Note: Descriptions are shown in the official language in which they were submitted.
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Methods, Strings and Tools to Enhance Wellbore Fracturing
Cross Reference to Related Applications
This application claims priority from U.S. provisional patent application no.
61/886,784,
filed October 4, 2013.
Field
The present invention relates to methods, strings and tools for fracturing a
wellbore.
Background
Wellbore treatments by fracturing have proven to be quite successful.
In a cemented well, that is where cement is placed in the annulus between the
well liner
and the wellbore wall, fracturing can be difficult. In particular, the cement
blocks the
annulus and, when ported tubulars are employed, the cement inhibits the
fracture fluid
from passing from the port of the ported tubular forming the well liner to the
wellbore
wall. As such, the fracture is often difficult to achieve.
To address these problems, Packers Plus Energy Services Inc., the present
applicant,
invented a cement diffuser to facilitate fracturing in cemented wells. For
example, US
Patents no. 7,798,226 and no. 8,033,331 describe the cement diffuser. The
cement
diffuser is installed over the port of a ported tubular. When the ported
tubular is in place
with the cement diffuser over its port, cement can be introduced to the
annulus. When
the cement is set, a path is created through the cement from the ported
tubular to the
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wellbore wall. However, with such a cement diffuser, the fracture fluid
reaches the
formation in only one location; radially out from the port of the tubular.
While this may
facilitate fracturing over fracturing in a standard cemented well, the
wellbore accessed
may not be the best rock in which to have a fracture form and only a simple
fracture is
likely to form.
In fracturing, it has been found that fracturing can be enhanced by having
fracture
complexity and fracturing into natural weaknesses. Complexity is where plural
fractures, including for example, both primary and secondary fractures, are
generated
along a single fracture site in a wellbore. Natural fractures are where a
fracture opens
via a natural weakness in the wellbore wall. Fracture complexity and natural
fracturing
has been difficult to achieve in cemented wells, even where a cement diffuser,
as
described in the above-noted US Patents, is employed.
Summary
In accordance with a broad aspect of the present invention, there is provided
a tubular
installation in place in a borehole, the tubular installation creating an
annular space
between the tubular installation and a wall of the borehole, the tubular
installation
comprising: a tubular including a wall having an inner surface and an outer
surface; a
port extending through the wall, the port including an upper end wall and a
lower end
wall the distance between the upper end wall and the lower end wall defining
the open
axial length of the port; and an external structure carried on the outer
surface, the
external structure overlying at least a portion of the axial length and
extending axially
from the port beyond at least one of the upper end wall and the lower end wall
and
remaining in place overlying at least a portion of the axial length when the
port is
opened.
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In accordance with another broad aspect of the invention, there is provided a
wellbore
tubular comprising: a wall having a first end, an opposite end, an inner
surface and an
outer surface; a port extending through the wall, the port including an upper
end wall
and a lower end wall, the distance between the upper end wall and the lower
end wall
defining the open axial length of the port; and an external structure carried
on the outer
surface, the external structure overlying at least a portion of the axial
length and
extending axially from the port beyond at least one of the upper end wall and
the lower
end wall, the external structure operable to create a pathway through hardened
cement
for passage of fracturing fluid from the port axially along the outer surface
away from the
port and toward the first end.
In accordance with another broad aspect of the present invention, there is
provided a
method for fracturing a wellbore, the method comprising: injecting fluid
through a tubing
string and out through a port into a cemented annulus between the tubing
string and a
wellbore wall, the fluid following a pathway through the cemented annulus, the
pathway
extending longitudinally away from the port and into contact with the wellbore
wall.
It is to be understood that other aspects of the present invention will become
readily
apparent to those skilled in the art from the following detailed description,
wherein
various embodiments of the invention are shown and described by way of
illustration.
As will be realized, the invention is capable for other and different
embodiments and its
several details are capable of modification in various other respects, all
without
departing from the spirit and scope of the present invention. Accordingly the
drawings
and detailed description are to be regarded as illustrative in nature and not
as
restrictive.
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Brief Description of the Drawings
Referring to the drawings, several aspects of the present invention are
illustrated by way
of example, and not by way of limitation, in detail in the figures, wherein:
Figure 1A is a schematic sectional view along a portion of a well bore with a
ported
tubular therein.
