HIGH STRENGTH DISSOLVABLE STRUCTURES FOR USE IN A
SUBTERRANEAN WELL
TECHNICAL FIELD
This disclosure relates generally to equipment utilized
and operations performed in conjunction with a subterranean
well and, in an example described below, more particularly
provides high strength dissolvable structures for use in a
subterranean well.
BACKGROUND
It is frequently useful to actuate, or otherwise
activate or change a configuration of, a well tool in a
well. For example, it is beneficial to be able to open or
close a valve in a well, or at least to be able to permit or
prevent flow through a flow path, when desired.
The present inventors have developed methods and
devices whereby high strength dissolvable structures may be
used for accomplishing these purposes and others.
SUMMARY
In the disclosure below, well tools and associated
methods are provided which bring advancements to the art.
One example is described below in which a high strength
structure formed of a solid mass comprising an anhydrous
boron compound is used in a well tool. Another example is
described below in which the structure comprises a flow
blocking device in the well tool.
In one aspect, this disclosure provides to the art a
unique well tool. The well tool can include a flow path,
and a flow blocking device which selectively prevents flow
through the flow path. The device includes an anhydrous
boron compound.
In another aspect, a method of constructing a downhole
well tool is provided by this disclosure. The method can
include: forming a structure of a solid mass comprising an
anhydrous boron compound; and incorporating the structure
into the well tool.
These and other features, advantages and benefits will
become apparent to one of ordinary skill in the art upon
careful consideration of the detailed description of
representative examples below and the accompanying drawings,
in which similar elements are indicated in the various
figures using the same reference numbers.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic partially cross-sectional view of
a well system and associated method embodying principles of
the present disclosure.
FIGS. 2A & B are enlarged scale schematic crosssectional
views of a well tool which may be used in the
system and method of FIG. 1 , the well tool blocking flow
through a flow path in FIG. 2A, and permitting flow through
the flow path in FIG. 2B.
FIG. 3 is a schematic cross-sectional view of another
well tool which may be used in the system and method of FIG.
1 .
FIGS. 4A & B are enlarged scale schematic crosssectional
views of another well tool which may be used in
the system and method of FIG. 1 , the well tool blocking flow
through a flow path in FIG. 4A, and permitting flow through
the flow path in FIG. 4B.
FIG. 5 is a schematic cross-sectional view of another
well tool which may be used in the system and method of FIG.
1 .
FIG. 6 is a schematic cross-sectional view of another
configuration of the well tool of FIG. 5 .
DETAILED DESCRIPTION
Representatively illustrated in FIG. 1 is a well system
10 and associated method which embody principles of this
disclosure. In the system 10, various well tools 12a-e are
interconnected in a tubular string 14 installed in a
wellbore 16. A liner or casing 18 lines the wellbore 16 and
is perforated to permit fluid to be produced into the
wellbore .
At this point, it should be noted that the well system
10 and associated method are merely one example of a wide
variety of systems and methods which can incorporate the
principles of this disclosure. In other examples, the
wellbore 18 may not be cased, or if cased it may not be
perforated. In further examples, the well tools 12a-e, or
any of them, could be interconnected in the casing 18. In
still further examples, other types of well tools may be
used, and/or the well tools may not be interconnected in any
tubular string. In other examples, fluid may not be
produced into the wellbore 18, but may instead be flowed out
of, or along, the wellbore. It should be clearly
understood, therefore, that the principles of this
disclosure are not limited at all by any of the details of
the system 10, the method or the well tools 12a-e described
herein .
The well tool 12a is representatively a valve which
selectively permits and prevents fluid flow between an
interior and an exterior of the tubular string 14. For
example, the well tool 12a may be of the type known to those
skilled in the art as a circulation valve.
The well tool 12b is representatively a packer which
selectively isolates one portion of an annulus 20 from
another portion. The annulus 20 is formed radially between
the tubular string 14 and the casing 18 (or a wall of the
wellbore 16 if it is uncased) .
The well tool 12c is representatively a valve which
selectively permits and prevents fluid flow through an
interior longitudinal flow path of the tubular string 14.
Such a valve may be used to allow pressure to be applied to
the tubular string 14 above the valve in order to set the
packer (well tool 12b), or such a valve may be used to
prevent loss of fluids to a formation 22 surrounding the
wellbore 16.
The well tool 12d is representatively a well screen
assembly which filters fluid produced from the formation 22
into the tubular string 14. Such a well screen assembly can
include various features including, but not limited to,
valves, inflow control devices, water or gas exclusion
devices, etc.
