Note: Descriptions are shown in the official language in which they were submitted.
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ISOLATION TOOL WITH RUPTURABLE DISC
This invention relates to a tool used in wells extending into
the earth and, more particularly, to a tool for isolating one
section of a pipe string from another section.
BACKGROUND OF THE INVENTION
There are a number of situations, in the completion of oil and
gas wells, where it is desirable to isolate one section of a
subterranean well from another.
For example, in U.S. Patent
5,924,696, there is disclosed an isolation tool used alone or in
combination with a packer to isolate a lower section of a produc-
tion string from an upper section. This tool incorporates a pair
of oppositely facing frangible or rupturable discs or half domes
which isolate the well below the discs from pressure operations
above the discs and which isolate the tubing string from well bore
pressure. When it is desired to provide communication across the
tool, the upper disc is ruptured by dropping a go-devil into the
well from the surface or well head which falls into the well and,
upon impact, fractures the upwardly convex ceramic disc.
The
momentum of the go-devil normally also ruptures the lower disc but
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the lower disc may be broken by application of pressure from above,
after the upper disc is broken, because the lower disc is concave
upwardly and thereby relatively weak against applied pressure from
above.
An important development in natural gas production in recent
decades has been the drilling of horizontal sections through zones
that have previously been considered uneconomically tight or which
are shales.
By fracing the horizontal sections of the well,
considerable production is obtained from zones which were previous-
ly uneconomical. For some years, the fastest growing segment of
gas production in the United States has been from shales or very
silty zones that previously have not been considered economic. The
current areas of increasing activity include the Barnett Shale, the
Haynesville Shale, the Fayetteville Shale, and the Marcellus Shale
in the United States, the Horn River Basin of Canada and other
shale or shaley formations in North America and Europe.
It is no exaggeration to say that the future of natural gas
production in the continental United States is from these hereto-
fore uneconomically tight gas bearing formations.
In addition,
there are many areas of the world where oil and gas is produced and
costs are, from the perspective of a United States operator,
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exorbitantly high. These areas currently include offshore Africa,
the Middle East, the North Sea and deep water parts of the Gulf of
Mexico. Accordingly, a development that allows well completions at
overall lower costs is important in many areas of the world and in
many different situations.
Disclosures of interest relative to this invention are found
in U.S. Patents 7,044,230; 7,210,533 and 7,350,582 and U.S. Printed
Patent Applications S.N. 20070074873; 20080271898 and 20090056955.
SUMMARY OF THE INVENTION
The device disclosed in U.S. Patent 5,924,696 can be used in
a horizontal section of a well to isolate the well below the tool
from pressure operations above the tool. However, the upper disc
has to be broken or weakened in a mechanical fashion requiring a
bit trip, typically a coiled tubing trip in modern high tech wells
or a bit trip with a workover rig in more traditional environments,
to fracture the upper disc because a go-devil dropped through the
vertical section of the well does not have sufficient momentum to
reach and then fracture the upper disc. Theoretically, sufficient
pressure could be applied from above to break the upper disc from
the concave side but this pressure is commonly so high that it
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would damage or destroy other components of the production string.
It has been realized that it would be desirable to provide an
isolation tool which can be used in a horizontal section of a well
without requiring a bit trip.
As disclosed herein, a pressure differential that is uniform
across the pressure disc is created by manipulating pressure at the
surface or through the well head to fracture a first of the discs.
The other disc may be ruptured using pressure in the well. The
exact sequence of breaking the discs may depend on the particular
design employed and whether the isolation tool is located above or
below a packer or other sealing element isolating the production
string, typically from a surrounding pipe string.
Several embodiments of an isolation tool are disclosed that
may be used in wells to temporarily isolate a section of the well
below the tool from a section above the tool. These embodiments
use a pressure differential to fracture a first of the discs. In
one embodiment, a capillary tube is provided from above the upper
disc to a location between the discs. In a second embodiment, a
check valve admits pressurized well fluid between the discs so that
one of the discs may be broken by reducing the pressure on one side
of the isolation tool. In a third embodiment, an unvalved opening
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admits pressurized well fluid between the discs so that one of the
discs may be broken by reducing the pressure on one side of the
isolation tool.
