U.S. patent application number 12/185580 was filed with the patent office on 2009-02-12 for use of nanosized particulates and fibers in elastomer seals for improved performance metrics for roller cone bits.
This patent application is currently assigned to SMITH INTERNATIONAL, INC.. Invention is credited to Anthony Griffo, Madapusi K. Keshavan.
Application Number | 20090038858 12/185580 |
Document ID | / |
Family ID | 39767642 |
Filed Date | 2009-02-12 |
United States Patent
Application |
20090038858 |
Kind Code |
A1 |
Griffo; Anthony ; et
al. |
February 12, 2009 |
USE OF NANOSIZED PARTICULATES AND FIBERS IN ELASTOMER SEALS FOR
IMPROVED PERFORMANCE METRICS FOR ROLLER CONE BITS
Abstract
A bit for drilling subterranean formations that includes a bit
body including a bearing surface; a cutting structure mounted on
the bit body, and including a bearing surface, and an annular seal
for retaining a grease between the bearing surfaces, the annular
seal comprising a flexible and resilient seal body formed from an
elastomer composition, wherein the elastomer composition comprises
an elastomer material, a curing agent, and 10% or less by volume of
a nanomaterial additive selected from one of nanotubes and
clustered nanodiamonds is disclosed.
Inventors: |
Griffo; Anthony; (The
Woodlands, TX) ; Keshavan; Madapusi K.; (The
Woodlands, TX) |
Correspondence
Address: |
OSHA, LIANG LLP / SMITH
TWO HOUSTON CENTER, 909 FANNIN STREET, SUITE 3500
HOUSTON
TX
77010
US
|
Assignee: |
SMITH INTERNATIONAL, INC.
Houston
TX
|
Family ID: |
39767642 |
Appl. No.: |
12/185580 |
Filed: |
August 4, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60954272 |
Aug 6, 2007 |
|
|
|
Current U.S.
Class: |
175/371 ;
977/788 |
Current CPC
Class: |
E21B 10/25 20130101 |
Class at
Publication: |
175/371 ;
977/788 |
International
Class: |
E21B 10/25 20060101
E21B010/25 |
Claims
1. A bit for drilling subterranean formations comprising: a bit
body including a bearing surface; a cutting structure mounted on
the bit body, and including a bearing surface; and an annular seal
for retaining a grease between the bearing surfaces, the annular
seal comprising a flexible and resilient seal body formed from an
elastomer composition, wherein the elastomer composition comprises
an elastomer material, a curing agent, and 10% or less by volume of
a nanomaterial additive selected from one of nanotubes and
clustered nanodiamonds.
2. The bit of claim 1, wherein the elastomer material comprises at
least one of a highly saturated nitrile elastomer, a
nitrile-butadiene rubber, a highly saturated nitrile-butadiene
rubber, a fluorocarbon, an ethylene-propylene, a silicone, a
chloroprene, a neoprene, a fluorosilicone, a polyurethane, a
perfluoroelastomer, a polyacrylate, a copolymer of
tetrafluoroethylene and propylene, an ethylene-acrylic rubber, a
chlorosulfonyl polyethylene rubber, an epichlorohydrin polymers, a
styrene butadiene polymer, and mixtures or copolymers thereof.
3. The bit of claim 1, wherein the curing agent, comprises at least
one of an organometallic catalyst, an inorganic oxide, an inorganic
peroxide, a metal oxide salt, an organic peroxide, an organic
hydroperoxide, and mixtures thereof.
4. The bit of claim 1, wherein the nanomaterial additive comprises
a functionalized nanotube.
5. The bit of claim 1, wherein the elastomer composition comprises
0.01 to 1.5% by volume of nanomaterial additives.
6. The bit of claim 1, wherein the elastomer composition comprises
from about 2 to 4% by volume of nanomaterial additives.
7. The bit of claim 1, further comprising an additive which is at
least one of a coagent, a plasticizer, a lubricant, an antioxidant,
a filler, an accelerator, and a retardant.
8. The bit of claim 7, wherein the plasticizer comprises at least
one of a phthalate, a chlorinated paraffin, an adipate, a
trimellitate, a maleate, a sehacate, a benzoate, an epoxidated
vegetable oil, sulfonamides, an organophosphate, a glycol and a
polyether.
9. The bit of claim 7, wherein the lubricant comprises at least one
of a graphite, an oleamide, an erucarnide, a soy oil, waxes, or a
mixture of blend thereof.
10. The bit of claim 7, wherein the antioxidant comprises at least
one of zinc 2-mercaptotolumimidazole,
4,4'-Bis(alpha,alpha-dimethylbenzyl) diphenylamine.
11. The bit of claim 7, where the filler comprises at least one of
a calcium carbonate, a carbon black, a titanium dioxide, a
non-acidic clay, a fumed silica, a metal oxide, a metal chromate, a
metal sulfate, and a mixture thereof.
12. The bit of claim 7, wherein the accelerator comprises at least
one of an amine, a sulfonamide, and a disulfide.
13. The bit of claim 7, wherein the retardant comprises least one
of a stearate, an organic carbamate and salts thereof, a lactone,
and a stearic acid.