The well tool 12e is representatively a bridge plug
which selectively prevents fluid flow through the interior
longitudinal flow path of the tubular string. Such a bridge
plug may be used to isolate one zone from another during
completion or stimulation operations, etc.
Note that the well tools 12a-e are described herein as
merely a few examples of different types of well tools which
can benefit from the principles of this disclosure. Any
other types of well tools (such as testing tools,
perforating tools, completion tools, drilling tools, logging
tools, treating tools, etc.) may incorporate the principles
of this disclosure.
Each of the well tools 12a-e may be actuated, or
otherwise activated or caused to change configuration, by
means of a high strength dissolvable structure thereof. For
example, the circulation valve well tool 12a could open or
close in response to dissolving of a structure therein. As
another example, the packer well tool 12b could be set or
unset in response to dissolving of a structure therein.
In one unique aspect of the system 10, the high
strength dissolvable structure comprises an anhydrous boron
compound. Such anhydrous boron compounds include, but are
not limited to, anhydrous boric oxide and anhydrous sodium
borate.
Preferably, the anhydrous boron compound is initially
provided as a granular material. As used herein, the term
"granular" includes, but is not limited to, powdered and
other fine-grained materials.
As an example, the granular material comprising the
anhydrous boron compound is preferably placed in a graphite
crucible, the crucible is placed in a furnace, and the
material is heated to approximately 1000 degrees Celsius.
The material is maintained at approximately 1000 degrees
Celsius for about an hour, after which the material is
allowed to slowly cool to ambient temperature with the
furnace heat turned off.
As a result, the material becomes a solid mass
comprising the anhydrous boron compound. This solid mass
may then be readily machined, cut, abraded or otherwise
formed as needed to define a final shape of the structure to
be incorporated into a well tool.
Alternatively, the heated material may be molded prior
to cooling (e.g., by placing the material in a mold before
or after heating) . After cooling, the solid mass may be in
its final shape, or further shaping (e.g., by machining,
cutting abrading, etc.) may be used to achieve the final
shape of the structure.
Such a solid mass (and resulting structure) comprising
the anhydrous boron compound will preferably have a
compressive strength of about 165 MPa, a Young's modulus of
about 6.09E+04 MPa, a Poisson's ratio of about 0.264, and a
melting point of about 742 degrees Celsius. This compares
favorably with common aluminum alloys, but the anhydrous
boron compound additionally has the desirable property of
being dissolvable in an aqueous fluid.
For example, a structure formed of a solid mass of an
anhydrous boron compound can be dissolved in water in a
matter of hours (e.g., 8-10 hours). Note that a structure
formed of a solid mass can have voids therein and still be
"solid" (i.e., rigid and retaining a consistent shape and
volume, as opposed to a flowable material, such as a liquid,
gas, granular or particulate material).
If it is desired to delay the dissolving of the
structure, a barrier (such as, a glaze, coating, etc.) can
be provided to delay or temporarily prevent hydrating of the
structure due to exposure of the structure to aqueous fluid
in the well.
One suitable coating which dissolves in aqueous fluid
at a slower rate than the anhydrous boron compound is
polylactic acid. A thickness of the coating can be selected
to provide a predetermined delay time prior to exposure of
the anhydrous boron compound to the aqueous fluid.
Other suitable degradable barriers include
hydrolytically degradable materials, such as hydrolytically
degradable monomers, oligomers and polymers, and/or mixtures
of these. Other suitable hydrolytically degradable materials
include insoluble esters that are not polymerizable . Such
esters include formates, acetates, benzoate esters,
phthalate esters, and the like. Blends of any of these also
may be suitable.
For instance, polymer /polymer blends or monomer /polymer
blends may be suitable. Such blends may be useful to affect
the intrinsic degradation rate of the hydrolytically
degradable material. These suitable hydrolytically
degradable materials also may be blended with suitable
fillers (e.g., particulate or fibrous fillers to increase
modulus), if desired.
In choosing the appropriate hydrolytically degradable
material, one should consider the degradation products that
will result. Also, these degradation products should not
adversely affect other operations or components.
The choice of hydrolytically degradable material also
can depend, at least in part, on the conditions of the well,
e.g., well bore temperature. For instance, lactides may be
suitable for use in lower temperature wells, including those
within the range of 15 to 65 degrees Celsius, and
polylactides may be suitable for use in well bore
temperatures above this range.
