US3765493A

US3765493A - Dual bit drilling tool

Info

Publication number: US3765493A
Application number: US00203536A
Authority: US
Inventors: E Rosar; I Nielsen
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-12-01
Filing date: 1971-12-01
Publication date: 1973-10-16
Anticipated expiration: 1990-10-16

Abstract

A dual bit head drilling mechanism for use on the end of a conventional drill string for drilling through all types of subterranean structure, both hard and soft, without requiring pulling of the drill string to change bits whenever a different type or hardness of rock is encountered. The mechanism includes a two-pronged drag bit using tungsten carbide inserts and a surface set diamond bit. The two bits can be alternately brought into use merely by increasing or decreasing the amount of thrust on the bit head mechanism. A cable and sheave assembly interconnects the driving sleeve, tungsten carbide bit head and diamond bit head, and compressible Belleville washer springs are provided for normally biasing the diamond drill bit head into drilling operation.

Description

[ Oct. 16, 1973 Primary ExaminerDavid H. Brown Att0rney-Ralph F. Crandell et al.

[57] ABSTRACT A dual bit head drilling mechanism for use on the end of a conventional drill string for drilling through all types of subterranean structure, both hard and soft, without requiring pulling of the drill string to change bits whenever a different type or hardness of rock is encountered. The mechanism includes a two-pronged drag bit using tungsten carbide inserts and a surface set diamond bit. The two bits can be alternately brought into use merely by increasing or decreasing the amount of thrust on the bit head mechanism. A cable and sheave assembly interconnects the driving sleeve, tungsten carbide bit head and diamond bit head; and compressible Belleville washer springs are provided for' normally biasing the diamond drill bit head into drilling operation.

Irvin P. Nielsen, 1315 S. Clarkson St., Denver, both of Colo.

Dec. 1, 1971 Inventors: Edward C. Rosar, 13352 W.

Dakata Ave., Lakewood;

Filed:

Appl. No.: 203,536

US. 175/319, 175/329, l75/38l Int. E2lb 9/00, E2lb 9/36 Field ofSearch...........175/381-383, 319,

References Cited UNITED STATES PATENTS United States Patent Rosar et al.

[ DUAL BIT DRILLING TOOL 175/330 l75/38l X r 14 Claims, 9 Drawing Figures Sorensen.........................

Henderson...... Hildebrandt l llldebrandt PATENTED OCT 16 I975 SHEET 30F 4 SHEET 0F 4 JPMENTEDUBT 16 I975 FIG? DUAL BIT DRILLING TOOL BACKGROUND OF THE INVENTION This invention relates to drilling tools and more particularly to drilling tools of the multiple bit type. When reference is made to drilling in the present application, it will be understood that rotary drilling is intended and is distinguished from percussion or impact drilling.

In many, if not most, drilling operations in which it is desired to drill deep holes through earth and rock materials, there is normally encountered a wide variety of subterranean strata, the structures of which vary widely and include both hard and soft rock and earth formations. Conventional practice requires that a particular type of bit be utilized depending upon the structure being drilled. The type of rotary drilling tool utilized depends primarily upon the structure being drilled. Two widely known types of rotary drilling tools are the tungsten carbide drag bit, which includes a pair of drilling blades having tungsten carbide inserts secured to their drilling edges. This type of tool is conventionally used for relatively soft structures. Where hard, dense structures are encountered, the conventional practice is to utilize a diamond drill bit which involves a bit head with a number of diamond studs inset into its drilling surface.

Conventional drilling practice requires that the bit be changed when a change in subterranean structure is encountered. For example, if a tungsten carbide bit is being used and a hard strata is encountered, it is necessary to pull the entire drill string, change the bit to a diamond drill bit, and then lower the string back into the hole. Obviously, the deeper the hole the more difficult and time consuming is the process of changing drill bits. Much drilling time is lost in pulling the string and changing the bit, thus substantially increasing the cost of the drilling operation.

Because the diamond inserts are extremely hard, but

relatively fragile, the diamond drilling operation must be carried out under lower drilling forces than are utilized in drilling with tungsten carbide bits. The diamond bit depends primarily upon a wearing or grinding action under relatively low thrusts, whereas the tungsten carbide drag bits involve a digging type of action under relatively higher thrusts. If too large a force is used on the diamond drill bits, the diamonds can be shattered. On the other hand, it is desired to use much higher drilling forces and thrusts in order to obtain adequate drilling action with the tungsten carbide bits.

V In the prior art there has been suggested the possibility of using dual bits. In U.S. Pat. No. 1,748,341 issued Feb. 25, I930 to J. Grant et al. there is disclosed a Rotary Rock Bit which includes rotary drilling teeth in combination with percussion teeth. When the drilling teeth meet a strata which increases the resistance to rotation, the tool rotates and actuates the percussion teeth to break through the particular strata causing the resistance.

In U.S. Pat. No. 2,819,043 issued Jan. 7, 1958 to H. 1. Henderson for a Combination Drilling Bit, there is disclosed a combination of a tungsten carbide bit and a diamond bit. The Henderson structure is so constructed that the tungsten carbide bits are operative under relatively low drilling pressures. These bits are spring mounted so that when drilling in soft formation they will spring downwardly and slightly imbed the cutting edge into the soft formation. If, while drilling in a soft formation, the tungsten carbide bit drills into a hard formation, then, upon an increase in drilling pressure, the spring blades on which the tungsten carbide bits are mounted will be deflected to allow the diamond drill bit to bear on the hard formation. The drill structure as disclosed by Henderson operates contrary to accepted practice in that it requires relatively high forces for the diamond drilling bit to be utilized and relatively low forces for the tungsten carbide bit to be utilized. Also, it will be noted that the tungsten carbide bit blades continue to ride on the bore hole end even while the diamond bit is drilling.

