The present invention relates generally to drill bit assemblies for drilling through materials including superhard rock and more particularly to a specific improvement to such an assembly.

Tricone drill bit assemblies are well-known in the art. A typical assembly of this type includes an arrangement of lugs having shafts which rotatably support three equally spaced-apart cone-type cutter heads circum- ferentially about a common central axis of the assembly such that a segment of each drill bit defines a corres¬ ponding segment of the drill face of the assembly between its central axis and the outermost periphery of the drill face.

While a standard cone-type drill bit assembly is generally satisfactory for its intended purpose, applicants have discovered a way to substantially improve its performance in an uncomplicated, reliable and yet economical way by utilizing fluid cutting jets to assist the tricone bits, as will be described hereinafter. In this regard, it is to be understood that the present invention does not reside in the general concept of fluid jet assisted drill bit assemblies. One such assembly in the prior art is described in U.S. Patent 3,112,800 (Bobo) while another is described in U.S. Patent 4,174,759 (Arbuckle) .

While the Bobo technique certainly describes a cone-type drill bit assembly including fluid cutting jets, it is only of limited effect since the cutting jets are located only along the outer periphery of the its drill face, that is, at the gauge of the hole being drilled. If this type of assembly is used in medium to hard rock where the gauge jets cannot kerf the rock, the jets serve only to clean the rock underneath the gauge row teeth forming the outer periphery of the assembly's drill face. There is no benefit at all to the inner rows of teeth forming the rest of the drill face. In softer formations where kerfing is possible, cutting jets at the gauge may well cause damage to the walls of the holes being drilled, thereby resulting in hole instability and added completion costs.

A way to overcome the limited effect resulting from using only gauge jets as in Bobo is described in Arbuckle. There, a more complex type of tricone drill bit assembly is disclosed. That assembly includes an arrangement of lugs which rotatably support three segmented cutter heads circumferentially about a common axis, as generally described above. However, each of the cutter heads in Arbuckle is comprised of a plurality of separately rotating segments along a common shaft. In that way, Arbuckle provides cutting jets between adjacent ones of these segments. As a result, the overall drill bit assembly includes cutting jets radially inward of its gauge, that is, radially inward of its drill face's outer periphery.

In view of the foregoing, it is an object of the present invention to provide still another type of fluid jet assisted drill bit assembly which provides for a substantial improvement in performance relative

to the standard type of tricone drill bit assemblies described above.

A more particular object of the present invention is to provide a jet assisted drill bit assembly which is substantially more effective than the gauge-type of fluid jet assisted drill bit assembly disclosed in Bobo and yet one which does not require the complicated features disclosed in Arbuckle.

As will be described in more detail hereinafter, the drill bit assembly disclosed herein is preferably only a slightly modified tricone-type of drill bit assembly. This modified version includes the same type of lug arrangement used in the standard tricone assembly. In fact, in an actual embodiment, the lug arrangement used has been modified from one used in a standard tricone drill bit. The cone-type cutter heads are designed so as not to be equally spaced about the central axis of the overall assembly whereby to define the entire drill face as in a standard tricone drill bit assembly. Rather, the lugs are designed to leave space (e.g., a pie-shaped angular segment) between two adjacent lugs, for example, approximately 20°, so as to accommodate a nozzle arrangement designed in accordance with the present invention. This nozzle arrangement includes at least one nozzle located on a line which lies between the two adjacent cutter heads and which extends radially from the outer periphery of the assembly's drill face to its central axis.

At least one nozzle in the embodiment just described is located radially inward of the drill face's outermost periphery. In one embodiment disclosed herein, a single nozzle is utilized. In another embodiment, three such nozzles are provided and in still another

embodiment more than three nozzles are utilized, one of which is located at the gauge of the drill face (its outer periphery) and a second one of which is located adjacent the central axis of the assembly. In all of these embodiments, the nozzle or nozzles are located within the angular segment described above.

While the present invention is particularly applicable to tricone drill bit assemblies, it will be apparent that other cone-type drill bit assemblies using more or less than three cone-type drill bits can be readily modified in accordance with the present invention to provide the appropriate fluid jet assistance in an uncomplicated and reliable manner.

The present invention will be described in more detail below in conjunction with the drawings wherein:

FIGURE 1 is a diagrammatic illustration, partially in vertical section view, of a fluid jet assisted tricone drill bit assembly designed in accordance with one embodiment of the present invention;

FIGURE 2 is a plan view of the assembly illustrated in Figure 1, taken generally along lines 2-2 in Figure 1?

