Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Seal Cup for a Wellbore Tool and Method
Field of the Invention
This invention relates to a seal cup for a wellbore tool and, in particular, a
seal cup for
sealing and anchoring against a differential pressure in a wellbore and a
method for
enhancing the resistance of a seal cup to axial sliding when under operational
differential pressure.
Background of the Invention
Seal cups, also called cup seals, can be used in wellbore applications to seal
against
differential pressures in a pipe string. A seal cup includes a base and a
tubular wall or
skirt extending therefrom. A seal cup can be deployed downhole in a non-
sealing
configuration, but will tend to expand and promote sealing against the pipe
wall in
which it is positioned when exposed to 'a differential pressure and, in
particular, a
pressure differential with a greater pressure at its tubular wall end.
Furthermore, the differential pressure across the seal cup gives rise to axial
load that
must be reacted to prevent the seal cup from displacing in the direction of
differential
pressure. In certain applications where it is desirable to position the seal
cup in a fixed
position, it is necessary to provide an anchoring mechanism on the tool to
work with
the cup.
Summary of the Invention
A seal cup for a wellbore tool has been invented and a method to promote
pressure
activated anchoring of a seal cup.
In accordance with a broad aspect of the present invention, there is provided
a seal
cup including: a base, an elongate substantially tubular interval extending
from the
base and ending at a lip, at least a portion of the tubular interval being
capable of
radially expanding under application of operational pressure, an outer surface
extending from the lip to the base, and at least one circumferential seal land
on the
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outer surface adjacent the lip of the tubular interval; at least a portion of
the outer
surface being capable, under operational pressure for which the seal cup is to
be used,
of conducting seepage fluid from adjacent the seal land toward the base to act
against
pressure invasion about the outer surface.
In accordance with a broad aspect of the present invention, there is provided
a seal
cup for mounting on a wellbore tool to seal the annulus about the tool when
used in a
wellbore defined by a wellbore wall, the seal cup including: a base including
a portion
mountable to the tool, an elongate substantially tubular interval extending
from the
base and ending at a lip, an outer surface extending from the lip to the base,
and at
least one circumferential seal land on the outer surface adjacent the lip of
the tubular
interval, the seal land including a diameter selected to allow sealing in the
annulus
about the tool in the wellbore in which the seal cup and tool are to be used;
at least a
portion of the tubular interval being capable of radially expanding under
application
of operational wellbore pressure to drive a portion of the outer surface into
frictional
contact with the wellbore wall and at least a portion of the outer surface
being
capable, under wellbore pressure, of conducting seepage fluid from adjacent
the seal
land toward the base to act against pressure invasion about the outer surface
in the
portion of contact.
In accordance with another aspect of the present invention, there is provided
a method
for enhancing resistance to axial sliding of a seal cup in a tubular member
under
application of operational differential pressure, the method including:
providing a seal
cup including a base, a cup skirt extending from the base and a skirt lip;
forming the
cup skirt such that a sealing ban-ier can form adjacent the skirt lip;
selecting the cup
skirt to expand radially under the operational differential pressure to create
an
interfacial region of contact of the cup skirt against the tubular member
between the
sealing barrier and the base; selecting the cup skirt to provide for drainage
of fluid
from the interfacial region of contact away from the seal banger, which fluid
seeps
past the sealing barrier under the operational differential pressure.
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Brief Description of the Drawings
A further, detailed, description of the invention, briefly described above,
will follow
by reference to the following drawings of specific embodiments of the
invention.
These drawings depict only typical embodiments of the invention and are
therefore
not to be considered limiting of its scope. In the drawings:
Figure 1 is a perspective view of a seal cup.
Figure 2 is a vertical section through a portion of well casing including a
wellbore
tool with a seal cup as in Figure 1.
Figure 3 is an illustrative cross section through a seal cup wall in a
wellbore as it
would appear in the absence of a pressure differential.
Figure 4 is .an illustrative cross section through the wall of a seal cup in a
wellbore
configured with seepage grooves as it would appear in the presence of a
pressure
differential showing the distribution of radial stresses in the interfacial
region between
the seal cup and borehole.
Figure 5 is an illustrative cross section through. the wall of a seal cup in a
wellbore
configured as it would appear in the presence of a pressure differential
showing the
distribution of radial stresses in the interfacial region between the seal cup
and
borehole.
Figure 6 is a perspective view of another seal cup.
Description of the Invention
A seal cup for a wellbore tool and method are described herein.