OBJECTS OF THE PRESENT INVENTION It is the principal object of the present invention to provide a new and improved drilltool for use on the end of a conventional drill string for drilling through all types of subterranean structures, both hard and soft, without requiring the pulling of the drill string to change bits whenever a different type or hardness of rock is encountered.

More particularly, it is an object of the present invention to provide a drill tool of the above character which utilizes both a tungsten carbide drag bit and a diamond insert drill bit. More specifically, it is an object of the invention to provide a dual bit structure of the foregoing character in which the diamond insert drill bit is positioned in drilling operation under relatively low drilling thrusts while the tungsten carbide drag bit is positioned for drilling operation under relatively higher drill thrusts, and the drilling bit not in use is positively retracted from drilling engagement with the end of the bore hole.

r Another object of the present invention is to provide a drill tool of the foregoing character which affords time and cost savings associated with not having to pull a drill string to change bits.

A further object of the invention is to provide a drill tool of the above character which is simple yet rugged in construction, requires a minimum of maintenance under severe drilling conditions, and may be utilized in place of conventional single purpose drilling tools.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal elevation view, partly in section and with parts cut away for clarity, of a dual bit drilling tool embodying the present invention, with the diamond drill bit extended into drilling position and the tungsten carbide drill bit retracted.

FIG. 2 is a view similar to FIG. 1 but showing the tungsten carbide drag bit in drilling position and the diamond drill bit retracted.

FIG. 3 is a front or drilling end view of the drilling tool shown in FIG. 1.

FIG. 4 is a section view taken substantially in the plane of line 44 on FIG. 1.

FIG. 5 is a section view taken substantially in the plane of line 55 on FIG. 1.

FIG. 6 is a section view taken substantially in the plane of line 6-6 on FIG. 1.

FIG. 7 is a longitudinal section taken through a drilling tool embodying a modified form of the present invention and showing the diamond drilling bit in drilling position.

FIG. 8 is a longitudinal section view similar to FIG. 7 and showing the tungsten carbide bits in drilling position.

SUMMARY The invention, in accordance with the objects outlined above, resides in a dual bit head drilling mechanism designed for use on the end ofa conventional drill string for drilling through all types of subterranean structure, both hard and soft, without requiring pulling of the drill string to change bits whenever a different type or hardness of rock is encountered. The mechanism embodies two bit heads, a two-pronged drag bit using tungsten carbide inserts, and a butterfly" shaped surface set diamond bit head.- Either of the two bits can be brought into use by selectively increasing or decreasing the amount of thrust on the bit head mechanism. lf, while drilling through hard rock using the diamond drill bit head, the drill penetrates into a softer structure where the penetration rate could be increased by using a drag bit, the operator simply increases the drill pipe thrust above a level predetermined bythe mechanism design. This action withdraws the diamond bit head and extends the tungsten carbide bit head to do the cutting. If hard rock is again encountered, the operator decreases the drill pipe thrust until it is below the predetermined level, which action automatically extends the diamond bit into position for drilling the hard rock.

The bit mechanism is housed in a driving sleeve which is secured to the end of a drill pipe string. The tungsten carbide bit head is driven by a spline connection with the driving sleeve, while the diamond drill bit head nests between the two tungsten carbide bit prongs and is driven by a spline connection with the tungsten carbide bit head. A sheave and cable assembly, including sheaves mounted on the tungsten carbide bit head and cables passing over the sheaves and connected at one end to the diamond drill bit head and at the other end to the driving sleeve, provide the interconnecting arrangement between the bit heads. Housed between the diamond drill bit head and the tungsten carbide bit head are a series of spring or Belleville washers which normally urge the diamond drill bit head-into drilling position. When the washers are compressed, by increasing the thrust on the drill bit housing, the cable and sheave assembly serves to retract the diamond drill bit head inwardly or telescopingly into the tungsten carbide bit head, and simultaneously extend the tungsten drag bit into drilling position by compressing the springs. Coolant passages are provided through the drill bit head structure to allow the flow of coolant and lubricatingfluids.

An alternative mechanism is described for interconnecting the driving sleeve, tungsten carbide bit head and diamond drill bit head, including gears mounted on the tungsten carbide bit structuremeshing with racks on the driving sleeve and diamond 'bit head. Various types of resilient mechanisms such as coil springs, Belleville springs, or other compressible resilient materials may be utilized.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, there is indicated, by the general reference numeral 10, a drilling tool embodying the present invention and secured by a conventional tapered thread 11 to the end of a drill pipe string 12. The drill pipe string 12 forms a part of a conventional drilling rig and is adapted to be raised and lowered by an appropriate hoist mechanism (not shown), and rotated, to produce a rotary drilling action, by a conventional drill pipe rotating mechanism (not shown). The drill pipe string 12 is formed in sections,

- jointed together by threaded drill pipe connectors, and

for many drilling operations the drill pipe 12 may be composed of a number of such sections and be many feet in length, depending upon the depth of the hole to be drilled.

