Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ROLLER CUTTER DRILL BIT HAVING A TEXTURIZED SEAL MEMBER
Background of the invention
This invention relates to rotary drill bits used to drill oil and gas
wells in the earth, and more particularly to rotary drill bits of the
suckled sealed bearing roller cutter type.
This invention involves an improvement on the prior art sealed
bearing roller cutter drill bit, such as shown for example in US. Patent Nos.
3,397,928 and 3,765,495, comprising a bit body having a threaded pin at its
upper end adapted to be detachably secured to a drill string for rotating the
drill bit, and three depending legs at its lower end each having a generally
cylindrical bearing journal. Conical roller cutters having a recess ofgenerally circular section in the end thereof are rotatable mounted on the
bearing journal by bearing means. A lubrication system provides lubricant to
each bearing means. The system comprises a reservoir in the bit body holding
a supply of lubricant, massaging in the bit body providing fluid communication
between the reservoir and the bearing means for flow of lubricant to the
bearing means, and a seal member between the roller cutter and the bearing
journal for blocking flow of lubricant past the bearing means and out of the
but body. The seal member is a ring of elastomers material carried in an
20 annular groove or recess in the roller cutter and is radially compressed against the bearing journal.
Because of the limited quantity of lubricant in the lubrication
system, the seal member must be effective in blocking egress of lubricant from
the bit body so as to prevent the bearing from running "dry" and thus
25 destruction of bearing. Similarly, because the drilling fluid surrounding the
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bit when in a well bore is highly abrasive, the seal member must also be
effective in blocking ingress of drilling fluid into the bit body. To make
the seal substantially leak-proof, the seal is typically subject to a high
degree of radial compression (i.e., 10~ or more compression as disclosed in
US. Pat. No. 3,397,928, and something approaching but not reaching 10~
compression as disclosed in US. Pat. No. 3,765,495). Such levels of
compression are significantly higher than that recommended for other uses of
elastomeric sealing rings. Moreover, it is the accepted practice in the
industry, to make the face of the seal member which is in sliding, frictional
engagement with the bearing journal a smooth, flawless surface.
In this latter regard, each of the competitors in the drill bit
industry has developed quality control procedures to ensure that the engaging
face of each drill bit seal member us free of surface imperfections. These
quality control procedures are based on the "Rubber Manufacturers Association
0-Ring Inspection Guide Handbook" and Military Standard (MIL-STD-413B) forVisual Inspection Guide for Elastomeric 0-Rings. The inspection procedure of
; the assignee of this application, for example requires that the engaging face
of the seal member be a smooth, uniform, continuous surface free of all of the
fourteen kinds of unacceptable surface imperfections described in
MIL-STD-413C, when the seal member is visually examined under 3X
magnification. It has been the accepted wisdom in the industry that surface
imperfections are highly undesirable in that an imperfection may provide a
flow path (or at least a portion of a flow path) for lubricant or drilling
fluid leakage. In addition, such surface imperfection could also cause stress
concentrations in the highly compressed seal member which may result in
tearing of the the seal member due to the high frictional forces on the
engagement face of the seal member tending to shear the face from the
remainder of the seal member.
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Seal members having smooth engagement faces have been generally
satisfactory for sealed bearing roller cutter drill bits as evidenced by the
fact that such seal members have been the industry standard since the early
1970's. However, in recent years, improvements in drilling equipment
technology has enabled drillers to turn drill bits faster so as to deliver
more power to the drill bit for higher rates of drilling penetration through
the earth's formations, and a problem, described more fully hereinafter, has
developed with this seal member.