The seal cup can be used for running downhole to create a seal when exposed to
a
pressure differential. The seal cup can be mounted on a tool to create a seal
in the
annulus between the tool and the borehole wall or wellbore liner in which the
tool is
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positioned. Since the seal cup will most often be used in a wellbore liner,
such as
casing, the description will proceed with reference to casing. When in a
sealing
configuration, the seal cup can exhibit a pressure activated anchoring effect
to act
against undesirable axial movement along the wellbore, as may be caused by the
pressure differential or other applied forces.
The seal cup can include a base, an elongate substantially tubular interval
extending
from the base, which ends at an outboard lip, an outer surface extending from
the lip
to the base, and at least one circumferential seal land on the outer surface
adjacent the
lip of the tubular interval. The outer surface of the tubular interval can be
capable,
under operational pressure under which it is to be used, of conducting seepage
fluid
from adjacent the seal land toward the base to act against pressure invasion
about the
outer surface.
The base can include a mounting portion for mounting to the tool. It will be
appreciated that there are many ways to attach a seal cup to a tool. In an
embodiment
wherein the seal cup is to be used on a tool having a bore therethrough for
controlled
passage therethrough, the seal cup base can include a bore through its base.
The elongate generally tubular interval extends from the base. It usually can
be
formed integral with the material of the base but could be connected in other
ways, for
example by polymeric welding, etc., to the base.
The seal cup further includes, as will be appreciated, an outer surface. When
the seal
cup is positioned in a casing string, its outer surface will face the casing
inner surface.
At least one circumferential external seal land is provided on the outer
surface
adjacent the outer lip of the tubular interval. The diameter of the seal land
can be
selected to allow sealing engagement with the casing inner diameter in which
it is to
be used and therefore in its unconstrained expanded position will generally be
of a
diameter greater than the casing inner diameter.
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At least a portion of the tubular interval can be capable of radially
expanding under
application of operational wellbore pressure to drive a portion of the outer
surface into
frictional contact with the wellbore wall in which the seal is positioned.
5 ~ The portion of the outer surface that is driven into frictional contact
with the wellbore
wall can include, as by coating with, supporting or forming with materials
selected to
increase the friction coefficient between the outer surface and the borehole
wall. Such
materials can include, for example, grit, metal particles, carbide particles,
ceramic
particles, etc.
At least a portion of the seal cup outer surface can permit fluid drainage
from adjacent
the seal land toward the base to act against pressure invasion. Such fluid may
arise,
for example, due to seepage past the seal land. If such fluid pressure is not
relieved
from the interfacial region between the seal cup and the casing inner surface,
it can
reduce the engagement of the seal cup against the casing. In one embodiment,
the
outer surface along the tubular interval between the seal land and the base
can be
capable of conducting seepage fluid by for example including passages along or
through the material of the outer surface through which fluid can drain from
the
region in which the outer surface contacts the casing. In another embodiment,
a
greater portion of the outer surface approaching or extending to the end of
the base,
can be formed to permit such drainage. As will be appreciated the outer
surface
formation capable of conducting seepage fluid need only be at that portion of
the
outer surface which will be in contact with the casing wall when in sealing
configuration. however, the entire outer surface can be capable of conducting
~5 seepage fluid, if desired or convenient.
The portion of the outer surface that permits seepage, can, for example, be
roughened,
undulating, knobby, scored, formed with seepage grooves, or formed of porous
material such that passages are formed for evacuation of fluids out of the
region of
contact.
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The outer diameter of the seal cup along the tubular interval can taper from
the seal
land to the base. The wall thickness of the tubular interval can generally
increase
from the lip to the base. The base can have a diameter less than or
substantially
matching the drift or minimum running diameter of the casing in which it is to
be
used. These geometries can facilitate radial expansion of the tubular interval
to have
a relatively large contact region between the cup and the casing and can
enhance
contact stress between the cup and the casing by creating a steep pressure
gradient at
the land, when a differential pressure is exerted across the cup.
The seal cup material, as will be appreciated, is selected to be more
compliant than
the casing material, for example steel, in which it is to be used. The seal
cup
materials can also be selected with consideration as to the pressure loads
under which
the seal cup must operate to seal. Of course, the material attributes, such as
for
expansion and compliancy, can also be considered for thermal response and
wellbore
conditions to achieve a sealing action. The seal cup material can be, for
example,
rubber, structural plastic, etc. As will be appreciated, structural plastic,
such as
polyurethane or glass reinforced polyurethane may be useful to accommodate
some
downhole pressure loads that are too great for some elastomers such as rubber.
