Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED SEALING APPARATUS
Field of the Invention
The present invention belongs to the field of oil and gas wells drilling and
production of oil and gas from wells drilled on the earth. More particularly
it relates
to the field of zonal isolation wherein different sections of an oil or gas
well are
sealingly isolated from other well sections to avoid cross-contamination with
fluids such as water, undesired pressure transmission between sections or for
other reasons.
Background to the Invention
In the oil and gas exploration and extraction industries it is often desirable
to be able to modulate downhole pressure when required. For example, it may
be desirable to isolate a section of well bore to create sections of
differential
pressure within the bore. A sealing device may be used to create a seal within
the bore, such that fluid pressure on one side of the seal increases relative
to
fluid pressure on the other side. Further, a temporary decrease in well
pressure
can be used to initiate flow from the reservoir in a process known as
'swabbing'.
One means of doing this is to make use of a swab cup, which is a cup-shaped
resilient member which is lowered on a mandrel into the well. As a pressure
differential develops across the cup, the walls of the cup are pushed into
contact
with the well tubing or bore wall, thereby sealing a portion of the well.
Thus, the
pressure below the cup may decrease, while the pressure above may increase.
Similarly constructed pressure cups are also used in a wide variety of other
sealing and fluid lifting applications. For example, variations in pressure
may also
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be used to actuate or to control other downhole tools and instruments which
rely
on fluid pressure for their operation. Such cups may be constructed with an
outer
diameter slightly less than the bore diameter, such than an initial inflation
is
required before a seal is created, or may have an outer diameter slightly
larger
than that of the bore, such that a seal is present even when the cup is not
inflated.
Alternatively, a pressure differential may be achieved by means of a
packer. The sealing element on a packer is compressed and activated via a
setting load caused by mechanical or hydraulic or other forces. These are used
to isolate different parts of the well for numerous downhole operations, such
as
well testing or completions.
Conventional pressure seals suffer from a number of disadvantages. The
seals are usually made from rubber or other elastomer, which must be made
relatively thick in order to resist the pressures downhole. This means that
such
seals may be unsuitable for use at relatively low pressures, since they will
not
seal the well effectively under these conditions. The relatively thick
elastomer can
also suffer from slow recovery times after pressure has been removed. Seals
may be reinforced in order to resist higher pressures with metal or wire hoops
or
rings embedded within the elastomer; however, this can lead to shear failure
of
the elastomer, with the reinforcing wire cutting through the elastomer.
In addition, conventional seals may only operate over a restricted range of
pressures and temperatures, and with a small gap between the seal and the bore
wall. If the gap between the seal and the bore is increased, the pressure that
the
seal will hold drops considerably.
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Further, elastomers under pressure can flow or extrude in certain
conditions. This may arise in seals or packers, and will reduce the
effectiveness
of such seals or packers, because elastomer flows or extrudes while the seal
is
under pressure. Any tendency to flow or extrude is also exacerbated at higher
temperatures.
Summary of the Invention
According to a first aspect of the present invention, there is provided a
pressure control device for mounting on a mandrel, the device comprising:
a flexible sealing element;
a first support member; and
a second support member comprising a composite,
wherein the pressure control device is adapted to move from a run in
position to an expanded position when exposed to a source of pressure, the
flexible sealing element is adapted to form a seal against a bore wall in the
expanded position, the first and second support members being adapted, in the
expanded position, to resist extrusion of the flexible sealing element, in
use,
along the bore wall away from the source of pressure, the second support
member being further adapted to resist extrusion into the first support
member.
In at least one embodiment of the present invention an apparatus as
described above is able to sealingly isolate two sections of an oil or gas
well and
at the same time maintain its integrity under wellbore pressure differentials,
thus
preventing extrusion and deformation of the flexible sealing element and of
the
second support member and therefore maintaining the seal leak-free. This
invention is particularly suitable to achieve effective zonal isolation under
extreme
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pressures and temperatures, such as those encountered in high pressure, high
temperature wells (HPHT wells).
