U.S. patent application number 11/273713 was filed with the patent office on 2007-05-17 for drill bit lubricant utilizing a sulfur-phosphorous ep agent.
This patent application is currently assigned to Smith International, Inc.. Invention is credited to Robert Denton, Alan W. Lockstedt.
Application Number | 20070107940 11/273713 |
Document ID | / |
Family ID | 38039577 |
Filed Date | 2007-05-17 |
United States Patent
Application |
20070107940 |
Kind Code |
A1 |
Lockstedt; Alan W. ; et
al. |
May 17, 2007 |
Drill bit lubricant utilizing a sulfur-phosphorous EP agent
Abstract
A lubricant is shown and described. The lubricant includes about
1 to 15 weight percent of a sulfur-phosphorus extreme pressure
agent, about 5 to 40 weight percent of a thickener, preferably a
metal-complex soap, and a basestock. The basestock may be a mineral
oil, a synthetic oil, or a combination thereof. Lubricant additives
such as corrosion inhibitors, oxidation inhibitors, and anti-wear
agents may also be added.
Inventors: |
Lockstedt; Alan W.;
(Houston, TX) ; Denton; Robert; (Pearland,
TX) |
Correspondence
Address: |
OSHA LIANG L.L.P.
1221 MCKINNEY STREET
SUITE 2800
HOUSTON
TX
77010
US
|
Assignee: |
Smith International, Inc.
Houston
TX
|
Family ID: |
38039577 |
Appl. No.: |
11/273713 |
Filed: |
November 14, 2005 |
Current U.S.
Class: |
175/57 ;
175/227 |
Current CPC
Class: |
E21B 10/24 20130101 |
Class at
Publication: |
175/057 ;
175/227 |
International
Class: |
E21B 10/24 20060101
E21B010/24 |
Claims
1. A lubricant for a drill bit, comprising: from about 1 to about
15 weight percent of a sulfur-phosphorus EP agent, wherein the
sulfur-phosphorus EP agent comprises at least one selected from a
substituted 1,3,4-thiadiazole, a sulfunized oxymolybdenum organo
phosphorodithioate, sulfur-phosphorus ester amine salts, a zinc
dithiophosphate, and combinations thereof. from about 5 to about 40
weight percent of a thickener; and a basestock.
2. The lubricant of claim 1, wherein the sulfur-phosphorus EP agent
comprises: about 1 to about 5 weight percent of
1,3,4-thiadiazole-2(3H)-thione,5,5-dithiobis; and about 1 to about
10 weight percent of molybdenum
di(2-ethylhexyl)phosphorodithioate;
3. The lubricant of claim 1, further comprising: at least one
additive selected from the group consisting of corrosion
inhibitors, oxidation inhibitors, anti-wear agents, and zinc- and
chlorine-based EP agents.
4. The lubricant of claim 1, wherein the thickening agent is
selected from at least one from the group consisting of a soap and
a non-soap, wherein the soap includes soaps of calcium, aluminum,
titanium, barium, lithium, and complexes thereof, and the non-soap
includes urea, fine silica, fine clay, and silica gel.
5. The lubricant of claim 1, wherein the combination of basestock
comprises from 0 to 100% mineral oil and 100 to 0% synthetic oil,
or any percentage therebetween.
6. The lubricant of claim 1, further comprising from about 1 to
about 10 weight percent of silica, about 5 to about 40 percent of a
metal-complex soap by weight, and wherein the basestock comprises
from 100 to 0% mineral oil and 0 to 100% synthetic oil, or any
percentage therebetween.
7. The lubricant of claim 6, further comprises from about 1 to
about 10 weight percent of copper particles, about 1 to about 15 of
molybdenum disulfide.
8. The lubricant of claim 7, further comprising an ester-based
swelling agent.
9. A roller cone drill bit, comprising: a bit body; at least one
leg extending downward from the bit body, wherein each leg has a
journal and each journal has a bearing surface; a roller cone
mounted on each journal, wherein each roller cone has a bearing
surface; a grease reservoir in communication with the bearing
surfaces; and a lubricating composition in the grease reservoir and
adjacent the bearing surfaces, the lubricating composition
comprising: from about 1 to about 15 weight percent of a
sulfur-phosphorus EP agent, wherein the sulfur-phosphorus EP agent
comprises at least one selected from a substituted
1,3,4-thiadiazole, a sulfunized oxymolybdenum organo
phosphorodithioate, sulfur-phosphorus ester amine salts, a zinc
dithiophosphate, and combinations thereof; from about 5 to about 40
percent lubricant weight of a thickener; and a basestock.