FIGURE 3 is a view similar to Figure 1 illustrating a fluid jet assisted drill bit assembly designed in accordance with a second embodiment of the present invention;

FIGURE 4 is a plan view of the drill bit assembly of Figure 3, taken generally along line 4-4 in Figure 3; and

FIGURE 5 is a view similar to Figures 1 and 3 illustrating a fluid jet assisted tricone drill bit assembly designed in accordance with a third embodiment of the present invention.

Turning now to the drawings, wherein like components are designated by like reference numerals throughout the various figures, attention is first directed to Figures 1 and 2. As illustrated in these figures and as indicated immediately above, the fluid jet assisted 0 tricone drill bit assembly designed in accordance with the present invention is shown. This assembly, generally indicated at 10, is diagrammatically depicted in Figure 1 within a hole 12 being drilled through rock 14. The drill bit assembly is connected to the free 5 end of a drill shaft generally indicated by dotted lines at 16.

Still referring to Figures 1 and 2, drill bit assembly 10 is shown including an arrangement of lugs 18, three in all, which may be identical to the lugs used in _Q prior art tricone drill bits, except slightly modified in the manner to be described. Each lug 18 is preferably an integrally formed steel member including a main body 20, a stem 22 extending rearwardly from the main body 20 and a shaft 24 angled inward from body 20 5 relative to stem 22. The three lugs are welded or otherwise suitably fixedly connected together so that their respective stems 22 accommodate the free end of drill shaft 16 in a known and readily providable manner. In this regard, for purposes of providing a 0 frame of reference, the overall drill bit assembly may be said to have a central axis 26 which is coaxial with the axis of drive shaft 16. The lugs are designed so that when connected together in the manner just recited the lug shafts 24 are spaced from one another

circumferentially about common axis 26 and extend in forward, inclined directions toward but stop short of the central axis. One such lug shaft is specifically illustrated in Figure 1. The others are inclined in a similar fashion.

In a typical prior art type of tricone drill bit assembly of the type described previously, similar lugs including their own stems and lug shafts are utilized and connected together in a similar manner so that their respective stems receive the free end of a cooperating drill shaft. In this typical assembly, the lugs are configured so that their respective lug shafts are equally circumferentially spaced about their central axis, that is, 120° from one another. These equally spaced lug shafts are provided to rotatably receive cooperating roller cone cutter heads which are themselves equally spaced about the central axis such that a segment of each cutter head defines a corres¬ ponding segment of the drill face of the assembly between its central axis and the outermost periphery of the drill face. The drill face of this typical assembly is comprised entirely of these cutter head segments. As will be seen immediately below, the lugs 20 of the present invention differ from this conventional arrangement.

Like the standard tricone drill bit assembly, assembly 10 also includes three cone-type cutter heads 30, 32 and 34 which are respectively mounted for rotation about the three lug shafts 24. However, the lugs 20 are specially configured so that they are connected together in the manner shown and rotatably support cutter heads 30, 32 and 34 on their respective lug shafts 24 such that there is a relatively large pie- shaped space (for example a pie-shaped angular segment

or other suitable shape) between two adjacent cutter heads, for example the two cutter heads 32 and 34, as best illustrated in Figure 2. The lugs 20 can be initially designed in this manner or, as is preferred, they can be modified from readily available lugs used in the previously described typical tricone drill bit assembly, but shaved or otherwise modified to provide the spacing desired. In an actual working embodiment, there is approximately 20° of spacing between cutter heads 32 and 34. This, of course, requires specifi¬ cally designed cone-type cutter heads, as contrasted with those readily available for use in the previously described typical assembly.

Except for their sizes, shapes and relative positions, the components making up overall drill bit assembly 10 thus far described are conventional (functionally) or otherwise well-known in the art. That is, the typical tricone drill bit assembly described previously includes all of these components. Additional components forming part of assembly 10 which also are present in the prior art assembly include suitable means for defining low pressure mud jets 38. In assembly 10 only two such jets are utilized whereas in the typical prior art assembly there are three equally spaced low pressure mud jets disposed along the outer periphery of its drill face. This third mud jet has been eliminated from assembly 10 in order to incorporate the present invention, as will be seen. It is also possible to incorporate a third low pressure and jet along side the high pressure jet manifold 40.