Furthermore, by provision of a second support member in the form of a
composite, extrusion into the first support member of flexible sealing element
material or second support member material is resisted, allowing for greater
recovery of the first support member, when the source of pressure is released,
towards the run in position.
The pressure control device may be a cup seal or a swab cup.
Alternatively, the pressure control device may be a packer or any suitable
pressure control device comprising a flexible sealing element.
A portion of the flexible sealing element, the first support member and/or
the second support member may be arranged concentrically.
The first support member may further comprise a circumferential spring.
The circumferential spring may be biased to the run-in position.
The first support member may be located at an outer portion of the flexible
sealing element. Such an arrangement assists in recovery of the flexible
sealing
element from the expanded position to the run in position, when source of
pressure is reduced or eliminated.
In certain embodiments of the invention, the first support member may also
be urged outwardly against the bore wall, in use, to help to create the seal.
In at least one embodiment of the present invention the spring is a helical
spring.
In other embodiments the spring may be a garter spring.
In some embodiments the spring may comprise a first spring with a second
spring in its interior. The second spring may be mounted within the first
spring
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such that the helix of one spring is wound in the opposite direction to the
spiral
of the other spring in order to resist canting of the first support member
under
high pressure. In some embodiments this arrangement of the springs also
confers benefits for reducing the extrusion of the second support member into
the first support member.
Alternative spring forms and/or arrangements may be used without
departing from the principles of the invention.
The first support member may alternatively or additionally comprise a petal
arrangement.
The petals may be overlapping. In moving from the run-in position to the
expanded position, the petals open up but still form a continuous surface to
resist
extrusion of the flexible seal element along the bore wall away from the
source
of pressure.
The first support member may be located so as to abut the second support
member. Such an arrangement restricts movement of the first support member
to some degree when the device is pressurised, and may be used to direct
movement of the first support member to improve formation of a seal.
The pressure control device may comprise a rigid body adapted for
mounting on a mandrel or the like.
The rigid body may comprise an annular member.
The first support member may be mounted to the annular member.
The rigid body may comprise a cammed surface adapted to be engaged
by the first support member.
The cammed surface may be arranged to direct the first support member
radially outward when the device is under pressure. This may be achieved by
the
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cammed surface being inclined axially downwardly from the centre of the device
and radially outward. Such an arrangement also provides further integrity of
sealing by ensuring the first support member has to overcome both the pressure
within the pressure control device and the direction of the cammed surface to
return to the run-in position.
Alternatively, the cammed surface may be inclined upwardly, or may be
generally horizontal; these arrangements may be used to delay or restrain
expansion of the first support member and/or flexible sealing element, which
may
be useful in certain applications.
The first support member may be bonded to the second support member.
In alternative embodiments the first support member may be located on or
adjacent the second support member.
In at least one embodiment of the present invention the second support
member comprises a composite of greater hardness than the flexible sealing
element located at an outer portion of the flexible sealing element. When the
composite portion is of greater hardness than the flexible sealing element
itself,
it will be less susceptible to flow or extrusion due to the pressure, so
improving
effectiveness of the device. This feature also allows the flexible sealing
element
to be made of somewhat thinner or less hard material than in previous devices.
The composite of the second support member may comprise a composite
matrix and a reinforcing material.
The reinforcing material may be more rigid than the composite matrix
material. In at least one embodiment of the present invention the reinforcing
material adds rigidity to the second support member and improves its anti-
extrusion properties at high pressures. This is of benefit because when in
use, it
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will resist extrusion into the first support member and therefore it will not
hamper
the recovery of the cup or packer original size and shape upon removal or
reduction of deforming pressure.
In at least one embodiment of the present invention the reinforcing
material may comprise a plurality of separate members, particles or fibres.
In other embodiments the reinforcing material may comprise at least one
aggregated member. In at least one embodiment of the present invention one or
more aggregated members provide(s) enhanced anti-extrusion properties to the
second support member and also helps resist better the extrusion of the
flexible
sealing element by providing better tensile strength.