The degradability of a polymer depends at least in part
on its backbone structure. The rates at which such polymers
degrade are dependent on the type of repetitive unit,
composition, sequence, length, molecular geometry, molecular
weight, morphology (e.g., crystallinity , size of spherulites
and orientation), hydrophilicity , hydrophobicity , surface
area and additives. Also, the environment to which the
polymer is subjected may affect how it degrades, e.g.,
temperature, amount of water, oxygen, microorganisms,
enzymes, pH and the like.
Some suitable hydrolytically degradable monomers
include lactide, lactones, glycolides, anhydrides and
lactams .
Some suitable examples of hydrolytically degradable
polymers that may be used include, but are not limited to,
those described in the publication of Advances in Polymer
Science, Vol. 157 entitled "Degradable Aliphatic Polyesters"
edited by A . C . Albertsson. Specific examples include
homopolymers , random, block, graft, and star- and hyperbranched
aliphatic polyesters.
Such suitable polymers may be prepared by
polycondensation reactions, ring-opening polymerizations,
free radical polymerizations, anionic polymerizations,
carbocationic polymerizations, and coordinative ring-opening
polymerization for, e.g., lactones, and any other suitable
process. Specific examples of suitable polymers include
polysaccharides such as dextran or cellulose; chitin;
chitosan; proteins; aliphatic polyesters; poly (lactides );
poly (glycolides ); poly (e-caprolactones );
poly (hydroxybutyrates ); aliphatic polycarbonates;
poly (orthoesters ); poly (amides ); poly (urethanes );
poly (hydroxy ester ethers); poly (anhydrides ); aliphatic
polycarbonates; poly (orthoesters ); poly(amino acids);
poly (ethylene oxide); and polyphosphazenes .
Of these suitable polymers, aliphatic polyesters and
polyanhydrides may be preferred. Of the suitable aliphatic
polyesters, poly (lactide) and poly (glycolide) , or copolymers
of lactide and glycolide, may be preferred.
The lactide monomer exists generally in three different
forms: two stereoisomers L- and D-lactide and racemic D,Llactide
(meso-lactide ). The chirality of lactide units
provides a means to adjust, among other things, degradation
rates, as well as physical and mechanical properties.
Poly (L-lactide) , for instance, is a semi-crystalline
polymer with a relatively slow hydrolysis rate. This could
be desirable in applications where a slower degradation of
the hydrolytically degradable material is desired.
Poly (D, L-lactide) may be a more amorphous polymer with
a resultant faster hydrolysis rate. This may be suitable for
other applications where a more rapid degradation may be
appropriate .
The stereoisomers of lactic acid may be used
individually or combined. Additionally, they may be
copolymerized with, for example, glycolide or other monomers
like e-caprolactone , 1,5-dioxepan-2-one, trimethylene
carbonate, or other suitable monomers to obtain polymers
with different properties or degradation times.
Additionally, the lactic acid stereoisomers can be modified
by blending high and low molecular weight poly (lactide ) or
by blending poly (lactide ) with other polyesters.
Plasticizers may be present in the hydrolytically
degradable materials, if desired. Suitable plasticizers
include, but are not limited to, derivatives of oligomeric
lactic acid, polyethylene glycol; polyethylene oxide;
oligomeric lactic acid; citrate esters (such as tributyl
citrate oligomers, triethyl citrate, acetyltributyl citrate,
acetyltriethyl citrate); glucose monoesters; partially fatty
acid esters; PEG monolaurate; triacetin; poly(ecaprolactone
); poly (hydroxybutyrate) ; glycerin-l-benzoate-
2,3-dilaurate ; glycerin-2-benzoate-l ,3-dilaurate ; starch;
bis (butyl diethylene glycol )adipate ; ethylphthalylethyl
glycolate; glycerine diacetate monocaprylate; diacetyl
monoacyl glycerol; polypropylene glycol (and epoxy,
derivatives thereof); poly (propylene glycol )dibenzoate,
dipropylene glycol dibenzoate; glycerol; ethyl phthalyl
ethyl glycolate; poly (ethylene adipate )distearate ; di-isobutyl
adipate; and combinations thereof.
The physical properties of hydrolytically degradable
polymers depend on several factors such as the composition
of the repeat units, flexibility of the chain, presence of
polar groups, molecular mass, degree of branching,
crystallinity, orientation, etc. For example, short chain
branches reduce the degree of crystallinity of polymers
while long chain branches lower the melt viscosity and
impart, among other things, elongational viscosity with
tension-stiffening behavior.
