Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02482507 2004-09-24
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SELF-PROPELLED SWABBING DEVIGE AND METHOD
Field of the Invention
The present invention relates generally to oil and natural gas well production
devices and techniques, and more particularly to a swabbing device and
method for the removal of liquids from wells incapable of lifting these
liquids
on their own.
Backqiround of the Invention
Wells that produce gas and liquids such as water, oil or petroleum
condensates are often incapable of clearing the liquids from the wellbore as
gas is produced, especially in depleted reservoirs and low-rate gas wells.
These liquids accumulate over time until they exert enough backpressure
within the wellbore and on the reservoir to reduce the flow of natural gas, or
stop it completely.
Prior art methods for dealing with this problem have included the use of down-
hole pumps. The problem is that these methods are labor intensive, require
regular attention by employees, and some use expensive equipment to
provide an external source of lifting capacity to clear the wellbore of the
liquids.
What is needed is a way to optimize the production from oil and gas wells
where the reservoir delivers a sufficient quantity of gas to lift the
accumulated
liquids to surface using the reservoir's own energy. In addition, any proposed
solution should be capable of running automatically once set for the operating
conditions of a particular well without need for constant attention.
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For the foregoing reasons, there is a need for an improved device for
swabbing wellbores.
Summam of the Invention
The present invention is directed to a self-propelled swabbing device and
method for use in removing liquids to surface frorr~ within an installed
wellbore
casing. The device includes a longitudinally extending plunger sized to fit
within the wellbore casing, and has an internal surface defining an internal
flow passage that extends longitudinally therethrough.
The device further includes a seal between the plunger and the casing, and a
valve stem having a valve operative to be shuttled between an opened
position and a closed position to seal the internal flow passage. The valve
stem extends longitudinally through the plunger to form a piston and sealed
chamber maintained at a pressure below that desired for closing the valve. A
biaser is further included for biasing the valve in the opened position until
a
set pressure is reached, whereby the valve is shuttled to the closed position
and flow through the internal flow passage is stopped.
In an aspect of the present invention, the biaser is located within the sealed
chamber. In another aspect of the present invention, the biaser forms one or
more surtaces defining the sealed chamber.
In another aspect of the present invention, the device further includes a snap-
closed/snap-open device for ensuring that the valve remains fully open until
reaching the set pressure, and a positive seal is maintained to prevent any
leakage through the internal flow passage from events such as pressure
changes during ascent.
The self-propelled swabbing method includes the steps of sealing spacing
between the welibore casing and a swabbing device having a valve, biasing
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the valve in an opened position until a set pressure is reached, allowing
liquid
to flow from below, through and above the swabbing device while the valve is
opened, allowing the valve to close upon achieving the set pressure created
by the liquid accumulating above the swabbing device, allowing pressure from
liquids andlor gases within the weiibore and below the swabbing device to
build below the swabbing device until combined weight of the swabbing
device and accumulated liquid are overcome by the building pressure and
begin to rise to surface, releasing the trapped liquid at surface; and
allowing
the valve to open upon a set pressure once the trapped liquid is released,
enabling the swabbing device to fall back to bottom.
No external power is required when using the device, and none of the
physical infrastructure or cost that goes with that requirement. The device is
also cheap and efficient to run.
Other aspects and features of the present invention will become apparent to
those ordinarily skilled in the art upon review of the following description
of
specific embodiments of the invention in conjunction with the accompanying
figures.
Brief Description of the Drawings
These and other features, aspects, and advantages of the present invention
will become better understood with regard to the following description,
appended claims, and accompanying drawings where:
Figure 1 illustrates a self-propelled swabbing device at the bottom of a
well in accordance with an embodiment of the present invention;
Figure 2 illustrates the valve closed with pressure building;
Figure 3 illustrates the valve about to be bumped open; and
Figure 4 illustrates a variation of the embodiment shown in Figures 1-3.
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Detailed Description of the Presently Preferred Embodiment
An embodiment of the present invention is directed to a self-propelled
swabbing device 10 and method for use in removing liquids to surface from
within an installed wellbore casing 12. As illustrated in Figure 1, the device
10
includes a longitudinally extending plunger 14 sized to fit within the
wellbore
casing 12, and has an internal surface defining an internal flow passage 16
extending longitudinally therethrough.
The device 10 further includes a seal 18 between the plunger 14 and the
casing 12, and a valve stem 20 having a valve 22 operative to be shuttled
between an opened position and a closed position to seal the internal flow
passage 16. The valve stem 20 extends longitudinally through the plunger 14
to form a piston 24 and sealed chamber 26 maintained at a pressure below
that desired for closing the valve 22. A biaser 28 is further included for
biasing
the valve stem 20 in the opened position until a set pressure is reached,
whereby the valve 22 is shuttled to the closed position and flow through the
internal flow passage 16 is stopped.