14. A rock bit for drilling subterranean formations comprising: a
bit body including at least one journal pin, each having a bearing
surface; a roller cone mounted on the at least one journal pin and
including a bearing surface; an annular seal for retaining a grease
between the bearing surfaces, the annular seal comprising a
flexible and resilient seal body formed from an elastomer
composition, wherein the elastomer composition comprises; 100 parts
by weight of highly saturated nitrile elastomer; furnace black in
the range of up to 70 parts by weight; peroxide curing agent in the
range of from 7 to 10 parts by weight; zinc oxide in the range of
from 4 to 7 parts by weight; stearic acid in the range of from 0.5
to 2 parts by weight; nanomaterial additives selected from one of
nanotubes and clustered nanodiamonds in the range of up to 10
percent by volume, and sufficient plasticizer to provide a Shore
Hardness of no more than A 80.
15. The rock bit of claim 14, wherein the nanoadditive materials
comprises functionalized nanotubes.
16. The rock bit of claim 14, wherein the elastomer composition
comprises 0.01 to 1.5% by volume of nanomaterial additives.
17. The rock bit of claim 14, wherein the plasticizer comprises at
least one of a phthalate, a chlorinated paraffin, an adipate, a
trimellitate, a maleate, a sebacate, a benzoate, an epoxidated
vegetable oil, sulfonamides, an organophosphate, a glycol and a
polyether.
18. The rock bit of claim 14, further comprising an additive which
is at least one of a coagent, an antioxidant, and an
accelerator.
19. The rock bit of claim 18, wherein the coagent is at least one
of polybutadiene. The rock bit of claim 18, wherein the antioxidant
comprises at least one of zinc 2-mercaptotolumimidazole,
4,4'-Bis(alpha,alpha-dimethylbenzyl) diphenylamine.
20. The rock bit of claim 18, wherein the accelerator comprises at
least one of an amine, a sulfonamide, and a disulfide.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application, pursuant to 35 U.S.C. .sctn.119(e), claims
priority to U.S. Patent Application No. 60/954,272, filed on Aug.
6, 2007, which is herein incorporated by reference in its
entirety.
BACKGROUND OF INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments disclosed herein relate generally to the use of
composite materials in seals for cutting tools. More particularly,
embodiments disclosed herein relate to the incorporation of
nanosized particulates and fibers into elastomer seals for improved
wear resistance, thereby enhancing the performance and service life
of the roller cone bit.
[0004] 2. Background Art
[0005] Drill bits are commonly used in, for example, the oil and
gas exploration industry for drilling wells in earth formations.
One type of drill bit commonly used in the industry is the roller
cone drill bit. Roller cone drill bits generally comprise a bit
body connected to a drill string or bottom hole assembly (BHA).
Roller cone drill bits typically include a plurality of roller
cones rotatably attached to the bit body. The roller cones are
generally mounted on steel journals integral with the bit body at
its lower end. The roller cones further comprise a plurality of
cutting elements disposed on each of the plurality of roller cones.
The cutting elements may comprise, for example, inserts (formed
from, for example, polycrystalline diamond, boron nitride, and the
like) and/or milled steel teeth that are coated with appropriate
hardfacing materials.
[0006] When drilling an earth formation, the roller cone drill bit
is rotated in a wellbore, and each roller cone contacts the bottom
of the wellbore being drilled and subsequently rotates with respect
to the drill bit body. Drilling generally continues until, for
example, a bit change is required because of a change in formation
type is encountered in the wellbore or because the drill bit is
worn and/or damaged. High temperatures, high pressures, tough,
abrasive formations, and other factors all contribute to drill bit
wear and failure.
[0007] When a drill bit wears out or fails as the wellbore is being
drilled, it is necessary to remove the BHA from the well so that
the drill bit may be replaced. The amount of time required to make
a bit replacement trip produces downtime in drilling operations.
The amount of downtime may be significant, for example, when
tripping in and out of relatively deep wells. Downtime may be add
to the cost of completing a well and is a particular problem in
offshore operations where costs are significantly higher. It is
therefore desirable to maximize the service life of a drill bit in
order to avoid rig downtime.
[0008] One reason for the failure of a roller cone drill bit is the
wear that occurs on the journal bearings that support the roller
cones. The journal bearings may be friction-type or roller-type
bearings, and are subjected to high loads, high pressures, high
temperatures, and exposure to abrasive particles originating from
the formation being drilled. The journal bearings are typically
lubricated with grease adapted to withstand tough drilling
environments. Thus, such lubricants are an important element in the
life of a drill bit.
[0009] Lubricants are retained by a journal bearing seal, which is
typically an O-ring type seal, typically located in a seal groove
formed on an interior surface of a roller cone. The seal generally
includes a static seal surface adapted to form a static seal with
the interior surface of the roller cone and a dynamic seal surface
adapted to form a dynamic seal with the journal upon which the
roller cone is rotatably mounted. The seal must endure a range of
temperature and pressure conditions during the operation of the
drill bit to prevent lubricants from escaping and/or contaminants
from entering the journal bearing. Elastomer seals known in the art
are conventionally formed from a single type of rubber or elastomer
material, and are generally formed having identically configured
dynamic and static seal surfaces with a generally regular cross
section.
[0010] The rubber or elastomer material selected to form the seal
for the journal hearings has particular hardness, modulus of
elasticity, wear resistance, temperature stability, and coefficient
of friction, among other properties. Additionally, the particular
geometric configuration of the seal surfaces produces a selected
amount of seal deflection that defines the degree of contact
pressure or "squeeze" applied by the dynamic and static seal
surfaces against respective Journal bearing and roller cone
surfaces.