The properties of the material utilized can be further
tailored by blending, and copolymerizing it with another
polymer, or by a change in the macromolecular architecture
(e.g., hyper-branched polymers, star-shaped, or dendrimers,
etc.). The properties of any such suitable degradable
polymers (e.g., hydrophobicity , hydrophilicity , rate of
degradation, etc.) can be tailored by introducing select
functional groups along the polymer chains.
For example, poly (phenyllactide) will degrade at about
l/5th of the rate of racemic poly (lactide ) at a pH of 7.4 at
55 degrees C . One of ordinary skill in the art with the
benefit of this disclosure will be able to determine the
appropriate functional groups to introduce to the polymer
chains to achieve the desired physical properties of the
degradable polymers.
Polyanhydrides are another type of particularly
suitable degradable polymer. Examples of suitable
polyanhydrides include poly(adipic anhydride), poly (suberic
anhydride), poly(sebacic anhydride), and poly (dodecanedioic
anhydride). Other suitable examples include, but are not
limited to, poly(maleic anhydride) and poly(benzoic
anhydride ).
An epoxy or other type of barrier which does not
dissolve in aqueous fluid may be used to completely prevent
exposure of the anhydrous boron compound to the aqueous
fluid until the barrier is breached, broken or otherwise
circumvented, whether this is done intentionally (for
example, to set a packer when it is appropriately positioned
in the well, or to open a circulation valve upon completion
of a formation testing operation, etc.) or as a result of an
unexpected or inadvertent circumstance (for example, to
close a valve in an emergency situation and thereby prevent
escape of fluid, etc.).
Referring additionally now to FIGS. 2A & B , the well
tool 12c is representatively illustrated in respective flow
preventing and flow permitting configurations. The well
tool 12c may be used in the system 10 and method described
above, or the well tool may be used in any other system or
method in keeping with the principles of this disclosure.
In the configuration of FIG. 2A, the well tool 12c
prevents downward fluid flow, but permits upward fluid flow,
through a flow path 24a which may extend longitudinally
through the well tool and the tubular string 14 in which the
well tool is interconnected. In the configuration of FIG.
2B, the well tool 12c permits fluid flow in both directions
through the flow path 24a.
The well tool 12c preferably includes a structure 26a
in the form of a ball which sealingly engages a seat 28 in a
housing 30. The housing 30 may be provided with suitable
threads, etc. for interconnection of the housing in the
tubular string 14. The structure 26a may be installed in
the well tool 12c before or after the tubular string 14 is
installed in the well.
The structure 26a comprises an anhydrous boron compound
32a with a barrier 34a thereon. The anhydrous boron
compound 32a may be formed of a solid mass as described
above. The barrier 34a preferably comprises a coating which
prevents exposure of the anhydrous boron compound 32a to an
aqueous fluid in the well, until the barrier is compromised.
With the structure 26a sealingly engaged with the seat
28 as depicted in FIG. 2A, a pressure differential may be
applied from above to below the structure. In this manner,
pressure may be applied to the tubular string 14, for
example, to set a packer, actuate a valve, operate any other
well tool, etc. As another example, the sealing engagement
of the structure 26a with the seat 28 can prevent loss of
fluid from the tubular string 14, etc.
When it is desired to permit downward flow through the
flow path 24a, or to provide access through the well tool
12c, a predetermined elevated pressure differential may be
applied from above to below the structure 26a, thereby
forcing the structure through the seat 28, as depicted in
FIG. 2B. This causes the barrier 34a to be compromised,
thereby exposing the anhydrous boron compound 32a to aqueous
fluid in the well. As a result, the anhydrous boron
compound 32a will eventually dissolve, thereby avoiding the
possibility of the structure 26a obstructing or otherwise
impeding future operations.
Note that the barrier 34a could be made of a material,
such as a coating, which dissolves at a slower rate than the
anhydrous boron compound 32a, in order to delay exposure of
the anhydrous boron compound to the aqueous fluid.
Referring additionally now to FIG. 3 , a cross-sectional
view of the well tool 12e is representatively illustrated.
The well tool 12e is similar in some respects to the well
tool 12c described above, in that the well tool 12e includes
a structure 26b which selectively prevents fluid flow
through a flow path 24b.
However, the structure 26b includes a barrier 34b which
isolates an anhydrous boron compound 32b from exposure to an
aqueous fluid in the well, until the barrier 34b dissolves.
Thus, the structure 26b blocks flow through the flow path
24b (in both directions) for a predetermined period of time,
after which the structure dissolves and thereby permits
fluid flow through the flow path.