In a fourth embodiment, a movable member is
displaced by pressure supplied from above to break a first of the
discs.
It is an object of this invention to provide an improved down
hole well tool to isolate one section of a well from another.
A more specific object of this invention is to provide an
improved isolation sub that can be manipulated by a pressure
differential to place isolated sections of a well into communicati-
on.
These and other objects and advantages of this invention will
become more apparent as this description proceeds, reference being
made to the accompanying drawings and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-sectional view of one embodiment of an
isolation tool that incorporates a pair of oppositely facing
pressure discs;
Figure 2 is an exploded view of a component of the device of
Figure 1;
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Figure 3 is a schematic view of a well in which the isolation
tool of Figure 1 is employed;
Figure 4 is a cross-sectional view of another embodiment of an
isolation tool that incorporates a pair of oppositely facing
pressure discs;
Figure 5 is an enlarged view of a valve assembly used in the
embodiment of Figure 4;
Figure 6 is a view similar to Figure 2, illustrating operation
of the embodiment of Figures 4 and 5;
Figure 7 is a partial view of another embodiment of this
invention, based on the embodiment of Figure 4;
Figure 8 is a cross-sectional view of another embodiment of an
isolation tool that incorporates a pair of oppositely facing
pressure discs, illustrating the tool in a position where upper and
lower sections of the well are isolated;
Figure 9 is a cross-sectional view of the embodiment of Figure
illustrating the tool in the process of breaking one of the
pressure discs;
Figure 10 is an isometric view of a modified pressure dome;
and
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Figure 11 is a view of the pressure dome of Figure 10 in an
isolation tool.
DETAILED DESCRIPTION OF THE INVENTION
Referring to Figures 1-2, there is illustrated an isolation
tool or sub 10 comprising a housing 12 having a passage 14
therethrough, upper and lower rupturable pressure discs 16, 18 and
a capillary tube 20 opening into a chamber 22 between the discs 16,
18.
The housing 12 may comprise a lower end, pin body or pin 24,
a central section 26, an upper end or box body 28 and suitable
sealing elements or O-rings 30, 32 captivating the discs 16, 18 in
a fluid tight manner. Except for the capillary tube 20, those
skilled in the art will recognize the isolation sub 10, as
heretofore described, as being typical of isolation subs sold by
Magnum International, Inc. of Corpus Christi, Texas and as also
described in U.S. Patent 5,924,696.
The capillary tube 20 may be external to the housing 12, or an
internal passage may be provided, and may terminate in an extension
of the central section 26 or in the upper section 28. One problem
that is occasionally encountered is sufficient debris above the
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upper disc 16 which might seal off pressure from reaching the
capillary tube 20. To overcome this problem, the capillary tube 20
may be of greater length as by providing one or more pipe sections
34 of any suitable length connected to a collar or other sub 36
thereby elongating the housing 12. This will accommodate debris,
such as sand or the like, from bridging off access to the top of
the capillary tube 20.
The discs 16, 18 may be of any suitable type having the
capability of being stronger in one direction than in an opposite
direction.
Conveniently, the discs 16, 18 may be curved or
generally hemispherical domes made of any suitable material, such
as ceramic, porcelain, glass and the like.
Suitable ceramic
materials, such as alumina, zirconia and carbides are currently
commercially available from Coors Tek of Golden, Colorado. These
materials are frangible and rupture in response to either a sharp
blow or in response to a pressure differential where high pressure
is applied to the concave side of the discs 16, 18. Because of
their curved or hemispherical shape, half domes may be a preferred
selection because of their considerable ability to resist pressure
from the convex side, their much lower ability to resist pressure
from the concave side, cost, reliability and frangibility. Ceramic
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discs of this type are available in a variety of strengths but a
typical disc may have the capability of withstanding 25,000 psi
applied on the convex side but only 1500 psi applied on the concave
side. In a typical situation, the discs 16, 18 may be 10-20 times
stronger against pressure applied to the convex side than to the
concave side. Any pressure disc which has greater strength in one
direction than in the opposite may be used, another example of
which are metal Scored Rupture Disc Assemblies available from Fike
Corporation of Blue Springs, Missouri or BS&B of Tulsa, Oklahoma.
