U.S. patent application number 09/847704 was filed with the patent office on 2001-10-11 for inflation element for a downhole tool having a pre-disposed bladder and/or cover, and method shaping tool for pre-disposing the bladder and/or cover.
Invention is credited to Carisella, James V..
Application Number | 20010027868 09/847704 |
Document ID | / |
Family ID | 23122335 |
Filed Date | 2001-10-11 |
United States Patent
Application |
20010027868 |
Kind Code |
A1 |
Carisella, James V. |
October 11, 2001 |
Inflation element for a downhole tool having a pre-disposed bladder
and/or cover, and method shaping tool for pre-disposing the bladder
and/or cover
Abstract
A method for pre-disposing the expansion profile in an
expandable, elastomeric component of a downhole tool, includes the
steps of (a) surrounding at least a portion of the length of an
elastomeric component with a shaping tool or vessel having an inner
diameter that defines a profiled limit for pre-disposing the
expansion profile in the component; (b) applying fluid under
pressure to the elastomeric component for expanding it into contact
with the inner diameter of the shaping tool and creating a
pre-disposed expansion profile in the component; and (c) reducing
the pressure of the fluid for allowing the elastomeric component to
return generally to its original shape. A downhole tool with an
improved expandable, elastomeric component includes an expandable,
elastomeric component having a pre-disposed expansion profile. A
vessel for providing a pre-disposed expansion profile in an
expandable, elastomeric component of a downhole tool includes a
vessel body shaped and dimensioned to surround at least a portion
of the expandable, elastomeric component. The vessel body includes
an inner diameter that defines a profiled limit in which the
component can be expanded for forming a pre-disposed expansion
profile in the component.
Inventors: |
Carisella, James V.;
(Harahan, LA) |
Correspondence
Address: |
FULBRIGHT & JAWORSKI L.L.P.
Alberto Q. Amatong, Jr.
Suite 5100
1301 McKinney
Houston
TX
77010-3095
US
|
Family ID: |
23122335 |
Appl. No.: |
09/847704 |
Filed: |
May 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09847704 |
May 2, 2001 |
|
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|
09291896 |
Apr 14, 1999 |
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Current U.S.
Class: |
166/387 ;
166/187 |
Current CPC
Class: |
B29L 2022/025 20130101;
B29K 2995/005 20130101; B29C 49/00 20130101; B29C 55/22 20130101;
B29K 2021/00 20130101; B29C 71/00 20130101; E21B 33/1277 20130101;
B29C 2949/08 20220501; B29K 2105/258 20130101 |
Class at
Publication: |
166/387 ;
166/187 |
International
Class: |
E21B 033/12 |
Claims
I claim:
1. A method for pre-disposing the expansion profile in an
expandable, elastomeric component of a downhole tool, comprising
the steps of: (a) surrounding at least a portion of the length of
an elastomeric component with a vessel having an inner diameter
that defines a profiled limit for pre-disposing the expansion
profile in the component; (b) applying fluid under pressure to the
elastomeric component for expanding it into contact with the inner
diameter of the vessel and creating a pre-disposed expansion
profile in the component; and (c) reducing the pressure of the
fluid for allowing the elastomeric component to return generally to
its original shape.
2. The method of claim 1, wherein the expandable, elastomeric
component comprises a bladder formed of an elastomeric
material.
3. The method of claim 1, wherein the expandable, elastomeric
component comprises a cover section for an expansion element.
4. The method of claim 1, wherein the expandable, elastomeric
component comprises a bladder formed of an elastomeric material, a
sheath formed of expandable ribs extending lengthwise along the
bladder and overlapping each other, and at least one cover section
formed of an elastomeric material covering at least a portion of
the outer surface of the ribs.
5. The method of claim 4, and further including the step of
combining the ribs and cover with the bladder after the bladder is
pre-disposed.
6. The method of claim 1, wherein the inner diameter of the vessel
includes a pair of truncated conical tapers that expand outwardly
extending toward the middle of the vessel.
7. The method of claim 1, wherein the inner surface of the vessel
comprises a single truncated conical taper extending from one end
of the vessel to the other.
8. The method of claim 6, wherein the inner diameter has a
cylindrical section located between the truncated conical
tapers.