. A modern rotary drill rig can rotate the drill string and thus a
roller cutter drill bit at 150 rum as compared to an older drill rig which
could rotate at only 110 rum. In addition, positive displacement down hole
motors with speeds of rotation of up to 500 rum and down hole turbine motors
with speeds of up to 1000 rum, which had previously been used only with
diamond drag drill bits, are now being used to rotate roller cutter type drill
bits. Because each roller cutter rotates approximately 1 1/2 times for each
rotation of the drill bit body and the length of the circumference of the
; bearing journal engaged by the seal member increases with drill bit body
diameter, seal members (particularly those in large diameter bits) are now
subject to high linear speeds, as measured in feet per second, at their
engagement faces. For example, in one common application in which a 17 1/2
inch diameter drill bit is run on a turbine motor at 750 rum, the engagement
face of the seal member is subject to a linear speed in excess of 20 feet per
second. Such speeds exceed the recommended speed for an 0-ring seal member
used in even the most ideal conditions, much less in a drill bit in which the
seal member is highly compressed, is exposed to highly abrasive material
(i.e., the drilling fluid) and to high operating temperatures, and is carried
in a bearing member (i.e., the roller cutter) that wobbles and reciprocates,
as well as rotates on the bearing journal. With these high speeds of drill
bit rotation, the smooth surface seal members have shown a tendency to fail
well before the remainder of the drill bit is fully worn.
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The reasons for such failure are not fully understood. However,
applicants believe that this is due in significant part to an inability of the
seal member to adequately hold lubricant to its engagement face, with the
result that the engagement face becomes overheated. Excess heat in the seal
S member causes vulcanization of the seal member's elastomeric material, thereby
resulting in the seal member losing its elasticity and hence its ability to
remain in scaling engagement with the bearing journal as the roller cutter
wobbles. Excess heat thus results in leakage of lubricant and/or drilling
fluid past the seal member, and shortly thereafter failure of the bearing and
lo the entire drill bit.
Summary of the Invention
Among the several features of this invention may be noted the
provision of a sealed bearing roller cutter drill bit having an improved seal
member which enables the drill but to be turned at high speeds yet provides
; 15 satisfactory seal life; the provision of such a seal member for which less
heat is generated at its engaging face than at the engaging face of a
conventional seal member; the provision of such a seal member which may be
made of harder elastomeric materials than a conventional seal member, and the
provision of such a seal member which may be made of an elastomeric material
which has less tear strength than the materials used for the conventional seal
member.
In general, the rotary drill bit of this invention comprises a bit
body having a threaded pin at its upper end adapted to be detachably secured
to a drill strung for rotating the drill bit, and at least one depending leg
at its lower end having a generally cylindrical bearing journal, constituting
a first bearing member of the bit. The bit further comprises a roller cutter
of generally conical shape constituting a second bearing member of the bit,
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with the roller cutter having a recess therein of generally
circular section for receiving the bearing journal. Bearing
means rotatable mount the roller cutter on the bearing journal.
A lubrication system in the bit provides lubricant to the
bearing means. This system comprises a reservoir holding
a supply of lubricant, massaging in the bit body providing
fluid communication between the reservoir and the bearing
means, and seal means in an annular seal cavity between the
roller cutter and the bearing journal for blocking flow of
lubricant past the bearing means and out of the bit body,
and for blocking flow of drilling fluid past the seal means and
into the bit body. The seal means comprise an annular seal
member of elastomeric material compressed radially between the
bearing members and having a circumferential continuous an-
nailer engagement face in sealing, sliding frictional engagement with one of the bearing members. The annular engagement face
has a surface texture defining a pattern of alternating depress
sons and projections to form a plurality of radially compressed
pockets to hold lubricant therein against the one bearing
member. The pattern of alternating depressions and projections
on the surface texture are arranged and constructed to sub-
staunchly block the flow of lubricant past the seal member and
out of the bit body, and to substantially block the flow of
drilling fluid past the seal member inwardly to the bearing
means and inside the bit body. The seal means comprises an
annular seal member of elastomeric material compressed radially
between the bearing members, with an annular engagement face
- of the seal member in sealing, sliding frictional engagement
with said one of the bearing members. The annular engagement
face has a surface texture such that with the seal member
compressed against said one bearing member a plurality of
pockets are formed in the annular engagement face adapted to
hold lubricant for lubricating the seal member, yet the
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annular engagement face is effective to substantially block
leakage past the seal member.