In operation the seal cup, in one embodiment, can exhibit a pressure activated
anchoring effect under application of bottom differential pressure. The axial
load
generated by the pressure differential can be reacted by frictional sliding
resistance
between the seal cup tubular interval and the confining casing wall. This
pressure
activated anchoring effect can be permitted by providing at least a portion of
the outer
cup surface between the seal land and the base, to be capable, under
operational
pressures, of conducting seepage fluid from adjacent the seal land toward the
base and
out from the interfacial region of contact between the seal cup outer surface
and the
confining casing wall. The pressure activated anchoring effect can also be
enhanced
by forming the seal land adjacent the outer lip and forming the seal cup, at
least along
a length of the tubular interval, to have a outer diameter selected to contact
the casing
wall, when under pressure load.
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In operation, the compliance of the selected seal cup material allows the
tubular
interval to expand readily under application of modest pressure until it
contacts the
much lower compliance confining casing wall. Application of additional
pressure can
serve to directly increase the interfacial contact stress and proportionately
the axial
force required to induce frictional sliding between the seal cup tubular
interval and the
casing wall. Axial load arising from differential pressure acting across the
base may,
thus, be reacted in part by tension where it is joined to the tubular
interval.
It will be appreciated that, when mounted on a downhole tool including an
anchoring
system for anchoring along the wellbore, the pressure activated anchoring
effect of
the seal cup can reduce the load capacity required from the tool's anchoring
system
and thus, can enhance the overall anchoring properties of the tool. For
example, use
of the pressure activated anchoring effect of the seal cup can reduce the
axial pressure
end load that needs to be reacted through the tool's anchoring system. This
seal cup
can provide a substantial improvement in the ability to use lower strength,
readily
drillable materials in the anchoring mechanisms and bodies of downhole tools.
Figure 1 shows a seal cup 13. Figure 2 shows the seal cup of Figure 1
installed on a
wellbore tool 10, the tool and the seal cup being positioned in a string of
casing 1
including a profile nipple 3.
Seal cup 13 in the illustrated embodiment can include a base 22 with a
diameter
selected to pass through the casing inner diameter ID1 in which it is to be
used and a
tubular wall interval 23 extending from the base and including an outer end
lip 25.
Outer end 25 is open such that the base and the tubular wall form a cup. The
seal cup
can include at least one external circumferential seal land 27, the diameter
at the seal
land being selected to allow substantial sealing engagement with the casing
inner
diameter II?1 in which it is to be used. The seal cup includes an outer
surface 26
permitting seepage of fluid from adjacent the seal land past the base to act
against
pressure invasion about the external surface.
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Seal cup 13 can be shaped as by molding, polymeric welding or machining to
form
base 22 integral with elongate seal tube 23. The seal tube can include an end
24
adjacent base 22 and opposite open end 25. The external surface 26 of seal cup
13
defines circumferential external seal land 27 adjacent end 25. In the
illustrated
embodiment, the seal cup diameter at base 22 is substantially similar to the
drift or
minimum running diameter of the casing. The seal cup diameter along the
tubular
interval, indicated generally at 23' and extending from seal land 27 to the
seal tube
end 24, can be generally tapered to blend with the base 22. The tubular wall
of seal
tube 23 can have a thickness that substantially increases from the outer end
25 to the
base. This wall thickness can correlatively increase the axial load-
accommodating
capacity with increased distance from the seal land. The thinner wall area,
being at
outer end 25, decreases radial stiffness at that end to, thereby, reduce
contact stress
and wear while running in and promotes higher radial contact stress from the
pressure
energization effect while sealing and anchoring.
External surface 26 can be provided with a circumferential seepage groove 28
adjacent seal land 27 on its sealed side (closest to base 22) and one or more
seepage
grooves 28' extending from groove 28 toward the base, which grooves 28, 28'
are
sized to permit passage therethrough, and drainage, of well bore fluids that
might seep
past seal land 27 when acting to seal against borehole pressure. As such,
fluid
seeping past the seal land can be drained from the interfacial contacting
region
adjacent the seal land to increase the portion of the radial compressive
stress in the
interfacial region. This can increase friction between the seal cup and the
casing
against which it is intended to seal.