9. The method of claim 6, wherein the inner diameter includes a
pair of truncated conical tapers abutting each other.
10. The method of claim 1, wherein the tool comprises a cylindrical
sleeve arranged concentrically over the expandable, elastomeric
component, and the inner diameter is formed of at least one end cap
with a tapered inner surface located between the expandable,
elastomeric element and the sleeve.
11. The method of claim 6, wherein the inner diameter is formed of
two end caps abutting each other.
12. The method of claim 1, wherein the step of surrounding at least
a portion of the expandable, elastomeric element comprises the
steps of: (a) placing the sleeve in a concentric position over the
elastomeric element; and (b) placing a pair of end caps between the
sleeve and elastomeric element for defining the inner diameter of
the vessel.
13. The method of claim 1, wherein the step of supplying fluid
under pressure comprises supplying fluid under pressure
continuously.
14. The method of claim 1, wherein the step of supplying fluid
under pressure comprises supplying fluid under pressure
intermittently.
15. The method of claim 1, and further including the step of
calendering the elastomeric material before the elastomeric
component is formed.
16. A downhole tool having an improved expandable, elastomeric
component, comprising, an expandable, elastomeric component having
a pre-disposed expansion profile.
17. The tool of claim 16, wherein the component having a
pre-disposed expansion profile includes a bladder for an inflation
element.
18. The tool of claim 16, wherein the component having a
pre-disposed expansion profile includes a cover section for an
inflation element that includes a bladder and a plurality of ribs
extending axially over the ribs, and the cover section covering at
least a portion of the ribs.
19. The tool of claim 16, and further including: (a) a pair of end
collars: (b) an inflation element connected between the end
collars; (c) the inflation element having at least one expandable,
elastomeric component with a pre-disposed expansion profile.
20. The tool of claim 19, wherein the inflation element includes a
bladder, a plurality of expandable ribs extending axially over the
surface of the bladder, and a cover section formed of an
expandable, elastomeric material covering at least a portion of the
ribs, with at least the bladder having a pre-disposed expansion
profile.
21. The tool of claim 19, wherein the inflation element includes a
bladder, a plurality of expandable ribs extending axially over the
surface of the bladder, and a cover section formed of an
expandable, elastomeric material covering at least a portion of the
ribs, with at least the cover section having a pre-disposed
expansion profile.
22. The tool of claim 21, wherein the inflation element includes a
plurality of cover sections having pre-disposed expansion
profiles.
23. The tool of claim 19, wherein the inflation element has a
pre-disposed expansion profile formed by the steps of (a)
surrounding the inflation element with a vessel having an inner
diameter that defines a profiled limit for pre-disposing the
element, and (b) applying fluid under pressure to the inflation
element for expanding it into contact with the inner diameter of
the vessel and creating a pre-disposed expansion profile in the
element before running the inflation element downhole.
24. A vessel for providing a pre-disposed expansion profile in an
expandable, elastomeric component of a downhole tool, comprising:
(a) a vessel body shaped and dimensioned to surround at least a
portion of the expandable, elastomeric component; (b) the vessel
body including an inner diameter that defines a profiled limit in
which the component can be expanded for forming a pre-disposed
expansion profile in the component.
25. The vessel of claim 24, wherein the vessel body includes a
sleeve for surrounding the component and a pair of end caps for
insertion between the sleeve and component.
26. The vessel of claim 25, wherein the inner surface of the end
caps define a pair of truncated conical surfaces separated by a
cylindrical section.
27. The vessel of claim 25, wherein the inner surface of the end
caps defines a pair of truncated conical surfaces abutting each
other.
28. The vessel of claim 24, wherein the expandable, elastomeric
component comprises a bladder formed of an elastomeric
material.
29. The vessel of claim 24, wherein the expandable, elastomeric
component comprises expandable ribs covered at least in part by one
or more elastomeric cover sections.
30. The vessel of claim 24, wherein the expandable, elastomeric
component comprises a bladder formed of an elastomeric material, a
sheath formed of expandable ribs extending lengthwise along the
bladder and overlapping each other, and at least one elastomeric
cover section covering at least a portion of the ribs.