In an embodiment of the present invention, the device 10 further includes a
snap-closed device 30 in the form of a magnet for ensuring that the valve 22
does not partially close until the set pressure is reached. A snap-open device
32 in the form of a magnet is included to ensure that a positive seal is
maintained to prevent any leakage through the internal flow passage 16 from
such things as pressure changes during ascent and to enable the valve 22 to
shuttle from closed to fully open once the pressure is reduced.
In an embodiment of the present invention shown in Figures 1-3, the biaser 28
is located within the pressurized sealed chamber 26 in the form of a coil
spring. In another embodiment of the present invention shown in Figure 4, the
biaser 28 forms elements of the pressurized sealed chamber 26.
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The self-propelled swabbing method includes the steps of sealing spacing
between the wellbore casing and a swabbing device having a valve, biasing
the valve in an opened position until a set pressure is reached, allowing
liquid
to flow from below, through and above the swabbing device while the valve is
5 opened, allowing the valve to close upon achieving the set pressure created
by the liquid accumulating above the swabbing device, allowing pressure from
liquids and/or gases within the wellbore and below the swabbing device to
build below the swabbing device until combined weight of the swabbing
device and accumulated liquid are overcome by the building pressure and
begin to rise to surface, releasing the trapped liquid at surface; and
allowing
the valve to open upon a set pressure once the trapped liquid is released,
enabling the swabbing device to fall back to bottom.
When the valve 22 seals the internal flow passage 16, the reservoir pressure
builds below the plunger 14 and pushes the plunger 14 and all fluids above
the plunger 14 to surface out of the wellbore 12.
Figure 1 shows the device 10 at the bottom of a well, resting on top of a
landing platform located above the perforations that are producing the gas
that will provide the energy to drive the device 10 to surface. A seal 18 is
provided between the plunger 14 body and the wellbore 12, forcing the
reservoir fluids to flow through the internal flow passage 16 of the device
10.
The liquids produced collect above the device 10 slowly increasing the
backpressure exerted on the reservoir. A spring and the pressurized sealed
chamber 26 provide the force to bias the valve stem 20 in the opened
position. The embodiment shown in Figure 4 illustrates a variation of the
biaser 28 shown in Figures 1-3 that achieves the same results. As the liquids
accumulate around and above the device 10, the external pressure is
increased on the valve stem 20 and the piston 24 until a set pressure is
reached, which then overcomes the magnet force and pressure within the
sealed chamber 26, with the result that the valve 22 shuttles to the closed
position.
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As illustrated in Figure 2, once the valve 22 has closed, the pressure will
build
below the device 10 until the weight of the device 10 is overcome, and the
device 10 is pushed to surface by the reservoir gases. Since the piston 24,
which is connected to the biaser 28, is located on the high-pressure side of
the device 10, the additional pressure required to lift the device 10 and
overcome the frictional forces helps to ensure that the valve 22 remains in
the
closed position until the liquids are delivered to surface. With the valve 22
closed, the device 10 and liquids above it are pushed to surface, out a flow
tee and into a pipeline.
As illustrated in Figure 3, at the top of the wellbore 12, the valve 22 is
pushed
open as the extending end of the valve stem 20 contacts a striker plate, with
the result that the pressure is equalized across the device 10 allowing it to
fall
back to bottom to pick up the next liquid load. The plunger 14 is sized such
that while falling back to bottom, differential pressure along the length of
the
plunger 14 is less than the pressure required to support the plunger 14. If
the
pressure at the piston is reduced sufficiently to overcome the snap-open
device 32 magnetic force, the valve 22 will shuttle to the open position
without
contacting the striker plate.
A mechanism has been included in an embodiment of the device 10 that
enables the valve 22 to snap-closed and snap-open. Springs are generally
linear devices that would allow the valve 22 to close proportionately to the
pressure as it increases to the set close pressure. As the valve closes the
pressure differential across the valve from the gas flow also increases.
Without the snap-closed device 30, it is possible for the valve to partially
close
and for the pressure differential across the device 10 to increase
sufficiently to
lift the device 10 pre-maturely and deliver a partial load of liquids. As
well, the
device 10 may become hydraulically stuck in the wellbore 12 as it begins to
rise, hovering in place until an increase in pressure closes the valve 22
completely or the pressure decreases allowing the valve 22 to open and the
device 10 to fall back down the wellbore 12 to pick up additional liquids.
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Without the snap-open device 32, the valve 22 can partially open causing it to
hover in the wellbore instead of descending to pick up additional liquids.
No external power is required when using the device 10 or employing the
method, and none of the physical infrastructure or cost that goes with that
requirement. The device 10 is also cheap and efficient to run.
The device 10 and method optimize the production from oil and gas wells
where the reservoir delivers a sufficient quantity of gas to lift the
accumulated
liquids to surface using only the reservoir's own energy. The device 10 is
designed to run automatically once set for the operating conditions of a
particular well.
Although the present invention has been described in considerable detail with
reference to certain preferred embodiments thereof, other versions are
possible. Therefore, the spirit and scope of the appended claims should not
be limited to the description of the preferred embodiments contained herein.