[0011] The wear, temperature, and contact pressures encountered at
the dynamic seal surface are different than those encountered at
the static seal surface. Therefore, the type of seal material and
seal geometry that is ultimately selected to form both seal
surfaces represents a compromise between satisfying the operating
conditions that occur at the different dynamic and static seal
surfaces.
[0012] Conventional seals formed from a single-type of material,
having symmetric axial cross-sectional geometries, may have reduced
wear resistance and temperature stability at the dynamic seal
surface where wear and temperature conditions are generally more
severe than at the static seal surface. Therefore, the service life
of drill bits that contain such seals may be limited by the service
life of the journal bearing seal. It is desirable to produce a seal
that is capable of withstanding the harsh downhole conditions, such
as high pressures and temperatures. Accordingly, there exists a
need for a tough, long-lasting seal, and drill bits containing such
seals.
SUMMARY OF INVENTION
[0013] In one aspect, embodiments disclosed herein relate to a bit
for drilling subterranean formations that includes a bit body
including a bearing surface; a cutting structure mounted on the bit
body, and including a bearing surface, and an annular seal for
retaining a grease between the bearing surfaces, the annular seal
comprising a flexible and resilient seal body formed from an
elastomer composition, wherein the elastomer composition comprises
an elastomer material, a curing agent, and 10% or less by volume of
a nanomaterial additive selected from one of nanotubes and
clustered nanodiamonds.
[0014] In another aspect, embodiments disclosed herein relate to a
rock bit for drilling subterranean formations that includes a bit
body including at least one journal pin, each having a bearing
surface; a roller cone mounted on the at least one journal pin and
including a bearing surface; an annular seal for retaining a grease
between the bearing surfaces, the annular seal comprising a
flexible and resilient seal body formed from an elastomer
composition, wherein the elastomer composition comprises: 100 parts
by weight of highly saturated nitrile elastomer; furnace black in
the range of up to 70 parts by weight; peroxide curing agent in the
range of from 7 to 10 parts by weight; zinc oxide in the range of
from 4 to 7 parts by weight; stearic acid in the range of from 0.5
to 2 parts by weight; nanomaterial additives selected from one of
nanotubes and clustered nanodiamonds in the range of up to 10
percent by volume, and sufficient plasticizer to provide a Shore
Hardness of no more than A 80.
[0015] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1 is a semi-schematic perspective of a drill bit
according to one embodiment of the present invention.
[0017] FIG. 2 is a partial cross-section of the drill bit according
FIG. 1.
DETAILED DESCRIPTION
[0018] In one aspect, embodiments disclosed herein relate to
elastomer seals used in components of downhole cutting tools,
including drill bits, core bits, etc. In particular, embodiments
disclosed herein relate to seals reinforced with nanomaterials.
[0019] In addition, embodiments of the present disclosure provide
rock bits comprising seals which are reinforced by nanomaterials.
Such a reinforced seal may have enhanced bulk properties such as
tensile modulus, elastic modulus, hardness, and such like, as
compared with the native seal, while maintaining wear and erosion
resistance. Embodiments of the present disclosure are based, in
part, on the determination that the life of a seal is directly
related to the service life of the rock bit.
[0020] It is therefore desirable to provide a consistently reliable
seal for maintaining the lubricant within a rock bit, where the
seal has a long useful life, is resistant to oil well chemical
compositions, has high heat resistance, and is highly resistant to
abrasion.
[0021] Referring to FIG. 1, a drill bit in accordance with an
embodiment of the invention is shown. In this embodiment, as shown
in FIG. 1, a drill bit 5 comprises a body 10 having three roller
cones 11 mounted on its lower end. A threaded pin 12 is at the
upper end of the body 10 for assembly of the drill bit 5 onto a
drill string (not shown separately) for drilling oil wells or the
like. A plurality of cutting elements 13 are pressed into holes in
the surfaces of the roller cones 11 for bearing on the rock
formation being drilled. Nozzles 15 in the bit body 10 introduce
drilling mud into the space around the roller cones 11 for cooling
and carrying away formation chips drilled by the drill bit 5. While
reference is made to an insert-type bit, the scope of the present
invention should not be limited by any particular cutting
structure. Embodiments of the present invention generally apply to
any rock bit (whether roller cone, disc, etc.) that requires an
elastomer seal to retain grease.
[0022] FIG. 2 shows a part of a longitudinal cross section of the
drill bit 5 of FIG. 1, extending radially from the rotational axis
14 of the rock bit through one of the three legs on which the
roller cones 11 are mounted. Each leg includes a journal 16
extending downwardly and radially inwardly on the rock bit body 10.
The journal 16 includes a cylindrical bearing surface having a hard
metal insert 17 on a lower portion of the journal 16.
[0023] Each roller cone 11 is in the form of a hollow,
frustoconical steel body having cutting elements 13 pressed into
holes on the external surface. For long life, the cutting elements
13 may be tungsten carbide inserts tipped with a polycrystalline
diamond layer. Such tungsten carbide inserts provide the drilling
action by engaging a subterranean rock formation as the rock bit is
rotated. Some types of bits have hard-faced steel teeth milled on
the outside of the cone instead of carbide inserts.