The tool 10 is a dual bit drilling mechanism formed by a housing or tool joint 14, mounting a tungsten carbide drag bit 15, and a diamond drill bit 16. As discussed above, the tungsten carbide drag bit 15 is adapted for drilling through relatively softer strata by the application of relatively higher drilling thrusts on the drill pipe, while the diamond drill bit 16 is adapted for drilling in hard strata but with the application of lower drilling thrusts. The tungsten carbide bit head is a two prong drag bit of conventional design utilizing heavy tungsten carbide inserts .18 to do the cutting. The inserts are backed up by heavy members extending down from a flat face and are braised or welded to these extensions. The diamond drill bit 16 is formed with a head 21 which is, in plan view as seen in FIG. 3, of a butterfly shape, the face and peripheral surfaces of which are studded with a plurality of surface set diamond studs 22.

The housing or tool joint 14, tungsten carbide drag bit 15 and diamond drill bit 16 are operatively associated and interconnected by structural means which position the tool bits relative to each other in such a manner that they can be alternately brought into use merely by increasing or decreasing the amount of thrust on the drilling tool. In the construction shown, the diamond drill bit 16 is normally extended into drilling position and the tungsten carbide bit 15 is normally retracted (FIG. 1). Thus, assuming that the first strata to be drilled is hard, the diamond drill bit 16 is utilized. If, while drilling through the hard rock using the diamond bit 16, the drill penetrates into a soft structure where the penetration rate could be increased by using the tungsten carbide drag bit 15, the operator simply increases the drill pipe thrust above a level predetermined by the mechanical design of the operatively interconnecting means in the tool. This action withdraws the diamond bit 16 and extends the tungsten carbide bit 15 to do the cutting (FIG. 2)..If hard rock is again encountered, the operator decreases the drill pipe thrust until it is below the predetermined level, which action automatically extends the diamond bit 16 permitting it to cut the hard rock, and simultaneously and positively retracts the tungsten carbide bit 15 so that it does not drag or wear on the hard rock.

For rotatively driving the drill bits and providing an operative positioning connection therebetween, as well as for securing the tool 10 to the drill pipe 12, the housing or tool joint 14 is formed as a generally sleeveshaped two-part member. The housing or tool joint sleeve 14 houses the bit assembly and is slidingly and drivingly connected therewith to rotate the bits as the drill pipe string 12 is rotated. To this end, the housing or tooljoint sleeve 14 is formed with an upper joint section 24 which is sleeve-shaped in configuration and embodies, atone end, a tapered thread 11 for securing the tool to the drill pipe string 12. At its opposite end, the upper. tool joint section 24 is internally threaded with a tapered thread 25 which engages the upper end of a lower tool joint section 26. For engaging with the internal threads 25 of the upper tool joint section 24, the lower tool joint section 26 is externally threaded with a tapered thread 28. For convenience in description, as hereinafter used the terms upper, rearward, inner or drill pipe end of the tool will be considered as referring to that end which is secured to the drill pipe string 12, and is the right-hand end of the tool as shown in FIGS. 1 and 2. The lower, forward, outer or drilling end of the tool will be denominated as the drilling end and is the left-hand portions of the tool illustrated in FIGS. 1 and The lower tool joint section 26 may, for convenience in fabrication, be formed in two parts 26a and 26b which are welded or otherwise secured together by any suitable means, such as the weld illustrated at 29. The lower tool joint section part 26a is generally sleeveshaped in cross section and telescopingly receives the tungsten carbide drag bit 15. For providing rotary driving power to the tungsten carbide bit 15, as well as for permitting the tungsten carbide bit to slide or telescope axially within the tool joint 14, the lower tool joint part 260 is provided, at a point adjacent its forward end, with internal splines 30. These splines slidingly and drivingly engage with corresponding external splines 31 on the tungsten carbide bit 15.

The tungsten carbide drag bit is telescopingly inserted for sliding movement within the tool joint housing 14, and the splines 30 on the housing sleeve 26a drivingly engage spline 31 on the tungsten carbide bit. To this end the tungsten carbide drag bit 15 includes a tubular or sleeve portion 32 threaded with external threads 34 at its rear or inner end, and formed at its outer end with a two-pronged head 35. The bit head 35 is also tubular, having a bore 36 therethrough which is smaller in diameter than the bore 38through the sleeve portion 32 of the tungsten carbide bit, thereby defining an internal shoulder 39 within the bit. The head 35 includes two prongs or blades 40, on which the tungsten carbide inserts 18 and their backing portions are mounted. The rear or upper end of the bit sleeve 32 is engaged, by means of the external threads 34, with a tungsten carbide bit head closure assembly 41.

As indicated above, the diamond drill bit head 16 is butterfly" shaped, and nests between the two tungsten carbide inserts 18, as shown in FIG. 3. The diamond drill bit head 21 is secured to a diamond drill bit shaft 42, which is telescopingly received within the bore 36, 38 through the sleeve portion 32 and head 35 of the tungsten carbide bit 15. The head 21 is secured to the shaft 42 by means of a bolt 44, and a recess 45 isprovided in the tungsten carbide bit head 35 for receiving the bolt 44 when the diamond drill bit head 21 and shaft is in the retracted position. The. shaft 42 further includes an external flange 46 which provides a forward shoulder 48 in opposition to the tungsten carbide bit head shoulder 39. As shown in FIGS. 1 and 3, the butterfly-shaped diamond drill bit head 2l is provided with drive lugs 43 which are slidably and drivingly engaged with corresponding external grooves 47 in the tungsten carbide bit head 35. The coaction of the lugs 43 and the grooves 47 operatively couples the diamond drill bit 16 to the tungsten carbide bit 15 for rotary driving movement thereby.