Another aspect of the invention pertains to a rotary
drill bit having a bearing journal defining one bearing member,
a roller cutter on the bearing journal defining a second
bearing member, bearing means mounting the roller cutter for
rotation on the bearing journal, and a lubrication system
for providing lubricant to the bearing means including pressure
compensation means to effect balancing of fluid pressure
differentials between the drilling fluid outside the bit and
the lubricant inside the bit. The improvement provides an
O-ring type annular seal member having inner and outer radial
sealing faces compressed between and in contact with opposed
bearing surfaces on the roller cutter and bearing journal
to form circumferential continuous sealing surfaces, the
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seal member being exposed to liquid drilling fluid outside
the bit on one side thereof and to liquid lubricant inside
the bit on an opposite side thereof. One of the sealing faces
has pockets directly adjacent its circumferential continuous
sealing surface for retaining lubricant therein against one
of the bearing members, the pockets defining a plurality of
projections and intervening recesses arranged in a pattern
to block the flow of lubricant inside the bit past the seal
member outwardly of the bearing means, and to block the flow
of drilling fluid outside the bit past the seal member inwardly
to the bearing means under fluid pressure differentials between
the drilling fluid and lubricant encountered during normal
operation of the drill bit.
Other aspects and features will be in part apparent
and in part pointed out hereinafter.
Brief Description of the Drawings
Fig. l is an elevation of a rotary drill bit of this
invention having a plurality of roller cutters;
Fig. 2 is an enlarged partial vertical section of
the bit of Fig. l showing one of the roller cutters rotatable
mounted on a bearing journal with a seal member there between;
Fig. 3 is an enlarged perspective of the seal member
showing its texturized engagement face;
Fig. 4 is a central section of the seal member on
line 4--4 of Fig. 3;
Fig. PA is a view similar to Fig. 4 showing an
alternate ridge design;
Fig. 5 is an enlarged section of the seal member
on line 5--5 of Fig. 4 showing a pocket at the engagement
face thereof for holding lubricant;
Fig. 6 is a partial section of the seal member on
-.~
line 6--6 of Fig. 5;
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Fig. PA is a view similar to Fig. 5 of a second
embodiment of the seal member in its uncompressed condition;
Fig. 7B is a view similar to Fig. PA but with the
seal member shown as it would appear when compressed against
a bearing member, with pockets formed in the engagement face
thereof;
Fig. PA is an enlarged section on line AYE of
Fig. 7;
Fig 8B is an enlarged section on line 8B--8B, with
lo a portion of the bearing member engaged by the seal member
being shown;
Fig. PA is a view similar to Fig. 5 showing a third
embodiment of the seal member having a large number of small
projections on its engaging face;
Fig. 9B is a view similar to Fig. PA showing a fourth
embodiment of the seal member having an engagement face having
alternate segments of texturized surface and smooth surface;
Fig. lo is an enlarged section on line Lowe of
Fig. PA; and
Fig. if is an enlarged section of a fifth embodiment
of the seal member having a generally tapered shape in section
and recesses in its engagement face.
Corresponding reference characters indicate core-
sponging parts throughout the several views of the drawings.
Description of the Preferred Embodiments
Referring to Fig. l there is generally indicated
at l a rotary drill bit of this invention for drilling oil
and gas wells in the earth. The drill bit comprises a bit
body 3 having a threaded pin 5 at its upper end adapted to
be detachably secured to a drill string (not shown) suspended
from a drill rig (not shown). The drill string is used to
rotate the drill bit in the well bore and to deliver drilling
fluid under pressure to the drill bit. The drilling fluid
is pumped by fluid circulation pumps (not shown) at the drill
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rig down the passage in the drill string, through nozzles
in the drill bit to clean the well bore bottom and back up
to the drill rig via the annuls between the drill string
and the side of the well bore to remove formation cuttings.
At its lower end, the bit body has a plurality of legs 7 each
having a generally cylindrical bearing journal 9, constituting
a first bearing member of the bit. The drill bit further
comprises a plurality of generally frustoconical roller cutters
11, one for each bearing journal. These roller cutters
constitute second bearing members of the drill bit.
