U.S. patent number 3,744,580 [Application Number 05/206,425] was granted by the patent office on 1973-07-10 for lubricant reservoir for rock bits.
This patent grant is currently assigned to Dresser Industries, Inc.. Invention is credited to Morgan LeVon Crow.
United States Patent |
3,744,580 |
Crow |
July 10, 1973 |
LUBRICANT RESERVOIR FOR ROCK BITS
Abstract
A cone cutter is rotatably mounted upon a bearing pin extending
from the arm of a rotary rock bit. Lubricant is supplied to the
bearings between the cone cutter and the bearing pin by a
protracted passageway containing lubricant. The protracted
passageway extends through the arm and bearing pin of the bit to
the bearing area with the outer end of the protracted passageway
connected to the exterior surface of the bit. The protracted
passageway provides pressure equalization between the pressure of
the lubricant and the pressure of fluid in the well bore and
insures that lubricant reaching the bearing area is free of
contaminants.
Inventors: |
Crow; Morgan LeVon (Dallas,
TX) |
Assignee: |
Dresser Industries, Inc.
(Dallas, TX)
|
Family
ID: |
22766319 |
Appl.
No.: |
05/206,425 |
Filed: |
December 9, 1971 |
Current U.S.
Class: |
175/228; 384/93;
175/372 |
Current CPC
Class: |
E21B
10/24 (20130101) |
Current International
Class: |
E21B
10/08 (20060101); E21B 10/24 (20060101); F16c
019/00 (); E21b 009/10 () |
Field of
Search: |
;175/227-229,371,372
;308/8.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Brown; David H.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A drill bit comprising:
a bit body;
at least one arm extending from said bit body;
a cutter rotatably mounted upon said arm;
bearing means between said cutter and said arm for promoting
rotation of said cutter;
a seal positioned between said cutter and said arm; and
a passageway extending from an area on the exterior surface of said
bit through said arm to said bearing means, wherein said passageway
includes a series of helical grooves, said passageway containing
lubricant.
2. A drill bit comprising:
a bit body;
at least one arm extending from said bit body;
a cutter rotatably mounted upon said arm;
bearing means between said cutter and said arm for promoting
rotation of said cutter;
a seal positioned between said cutter and said arm; and
a passageway extending from an area on the exterior surface of said
bit through said arm to said bearing means, wherein said passageway
includes a coiled tube, said passageway containing lubricant.
3. A rotary rock bit comprising:
a bit body;
at least one arm extending from said bit body;
a cone cutter positioned upon said arm;
bearing means between said cone cutter and said arm for promoting
rotation of said cone cutter;
a seal positioned between the open end of said cone cutter and said
arm; and
passage means extending from the exterior surface of said bit to
said bearing means for storing a supply of lubricant that will be
transmitted to said bearing means, said passage means including a
series of helical grooves.
4. A rotary rock bit comprising:
a bit body;
at least one arm extending from said bit body;
a cone cutter positioned upon said arm;
bearing means between said cone cutter and said arm for promoting
rotation of said cone cutter;
a seal positioned between the open end of said cone cutter and said
arm; and
passage means extending from the exterior surface of said bit to
said bearing means for storing a supply of lubricant that will be
transmitted to said bearing means, said passage means including a
coiled tube.
5. A rotary rock bit comprising:
a bit body;
at least one arm extending from said bit body;
a cone cutter positioned upon said arm;
bearing means between said cone cutter and said arm for promoting
rotation of said cone cutter;
a seal positioned between the open end of said cone cutter and said
arm; and
passage means extending from the exterior surface of said bit to
said bearing means for storing a supply of lubricant that will be
transmitted to said bearing means, the length to area ratio of said
passage means being at least 50 to 1.