10. The roller cone drill bit of claim 9, wherein the basestock
comprises from 0 to 100% mineral oil and 100 to 0% synthetic oil,
or any percentage therebetween.
11. The roller cone drill bit of claim 9, further comprising: an
additive comprising at least one element selected from the group
consisting of corrosion inhibitors, oxidation inhibitors, anti-wear
agents, and zinc- and chlorine-based EP agents.
12. The roller cone drill bit of claim 9, wherein the thickener is
at least one selected from the group consisting of a soap and a
non-soap, wherein the soap includes soaps of calcium, aluminum,
titanium, barium, lithium, and complexes thereof, and the non-soap
includes urea, fine silica, fine clay, and silica gel.
13. A method for lubricating a roller cone drill bit, comprising:
providing a roller cone drill bit having a bit body, a grease
reservoir, and at least one roller cone mounted on the bit body
with at least one rotatable journal bearing; and filling the grease
reservoir with a lubricant, the lubricant comprising: from about 1
to about 15 weight percent of a sulfur-phosphorus EP agent, wherein
the sulfur-phosphorus EP agent comprises at least one selected from
a substituted 1,3,4-thiadiazole, a sulfunized oxymolybdenum organo
phosphorodithioate, sulfur-phosphorus ester amine salts, a zinc
dithiophosphate, and combinations thereof; from about 5 to about 40
percent lubricant weight of a thickener; and a basestock.
14. The method of claim 13, further comprising: contacting the at
least one journal bearing with the lubricant.
15. The method of claim 13, wherein the basestock comprises from 0
to 100% mineral oil and 100 to 0% synthetic oil, or any percentage
therebetween.
16. The method of claim 13, wherein the lubricant further comprises
an additive comprising at least one additive selected from the
group consisting of oxidation inhibitors, corrosion inhibitors,
anti-wear agents, and zinc- and chlorine-based EP agents.
17. A method for drilling through an earth formation, comprising:
providing a roller cone drill bit having a bit body, a grease
reservoir, and at least one roller cone mounted on the bit body
with at least one rotatable journal bearing, wherein the grease
reservoir contains a lubricant, the lubricant comprising: from
about 1 to about 15 weight percent of a sulfur-phosphorus EP agent,
wherein the sulfur-phosphorus EP agent comprises at least one
selected from a substituted 1,3,4-thiadiazole, a sulfunized
oxymolybdenum organo phosphorodithioate, sulfur-phosphorus ester
amine salts, a zinc dithiophosphate, and combinations thereof; from
about 5 to about 40 percent lubricant weight of a thickener; and a
basestock; securing the drill bit to the end of a drill string; and
rotating the drill bit under an applied load on the earth
formation.
18. The method of claim 17, further comprising: introducing the
lubricating composition to the journal bearings.
19. The method of claim 17, wherein the basestock comprises from 0
to 100% mineral oil and 100 to 0% synthetic oil, or any percentage
therebetween.
20. The method of claim 17, wherein the lubricating composition
further comprises an additive comprising at least one additive
selected from the group consisting of oxidation inhibitors,
corrosion inhibitors, anti-wear agents, and zinc- and
chlorine-based EP agents.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates generally to a lubricant for
lubricating journal bearings in a rock bit for drilling earth
formation.
[0003] 2. Background Art
[0004] Rock bits are employed for drilling wells in subterranean
formations. Such bits have a body connected to a drill string and a
single roller cone or a plurality (typically two or three) of
roller cones mounted on the body for drilling rock formations. The
roller cones are mounted on journals or pins integral with the bit
body at its lower end. In use, the drill string and bit body are
rotated in the bore hole, and each cone rotates on its respective
journal as the cone contacts the bottom of the bore hole being
drilled.
[0005] Drill bits are used in hard, often tough formations and,
therefore, high pressures and temperatures are encountered. The
total useful life of a drill bit is typically on the order of 20 to
200 hours for bits in sizes of about 6 to 28 inch diameter at
depths of about 5,000 to 20,000 feet. Useful lifetimes of about 65
to 150 hours are typical. When a drill bit wears out or fails as a
bore hole is being drilled, it is necessary to withdraw the drill
string to replace the bit which is a very expensive and time
consuming process. Prolonging the lives of drill bits minimizes the
lost time in "round tripping" the drill string for replacing
bits.