After the structure 26b dissolves, the only remaining
components left in the housing 30b are seals and/or slips 36
which may be used to sealingly engage and secure the
structure in the housing. The seals and/or slips 36
preferably do not significantly obstruct the flow path 24b
after the structure 26b is dissolved.
Instead of using separate seals, the structure 26b
could sealing engage a seat 28b in the housing 30b, if
desired.
Referring additionally now to FIGS. 4A & B , another
construction of the well tool 12c is representatively
illustrated. In FIG. 4A, the well tool 12c is depicted in a
configuration in which downward flow through the flow path
24c is prevented, but upward flow through the flow path is
permitted. In FIG. 4B, the well tool 12c is depicted in a
configuration in which both upward and downward flow through
the flow path 24c are permitted.
One significant difference between the well tool 12c as
depicted in FIGS. 4A & B , and the well tool 12c as depicted
in FIGS. 2A & B , is that the structure 26c of FIGS. 4A & B
is in the form of a flapper which sealingly engages a seat
28c. The flapper is pivotably mounted in the housing 30c.
Similar to the structure 26a described above, the
structure 26c includes an anhydrous boron compound 32c and a
barrier 34c which prevents exposure of the anhydrous boron
compound to aqueous fluid in the well. When it is desired
to permit fluid flow in both directions through the flow
path 24c, the structure 26c is broken, thereby compromising
the barrier 34c and permitting exposure of the anhydrous
boron compound 32c to the aqueous fluid.
Preferably, the structure 26c is frangible, so that it
may be conveniently broken, for example, by applying a
predetermined pressure differential across the structure, or
by striking the structure with another component, etc.
Below the predetermined pressure differential, the structure
26c can resist pressure differentials to thereby prevent
downward flow through the flow path 24c (for example, to
prevent fluid loss to the formation 22, to enable pressure
to be applied to the tubular string 14 to set a packer,
operate a valve or other well tool, etc.).
After the anhydrous boron compound 32c is exposed to
the aqueous fluid in the well, it eventually dissolves. In
this manner, no debris remains to obstruct the flow path
24c.
Note that the barrier 34c could be made of a material,
such as a coating, which dissolves at a slower rate than the
anhydrous boron compound 32c, in order to delay exposure of
the anhydrous boron compound to the aqueous fluid.
Referring additionally now to FIG. 5 , a schematic
cross-sectional view of the well tool 12d is
representatively illustrated. The well tool 12d comprises a
well screen assembly which includes a filter portion 38a
overlying a base pipe 40a. The base pipe 40a may be
provided with suitable threads, etc. for interconnection in
the tubular string 14.
The filter portion 38a excludes sand, fines, debris,
etc. from fluid which flows inward through the well screen
assembly and into the interior of the base pipe 40a and
tubular string 14. However, when the well screen assembly
is initially installed in the well, a structure 26d prevents
fluid flow between the interior and the exterior of the base
pipe 40a.
By preventing fluid flow through the well screen
assembly, clogging of the filter portion 38a can be avoided
and fluid can be circulated through the tubular string 14
during installation. In this manner, use of a washpipe in
the well screen assembly can be eliminated, thereby
providing for a more economical completion operation.
After a predetermined period of time (e.g., after
installation of the well tool 12d, after a completion
operation, after gravel packing, etc.), a barrier 34d
dissolves and permits exposure of an anhydrous boron
compound 32d to an aqueous fluid in the well. The anhydrous
boron compound 32d eventually dissolves, thereby permitting
fluid flow through a flow path 24d. Thereafter, relatively
unimpeded flow of fluid is permitted through the filter
portion 38a and the flow path 24d between the exterior and
the interior of the well screen assembly.
Referring additionally now to FIG. 6 , another
construction of the well tool 12d is representatively
illustrated. The well tool 12d depicted in FIG. 6 is
similar in many respects to the well tool depicted in FIG.
5 . However, the well tool 12d of FIG. 6 also includes a
check valve 42 which permits inward flow of fluid through
the well screen assembly, but prevents outward flow of fluid
through the well screen assembly.
The check valve 42 includes a flexible closure device
44 which seals against the base pipe 40b to prevent outward
flow of fluid through the filter portion 38b. This allows
fluid to be circulated through the tubular string 14 during
installation (without the fluid flowing outward through the
filter portion 38b), but also allows fluid to subsequently
be produced inward through the well screen assembly (i.e.,
inward through the filter portion and check valve 42). A
flow path 46 permits fluid flowing inward through the check
valve 42 to flow into the interior of the base pipe 40b
(and, thus, into the tubular string 14).