Description
FIELD OF THE INVENTION
[0001] This invention relates to inflation elements for use in
downhole well tools and, more particularly, to such an element and
a method and mold for making the bladder and/or cover portions of
such elements where the elastomeric material used to form the
bladder and/or cover is processed to impart improved performance
characteristics by pre-disposing directional properties via
stretching and expansion operations before the tool is run in
service.
BACKGROUND OF THE INVENTION
[0002] Downhole inflatable tools such as packers, bridge plugs and
the like, have been utilized in subterranean wells for many years.
Such tools normally include an inflation element that includes an
elastomeric bladder concentrically disposed around a central body
portion such as a tube or mandrel. A sheath of axially oriented
reinforcing slats or ribs is typically disposed around the bladder.
One or more elastomeric cover or seal sections are concentrically
disposed around at least a portion of the ribs. Reinforcing
structures other than slats and ribs are also common among such
tools. Fluid under pressure is introduced from the top of the well
or from the interior of the well bore into the central body and
through radial passages, or around the exterior body to the
interior of the bladder, to cause the bladder and, consequentially,
the element to expand. The subject invention is applicable to all
known downhole inflatable tools that include a bladder and/or one
or more covers.
[0003] Typically, the upper ends of the inflatable bladder and ribs
are secured relative to the body, while the lower ends of the
bladder and reinforcing sheath are secured to a seal which is
movable relative to the body. The movable seal responds to
inflation forces and allows the inflation element to expand without
causing damage to any of its component parts.
[0004] For inflation elements of this type, the exposed sections of
the reinforcing slats or ribs typically operate as anchor sections,
while the elastomeric cover elements typically operate as seals.
The anchor section(s) and cover element(s) expand until they engage
the wall of the well bore to isolate sections of the well bore on
opposite sides of the tool from each other.
[0005] Ideally, inflation elements should first expand in the
center and then uniformly propagate outwardly in both directions so
that fluid is not trapped between the outer surface of the element
and the well bore. In addition, the outward expansion should be
controlled to prevent relatively steep slopes from occurring in the
profile of the bladder during inflation. A steep slope in the
profile can cause the bladder to stretch in the axial direction and
result in unwanted conditions.
[0006] Axial stretching of the bladder during inflation can create
two deleterious conditions, 1) localized tri-axial strains in the
bladder and 2) pinching seals with related folds in the bladder.
Alone, either one of these conditions can cause bladder failure.
The presence of both conditions is almost certain to cause failure.
Failures occur because the physical properties of the elastomeric
material composing the bladder are not adequate to survive service
conditions, i.e., highly localized tri-axial strains, high fluid
pressure pressing the bladder against the edges of the ribs,
elevated temperatures, chemically active (sometimes aggressive)
inflation and treatment fluids, etc.
[0007] These problems are discussed in an article entitled "Design
and Testing of a High-Performance Inflatable Packer," D. M.
Eslinger and H. S. Kohli, SPE Pub. 37483 (1997). FIG. 3 of that
article is reproduced as FIG. 3 of the appended drawings to
illustrate the pinching and folding problem. Although several
solutions were suggested in the article, including the use of
specially developed elastomers, slats in the carcass with specific
structural features and software to aid in the design and execution
of specific jobs, the problems of folds and bladder failure still
remain.
[0008] Bladder failure was also discussed in my U.S. Pat. No.
5,495,892, which recognized conditions where the bladder tends to
pinch and form a seal on the mandrel (central body) during
inflation and obstruct the passage of pressurized fluid. The
obstruction problem was solved by providing a concentric tube
between the outside of the mandrel and the bladder to facilitate
fluid communication along the entire length of the bladder
regardless of the presence of pinching seals. However, the
concentric tube did not eliminate of the formation of folds and the
occurrence of other phenomena that cause bladder failures.
[0009] Three other patents of mine, U.S. Pat. Nos. 5,469,919,
5,564,504 and 5,813,459, also discuss pinching seals, bladder
folding, rib kinking, and rib cutting of the bladder. These patents
describe the use of structural elements along the length of the
bladder to cause relatively uniform expansion such that the ratio
of the largest diameter of the bladder to the smallest diameter
during inflation is always below a pre-determined maximum value.