[0006] Replacement of a drill bit can be required for a number of
reasons, including wearing out or breakage of the structure
contacting the rock formation. One reason for replacing the rock
bits includes failure or wear of the journal bearings on which the
roller cones are mounted. The journal bearings are subjected to
very high drilling loads, high hydrostatic pressures in the hole
being drilled, and high temperatures due to drilling, as well as
elevated temperatures in the formation being drilled. The operating
temperature of the grease in the drill bit can exceed 300.degree.
F. Considerable work has been conducted over the years to produce
bearing structures and employ materials that minimize wear and
failure of such bearings.
[0007] A variety of grease compositions have been previously
employed. U.S. Pat. No. 4,358,384 discloses one prior art grease
composition that consists of a petroleum derived mineral oil
lubricant basestock and a metal soap or metal complex soap
including aluminum, barium, calcium, lithium, sodium or strontium
metals. A lighter, lower-viscosity basestock is generally employed
to obtain low temperature greases, and a heavier, higher-viscosity
basestock is used to obtain high temperature greases.
[0008] In order to enhance the lubricating capacity of typical
petroleum basestock greases, solid additives such as molybdenum
disulfide, copper, lead or graphite have been previously added.
Synthetic polymer extreme pressure (EP) agents and high viscosity
synthetic polymers may also be used. These materials serve to
enhance the ability of the lubricant base stock to form a
friction-reducing film between the moving metal surfaces under
conditions of extreme pressure and to increase the load carrying
capacity of the lubricants. The function of the lubricant is to
minimize wear and to prevent scuffing and welding between
contacting surfaces. U.S. Pat. Nos. 4,358,384, 3,062,741,
3,107,878, 3,281,355, and 3,384,582 disclose the use of molybdenum
disulfide, and other solid additives such as copper, lead and
graphite, which have been employed to attempt to enhance the
lubrication properties of oils and greases.
[0009] Without being restricted to any method, in drilling
applications, the mechanism of lubrication is by way of
hydrodynamic lubrication. When at rest, the journal and the journal
bearings of a drill bit squeeze out the lubricant and make direct
contact. As the journal begins to rotate, the lubricant is drawn
into the space between contacting surfaces to form a fluid wedge
there between. As the journal rotation increases speed, this fluid
wedge pushes the journal off the bearings and forms a lubricating
film between the contacting surfaces. The film thickness is
determined by both the rotation speed and load capacity of the
lubricant. If a film is too thin, the asperities may make contact
with a greater force, resulting in shearing action between the
surfaces instead of a sliding action, which in turn generates heat
and wears down the contacting surfaces. When this happens, EP
additives in the lubricant are activated by the high temperature
resulting from the extreme pressure to react with the exposed metal
surfaces and form a protective coating thereon.
[0010] However, the use of solid EP agents, which improve the load
carrying capacity of a lubricant, has been shown to contribute to
excessive seal and gland wear and drill bit seal failure. For
example, drill bit lubricant compounds comprising a copper EP agent
have displayed seal failure due to copper deposits and loading near
the seal area. The copper accumulates near the seal area until the
seal is abraded by the constant and progressive erosive contact
with the copper deposit. The abraded seal eventually loses its
capacity to retain the grease composition in the journal area,
permitting metal to metal contact between the roller cone and the
journal, causing drill bit failure. Conversely, lubricants that
reduce seal and gland wear typically lack sufficient film strength,
that is, load carrying capacity, to be used as a drill bit
lubricant.
[0011] Additionally, the use of solid EP agents comprising heavy
metal complexes is not desirable due to their general toxicity and
environmental impact for risks of leaking or spilling of heavy
metal-containing lubricant during use, storage or disposal of the
lubricant.
[0012] Accordingly, there exists a need for a lubricant that
exhibits both a tight seal and good load carrying capacity with
reduced seal and gland wear.
SUMMARY OF THE INVENTION
[0013] In one aspect, embodiments of the present invention relate
to a lubricant for a drill bit, that includes from about 1 to about
15 weight percent of a sulfur-phosphorus EP agent, wherein the
sulfur-phosphorus EP agent comprises at least one selected from a
substituted 1,3,4-thiadiazole, a sulfunized oxymolybdenum organo
phosphorodithioate, sulfur-phosphorus ester amine salts, a zinc
dithiophosphate, and combinations thereof, from about 5 to about 40
weight percent of a thickener, and a basestock.