After a predetermined period of time (e.g., after
installation of the well tool 12d, after a completion
operation, after gravel packing, etc.), a barrier 34e
dissolves and permits exposure of an anhydrous boron
compound 32e to an aqueous fluid in the well. The anhydrous
boron compound 32e eventually dissolves, thereby permitting
fluid flow through a flow path 24e. Thereafter, relatively
unimpeded flow of fluid is permitted through the filter
portion 38b and the flow path 24e between the exterior and
the interior of the well screen assembly.
In this manner, the check valve 42 is bypassed by the
fluid flowing through the flow path 24e. That is, fluid
which flows inward through the filter portion 38b does not
have to flow through the check valve 42 into the base pipe
40b. Instead, the fluid can flow relatively unimpeded
through the flow path 24e after the structure 26e has
dissolved.
Note that the structure 26a-e in each of the well tools
described above comprises a flow blocking device which at
least temporarily blocks flow through a flow path 24a-e.
However, it should be clearly understood that it is not
necessary for a structure embodying principles of this
disclosure to comprise a flow blocking device.
Furthermore, the structure 26a-e in each of the well
tool described above can be considered a closure device in a
valve of the well tool. Thus, the structure 26a-e in each
of the well tools initially prevents flow in at least one
direction through a flow path, but can selectively permit
flow through the flow path when desired.
One advantage of using the anhydrous boron compound
32a-e in the structures 26a-e can be that the anhydrous
boron compound, having a relatively high melting point of
about 742 degrees Celsius, can be positioned adjacent a
structure which is welded and then stress-relieved. For
example, in the well tool 12d configurations of FIGS. 5 & 6 ,
the filter portion 38a, b or housing of the check valve 42
may be welded to the base pipe 40a, b and then stressrelieved
(e.g., by heat treating), without melting the
anhydrous boron compound 32a-e.
It may now be fully appreciated that the above
disclosure provides significant improvements to the art of
constructing well tools for use in subterranean wells. In
particular, use of the anhydrous boron compound permits
convenient, reliable and economical actuation and operation
of well tools.
Those skilled in the art will recognize that the above
disclosure provides to the art a method of constructing a
downhole well tool 12a-e. The method can include forming a
structure 26a-e of a solid mass comprising an anhydrous
boron compound 32a-e; and incorporating the structure 26a-e
into the well tool 12a-e.
Forming the structure 26a-e can include at least one of
molding, machining, abrading and cutting the solid mass.
The structure 26a-e can comprise a flow blocking
device, and the incorporating step can include blocking a
flow path 24a-e in the well tool 12a-e with the structure
26a-e .
The anhydrous boron compound 32a-e may comprise at
least one of anhydrous boric oxide and anhydrous sodium
borate .
The method can include the step of providing a barrier
34a-e which at least temporarily prevents the anhydrous
boron compound 32a-e from hydrating. The barrier 34a-e may
comprise a coating, and may comprise poly lactic acid.
The barrier 34a-e may dissolve in an aqueous fluid at a
rate slower than a rate at which the anhydrous boron
compound 32a-e dissolves in the aqueous fluid. The barrier
34a-e may be insoluble in an aqueous fluid.
The barrier 34a-e can prevent hydrating of the
anhydrous boron compound 32a-e until after the well tool
12a-e is installed in a wellbore 16. A pressure
differential may be applied across the structure 26a-e prior
to the barrier 34a-e permitting the anhydrous boron compound
32a-e to hydrate.
The structure 26a-e may selectively permit fluid
communication between an interior and an exterior of a
tubular string 14.
The structure 26a-e may selectively block fluid which
flows through a filter portion 38a, b of a well screen
assembly.
The well tool 12d may comprise a well screen assembly
which includes a check valve 42, with the check valve
preventing flow outward through the well screen assembly and
permitting flow inward through the well screen assembly.
Flow inward and outward through the well screen assembly may
be permitted when the anhydrous boron compound 32d,e
dissolves .
The structure 26a-c can selectively block a flow path
24a-c which extends longitudinally through a tubular string
14.
The structure 26a-e may comprise a closure device of a
valve. The closure device may comprise a flapper (e.g.,
structure 26c) or a ball (e.g., structure 26a), and the
closure device may be frangible (e.g., structures 26a, c).
The anhydrous boron compound 32a, c can hydrate in response
to breakage of the closure device.