The Fike discs that are stronger in one direction than the other
are also concave on the weak side and convex on the other which is
a convenient technique for making the discs stronger in one
direction than in an opposite direction and thus responsive to
different sized pressure differentials.
The capillary tube 20 includes a tube 38 of any suitable
outside and inside diameter so long as it transmits pressure,
either higher or lower than hydrostatic pressure in the well
applied from above the tool 10. The tube 20 may be connected to
the central section 26 in a recess 40 by a nipple 42 threaded,
pressed or otherwise connected to the central section 26.
The
nipple 42 communicates with a passage 44 opening into the chamber
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22 so any pressure, higher or lower than hydrostatic pressure,
applied above the tool 10 is delivered between the discs 16, 18.
A connector 46 may be threaded into the nipple 42 as driven by a
wrench (not shown) acting on a polygonal nut 48. A similar or
dissimilar fitting 50 may connect an upper end of the tube 38 to
the collar 36.
Referring to Figure 3, a typical example of using the
isolation tool 10 is illustrated.
The isolation tool 10 may
comprise part of a horizontal or inclined section of a production
string 52 inside a casing string 54 which intersects a productive
zone where one or more pipe joints 56 may be disposed below the
tool 10 and a series of pipe joints 58 may be disposed above the
tool 10 leading to the surface or well head so formation fluids may
be produced. A typical use of the isolation tool 10 is to isolate
the productive zone below a packer 60 from pressure operations
above the tool 10 which operations typically set the packer 60.
Another typical use of the isolation tool 10 is in setting a liner
during drilling of a deep well.
At the outset and throughout the packer setting operation,
there is hydrostatic pressure inside the production string 52 and
in the annulus between the production string 52 and the casing
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string 54, meaning there is hydrostatic pressure above the upper
disc 16, in the chamber 22 and below the lower disc 18, so there is
no pressure differential operating on the discs 16, 18 which would
tend to break them. The packer 60 is set by applying pressure
downwardly through the production string 52. Any pressure applied
from above acts on both sides of the upper disc 16 so the upper
disc 16 sees no pressure differential and there is no tendency of
the upper disc 16 to fail. So long as the packer 60 is set by a
pressure that is less than the sum of hydrostatic pressure at the
tool 10 and the strength of the disc 18 against pressure applied on
the concave side, the packer 60 may be manipulated without
fracturing the lower disc 18.
After the packer 60 is set, pressure is applied from above and
transmitted through the capillary tube 20 to a location between the
discs 16, 18. This applied pressure is greater than the hydrostat-
ic pressure in the well and creates a pressure differential which
is uniform over the area of the disc 18 and which exceeds the
ability of the concave side of the lower disc 18 to withstand it.
The lower disc 18 then shatters or ruptures allowing well pressure
to enter the chamber 22. When pressure in the production string 52
above the tool 10 is lowered, as by stopping the pumps which have
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created the pressure to set the packer 60, by swabbing the
production string 52, gas lifting the production string 52 or
simply opening the production string 52 to the atmosphere at the
surface or well head, well pressure acting on the concave side of
the upper disc 16 exceeds its ability to withstand pressure in this
direction whereupon the upper disc 16 fails thereby placing the
production string 52, above and below the tool 10, in communication
and allowing the well to produce.
Thus, the tool 10 allows
breaking of the discs 16, 18 to place the heretofore isolated parts
of the well in communication by the application of pressure from
above. In this situation, the pressure that breaks the lower disc
18 is applied from above and produces a pressure at the tool 10
that is greater than hydrostatic pressure but far less than what
would rupture the disc 16 if applied from above.