[0014] In another aspect, embodiments of the present invention
relate to a roller cone drill bit including a bit body, at least
one leg extending downward from the bit body, wherein each leg has
a journal and each journal has a bearing surface, a roller cone
mounted on each journal, wherein each roller cone has a bearing
surface, a grease reservoir in communication with the bearing
surfaces; and a lubricating composition in the grease reservoir and
adjacent the bearing surfaces, where the lubricating composition
includes from about 1 to about 15 weight percent of a
sulfur-phosphorus EP agent, wherein the sulfur-phosphorus EP agent
includes at least one selected from a substituted
1,3,4-thiadiazole, a sulfunized oxymolybdenum organo
phosphorodithioate, sulfur-phosphorus ester amine salts, a zinc
dithiophosphate, and combinations thereof, from about 5 to about 40
percent lubricant weight of a thickener, and a basestock.
[0015] In another embodiment, the present invention relates to a
method for lubricating a roller cone drill bit. The method includes
the steps of providing a roller cone drill bit having a bit body, a
grease reservoir, and at least one roller cone mounted on the bit
body with at least one rotatable journal bearing; and filling the
grease reservoir with a lubricant, where the lubricant includes
from about 1 to about 15 weight percent of a sulfur-phosphorus EP
agent, wherein the sulfur-phosphorus EP agent comprises at least
one selected from a substituted 1,3,4-thiadiazole, a sulfunized
oxymolybdenum organo phosphorodithioate, sulfur-phosphorus ester
amine salts, a zinc dithiophosphate, and combinations thereof; from
about 5 to about 40 percent lubricant weight of a thickener, and a
basestock.
[0016] In yet another embodiment, the present invention relates to
a method for drilling through an earth formation. The method
includes the steps of providing a roller cone drill bit having a
bit body, a grease reservoir, and at least one roller cone mounted
on the bit body with at least one rotatable journal bearing,
wherein the grease reservoir contains a lubricant that includes
from about 1 to about 15 weight percent of a sulfur-phosphorus EP
agent, wherein the sulfur-phosphorus EP agent comprises at least
one selected from a substituted 1,3,4-thiadiazole, a sulfunized
oxymolybdenum organo phosphorodithioate, sulfur-phosphorus ester
amine salts, a zinc dithiophosphate, and combinations thereof, from
about 5 to about 40 percent lubricant weight of a thickener, and a
basestock; securing the drill bit to the end of a drill string; and
rotating the drill bit under an applied load on the earth
formation.
[0017] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a semi-schematic perspective of a rock bit
lubricated with a lubricant according to the present invention;
[0019] FIG. 2 is a partial cross-section of the drill bit in FIG.
1.
DETAILED DESCRIPTION OF THE INVENTION
[0020] In one aspect, embodiments of the present invention relate
to lubricants having a sulfur-phosphorus EP agent. In particular,
embodiments of the invention relate to lubricants for drill bits,
methods for lubricating, drill bits comprising the lubricants, and
methods for drilling.
[0021] A lubricant according to the present invention comprises a
sulfur-phosphorus EP agent, a basestock, and one or more
thickeners. Additionally, additives such as anti-wear agents,
corrosion inhibitors, wetting agent, and antioxidants may also be
added. Details of each component are further explained below:
Sulfur-Phosphorus EP Agents:
[0022] Applications under extreme pressure conditions often rely on
additives. Lubricants containing additives that protect against
extreme pressure are called EP lubricants. Common EP compounds
include compounds of boron, phosphorus, sulfur, and chlorine. The
compounds are typically activated by the high temperature that
results from the extreme pressure. It has been shown that the
activated compounds react with exposed metal surfaces and form a
protected coating which covers exposed asperities.
[0023] In one embodiment, a sulfur-phosphorous EP agent according
to the present invention includes at least one selected from a
substituted 1,3,4-thiadiazole, a sulfunized oxymolybdenum organo
phosphorodithioate, phosphorous-sulfur ester amine salts, a zinc
dithiophosphate, or combinations thereof. In another embodiment, a
sulfur-phosphorus EP agent according to the present invention
includes a blend of a substituted 1,3,4-thiadiazole and a
sulfunized oxymolybdenum organo phosphorodithioate. Specifically,
when making a lubricant of the present invention, the lubricant may
include from about 1 to about 5 weight percent of the substituted
1,3,4-thiadiazole and from about 1 to about 10 weight percent of
the sulfunized oxymolybdenum organo phosphorodithioate. Preferably,
about 3 weight percent of the substituted 1,3,4-thiadiazole and
about 4 weight percent of the sulfunized oxymolybdenum organo
phosphorodithioate are added to the lubricant. One example of
1,3,4-thiadiazole is 1,3,4-thiadiazole-2(3H)-thione,5,5-dithiobis.