6. A sealed bearing rotary bit comprising:
a main bit body;
at least one arm extending from said main bit body, said arm
terminating in a bearing pin;
a cone cutter rotatably mounted upon said bearing pin;
cutting means on the surface of said cone cutter for disintegrating
earth formations;
bearing means between said cone cutter and said bearing pin for
promoting rotation of said cone cutter;
a seal positioned between the open end of said cone cutter and said
bearing pin; and
a protracted passageway having a small diameter, said passageway
extending from an area on the exterior surface of said arm to said
bearing means for storing a supply of lubricant that will be
supplied to said bearing means, the length to area ratio of said
protracted passageway being greater than 50 to 1.
7. A drill bit comprising:
a bit body;
at least one arm extending from said bit body;
a cutter rotatably mounted on said arm;
bearing means between said cutter and said arm for promoting
rotation of said cutter;
a seal sealingly engaging said cutter and said arm;
a lubricant reservoir communicating with the exterior of the bit
and containing lubricant for said bearing means, said reservoir
having a length to area ratio of at least 50 to 1; and
a passageway communicating said lubricant reservoir with said
bearing means.
Description
BACKGROUND OF THE INVENTION
The present invention relates to the art of earth boring and more
particularly to a system for providing lubricant to the bearings
between the cutter and the bearing pin of a rotary rock bit that
will allow the bit to be operated for an extended period of time
under changing pressure conditions.
A rotary rock bit in general consists of a main bit body adapted to
be connected to a rotary drill string. The bit includes at least
one rotatable cutter mounted upon a bearing pin extending from the
main bit body. Bearings are provided between the cutter and the
bearing pin to promote rotation of the cutter and means are
provided on the outer surface of the cutter for disintegrating the
formations as the bit and cutter rotate. A sufficient supply of
lubricant must be provided to the bearings throughout the lifetime
of the bit.
Problems have been encountered with prior art systems of supplying
lubricant to the bearings because of the relatively long lifetime
of the bits and the wide variation of environmental conditions
encountered during the drilling operation. When a rotary rock bit
is lowered into a well bore, the environmental pressure surrounding
the bit increases at the rate of approximately 1/2 pound per square
inch for each foot of depth. This means that at a depth of 10,000
feet, the hydrostatic pressure on the outside of the bit could be
5,000 psi or more because of the weight of the drilling fluid in
the well bore above the bit. In order for a lubrication system to
function properly at the elevated downhole pressures, some means
must be provided to equalize the internal pressure of the lubricant
in the system with the hydrostatic pressure of the drilling fluid
in the well bore.
When providing pressure equalization, a wide variety of
environmental conditions must be considered. For example, the
temperatures will rise as the well bore penetrates deeper into the
earth and temperatures in the range of 250.degree. to 350.degree. F
at 10,000 feet depth and still higher temperatures at greater
depths may be expected. As the bit is rotated and the cutters
engage the formations, a large amount of heat is generated causing
the environmental temperature of the bit to rise. Friction in the
bearings and seals generates a large amount of heat and a large
amount of heat is generated by the action of the bit on the
formations. The elevated temperature has an adverse effect on the
lubricant and the elements of the lubrication and bearing systems.
Changing pressure conditions are also detrimental to a lubrication
system. Periodic pressure variations are produced during the
drilling operation and these pressure variations can damage the
structural elements of the lubrication system. During drilling,
joints of pipe must be added to the drill string for progressively
deeper penetration. This may mean that 50 or 60 joints of pipe are
added to the drill string during the normal life of a rotary rock
bit. In order to add a joint of pipe, which is usually 30 feet in
length, rotation of the drill bit must be stopped and the entire
string of pipe, including the bit, must be raised high enough to
allow the kelly to clear the rotary table (35-50 feet). Since
operating costs of an oil well drilling rig are quite high, the
time that the bit is off bottom and not drilling must be kept to a
minimum. Therefore, the addition of a joint pipe must be
accomplished quickly and the drill string must be raised and
lowered as rapidly as possible. This raising and lowering of the
drill stem creates pressure variations that affect the lubrication
system.
