Note: Descriptions are shown in the official language in which they were submitted.
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DRILL BIT WITH SEAL HAVING SPHERES
IN A MATRIX SEAL MATERIAL
TECHNICAL FIELD
This disclosure relates generally to equipment utilized
and operations performed in conjunction with a subterranean
well and, in one example described below, more particularly
provides a drill bit with a seal having spheres in a matrix
seal material of the seal.
BACKGROUND
Drill bits used to drill wellbores have to operate in
an extremely hostile environment. As a result, such drill
bits are highly specialized for their purpose. One such
drill bit is of the type known as a roller cone bit, in
which cutting elements are mounted on cones which rotate as
the drill bit is rotated downhole to drill a wellbore.
To facilitate rotation of the cones, bearings are
provided between the cones and a body of the bit, and
lubricant is provided for the bearings. To prevent external
debris from damaging the bearings or otherwise causing
excessive wear in the rotating cones, and to prevent escape
of the lubricant, seals are also provided in such bits.
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Unfortunately, in the harsh downhole environment, seals
in drill bits tend to fail (e.g., permit excessive wear, no
longer exclude debris, fail to contain the lubricant, etc.)
sooner than is desired. Drilling operations could be made
much more economical and expeditious if drill bit seals had
longer lives.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a representative elevational view of a drill
bit embodying principles of this disclosure.
FIG. 2 is a representative cross-sectional view through
one arm of the drill bit of FIG. 1.
FIG. 3 is a representative enlarged scale cross-
sectional view through a seal which can embody principles of
this disclosure.
FIG. 4 is a representative graph of sealing force over
time for two seal examples.
FIG. 5 is a representative cross-sectional view of
another configuration of the seal.
DETAILED DESCRIPTION
Representatively illustrated in FIG. 1 is a drill bit
10 which can embody principles of this disclosure. The drill
bit 10 is of the type known to those skilled in the art as a
roller cone bit or a tri-cone bit, due to its use of
multiple generally conical shaped rollers or cones 12 having
earth-engaging cutting elements 14 thereon.
Each of the cones 12 is rotatably secured to a
respective arm 16 extending downwardly (as depicted in FIG.
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1) from a main body 18 of the bit 10. In this example, there
are three each of the cones 12 and arms 16.
However, it should be clearly understood that the
principles of this disclosure may be incorporated into drill
bits having other numbers of cones and arms, and other types
of drill bits and drill bit configurations. The drill bit 10
depicted in FIG. 1 is merely one example of a wide variety
of drill bits which can utilize the principles described
herein.
Referring additionally now to FIG. 2, a cross-sectional
view of one of the arms 16 is representatively illustrated.
In this view it may be seen that the cone 12 rotates about a
journal 20 of the arm 16. Retaining balls 22 are used
between the cone 12 and the journal 20 to secure the cone on
the arm.
Lubricant is supplied to the interface between the cone
12 and the journal 20 from a chamber 24 via a passage 26. A
pressure equalizing device 28 ensures that the lubricant is
at substantially the same pressure as the downhole
environment when the drill bit 10 is being used to drill a
wellbore.
A seal 30 is used to prevent debris and well fluids
from entering the interface between the cone 12 and the
journal 20, and to prevent escape of the lubricant from the
interface area. As the cone 12 rotates about the journal 20,
the seal 30 preferably rotates with the cone and seals
against an outer surface of the journal, as described more
fully below. However, in other examples, the seal could
remain stationary on the journal 20, with the cone 12
rotating relative to the journal and seal.
Referring additionally now to FIG. 3, an enlarged scale
cross-sectional view of the seal 30 is representatively
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illustrated, along with a seal groove or gland 38 in which
the seal is retained, and an adjacent surface 44 of the
drill bit 10 against which the seal seals. In this example,
the seal gland 38 is formed in the cone 12, and the surface
44 is formed on the journal 20, but in other examples the
seal 30 could be otherwise retained and could seal against
other surfaces.