For biasing the diamond drill bit 16 and shaft 42 axially outwardly with respect to the tungsten carbide bit 15 and two-pronged bit head 35, resilient means 49 are mounted in the space defined between the diamond drill bit flange 46 and the tungsten carbide bit closure 41. Any appropriate means may be used, such as a coil spring or other compressible resilient material or structure. In the present instance, it has been found that a stack of Belleville spring washers 49 affords the desired spring action between the tungsten carbide drill bit 15 and the diamond drill bit 16. Belleville washers are conical spring washers which, when acted upon by an axial force, will flatten, and when the axial force is removed, will spring back to their conical shape. Each washer requires a certain force to flatten it, and when stacked as shown in FIGS. 1 and 2 of the drawings, it is possible to obtain a very high spring force with a small deflection, that is a high spring rate, in a limited space. By varying the number of spring washers in the stack, the axial spring force can be varied, and hence the drilling thrust required to position the tungsten carbide drag bit into drilling position can be predetermined. The limit of axial movement of the diamond drill bit 16 axially: outwardly with respect to the tungsten carbide bit 15 is determined by the engagement of the shoulder 39 with the tungsten bit head 35 and the forward flange shoulder 48 of the flange 46 on the diamond drill bit shaft 42. The Belleville spring stack 49 is compressed in place between the diamond drill bit shaft flange 46 and a shoulder 50 on the tungsten carbide bit head closure 41.

With the spring-structure as shown, the diamond drill bit 16 will be normally positioned in drilling position and the tungsten carbide bit head 35 will be retracted into the tooljoint 14 (FIG. 1). For positioning the tungsten carbide drag bit in drilling position, as a function of the thrust exerted by the drill pipe string 12 on the tooljoint housing 14, the tool joint 14, tungsten carbide bit 15 and diamond drill bit 16 are mechanically interconnected by a mechanism which retracts the diamond drill bit shaft 42 and correspondingly extends the tungsten carbide bit relative to the diamond drill bit when the thrust on the tool joint 14 exceeds a thrust value as predetermined by the spring force exerted by the Belleville spring stack 49. To this end, the tungsten carbide bit head closure 41 is slotted with four slots 52 to provide four sets of pairs of mounting

prongs

54, 55. Between each set of

prongs

54, 55, there is rotatably mounted a cable sheave or pulley 56, each sheave being rotatably mounted on a pin 58 extending between each set of mounting

prongs

54, 55. Four cables 59 are provided, each of which is secured at one end to a shaft cap cable mount 60 threadably engaged with the rear or inner end of the diamond drill bit shaft 42,

. passes over an associated sheave 56 and is secured at its other end to the end of the lower tool joint section 26. Adjustable cable anchors 61 are provided securing each cable 59 to the shaft cap 60, and cable anchors 62 are provided for securing the other end of the cable 59 to the tool joint section 26.

With the foregoing structure, it can be readily observed that a downward thrust on the tool joint 14, in excess of a value determined by the spring rate of the Belleville stack 49, will retract the diamond drill bit and extend the tungsten carbide drag bits as shown in FIG. 2. On the other hand, a thrust on the tool joint 14 which is less than the thrust value determined by the spring rate of the Belleville stack, will permit the spring stack 49 to extend the diamond drill bit into drilling position and consequently retract the tungsten carbide bit 15. The forces acting in the system are shown in the diagrammatic representation of the system illustrated as FIG. 9 in the drawings. As can be seen with this arrangement, a downward thrust W on the drill pipe is transferred, through tension in the cables 59, to exert an equal upward force on the diamond drill bit shaft 42. By virtue of the tension in the cables 49 and their 180 wrap over the sheaves 56, this thrust force W is two and transferred to the tungsten carbide bit head 35. So long as the thrust force W is equal to or less than the spring force,'indicated in the drawing by the reference character F the system will remain in balance with the thrust W reacted directly by the diamond bit against the bottom of the hole which is being drilled. As the thrust is increased, however, the downward force on the tungsten carbide bit head 15 exceeds the spring force F thereby compressing the stack of washers 49. This action extends the tungsten carbide bit 15 below the face of the diamond bit 16, transferring the drill pipe thrust W directly to the tungsten carbide bit. Any further increase in the drill pipe thrust beyond that required to flatten the washers will be reacted directly by the tungsten carbide bit 15.

In the embodiment shown, groups of the Belleville washers are preferrably alternated in the spring stack 49. This is a matter of design, as is the number of Belleville spring washers actually utilized. The relative movement between the tool joint housing 14 and the tungsten carbide bit 15 is limited by engagement of the splines 26 with a shoulder 64 defined on the tungsten carbide bit head 35, while the forward movement ofthe tungsten carbide bit head is limited by the total compressed thickness of the stack of spring washers 40 and engagement of the flange 46 with the bit head shoulder 39.

