Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02227858 1998-O1-27
PRESSURE-COMPENSATION SYSTEM
FIELD OF THE INVENTION
The field of this invention relates to pressure-compensation
to systems, particularly those useful for inflatable elements of downhole
packers for compensation to pressure changes induced by thermal
effects.
BACKGROUND OF THE INVENTION
Inflatable packers of varying design have been in use downhole.
When the downhole thermal conditions are fairly stable, there is a
negligible effect on the inflated pressure of the elastic sealing element.
If, however, after inflation, the surrounding temperature of the well
fluids increases, the thermal loads applied to the fluid within the
2O expanded element increase as the pressure rises in response to fluid
expansion. While some tolerance can be built into the design, the
temperature gradient can become sufficiently severe in an upward
direction so as to cause sufficient incremental pressure in the inflated
element to cause it to burst. In the other direction, where the
2 ~~ temperature of the surrounding well fluids cycles downwardly, a
resulting decrease in internal pressure is experienced within the inflated
element and, depending on the circumstances and the severity, a loss
of sealing and anchoring engagement of the packer or bridge plug
with the casing wall can occur.
3o Prior designs have emphasized relief of excess pressure by
allowing fluid from inside the element to escape into the well fluids
upon a rise in internal pressure within the element beyond a
predetermined level less than the failure pressure of the element.
CA 02227858 1998-O1-27
Accordingly, one of the objects of the present invention is to
provide a compensation system that responds to a rise or a fall or
cycling involving rises and falls in temperature and compensates for
the thermal effects by respectively allowing fluid to be removed from
under the inflated element or adding fluid to the space under the
to element. Another object of the present invention is to provide a system
that compensates for increases and decreases in thermally induced
pressure loads, while at the same time isolating the compensation
system from wellbore fluids.
SUMMARY OF THE INVENTION
A downhole tool, such as a packer or bridge plug, employing an
inflatable element, is disclosed. A pressure-compensation system is in
fluid communication with the annular space between the body of the
packer or plug and the inflatable element. The compensation system
responds to thermally induced pressure load changes within the
wellbore by allowing fluid to escape from beneath the inflated
element when increases in fluid temperature in the wellbore increase
the pressure under the element. The system additionally supplies fluid
behind the element should the wellbore fluids decrease in
temperature, thus lowering the pressure under the inflatable element.
The compensation system counteracts what would otherwise be a
tendency for a pressure increase, which could subject the inflatable
element to failure from overpressure and, conversely, supplies fluid to
under the inflated element so that it can prevent unwanted loss of
?.o sealing or anchoring integrity of the packer or plug due to what would
have otherwise been a pressure decrease behind the inflatable
element.
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CA 02227858 2004-O1-09
In accordance with one aspect of the present invention there is
provided a wellbore inflatable packer with a pressure compensation
feature, comprising:
a body;
an inflatable element movable from a first position adjacent said
body to an inflated position in contact with the wellbore;
said inflatable element defining an annular space between itself
and said body; and
a pressure-compensation system operative in said annular space
to compensate for a change in pressure condition in said annular
space.
In accordance with another aspect of the present invention
there is provided an inflatable packer with compensation for increases
or decreases in inflation pressure when the packer is set, comprising:
a compensation system in communication with an annular
space between a packer body and an inflatable element, said
compensation system relieving excess pressure build-up and
compensating for pressure decrease in said annular space which
occurs after the packer is inflated.
In accordance with yet another aspect of the present invention
there is provided a wellbore inflatable packer with a pressure
compensation feature, comprising:
a body;
an inflatable element movable from a first position adjacent said
body to an inflated position in contact with the wellbore;
said inflatable element defining an annular space between itself
and said body;
a pressure-compensation system operative in said annular space
to compensate for a change in pressure condition in said annular
space;
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CA 02227858 2004-O1-09
said pressure-compensation system compensating for increases
and decreases in annular space pressure while said inflatable element
is engaged to the wellbore; and
a first piston, one side of which communicates with said annular
space, said piston varying the volume of said annular space responsive
to pressure changes therein;
said first piston communicating with a first fluid reservoir which is
isolated from wellbore fluids;
said first fluid reservoir permitting fluid movement therein
responsive to movement of said first piston;
said first piston comprising two components separated by a
biasing device, whereupon when said inflatable element is inflated,
relative movement of said components occurs against said biasing
device.