[0024] The cavity in the cone 11 contains a cylindrical bearing
surface including a copper nickel tin insert 21 deposited in a
groove in the steel of the cone 11 or as a floating insert in a
groove in the cone 11. The alloy insert 21 in the cone 11 engages
the hard metal insert 17 on the leg and provides the main bearing
surface for the cone 11 on the bit body 10. A nose button 22 is
between the end of the cavity in the cone 11 and the nose 19 and
carries the principal thrust loads of the cone 11 on the journal
16. A bushing 23 surrounds the nose and provides additional bearing
surface between the cone 11 and journal 16. Other types of bits,
particularly for higher rotational speed applications, may have
roller bearings instead of the exemplary journal bearings
illustrated herein.
[0025] A plurality of bearing balls 24 are fitted into
complementary ball races in the cone 11 and on the journal 16.
These balls 24 are inserted through a ball passage 26, which
extends through the journal 16 between the bearing races and the
exterior of the drill bit 5. A cone 11 is first fitted on the
journal 16, and then the bearing balls 24 are inserted through the
ball passage. The balls 24 carry any thrust loads tending to remove
the cone 11 from the journal 16 and thereby retain the cone 11 on
the journal 16. The balls 24 are retained in the races by a ball
retainer 27 inserted through the ball passage 26 after the balls
are in place. A plug 28 is then welded into the end of the ball
passage to keep the ball retainer in place.
[0026] The bearing surfaces between the journal 16 and cone 11 are
lubricated by a lubricant or grease composition. Preferably, the
interior of the drill bit is evacuated and lubricant or grease is
introduced through a fill passage (not shown separately). The
lubricant or grease thus fills the regions adjacent the bearing
surfaces plus various passages and a grease reservoir. The grease
reservoir comprises a cavity 29 in the bit body 10, which is
connected to the ball passage 26 by a lubricant passage 31.
Lubricant or grease also fills the portion of the ball passage 26
adjacent the ball retainer, the open groove 18 on the upper side of
the journal 16, and a diagonally extending passage 32 therebetween.
Lubricant or grease is retained in the bearing structure by a
resilient and flexible seal 33 between the cone 11 and journal
16.
[0027] A pressure compensation subassembly is included in the
grease reservoir 29. This subassembly comprises a metal cup 34 with
an opening 36 at its inner end. A flexible rubber bellows 37
extends into the cup 34 from its outer end. The bellows 37 is held
in place by a cap 38 with a vent passage 39. The pressure
compensation subassembly is held in the grease reservoir by a snap
ring 41.
[0028] When the drill bit is filled with lubricant or grease, the
bearings, the groove 18 on the journal 16, passages in the journal
16, the lubrication passage 31, and the grease reservoir on the
outside of the bellows 37 are filled with lubricant or grease. If
the volume of lubricant or grease expands due to heating, for
example, the bellows 37 is compressed to provide additional volume
in the sealed grease system, thereby preventing accumulation of
excessive pressures. High pressure in the grease system may be
damage the seal 33 and permit abrasive drilling mud or the like to
enter the bearings. Conversely, if the grease volume should
contract, the bellows 37 may be expand to prevent low pressures in
the sealed grease systems, which could cause flow of abrasive
and/or corrosive substances past the seal 33.
[0029] To maintain the desired properties of the seal at the harsh
pressure and temperature conditions prevalent in a rock bit, to
inhibit undesired pumping of lubricant through the seal, and to
promote a long and useful life, it is desirable that the seal be
chemically and physically resistant to chemical compositions found
downhole, have a high heat and abrasion resistance, have a low
rubbing friction, and not be readily deformed under the pressure
and temperature conditions found in a well. Therefore, for certain
applications it is desirable that the seal have a modulus of
elasticity at 100% elongation from 800 to 1275 psi, a minimum
tensile strength of 2300 psi, elongation from 200 to 300 percent,
die C tear strength of at least 250 lbs/inch, durometer hardness
Shore A in the range from 75 to 85, and a compression set after 70
hours at 100.degree. C. of less than about 18% and preferably about
16%.
[0030] A variety of seals have been employed in such rock bits.
These seals usually are made of synthetic rubbers. Other components
in the seal are usually curing agents, other additives such as
plasticizers, fillers, coagents, accelerators, retardants,
antioxidants and lubricants. Seals of the type found in embodiments
of the present disclosure further comprise nanomaterial
additives.
[0031] Polymers and Elastomer Materials
[0032] Seals typically used in rock bits are usually made of
acrylontrile polymers or acrylonitrile/butadiene copolymers.
However, these synthetic rubbers typically exhibit poor heat
resistance and become brittle at elevated temperatures after
extended periods of time. Additionally, these rubbers often exhibit
undesirably low tensile strength and high coefficients of friction.
Such properties are undesirable in a seal to be used in a rock bit,
because the high operating temperatures of the bit may be result in
failure of the seal.
[0033] Preferred seals may be formed from elastomer compositions
such as fluoroelastomers, carboxylated nitriles, highly saturated
nitrite (HSN) elastomers, nitrile-butadiene rubbers, highly
saturated nitrile-butadiene rubbers (HNBR), fluorocarbons,
ethylene-propylenes, silicones, chloroprenes, neoprenes,
fluorosilicones, polyurethanes, perfluoroelastomers, polyacrylates,
copolymers of tetrafluoroethylene and propylene, ethylene-acrylic
rubbers, chlorosulfonyl polyethylene rubbers, epichlorohydrin
polymers, styrene butadiene polymers, and mixtures or copolymers
thereof.