When the bit is on bottom, the pressure of the lubricant is the
same as, or nearly the same as, the hydrostatic pressure of the
fluid in the well bore. However, as the drill stem is elevated in
the well bore, the bit body acts in much the same manner as a
piston in a cylinder. The enlarged diameter of the bit body exerts
a force on the column of drilling fluid above it due to the
velocity of the bit traveling up the well bore. The velocity of
fluid moving past the large diameter portion of the bit may be
fairly high causing a low pressure area in the zone between the
cutters and the main bit body where the seal is located. The
pressure differential between the pressure of fluid in the area of
the seal and the pressure of lubricant inside of the bit may be in
the order of 100 psi or more during periods of high acceleration of
the drill stem.
In a substantial number of rotary rock bits, the seals are designed
to hold pressure in one direction only. If the pressure on the
inside of the bit reaches 50 to 75 psi greater than the pressure on
the outside of the bit, the seals may leak. Thus, each time a joint
of pipe is added to the drill string, the bit is elevated in the
well bore causing a low pressure around the seal and forcing a
portion of the lubricant out past the seal. The entire supply of
lubricant may be pumped out in this manner resulting in a complete
failure of the lubrication system and the inevitable failure of the
bearings and the bit.
When seals are provided that resist flow in both directions, such
as an O-ring seal, a substantial pressure buildup within the
lubrication system may be encountered. Some of the potential
sources of the pressure buildup are the pressure differential
resulting from raising and lowering the bit, and thermal expansion
of the lubricant due to the elevated temperatures encountered
during the drilling operation. This pressure buildup has resulted
in destruction of prior art pressure equalizing systems. The
flexible reservoir diaphragms used in one of the prior art
lubrication systems generally fails under the pressure buildup
because the diaphragm is ruptured or pushed out of place and
damaged.
BRIEF DESCRIPTION OF THE ART
In U. S. Pat. No. 3,370,895 to G. A. Cason, Jr. patented Feb. 27,
1968, a sealed bearing rock bit with a lubricant reservoir is
shown. A movable piston is positioned in the lubricant reservoir
and the area above the piston is vented to the exterior of the bit
to expose the upper side of the piston to the environmental
pressure of the well bore. A seal is provided between each of the
cutters and the arm upon which they are mounted. The seal retains
lubricant in the bearing area and prevents ambient fluid and any
entrained materials from entering the bearing area.
In U. S. Pat. No. 3,476,195 to E. M. Galle patented Nov. 4, 1969, a
sealed bearing rock bit is shown that includes a lubricant
reservoir and a flexible diaphragm for equalizing the internal
pressure of lubricant in the lubricant reservoir with the
hydrostatic pressure of drilling fluid in the well bore. A check
valve is provided which operates at low pressures to permit flow
out of the lubricant reservoir to the outside of the bit but blocks
any flow in the reverse direction.
SUMMARY OF THE INVENTION
The present invention provides a lubrication system containing a
sufficient volume of lubricant to provide lubricant to the bearings
of a sealed bearing rock bit for an extended period of time and the
lubrication system will operate effectively under widely varying
environmental conditions. A rotatable cutter is mounted upon the
bearing pin portion of an arm extending from the main bit body. A
seal is positioned between the cutter and the arm to retain
lubricant in the area of the bearings and to prevent the bearings
from being contaminated by fluid and materials in the well bore. A
protracted passageway containing lubricant extends from the bearing
area to an area on the external surface of the bit.
It is therefore an object of the present invention to provide a
lubrication system for a rotary rock bit that contains a sufficient
supply of lubricant for the bit to operate over an extended period
of time.
It is a further object of the present invention to provide a
lubrication system for a rotary rock bit that will operate
effectively under changing pressure conditions.
It is a further object of the present invention to provide a
lubrication system for a rotary rock bit that will operate under
adverse environmental conditions including high temperature.
It is a still further object of the present invention to provide a
lubrication system that will extend the useful lieftime of a sealed
bearing rotary rock bit.
It is a still further object of the present invention to provide a
lubrication system for a sealed bearing rotary rock bit that will
operate effectively with a seal that permits a limited amount of
lubricant flow out of the bit.
