Rotary drill bit compensating for changes in hardness of geological formations

Abstract

A long lasting rotary drill bit for drilling a hole into variable hardness geological formations that has a self-actuating mechanism responsive to the hardness of the geological formation to minimize the time necessary to drill a borehole. A long lasting rotary drill bit for drilling a hole into variable hardness geological formations that has a mechanism controllable from the surface of the earth to change the mechanical configuration of the bit to minimize the time necessary to drill a borehole. A monolithic long lasting rotary drill bit for drilling a hole into a geological formation having hardened rods composed of hard material such as tungsten carbide that are cast into a relatively soft steel matrix material to make a rotary drill bit that compensates for wear on the bottom of the drill bit and that also compensates for lateral wear of the drill bit using passive, self-actuating mechanisms, triggered by bit wear to drill relatively constant diameter holes.

Description

Portions of this application have been disclosed in U.S. Disclosure Document No. 445,686 filed with the United States Patent and Trademark Office on Oct. 11, 1998, an entire copy of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention relates to an article of manufacture that is a long lasting rotary drill bit for drilling a hole into variable hardness geological formations that has at least one self-actuating compensation mechanism triggered by bit wear that is responsive to the hardness of the geological formation to minimize the time necessary to drill a borehole using rotary drilling techniques typically used in the oil and gas drilling industries. The field of the invention also relates to a long lasting rotary drill bit for drilling a hole into variable hardness geological formations that has a compensating mechanism controllable from the surface of the earth to change the mechanical configuration of the bit in the well to minimize the time necessary to drill a borehole. The field of invention further relates to an article of manufacture that is a drill bit possessing hard abrasive rods cast into steel, such as tungsten carbide rods cast into steel, that is used to drill holes into geological formations. The field of invention also relates to a composition of matter comprised of tungsten carbide rods cast into relatively softer bit matrix materials, such an alloy steel, to make a self-sharpening drill bit as the bit wears during drilling. The field of invention further relates to the method using the drill bit having tungsten carbide rods cast in steel to drill holes into geological formations that relies upon the progressive exposure of the tungsten carbide rods during the natural wear and erosion of the softer steel alloy matrix material in the drilling bit which results in the self-sharpening of the drill bit. The field of invention further relates to the method of making a long-lasting drill bit comprised of hard abrasive rods cast into steel that is self-sharpening upon the wear of the drill bit during drilling operations. The field of invention further relates to the method of making a long-lasting drill bit by pre-stressing mechanical elements comprising the drill bit that results in the expansion of the drill bit at its bottom during wear of the drill bit thereby producing a constant diameter hole as the bit wears. The field of invention also relates to a method of making the self-sharpening drill bit that relies upon using hardened metal scrapers that become exposed as the bit undergoes lateral wear which tend to produce a constant diameter hole as the bit wears. And finally, the field of invention relates to a method of making the self-sharpening drill bit that relies upon the lateral drill bit wear to uncover and expose new mud channels that results in lateral mud flow which in turn tends to produce a constant diameter hole as the bit undergoes lateral wear.

2. Description of Prior Art

Other than the applications of the inventor previously cited above, at the time of the filing of the application herein, the applicant is unaware of any art in the field that is relevant to the invention.

SUMMARY OF THE INVENTION

The rotary drilling industry presently uses the following types of drill bits that are listed in sequence of their relative importance: roller cone bits; diamond bits; and drag bits (please refer to page 1 of the book entitled “The Bit”, Unit 1, Lesson 2, of the “Rotary Drilling Series”, Third Edition, published by the Petroleum Extension Service, Division of Continuing Education, The University of Texas at Austin, Austin, Tex., hereinafter defined as “Ref. 1”, and an entire copy of “Ref. 1” is included herein by reference, and furthermore, entire copies of all of the lessons, or volumes, in the entire “Rotary Drilling Series” are also included herein by reference).

