Elastomer Material for High Temperature Roller Cone Bits

Abstract

An earth boring bit has a bit body with at least one bearing pin. A cone is rotatably mounted on the bearing pin. A seal assembly is located between the cone and the bearing pin, the seal assembly having at least one flexible seal member. A flexible pressure compensating diaphragm is mounted in the body. The diaphragm has one side adapted to be exposed to borehole fluids and another side in contact with lubricant contained in bearing spaces between the cone and the bearing pin. The flexible seal member and the diaphragm are formed of a fluorinated elastomer. The elastomer is either a perfluoroelastomer (FFKM) or a fluoroelastomer (FKM).

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to provisional application 60/912,350, filed Apr. 17, 2007.

FIELD OF THE INVENTION

This invention relates in general to rolling cone earth-boring bits of the roller cutter variety. More particularly, the invention relates to a system of sealing components for retaining lubricant within the bit and excluding drilling fluids from entering the bearing and lubricant spaces in the bit.

BACKGROUND OF THE INVENTION

A rolling cone earth boring bit typically has one or more flexible elements, such as seal rings and pressure compensating diaphragms. The seal ring seals lubricant within bearing spaces between the cone and the bearing shaft. The pressure compensating diaphragm reduces the pressure difference between the drilling fluid in the borehole and the grease. Both the seal assembly and the pressure compensator are exposed to drilling fluid on one side and lubricant on the other. They are designed to withstand corrosive chemicals in the drilling fluid as well as impacts from earth formation cuttings flowing past. They also must be sufficiently flexible to perform the sealing and compensating functions. In addition, they must withstand the temperatures in the wellbore, which can be several hundred degrees Fahrenheit.

Normally the pressure compensating and at least part of the seal assembly are formed of a rubber material, such as hydrogenated acrylonitrile butadiene rubber (HNBR) or acrylonitrile butadiene rubber (NBR). HNBR has excellent properties in regard to chemical resistance, compression set, elasticity and tear strength. However, service life of HNBR parts will be reduced in drilling applications with continuous bottom hole circulating temperatures above 300° F. Some geographic areas, particularly geothermal wells, have bottom hole temperatures that exceed that amount. It is desired to be able to operate a bit having elastomers capable of withstanding temperatures of at least 400° F. on a continuous basis as well as meeting all of the other requirements.

SUMMARY

In this invention, the rotating cone earth boring bit has a plurality of flexible elements. At least one of the flexible elements comprises an elastomer containing fluorine. In one embodiment, the elastomer comprises a perfiluoroelastomer (FFKM). In another embodiment, the elastomer comprises a fluoroelastomer (FKM). The flexible element may comprise a seal ring that is at least part of a seal assembly between a cone and a bearing pin. The flexible element may also comprise a lubricant pressure compensator diaphragm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of one leg of an earth-boring bit having a seal assembly and pressure compensator in accordance with this invention.

FIG. 2 is an enlarged sectional view of the seal assembly of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, bit 11 has a body 13. Body 13 has at least one leg with a depending bearing pin 15 extending downward and inward. Bit 11 of the embodiment shown will have as many as three legs and bearing pins 15, but only one is shown. A cone 16 is rotatably mounted to each bearing pin 15. Cone 16 has a plurality of external teeth that may be integrally formed with the body of cone 16, or formed of tungsten carbide and pressed into holes, as shown.

The bearing spaces between bearing pin 15 and cone 16 are filled with a lubricant 18 (FIG. 2). A lubricant compensator 17 equalizes pressure on the exterior of bit 11 with the pressure of lubricant 18 contained in the bearing spaces. Lubricant compensator 17 comprises a cup-shaped diaphragm or bladder that has one side exposed to drilling fluid and the other to lubricant 18. Lubricant compensator 17 is located within a cavity in the body and in communication with the bearing spaces via passages. Pressure compensator 17 flexes inward and outward to equalize pressure, but its engagement with bit body 13 is static.

A seal assembly 19 located near the base of bearing pin 15 seals lubricant 18 within the bearing spaces. Referring to FIG. 2, in the preferred embodiment, seal assembly 19 includes a rigid ring 21 surrounding bearing pin 15 near the base of bearing pin 15. Rigid ring 21 is urged into sliding contact with an annular insert 23, which is a ring or sleeve shrink-fitted into the cavity of cone 16. Insert 23 rotates in unison with cone 16, while rigid ring 21 remains stationary with bearing pin 15.

An elastomeric energizing ring 25 is deformed between an inner diameter surface 27 of rigid ring 21 and seal cavity 29. The engagement of energizing ring 25 with ring 21 and seal cavity 29 is static; that is the contacting surfaces are not sliding or dynamic relative to each other. Energizing ring 25 exerts a spring force on rigid ring 21, which acts against insert 23. Energizing ring 25 also seals lubricant 18 located within the bearing spaces, but as a secondary seal to the primary seal formed by rigid ring 21 and annular insert 23.

In this embodiment, an elastomeric excluder ring 31 is also utilized. Excluder ring 31 is deformed between a portion of seal cavity 29 in bearing pin 15 and both energizing ring 25 and an end of rigid seal ring 21. Excluder ring 31 serves to prevent the entry of debris into contact with energizing ring 25 and is in static engagement with seal cavity 29 and rigid seal ring 21.