As stated immediately above, overall assembly 10 includes only two low pressure mud jets 38 and the three cutter heads 30, 32 and 34 are configured and positioned so that an arcuate space of approximately

20° (actually pie-shaped) is present between two of the cutter heads, specifically cutter heads 32 and 34, as illustrated in Figure 2. In accordance with the present invention, this space serves to accommodate an arrangement generally indicated at 40 for directing a plurality of high pressure fluid cutting jets 42 (see Figure 1) in front of the overall drill face 44 of assembly 10 in order to assist cutter heads 30, 32 and 34 in drilling hole 12 during operation of the overall assembly. Cutting jets 42 are to be distinguished from the low pressure mud jets 38 by their high pressure, for example on the order of 15,000 to 60,000 psi, as compared to the low pressures of approximately 1,500 psi exerted by the mud jets. They are also to be distinguished from the mud jets by their positions on drill face 44. Specifically, as illustrated best in Figure 2, the cutting jets 42 are spaced short distances from one another with the angular segment which is located between the two cutter heads 32 and 34 and which extends radially from the outer periphery 46 of drill face 44 to common axis 26. In an actual embodiment the cutting jets are located on a common radial line, although they do not have to be. They could be staggered within the angular segment. In other words, the arrangement 40 could provide a staggered array of jets rather than a line of them. In From both Figures 1 and 2 , it can be seen that this group of cutting jets includes at least one and preferably more than one cutting jet located inwardly of outer periphery 46, in other words, inward of the assembly's outer gauge. This is critical, as indicated previously.

Still referring to Figures 1 and 2, overall cutting jet arrangement 40 is shown including its own housing 48 which defines a series of passageways 49, one for each

cutting jet 42, a common manifold 50 at the back end of passageways 49, and a single passageway 52 extending rearwardly from manifold 50. Housing 48 includes a high pressure nozzle 52 at the front end of each passageway 49 whereby to provide fluid cutting jets 42 and its rearward end is configured to be readily connected to a suitable high pressure source of fluid through shaft 16.

Overall drill bit assembly 10 has been shown in Figures 1 and 2 including a large number of cutting jets, for example six in all. This configuration is especially suitable for use in hard rock. It is expected that the full force of this line of high pressure cutting jets will provide "perfect" cleaning of the hole bottom as defined, for example, in an article by W.C. Maurer entitled THE "PERFECT CLEANING" THEORY OF ROTARY

DRILLING, Journal of Petroleum Technology. Nov. 1962, pp. 1270-1274. Moreover, in many cases this line of jets will provide additional rock removal down to a depth defined by the damage zone of rock beneath the drill bits. Removal of this zone of damaged but unfailed rock is referred to as "supercleaning".

In those softer or more permeable rock formations which are kerfable, it may be desirable to reduce the number of cutting jets forming part of the overall drill bit assembly. Two such examples are illustrated in Figures 3-5. In Figures 3 and 4, an overall assembly 10' is shown. This assembly may be identical to assembly 10, with one exception. Assembly 10' includes a cutting jet arrangement 40' comprised of a housing 48' which provides for three high pressure cutting jets 42', rather than the six illustrated in Figures l and 2. Like arrangement 40, the cutting jets 42' are located on the angular segment which is between two cutter

heads and which extends radially from the outer periphery of the assembly's face to its center axis. As illustrated in Figure 4, one of these cutting jets is located at the gauge and two are located radially inwardly therefrom.

Figure 5 illustrates an overall drill bit assembly 10" which also may be identical to assembly 10, except for its cutting jet arrangement. The assembly 10" includes a cutting jet arrangement 40" which defines but a single cutting jet 42". This particular cutting jet is located on the same line as the cutting jets 42 and 42* , radially inward of the outer periphery of the assembly's cutting face. In this softer or more permeable rock formation, even a single jet located radially inward of the hole gauge will create a deep and wide trench of spalled rock as the jet enters into existing fractures and spalls large pieces of rock. This region can cover the entire hole bottom so that it is not necessary to provide jets in the central region of the hole. Thus, by utilizing a single fluid cutting jet, the overall cutting jet arrangement 40" can be smaller and the drill bits can be larger.

Each of the cutting jet arrangements (manifold blocks) associated with the three embodiments above, is preferably fabricated from a single block of steel. This block is preferably shaped into a wedge so that it provides a simple add on modification to a large variety of bit designs. Thus, identical assemblies, less their jet arrangements can be "finished", with one type of jet cutting arrangement or another, depending upon its ultimate intended use in a relatively simple manner.