The method may include forming the solid mass by
heating a granular material comprising the anhydrous boron
compound 32a-e, and then cooling the material. The granular
material may comprise a powdered material.
Also provided by the above disclosure is a well tool
12a-e which can include a flow path 24a-e, and a flow
blocking device (e.g., structures 26a-e) which selectively
prevents flow through the flow path. The device may include
an anhydrous boron compound 32a-e.
The flow blocking device may be positioned adjacent a
welded and stress-relieved structure.
The anhydrous boron compound 32a-e may comprise a solid
mass formed from a granular material.
In a specific example described above, a method of
constructing a downhole well tool 12a-e includes forming a
frangible structure 26a-e, the frangible structure
comprising a solid mass including an anhydrous boron
compound; and incorporating the frangible structure 26a-e
into a valve of the well tool 12a-e.
In another specific example described above, a well
screen assembly (well tool 12d) includes a filter portion
38, a flow path 24e arranged so that fluid which flows
through the flow path also flows through the filter portion
38, and a flow blocking device (structure 26e) which
selectively prevents flow through the flow path 24e, the
device including an anhydrous boron compound 32e.
In other specific examples described above, a well tool
12d includes a flow path 24d,e which provides fluid
communication between an interior and an exterior of a
tubular string 14, and a flow blocking device (structure
26d,e) which selectively prevents flow through the flow path
24d,e. The flow blocking device includes an anhydrous boron
compound 32d,e.
Another example described above comprises a well tool
12c which includes a flow path 24c and a flapper (structure
26c) which selectively prevents flow through the flow path.
The flapper includes an anhydrous boron compound 32c.
It is to be understood that the various examples
described above may be utilized in various orientations,
such as inclined, inverted, horizontal, vertical, etc., and
in various configurations, without departing from the
principles of the present disclosure. The embodiments
illustrated in the drawings are depicted and described
merely as examples of useful applications of the principles
of the disclosure, which are not limited to any specific
details of these embodiments.
In the above description of the representative examples
of the disclosure, directional terms, such as "above,"
"below," "upper," "lower," etc., are used for convenience in
referring to the accompanying drawings. In general,
"above," "upper," "upward" and similar terms refer to a
direction toward the earth's surface along a wellbore, and
"below," "lower," "downward" and similar terms refer to a
direction away from the earth's surface along the wellbore.
Of course, a person skilled in the art would, upon a
careful consideration of the above description of
representative embodiments, readily appreciate that many
modifications, additions, substitutions, deletions, and
other changes may be made to these specific embodiments, and
such changes are within the scope of the principles of the
present disclosure. Accordingly, the foregoing detailed
description is to be clearly understood as being given by
way of illustration and example only, the spirit and scope
of the present invention being limited solely by the
appended claims and their equivalents.
WHAT IS CLAIMED IS:
1 . A method of constructing a downhole well tool, the
method comprising:
forming a structure of a solid mass comprising an
anhydrous boron compound; and
incorporating the structure into the well tool.
2 . The method of claim 1 , wherein forming the
structure further comprises at least one of molding,
machining, abrading and cutting the solid mass.
3 . The method of claim 1 , wherein the structure
comprises a flow blocking device, and wherein the
incorporating step further comprises blocking a flow path in
the well tool with the structure.
4 . The method of claim 1 , wherein the anhydrous boron
compound comprises at least one of anhydrous boric oxide and
anhydrous sodium borate.
5 . The method of claim 1 , further comprising the step
of providing a barrier which at least temporarily prevents
the anhydrous boron compound from hydrating.
6 . The method of claim 5 , wherein the barrier
comprises a coating.
7 . The method of claim 5 , wherein the barrier
comprises poly lactic acid.
8 . The method of claim 5 , wherein the barrier
dissolves in an aqueous fluid at a rate slower than a rate
at which the anhydrous boron compound dissolves in the
aqueous fluid.
9 . The method of claim 5 , wherein the barrier is
insoluble in an aqueous fluid.
10. The method of claim 5 , wherein the barrier
prevents hydrating of the anhydrous boron compound until
after the well tool is installed in a wellbore.
11. The method of claim 5 , wherein a pressure
differential is applied across the structure prior to the
barrier permitting the anhydrous boron compound to hydrate.
12. The method of claim 1 , wherein the structure
selectively permits fluid communication between an interior
and an exterior of a tubular string.
13. The method of claim 1 , wherein the structure
selectively blocks fluid which flows through a filter
portion of a well screen assembly.