Note that the seal 30 rotates with the cone 12 about
the journal 20 during operation, so the seal dynamically
contacts the surface 44 (e.g., there is relative
displacement between the seal and the surface while the seal
sealingly contacts the surface). However, in other examples,
the seal 30 could dynamically contact the cone 12 (e.g., the
gland 38 could be formed on the journal 20, and the surface
44 could be formed in an interior of the cone, etc.).
This dynamic contact coupled with abrasive particles in
the environment surrounding the drill bit 10 (for example,
in drilling mud circulated through a drill string and
wellbore during a drilling operation) can result in rapid
wear of the seal 30, particularly where it contacts the
surface 44.
However, the seal 30 depicted in FIG. 3 comprises many
spheres 32 distributed in a matrix seal material 34. The
spheres 32 enhance the wear resistance of the seal 30.
In this example, the spheres 32 comprise hollow glass
microspheres. Suitable hollow glass microspheres are
marketed by Dyneon LLC of Oakdale, Minnesota USA (e.g.,
Product No. iM30K), and manufactured by 3M of St. Paul,
Minnesota USA.
In other examples, the spheres 32 may not be hollow,
glass or micrometer-sized (e.g., approximately 1 to 1000
micrometers). The spheres 32 could instead be solid, made of
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another material and/or nanometer-sized, or otherwise
dimensioned or configured.
The spheres 32 may have a hardness which is less than
that of the journal 20, or at least less than that of the
surface 44. In this manner, the spheres 32 will not
significantly abrade the surface 44 during operation.
However, the spheres 32 can have a hardness greater than
that of the matrix seal material 34, so that the spheres do
not wear away as quickly as the seal material, thereby
reducing the total wear of the seal 30.
The matrix seal material 34 in this example comprises
an elastomer--more particularly, a nitrile material (e.g.,
NBR). The nitrile material may be hydrogenated (e.g., HNBR
or HSN). However, other materials (such as, fluorocarbon
seal materials, EPDM, AFLAS(TM), FKM(TM), etc.) may be used
in keeping with the scope of this disclosure.
The inventors have discovered that hollow glass
microspheres can desirably share a compressive load in the
seal 30 with the matrix seal material 34. This results in
reduced contact pressure between the seal 30 and the surface
44, which reduces wear. In tests, solid spheres do no share
the compressive load as desirably, perhaps because of the
greater mismatch between the compressibility of the matrix
seal material 34 and the compressibility of the solid
spheres.
However, as representatively depicted in FIG. 4, less
sealing force is available over time from a compressed seal
with the spheres 32 therein (as indicated by curve 36 in
FIG. 4), as compared to a compressed seal without the
30 spheres therein (as indicated by curve 40 in FIG. 4). This
unexpected result can be compensated for by increasing the
initial compression of the seal 30 with the spheres 32
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therein, so that it retains a desired sealing force over a
desired period of time. This increase in initial compression
can help to exclude debris and abrasive particles from the
journal 20 and bearings 22, and wear effects due to the
increased compression can be more than offset by the
increased wear resistance of the seal 30 with the spheres 32
therein.
Referring additionally now to FIG. 5, another
configuration of the seal 30 is representatively
illustrated. In this configuration, the spheres 32 are
predominately in a portion 42 of the matrix seal material 34
which sealingly and dynamically contacts the drill bit 10
surface 44.
The spheres 32 may, in some examples, be exclusively
confined to only the portion 42 of the matrix seal material
34. In other examples, the spheres 32 may be more dense in
the portion 42 of the seal material 34, as compared to in
the remainder of the seal material.
As depicted in FIG. 5, the portion 42 comprises an
inner diameter portion of the seal 30 which contacts the
journal 20. In other examples, the portion 42 could comprise
an outer diameter portion of the seal 30, the portion 42
could be in sealing contact with the cone 12 or another
drill bit surface, etc.