During actual drilling operation it is desirable to circulate drilling fluid, coolant, mud or the like through the tool. Passages for the flow of coolant are provided by slotted holes 65 at the bottom of the sheave slots 52 in the bit head closure 41. These holes 65 extend radially inwardly in line with passages 66 in the diamond drill bit shaft cap 60 to allow coolant to flow into and down through a passage 68 extending axially through the diamond drill bit shaft 42. From the shaft passage 68 the coolant fiows outwardly through two ports 69 opening in the surface of the diamond bit head 21. To provide coolant to lubricate the

splines

30, 31, passages 70 are provided in the upper or rearward ring of the driving sleeve portion 26b of the tool joint (FIG. From the splines, the coolant passes through further holes 71 at the lower end of the splines to the face of the tungsten carbide bit where it is directed against the tungsten carbide inserts 18. Additional cooling ports and passages may be provided as required to prolong tool life.

MODIFIED EMBODIMENT OF THE INVENTION A modified form of the invention is illustrated in FIGS. 7 and 8. In this modification, the operation of the tool is similar to that described above. A modified form of the mechanism interconnecting the tool joint, tungsten carbide drag bit and diamond drill bit is employed. Essentially, the change resides in the use of interengaging gear and rack mechanisms in lieu of the sheave and cable interconnecting mechanism described above. The structure is shown in FIGS. 7 and 8 in a somewhat diagrammatic form in order to illustrate with greater clarity the modified embodiment of the invention.

In the modified form of the drilling tool, indicated at in FIGS. 7 and 8, there is provided a housing or tool joint 84, telescopingly and drivingly mounting a tungsten carbide drag bit 85, which in turn telescopingly and drivingly mounts a diamond drill bit 86. The tool joint is adapted to be secured to the end of a drill pipe string (not shown) and the tool is illustrated at the bottom of a bore hole 87. In FIG. 7 the diamond drill bit 86 is shown in drilling position, while in FIG. 8 the tungsten carbide drag bit is shown in drilling position. A coil spring 88 is utilized as the compressible resilient structure to normally position the diamond drill bit 85 into drilling position relative to the tungsten carbide drag bit 85 as illustrated in FIG. 7.

For operatively positioning the tungsten carbide drag bit into drilling position in response to an increase in thrust on the tool joint or housing 84, the tungsten carbide drag bit structure is provided, at its upper or inner end, with three bifurcated supports 89, each rotatably supporting a gear wheel 90. The gear wheels 90 on the tungsten carbide bit structure 85 mesh with corresponding racks 91 on the internal surface of the tool joint or housing 84, and also with a three-sided rack 92 extending upwardly from the diamond drill bit structure 86. It can be readily observed that, with this mechanism, the coil spring 88 will ordinarily position the diamond drill bit 85 in drilling position. Upon an increase in thrust on the tool joint housing 84 in excess of the force determined by the spring rate of the coil spring 88, the tool joint racks 91 will rotate the gear wheels 89, which will in turn drive the rack 92 to raise the diamond drill bit 86 against the force of the spring 88 and out of drilling position. The downward force on the tool joint 84 will simultaneously position the tungsten carbide drag bit 85 into drilling position against the bottom of the bore hole 87. The operation of and internal forces within the modified structure is the same as described above and illustrated diagrammatically in FIG. 9.

While certain illustrative embodiments of the present invention have been shown in the drawings and described above in considerable detail, there is no intention to limit the invention to the specific forms disclosed. On the contrary, the intention is to cover all modifications, alternative constructions, equivalents and uses falling within the spirit and scope of the invention as expressed in the appended claims.

We claim as our invention:

1. A drilling tool comprising, in combination, a tool joint housing, a tungsten carbide drag bit, a diamond drill bit, and means interconnecting said bits and said housing for positioning said tungsten carbide bit in drilling position and positively retracting said diamond drill bit in response to a thrust on said housing in excess of a predetermined thrust force, and for positioning said diamond drill bit in drilling position and positively retracting said tungsten carbide bit upon the application of a thrust to said tool joint housing below said predetermined thrust force.

2. A drilling tool as defined in Claim 1 wherein said tool joint housing comprises a two part sleeve with an upper section having a threaded portion adapted to be secured to the end of a drill pipe string and a lower sleeve section secured to said upper section in axial alignment therewith and having internal splines therein alidably and drivingly engageable with external splines on said tungsten carbide drag bit.

3. A drilling tool as defined in claim 1 wherein said tungsten carbide drag bit and said diamond drill bit include coolant flow passages therethrough.

4. A drilling tool comprising, in combination, a tubular tool joint housing adapted to be secured to the end ofa drill pipe string, a first drill bit mounted within said tool joint housing in driving engagement therewith, a second drill bit mounted within said tool joint housing in driving engagement with said first drill bit, and means operatively interconnecting said tool joint housing, said first drill bit and said second drill bit for extending said first drill bit into drilling position and simultaneously retracting said second drill bit in response to a downward thrust on said tool joint housing by'said drill pipe string in excess of a predetermined thrust force, and for extending said second drill bit into drilling position and positively retracting said first drill bit in response to a downward thrust on said tool joint housing by said drill pipe string less than said predetermined thrust force.