14. The method of claim 1 , wherein the well tool
comprises a well screen assembly which includes a check
valve, the check valve preventing flow outward through the
well screen assembly and permitting flow inward through the
well screen assembly, and wherein flow inward and outward
through the well screen assembly is permitted when the
anhydrous boron compound dissolves.
15. The method of claim 1 , wherein the structure
selectively blocks a flow path which extends longitudinally
through a tubular string.
16. The method of claim 1 , wherein the structure
comprises a closure device of a valve.
17. The method of claim 16, wherein the closure device
comprises a flapper.
18. The method of claim 16, wherein the closure device
comprises a ball.
19. The method of claim 16, wherein the closure device
is frangible.
20. The method of claim 19, wherein the anhydrous
boron compound hydrates in response to breakage of the
closure device.
21. The method of claim 1 , further comprising forming
the solid mass by heating a granular material comprising the
anhydrous boron compound, and then cooling the material.
22. The method of claim 21, wherein the granular
material comprises a powdered material.
23. A well tool, comprising:
a flow path; and
a flow blocking device which selectively prevents flow
through the flow path, the device including an anhydrous
boron compound.
24. The well tool of claim 23, wherein the anhydrous
boron compound comprises at least one of anhydrous boric
oxide and anhydrous sodium borate.
25. The well tool of claim 23, further comprising a
barrier which at least temporarily prevents the anhydrous
boron compound from hydrating.
26. The well tool of claim 25, wherein the barrier
comprises a coating.
27. The well tool of claim 25, wherein the barrier
comprises poly lactic acid.
28. The well tool of claim 25, wherein the barrier
dissolves in an aqueous fluid at a rate slower than a rate
at which the anhydrous boron compound dissolves in the
aqueous fluid.
29. The well tool of claim 25, wherein the barrier is
insoluble in an aqueous fluid.
30. The well tool of claim 25, wherein the barrier
prevents hydrating of the anhydrous boron compound until
after the flow path is installed in a wellbore.
31. The well tool of claim 25, wherein a pressure
differential is applied across the flow blocking device
prior to the barrier permitting the anhydrous boron compound
to hydrate .
32. The well tool of claim 23, wherein the flow path
provides fluid communication between an interior and an
exterior of a tubular string.
33. The well tool of claim 23, wherein the well tool
comprises a well screen assembly, and wherein fluid which
flows through the flow path also flows through a filter
portion of the well screen assembly.
34. The well tool of claim 33, wherein the flow path
bypasses a check valve.
35. The well tool of claim 33, wherein a barrier at
least temporarily prevents the anhydrous boron compound from
hydrating until after the well screen assembly is installed
in a wellbore.
36. The well tool of claim 23, wherein the well tool
comprises a well screen assembly which includes a check
valve, the check valve preventing flow outward through the
well screen assembly and permitting flow inward through the
well screen assembly, and the flow path permitting flow
inward and outward through the well screen assembly when the
anhydrous boron compound dissolves.
37. The well tool of claim 23, wherein the flow path
extends longitudinally through a tubular string.
38. The well tool of claim 23, wherein the well tool
comprises a valve, and wherein the flow blocking device
comprises a closure device of the valve.
39. The well tool of claim 38, wherein the closure
device comprises a flapper.
40. The well tool of claim 38, wherein the closure
device comprises a ball.
41. The well tool of claim 38, wherein the closure
device prevents flow in a first direction through the flow
path, and the closure device permits flow through the flow
path in a second direction opposite to the first direction.
42. The well tool of claim 38, wherein the closure
device is frangible.
43. The well tool of claim 42, wherein the anhydrous
boron compound hydrates in response to breakage of the
closure device.
44. The well tool of claim 38, further comprising a
barrier which at least temporarily prevents the anhydrous
boron compound from hydrating.
45. The well tool of claim 44, wherein the barrier
comprises a coating.
46. The well tool of claim 44, wherein the barrier
dissolves in an aqueous fluid at a rate slower than a rate
at which the anhydrous boron compound dissolves in the
aqueous fluid.
47. The well tool of claim 44, wherein the barrier is
insoluble in an aqueous fluid.
48. The well tool of claim 44, wherein a pressure
differential is applied across the flow blocking device
prior to the barrier permitting the anhydrous boron compound
to hydrate .
49. The well tool of claim 23, wherein the flow
blocking device is positioned adjacent a welded and stressrelieved
structure.
50. The well tool of claim 23, wherein the anhydrous
boron compound comprises a solid mass formed from a granular
material .