However, although the designs in these patents resulted in elements
with more uniform expansion, they did not completely eliminate the
occurrence of folds, rib kinking, rib cutting or the occurrence of
high tri-axial strains in the bladder.
[0010] Another problem caused by folds is that they remain when the
bladder is deflated. This causes difficulty when the tool is to be
retrieved because the bladder cannot deflate to a size that is
equal to or smaller than its original run-in size and the tool
might not be retrievable. This problem would eliminate the use of
relatively low cost thru-tubing inflatable tools from a great many
service jobs, and possibly necessitate an expensive "rig job",
i.e., such as pulling tubing and requiring other expensive support
operations.
[0011] In addition, a pinching seal can cause an inflation element
to inflate only partially, leaving a significant portion of the
element not inflated. At the surface, the tool is thought to be
completely inflated and surface operations are continued. However,
the pinched seal loses its seal within minutes after inflation
operations are terminated. This results in loss of inflation
pressure, loss of seal between the inflation element and the well
bore, loss of anchor between the inflation element and the well
bore and failure of the well tool. This type of failure falls under
the general category of a "soft set failure".
SUMMARY OF THE INVENTION
[0012] The present invention is directed to a method for solving
the problems discussed above, a shaping tool or vessel for use in
the method, and a downhole tool with a bladder and/or cover
sections that are pre-disposed in accordance with the method, where
the bladder and/or cover sections have improved inflation
characteristics and their elastomeric components have improved
physical properties.
[0013] Pre-disposing elastomeric components means to better align
the long axes of the molecular chains of the elastomer in a
direction transverse to the long axis of the tool before the tool
is run downhole so that the inflation profiles of the inflation
element during inflation are improved and the physical properties
of the elastomeric material composing the bladder and/or covers are
improved and impart enhanced integrity of the bladder and/or covers
in service.
[0014] The preferred method of pre-disposing (i.e., stretching)
elastomeric components (bladders and covers) is by inflating the
components within a shaping tool or vessel having a deliberate
interior profile. The interior profile imparts different magnitudes
of expansion along the length of the elastomeric component.
Pre-disposing of an inflation element in an optimally designed
vessel will facilitate improved expansion profiles throughout
inflation of the well tool and will abate the formation of pinching
seals and folds in the inflation element. Additionally,
pre-disposing elastomeric components increases the tear resistance
of the elastomer and thereby, increases the tolerance of bladders
to rib kinking, rib cutting and folds.
[0015] When an elastomeric component such as a bladder or cover
section is stretched via inflation, its long molecular chains slide
over one another and tend to rotate and translate to become more
aligned with the direction of maximum principal strain, i.e., the
circumferential direction in the plane normal to the longitudinal
axis of the tool. When the component is unloaded (deflated) and
allowed to recover, the molecular chains tend to move back toward
their original spacial locations and orientations, but do not
return entirely back to their original spacial locations.
Generally, they return to an intermediate position somewhere
between their initial location and the location at the peak of
their stretch.
[0016] If the elastomeric component is stretched again in the same
fashion, the resistance to stretching is less than it was during
the first stretching because the molecular chains have already
traveled over the same route and their movement is relatively
unobstructed. Thus, it can be said that the first stretching
produces a pre-disposition in the elastomeric material toward
stretching it in the same direction and in the same fashion as had
previously been done. This means that the molecular chains in the
elastomeric material in their new pre-disposed locations have their
long axes more aligned with the direction of the maximum principal
strain, which is the direction of stretching.
[0017] Thus, when a bladder is inflated in diameter and there is no
change in its length, the maximum principal strain is in the
circumferential direction in the plane normal to its longitudinal
axis. A bladder can therefore be pre-disposed by inflating it in a
cylindrical mold. It can then be allowed to deflate and recover to
its original size and shape. It can then be installed in an
inflation element, or it could be pre-disposed after it is
installed in the element. It has been found that when a bladder is
pre-disposed in this manner the tear resistance is substantially
increased when compared with the tear resistance of a bladder that
is not predisposed.