[0034] HSM elastomer seals are disclosed in U.S. Pat. No.
5,323,863, which is assigned to the same assignee as the present
disclosure and is hereby incorporated by reference. An exemplary
elastomer composition may comprise per 100 parts by weight of
elastomer (e.g. HSN, HNBR, etc.), furnace black in the range of
from 40 to 70 parts by weight, peroxide curing agent in the range
of from 7 to 10 parts by weight, graphite in the range from 10 to
20 parts by weight, zinc oxide or magnesium oxide in the range of
from 4 to 7 parts by weight, stearic acid in the range from 0.5 to
2 parts by weight, and plasticizer up to about 10 parts by
weight.
[0035] In elastomer materials, the tensile modulus of the
elastomer, its tear strength, and its hardness are positively
correlated. As such, when the hardness of the elastomer is
increased, one normally finds that the tear strength and tensile
modulus similarly increase. Hardness is therefore a convenient
method to compare elastomer compositions.
[0036] The hardness of an elastomer material is defined as the
material's ability to withstand indentation. Durometer is typically
used as a measure of hardness for polymers, elastomers, and
rubbers, and is described in U.S. Pat. No. 1,770,045 issued to A.
F. Shore. Commonly called the Shore hardness, durometer is measured
using the ASTM D2240-00 testing standard. There are a total of 12
scales, depending on the intended use: types A, B, C, D, DO, E, M,
O, OO, OOO, OOO--S, and R. The A scale is usually reserved for
softer plastics, while the D scale is for harder ones. Each scale
results in a value between 0 and 100, with higher values indicating
a harder material. For a rock bit seal, it is desirable that the
durometer hardness is in the range of from about 75 to 85 on the
Shore A scale. A hardness of 85 or higher may result in premature
failure of the seal.
[0037] Curing Agents
[0038] Curing refers the thickening or hardening of a polymer
material, which is also called vulcanization when the polymer is
rubber. Curing agents are agents or substances added to a polymer
composition to promote or control the curing reaction, either
catalytically or as a reactant, such as cross-linkers, heat,
electron beam, UV radiation, or chemical catalysts.
[0039] In some embodiments, the catalyst may include organometallic
catalysts such as organic complexes of Sn, Ti, Pt, Pb, Sb, Zn, or
Rh, inorganic oxides such as manganese (IV) oxide, calcium
peroxide, or lead dioxide, and combinations thereof, metal oxide
salts such as sodium perborates and other borate compounds, or
organic peroxides such as cumene hydroperoxide. In a particular
embodiment, the organometallic catalyst may be dibutyltin
dilaurate, a titanate/zinc acetate material, tin octoate, a
carboxylic salt of Pb, Zn, Zr, or Sb, and combinations thereof.
[0040] The catalyst may be present in an amount effective to
catalyze the curing of the liquid elastomer composition. In various
embodiments, the catalyst may be used in an amount ranging from
about 0.01 to about 10 weight percent, based on the total weight of
the elastomer(s), from about 0.05 to about 5 weight percent in
other embodiments, and from about 0.10 to about 2 weight percent in
yet other embodiments.
[0041] In general, the crosslinker may be any nucleophilic or
electrophilic group that may react with the reactive groups
available in the elastomer composition. In a further embodiment,
the crosslinking agent may comprise a polyfunctional molecule with
more than one reactive group. Such reactive groups may include for
example, amines, alcohols, phenols, thiols, carbanions,
organofunctional silanes, and carboxylates.
[0042] Other Additives
[0043] Additives are widely used in elastomer compositions to
tailor the physical properties of the resultant elastomer
composition. In some embodiments, additives may include
accelerators and retardants, plasticizers, thermal and light
stabilizers, flame-retardants, fillers, adhesion promoters, or
Theological additives.
[0044] Accelerators and retardants may optionally be used to
control the cure time of the liquid elastomer. For example, an
accelerator may be used to shorten the cure time while a retardant
may be used to prolong the cure time. In some embodiments, the
accelerator may include an amine, a sulfonamide, or a disulfide,
and the retardant may include a stearate, an organic carbamate and
salts thereof, a lactone, or a stearic acid.
[0045] Addition of plasticizers may reduce the modulus of the
polymer at the use temperature by lowering its Tg. This may allow
control of the viscosity and mechanical properties of the elastomer
seal. In some embodiments, the plasticizer may include phthalates,
epoxides, aliphatic diesters, phosphates, sulfonamides, glycols,
polyethers, trimellitates or chlorinated paraffin. In some
embodiments, the plasticizer may be a diisooctyl phthalate,
epoxidized soybean oil, di-2-ethylhexyl adipate, tricresyl
phosphate, or trioctyl trimellitate.
[0046] Fillers are usually inert materials which may reinforce the
elastomer seal or serve as an extender. Fillers therefore affect
elastomer processing, storage, and curing. Fillers may also affect
the properties of the elastomer such as electrical and heat
insulting properties, modulus, tensile or tear strength, abrasion
resistance and fatigue strength. In some embodiments, the fillers
may include carbonates, metal oxides, clays, silicas, mica, metal
sulfates, metal chromates, or carbon black. In some embodiments,
the filler may include titanium dioxide, calcium carbonate,
non-acidic clays, or fumed silica.