While seepage grooves are shown in Figures 1 and 2, it is to be understood
that other
surface treatments, materials or forming can be used to permit seepage of
fluids away
from the seal land. For example, the outer surface can, for example, be
roughened,
scored, knobby, formed with seepage grooves, or formed of porous material. Any
surface treatments, materials or forming should be selected with consideration
as to
the fluids which are likely to seep past the seal land in order that the
passageways
through or along the surface, as formed by the pores of the porous material or
by
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surface forming (i.e. scoring, roughening, etc.) are capable of permitting
seepage of
that fluid.
While the outer surface in the illustrated embodiment includes seepage grooves
extending along its full length between seal land 27 and the end of the base,
the outer
surface need only be capable of seepage in the interfacial area where close
contact
occurs between the outeraurface and the casing.
In the illustrated embodiment, end 25 is inwardly radiused adjacent seal land
27 to
facilitate its riding over discontinuities, such as threaded connections, in
the casing
inner surface, for example during run in.
Seal cups can be formed in various ways and from various materials, as will be
appreciated. The seal cup material can be selected to be more compliant than
that
casing material (generally steel) against which the cup material is to seal.
The seal
cup material can also be selected with consideration as to the pressure loads
in which
it must seal. Of course, the material used can also be considered for borehole
conditions such as thermal expansion and compliancy and resistance to
corrosive
fluids. In one embodiment, the seal cup can be formed from a compliant
(relative to
casing material) and drillable material, such as polyurethane or fiber-
reinforced
polyurethane, and can have a surface including wear resistant and/or friction
coefficient enhancing materials.
Seal cup 13 includes a mounting portion 15 for mounting the seal cup to tool
10.
While various mounting mechanism can be used, in the illustrated embodiment
mounting between the seal cup and the tool is by way of threads providing a
substantially sealed interface. A threaded connection was used in the
illustrated
embodiment to facilitate manufacture and assembly and to allow options in
selection
of materials.
Tool 10 in the illustrated embodiment is a cement float. However, it is to be
understood that the seal cup can be used with other kinds of tools such as
plugs, etc.
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Since the tool includes a bore 17, seal cup 13 also has a bore 19
therethrough. Since a
check valve is required for a cement float, the valve has been, but need not
be,
mounted on seal cup 13. In the illustrated embodiment, therefore, seal cup
carnes a
valve 71 and defines a seat 74. In the illustrated embodiment seal cup 13
opens
5 downwardly relative to the tool and thereby acts to seal against fluid
pressures from
below the tool when valve 71 seats against 74 to seal the opening of bore 17.
Cement float tool 10 includes an anchoring mechanism generally shown as 50.
The
tool can be configured to pass through casing 1 and to latch, by way of
anchoring
10 mechanism 50, into an annular groove 2 in profile nipple 3. The diameter D2
in
groove 2 is slightly larger than the minimum inner diameter of the casing
tubing.
Figure 2 shows the cement float tool 10 secured in the casing in the annular
groove of
a profile nipple. While particular embodiments of a tool and an anchoring
mechanism
are shown, it is to be understood that the seal cup can be used with other
tools with or
without anchoring mechanisms.
Cement float 10 includes a mandrel 11 to which is connected a top seal cup 12
and
seal cup 13 at its lower end. The cement float is sized to pass through ID1,
of the size
of casing in which it is intended to be used, with seal cups 12, 13 sealing
against the
ID1. Top seal cup 12 can include an elongate upper tubular interval,
configured with
at least one external upper seal land 21 and selected to adequately seal
between the
casing and main body against top pressure required to pump the cement float
tool
down the casing until latched in the profile nipple 3 and any subsequent top
. pressuring as may be required to, for example, fail a shear plug as
described
hereinafter.
As was described hereinbefore, seal cup 13 is configured to create a seal
about the
annulus of the tool and can assist with anchoring of the tool.
In operation, a tool as shown in Figure 2 can be run into a casing string and
seal cup
13 can be used to seal the annulus between the tool and the easing inner
diameter. In
its operation, tool 10, which is a cement float, is placed inside casing 1 and
displaced
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downhole by pumping fluid, typically drilling fluid, through the casing
string. Top
seal cup 12 and a plug (not shown) in bore 17 tend to prevent flow of the
pumping
fluid past the cement float tool creating a downward axial force as a function
of the
applied top differential pressure required to overcome drag where the top seal
cup 12,
bottom seal cup 13 and anchoring mechanism 50 contact.the casing.