One example of sulfunized oxymolybdenum organo phosphorodithioates
is molybdenum di(2-ethylhexyl) phosphorodithioate. One example of a
phosphorous-sulfur ester amine salt includes Lubrizol.TM. 5080A,
commercially available from The Lubrizol Corporation (Wickliffe,
Ohio). Examples of zinc dithiophosphates include Lubrizol.TM. 677A,
Lubrizol.TM. 139, and Lubrizol.TM. 5002, all commercially available
from The Lubrizol Corporation (Wickliffe, Ohio).
[0024] In other embodiments, a sulfur-phosphorus EP agent may be
added as an additive to a commercially available grease
composition. Advantageously, sulfur-phosphorus EP agents, in
accordance with embodiments of the present invention, may be used
as an additive in a wide range of basestocks and greases, such as
Molykote.TM. G-0101, available from Dow Corning (Midland, Mich.),
Mobilith.TM. AW-2, available from ExxonMobil Corporation (Fairfax,
Va.), and Lucant 600 and Lucant 2000, both available from Mitsui
Petrochemical (New York, N.Y.).
Basestocks:
[0025] The basestock, or base oil, form the main lubricating
component. Oils are generally classified as refined and synthetic.
Refined oils are also referred to as mineral oils or petroleum
oils. For example, paraphinic and naphthenic are refined from crude
oil while synthetic oils are manufactured by chemical synthesis.
The basestock may be selected from any of the basestocks known in
the art, including a synthetic base oil, a petroleum or mineral
oil, or combinations thereof. In some embodiments, a synthetic
lubricant basestock may be preferred over a petroleum derived
basestock to increase viscosity. In other embodiments, a high
viscosity petroleum derived mineral oil basestock may be used.
[0026] Suitable synthetic oils for use in a basestock may include
synthetic polyalphaolefins, other hydrocarbon fluids and oils,
synthetic polyethers, poly-esters, alkylene oxide polymers, and
interpolymers, esters of phosphorus containing acids, silicon based
oils and mixtures thereof. In one embodiment, the basestock may
include a high viscosity index polyalphaolefin based fluid.
Suitable polyalphaolefins include those discussed in U.S. Pat. Nos.
5,589,443, 5,668,092, and 4,827,064, which are incorporated herein
by reference in their entirety. Other suitable synthetic oils
include alkylated naphthalenes, such as Synesstic.TM. AN, which is
available from ExxonMobil Corporation (Fairfax, Va.), polybutenes,
such as Indopol.TM. polybutenes which are available from BP P.L.C.
(Warrenville, Ill.), and hydrogenated polybutenes, such as
Panalane.TM. hydrogenated polybutenes, which are available from BP
P.L.C. (Warrenville, Ill.).
[0027] Suitable mineral or petroleum oils may include naphthenic or
paraffinic oil. Other suitable mineral oils may include high
viscosity index hydroprocessed basestock and bio-based esters.
Thickeners:
[0028] Thickeners give a lubricant its characteristic consistency
and are sometimes thought of as a "three-dimensional fibrous
network" or "sponge" that holds the oil in place.
[0029] In one embodiment, the base oil may be thickened with a
soap, such as soaps of calcium, aluminum, titanium, barium,
lithium, and their complexes. Metal complex soaps may include
alkali metals, alkaline earth metals, Group IVB metals, and
aluminum. Simple soaps may be formed by combining a fatty acid or
ester with a metal and reacting through a saponification process,
with the application of heat, pressure, or agitation. While simple
soaps are formed by reacting one single organic acid with a metal
hydroxide, complex soaps may be formed by reacting two or more
organic compounds with the metal hydroxide.
[0030] In another embodiment, the base oil may be thickened with a
non-soap, such as urea, fine silica, fine clay, and/or silica gel.
In yet another embodiment, the basestock may be thickened with both
soap and non-soap thickening agents. While the above description
lists several specific thickening agents, no limitation is intended
on the scope of the invention by such a description. It is
specifically within the scope of the present invention that other
soap and non-soap thickening agents may be used.
