Note: Descriptions are shown in the official language in which they were submitted.
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1 UNIVERSAL BACKUP FOR SWELLABLE PACKERS
2
3 FIELD OF THE INVENTION
4 Embodiments of the invention relate to the field of downhole
apparatus, and in particular to downhole apparatus for use with swellable
materials.
6
7 BACKGROUND OF THE INVENTION
8 In the field of hydrocarbon exploration and production, various tools
9 are used to provide fluid seals between two components in a wellbore.
Annular
barriers have been designed for preventing undesirable flow of wellbore fluids
in the
11 annulus between a welibore tubular and the inner surface of a surrounding
tubular
12 or the borehole wall. In many cases, the annular barriers provide a fluid
seal
13 capable of holding a significant pressure differential across its length.
In one
14 application, a wellbore packer is formed on the outer surface of a
completion string
that is run into an outer casing in a first condition having a particular
outer diameter.
16 When the packer is in its desired downhole location, it is inflated or
expanded into
17 contact with the inner surface of the outer casing to create a seal in the
annulus.
18 Similar wellbore packers have been designed for use in openhole
environments, to
19 create a seal between a tubular and the surrounding wall of the welibore.
Conventional packers are actuated by mechanical or hydraulic
21 systems. A force or pressure is applied from the wellhead to move a
mechanical
22 packer element radially into contact with the surrounding surface. In an
inflatable
23 packer, fluid is delivered from the wellhead to inflate a chamber defined
by a
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1 bladder around the tubular body.
2 More recently, wellbore packers have been developed which include a
3 mantle of swellable material formed around the tubular. The swellable
material is
4 selected to increase in volume on exposure to at least one predetermined
fluid,
which may be a hydrocarbon fluid or an aqueous fluid or brine. The swellable
6 packer may be run to a downhole location in its unexpanded state, where it
is
7 exposed to a wellbore fluid and caused to increase in volume. The design,
8 dimensions, and swelling characteristics are selected such that the
swellable packer
9 element expands to create a fluid seal in the annulus to isolate one
wellbore section
from another. Swellable packers have several advantages over conventional
11 packers, including passive actuation, simplicity of construction, and
robustness in
12 long-term isolation applications.
13 In addition, swellable packers may be designed for compliant
14 expansion of the swellable mantle into contact with a surrounding surface,
such that
the force imparted on the surface prevents damage to a rock formation or
sandface,
16 while still creating an annular barrier or seal. Swellable packers
therefore lend
17 themselves well to openhole completions in loose or weak formations.
18 The materials selected to form a swellable element in a swellable
19 packer vary depending on the specific application. Swellable materials are
elastomeric (i.e. they display mechanical and physical properties of an
elastomer or
21 natural rubber). Where the swellable mantle is designed to swell in
hydrocarbons, it
22 may comprise a material such as an ethylene propylene diene monomer (EPDM)
23 rubber. Where the swellable mantle is required to swell in aqueous fluids
or brines,
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1 the material for example may comprise an N-vinyl carboxylic acid amide-based
2 cross-linked resin and a water swellable urethane in an ethylene propylene
rubber
3 matrix. In addition, swellable elastomeric materials may be designed to
increase in
4 volume in both hydrocarbon fluids and aqueous fluids.
Expandable metal backups are used to prevent extrusion on swellable
6 packer elements. Since the swellable elements are manufactured using a
variety of
7 materials designed to swell in oil, water, or both, there is a need to
develop these
8 backup systems for each of the various elastomers. This also requires
9 manufacturing to stock the various types of back-up units, which adds extra
cost to
the manufacturing process and creates a situation where mistakes can be made
11 and the wrong type of back up assembled onto packers.
12
13 SUMMARY OF THE INVENTION
14 In one embodiment, an apparatus for use with a downhole tool having
a swellable element is disclosed. The apparatus comprises an attachment
portion,
16 configured for attachment of the apparatus to the downhole tool; a ring
portion,
17 connected to the attachment portion, having an expanded condition and an
18 unexpanded condition; and an elastomer portion, disposed radially inwardly
of the
19 ring portion, composed of a first elastomer selected to expand upon
exposure to
both aqueous solutions and hydrocarbons, wherein expansion of the elastomer
21 portion upon exposure to an aqueous solution or a hydrocarbon urges the
ring
22 portion radially outwardly from the unexpanded condition to the expanded
condition.
