Chip relief for rock bits

Abstract

This invention relates to roller cone, air circulation type rock bits. Means are provided on the rock bit body as well as on the shirttail portion of each of the legs extending from the body to provide a relief to pass rock chips from the borehole bottom and up the drill string as the air circulation roller cone bit works in a formation.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No. 337,929, filed Jan. 8, 1982 annular cross-sectional area formed by defined by the shoulder of the threaded pin end or connection and the wall of the borehole 32 through the plane 37.

Turning now to FIG. 2, the leg portion is shown in a borehole 32. Cone 15 is illustrated in contact with the bottom of the borehole and, as the roller cone rotates in the borehole bottom, the cutting elements (tungsten carbide inserts 23) scrape, gouge, and crush the formation, thus creating detritus or rock chips 34 which must be removed from the borehole bottom. In mining bits, air is used as both a bit lubricant and a means to remove detritus from the borehole bottom. Air is directed through the nozzle 30 (FIG. 1) toward the borehole bottom and the rock chips 34 are blown out of the borehole bottom past the bit body and up the borehole 32. The rock bit leg then is relieved by removing material from the shirttail 20 in the area indicated as 28 and by providing a concave groove 21 in the leading and trailing edges 22 and 24 of the leg 18 of the rock bit body 12. Detritus 34 than easily pases by the cutter cones 15, past the bit body 12 and up the borehole, being enhanced by the relieved portions in both the shirttail surface and the leading and trailing edges of the leg 18 of the bit 10.

With reference now to FIG. 3, the bit body 12, being turned 90° from FIG. 2, further illustrates the areas of the leg 18 which are removed, namely the stepped area 28 of the shirttail portion 20 and the scalloped grooves 21 along the leading edge 22 and trailing edge 24.

Turning now to FIG. 4, the annular space 36 through plane 37 defines a cross-sectional area at least thirty-five to thirty-seven percent of the annular cross-sectional area formed by defined by the shoulder of the threaded pin end or connection and the walls 33 of the borehole 32. The cross-hatched portion of the illustration represents each of the legs that support cutter cones 15. As heretofore mentioned, jet air nozzles 30 direct compressed gaseous fluid toward the borehole bottom to lift variously sized detritus out of the borehole.

This relatively simple procedure produced a dramatic increase in borehole penetration in the mining field. For example, recent tests have revealed a standard 63/4 inch mining bit, without chip relief, would normally cut 2500 feet of earth formation. A 63/4 inch bit with chip removal features as taught in this invention, in the very same formation, cut 4500 feet of earth formation, resulting in a 77% increase in rock bit performance. Several bits were run to confirm this phenomenal increase in rock bit penetration with an average increase in performance of about 75% overall. This indeed is a new and unusual result from a rock bit modification, especially in air circulation mining bits. Field reports have shown that chip grooves, such as the scalloped grooves 21 in leading edges 22 and trailing edges 24 of the rock bit, adds significantly to chip flow with increased bit life and performance. It was also confirmed that the chip relief is equally effective for milled tooth and tungsten carbide insert bits, the latter being illustrated in the instant invention. Field engineers have observed that when large rock bit stabilizers are attached to the rock bits, the diameter of the stabilizer being near the diameter of the borehole, rock chip removal is again inhibited, even with a bit with chip relief. This observation confirmed that rock chips or detritus is reground over and over again to enable them to finally pass by the large diameter stabilizer. Where stabilizers are used in conjunction with air circulation bits with chip relief, the diameter of the stabilizer must be reduced accordingly to complement the modified bit and its greater capacity to pass detritus material thereby. Where this practice is followed, a 75% increase in bit performance can be expected. Air flow through an air circulation bit must have a clear path of escape once it passes through the nozzles 30 of the rock bit. Free flow of air is needed if remilling or recutting of the chips is to be prevented. Engineering tests confirm that mining bits, as modified by the teachings of this invention, do indeed exhibit increased rock bit penetration rates. The life of the cutting end of the bit is prolonged with a more efficient means to remove more and larger detritus from the borehole bottom, thus contributing to the phenomenal increase in rock bit efficiency and performance.

Chip relief for sealed bearing rock bits used in the oilfield will enhance their performance as well. Detritus material washed out of the bottom of a borehole by drilling mud will more easily pass by the bit with chip relief.