[0047] Addition of adhesion promoters may improve adhesion to
various substrates. In some embodiments, adhesion promoters may
include epoxy resins, modified phenolic resins, modified
hydrocarbon resins, polysiloxanes, silanes, or primers.
[0048] Addition of rheological additives may control the flow
behavior of the compound. In some embodiments, Theological
additives may include fine particle size fillers, organic agents,
or combinations of both. In some embodiments, Theological additives
may include precipitated calcium carbonates, non-acidic clays,
famed silicas, or modified castor oils.
[0049] Nanomaterial Additives
[0050] Nanomaterials possess dimensions on the order of a billionth
of a meter. In a particular embodiment, the nanomaterial additive
may have dimensions ranging from about 0.1 to 100 nanometers. In
another embodiment, the nanomaterial may have dimensions ranging
from 0.5 to 50 nanometers. In yet another embodiment, the
nanomaterial may have dimensions ranging from about 1.0 to 10
nanometers.
[0051] Nanomaterials typically have a very high aspect ratio, that
is, the ratio of length to diameter. In a particular embodiment,
the nanomaterials used in the present disclosure may have an aspect
ratio ranging from about 1.0 to 1,000,000. In one embodiment, the
nanomaterial may have an aspect ratio ranging from 1.0 to 300. In
yet another embodiment, the nanomaterial may have an aspect ratio
ranging from 3.0 to 100.
[0052] In particular embodiments, the at least one nanomaterial
additive may be selected from at least one of nanoclays, carbon
nanotubes, functionalized nanotubes, inorganic nanotubes, clustered
nanodiamonds, fullerenes, other inorganic nanomaterial additives,
and mixtures thereof. Nanomaterial additives may be added to
elastomer composition disclosed herein in an amount greater than
about 0.1, 0.2, 0.3, 0.5, 1, and 2 volume percent in some
embodiments, and less than 10, 5, 4, 2, and 1 volume percent in
other embodiments.
[0053] Nanoclays
[0054] The nanoclay raw material may be montmorillonite (magnesium
aluminum silicate) or bentonite (aluminum phyllosilicate), a 2-to-1
layered smectite clay mineral with a platy or tubular structure.
Individual plate thickness of nanoclays may be just one nanometer,
but the surface dimensions may generally range from about 300 to
more than 600 nanometers, resulting in an unusually high aspect
ratio. Naturally occurring montmonrllonite is hydrophilic. Since
polymers are generally organophilic, unmodified nanoclays disperse
in polymers with great difficulty. Through clay surface
modification, montmorillonite may be made organophilic and,
therefore, compatible with conventional organic polymers.
[0055] A number of chemistries may be conventionally applied to
modify the surfaces of nanoclays. For example, in the traditional
"onuim ion" modification, a clay-chemical complex is formed using
an intercalant (surface treatment) containing an ammonium or
phosphonium functional group. These groups modify the nanoclay
surface by ionically bonding to it, thereby converting the surface
from a hydrophilic to an organophilic species.
[0056] Other means for modification involve leaving the sodium ion
on the surface and coordinating it via ion-dipole interaction.
Regardless of the modification technology used, the resulting
clay-chemical complex, which exhibits a definite gallery spacing
between the plates, may be easily dispersed in a polymer matrix to
form a nanocomposite material.
[0057] In some embodiments, nanoclays are dispersed into the
elastomer composition of the seal body, generally at less than 5 wt
% levels. When a nanoclay is substantially dispersed within the
polymer it is said to be exfoliated. Exfoliation is facilitated by
surface modification chemistries described above, which through
ionic interactions, separate the nanoclay plates to the point where
individual plates may be further separated from another by
mechanical shear or heat of polymerization. Nanocomposites may be
created using both thermoplastic and thermoset polymers, and the
specific surface modification chemistries designed and employed are
necessarily a function of the host polymer's unique chemical and
physical characteristics. In some cases, the final nanocomposite
will be prepared in the reactor during the polymerization stage.
For other polymer systems, processes may be used to incorporate
nanoclays into a hot-melt compounding operation.
[0058] In general, nanocomposites exhibit gains in barrier, flame
resistance, structural, and thermal properties yet without
significant loss in hardness or clarity. Because of the
nanometer-sized dimensions of the individual plates in one
direction, exfoliated nanoclays are transparent in most polymer
systems. However, with surface dimensions extending to 1 micron,
the tightly bound structure in a polymer matrix is impermeable to
gases and liquids, and offers superior barrier properties over the
native polymer. Such nanocomposites may also exhibit enhanced heat
resistive properties.
[0059] Nanoclays are commercially available as Nanomer.RTM.
nanoclays from Nanocor.RTM., Cloisite.RTM. additives from Southern
Clay Products, Nanolin from FCC Inc., Halloysite from Nanoclay
Technologies.
[0060] Fullerenes and Nanotubes
[0061] Fullerenes are a family of carbon allotropes named after
Richard Buckminster Fuller and are sometimes called buckyballs.
They are closed cages molecules composed entirely of
sp.sup.2-hybridized carbons and may be in the form of a hollow
sphere, ellipsoid, or tube. Cylindrical fullerenes are called
carbon nanotubes or buckytubes. Fullerenes are similar in structure
to graphite, which is composed of a sheet of linked hexagonal
rings, but they contain pentagonal (or sometimes heptagonal) rings
that prevent the sheet from being planar. Fullerenes may be
produced by carbon arc methods of condensation of vaporized
carbon.