Once the cement float tool has been displaced downward to the point where the
anchor mechanism is latched into the groove 2 (Figure 2), application of top
pressure
produces a downward acting axial load that is transmitted through the main
body 11
to the anchoring mechanism, a part of which is pressed outwardly into groove
2.
Continued axial force on the tool, once it is in the groove, is reacted into
the casing at
lower shoulder 5. It will be apparent that the interacting mandrel and anchor
carriage
functions as an anchor so that pressure load sealed across top seal cup 12 is
reacted by
the anchoring mechanism into the casing allowing the bore plug to be blown
out.
Following placement of the tool, cement can be introduced to the casing string
and be
displaced into the casing annulus through tool 10 (Figure 2). Flapper valve 70
functions as a check valve during flow of fluids as required for cementing. If
casing
string conditions permit, there can be a tendency for the heavier cement
column in the
annulus to 'U-tube' from the annulus back into the casing. This flow is
prevented by
the flapper valve 70 with consequent increase of differential bottom pressure
across
bottom seal cup 13. Initial bottom pressure load across the bottom seal cup 13
tends to
make it inflate, seal and can cause it to slide uphole; but this sliding can
be limited by
the interaction of anchoring mechanism 50 engaging in groove 2 and by the
pressure
activated anchoring of seal cup 13.
This pressure activated anchoring mechanism is induced under application of
differential pressure from below due to the seepage grooves 28 and 28' which
relieve
fluid pressure, by permitting drainage thereof, in the interfacial contact
region
between the seal cup and the casing. In addition, the seal land 27 is
positioned
adjacent end 25 of the seal tube 23 so that the full pressure differential
occurs across
the wall of seal tube 23 under application of sufficient pressure, driving it
to radially
expand, contact and become restrained against the liner wall, which in the
illustrated
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case is a part of the profile nipple. Application of additional pressure
serves to
increase the interfacial contact stress, which contact stress gives rise to
frictional
resistance to axial sliding of the seal tube 23. The further combination of
selecting the
lower cup material to be more compliant than the casing and ensuring minimum
clearance is maintained between the seal tube and inner diameter ID1, promotes
contact at lower differential pressure and thus greater resistance to sliding
for a given
differential pressure. The wall thickness and length of seal tube 23 can be
arranged to
promote pressure activated anchoring under application of differential
pressure where
the wall thickness of seal tube 23 is generally formed to thicken from its end
25 to its
end 24.. Its length can be selected to be long enough to ensure all or a
significant
amount of the differential pressure end load for the intended application is
thus
reacted by this pressure activated anchoring mechanism. The bottom seal cup
can,
therefore, function both to seal against bottom pressure and to react the
associated end
load to assist with anchoring of the tool to which it is attached.
The method for enhancing resistance to axial sliding of a seal cup in a
tubular
member, such as for example casing, under application of an operational
differential
pressure acting in a direction tending to induce flow toward the open cup can
include:
providing a seal cup including a base, a cup skirt extending from the base and
a skirt
lip; forming the cup skirt such that in operation a sealing barrier forms
adjacent the
skirt lip; selecting the cup skirt to expand radially under the operational
differential
pressure to create an interfacial region of contact of the cup skirt against
the tubular
member between the sealing barrier and the base; and selecting the cup shirt
to
provide for drainage of fluid from the interfacial region of contact away from
the seal
barrier, which , fluid may bypass the seal burner under the operational
differential
pressure. The cup shirt in the region of contact can be selected to include
materials
enhancing the frictional coefficient between the cup slcirt and the tubular
member.
The region of contact can be selected to have a frictional coefficient
sufficient to resist
axial sliding under operational differential pressure. The step of providing
for
drainage of fluid can include forming passages for evacuation of fluid away
from the
seal barrier. The passages can be formed on the external surface of the cup
skirt, as
by forming grooves, striations, scoring, a knobby or undulating surface.
Alternately
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or in addition, the passages can be formed by selection of material properties
such that
porous passages are formed through the skirt. The drainage can alleviate or
prevent a
differential pressure build up in the interracial region.
The method of pressure activated anchoring operative when seal cup 13 is
sealing
against differential pressure is further illustrated with reference to Figures
3, 4 and 5
indicating the nature of the contact in the interfacial region between the
seal cup and
wellbore and hence the manner in which radial and axial loads may be reacted.