[0018] Favorable alignment of the molecular chains are further
enhanced if the raw elastomer is processed by calendering it
through rollers before it is formed into a bladder or cover. This
procedure imparts a strong degree of molecular alignment in the
elastomer. This can be been done by forming the elastomer into a
thin elongated sheet, wrapping the sheet onto a cardboard mandrel
and then slicing the sheet into narrow ribbons approximately 3"-6"
wide. Calendering to acquire a ribbon form to produce a bladder is
well known to those skilled in the art. However, calendering to
acquire molecular alignment and enhanced physical properties is
believed not to be known.
[0019] Calendering aligns the long axes of the molecular chains
with the long axis of the ribbon before forming it into a bladder.
The calendered ribbon is then wrapped onto a mandrel so that the
long axis of the ribbon is aligned circumferentially around the
bladder or cover, that is, the longitudinal axis of the bladder or
cover is transverse to the long axes of the molecular chains.
[0020] Pre-disposition of elastomeric components and/or
sub-assemblies such as inflation elements can be accomplished by
surrounding the component and/or element with a tool having an
inner diameter that defines a profiled expansion limit. Fluid is
then supplied under pressure for expanding the component and/or
element into contact with the inner diameter to impart the
pre-disposition. The component is then deflated so it returns
generally to its original shape. A component and/or element can be
subjected to multiple inflation/deflation cycles.
[0021] Because elastomers are inelastic in nature, the component
and/or element is kept inflated for a predetermined lapse of time
to allow the time-dependent response of the molecular chains to be
fully realized. Correspondingly, the magnitude of the stretching,
the rate of stretching, the inside contour of the shaping tool,
dwell times, the temperature at which the stretching process is
performed and the number of stretching cycles performed on a
component are all inter-related and can effect the magnitude of
pre-disposition and enhancement.
[0022] In one embodiment, the shaping tool includes a sleeve that
is concentrically positioned to surround the expandable component.
The inner diameter of the shaping tool is formed by inserting a
pair of structural parts called end caps between the component(s)
and sleeve. The end caps define a smooth tapering surface that
decreases in diameter from near the center of the tool toward both
ends.
[0023] Preferably, the inner diameter of the tool has a cylindrical
section in the middle, with truncated conical sections at both
ends. However, if the expandable component is designed so that it
tends to expand initially at the upper end, the truncated conical
section at the upper end can be shorter than the one at the lower
end, with the cylindrical center section being located closer to
the upper end of the shaping tool. The tool can be customized in
other ways to impart favorable pre-disposed properties in
components having unique physical shapes.
[0024] In another embodiment, the cylindrical center section is
eliminated, with the inner diameter of the tool being formed of a
pair of abutting truncated conical sections with their bases in
contact with each other. Other suitable shapes can be used,
depending on the pre-disposed profile desired.
[0025] This pre-disposition is preferably done at ambient
temperature before the downhole tool is run in the well bore.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] A better understanding of the invention can be obtained when
a detailed description of preferred embodiments set forth below is
considered in conjunction with the appended drawings, in which:
[0027] FIG. 1 is a plan view, partially in section, of an inflation
element of a downhole tool which has an exposed rib anchor section
and elastomeric cover elements on both sides of the exposed
ribs;
[0028] FIG. 2 is a sectional view of a portion of the element shown
in FIG. 1, which shows the relationship of the bladder to the ribs
and cover section;
[0029] FIG. 3 is an illustrative schematic view of a bladder being
pinched to illustrate the problem solved by the invention;
[0030] FIG. 4 is a schematic view of a thin strip of elastomeric
material being wrapped onto a mandrel to form a bladder or cover
section;
[0031] FIG. 5 is a schematic view, partially in section, of a
bladder or cover section formed as shown in FIG. 4, being cured in
an oven;
[0032] FIG. 6 is a plan view, partially in section, showing a
bladder or cover section being predisposed in one embodiment of a
shaping tool or vessel;
[0033] FIG. 7 is a plan view, partially in section, showing a
bladder or cover section being predisposed in another embodiment of
a shaping tool; and
[0034] FIG. 8 is a plan view, partially in section, of an inflation
element of the type shown in FIGS. 1 and 2 being pre-disposed in a
shaping tool of the type shown in FIG. 6.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0035] The details and advantages of the invention will be
understood from the following detailed description. The invention
generally relates to improved expandable, elastomeric components
for an inflation element of a downhole tool, such as bladders and
cover sections, which have pre-disposed expansion profiles and
enhanced physical properties, and a method for pre-disposing the
expansion profiles of such components, and a shaping tool or vessel
for use in the method.