Furthermore, the portion 42 could comprise an entire
outer surface portion of the seal 30 (e.g., the seal having
a core of the matrix seal material 34 with none, or at least
less density, of the spheres 32 in the core), so that any
surface contacted by the seal also contacts the portion 42.
Thus, it will be appreciated that the principles of this
disclosure are not limited to the specific details of the
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seal 30 examples described above, or to any specific
positioning of the spheres 32 in the seal.
It may now be fully appreciated that this disclosure
provides significant advancements to the art of constructing
drill bits with seals therein. In examples described above,
the wear resistance of a seal 30 can be substantially
increased by incorporating spheres 32 into at least a
portion 42 of a matrix seal material 34.
In one example, a drill bit 10 can include a seal 30
which seals against a drill bit surface 44. The seal 30
comprises a matrix seal material 34 and a plurality of
hollow spheres 32 in the matrix seal material 34.
The hollow spheres 32 may comprise hollow microspheres
and/or hollow glass spheres.
The hollow spheres 32 may be are confined to a portion
42 of the matrix seal material 34. The portion 42 of the
matrix seal material 34 may contact a journal 20 and/or a
cone 12 of the drill bit 10. The portion 42 of the matrix
seal material 34 may be in dynamic contact with at least one
of a journal 20 of the drill bit 10 and a cone 12 of the
drill bit 10 during operation.
The matrix seal material 34 can include at least one of
nitrile and hydrogenated nitrile.
The hollow spheres 32 may have a hardness less than a
hardness of a journal 20 of the drill bit 10.
Also described above is a drill bit 10 which, in one
example, comprises a seal 30 including a matrix seal
material 34. A portion 42 of the matrix seal material 34 has
a greater density of spheres 32 therein, as compared to
outside of the portion 42. The portion 42 of the matrix seal
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material 34 is in dynamic sealing contact with a drill bit
surface 44 during operation.
The above disclosure also describes an example of a
drill bit 10 which comprises a journal 20, a cone 12 which
rotates about the journal 20, and a seal 30 between the cone
12 and the journal 20. The seal 30 comprises a matrix seal
material 34 and a plurality of spheres 32 in the matrix seal
material 34. The matrix seal material 34 comprises nitrile.
Although various examples have been described above,
with each example having certain features, it should be
understood that it is not necessary for a particular feature
of one example to be used exclusively with that example.
Instead, any of the features described above and/or depicted
in the drawings can be combined with any of the examples, in
addition to or in substitution for any of the other features
of those examples. One example's features are not mutually
exclusive to another example's features. Instead, the scope
of this disclosure encompasses any combination of any of the
features.
Although each example described above includes a
certain combination of features, it should be understood
that it is not necessary for all features of an example to
be used. Instead, any of the features described above can be
used, without any other particular feature or features also
being used.
It should be understood that the various embodiments
described herein may be utilized in various orientations,
such as inclined, inverted, horizontal, vertical, etc., and
in various configurations, without departing from the
principles of this disclosure. The embodiments are described
merely as examples of useful applications of the principles
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of the disclosure, which is not limited to any specific
details of these embodiments.
In the above description of the representative
examples, directional terms (such as "above," "below,"
"upper," "lower," etc.) are used for convenience in
referring to the accompanying drawings. However, it should
be clearly understood that the scope of this disclosure is
not limited to any particular directions described herein.
The terms "including," "includes," "comprising,"
"comprises," and similar terms are used in a non-limiting
sense in this specification. For example, if a system,
method, apparatus, device, etc., is described as "including"
a certain feature or element, the system, method, apparatus,
device, etc., can include that feature or element, and can
also include other features or elements. Similarly, the term
"comprises" is considered to mean "comprises, but is not
limited to."
Of course, a person skilled in the art would, upon a
careful consideration of the above description of
representative embodiments of the disclosure, readily
appreciate that many modifications, additions,
substitutions, deletions, and other changes may be made to
the specific embodiments, and such changes are contemplated
by the principles of this 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 invention being limited solely by
the appended claims and their equivalents.