Figure 1B is a sectional view along line I-I of Figure 1A.
Figure 2 is a plan view of a cement diffuser plate useful in the present
invention.
Figure 3 is a perspective view of a cement diffuser installed on a wellbore
tubular.
Figure 4 is a sectional view of a cement diffuser installed on a tubular.
Reference may
be made to line II-11 of Figure 3 for orientation of the section through the
cement diffuser
and tubular wall.
Figure 5A is a schematic sectional view along a portion of another wellbore
with a
ported tubular therein.
Figure 5B and 50 are perspective views of further wellbore tubulars including
cement
diffusers.
Figure 6 is a schematic sectional view of a string installed in a well.
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Description of Various Embodiments
The detailed description set forth below in connection with the appended
drawings is
intended as a description of various embodiments of the present invention and
is not
intended to represent the only embodiments contemplated by the inventor. The
detailed
description includes specific details for the purpose of providing a
comprehensive
understanding of the present invention. However, it will be apparent to those
skilled in
the art that the present invention may be practiced without these specific
details.
With reference to Figures 1A and 1B, a ported tubular 12 is shown that
facilitates
wellbore fracturing in a cemented wellbore. In particular, tubular 12
facilitates fracturing
by promoting complex fracturing and/or by facilitating access of fracturing
fluid to natural
weaknesses in a cemented installation. The ported tubular 12 can be cemented
in
place in a wellbore, as defined by wellbore wall 14, wherein cement C resides
and is
allowed to set in an annular area 18 between the outer surface 12a of the
tubular and
wellbore wall 14.
The ported tubular 12 includes an external structure that is a cement diffuser
10. The
cement diffuser is carried on outer surface 12a of the ported tubular. When in
place in a
cemented well, cement diffuser 10 creates a pathway P through the cement
annulus
both radially adjacent and extending axially of the port 16 of the tubular. In
this
embodiment, the pathway P is formed within the cement diffuser. To create the
pathway, the external structure can create an area of the annulus generally
free of set
cement by blocking infiltration of the cement, by deforming or degrading to
leave a
space in the set cement and/or by preventing proper setting of the cement. The
pathway follows the position of the cement diffuser. The cement diffuser is
positioned
both radially outwardly of the port and axially away from at least one of the
upper and
lower limits of the port and, as such, the pathway through the cement extends
both
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radially outwardly and axially beyond the port towards one or both ends of the
ported
tubular.
Various external structures can form the cement diffuser. For example,
materials that
prevent infiltration of cement into their inner portions such as a hollow
tubular structure,
a collection of fibers (a brush, wool, twisted, woven, knit or compressed
arrangements,
etc.), foam such as sponge or closed cell foam such a styrofoam, degradable or
deformable materials, straps, etc. are all useful to form a cement diffuser.
In Figures 1A and 1B, cement diffuser 10 includes a collection of fibers
secured over the
port 16 at the outer surface and extending along at least an expanse of the
outer
surface of tubular 12 axially (aka longitudinally) adjacent port 16. The
fibers can be
metal, synthetic such as of polymers or natural organic materials such as of
cellulose,
hemp, wood, cotton, etc. The collection of fibers is carried along with
tubular 12 while
running the tubular into a borehole.
The cement diffuser becomes useful when it is desired to cement the annular
area 18
about the tubular. As will be appreciated, a cementing operation includes
pumping
liquid cement, arrows C, into the annular area between a tubular installation
and a
borehole wall. This is generally done by pumping cement from surface down
through
the inner diameter of the tubular installation and out into the annulus,
either by pumping
the cement out the bottom of the tubular installation or out through a port in
the tubular
wall.
The fibers of the cement diffuser are positioned to create pathway P through
the
cement, when it sets. The pathway is a cement-free space or weakened area of
cement, through which fluids can flow more readily than through set cement.