The/each aggregated member may comprise a mesh.
The mesh may comprise metal wire. Other semi-rigid materials may be
used for the mesh without departing from the principles of the invention.
Metal
wire meshes are easily available at affordable prices and provide the required
mechanical and anti-extrusion properties to the second support member in
conjunction with the composite matrix.
The mesh may be a diamond shape mesh.
Alternatively, the mesh may be a chicken-wire style mesh (hexagonal
mesh).
Other mesh shapes may be used without departing from the principles of
the present invention.
In some embodiments the second support member may also be urged
outwardly against the bore wall, in use, to help create a seal.
Suitable materials for the various components include, but are not limited
to elastomers such as nitrile, hydrogenated nitrile, fluoroelastomers,
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perfluoroelastomers, thermoplastic materials, EPDM, polyurethane, and the like
for the flexible sealing element and/or the composite matrix; metals such as
steel,
brass, or the like, or polymeric materials such as PEEK, nylon, Kevlar and/or
metal fabrics or the like for the first support member and/or the composite
reinforcing material.
The second support member may be located adjacent the first support
member at an outer portion of the flexible sealing element.
At least a portion of the second support member may extend radially
inwards of the first support member.
The second support member may comprise a free end which is not bonded
to the flexible sealing element.
The second support member may comprise a free end and a bonded end,
which is bonded to the flexible sealing element. The free end allows movement
and expansion of the flexible sealing element relative to the second support
member, while the bonded end serves to both retain the second support member
in place relative to the flexible sealing element, and further reduces the
risk of
flow and/or extrusion of the flexible sealing element.
The first support member may be located adjacent to the free end of the
second support member. In at least one embodiment of the present invention
this
arrangement allows the combination of the first support member and the second
support member to move relative to the flexible sealing element when under
pressure.
Preferably, the flexible sealing element is selectively bonded to the body
of the first and/or second support member.
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A portion of the flexible sealing element may be bonded to a portion of the
first support member and a further portion of the flexible sealing element may
be
bonded to a portion of the second support member.
Any suitable means may be used to bond the components of the device;
for example, glue or other adhesive, welding, vulcanisation, heat treatment,
mechanical fasteners, bonding agents, and the like.
Brief Description of the Drawings
An embodiment of the present invention will now be described with
reference to the accompanying drawings in which:
Figure 1 is a section through a pressure control device for sealing an
annulus between a mandrel and a wellbore, according to a first embodiment of
the present invention, the pressure control device shown in a run-in
configuration;
Figure 2 is a close-up of part of the pressure control device of Figure 1 in
the run-in configuration;
Figure 3 is a close-up of part of the pressure control device of Figure 1 in
the set configuration;
Figure 4 is a perspective view of a section of the deformable reinforcing
element, and
Figure 4A shows a close-up of part of the section of the reinforcing
element.
Detailed Description of the Drawings
Reference is first made to Figure 1, a section through a pressure control
device 10 for sealing an annulus 12 between a mandrel 14 and a wellbore 16,
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according to a first embodiment of the present invention; the pressure control
device 10 is shown in a run-in configuration. The pressure control device 10
is a
packer and comprises a flexible sealing element 18 comprising an upper
flexible
sealing element portion 20, a central flexible sealing element portion 22 and
a
lower flexible sealing element portion 24. The central flexible sealing
element
portion 22 is separated from the upper flexible sealing element 20 and the
lower
flexible sealing element 24 by first and second seal rings 26, 28
respectively.
The sealing element portions 20, 22, 24 comprise an elastomer, particularly
nitrile
butadiene rubber.
The pressure control device 10 further comprises two first support
members 30, 32 and two second support members 34, 36. The structure and
operation of the first and second support members 30, 32, 34, 36 will be
discussed in due course.