It is a still further object of the present invention to provide a
lubrication system for a sealed bearing rotary rock bit that will
operate effectively with a seal that prevents flow in either
direction.
It is a still further object of the present invention to provide a
sealed bearing rotary rock bit that includes a protracted lubricant
passageway for supplying lubricant to the bearings.
The above and other objects and advantages will become apparent
from a consideration of the following detailed description of the
invention when taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a three cone rotary rock bit constructed in accordance
with the present invention.
FIG. 2 is a sectional view of one arm of the rock bit of FIG. 1
showing the lubrication system.
FIG. 3 is a sectional view of one arm of a rotary rock bit
illustrating another embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings and to FIG. 1 in particular, shown
therein and generally designated by the reference character 10 is a
three cone rotary rock bit. As illustrated, the bit 10 includes a
bit body 11 including an upper threaded portion 12. The threaded
portion 12 allows bit 10 to be connected to the lower end of a
rotary drill string (not shown). Depending from the bit body 11 are
three substantially identical arms. The arms 13 and 13' are shown
in FIG. 1. The lower end of each of the arms is provided with an
extended journal portion or bearing pin and the details of this
journal portion will be discussed subsequently. Three rotary cone
cutters 14, 14', 14" are rotatably positioned upon the three
journal portions of the arms. Each of the cone cutters includes
cutting structure 15, 15', 15" on its outer surface adapted to
disintegrate the formations as the bit is rotated and moved
downward. The cutting structure 15, 15', 15" is shown in the form
of tungsten carbide inserts; however, it is to be understood that
other cutting structure such as steel teeth may be used as a
cutting structure on the cone cutters.
The bit 10 includes a central passageway 16 extending along the
central axis of body 11 to allow drilling fluid to enter from the
upper section of the drill string immediately above and pass
downward through three jet nozzles. One of the jet nozzles 17 is
shown in FIG. 1. In use, the drill bit 10 is connected as the lower
member of a rotary drill string (not shown) and lowered into a well
bore until the rotatable cone cutters 14, 14', 14" engage the
bottom of the well bore. Upon engagement with the bottom of the
well bore, the drill string is rotated rotating bit 10 therewith.
Drilling fluid is forced down through the interior passage of the
rotary drill string and continues through the central passageway 16
of bit 10 passing through the three nozzles past the cutting
structure of the cutters to the bottom of the well bore, thence
upward in the annulus between the rotary drill string and the wall
of the well bore carrying with it the cuttings and debris from the
drilling operation.
In order to add additional sections of the drill string, the bit 10
must be lifted a short distance in the well bore, the new section
of drill string added and the bit 10 lowered until it again reaches
the bottom of the well bore wherein drilling continues. As each
section of the drill string is added, the bit is elevated in the
hole causing a pressure change in certain areas along the bit. In
prior art sealed bearing rock bits, the lubricant would be pumped
out past the seal. The loss of lubricant, of course, has a
deleterious effect on the bearing systems and the bit would be
subject to early failure. In addition, the periodic pressure
differentials result in failure of structural elements of the
lubrication system of the bit. The present invention overcomes the
pressure differential problem and provides a sufficient volume of
lubricant to supply lubricant to the bearings for an extended
period of time.
Referring now to FIG. 2, a sectional view of one arm 13 of the
earth boring bit 10 is shown. The cutter 14 is rotatably positioned
on the journal portion of the arm 13 and adapted to disintegrate
earth formations as the bit is rotated. The cutting structure 15 on
the outer surface of cutter 14 contacts and disintegrates the
formations. The journal portion of arm 13 consists of a bearing pin
18 upon which the cutter 14 is mounted. A plurality of bearing
systems are located in the bearing area between the cutter 14 and
the bearing pin 18. The bearing systems in the bearing area include
a series of roller bearings 19, a series of ball bearings 20, a
friction bearing 21 and a thrust button 22. A seal 23 is positioned
between the cutter 14 and the bearing pin 18. This seal 23 retains
lubricant in the bearing area around the bearing systems and
prevents any materials in the well bore from entering the bearings.