23 In another embodiment, a downhole tool is disclosed. The downhole
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1 tool comprises a body; a swellable element, disposed about the body,
composed of
2 a first elastomer selected to expand upon exposure to a predetermined
wellbore
3 fluid; a backup unit, disposed about the body at an end of the swellable
element.
4 The backup unit comprises an attachment portion, attached to the body; a
ring
portion, connected to the attachment portion, having an expanded condition and
an
6 unexpanded condition; and an elastomer portion, disposed between the ring
portion
7 and the body, composed of a second elastomer selected to expand upon
exposure
8 to both aqueous solutions and hydrocarbons regardless of the predetermined
9 wellbore fluid, wherein expansion of the elastomer portion urges the ring
portion
radially outwardly from the unexpanded condition to the expanded condition.
11 In yet another embodiment, a method for assembling a downhole tool
12 is disclosed. The method comprises selecting a swellable element for a
downhole
13 tool responsive to a fluid in a wellbore; disposing the swellable element
on a body
14 member of the downhole tool; disposing a backup unit on the body member
adjacent an end of the swellable element, and attaching the universal backup
unit to
16 the body, where the backup unit comprises a ring portion having an expanded
17 condition and an unexpanded condition; and an elastomer portion, disposed
18 between the ring portion and the body, composed of a second elastomer
selected
19 without regard to the fluid in the wellbore.
21 BRIEF DESCRIPTION OF DRAWINGS
22 Figure 1 is a cutaway view of a downhole tool according to one
23 embodiment.
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1 DESCRIPTION OF EMBODIMENTS OF THE INVENTION
2 In the following description, for purposes of explanation, numerous
3 specific details are set forth in order to provide a thorough understanding
of the
4 invention. It will be apparent, however, to one skilled in the art that the
invention
may be practiced without these specific details. In other instances, structure
and
6 devices are shown in block diagram form in order to avoid obscuring the
invention.
7 References to numbers without subscripts or suffixes are understood to
reference
8 all instance of subscripts and suffixes corresponding to the referenced
number.
9 Moreover, the language used in this disclosure has been principally selected
for
readability and instructional purposes, and may not have been selected to
delineate
11 or circumscribe the inventive subject matter, resort to the claims being
necessary to
12 determine such inventive subject matter. Reference in the specification to
"one
13 embodiment" or to "an embodiment" means that a particular feature,
structure, or
14 characteristic described in connection with the embodiments is included in
at least
one embodiment of the invention, and multiple references to "one embodiment"
or
16 "an embodiment" should not be understood as necessarily all referring to
the same
17 embodiment.
18 FIG. 1 is a cutaway view of a portion of a swellable packer 100
19 according to one embodiment. Some common features of the swellable packer
known to the art are omitted for clarity of the drawing. The swellable packer
100
21 comprises a central body 110, such as a tubular or mandrel, about which is
22 disposed a swellable elastomer mantle 120. The swellable mantle 120 may be
23 formed of one or more sections as desired, using any known technique for
forming
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1 a swellable mantle about a central body. In one embodiment, the swellable
mantle
2 120 may be bonded or otherwise attached to the body 110. In one embodiment,
the
3 swellable mantle 120 is formed of an elastomer designed to swell when
exposed to
4 an aqueous solution such as water or brine. In another embodiment, the
swellable
mantle 120 is formed of an elastomer designed to swell when exposed to a
6 hydrocarbon fluid. In yet another embodiment, the swellable mantle is formed
of a
7 hybrid elastomer that is designed to swell when exposed to either an aqueous
8 solution or a hydrocarbon fluid.
9 Upon insertion into the well, the elastomer of the mantle 120 swells
upon exposure to the fluid surrounding the packer 100 in the wellbore. As the
11 elastomer of the mantle 120 swells, it expands radially outwardly, engaging
a
12 surrounding casing or open hole wellbore (not shown in FIG. 1) sealing the
packer
13 100 to the casing or wellbore. The elastomer of the mantle 120 may also
swell
14 axially, and if not prevented from doing so, may extrude axially around the
other
elements disposed at the ends of the mantle 120, reducing the pressure that is
16 exerted by the expanded mantle 120 on the surrounding casing or wellbore.