The early types of roller cone bits were steel-toothed (milled) bits that are still in general use today (Ref. 1, FIG. 7 ). The longest lasting generally available variety of roller cone bits are presently the tungsten carbide insert roller cone bits that have sealed, pressure compensated, bearings. Small tungsten carbide inserts are embedded in the rollers that are used to scrape and fracture the formation while the bit rotates under load. However, there are a large number of rapidly moving parts in a tungsten carbide insert roller cone bit, including the bearings, which make it relatively expensive and prone to eventual failure. Further, the small tungsten carbide inserts in such bits eventually tend to fall out of the cones into the well that results in the failure of the bits (Ref. 1, page 21).

Under ideal operational conditions, the diamond bits can last the longest downhole (Ref 1, page 27). Even though the diamond bits can wear, they have no rapidly moving parts such as bearings, ie., they are “monolithic”. For the purposes of this application the definition of “monolithic” shall be defined to be a one piece item that has no rapidly moving parts. (For the purposes herein, the very slow deformation of mechanical parts due to interior stresses or due to mechanical wear shall not classify the part as a “moving part”.) Monolithic structure is a considerable design advantage over the tungsten carbide insert roller cone type bits which have many rapidly moving parts. However, a diamond bit costs 3 to 4 times as much as an equivalent tungsten carbide insert roller cone bit (Ref. 1, page 27). The expense of the diamond bits are a major disadvantage to their routine use.

The earliest drill bits were a form of drag bit (Ref. 1, page 35). Some modern drag bits have replaceable blades. These bits have no moving parts and are relatively inexpensive. These bits are still used today to drill relatively soft geological formations.

All of the above drill bit designs provide for circulation of the mud from the drill string through the drill bit and into the well. Roller cone bits have drilled watercourses in a “regular bit” and fluid passageways in a “jet bit” (Ref. 1, pages 3-4). Diamond bits have typically “cross-pad” or “radial flow” watercourses (Ref. 1, pages 27-29). Drag bits can have a modified “jet bit” type watercourse (Ref. 1, page 36).

When any of the present drill bits are brand new and unused, many of the above drill bit designs provide various methods to minimize “undergauging” wherein a smaller hole is drilled than is desired (Ref. 1, page 19). Sending a fresh bit into an undergauged hole can result in “jamming” or other significant problems (Ref. 1, page 1). When the bits are new, many of the various designs provide a relatively controlled inside diameter of the well and also prevent the tool from being stuck or “jammed” in the well. The outer teeth on the cones of a roller cone drill bit (“gauge teeth” or “gauge cutters”) determine the inside diameter of the hole and prevent sticking or jamming of the bit (Ref. 1, pages 8 and 19). The oversize lower portion of the diamond bit determines the inside diameter of the hole and prevents sticking or jamming of the bit. The lower flared taper on the drag bits determine the inside diameter of the hole and prevents sticking or jamming of the bit.

However, as any well is drilled, the roller cone bits, the diamond bits, and the drag bits undergo wear towards the ends of the bit. In this application, the definition of “longitudinal” shall mean along the axis of the bit—i.e., in the direction of hole being drilled at any instant. Therefore, the roller cone bits, the diamond bits, and the drag bits all undergo longitudinal wear during drilling operations. As the bit undergoes progressive longitudinal wear, the drill bit becomes dull, and the drilling rate of penetration (feet per hour) slows. The bit can undergo wear to the point that it ultimately fails. Put simply, the roller cone bits, the diamond bits, and the drag bits become progressively duller and wear-out during drilling. The drilling industry instead desires long-lasting, self-sharpening drill bits. In this application the definition of “long-lasting” shall mean a drill bit that tends to self-sharpen under use. In this application, the definition of self-sharpen shall mean any drill bit that tends to compensate for longitudinal wear during drilling operations. The roller cone bits, the diamond bits, and the drag bits do not provide intrinsic self correcting means to produce a self-sharpening drill bit as the drill bit undergoes wear. The definition of the term “longitudinal compensation means” shall mean any means that tends to produce a self-sharpening bit as the bit undergoes longitudinal wear. Put simply, the roller cone drill bits, the diamond drill bits, and the drag bits do not provide longitudinal compensation means to compensate for the longitudinal wear of the drill bit during drilling operations.