A passage 24 extends from the area around the bearings to allow
lubricant to be transmitted to the bearings. The passage 24, as
shown, allows the balls that make up the ball bearing system 20 to
be inserted into position after the cone cutter 14 is placed on the
bearing pin 18. The series of ball bearings 20 serves to lock the
cone cutter 14 on bearing pin 18. After the balls are in place, a
plug 25 is inserted into the passage 24 and welded therein by weld
26. Plug 25 has a reduced diameter throughout the major portion of
its length to allow lubricant to be transmitted to the bearing
systems. Additional passages 27, 28 and 29 extend from passage 24
to the bearing area to insure a sufficient supply of lubricant to
bearings 19, 20, 21 and 22.
The seal 23 is a positive seal in one direction only, that being
from the fluid in the well bore to the bearing area. If the
pressure of the lubricant in the bearing area reaches 50 to 75 psi
greater than the pressure outside of the bit, lubricant will be
forced out past seal 23 into the well bore. In prior art rotary
rock bits, the lubricant pressure inside of the bit would build up
periodically resulting in pressure pulses forcing lubricant out
past the seal. In addition, difficulties were experienced because
the pressure pulses would form an emulsion within the lubricant and
bearing damage would result. Temperature changes were also
encountered that lead to pressure buildup with an associated
lubricant loss resulting in bearing failure.
A protracted lubricant passageway 30 positioned in arm 13 provides
a sufficient volume of lubricant to provide lubrication for the bit
even though the bit may run for an extended period of time. The
protracted lubricant passageway 30 provides a long, small cross
sectional area flow passage for lubricant. The passageway 30
extends through a series of helical grooves from an area on the
outside of the bit to a passage 31. The passage 31 in turn is
connected to passage 24 to allow lubricant to be transmitted to the
bearings. Drilling fluid pressure may enter the open end of
passageway 30 through a screen or filter 32 and equalize the
pressure of lubricant inside of the bit 10 with the pressure of
fluid outside of the bit 10. Expansion of lubricant due to heating
or other causes will simply displace lubricant away from the
bearings through the chain of passages 27, 28, 29, 24, 31 and 30.
Lubricant compression due to hydrostatic pressure and thermal
contraction upon cooling will be equalized in pressure by flow of
the drilling fluid toward the bearings. The protracted passageway
30 will keep an interface between the drilling fluid and the
lubricant and keep the drilling fluid and any materials in the
drilling fluid away from the bearings. Sufficient lubricant volume
is provided in the chain of passages 27, 28, 29, 24, 31 and 30 to
allow some lubricant loss due to thermal expansion and yet provide
a sufficient volume of lubricant to maintain a supply of lubricant
to the bearings for an extended period of time. A screen of filter
32 may be provided at the mouth of passageway 30 to prevent large
particles from entering the small diameter passageway 30. The
passageway 30 extends through a series of baffles and the lubricant
cannot emulsify with the drilling fluid throughout the entire
length of the chain of passageways. Therefore, lubricant reaching
the bearings will be free of any contaminants.
The passageway 30 should have a length-to-area ratio great enough
to insure that the fluid in the well bore outside of the bit 10
will not migrate through the lubricant to the bearings. For
example, the passageway 30, shown in FIG. 2, may have a cross
sectional area of 0.2 square inches and be 10 inches in length.
This will provide a length-to-area ratio of 50 to 1 and insure that
the bearings will not be contaminated by material in the well bore.
The cross sectional shape of the passageway 30 may take any form.
For example, the cross sectional shape of passageway 30 may be
circular, square, rectangular or irregular as long as the
length-to-area ratio is great enough to prevent fluid in the well
bore from migrating to the bearings.