The elastomeric components of the bit are formed of a fluorinated elastomer having a fluorine content. One material suitable for that purpose is a perfluoroelastomer (FFKM). FFKM is defined in ASTM D1418-06 as perfluorinated rubbers of the polymethylene type having all fluoro, perfluoroalkyl, or perfluoroalkyoxy substituent groups on the polymer chain; a small fraction of this group may contain functionality to facilitate vulcanization. FFKM is a polymer that does not degrade under continuous operating temperatures up to 400° F. FFKM has a high fluorine content, which offers a high and broad chemical resistance. FFKM polymers are typically compounded with fillers namely: carbon black and curative materials such as peroxides. These fillers or ingredients are tailored to provide a material that has good chemical resistance, a good resistance to compression set, adequate elasticity and tear resistance. FFKM resists oil, high pH aqueous drilling fluids and formation gases such as hydrogen sulfide and methane. One manufacturer of such polymer is Dupont which markets the polymer as the trademark “KALREZ”.

Another suitable fluorinated elastomer material is the fluoroelastomer (FKM). According to ASTM. D1418-06, FKM is a fluoro rubber of the polymethylene type that utilizes vinylidene fluoride as a comonomer and has substituent fluoro, alkyl, perfluoroalkyl or perfluoroalkyoxy groups on the polymer chain; with or without the cure site monomer. FKM is also designed for high temperature operation. FKM materials provide high levels of resistance to chemicals, heat and oil. The higher the content of the fluorine is, the higher the resistance to chemicals. FKM is also less costly than FFKM.

FKM is compounded with fillers to achieve a desired modulus of elasticity, resiliency, tear strength, and the like for drill bit static elastomeric components. One manufacturer of FKM polymer is Dupont, which markets the polymer under the trademark “VITON”.

Preferably, energizing ring 25, excluder ring 31 and lubricant compensator 17 are manufactured from either FFKM or FKM. Other static elastomer components of bit 11, such as nozzle seals and the seal for the pressure compensator cavity cap may also be formed of FFKM or FKM. These components are manufactured in a conventional manner by a conventional molding process.

While the invention has been described in only two of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.

Claims

1. A rotating cone earth boring bit having a plurality of flexible elements therein, and wherein at least one of the flexible elements comprises an elastomer containing fluorine.

2. The bit according to claim 1, wherein the elastomer comprises a perfluoroelastomer (FFKM).

3. The bit according to claim 1, wherein the elastomer comprises a fluoroelastomer (FKM).

4. The bit according to claim 1, wherein said at least one of the flexible elements comprises a seal ring that is at least part of a seal assembly between a cone and a bearing pin.

5. The bit according to claim 1, wherein said at least one of the flexible elements comprises a lubricant pressure compensator diaphragm.

6. An earth boring bit, comprising:

a bit body having at least one bearing pin;

a cone rotatably mounted on the bearing pin;

a seal assembly between the cone and the bearing pin, the seal assembly having at least one flexible seal member;

a flexible pressure compensating diaphragm in the body having one side adapted to be exposed to borehole fluids and another side in contact with lubricant contained in bearing spaces between the cone and the bearing pin; and

wherein the flexible seal member and the diaphragm are formed of a fluorinated elastomer.

7. The bit according to claim 6, wherein the elastomer comprises a perfluoroelastomer (FFKM).

8. The bit according to claim 6, wherein the elastomer comprises a fluoroelastomer (FKM).

9. The bit according to claim 6, wherein the seal assembly comprises a dynamic rigid seal ring;

and wherein said at least one flexible seal member comprises: an energizing ring that acts against the rigid seal ring.

10. The bit according to claim 6, wherein the seal assembly comprises a rigid seal ring that dynamically engages a rigid insert mounted in and rotating with the cone; and wherein said at least one the flexible seal member comprises:

an energizing ring deformed between the bit body and the rigid seal ring; and

an excluder ring deformed between the body, the energizing ring and the rigid ring.

11. An earth boring bit, comprising:

a bit body having at least one bearing pin;

a cone rotatably mounted on the bearing pin and having a rigid insert mounted therein for rotation therewith;

a rigid ring that engages the rigid insert in sliding and sealing contact;

an energizer ring statically engaging a portion of the bearing pin and the rigid ring and urging the rigid ring into engagement with the rigid insert;

a flexible pressure compensating diaphragm in the body, having one side adapted to be exposed to borehole fluids and another side in contact with lubricant contained in bearing spaces between the cone and the bearing pin; and

wherein the energizer ring and the diaphragm are formed of a fluorinated elastomeric compound.

12. The bit according to claim 11, further comprising:

an excluder ring statically engaging a portion of the bearing pin, the energizing ring and the rigid ring; and

wherein the excluder ring is formed of a fluorinated elastomeric compound.

13. The bit according to claim 11, wherein the elastomer comprises a perfluoroelastomer (FFKM).

14. The bit according to claim 11, wherein the elastomer comprises a fluoroelastomer (FKM).