Refernng now to Figure 3, seal cup 13 is shown as it would appear in the
absence of
differential pressure. Seal cup 13, in the illustrated embodiment, includes a
seal land
27 with a diameter selected to be equal to the wellbore diameter at the
location where
sealing is desired. Without differential pressure, tubular wall interval 23 is
not
expanded and does not contact the wellbore. Therefore the only radial stress
in the
interface is the ambient pressure as indicated by curve C1 in the graph shown
opposite
the seal cup cross section plotting radial stress as a function of axial
position along the
tubular wall interval 23. The contact or effective stress in the interfacial
region, shown
by curve C2, is negligible.
By reference to Figure 4 consider next the interfacial radial stress state
existing when
sufficient internal differential pressure is applied to a seal cup to expand
the tubular
wall interval 23. Seal cup 13 includes seepage passages, for example including
groove 2~, for drainage of fluid in a direction along arrows S. As curve C2
shows, in
the graph corresponding to this configuration and load case, significant
contact stress
is developed over the intervals labelled ~Z1 and OZ2. Interval OZ1 corresponds
to the
location where the seal land is forced into contact with the wellbore
resulting in
contact stress that tends to strongly exceed the pressure to be contained.
This
condition advantageously promotes sealing at the corresponding axial position
and
thus the fluid pressure curve C1 is seen to decrease across this same interval
by an
amount corresponding to the applied differential pressure. This result is
assured
against incidental seepage by the presence of the seepage passages, which
conduct
any such seepage flow out of the region of contact. The full pressure
differential is
thus present across the seal tube wall tending to drive it into contact with
the well bore
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resulting in the large interval of contact ~Z2. It will be appreciated that
the axial load
required to move or slide a seal cup thus configured and pressured, is a
product of the
contact stress, the contact area and ~ the friction coefficient operative in
the region of
contact area. Thus the anchoring capacity of the seal cup may, in general, be
considered as proportional to the area under the curve C2.
This method of pressure activated anchoring provided by the present invention
can be
even more fully appreciated by comparing the contact stress state that would
tend to
develop if a seal cup 13a is used without seepage passages from groove 28,
which
configuration is now considered by reference to Figure 5. The same
differential
pressure load is again assumed as in Figure 4 and the radial stress state in
the
interfacial region is shown. In this case, seepage flow is allowed to invade
far down
the seal cup tubular wall interval 23, greatly reducing the area under curve
C2 and
hence the axial load required to induce sliding, effectively negating most of
the
pressure activated anchoring function.
The use of a seal cup 13 can, therefore, permit the use of weaker materials,
such as
drillable materials, for anchoring mechanism 50 and mandrel 11 of a tool to be
anchored.
Another seal cup 113 is shown in Figure 6. Seal cup 113 includes a base 122
with a
diameter selected to pass through the casing inner diameter in which it is to
be used, a
tubular wall interval 123 extending from the base and including an outer end
lip 125
and a raised external circumferential seal land 127 on the outer surface 126.
The seal
cup outer surface includes seepage grooves 128, 128' permitting drainage of
fluid
away from the seal land to act against pressure invasion, and thereby
reduction of
friction, about the outer surface.
Outer surface 126 can include wear resistant inserts 129 in the form of an
annular
hardened steel wire, rods or buttons mounted in glands, as by dovetailing
engagement,
in the seal region adjacent to or on the seal land.
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The diameter at the seal land can be selected to allow substantial sealing
engagement
with the casing inner diameter, for example, ID1 in Figure 2, in which it is
to be used
. and can therefore be greater than the casing inner diameter, even when
unenergized.
Thus, the inserts can be used to protect the seal land of the cup from excess
wear,
5 resulting for example from running in, that may deleteriously affect the
seal
performance of the seal cup.
The inserts can be spaced and configured to provide spaced or substantially
uniform
circumferential coverage, but to allow sufficient end clearance to permit
radial
10 compliance to pass over diameter reductions along the casing, as at
threaded
connections, and sealing expansion as is required in the sealing region. In
the
illustrated embodiment, the inserts are spaced apart and clearance is provided
between
their ends to accommodate radial compression/expansion of the seal cup.
15 While inserts of annular steel wire have been shown, other wear resistant
inserts or
surface coatings can be used as desired. While two rows of inserts have been
shown
positioned on either side of seal land, other numbers (i.e. one or more) and
positions
can be used.
It will be apparent that many other changes may be made to the illustrative
embodiments, while falling within the scope of the invention and it is
intended that all
such changes be covered by the claims appended hereto.