Many, if not most, hydraulically set packers require more
pressure above hydrostatic than the concave side of the lower disc
18 can withstand. To overcome this problem, an inline pressure
disc 62 may be provided in the capillary tube 20 as shown best in
Figure 3. In some embodiments, the pressure disc 62 may be located
between the nipple 42 and the passage 44, may be located inside the
nipple 42, inside the fitting 50 or any other suitable location.
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The pressure disc 62 may be of any suitable type to provide a
sufficient resistance to allow the packer 60 to be hydraulically
set without rupturing the lower disc 18. In some embodiments, the
pressure disc 62 is commercially available from Fike Corporation of
Blue Springs, Missouri and known as Scored FSR Rupture Disc
Assembly. In a typical situation, the packer 60 may require an
applied pressure of 3500 psi above hydrostatic to set. In such
situations, the pressure disc 62 may be selected to rupture at a
substantially greater pressure, e.g. 4500 psi. Thus, the packer 60
would be set and then additional pressure would be applied to
rupture the disc 62 which would place sufficient pressure in the
chamber 22 to fracture the lower disc 18. The upper disc 16 would
not rupture immediately because there is initially no pressure
differential across the upper disc 16 because the pressure applied
from the surface is on both sides of the upper disc 16. After the
lower disc 18 fails, pump pressure applied from the surface is
reduced whereupon formation pressure applied from below produces a
pressure differential sufficient to rupture the upper disc 16.
In some embodiments, a check valve (not shown) may be provided
in the fitting 50 to allow flow inside the tubing string 58 to
enter the chamber 22 but prevent flow out of the chamber 22.
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It will be seen that the tool 10 is designed to cause one of
the pressure discs 16, 18 to fail by creation of a pressure
differential that is substantially below the differential pressure
which would cause failure if applied to the strong or convex side
of the pressure discs 16, 18.
Referring to Figure 4, there is illustrated another isolation
tool 70 providing a passage 72 therethrough and comprising, as
major components, a housing 74, first and second pressure discs 76,
78 and a valve assembly 80 allowing hydrostatic pressure from
outside the tool 70 to enter a chamber 82 between the pressure
discs 76, 78.
The housing 74 may comprise a lower end or pin body 84, a
central section or collar 86 providing a passage 88 into the
chamber 82, an upper end or box body 90 and suitable sealing
elements or 0-rings 92, 94 captivating the discs 76, 78 in a fluid
tight manner. The pressure discs 76, 78 may be of the same type
and style as the pressure discs 16, 18 and are capable of resisting
a greater pressure from one direction than the other. Except for
the valve assembly 80, those skilled in the art will recognize the
isolation sub 70, as heretofore described, as being typical of
isolation subs sold by Magnum International, Inc. of Corpus
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Christi, Texas and as also being described in U.S. Patent 5,924,-
696.
The valve assembly 80 comprises a check valve which allows
flow into the chamber 82 so hydrostatic pressure is delivered
between the discs 76, 78 during normal operations, such as when the
tool 70 is being run into a well.
The valve assembly 80 may
comprise a spring 96 biasing a ball check 98 against a valve seat
100. It will be seen that the check valve 80 allows the maximum
hydrostatic pressure to which the tool 70 is subjected to appear in
the chamber 82. Under normal conditions, there is no tendency for
the pressure in the chamber 82 to rupture the discs 76, 78 because
the same pressure exists on the inside and outside of the tool 70.
Referring to Figure 6, the isolation tool 70 is illustrated in
a production string 102 inside a casing string 104. A pressure
actuated packer 106 may be above the isolation tool 70.