For
example, to form pathway P, the fibers may substantially block clear access of
the
cement into the cement diffuser, as the cement moves through the annulus, thus
the
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cement may tend not to infiltrate, or infiltrate only partially into, the
spaces between the
fibers of the collection of fibers due to fluid dynamics: leaving an open
space within the
cement diffuser which is free of cement. Alternately or in addition, the
cement may tend
not to infiltrate the fibers of the collection of fibers due to a chemical
applied to block
access into any voids between the fibers. Alternately, the cement may pass
between
the fibers of the cement diffuser, but the cement when set may be so thin,
porous or
unstable that the cement in that area is relatively weak. Alternately, the
cement may
pass between the fibers of the cement diffuser, but the fibers may degrade or
be
deformable (i.e. are able to be pushed aside), such that a space is formed in
the set
cement. Thus, in any event, a pathway is created by the cement diffuser
through the
set cement.
In one embodiment, the radially extended length of the collection of fibers is
selected to
span the annulus such that the collection of fibers at their outboard ends are
at least
closely adjacent or possibly touching the borehole wall 14. In this way, the
entire
annular radial length outwardly of the port and the outer surface on which the
cement
diffuser is installed is either devoid of cement or includes only relatively
weak deposits
of cement. In such an embodiment, the outward extended length of fibers from
the
outer surface of the tubular may be selected at surface with consideration as
to the
expected annulus radial spacing between the tubular and the borehole wall,
which will
be known based on the drilling information and the tubular's known outer
diameter.
So as not to interfere with the passage of cement through the annulus and the
integrity
of the annular cement seal above and below the cement diffuser, the cement
diffuser
may not extend fully about the circumference of the tubular. Thus, one or more
open
areas 19 are formed about the circumference of the tubular. For example, in
the
illustrated embodiment, where the tubular has a plurality of ports at one
axial position
and a cement diffuser over each port, the two cement diffusers may be spaced
apart
about the circumference of the tubular leaving open areas 19 therebetween
through
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which the cement may flow through the annulus past the cement diffusers, when
the
tubular is positioned in a borehole.
The cement diffuser is installed with a port-located portion thereof overlying
at least a
portion, for example herein illustrated as fully, over the open axial length L
of its port 16
and an end portion of the cement diffuser is installed on the outer surface of
the tubular
positioned axially beyond the port. The cement diffuser is continuous with the
port-
located portion and the end portion directly adjacent each other. Together the
port-
located portion and the end portion ensure the pathway through the cement
extends
axially along the tubular body beyond the open axial length L of its port and
longitudinally towards one or both of the ends of the tubular body. The cement
diffuser
end portions are installed on the outer surface axially below and/or above the
opening of
the port. With respect to the port-located portion, which is the portion
overlying the port
open axial length L, fluid from within the tubular can pass up through the
port and
through that portion of the cement diffuser. Additionally, the fluid can
continue into and
pass through the extending ends of the cement diffuser. While the fluid is
supplied
through the port, it travels along the tubular outer surface through the
diffuser axially
away from the port. In this way, the fluid can move through the pathway
created by the
cement diffuser to access a length of the wellbore, as determined by the
length of the
end portions. This facilitates the fracturing operation by accessing a length
of the
wellbore beyond the axial length of the port and increases the chances of the
fracturing
fluid locating a natural weakness in the borehole wall and of generating
complexity in
the fracture. It is likely that the breakdown pressure to achieve a successful
fracture will
be reduced over the breakdown pressure for fracturing in a standard cemented
well and
in a well with a fracturing cement diffuser only at the port.
The position of the end portion of the cement diffuser as axially beyond the
port means
that the end portion extends longitudinally, along the long axis x, and
generally toward
the ends of the tubular. While, for example, cement diffuser 10 is shown in
Figures 1A
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and 1B as parallel with the long axis x of the tool, this need not be the
orientation. For
example, the cement diffuser can be straight or curved. For example, in one
embodiment, the cement diffuser is curved: installed in a spiral fashion along
the outer
surface of the tubular (see for example Figure 5B, where cement diffuser 210'
is
mounted on a tubular overlying a port 216' through the tubular's wall and
cement
diffuser 210' spirals about the surface of the tubular as it extends axially
away from the
port 216').
Additionally, the cement diffuser can have a portion extending
circumferentially beyond
the side edges of the port.