17 To prevent this extrusion, backup unit 160 is disposed at least one end
18 of the mantle 120, according to one embodiment. Although only one end of
the
19 swellable mantle 120 is illustrated in FIG. 1, similar elements may be
disposed at
both ends of the mantle 120.
21 In one embodiment, the backup unit 160 comprises three elements:
22 an attachment portion 150, designed for attaching the backup unit 160 to
the body
23 110, a backup ring portion 140, typically made of metal, and an elastomer
backup
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1 element 130. Axial pressure on the elastomer backup element 130 urges the
2 backup portion 140 of the backup unit 160 radially outwardly, while the
attachment
3 portion 150, secured to the body 110, presents axial or rotational movement
of the
4 backup unit 160 relative to the body 110. The backup element 130 also exerts
force
on the mantle 120, contributing to the prevention of axial extrusion of the
mantle
6 120.
7 In addition to force generated by the axial expansion of the mantle
8 120, in one embodiment, the elastomer backup element 130 is also formed of a
9 swellable material. Although the elastomer forming the mantle 120 is
typically
selected based on the types of fluids found in the well, the elastomer backup
11 element 130 is formed of a hybrid swellable material that is selected for
expansion
12 on exposure to both aqueous solutions and hydrocarbon fluids. Thus, the
same
13 backup unit 160 may be used regardless of the composition of the mantle
120, in
14 wells with any type of wellbore fluid suitable for a downhole tool with a
swellable
member.
16 Such hybrid elastomers are known to the art, but have not previously
17 been used for constructing the backup elastomer element 130. For example,
one
18 type of hybrid swellable elastomer is an elastomeric matrix material such
as EPDM,
19 impregnated with super absorbent polymer (SAP) particles. The SAPs have
hydrophilic characteristics. In another example, the hybrid swellable
elastomer
21 comprises the reaction product of linear or branched polymers having
residual
22 ethylenic unsaturation with an unsaturated organic monomer having at least
one
23 reactive moiety. Other examples of hybrid swellable elastomers are known
and may
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1 be used.
2 By using a hybrid elastomer as the elastomer backup element 130,
3 regardless of the wellbore fluid, instead of one designed specifically for
aqueous
4 solutions or hydrocarbon fluids, a universal backup unit may be manufactured
and
used on packers intended for use in the presence of either type of fluid, thus
6 reducing manufacturing and inventory costs, as well as reducing the risk
that a
7 packer 100 may be assembled with a backup unit 160 that is designed for the
8 wrong type of solution.
9 As the packer 100 is exposed to wellbore fluids, expansion of the
backup elastomer 130 resists axial expansion of the mantle 120, and also
swells
11 radially outwardly, causing the backup ring portion 140 to deform and
expand
12 radially outwardly, further preventing extrusion of the mantle 120 axially.
13 In some embodiments, the backup ring portion 140 is a solid unit. In
14 other embodiments, the backup ring portion 140 may be divided into a
plurality of
sections or fingers that separate as the mantle 120 and backup elastomer 130
swell
16 and expand. Multiple layers of fingers may be provided in some embodiments,
17 disposed so that expansion of the layers of fingers maintains an overlap,
preventing
18 extrusion of the elastomer of the mantle 120 between adjacent fingers of
the backup
19 ring portion.
Although the above description is written in terms of a packer, the
21 universal backup unit 160 may be used in other downhole tools that
incorporate
22 swellable members.
23 It is to be understood that the above description is intended to be
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1 illustrative, and not restrictive. For example, the above-described
embodiments may
2 be used in combination with each other. Many other embodiments will be
apparent
3 to those of skill in the art upon reviewing the above description. The scope
of the
4 invention therefore should be determined with reference to the appended
claims,
along with the full scope of equivalents to which such claims are entitled. In
the
6 appended claims, the terms "including" and "in which" are used as the plain-
English
7 equivalents of the respective terms "comprising" and "wherein."
8
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