As any well is drilled, the roller cone bits, the diamond bits, and the drag bits undergo wear on the sides of the bits. In this application, the definition of lateral shall mean the “side of” the bit—i.e., in a plane perpendicular to the direction of hole being drilled at any instant. Therefore, the roller cone bits, the diamond bits, and the drag bits all undergo lateral wear during drilling operations. As a roller cone bit, diamond bit, or drag bit undergoes progressive lateral wear, the bit drills a tapered hole that is undesirable in the industry. The industry instead desires a “constant diameter hole” or constant “gauge” hole. In this application, the definition of “gauge” shall mean the inside diameter of the hole. The roller cone bits, the diamond bits, and the drag bits do not provide intrinsic self correcting means to produce a constant diameter or gauge hole as the bit undergoes lateral wear. The definition of the term “lateral compensation means” shall mean any means that tends to produce a constant diameter or gauge hole as the bit undergoes lateral wear. Put simply, the roller cone drill bits, the diamond drill bits, and the drag bits do not provide lateral compensation means to compensate for the lateral wear of the drill bit during drilling operations.

All the various different types of commercially available bits described above wear during drilling activities. All other parameters held constant, as the bits wear during drilling, the worn bits tend to slow the drilling process and the worn bits produce a smaller diameter hole as the bits wear. The industry would prefer a bit that does not become dull with use—ie, that “self-sharpens” during drilling. The industry would prefer a bit that produces a constant gauge hole during drilling in spite of any wear on the bit. This application addresses the industry needs for a self-sharpening drill bit that drills relatively constant gauge holes.

An article of manufacture is described herein that combines many advantages of the above basic three types of drilling bits into one new type of drilling bit. Several preferred embodiments of the invention describe a new bit that is a one-piece monolithic structure that has no rapidly moving parts that therefore has the inherent advantages of the diamond bit and of the drag bit. That new bit uses individual tungsten carbide rods cast into steel which provides some of the bottom cutting action of the bit. Such a bit has the cost advantage of tungsten carbide insert roller cone bits in that relatively inexpensive tungsten carbide materials are used for fabrication of the new bit instead of expensive diamonds. Further, the long tungsten rods tend not to fall out of the new drill bit whereas the diamonds can fall out of the diamond bit (Ref. 1, page 35) and the tungsten carbide inserts can fall out of the tungsten carbide insert roller cones (Ref. 1, page 21). Lost tungsten carbide inserts can cause great difficulties during the drilling process (Ref. 1, page 21). Lost diamonds from a diamond bit can cause great problems during drilling (Ref. 1, page 35). Therefore, the fact that the relatively long tungsten carbide rods in the preferred embodiments of the invention herein tend not to become dislodged and tend not to become lost in the well is of considerable economic importance.

The tungsten carbide rods become gradually and progressively exposed on the bottom of the bit as the drill bit wears while drilling the well thereby providing a self-sharpening of the drill bit. The bit wears under the separate influences of the abrasive rock present and the abrasive nature of drilling mud or other drilling fluids. The tungsten carbide rods are eroded at a slower rate than the alloy steel in which it is cast. Broken ends of the tungsten carbide rods can actually speed the drilling process in analogy with certain phenomena observed with tungsten carbide insert roller cone bits (Ref. 1, page 20). Several hardened metal scrapers are also cast into the sides of the new bit that act analogously to the blades of a drag bit which provide some of the wall cutting action. As the steel alloy matrix material of the bit erodes, these hardened metal scrapers become progressively more exposed that results in self-sharpening of the bit.

It is also desirable that the bit produce a constant gauge hole as the bit wears. Various different embodiments of the invention disclose different methods to accomplish this goal. However, many of the different methods rely upon the wear of the bit during drilling to cause physical changes in the drill bit that result in the compensation for lateral bit wear.