Other Additives:
[0031] Additives that are commonly added to lubricants to improve
their performances may also be added to a lubricant of the present
invention. Examples of such additives are anti-wear agents,
corrosion inhibitors, anti-oxidants, zinc- and chlorine-based EP
agents, etc, including copper powder molybdenum disulfide, and
bismuth ethylhexanoate. Examples of zinc- and chlorine-based EP
agents include Lubrizol.TM. 885 and Lubrizol.TM. 2501, which are
both commercially available from The Lubrizol Corporation
(Wickliffe, Ohio). Bismuth ethylhexanoate is commercially available
from OMG Americas, Inc. (Cleveland, Ohio).
[0032] For an excellent review of common lubricant additives, see
Lubricant Additives: Chemistry and Applications, edited by Leslie
R. Rudnick (2003, ISBN 0824708571).
Application of the Lubricant in a Drill Bit:
[0033] Referring now FIGS. 1 and 2, a sealed bearing rotary cone
rock bit, generally designated as 10, consists of bit body 12
forming an upper pin end 14 and a cutter end of roller cones 16
that are supported by legs 13 extending from body 12. The threaded
pin end 14 is adapted for assembly onto a drill string (not shown)
for drilling oil wells or the like. Each of the legs 13 terminate
in a shirttail portion 22. Each of the roller cones 16 typically
have a plurality of cutting elements 17 pressed within holes formed
in the surfaces of the cones for bearing on the rock formation to
be drilled. Nozzles 20 in the bit body 12 introduce drilling mud
into the space around the roller cones 16 for cooling and carrying
away formation chips drilled by the drill bit. 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 lubrication by
grease.
[0034] Each roller cone 16 is in the form of a hollow,
frustoconical steel body having cutting elements 17 pressed into
holes on the external surface. For long life, the cutting elements
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 hardfaced steel teeth milled on
the outside of the cone instead of carbide inserts.
[0035] Each leg 13 includes a journal 24 extending downwardly and
radially inward on the rock bit body. The journal 24 includes a
cylindrical bearing surface 25 which may have a flush hardmetal
deposit 62 on a lower potion of the journal 24.
[0036] The cavity in the cone 16 contains a cylindrical bearing
surface 26. A floating bearing 45 may be disposed between the cone
and the journal. Alternatively, the cone may include a bearing
deposit in a groove in the cone (not shown separately). The
floating bearing 45 engages the hardmetal deposit 62 on the leg and
provides the main bearing surface for the cone on the bit body. The
end surface 33 of the journal 24 carries the principal thrust loads
of the cone 16 on the journal 24. Other types of bits, particularly
for higher rotational speed applications, may have roller bearings
instead of the exemplary journal bearings illustrated herein.
[0037] A plurality of bearing balls 28 are fitted into
complementary ball races 29, 32 in the cone 16 and on the journal
24. These balls 28 are inserted through a ball passage 42, which
extends through the journal 24 between the bearing races and the
exterior of the drill bit. A cone 16 is first fitted on the journal
24, and then the bearing balls 28 are inserted through the ball
passage 42. The balls 28 carry any thrust loads tending to remove
the cone 16 from the journal 24 and thereby retain the cone 16 on
the journal 24. The balls 28 are retained in the races by a ball
retainer 64 inserted through the ball passage 42 after the balls
are in place. A plug 44 is then welded into the end of the ball
passage 42 to keep the ball retainer 64 in place.
[0038] Contained within bit body 12 is a grease reservoir system
generally designated as 18. Lubricant passages 21 and 42 are
provided from the reservoir to bearing surfaces 25, 26 formed
between a journal bearing 24 and each of the cones 16. Drilling
fluid is directed within the hollow pin end 14 of the bit 10 to an
interior plenum chamber 11 formed by the bit body 12. The fluid is
then directed out of the bit through the one or more nozzles
20.
[0039] The bearing surfaces between the journal 24 and cone 16 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 46. The lubricant or grease thus
fills the regions adjacent the bearing surfaces plus various
passages and a grease reservoir. The grease reservoir comprises a
chamber 19 in the bit body 10, which is connected to the ball
passage 42 by a lubricant passage 21. Lubricant or grease also
fills the portion of the ball passage 42 adjacent the ball
retainer. Lubricant or grease is retained in the bearing structure
by a resilient seal 50 between the cone 16 and journal 24
[0040] Lubricant contained within chamber 19 of the reservoir is
directed through lube passage 21 formed within leg 13. A smaller
concentric spindle or pilot bearing 31 extends from end 33 of the
journal bearing 24 and is retained within a complimentary bearing
formed within the cone. A seal generally designated as 50 is
positioned within a seal gland formed between the journal 24 and
the cone 16.