As best illustrated in Fig. 2, each roller cutter
11 has a recess 13 therein of generally circular section for
receiving the respective bearing journal 9. Bearing means
designated generally at 15 such as bushing 17 for supporting
generally vertical loads on the roller cutter and ball bearings
19 for holding the roller cutter on the journal, rotatable
mount the roller cutter on the journal. A lubrication system
designated generally at 21 in the bit body 3 provides lubricant
to the bearing means 15. This system comprises a reservoir
23 of lubricant formed in the side of the bit body and closed
by a pressure compensating diaphragm 25 for effecting a balance
in of fluid pressure between the drilling fluid outside the
bit and the lubricant inside the bit, massaging 27 extending
down from the reservoir to the surface of the bearing journal
9 for flow of lubricant to the bearing means, and seal means
29 between the roller cutter and the bearing journal for block-
in flow of lubricant past the bearing means and out of the
bit body. The seal means comprises an annular seal member
of elastomeric material held in an annular recess or seal
cavity 30 in the roller cutter in sealing relationship there-
with. The seal member is compressed radially against the
bearing journal 9 and has an annular engagement face 31 in
sealing, sliding frictional engagement with the bearing
journal.
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I 7~7 9
As illustrated in Figs. 3-6, the annular engagement face 31 of the
seal member presents a roughened or textured surface. More particularly,
the engaging face has two sets of generally parallel ridges, one set AYE being
angled in one direction relative to the longitudinal centerline 35 of the seal
member and the other set 33 B being angled in the qppositedirection, with the
sets of ridges intersecting each other generally at the central radial plane
37 of the seal member. This pattern of ridges forms a plurality of generally
diamond shaped recesses in side-by-side relationship around the annular
engagement face 31 of the seal member. With the seal member radially
I compressed on the bearing journal, the ridges and recesses form, together with
the bearing member, a plurality of closed pockets 39 for holding lubricant.
It is important to note, that at the same time, this annular engagement face
has been found to be effective in substantially blocking flow of lubricant
past the seal member out of the bit body, as well as, blocking flow of
drilling fluid from the annuls into the bit body.
A similar pattern of ridges is shown in Fig. PA. In this arrangement
the ridges, 34 and AYE, do not intersect in the central radial plane of the
seal member, but rather intersect a continuous circumferential ridge, 32.
This arrangement functions in a manner similar to the seal member in Fig. 4
and can facilitate manufacture.
By holding lubricant at the frictional engagement surface of the seal
member and the bearing journal, the seal member 29 of this invention provides
a lower coefficient of friction and lower heat generation than the
conventional smooth surface seal member. These properties enable the seal
member to be made of harder elastomeric material than the conventional smooth
surface seal member. Harder elastomeric seal material is desirable because
such material offers greater wear resistance than softer materials. However,
at the same time, harder elastomeric seal material requires greater radial
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compressive forces for an effective seal and thus causes greater wear of the
engaging surface of the bearing journal than softer material. Thus, the
hardness of the seal member must be chosen so as to balance the wear on the
seal member and the wear on the bearing journal so as to provide the greatest
overall life in the seal assembly. For conventional smooth surface seal
members, the greatest overall seal assembly life is provided when the hardness
of the elastomeric material is as low as approximately 70 dormitory (Shore
A). In contrast, because the seal member 29 of this invention offers a
reduced coefficient of friction and thus lower wear on the bearing journal,
the seal member 29, may be significantly harder than the conventional seal
member (erg., as hard as 80 dormitory or more), which offers significantly
greater overall seal assembly life.
The reduction in the coefficient of friction provided by the seal
member 29 of this invention also results in a reduction in the shear forces
; 15 applied to the engagement face of the seal member. This enables the seal
member to be made of an elastomeric material having relatively low tensile
strength and tear strength and thus enables the other properties necessary for
an effective seal (such as resistance to thermal deterioration and abrasion
resistance), to be emphasized in selecting an appropriate elastomeric
20 material. Conventional smooth surface seal members are typically formed of abutadiene acrylonitide rubber (Bun N), which has not only satisfactory
thermal deterioration and abrasion resistance but also relatively high tensile
and tear strength. In contrast, the seal member of this invention may be made
from a fluoroelastomer, such as that sold under the trademarkYITON by the
25 Dupont Chemical Company of Wilmington, Delaware, which has better thermal
Jo deterioration and abrasion resistance than Bun N but less tensile and tear
strength than Bun N. Fluoroelastomer material is particularly well suited
for a seal member in a drill bit for drilling well bores in high temperature
formations. Such formations are encountered in drilling geothermal wells and
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in drilling extremely deep holes, in that the formation temperature increases
with drilling depth.