[0062] As used herein, the term "nanotube" refers to various
materials having having a cylindrical or tubular configuration with
at least one dimension, such as length or diameter, between 1 and
100 nanometers. Types of nanotubes that may find use as a
reinforcing nanotubes material in the present disclosure may
include carbon nanotubes (CNTs), including single-walled (SWNT),
double-walled (DWNT), multi-walled (MWNT), inorganic nanotubes,
multibranched nanotubes, functionalized nanotubes, and CNT-C.sub.60
hybrids. Additionally, in some embodiments, at least a portion of
the surface of the reinforcing nanotubes may be modified.
[0063] Carbon nanotubes are polymers of pure carbon, which may be
functionalized or otherwise modified. Both SWNTs and MVVNTs are
known in the art and the subject of a considerable body of
published literature. Examples of literature on the subject are
Dresselhaus, M. S., et al., Science of Fullerenes and Carbon
Nanotubes, Academic Press, San Diego (1996), and Ajayan, P- M., et
al., "Nanometre-Size Tubes of Carbon," Rep. Prog. Phys. 60 (1997);
1025-1062. The structure of a single-wall carbon nanotube may be
described as a single graphene sheet rolled into a seamless
cylinder whose ends are either open or closed. When closed, the
ends are capped by either half fullerenes or more complex
structures including pentagons.
[0064] Nanotubes frequently exist as "ropes," or bundles of 10 to
100 nanotubes held together along their length by van der Waals
forces, with individual nanotubes branching off and joining
nanotubes of other "ropes." Multi-walled carbon nanotubes are
multiple concentric cylinders of graphene sheets. The cylinders are
of successively larger diameter to fit one inside another, forming
a layered composite tube bonded together by van der Waals forces,
with a typical distance of approximately 0.34 nm between layers, as
reported by Peigney, A., et al., "Carbon nanotubes in novel ceramic
matrix nanocomposites," Ceram. Inter. 26 (2000) 677-683.
[0065] Carbon nanotubes are commonly prepared by arc discharge
between carbon electrodes in an inert gas atmosphere. The product
is generally a mixture of single-wall and multi-wall nanotubes,
although the formation of single-wall nanotubes can be favored by
the use of transition metal catalysts such as iron or cobalt. The
electric arc method, as well as other methods for the synthesis of
carbon nanotubes is described in, for example, "Nanometre-Size
Tubes of Carbon," P. M. Ajayan and T. W. Ebbesen, Rep. Prog. Phys.,
60, 1025-1062 (1997). Inorganic nanotubes may include those
prepared from a range of materials including boron nitride, silicon
nitride, silicon carbide, dichalcogenides, for example, WS.sub.2,
oxides such as HfO.sub.2 and MoO.sub.3, metallic nanotubes, such as
Co and Au, and materials having a composition
B.sub.xC.sub.yN.sub.z, where x, y, and z may be independently
selected from 0 to 4, including for example, BC.sub.2N.sub.2 and
BC.sub.4N, and combinations thereof.
[0066] In a particular embodiment, the average diameter of the
nanotube materials may range from about 1 to 100 nanometers. In
various other embodiments, the reinforcing phase may include SWNTs
having an average diameter of about 1 to 2 nanometers and/or MWNTs
having an average diameter of about 2 to 30 nanometers. Nanotube
materials typically have a very high aspect ratio. In a particular
embodiment, the nanotubes used in the present disclosure may have
an aspect ratio ranging from about 25 to 1,000,000, and preferably
from about 100 to about 1,000.
[0067] The surface of the carbon nanotubes of fullerene may, in one
embodiment, be modified prior to incorporation into the composites
of the present disclosure. In some embodiments, the nanostructured
carbon material is modified by a chemical means to yield
derivatized nanostructured carbon material. As used herein,
"derivatization" refers to the attachment of other chemical
entities to the nanostructured carbon material, which may be by
chemical or physical means including, but not limited to, covalent
bonding, van der Waals forces, electrostatic forces, physical
entanglement, and combinations thereof. In other embodiments, the
nanostructured carbon material is modified by a physical means
selected from the group consisting of plasma treatment, heat
treatment, ion bombardment, attrition by impact, milling and
combinations thereof In yet other embodiments, the nanostructured
carbon material is modified by a chemical means selected from the
group consisting of chemical etching by acids either in liquid or
gaseous form, chemical etching by bases either in liquid or gaseous
form, electrochemical treatments, and combinations thereof.
[0068] One of ordinary skill in the art would appreciate that
derivatization or functionalization may be desired so as to
increase ease in solubilization and/or disperson of the nanotubes
into at least one of the component phases prior to formation of a
composite material. Functionalization or derivatization may occur
by the incorporation of various chemical moieties on either end
caps and/or sidewalls (either exterior or interior) of the
nanostructured carbon material, or with a coating placed
thereon.
[0069] For example, functionalization may occur through covalent
and/or non-covalent functionalization, endcap and/or sidewall
functionalization, exohedral and/or endohedral functionalization
and supramolecular complexation. A variety of functionalized
nanostructured carbon materials have been developed so as to enable
dispersion of the nanostructures into composite materials,
including fluoronanotubes, carboxy-nanotubes, and various
covalently bonded nanotubes, including amino-CNTs, vinyl-CNTs,
epoxy-CNTs. Oxidation of nanostructured carbon materials may result
in carboxyl, hydroxyl, or carbonyl groups, which may be further
modified via amidation or etherification, for example.