It will of course be realized that various modifications can be made in the design and operation of the presend present invention without departing from the spirit thereof. Thus, while the principal preferred construction and mode of operation of the invention have been explained in what is now considered to represent its best embodiments, which have been illustrated and described, it should be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

REFERENCES

¹ Piggot, R. J. S., "Mud Flow in Drilling", Drilling and Production Practices, API (1941), pp. 91-103

² Allen, James H., "How to Relate Bit Weight and Rotary Speed to Bit Hydraulic Horsepower", Drilling DCW, May 1975

³ Gray, K. E., "The Cutting Carrying Capacity of Air at Pressure Above Atmospheric", M.S. Thesis, University of Tulsa, Oklahoma (1957)

Claims

1. An air circulation, air lubricated, roller cone rock bit comprising:

a rock bit body having a first cutting end and a second threaded pin end having a shoulder, said body forming a chamber therein, said chamber communicates with said circulation air through an opening formed in said second pin end, said pin end being connected to a drill string,

at least a pair of legs extending from said bit body, each leg forming a shirttail portion and a bearing, each bearing serves to support a roller cutter cone at said first cutting end of said bit, cutting elements adjacent the largest diameter of each roller cone form a gage of a borehole in a formation,

at least one nozzle formed in said bit body in communication with said chamber, said nozzle directs air past each roller cone into said borehole to lift detritus material out of the bottom of the borehole, and

relief means formed by said legs, said relief means serves to pass said detritus material from the bottom of said borehole by the rock bit body and out of said borehole by providing an annular space between an outer surface of said legs and walls formed by said borehole, said annular space, in a plane perpendicular to an axis of said bit, about adjacent an exit end of said at least one nozzle, is thirty-five percent or more of the annular area formed by between the shoulder of the threaded pin end and the walls of said borehole through said plane, said annular space progressively enlarges in perpendicular planes between said exit end of said at least one nozzle and a shoulder formed in said bit body, said shoulder forms a thread termination base end for said second threaded pin end of said rock bit.

2. An air circulation, air lubricated, roller cone rock bit comprising:

a rock bit body having a first cutting end and a second threaded pin end, said body forming a chamber therein, said chamber communicates with said circulation air through an opening formed in said second pin end, said pin end being connected to a drill string,

at least a pair of legs extending from said bit body, each leg forming a shirttail portion and a bearing, each bearing serves to support a roller cutter cone at said first cutting end of said bit, cutting elements adjacent the largest diameter of each roller cone form a gage of a borehole in a formation,

at least one nozzle formed in said bit body in communication with said chamber, said nozzle directs air past each roller cone into said borehole to lift detritus material out of the bottom of the borehole, and

relief means formed by said legs, said relief means serves to pass said detritus material from the bottom of said borehole by the rock bit body and out of said borehole by providing an annular space between an outer surface of said legs and walls formed by said borehole, said annular space progressively enlarges in perpendicular planes between said exit end of said at least one nozzle and a shoulder formed in said bit body, said shoulder forms a thread termination base end for said second threaded pin end of said rock bit, said relief means formed by said legs include channel grooves formed in the sides of the leg in a leading edge and a trailing edge of said shirttail portion of said leg, said relief means formed by said legs further include a space formed between said shirttail portion of each of said legs and said wall of said borehole, said space is formed by relieving the surface of said shirttail substantially paralleling said borehole wall, said leading and trailing edge grooves and said relieved portion of said shirttail portion paralleling said borehole wall serve to enhance the removal of relatively large detritus material from the bottom of said borehole, a cross-sectional area of said annular space measured in a plane through said at least one or more nozzle exceeds thirty-five percent of the cross-sectional annular space defined by between said shoulder of the second threaded pin end and the borehole wall and increases as the bit cross section approaches said shoulder of said second pin end of said bit.

3. An air circulation, air lubricated roller cone rock bit comprising:

a rock bit body having a first cutting end and a second threaded pin end for connection to a drill string;

a shoulder on the bit body forming a thread termination base for the second threaded pin end of the rock bit;

an interior chamber in the body communicating with circulation air from the drill string through an opening formed in the second pin end of the bit body;

at least a pair of legs extending downwardly from the bit body, each leg including a shirttail portion at the outside of the bit body and adjacent to the wall of a bore hole drilled by such a rock bit, each leg also comprising a bearing supporting a roller cutter cone at the first cutting end of the bit, such a roller cone including cutting elements adjacent to the largest diameter of the roller cone for forming the gage of a bore hole drilled by such a rock bit;

at least one air nozzle in the bit body in communication between the chamber and the exterior of the bit body for directing air past each roller cone into a bore hole to lift detritus material out of the bottom of the bore hole; and

an annular space between the outer surface of the bit body and walls formed by such a bore hole drilled by the rock bit for passing the detritus material from the bottom of the bore hole past the rock bit body and out of the bore hole, the cross-sectional area of the annular space between the outside surface of the rock bit body and the walls of the bore hole in a plane at the exit end of such a nozzle being at least 35% of the cross-sectional area of the annular area between said shoulder of the threaded pin end and the bore hole wall, the cross-sectional area of the annular space progressively increasing in successive planes perpendicular to the axis of the rock bit from a lower portion of the shirttail to the shoulder. 4. A rock bit as recited in claim 3 further comprising a longitudinally extending channel groove in each of the leading edge and trailing edge of the shirttail portion of each leg. 5. A rock bit as recited in claim 4 wherein each of the channel grooves progressively increases in size from the lower end of the shirttail portion toward the pin end of the rock bit.