Referring now to FIG. 3, another embodiment of the present
invention is shown. One arm 33 of a rotary rock bit is shown in
section illustrating another embodiment of a lubrication system
constructed in accordance with the present invention. The arm 33
contains a spiral tube 34 that forms a portion of the lubricant
passageway. The spiral tube 34 is connected to the bearing area
between the bearing pin 35 extending from the arm 33 and the
rotatable cone cutter 36 by series of interconnecting passages. The
bearing systems positioned in the bearing area include an outer
friction bearing 37, a series of ball bearings 38, an inner
friction bearing 39 and a thrust button 40. An O-ring seal 41 is
located between the bearing pin 35 and the cutter 36. The seal 41
is positioned in a groove located near the upper end of the bearing
pin 35. The seal 41 prevents fluid flow in either direction and
maintains lubricant in the bearing area as well as preventing
materials in the well bore from entering the bearing area.
The passages that extend from the spiral tube to the bearing area
allow lubricant to be transmitted to the bearings. One of the
intermediate passageways, passageway 42, serves a dual purpose in
that it provides a portion of the passage for transmitting
lubricant to the bearings and also serves as a passage to allow the
balls that make up the ball bearing system 38 to be inserted into
position after the cone cutter 36 is placed on the bearing pin 35.
The series of ball bearings 38 serves to lock the cone cutter 36 on
the bearing pin 35. After the balls are in place, a plug 43 is
inserted into the passageway 42 and welded therein by a weld 44.
The plug 43 has a reduced diameter throughout the major portion of
its length to allow the lubricant to be transmitted to the bearing
area.
The seal 41 resists flow in both directions. When this type of seal
was used in rock bits of the prior art, a substantial pressure
buildup in the lubrication system would result. For example, during
the drilling operation, the lubricant would become heated due to
friction in the bearings and friction between the cutting structure
and the bottom of the well bore. Thermal expansion would produce an
internal pressure buildup, and the pressure buildup would soon lead
to the destruction of one or more elements of the bit if some means
of equalizing the internal lubricant pressure with the hydrostatic
pressure of the fluid in the well bore were not provided.
The spiral tube 34 provides a long, small cross-sectional area flow
passageway for the lubricant. The spiral tube 34 is connected
between the bearing area and the exterior surface of the bit,
thereby allowing drilling fluid to enter the open outer end of the
spiral tube 34 and equalize the pressure of the lubricant with the
pressure of the fluid outside of the bit. Expansion of lubricant
due to heating will simply displace lubricant away from the
bearings through the spiral tube 34. Lubricant compression due to
hydrostatic pressure and thermal contraction upon cooling will be
equalized in pressure by flow of the drilling fluid into the outer
end of the spiral tube 34. The long passageway made up of the
spiral tube 34 and the chain of passages 45, 42, 46, 47 and 48 will
keep an interface between the drilling fluid and the lubricant, and
the drilling fluid will be kept away from the bearings. Sufficient
lubricant volume is provided in the spiral tube 34 and the passages
45, 42, 46, 47 and 48 to allow some lubricant loss due to thermal
expansion and yet provide a sufficient volume of lubricant to
prevent drilling fluid from traveling back through the passages to
the bearings. A screen or filter may be used to prevent large
particles from entering the small diameter spiral tube 34. In this
way, any difference in specific gravity between the drilling fluid
and the lubricant cannot cause the drilling fluid to emulsify or
displace the entire length of lubricant so that the lubricant
reaching the bearings is contaminate free.
The length of the long passageway that extends from the exterior
surface of the bit to the bearing area and consists of the spiral
tube 34 and passages 45, 42, 46, 47 and 48 is substantially greater
than the linear distance between the outer end of tube 34 at the
exterior surface of the bit and the bearing area of the bit. In the
embodiment of the invention shown in FIG. 3, the length of the long
passageway is greater than one and one-half times the linear
distance between the outer end of tube 34 and the bearings 37, 38,
39 and 40. The spiral tube 34 has a length-to-area ratio of 50 to 1
thereby insuring that fluid in the well bore will not reach the
bearing area.
* * * * *