[0041] In one embodiment, a lubricant in accordance with this
aspect of the invention may include from about 1 to about 15 weight
percent of a sulfur-phosphorus EP agent; about 1 to about 10 weight
percent of silica; about 5 to about 40 weight percent of a
thickening agent, preferably a metal-complex soap, and a balance of
a heavy mineral basestock. In another embodiment, the lubricant may
further comprise solid additives. In one embodiment, the solid
additives are from about 1 to about 15 weight percent of molybdenum
disulfide and from about 1 to about 10 weight percent of copper
particles. In yet another embodiment, the basestock may be a blend
of mineral oil and synthetic oil. Specifically, in one embodiment,
the basestock may be a blend of 0 to 100% mineral oil and 100 to 0%
synthetic oil with any percentage therebetween, preferably about
50% of each.
[0042] In one embodiment, the lubricant or grease in the grease
reservoir may include from about 1 to about 15 weight percent of a
sulfur-phosphorus EP agent; about 1 to about 10 weight percent of
silica; about 5 to about 40 weight percent of a thickening agent,
preferably a metal-complex soap; and a balance of a heavy mineral
basestock. In another embodiment, the lubricant or grease may
further comprise solid additives such as molybdenum disulfide and
copper particles. In one embodiment, the solid additives are from
about 1 to about 15 weight percent of molybdenum disulfide and from
about 1 to about 10 weight percent of copper particles. In yet
another embodiment, the basestock may be a blend of 0 to 100%
mineral oil and 100 to 0% synthetic oil with any percentage
therebetween, preferably about 50% of each.
Use of the Lubricant in a Method of Drilling:
[0043] According to one aspect of the present invention, a method
for drilling is provided. In one embodiment, the method for
drilling includes the steps of providing a roller cone drill bit
having a bit body and a plurality of roller cones mount on the bit
body with rotatable journal bearings, introducing a lubricating
composition to the journal bearings, where the lubricating
composition includes a basestock, a thickener, and a
sulfur-phosphorus EP agent. In one embodiment, the lubricant in the
grease reservoir may include from about 1 to about 15 weight
percent of a sulfur-phosphorus EP agent; about 1 to about 10 weight
percent of silica; about 5 to about 40 weight percent of a
thickening agent, preferably a metal-complex soap; and a balance of
a heavy mineral basestock. In another embodiment, the lubricant may
further comprise solid additives such as molybdenum disulfide and
copper particles. In one embodiment, the solid additives are from
about 1 to about 15 weight percent of molybdenum disulfide and from
about 1 to about 10 weight percent of copper particles. In yet
another embodiment, the basestock may be a blend of 0 to 100%
mineral oil and 100 to 0% synthetic oil with any percentage
therebetween, preferably about 50% of each.
[0044] In the above embodiments, if the composition of the
basestock is predominantly synthetic oil, an ester-based swelling
agent may also be added to enhance the wetting and suspension of
silica. One suitable swelling agent includes Esterex C4461, which
is available from ExxonMobil Corporation (Fairfax, Va.).
[0045] Lubricants in accordance with embodiments of the invention
have been found to have superior properties, as compared to prior
art lubricants and as evidenced by the following examples.
EXAMPLES
Example 1
A Sulfur-Phosphorus EP Lubricant Containing Cu and MoS.sub.2
[0046] A lubricant in accordance with one embodiment of the present
invention was prepared with about 5 weight percent of silica, about
12 weight percent of molybdenum disulfide, about 32 weight percent
of a Li-complex soap, about 5 weight percent of copper particles,
and about 10 weight percent of a sulfur-phosphorus EP agent, and a
balance of a basestock containing 100% mineral oil. The
sulfur-phosphorus EP agent used in this example is a blend of about
3 parts of a substituted 1,3,4-thiadiazole (e.g.
1,3,4-thiadiazole,5,5-dithiobis available from R.T. Vanderbilt
Company, Inc. under the trade name Vanlube.RTM. 829) and about 4
parts of a sulfunized oxymolybdenum organo phosphorodithioate (e.g.
molybdenum di(2-ethylhexyl)phosphorodithioate available from R.T.