5. A drilling tool comprising, in combination, a tool joint housing adapted to be secured to the end ofa drill pipe string, a first drill bit mounted in said housing for axial telescoping movement with respect thereto and operatively engaged for rotary driving movement by said housing, a second drill bit mounted within said first drill bit for axial telescoping movement with respect thereto and operatively coupled with said first drill bit for rotary driving movement thereby, compressibly resilient means interposed between said first drill bit and said second drill bit for biasing said second drill bit axially outwardly of said first drill bit, and means interconnecting said tool joint housing, said first drill bit and said second drill bit for moving said second bit and said first bit axially with respect to each other and position said first bit in drilling position in opposition to said biasing means upon the exertion of a downward thrust on said tool joint housing in excess of a force required to compress said biasing means, and for releasing said biasing means to urge said second bit axially outwardly from said first hit upon the exertion of a downward thrust on said tool joint housing less than the force exerted by said biasing means.

6. A drilling tool as defined in claim 5 wherein said biasing means comprises a stack of compressed Belleville spring washers.

7. A drilling tool as defined in claim 5 wherein said interconnecting means comprises a plurality of sheaves mounted on said first drill bit and a corresponding number of cables secured at their ends to said tool joint housing and said second drill bit respectively and passing over said sheaves.

8. A drilling tool as defined in claim 5 wherein said interconnecting means comprises a plurality of 'gears secured to said first drill bit and racks on said tool joint housing and said drill bit meshing with said gears at diametrically opposed points thereon so that said second drill bit moves axially oppositely to said tool joint hous- 9. A drilling tool for selectively drilling relatively harder and softer rock materials in response to a change in the downward drilling force applied to said tool, said tool comprising, in combination. 2.. z nl joint adapted to be secured to the end of a drill pipe and including a driving sleeve, a first drill bit telescopingly mounted within said driving sleeve for limited axial movement with respect thereto, cooperatively engaging means on said driving sleeve and said first drill bit for providing a sliding and rotary driving connection therebetween, said first drill bit having an axial bore therein, a second drill bit having a shaft telescopingly mounted within said first bit bore for limited axial movement with respect thereto, cooperatively engaging means on said first and second drill bits for providing a sliding and rotary driving connection therebetween, means acting between said first drill bit and said second drill bit for biasing said bits axially apart, and means operatively coupling said first drill bit, said second drill bit and said tool joint sleeve for moving said second drill bit and said first drill bit axially with respect to each other and position said first drill bit in drilling position in opposition to said biasing means upon the exertion of a downward force on said tool joint sleeve greater than the force exerted by said biasing means, and for releasing said biasing means to urge said second drill bit axially outwardly from said first drill bit into drilling position upon the exertion of a downward force on said sleeve less than the force exerted by said biasing means whereby said drill bits can be selectively positioned into drilling position.

10. A drilling tool as defined in claim 9 wherein said biasing means comprises a stack of Belleville spring washers.

11. A drilling tool as defined in claim 9 wherein the means operatively coupling said first bit, said second bit and said tool joint sleeve comprises a plurality of sheaves on said first bit and a plurality of cables corresponding in number to said sheaves connected at one end to said tool joint sleeve and passing over said sheaves and having the 'other end connected to said secondbit whereby an increase in thrust on said tool joint sleeve in excess of the thrust determined by said biasing means retracts said second bit relative to said first bit and extends said first bit into drilling position.

12. A drilling tool adapted to be secured to the end of a drill pipe for selectively drilling both soft and hard rock materials comprising a tool housing, a tungsten carbide drag bit including a tubular body telescopingly and drivingly mounted within said housing, a diamond drill bit telescopingly mounted within said tungsten carbide drag bit body and rotatively drivingly engaged with said tungsten carbide drag bit, means operatively interposed between said tungsten carbide drag bit and said diamond drill bit for biasing said diamond drill bit into a forwardly extended drilling position relative to said tungsten carbide drag bit, and means operatively interconnecting said tungsten carbide drag bit, said diamond drill bit and said tool housing for retracting said diamond drill bit relative to said tungsten carbide drag bit in opposition to said biasing means in response to an applied drilling force transmitted to said tungsten carbide drag bit by the drill pipe which exceeds the force of said biasing means and positions said tungsten carbide drag bit in drilling position, said biasing means extending said diamond drill bit into drilling position in bit is positioned in drilling position in response to a reduction in drillingforce for drilling relatively hard materials.

13. A drilling tool including a tungsten carbide drag bit adapted to drill relatively softer materials upon application of a relatively larger downward drilling force, and a diamond drill bit adapted to drill relatively harder materials upon the application of a relatively lesser drilling force, said tool comprising, in combination:

a tool joint adapted to be secured to the end of a drill a driving sleeve secured to said joint;

a tungsten carbide drag bit head telescopingly mounted within said driving sleeve for limited axial movement with respect thereto and having an axial bore extending therethrough;

spline means on said driving sleeve and said head for providing a rotary driving connection therebetween;

tungsten carbide drill bit inserts secured to the drilling end of said head;

a diamond drill bit shaft telescopingly mounted within said drag bit head bore for limited axial movement with respect to said head;

said diamond drill bit secured to the outer drilling end of said shaft;

means on said diamond drill bit slidably engaging said tungsten carbide bit head for providing a rotary driving connection therebetween;

spring means acting between said drag bit head and said diamond drill bit shaft for urging said head and said shaft axially apart;