The pressure control device 10 further comprises an upper setting disc 38
and a lower setting disc 40, the discs 38, 40 being adapted to be moved
towards
each other and move the sealing element portions 20, 22, 24 from the run-in
configuration shown in Figure 1 to a set configuration shown in and discussed
in
connection with Figure 3.
Referring to Figure 2, which illustrates a close-up of part of the pressure
control device 10 of Figure 1 in the run-in configuration, the structure of
the first
support members 30, 32 and the second support members 34, 36 will be
discussed with particular reference to the lower pair of support members 32,
36.
The first support member 32 comprises a circular helical spring 42. The
helical spring 42 rests on a cammed surface 44 defined by the lower setting
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40 and is embedded in the matrix 46 of a composite material 48 which makes up
the second support member 36.
The matrix 46 of the composite material 48 is an elastomer such as nitrile
butadiene rubber and is reinforced by a deformable reinforcing element 50.
Figure 4 shows a perspective view of a section of the deformable
reinforcing element 50 and Figure 4A shows a close-up of part of the section
of
the reinforcing element 50. The reinforcing element 50 is frusto-conical in
shape
and is made from a length of steel mesh 52 wrapped around a former (not shown)
around forty to fifty times.
As can be seen from Figure 4A, the steel mesh 52 defines voids 54.
Between adjacent layers of mesh 52, there is partial but not complete
alignment
of the voids 54 through the reinforcing element 50. The reason for this
partial
alignment will now be discussed.
During manufacture of the second support member 36 the matrix material
46 is adapted to permeate into the reinforcing element voids 54 as the
reinforcing
element 50 is embedded in the second support member 36 as the second
support member 36 is pressure formed around the reinforcing element 50.
The pressure control device 10 is moved from the run-in configuration to
the set configuration by applying a force to the setting discs 38, 40 to move
the
setting discs towards each other, compressing the flexible sealing elements
20,
22, 24. Due to the presence of the mandrel 14, the sealing elements 20, 22, 24
can only expand radially outwardly and expand into engagement with a wellbore
wall 56 (best seen in Figure 3, a close-up of part of the pressure control
device
10 of Figure 1 in the set configuration).
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In the set configuration, the flexible sealing portions 20, 22, 24 are
engaged with the wellbore wall 56 and under pressure and temperature in the
wellbore 16 would be inclined to extrude into the gap indicated by the letter
"A"
on Figure 3.
As can be seen from Figure 3, however, the first support member 32 has
travelled down the cammed surface 44 as the second seal element 24 is
compressed, to substantially fill the gap A. In addition, because the first
support
member 32 is substantially encased within the second support member 36, the
softer elastomer of the seal element 24 is prevented from seeping through the
interface 60 between the first support member 32 and the cammed surface 44 or
the interface 62 between the first support member 32 and the wellbore wall 56.
The harder elastomer of the second support member 36 is selected so that
seepage through the interfaces 60, 62 is negligible under normal operating
pressures.
Continuing to refer to Figure 3, the second support member 36 also comes
into engagement with the wellbore wall 56 due to the reinforcing element 50
deforming under the setting pressure.
As previously stated, the first support member 32 is in the form of a helical
spring 42. The spring 42 is biased to the run-in position and is in an
expanded
state in the set position. In the set position adjacent coils will, therefore,
be
separated with a gap between. The use of a harder elastomer for the matrix 46
of the second support member 36 and the presence of the reinforcing element
50 reduces seepage of the second support member 36 into the gaps between
the separated coils. This allows the first support member 32 to recover to the
run-in configuration when the setting pressure is removed.
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Various modifications and improvements may be made to the above-
described embodiments without departing from the scope of the invention. For
example, in low-temperature environments, a mechanical force could be applied
to move the seal element to the sealed position.
Although the support element is shown as being a conical multilayer mesh
construction, other materials such as Kevlar could be used and other shapes
such a cylindrical can be adopted.
Similarly, although the embodiments shown a packer type pressure
control device, a further embodiment comprising a pressure control device
comprising a flexible cup would also fall within the scope of the invention.
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