Fillers such as chemicals, other fibers, hollow, degradable or frangible
components, etc.
can be positioned in the voids formed between the fibers of the collections,
such fillers
being selected to prevent the solidification of cement in the voids.
In use, the cement diffuser either directly provides a path for the injected
fluids to pass
therethrough, or the cement diffuser can be pushed aside, expelled or broken
down
immediately or over time to create the pathway or cement that infiltrates the
cement
diffuser, if any, is unstable, thin or weakly set to readily create a pathway
when injected
fluids enter the pathway. Injected fluids can be passed through the tubular
and out
through the port over which a cement diffuser has been installed. The injected
fluids
pass outwardly though the port and into the pathway. The injected fluids pass
through
the pathway, including that extending away from the port to access a length of
the
wellbore greater than the axial open length of the port to facilitate
fracturing of the
wellbore by creating complex fractures and/or forming fractures at naturally
weak rock.
The cement diffusers can be secured on the exterior of the tubular in various
ways.
With reference to Figures 2 to 4, in one embodiment, the cement diffuser
includes a
plate 120 with a plurality of holes 122a, 122b therethrough that can be
secured on the
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outside of a tubular 112 over a port 116 and along the outer surface of the
tubular. The
holes serve various purposes and may have various sizes and shapes, as
desired. For
example, in the presently illustrated embodiment of Figure 2, larger holes
122a, in this
illustrated case formed as slots, are included on the plate, where the plate
may be
installed over a port 116 and greater volume flows may be passed through the
slots.
Smaller holes 122b are formed over another area of the plate. The plate may
take
various forms. This plate shown fits over port 116 and has end portions 120a
for
mounting over a portion of the tubular outer surface axially beyond the axial
length L,
between upper end wall 116a and lower end wall 116b, of its port. However, the
plate
may be further elongated or more than one such plate may be installed to form
a longer
length cement diffuser extending axially away from the axial length L of the
port 116.
Fibers 124 may be threaded through the holes 122a, 122b. For example, the
holes may
be stuffed with fibers and the fibers may extend outwardly therefrom. The
fibers may be
linearly twisted in bundles, as shown. Alternately, the fibers may be
individually
extending or in the form of bunches, interengaged bundles, plugs, randomly
arranged,
linearly arranged, parallel, etc. The fibers together form a collection that
extends out
from the plate into the annulus about the tubular. In the illustrated
embodiment, for
example, fibers extend out substantially radially from the ports, relative to
the circular
dimension of the tubular. Fibers 124 may be selected to be long enough to
touch the
borehole wall of a borehole in which they are to be used. The fibers in this
embodiment,
form a brush like structure that can engage and ride along the borehole wall,
but are
threaded through the holes of the plate 120 such that they are substantially
not
dislodged by such engagement.
Fibers 124 may be secured to the plate such that they are forced out of the
way by fluid
flows through the port. In particular, the fibers over the ports may be forced
out of holes
122a, 122b of the plate when fluid injection occurs through the port 116 and
plate 120.
Alternately, the fibers may be installed or formed such that there remain
fluid flow
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passages between the fibers, when they remain in the holes. In another
possible
embodiment, fibers 124 may be formed of erodible or degradable
materials/construction
such that they break down at some point after cementing, for example, by the
erosive
power of the injected fluids.
Fillers, here shown as further fibers 126 of similar or, as shown, different
construction/materials, may be engaged between fibers 124 in the holes. In the
illustrated embodiment, for example, more delicate polymeric batting is placed
between
the tufts formed by the bundles of fibers extending from the holes 122a, 122b
of plate
120.
As noted hereinabove, other fillers can be positioned in the voids formed
between the
fibers of the collection of fibers, such fillers being selected to prevent the
entry or
solidification of cement in the voids between fibers. Other fillers include
for example,
one or more of hollow balls, sponge, sytrofoam, or chemicals such as, for
example, one
or more of grease, sugar, salt, cement retarder, etc.
Plate 120 can be secured over the port and along the surface in various ways,
such as
by fasteners 130 in apertures 132, welding, plastic deformation, etc. A recess
134 may
be provided on the outer surface of the tubular such that the plate can be
positioned
below the tubular's outer surface contour.