Vanderbilt Company, Inc. under the trade name Molyvan.RTM. L). Such
lubricant has a film strength of 1000 kg as determined by ASTM-2596
4 ball load EP test. The benefits of using only mineral oil may
include causing seal swell, which allows for a tighter seal and
wetting silica gel for easier suspension.
Example 2
A Sulfur-Phosphorus EP Lubricant Without Solid Additives
[0047] A lubricant in accordance with another embodiment of the
present invention was prepared with about 5% of silica, about 32%
of a Li-complex soap, and about 10% of the sulfur-phosphorus EP
agent and a balance of a basestock containing 100% mineral oil. The
sulfur-phosphorus EP agent used in this example is a blend of about
3 parts of a substituted 1,3,4-thiadiazole (e.g.
1,3,4-thiadiazole,5,5-dithiobis available from R.T. Vanderbilt
Company, Inc. under the trade name Vanlube.RTM. 829) and about 4
parts of a sulfunized oxymolybdenum organo phosphorodithioate (e.g.
molybdenum di(2-ethylhexyl)phosphorodithioate available from R.T.
Vanderbilt Company, Inc. under the trade name Molyvan.RTM. L). Such
lubricant has a film strength of 1000 kg as determined by ASTM-2596
4 ball load EP test. No solid particles such as copper or
molybdenum disulfide were added.
Example 3
A Sulfur-Phosphorus EP Lubricant with Synthetic Basestock
[0048] A lubricant in accordance with yet another embodiment of the
present invention was prepared with about 10% of a
sulfur-phosphorus EP agent, about 5% of silica, about 32% of a Li
complex-metal soap, and a balance of a one-to-one blend of
synthetic oil and mineral oil as the basestock. The
sulfur-phosphorus EP agent used in this example is a blend of about
3 parts of a substituted 1,3,4-thiadiazole (e.g.
1,3,4-thiadiazole,5,5-dithiobis available from R.T. Vanderbilt
Company, Inc. under the trade name Vanlube.RTM. 829) and about 4
parts of a sulfunized oxymolybdenum organo phosphorodithioate (e.g.
molybdenum di(2-ethylhexyl)phosphorodithioate available from R.T.
Vanderbilt Company, Inc. under the trade name Molyvan.RTM. L). No
solid particles such as copper or molybdenum disulfide were added.
The addition of synthetic oil may afford such a lubricant better
temperature characteristics, and the lack of solids may render the
lubricant more compatible with mechanical seal systems. To enhance
wetting and suspension of the silica gel thickening agent, an
ester-based swelling agents was also added.
Example 4
A Sulfur-Phosphorus EP Lubricant Containing Other Additives
[0049] A lubricant according to yet another embodiment of the
present invention was prepared with about 10% of the
sulfur-phosphorus EP, about 32% of a Li-complex soap, about 3% of a
corrosion inhibitor (such as, for example, Hi Tech 350 available
from Hi Tech Company), and a balance of a basestock. The
sulfur-phosphorus EP agent used in this example contains about 3
parts of a substituted 1,3,4-thiadiazole (e.g.
1,3,4-thiadiazole,5,5-dithiobis available from R.T. Vanderbilt
Company, Inc. under the trade name Vanlube.RTM. 829) and about 4
parts of a sulfunized oxymolybdenum organo phosphorodithioate (e.g.
molybdenum di(2-ethylhexyl)phosphorodithioate available from R.T.
Vanderbilt Company, Inc. under the trade name Molyvan.RTM. L). The
basestock is a blend of a mineral oil and ultra-high molecular
weight polyalphaolefin (such as Lucant 2000 and Lucant 600
available from Mitsui Petrochemical, New York, N.Y.) in one-to-one
ratio. About 6% of molybdenum disulfide and about 1.5% of silica
were also added. Such composition may have the advantage of
avoiding vulcanization of seals that are made of HSN elastomer
material.
[0050] Advantages of the embodiments of the invention may include
one or more of the following: adding a sulfur-phosphorus EP agent
to make a lubricant according to the present invention may
eliminate the need to add solid EP additives such as lead. A
lubricant thus produced may be non-toxic, environmentally friendly
and still retain exceptional load carrying ability required in
applications such as lubrication of rock bits. In addition, by
combining a high to medium viscosity synthetic base oil with an
almost equal amount of mineral oil, a lubricant that has efficient,
controlled seal swell may be produced to ensure the maintenance of
a tight seal during the drilling process without excessive seal
wear.
[0051] While the invention 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
can be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
* * * * *