleeve to move to the open position.
100211 In another embodiment, the barrel drain includes at least one barrel
drain port for
operatively retaining a corresponding rupture disk for sealing the at least
one drain port
and rupturing at a threshold pressure to open the at least one barrel drain
port.
[0022] In yet another embodiment, the barrel drain includes a precision slot
having a
specific thickness that will rupture at a threshold pressure.
[0023] In another aspect, the invention provides a method of releasing
hydrostatic
pressure in production tubing in a well having a top hold-down pump having a
barrel
drain, comprising the step of: applying a hydraulic pressure to the interior
of the
production tubing at sufficient pressure to open the barrel drain to permit
fluid within the
production tubing to flow to an annular space between the barrel and
production tubing
beneath the seating nipple.
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[0024] In another aspect of the invention, the invention provides a top hold-
down pump
drain for operative connection to a top hold-down pump barrel secured within a
hold-
down seating nipple within production tubing, the top hold-down pump drain for
operative connection to the pump barrel between the hold-down seating nipple
and
positive displacement pumping equipment retained within the pump barrel, the
top hold-
down pump drain for releasing hydrostatic fluid pressure from the production
tubing and
interior of the pump barrel to the exterior of the pump barrel beneath the
hold-down
seating nipple.
[0025] In a further embodiment, the invention provides a top hold-down pump
system
comprising:
a barrel having a top section for sealing engagement with a seating nipple
within
the production tubing and a bottom section operatively retaining positive
displacement pumping equipment, wherein the bottom section extends beneath
the seating nipple within the production tubing;
a barrel drain operatively connected to the barrel between the top section and
the
bottom section for releasing hydrostatic fluid pressure from the production
tubing
to the exterior of the barrel beneath the seating nipple above a threshold
pressure;
and,
at least one production tubing opening operatively connected to the production
tubing beneath the seating nipple and adjacent the barrel drain for allowing
fluid
flow from the annular space between the barrel and the exterior of the
production
tubing.
BRIEF DESCRIPTION OF THE FIGURES
[0026] The invention is described with reference to the accompanying figures
in which:
Figure 1 is a cross-sectional view of a top hold-down rod pump having a
hydraulic drain in accordance with the prior art;
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Figure 2A is a cross-sectional view of a top hold-down rod pump having a
hydraulic drain in accordance with the invention;
Figure 2B is a cross-sectional view of a top hold-down rod pump having a
hydraulic drain in accordance with the invention and a secondary check valve;
Figure 3A is a side and cross-sectional view of a hydraulic drain in
accordance
with one embodiment of the invention;
Figure 3B is a side and cross-sectional view of a hydraulic drain in
accordance
with one embodiment of the invention;
Figure 3C is a side and cross-sectional view of a hydraulic drain in
accordance
with one embodiment of the invention; and,
Figure 4 is a cross-sectional view of a secondary check valve in accordance
with
one embodiment of the invention.
DETAILED DESCRIPTION
[0027] With reference to the Figures, top hold-down pumps are described to
include a
hydraulic drain within a pump barrel. The design of the system promotes the
efficiency of
maintenance in the event that the hydraulic drain has been activated in that
the system
does not require that the production tubing string be withdrawn from the well
to re-set the
hydraulic drain.
[0028] With reference to Figure 1, a typical top hold-down rod pump 10 in
accordance
with the prior art is described. The pump is set within a wellbore 12 having
casing 13 and
casing perforations 13a adjacent to or near the bottom of production tubing
14. The
production tubing includes a seating nipple 16 for receiving a seating mandrel
18, seating
cup 18a and seating cup ring 18b on the pump and for securing the pump at its
upper end
within the production tubing 14. The pump 10 is connected to the surface via
sucker rod
20.
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100291 The pump 10 further includes a barrel 22 and plunger/piston 24 together
with
traveling valve 26 and standing valve 28. The traveling valve 26 is secured
within the
plunger 24 whereas the standing valve 28 is secured to the lower end of the
barrel 22.
[0030] In operation, the sucker rod 20 is made to reciprocate such that the
plunger 24
moves up and down within the barrel. Upward motion of the plunger causes the
traveling
valve 24 to close causing fluid above the plunger to be displaced upwardly.
This fluid
passes through the seating mandrel 18 wherein it is expelled to the interior
14a of the
production tubing 14 towards the surface. At the same time, the standing valve
28 will
open allowing fluid to enter the lower region of the barrel 22 to fill the
volume 22a
created by the upwardly moving plunger.
[0031] Subsequent downward motion of the plunger 24 causes the traveling valve
26 to
open and the standing valve 28 to close such that the plunger 24 moves
downwardly
through the barrel 22 so as to retain hydrostatic pressure within the
production tubing 14.