[0036] Before describing preferred embodiments of the invention in
detail, reference should be had to FIGS. 1 and 2, which illustrate
a known type of inflation element 10, to which the invention can be
applied. However, the invention can be applied to inflation
elements having a wide variety of shapes and sizes that are
different from those exhibited in FIGS. 1 and 2. The inflation
element 10 can used in tools such as a packer, bridge plug, tubing
hanger, cement retainer, or the like, depending upon the desired
application.
[0037] The inflation element 10 includes upper and lower end
collars 12, 14, respectively. A bladder 16, formed of an
expandable, elastomeric material, extends between the end collars
12, 14. The bladder 16 is expanded and contracted through the
introduction and withdrawal of pressurized fluid in a way that is
well known.
[0038] The bladder 16 is surrounded by and secured to a reinforcing
sheath formed of a plurality of longitudinally extending slats or
ribs 18, which are also well known. Each of the ribs 18 overlaps
the next adjacent rib when the bladder 16 is deflated. Each rib
also adequately overlaps the next adjacent rib when the bladder 16
is inflated forming a protective structural sheath over the bladder
16. Exposed sections of the ribs 18 also operate to anchor the tool
in a well bore.
[0039] The ends of the bladder 16 are held in place in the end
collars 12, 14, by means of a grip ring 20. Referring to the upper
end of the inflation element 10, the ends of the ribs 18 are held
between the bladder 16 and an extension transition sleeve 24, which
is part of the end collar 12. Typically, when the bladder 16
expands the lower end connection is configured to move relative to
the tool on which the inflation element 10 is mounted so that the
bladder 16 and ribs 18 expand outwardly without fear of being
damaged.
[0040] The inflation element 10 includes an exposed rib section 26
and cover sections 28, 30, formed of expandable, elastomeric
material, mounted on the ribs 18. The cover sections 28, 30, extend
between the exposed rib section 26 and the end collars 12, 14,
respectively. The inflation element 10 can include one or more
exposed rib sections along its length, or even be formed with no
exposed rib sections where the ribs 18 are totally covered by an
elastomeric cover.
[0041] In the embodiment of the tool 10 shown in FIG. 1, the
elastomeric cover sections 28, 30, have a uniform diameter and
thickness along their length. However, in other embodiments the
cover sections can be profiled in that they are formed of varying
thicknesses, or they can be shaped in other ways, to influence the
expansion characteristics of the inflation element.
[0042] One of the problems encountered by an inflation element 10
when it is expanded downhole is caused by localized tri-axial
strains in the bladder, which is illustrated in FIG. 3 of the
Eslinger and Kohli article cited above, reproduced as FIG. 3 of the
drawings. In that drawing, the inflation element 32 has been
expanded inside a well casing WC. The inflation element 32 includes
a bladder 34 and overlapping ribs 36 extending between end collars
38 and 40. In this embodiment of an inflation element, a single
elastomeric cover section 42 is mounted on the ribs 36. As the
bladder 34 expands, a portion 44 of the bladder 34 folds and is
pinched against a mandrel 46 that extends through the center of the
element 32. As discussed above, this pinching problem can cause
bladder failure and prevent the element 32 from decompressing when
the bladder is deflated.
[0043] This and other problems discussed above have been solved by
pre-disposing the bladder 34 prior to inflation for aligning the
long axis of the molecular chains that make up the elastomer from
which the bladder is formed, as discussed above. One aspect of
pre-disposing the bladder includes the process of forming the
bladder.
[0044] One way bladders have been formed in the prior art is by
extruding the elastomer used to form the bladder into a shape
suitable for the bladder. This method has proved to be
unsatisfactory in forming a bladder that is resistant to tearing
because the molecular chains of the elastomer are aligned with the
long axis of the inflation element. As discussed above, the chains
are not aligned in the direction of principal strain, which results
in a bladder that is less resistant to the propagation of tears in
the longitudinal direction of the bladder. Thus, the bladder should
be formed by wrapping strips of elastomer around a mandrel that is
either cylindrical or shaped in way that influences the inflation
profile of the bladder.