Referring to Figs. PA and PA, there is generally indicated at AYE a
second embodiment of the seal member which is similar to above-described seal
member 29 except that its annular engaging face AYE has a plurality of
projections 41 arranged in two parallel rows around the annular engagement
face of the seal members. Each projection is so sized and spaced from the
adjacent projections that with the seal member AYE compressed radially against
. the bearing journal 9, annular closed pockets 43 are formed in the engagement
face of the seal member around the projections (see Fig. 7B). As shown in
Fog. 8B, there are no fluid communication channels between adjacent annular
recesses 43 for flow (i.e., leakage) of lubricant or drilling fluid past the
seal member.
A third embodiment of the seal member 29B is illustrated in Fig. PA
and 10. This seal member is similar to the seal member AYE of the second
embodiment except that it has projections 45 on its engagement face 31B which
are smaller than the projections 41 both in their cross-sectional area and
their projecting height, and are randomly distributed over the annular
engagement face 31B of the seal member over the entire length thereof. More
particularly, the projections are so sized that with the seal member
compressed against the bearing journal 9 the diameter of the annular recesses
formed around the projections 45 is less than one-third the width W of the
annular engagement face 31B. Because the projections are randomly
distributed, any given recess may be in fluid communication with one or more
adjacent recesses and thus would not form a closed pocket. Nonetheless, the
seal member is substantially leak-proof because the flow path (i.e., path for
leakage) for lubricant or drilling fluid across the engagement face 31B of the
seal would be of such small cross-sectional area as to prevent significant
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flow. Fig. PA and 10 also show the seal member 29B to be of generally hour
glass shape in section for enabling the seal member to be more readilydeformed than the rectangular section seal members shown in Fogs. 1-8 .
A fourth embodiment of the seal member 29C of this invention similar
to the third embodiment 29B is shown in Fig. 9B. The engagement face 31C of
this seal member is divided into a plurality of segments AYE and 47B. Every
other segment AYE has projections thereon, with the remanning segments 47B
having a smooth surface.
Lastly, a fifth embodiment of the seal member 29D is shown at in
lo Fig. 11. In contrast to the above-described embodiments of the seal members
which are formed as by conventional nicotine or compression molding processes
so as to have projections on their engagement faces, thus seal member 29D is
formed so as to have recesses R on its engagement face. Moreover, the seal
member 29D is of a tapered shape on section for enabling the seal member to be
more readily deformed than the seal members 29 and AYE of rectangular section.
., .
It will be observed from the foregoing that all of the
above-descr~bed embodiments of the seal member, when compressed against the
bearing journal, form pockets in their engaging faces for holding lubricant,
yet are effective to substantially block flow of lubricant and drilling fluid
past the seal member.
The seal member of this invention thus provides not only an effective
block to leakage but also a lower coefficient of friction than that for a
conventional smooth surface seal member for lower heat generation.
Accordingly, as compared with the conventional smooth surface seals, the seal-
member of this invention offers longer life, particularly when used in bits rotated at high speeds and in bits used to drill in high temperature
formations.
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While the seal members have been shown in the Figs. and described
above as being of a generally elongated shape in section, it is contemplated
that they could be other sectional shapes including square, rectangular or
circular. In the case of the circular shape the entire outer surface of the
seal member would be texturized. In addition, while the annular face 31 of
the seal member in engagement with the bearing journal is shown and described
as being texturized it is contemplated that the face of the annular face in
engagement with the roller cutter could be texturized in addition to or in
lieu of face 31.
In view of the above, it will be seen that the several objects of the
invention are achieved and other advantageous results attained.
As various changes could be made in the above constructions without
departing from the scope of the invention, it is intended that all matter
contained in the above description or shown in the accompanying drawings shall
lo be interpreted as illustrative and not in a limiting sense.
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