[0032] As is well known, repetition of the cycle enables fluid to be drawn
from the well.
100331 Figure 1 also shows the location of a tubing drain 30 in accordance
with the prior
art above the seating nipple 16 in the production tubing 14. As is known, in
the event of
the need to relieve the hydrostatic pressure in the production tubing (for all
reasons
including production, maintenance and safety), by increasing the hydraulic
pressure
within the production tubing 14a will cause tubing drain 30 to open allowing
the fluid
within the production tubing 14a to flow into the annular space 32 between the
casing 13
and production tubing 14. Once opened, this system then requires that the
entire tubing
string 14 be removed from the well to replace the tubing drain 30.
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[0034] As known to those skilled in the art, the pump 10 may be assembled in
sections so
as to facilitate maintenance of the various sub-components of a pump.
[0035] As shown in Figures 2A and 2B and in accordance with the invention, a
pump 50
is described in which a barrel drain 52 is configured to the pump beneath the
pump
seating nipple 16 as a section of the barrel 22 and above the traveling 26 and
standing
valves 28. As such, in the event that the hydrostatic pressure within the
production tubing
14 must be relieved, an increase in hydraulic pressure within the production
tubing 14
will cause the barrel drain 52 to open. In the subject design, as the barrel
drain 52 is
located beneath the seating nipple 16 and in the barrel 22, hydrostatic
pressure will
equalize between the production tubing volume 14a and annular space 32 through
micro-
annular space 32a and the bottom of the production tubing 14. Importantly,
this design
will not require that the production tubing 14 be withdrawn from the well to
reset the
system but rather only requires that the pump 50 be returned to surface to be
reset. In a
further embodiment, the production tubing beneath the seating nipple 16 may
also be
provided with one or more slots 56 adjacent the barrel drain 52 such that in
the event that
the barrel drain 52 is opened, the fluid within the production will more
rapidly flow into
the well bore as fluid drag through the micro-annular space would be reduced.
This may
be especially advantageous in the event that surface pressure must be quickly
killed
within the well.
100361 As is readily understood by those skilled in the art, removal of the
pump 50 is
considerably more cost efficient than removing both the pump 50 and production
tubing
14.
[0037] In a further embodiment, as shown in Figure 2B and Figure 4, a
secondary check
valve 54 may be incorporated beneath the barrel drain 52 to replace any
secondary check
valve above the seating mandrel on select pump configurations. The secondary
check
valve is used to assist in opening the travelling valve when the plunger moves
downward
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as the check valve relieves the travelling valve of the weight of the
hydrostatic head. As
shown the secondary check valve 54 includes a valve sleeve 54a that is engaged
around
valve rod 16a between retaining cage 54b and check valve seat 54c. The
secondary check
valve does not interfere with the normal operation of the plunger and standing
and
traveling valves.
[0038] Figures 3A, 3B, and 3C show different embodiments of a barrel drain. In
Figure
3A, a barrel drain 70 includes a drain sleeve 72 around drain mandrel 74
having drain
ports 75. Seal rings 76a and 76b provide a seal between the interior of the
drain mandrel
74 and the exterior. Drain sleeve 72 is retained in a closed position as shown
in the Figure
by shear pin 78. In operation, by increasing the hydraulic pressure within the
drain
mandrel 74 will, at a desired pressure threshold, cause the shear pin 78 to
shear thereby
causing the drain sleeve to move to an open position where the drain ports 75
are opened.
The barrel drain 70 may be configured to the pump barrel by an appropriate
connection
system such as threads.
[0039] In Figure 3B, a barrel drain 80 is similar to the barrel drain 70 shown
in Figure 3A
with respect to a barrel sleeve 82 and a drain port 84. The drain port 84 is
fitted with a
rupture plug 86 designed to rupture at a desired pressure threshold.
[0040] In Figure 3C a barrel drain 90 includes a precision slot vertically
milled into the
joint. An increase in pressure above a threshold causes the precision slot to
rupture at the
precision slot based on the specific thickness of the slot material.
[0041] Progressive Cavity Pump
[0042] The technology may be similarly applied to top hold down insertable
progressive
cavity pump (PCP) which could use any of the barrel drains described above. In
a
progressive cavity pump system, the barrel drain would be configured to an
upper section
of a PCP stator beneath a top hold-down seating nipple and above the PCP
rotor.
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[0043] Although the present invention has been described and illustrated with
respect to
preferred embodiments and preferred uses thereof, it is not to be so limited
since
modifications and changes can be made therein which are within the full,
intended scope
of the invention.
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