In accordance with still yet another aspect of the present
invention there is provided a wellbore inflatable packer with a pressure
compensation feature, comprising:
a body;
an inflatable element movable from a first position adjacent said
body to an inflated position in contact with the wellbore;
said inflatable element defining an annular space between itself
and said body;
a pressure-compensation system operative in said annular space
to compensate for a change in pressure condition in said annular
space;
said pressure-compensation system compensating for increases
and decreases in annular space pressure while said inflatable element
is engaged to the wellbore;
a first piston, one side of which communicates with said annular
space, said piston varying the volume of said annular space responsive
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CA 02227858 2004-O1-09
to pressure changes therein;
said first piston communicating with a first fluid reservoir which is
isolated from wellbore fluids;
said first fluid reservoir permitting fluid movement therein
responsive to movement of said first piston; and
a second fluid reservoir isolated from wellbore fluids and in fluid
communication with said first fluid reservoir, whereupon fluid
movement between said first and second fluid reservoirs facilities
movement of said first piston.
In accordance with still yet another aspect of the present
invention there is provided an inflatable packer with compensation for
increases or decreases in inflation pressure when the packer is set,
comprising:
a compensation system in communication with an annular
space between a packer body and an inflatable element, said
compensation system relieving excess pressure build-up and
compensating for pressure decrease in said annular space which
occurs after the packer is inflated;
a first piston compensated for the fill pressure used to set the
packer;
said first piston being in two segments with said fill pressure
compensation disposed therebetween; and
an enclosed fluid reservoir system isolated from wellbore fluids
and operatively connected to said first piston to allow opposed
movements of said first piston resulting in part from movement of fluid
within said enclosed fluid reservoir system.
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BRIEF DESCRIPTION OF THE DRAWING
Figure 1 illustrates a typical downhole packer in sectional
elevational view, showing the compensation system of the present
invention in fluid communication with the area under the packer, in a
schematic manner which is not drawn to scale.
to
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 shows, in a relaxed state, an inflatable packer P. The
packer P has a top sub (not shown) on which is mounted sleeve 10,
which is connected to tubing or other means to properly position it in
the wellbore. The packer P has a sealing element 12 which expands
into contact with the casing or wellbore for a seal. The packer as
shown in the upper portion of Figure 1 is of a known design, and the
present invention relates to the pressure-compensation system. The
sealing element 12 is mounted over overlapping ribs 14, which expand
outwardly to push the sealing element 12 into contact with the casing
or wellbore. An annular space 16 receives the inflation pressure in a
manner well-known in the art. The annular space 16 is in fluid
communication with passage 18, which extends through sleeve 20. An
outer sleeve 22 retains ring 24 when the sealing element 12 is
5 expanded. Ring 24 is welded to ribs 14 in a manner as described in U.S.
patent 5,143,154.
Seals 26 and 28 prevent the escape of fluid and channel all flow
through passage 18. As shown in Figure 1, sleeve 20 can be made
from several components, including lower component 30 attached at
.30 thread 32. Seals 34 and 36 seal off the joint to ensure the integrity of
passage 18 down to chamber 38. Again, seals 40 and 42, along with
seals 44 and 46, maintain the integrity of chamber 38. When the
pressure is increased in annular space 16, that pressure is transmitted
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CA 02227858 1998-O1-27
through passage 18 into chamber 38, which in turn displaces piston 48.
Piston 48 (not drawn to scale) has a lower surface 50, against which
abuts spring 52. Spring 52 is in cavity 54, which is in fluid
communication with wellbore fluids through port 70 and sealed off by
seals 44 and 4b on piston 48, as well as seals 5b and 58 on piston 60.
to Piston 60 has a surface 62 which engages travel stop 64 on sleeve 66.
Piston b0 also has a top surface 68 which acts as a travel stop for piston
48 when contacted by bottom surface 50 of piston 48.