The
production string 102 may extend past the tool 70 toward a
hydrocarbon formation. Initially, the isolation tool 70 pressure
separates the production string 102 into two segments. Because of
the inherent strength of the convex side of the illustrated disc
76, the applied pressure may be sufficiently high to conduct any
desired pressure operation. After the packer 102 is set or when it
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is desired to place the well below the tool 70 in communication
with the production string 102 above the tool 70, steps are
conducted to reduce pressure above the upper disc 76. This may be
done in any suitable manner, as by opening the production string
102 at the surface or through the well head, swabbing the produc-
tion string 102, gas lifting the production string 102 or the like.
When the pressure above the upper disc 76 declines sufficiently, a
pressure differential is created across the upper disc 76 which is
sufficient to rupture the upper disc 76. This pressure differen-
tial is much smaller than a pressure differential caused by the
application of positive pressure to the convex side of the upper
disc 76 that is sufficient to rupture it. For example, the convex
side of the disc 76 may be rated to withstand a pressure differen-
tial of 25,000 psi but the embodiment of Figure 4 acts to rupture
the upper disc 76 upon creating a much smaller pressure differen-
tial applied to the concave side of the disc 76.
After the upper disc 76 ruptures, pressure may be applied at
the surface through the production string 102 by a suitable pump
(not shown) to create a pressure differential across the lower disc
78 sufficient to rupture it.
In this manner, the heretofore
pressure separated sections of the well are now in communication.
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Referring to Figure 7, there is illustrated another isolation
tool 110 which may be identical to the tool 70 except that the
check valve assembly 80 has been eliminated. Thus, the tool 110
may include a collar 112 having one or more continuously open or
unvalved passages 114 therein communicating between the pressure
discs. By continuously open, it is meant that the passage 114 is
open when the tool 110 is in the well. Surprisingly, the tool 110
works in the same manner as the tool 70 because the passage 114
allows hydrostatic pressure to build up between the discs. When
liquids above the upper disc are removed, a pressure differential
is created across the upper disc in its weak direction thereby
rupturing the upper disc. The lower disc is broken in the same
manner as the lower disc 78 which may be by pumping into the tool
110. Besides the advantage of simplicity, the tool 110 also has an
advantage when it becomes necessary or desirable to remove the
production string and packer from the well without setting the
packer. In the embodiment of Figures 4-5, pulling the tool 70 from
the well will reduce pressure above the upper disc 76 and below the
lower disc 78 so the trapped pressure in the chamber 82 will likely
cause one of the discs 76, 78 to fail. By removing the check valve
assembly 80, the isolation tool 110 may be pulled from the well
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without rupturing either of the pressure discs because hydrostatic
pressure will bleed off from between the discs at the same rate as
it falls above the upper disc and below the lower disc.
By
eliminating the check valve assembly 80, there is created an
isolation tool which will not rupture when the tool is pulled from
the well.
Referring to Figures 8-9, there is illustrated another
isolation tool 120 providing a passage 122 therethrough and
comprising, as major components, a housing 124, first and second
frangible pressure discs 126, 128 and an assembly 130 responsive to
pressure inside the tool 120 to rupture the discs 126, 128.
The housing 124 may comprise a lower end or pin body 132, a
central section or collar 134, a section 136 that cooperates with
the assembly 130, an upper end or box body 138, and suitable
sealing elements or 0-rings 140, 142 captivating the discs 126, 128
in a fluid tight manner. Another set of seals or 0-rings 144 seal
between the section 136 and the box body 138.
The section 136 includes a wall 146 of reduced thickness
providing a recess 148 open to the exterior of the tool 120 through
one or more passages 150. The assembly 130 may include a sleeve
152 having an annular rim 154 comprising a pressure reaction
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surface. An 0-ring or other seal 156 may seal between the rim 154
and the inside of the wall 146 to provide a piston operable by a
pressure differential between hydrostatic pressure in the well
acting through the passage 150 against the underside 158 of the rim
154 and pressure applied from above acting on the top 160 of the
rim 154. The sleeve 152 may normally be kept in place by a shear
pin 162 or other similar device.