[0045] However, before the bladder is formed, the elastomer is
preferably calendered in a known way in order to improve the
directional tear strength of the elastomer. The calendered
elastomer is preferably formed into strips that are 4" wide and
from 0.40"-0.50" thick, but other thicknesses can be used. Although
there are many suitable elastomers, a nitrile polymer (NBR) is
preferable.
[0046] The preferred method for forming a bladder or cover section
is shown in FIG. 4, where a strip 62 of the elastomer 50 is wrapped
onto a mandrel 64 in the direction of arrow A. The strip should be
wrapped in a spiral so that it will overlap about 50% of the
portion of the strip that is already wrapped. The strip 63 is
wrapped back-and-forth along the mandrel 64 in this manner until a
suitable thickness is achieved. This can be done with four or more
layers of the elastomer wrapped on the mandrel 64. The elastomer is
then cured in an autoclave 66, shown schematically in FIG. 5, in a
known way. After it is cured, the elastomeric component 68 is
removed from the mandrel 64 (not shown).
[0047] In order to further pre-dispose the component 68, it is
mounted on a holding tool 70 and connected to a source of
pressurized fluid (not shown). The expandable elastomeric component
68 is then inserted into and held in place in a shaping tool or
vessel 72. The tool shown in FIG. 6 includes a cylindrical sleeve
73 and a pair of end caps 74, 76, which are locked in place by any
suitable type of holding or clamping mechanism. The inner surfaces
of the sleeve 73 and the end caps 74, 76, define the profiled
expansion limit for the component 68 when fluid is introduced into
the component and it is expanded in the direction of arrows 78a and
78b as shown by the dotted lines in FIG. 7. The fluid can be
applied either continuously or intermittently. The expansion
profile in the vessel 72 is generally defined by the shape of the
component when it is expanded downhole, but other shapes and
configurations can be used to advantage for pre-disposing the
component.68.
[0048] An alternative expansion profile is shown in FIG. 7, where
the vessel 72 does not have a center cylindrical sleeve as shown in
FIG. 6, but has the form of two truncated conical sections abutting
each other as defined by the inner surfaces of the end caps 74, 76.
The pre-disposed expansion profile is defined by the inner surfaces
of the end caps 74, 76, as shown in FIG. 7.
[0049] By pre-disposing the bladder as shown, the elastomer from
which the bladder is formed is strengthened and will tend to expand
without creating folds of the type shown in FIG. 3. This, in turn,
will increase the service reliability of the tool by preventing
uneven expansion and the problems discussed above. Alternatively,
cover sections could be pre-disposed in a similar manner with a
desired profile before they are installed onto an inflation
element.
[0050] An alternative way for pre-disposing both the bladder and
the elastomeric cover sections for an inflation elements is shown
in FIG. 8 where the inflation element 10 of FIGS. 1 and 2 has been
inserted in a vessel 72 of the type shown in FIG. 6. The tool 10 is
expanded in the direction of arrows 78a, 78b, to where it achieves
the expansion profile shown by the dotted lines in FIG. 8. By
expanding the tool 10 in this manner, both the bladder (not shown)
and the expandable cover section 28, 30, will be pre-disposed in
the manner described above. The tool 10 can then be deflated, and
run downhole to be expanded as part of its normal operation. In
this way, by expanding the cover sections 28, 30, a more
predictable expansion profile and a reduced departure angle as the
tool expands will be provided. This has been found to have the
unexpected results of preventing bending or kinking in the exposed
rigs, and reducing the possibility of the bladder catching between
the kink rigs and being cut.
[0051] Thus, a method has been provided in accordance with the
invention, and a shaping tool or vessel formed in accordance with
the method, where the expansion profile of a downhole inflation
element is pre-disposed. This pre-disposition, as discussed above,
tends to make the bladder more resistant against folding and
pinching, as well as providing a more uniform expansion along the
length of the inflation element for enhanced performance.
[0052] Although the invention has been described in terms of
preferred embodiments as set forth above, it should be understood
that these embodiments are illustrative only and that the claims
are not limited to those embodiments. Those skilled in the art will
be able to make modifications and alternatives in view of the
disclosure which are contemplated as not departing from the spirit
of the described invention and falling within the scope of the
appended claims.
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