and means operatively coupling said shaft, said head and said sleeve for moving said head and said shaft axially with respect to each other in opposition to the force of said spring means upon the exertion of a downward force on said sleeve greater than said spring force, and for releasing said spring to urge said shaft axially outwardly from said head upon the exertion of a downward force on said sleeve less than said spring force;

whereby said tungsten carbide drag bit is positioned to drill relatively softer materials upon the application of a relatively larger downward drilling force on the drill pipe and said diamond drill bit is positioned to drill relatively harder materials upon the application of a relatively lesser drilling force on 12 said drillpipe. I j 14. A drilling tool including a tungsten carbide drag bit and a diamond drill bit comprising, in combination:

a housing generally tubular in configuration and adapted to be secured at one end to a drill pipe;

a driving sleeve secured at one end to said housing and having internal flutes at its other end;

a tungsten carbide drag bit head telescopingly mounted within said driving sleeve and having external flutes slidingly and drivingly engaged with said driving sleeve flutes;

said drag bit head having an axially extending bore therethrough and an internal shoulder defined in said bore adjacent the outer end of said drag bit head; I

tungsten carbide drill bit inserts secured to the outer drilling end of said drag bit head;

a diamond drill bit shaft telescopingly mounted within said drag bit head;

a diamond drill bit head secured to the outer end of said diamond drill bit shaft and drivingly engaged with said drag bit head;

an external flange on said diamond drill bit shaft defining a shoulder thereon, said flange being engagable with said internal shoulder on said drag bit head for limiting axial movement of said shaft with respect to said drag bit head;

means defining an internal shoulder adjacent the rear end of said drag bit head;

spring means intermediate said diamond bit shaft and said drag bit for urging said shaft forwardly and outwardly of said drag bit;

and means operatively connecting said shaft, drag bit and driving sleeve adjacent the tool joint ends thereof for retracting said shaft against the force of said spring upon movement of said driving sleeve forwardly with respect to said drag bit head to position said tungsten carbide bit in drilling position upon an increase in force upon the drill pipe, and for retracting said tungsten carbide drag bit head and enabling said spring to extend said diamond drill bit shaft to position said diamond drill bit in drilling position and simultaneously retract said tungsten carbide drag bit head upon a relaxation of pressure upon said drill pipe.

Claims

2. A drilling tool as defined in Claim 1 wherein said tool joint housing comprises a two part sleeve with an upper section having a threaded portion adapted to be secured to the end of a drill pipe string and a lower sleeve section secured to said upper section in axial alignment therewith and having internal splines therein slidably and drivingly engageable with external splines on said tungsten carbide drag bit.

4. A drilling tool comprising, in combination, a tubular tool joint housing adapted to be secured to the end of a drill pipe string, a first drill bit mounted within said tool joint housing in driving engagement therewith, a second drill bit mounted within said tool joint housing in driving engagement with said first drill bit, and means operatively interconnecting said tool joint housing, said first drill bit and said second drill bit for extending said first drill bit into drilling position and simultaneously retracting said second drill bit in response to a downward thrust on said tool joint housing by said drill pipe string in excess of a predetermined thrust force, and for extending said second drill bit into drilling position and positively retracting said first drill bit in response to a downward thrust on said tool joint housing by said drill pipe string less than said predetermined thrust force.

5. A drilling tool comprising, in combination, a tool joint housing adapted to be secured to the end of a drill pipe string, a first drill bit mounted in said housing for axial telescoping movement with respect thereto and operatively engaged for rotary driving movement by said housing, a second drill bit mounted within said first drill bit for axial telescoping movement with respect thereto and operatively coupled with said first drill bit for rotary driving movement thereby, compressibly resilient means interposed between said first drill bit and said second drill bit for biasing said second drill bit axially outwardly of said first drill bit, and means interconnecting said tool joint housing, said first drill bit and said second drill bit for moving said second bit and said first bit axially with respect to each other and position said first bit in drilling position in opposition to said biasing means upon the exertion of a downward thrust on said tool joint housing in excess of a force required to compress said biasing means, and for releasing said biasing means to urge said second bit axially outwardly from said first bit upon the exertion of a downward thrust on said tool joint housing less than the force exerted by said biasing means.

8. A drilling tool as defined in claim 5 wherein said interconnecting means comprises a plurality of gears secured to said first drill bit and racks on said tool joint housing and said drill bit meshing with said gears at diametrically opposed points thereon so that said second drill bit moves axially oppositely to said tool joint housing.

9. A drilling tool for selectively drilling relatively harder and softer rock materials in response to a change in the downward drilling force applied to said tool, said tool comprising, in combination, a tool joint adapted to be secured to the end of a drill pipe and including a driving sleeve, a first drill bit telescopingly mounted within said driving sleeve for limited axial movement with respect thereto, cooperatively engaging means on said driving sleeve and said first drill bit for providing a sliding and rotary driving connection therebetween, said first drill bit having an axial bore therein, a second drill bit having a shaft telescopingly mounted within said first bit bore for limited axial movement with respect thereto, cooperatively engaging means on said first and second drill bits for providing a sliding and rotary driving connection therebetween, means acting between said first drill bit and said second drill bit for biasing said bits axially apart, and means operatively coupling said first drill bit, said second drill bit and said tool joint sleeve for moving said second drill bit and said first drill bit axially with respect to each other and position said first drill bit in drilling position in opposition to said biasing means upon the exertion of a downward force on said tool joint sleeve greater than the force exerted by said biasing means, and for releasing said biasing means to urge said second drill bit axially outwardly from said first drill bit into drilling position upon the exertion of a downward force on said sleeve less than the force exerted by said biasing means whereby said drill bits can be selectively positioned into drilling position.