Fillers can also be positioned inwardly of plate 120 to act against passage of
or setting
of cement in port 116 and in the inner diameter of the tubular.
When tubular 112 with cement diffuser 110 of Figure 4 is placed within the
confines of
wellbore wall 114 and cement is introduced to cement the well, cement C
surrounds the
cement diffuser but cannot readily infiltrate the fibers 124 and filler 126 of
the cement
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diffuser. Any cement that does infiltrate the cement diffuser is weak. As
such, a
pathway is formed through cement diffuser 110 that is open to port 116.
Cement diffuser 110 remains in place over port 116 when the port is opened for
fluid
injection therethrough. Thus, while port 116 may have a closure (not shown),
cement
diffuser 110 does not in the illustrated embodiment act as a closure for the
port. In
particular, even after cementing fluid can exit port 116 while cement diffuser
is in place
or cement diffuser, or portions thereof, are pushed out of the way or degrade
after use
to create the pathway.
When fluid is injected to fracture the well, that fluid, arrows F, may pass
from the inner
diameter ID of the tubular 112 through the port 116. Fluid, arrows F, may then
pass
along the pathway in the cement created by fibers 124 and filler 126. Because
the
cement diffuser extends axially beyond the axial length of the port, the
weakened
pathway does so as well. Thus, the fluid may contact the wellbore wall 114 and
create
a complex fracture or locate an area of weakness in the rock, which may be
both
radially out from port 116 and/or axially spaced from the upper and lower
limits 116a,
116b of port 116 and enhance the fracture results by reducing break down
pressure and
creating more than one fissure into the formation.
Another embodiment of a cement diffuser is shown in Figure 5A. That external
structure
includes a rope type structure 224, wherein the rope fibers are twisted and
extend
axially along the length of the rope. In this drawing two structures 224 are
shown
secured to the external surface 112a of the tubular 112. Each structure 224
extends
over a plurality of ports 216 in the wall of the tubular and axially beyond
the axial lengths
L of the ports.
The external structure can take other forms. For example, the external
structure may
include anything that can be positioned on the external surface of a wellbore
tubular,
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holds to withstand the rigors of being run into a well, past which cement can
flow and
which creates a immediate or formable pathway in the cement, when the cement
sets.
Some structures of interest are centralizers (like a bow spring centralizer or
an open
vane centralizer), hollow tubes (like hollow tubes with frangible burst
members installed
in ports thereof), axially extending deformable structures (like rubber vanes
that can
deform to let a pressurized fluid pass), etc. These structures are mounted
adjacent a
port and positioned to receive a fluid supply from a port and to create a
weakened
pathway in the cement from the port, axially along the tubular away from the
axial length
of the port and in the annular area.
Figure 5B, as noted previously, includes a spirally oriented cement diffuser
210'. This is
formed of a foam that can be installed on the tubular's outer surface but
eventually
breaks down after cementing. Since the cement diffuser 210' remains in place
during
cementing, the helical wraps of cement diffuser 210' are installed to leave
open flow
areas 219' therebetween through which cement, arrows C, can pass. After
installation,
the fracture fluid can move through ports 216' and along the spiral pathway to
contact
an axial length of the wellbore well beyond the axial open lengths of the
ports. As such,
the chance of the fracture fluid contacting a natural weakness along the
spiral path is
increased over a situation where the fracture fluid passed radially out from
the ports
through the cement and into contact with the wellbore wall radially outwardly
of the ports
and only along a length substantially the same as the axial lengths of the
ports.
Figure 50 shows another cement diffuser 210" mounted on a tubular 212"
overlying a
plurality of ports 216" opened through the tubular's wall. This cement
diffuser 210" is
formed as a sleeve-type structure on the outer surface. The cement diffuser
extends
axially beyond the upper and lower limits of ports 216". In fact, the cement
diffuser
extends substantially the full length of the tubular leaving only the end
connections
exposed. Additionally, cement diffuser 210" extends circumferentially about
the tubular
beyond the side edges that limit the circumferential open width of ports 216".