It will be seen that a pressure applied from above through the
inside of the tool 120 passes through an opening 164 in the box
body 138 and acts on the top 160 of the rim 154. When the downward
force applied in this manner sufficiently exceeds the upward force
on the rim 134 by hydrostatic pressure outside the tool 120, the
shear pin 162 fails and the sleeve 152 moves from an upper position
shown in Figure 8 to a lower position shown in Figure 9.
The bottom of the sleeve 152 may be equipped with a suitable
aid to fracture the upper disc 126. This may be a pointed element
166 attached to the inside of the sleeve 152 in any suitable
manner, as by a lattice work frame 168.
As in the previously described embodiments, the isolation tool
120 may be used in any situation where it is desired to pressure
separate one section of a hydrocarbon well from another. Assuming
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the tool 120 is run in a production string analogous to those shown
in Figures 2 and 6, pressure applied from above is sufficient to
hydraulically set a packer (not shown) but is not sufficient to
shear the pin 162. After the packer (not shown) is set, additional
pressure is applied from above which is sufficient to shear the pin
162 but is not sufficient to fracture the convex side of the disc
126. When the pin 162 shears, the sleeve 152 moves downwardly with
sufficient force that the point 166 impacts the frangible disc 126
thereby rupturing it. Pressure inside the tool 120 is sufficient
to rupture the much weaker lower disc 128 because the pressure
differential is applied to the concave side of the disc 128.
Thus, in common with the tools 10, 70, the isolation tool 120
opens communication between the previously isolated parts of a well
upon the application of pressure from above that is less than the
rated capacity of the convex side of the upper disc 126.
Referring to Figures 10-11, an improved pressure disk 170 is
illustrated having a generally hemispherical central section 172
providing a circular edge 174, a convex outer surface 176, a
concave inner surface 178 and a cylindrical skirt 180 extending
substantially from the circular edge 174 below the curved portion
of the disk 170.
The cylindrical skirt 180 includes an inner
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cylindrical wall 182 and an outer cylindrical wall 184 providing an
extended sealing area as shown in Figure 11 where multiple sealing
elements or 0-rings 186, 188 seal between the disk 170 and a
housing 190 which may be part of an isolation tool 192 or other
tool where a frangible pressure disk is necessary or desirable.
The advantage of the elongate cylindrical skirt 180 is it
provides sufficient area for multiple sealing elements, such as a
pair of 0-rings or other seals or one or more seals with a backup
seal or device.
It is much simpler to seal against the outer
cylindrical wall 184 than against a curved portion of the hemi-
spherical central section 172. In fact, seals heretofore used with
hemispherical pressure disks of the type disclosed herein were
crushed to accommodate and seal against the arcuate side of the
pressure disk. Sealing against the cylindrical surface 182 is much
simpler, more reliable, more reproducible and more efficient.
Thus, the skirt 180 may be of any suitable length sufficient to
provide a cylindrical surface of sufficient length to receive at
least one seal member on the O.D. and, preferably, two seal
members. Thus, in a typical situation in disks 170 of 2" diameter
and greater the skirt 180 may be at least 1" long.
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The disk 170 may be made of any frangible material, such as
ceramic, porcelain or glass, i.e. from the same materials as the
pressure disks previously described.
It will be apparent that the outer cylindrical wall 184 may be
manufactured in a variety of techniques. One simple technique is
to grind the outer diameter of a hemispherical disk to provide the
cylindrical wall 184. A preferred technique may be to manufacture
the disk 170 with an elongate cylindrical skirt 180 as illustrated
in Figures 10-11 and then grind the outer diameter to a smoothness
compatible with O-ring type seals.
This smoothness, known to
machinists as a seal finish or O-ring seal finish is known more
technically as 63-32 on a scale known as RMS or Root Mean Square.
In this system, and simplified for purposes of illustration, the
number is a measure, in microns, of the difference between the
heights of small protrusions and the depths of small depressions in
the surface. The smaller the number, the smoother the surface.
The scope of the claims should not be limited by the preferred
embodiments set forth in the examples, but should be given the
broadest interpretation consistent with the description as a whole.
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