Additionally, functionalization frequently occurs through an
initial fluorination, and then subsequent nucleophilic attack, or
via a free radical reaction to form a covalent carbon-carbon bond.
Further, U.S. Pat. Nos. 7,122,165, 7,105,596, 7,048,999, 6,875,412,
6,835,366, 6,790,425, 2005/0255030, which are all herein
incorporated by reference in their entirety, disclose various
sidewall and endcap functionalization that may, for example, be
used to assist in integration of nanostructured carbon materials in
an elastomer seal of the present disclosure. Nanostructured carbon
materials may be added to elastomer seals disclosed herein in an
amount greater than about 0.1, 0.2, 0.5, 1, and 2 volume percent in
some embodiments, and less than 10, 5, 4, 2, and 1 volume percent
in other embodiments.
[0070] Other analogous nanostructures of similar geometry as
described above are farther contemplated for use in elastomer seals
of the present disclosure. For example, the boron analogs of
fullerenes recently described by researchers at Rice University,
Houston, Tex. fall within the spectrum of nanomaterial additives
contemplated as a nanomaterial additive to the elastomer seal.
[0071] Nanodiamonds
[0072] In particular embodiments, the at least one nanomaterial
additive may include diamond particles or diamond-like particles.
One suitable method for generating nanodiamonds may include, for
example, a detonation process as described in Diamond and Related
Materials (1993, 160-2), which is incorporated by reference in its
entirety, although nanodiamonds produced by other methods may be
used. Those having ordinary skill in the art will appreciate how to
form nanodiamond particles. Briefly, in order to produce
nanodiamond by detonation, detonation of mixed high explosives in
the presence of ultradispersed carbon condensate forms
ultradispersive diamond-graphite powder (diamond blend or DB),
which is a black powder containing 40-60 weight percent of pure
diamond. Chemical purification of DB generates pure nanodiamond
(ultradispersive detonational diamond or UDD), a grey powder
containing up to 99.5 weight percent of pure diamond. The ultrafine
diamond particles generated by the detonation process may comprise
a nanodiamond core, a graphite inner coating around the core, and
an amorphous carbon outer coating about the graphite. Both the
graphite coating and amorphous carbon coating may be optionally
removed by chemical etching. In some embodiments, the nanodiamond
particles may be clustered in loose agglomerates ranging in size
from nanoscale to larger than nanoscale. Diamond or diamond-like
particles may be added to elastomer seals disclosed herein in an
amount greater than about 0.1, 0.2, 0.5 volume percent in some
embodiments, and less than 10, 5, 2, and 1 volume percent in other
embodiments.
[0073] In particular embodiments, the nanomaterial additive may
include at least one of an inorganic nanomaterial, such as a metal
oxide nanoparticle. One suitable method for generating metal oxide
nanoparticles is by using plasma synthesis, although metal oxide
nanoparticles produced by other methods may be used. Those having
ordinary skill in the art will appreciate how to form metal oxide
nanoparticles. Metal oxide nanoparticles may comprise oxides of
zinc, iron, titanium, magnesium, silicon, aluminium, cerium,
zirconium, mixed metal compounds or mixtures thereof. Further,
other nanoparticles such as nanopowders, inorganic nanoparticles
such as calcium carbonate, nanofibers, and a mixture of
nanomaterials can be used in elastomer seals of the present
disclosure.
[0074] Integration of the nanomaterial additive into the elastomer
seal may include any means as known to those skilled in the art. As
used herein, integration refers to any means for adding the
nanomaterial additive to a component of the elastomer seal such
that the nanomaterial additive is a component of the formed
elastomer seal, i.e., by exfoliation, hot-melting, plastic
extrusion, or other forms of incorporation of the nanomaterial
additive as known to those skilled in the art. In some embodiments,
the nanomaterial additives may be integrated in such a manner so as
to achieve a generally uniform dispersion of the nanomaterial
additives through the formed composite body.
[0075] For example, nanomaterial additives may be integrated with
the elastomer composition prior to curing. These nanomaterial
additives may be added, compounded, or blended with the elastomer
seal precursors, prior to the curing process. For instance, the
base elastomer may be compounded or mixed with additives or agents
such as furnace black, peroxide curing agent, graphite, zinc oxide,
stearic acid, plasticizer, and nanomaterial additives.
Alternatively, the nanomaterial may be integrated into the
elastomer seal post-cure by methods such as spraying, hot melting,
plastic extrusion, and other methods known in the art.
[0076] Advantageously, embodiments of the present disclosure
contain elastomer seal containing nanomaterial additives, which may
confer superior properties such as enhanced elastic and tensile
moduli, hardness, and tear strength. These enhanced properties
would allow the seal to withstand the harsh conditions of elevated
temperatures, pressures, and constant friction for longer periods
of time. This may prolong the downhole life of the nanocomposite
elastomer seal and ultimately the rock bit. This seal life
extension would serve to significantly reduce drilling downtime,
and be invaluable in the oil and gas industry.
[0077] While the present disclosure has been described with respect
to a limited number of embodiments, those skilled in the art,
having benefit of this disclosure, will appreciate that other
embodiments may be devised which do not depart from the scope of
the present disclosure as disclosed herein. Accordingly, the scope
of the present disclosure should be limited only by the attached
claims.
* * * * *