11. A drilling tool as defined in claim 9 wherein the means operatively coupling said first bit, said second bit and said tool joint sleeve comprises a plurality of sheaves on said first bit and a plurality of cables corresponding in number to said sheaves connected at one end to said tool joint sleeve and passing over said sheaves and having the other end connected to said second bit whereby an increase in thrust on said tool joint sleeve in excess of the thrust determined by said biasing means retracts said second bit relative to said first bit and extends said first bit into drilling position.

12. A drilling tool adapted to be secured to the end of a drill pipe for selectively drilling both soft and hard rock materials comprising a tool housing, a tungsten carbide drag bit including a tubular body telescopingly and drivingly mounted within said housing, a diamond drill bit telescopingly mounted within said tungsten carbide drag bit body and rotatively drivingly engaged with said tungsten carbide drag bit, means operatively interposed between said tungsten carbide drag bit and said diamond drill bit for biasing said diamond drill bit into a forwardly extended drilling position relative to said tungsten carbide drag bit, and means operatively interconnecting said tungsten carbide drag bit, said diamond drill bit and said tool housing for retracting said diamond drill bit relative to said tungsten carbide drag bit in opposition to said biasing means in response to an applied drilling force transmitted to said tungsten carbide drag bit by the drill pipe which exceeds the force of said biasing means and Positions said tungsten carbide drag bit in drilling position, said biasing means extending said diamond drill bit into drilling position in response to a reduction in drilling force applied to said drill pipe below the force exerted by said biasing means whereby said tungsten carbide drag bit can be selectively positioned under an increased drilling force for drilling relatively soft materials and said diamond drill bit is positioned in drilling position in response to a reduction in drilling force for drilling relatively hard materials.

13. A drilling tool including a tungsten carbide drag bit adapted to drill relatively softer materials upon application of a relatively larger downward drilling force, and a diamond drill bit adapted to drill relatively harder materials upon the application of a relatively lesser drilling force, said tool comprising, in combination: a tool joint adapted to be secured to the end of a drill pipe; a driving sleeve secured to said joint; a tungsten carbide drag bit head telescopingly mounted within said driving sleeve for limited axial movement with respect thereto and having an axial bore extending therethrough; spline means on said driving sleeve and said head for providing a rotary driving connection therebetween; tungsten carbide drill bit inserts secured to the drilling end of said head; a diamond drill bit shaft telescopingly mounted within said drag bit head bore for limited axial movement with respect to said head; said diamond drill bit secured to the outer drilling end of said shaft; means on said diamond drill bit slidably engaging said tungsten carbide bit head for providing a rotary driving connection therebetween; spring means acting between said drag bit head and said diamond drill bit shaft for urging said head and said shaft axially apart; and means operatively coupling said shaft, said head and said sleeve for moving said head and said shaft axially with respect to each other in opposition to the force of said spring means upon the exertion of a downward force on said sleeve greater than said spring force, and for releasing said spring to urge said shaft axially outwardly from said head upon the exertion of a downward force on said sleeve less than said spring force; whereby said tungsten carbide drag bit is positioned to drill relatively softer materials upon the application of a relatively larger downward drilling force on the drill pipe and said diamond drill bit is positioned to drill relatively harder materials upon the application of a relatively lesser drilling force on said drill pipe.

14. A drilling tool including a tungsten carbide drag bit and a diamond drill bit comprising, in combination: a housing generally tubular in configuration and adapted to be secured at one end to a drill pipe; a driving sleeve secured at one end to said housing and having internal flutes at its other end; a tungsten carbide drag bit head telescopingly mounted within said driving sleeve and having external flutes slidingly and drivingly engaged with said driving sleeve flutes; said drag bit head having an axially extending bore therethrough and an internal shoulder defined in said bore adjacent the outer end of said drag bit head; tungsten carbide drill bit inserts secured to the outer drilling end of said drag bit head; a diamond drill bit shaft telescopingly mounted within said drag bit head; a diamond drill bit head secured to the outer end of said diamond drill bit shaft and drivingly engaged with said drag bit head; an external flange on said diamond drill bit shaft defining a shoulder thereon, said flange being engagable with said internal shoulder on said drag bit head for limiting axial movement of said shaft with respect to said drag bit head; means defining an internal shoulder adjacent the rear end of said drag bit head; spring means intermediate said diamond bit shaft and said drag bit for urging said shaft forwardly and outwardly oF said drag bit; and means operatively connecting said shaft, drag bit and driving sleeve adjacent the tool joint ends thereof for retracting said shaft against the force of said spring upon movement of said driving sleeve forwardly with respect to said drag bit head to position said tungsten carbide bit in drilling position upon an increase in force upon the drill pipe, and for retracting said tungsten carbide drag bit head and enabling said spring to extend said diamond drill bit shaft to position said diamond drill bit in drilling position and simultaneously retract said tungsten carbide drag bit head upon a relaxation of pressure upon said drill pipe.