Cavity 54 is vented through port 70 to allow the spring 52 to
compress and expand without creating fluid pressure on piston 60. It is
only with piston 48 bottomed on piston 60 that piston b0 is urged to
move downwardly, responsive to an increase in pressure in annular
space 16. However, for normal setting of the packer P, the pressure
developed is generally sufficient to compress spring 52 such that the
piston 48 moves a distance until it contacts top surface 68 of piston 60.
o While piston 48 is moving, the pressure integrity of chamber 38 is
maintained because of seals 44 and 46. That situation continues to
apply even when piston 48 displaces piston 60, which results in a
volume reduction of chamber 72. The displaced fluid from chamber
72 goes through passage 74 and into chamber 76. Chamber 76 is
a 5 isolated from well fluids by piston 78, which is biased by a spring 80
residing in chamber 82. Chamber 82 is vented through port 84 and is,
thus, exposed to well fluids. Chamber 76 is isolated from well fluids by
seals 86 and 88 on piston 78. Relief valve 90 in passage 74 allows fluid
to pass from chamber 72 to chamber 76, after a predetermined
3o pressure in chamber 72 is reached, as piston 60 is pushed down by
piston 48 in the event of a rise in wellbore fluid temperature, which
increases the pressure in annular space 16. Relief valve 90 relieves at a
pressure below the rupture limit of the packer P. Relief valve 90 delays
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CA 02227858 1998-O1-27
the onset of compensation when piston 48 is already in contact with
piston 60. The volume of chamber 72 represents the degree of
available compensation for pressure increases in annular space 16.
Chamber 72 also communicates with chamber 76 through
passage 92. Seals 94, 96, and 98 prevent bypassing around passage
92. A check valve 100 permits flow from chamber 76 into chamber 72
upon a predetermined differential pressure between chambers 76 and
72. Thus, if the wellbore temperature is reduced, decreasing the
pressure in space 16, thus lowering the pressure in chamber 72 as piston
60 begins to advance, spring 80 biases piston 78 to push fluid out of
chamber 76 through passage 92 and check valve 100 into chamber
72. As that is occurring, piston 60 moves in tandem with piston 48 to
displace fluid through passage 18 into annular space 16, thus compen-
sating for the decrease in pressure resulting from downward thermal
cycling within the well.
2 o It can readily be seen that chambers 72 and 76 remain isolated
from the wellbore fluids, while cavities 54 and 82 are in fluid
communication with well fluids. Through the use of the seals as
described, a compensation system is disclosed that compensates for
an increase or a reduction in pressure in annular space 16 in response
5 to external thermal effects. Movement of the components does not
introduce the wellbore fluids into passage 18 or annular space 16.
There can be a difference in piston areas between piston 60 and
piston 48, and the spring force of spring 52 is principally designed to
counteract the inflation pressure anticipated in chamber 16 acting on
:3o the area of piston 48. By design, the bottom surface 50 will come into
contact with top surface 68 of piston 60 as the sealing element 12 is
expanded into contact with the casing or wellbore. If there is a
reduction in pressure in the annular space 16, and piston 60 at that
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CA 02227858 1998-O1-27
time is not against the travel stop 64, spring 80 will push piston 78 so as
to displace fluid from chamber 76 to chamber 72 as pistons 60 and 48
move in tandem. Once piston 60 hits the travel stop 64, the spring 52
will continue to bias the piston 48, thus further displacing fluid from
passage 18 into annular space 16 until all the compensation for a
to temperature reduction of well fluid has occurred within the apparatus.
Those skilled in the art will appreciate that the components can be
designed with different configurations to accommodate different
expected temperature fluctuations in the wellbore.
The compensation apparatus is small and simple to construct
and reliably operates to compensate for numerous cycles of increase
and/or decrease in temperature while the packer P is held in position.
The components' reliability is further enhanced by virtue of the
configuration which excludes well fluids from the small passages where
solids or other objects could cause plugging, which would undermine
2 o the operation of the compensation system.
The foregoing disclosure and description of the invention are
illustrative and explanatory thereof, and various changes in the size,
shape and materials, as well as in the details of the illustrated
construction, may be made without departing from the spirit of the
5 invention.
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