While the
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cement diffuser may be formed of various materials, in the illustrated
embodiment
cement diffuser 210" is formed of a resilient material such as sponge that is
durable to
withstand the rigors of being run into a wellbore and is strong enough to hold
its shape
during cementing. Since the cement diffuser 210" resists deformation by cement
passing thereby, an open flow area 219" is provided through an axial length of
the
cement diffuser.
The sponge forming cement diffuser 210" can, however, be pushed aside (i.e.
cut into
and/or compressed) when fluid at fracturing pressures is pumped through ports
216".
As such, fracture fluid can pass through cement diffuser 210" and contact the
wellbore
along a length much greater than the axial open length and open width of the
individual
ports and about a substantial portion of the circumference of the tubular.
Fracturing
fluid is much more likely to find an area of weakness and/or to form complex
fractures
along the substantial portions, both axially and circumferentially, about the
ports. In
particular, almost the full length and circumference of the wellbore that
relates to the
length and circumference of the cement diffuser is free of set cement and can
be
accessed by fracture fluid, except that area of flow channel 219" which
contains set
cement.
As shown in Figure 6, a string 312 of ported tubulars with external cement
diffusing
structures 324a, 324b may be installed in a wellbore 314. Here the external
structures
324a are in the form of bow spring centralizers and external structures 324b
are in the
form of spirally extending cement diffuser formed of a collection of fibers.
The ported
tubulars may be connected into a string with an inner diameter ID through
which fluids
may be conveyed to treat the well and from production of the well. The
external
structures are in place on the external surface 312a of the ported tubulars
312 as the
string is installed in the well and when the string is in place in the well,
the external
structures are already positioned or can be activated and are adjacent a port
316. The
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external structures are also positioned to receive a fluid supply from a port
316 into a
pathway formed as a result of the external structure though annular cement.
As the wellbore is cemented, cement C surrounds the external cement diffuser
structures, but the structure of the external structures, wherein they include
hollow
sections, sections filled with fillers, etc., each create a pathway in the set
cement.
These pathways extend from the port at which they are positioned, axially in
the annular
area along the tubular outer surface longitudinally away from the open area of
the port.
In one embodiment, the external structures extend from the port open area and
have a
radial thickness such that they come close to touching or touch the wellbore
wall. As
such, the pathways likewise extend from the port open area towards the
wellbore wall,
while extending axially away from the port. The pathway may be open to the
wellbore
wall or only a thin sheathe of cement may be present between the pathway and
the
wellbore wall.
When fluid is injected to treat the wellbore, the fluid may pass through the
inner
diameter ID of the wellbore string, out through the ports 316 and along the
paths to
create complexity in the wellbore fracture and/or to create fractures in weak
rock.
These fractures may be axially spaced from the locations of the ports since
the injected
fluid can follow the axially extending pathways formed by the external cement
diffusing
structures. This is different than the wellbore treatment that can be effected
through a
port D without an external cement diffusing structure as described herein,
wherein the
annular cement prevents axial flow of the fracturing fluid and often only a
simple fracture
may be created, that being directly radially out from the port. The chance of
that
fracture being in a natural area of weak rock is unlikely, it being dependant
entirely on
the exact location of the port in the wellbore. The complex fracture causes
increased
contact at the wellbore wall compared to a simple fracture.
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The previous description of the disclosed embodiments is provided to enable
any
person skilled in the art to make or use the present invention. Various
modifications to
those embodiments will be readily apparent to those skilled in the art, and
the generic
principles defined herein may be applied to other embodiments without
departing from
the spirit or scope of the invention. Thus, the present invention is not
intended to be
limited to the embodiments shown herein, but is to be accorded the full scope
consistent
with the claims, wherein reference to an element in the singular, such as by
use of the
article "a" or "an" is not intended to mean "one and only one" unless
specifically so
stated, but rather "one or more". All structural and functional equivalents to
the
elements of the various embodiments described throughout the disclosure that
are
known or later come to be known to those of ordinary skill in the art are
intended to be
encompassed by the elements of the claims. Moreover, nothing disclosed herein
is
intended to be dedicated to the public regardless of whether such disclosure
is explicitly
recited in the claims. No claim element is to be construed under the
provisions of 35
USC 112, sixth paragraph, unless the element is expressly recited using the
phrase
"means for" or "step for".
16