A first class of preferred embodiments of the new bit provide for pre-stressed mechanical elements welded together to form the monolithic drill bit which naturally expand radially upon wearing of the welds on the bottom of the new bit resulting in a lower flair, or “bell shape”, of the new bit that in turn determines the inside diameter of the well and that prevents sticking of the bit in the well. The rods facing downward in the first class of preferred embodiments provide compensation for longitudinal bit wear and the lower flair provides compensation for lateral bit wear. A second class of preferred embodiments of the new bit provide a single cast unit having tungsten carbide rods, no welds, but extra lateral hardened metal scrapers to compensate for lateral bit wear. A third class of preferred embodiments of the invention provide a single cast unit having tungsten carbide rods, few welds, but that are heat treated so that the bottom of the bit naturally radially expands upon wear that provides compensation for lateral bit wear to provide a relatively constant gauge hole during drilling. A fourth class of preferred embodiments of the invention provide a single cast unit having tungsten carbide rods, few welds, that has relatively lateral facing hardened metal scrapers that become exposed during the natural wear of the bit which tend to produce a constant gauge hole as the bit undergoes lateral wear. A fifth class of preferred embodiments of the invention provides a single cast unit having tungsten carbide rods, few welds, that possess additional mud cavities that upon the natural wear of the bit, open to the well, causing lateral mud flow that produces a relatively constant gauge hole as the bits undergo lateral wear.

The new bit has watercourses similar to those of a diamond bit. The bit herein uses alternatively “cross-pad flow” or “radial flow” type watercourses discussed earlier.

The fact that the new drill bit can have a large length over diameter ratio, self-sharpens, and produces a relatively constant gauge hole as the bit wears results in a long-lasting drill bit that is of considerable importance to the drilling industry.

Accordingly, an object of the invention is to provide new articles of manufacture that are drill bits used to drill holes into the earth.

It is another object of the invention to provide new articles of manufacture that are drill bits which use tungsten carbide rods cast into steel to produce long-lasting self-sharpening drill bits.

It is yet another object of the invention to provide pre-stressed mechanical elements welded together to form a monolithic drill bit which expand radially in the well producing a flair on the bottom of the bit that determines the inside diameter of the well and that is used to prevent jamming of the bit in the well.

It is another object of the invention to provide a new composition of matter comprised of tungsten carbide rods cast into alloy steel to form a drill bit.

Further, it is another object of the invention to provide new methods of using the drill bit comprised of tungsten carbide rods cast into steel that results in a self-sharpening of the drill bit while the hole is being drilled.

It is yet another object of the invention to provide a method to manufacture long lasting drill bits by casting relatively hard rods into matrix materials such as by casting tungsten carbide rods into alloys of steel.

It is another object of the invention to provide a new composition of matter comprised of tungsten carbide rods cast into steel to form a drill bit that is heat treated to form a monolithic drill bit which, upon wear, naturally expands radially in the well producing a flair on the bottom of the bit that determines the inside of the well and that is used to prevent jamming of the bit in the well.

It is yet another object of the invention to provide a single cast drill bit having tungsten carbide rods cast into steel alloy matrix material, few welds, that has relatively lateral facing hardened metal scrapers that progressively become exposed during the wear of the bit that tend to produce a constant gauge hole as the bit undergoes lateral wear.

It is another object of the invention to provide a single cast drill bit having tungsten carbide rods cast into steel alloy matrix material, few welds, that possesses cavities which upon wear of the bit, open to the well, causing lateral mud flow into the well which in turn produce a constant gauge hole as the bit undergoes lateral bit wear.

It is also another object of the invention to provide a monolithic self-sharpening, long lasting, rotary drill bit having longitudinal compensation means to compensate for the longitudinal wear of the drill bit during drilling operations.

And it is another object of the invention to provide a monolithic rotary drill bit having lateral compensation means to compensate for the lateral wear of the drill bit to provide a bit capable of drilling relatively constant gauge holes during drilling operations.

It is further an object of the invention to provide an article of manufacture that is a long lasting rotary drill bit for drilling a hole into variable hardness geological formations that has at least one self-actuating compensation mechanism triggered by bit wear that is responsive to the hardness of the geological formation to minimize the time necessary to drill a borehole using rotary drilling techniques typically used in the oil and gas drilling industries.

And finally, it is another object of the invention to provide a long lasting rotary drill bit for drilling a hole into variable hardness geological formations that has a compensating mechanism controllable from the surface of the earth to change the mechanical configuration of the bit in the well to minimize the time necessary to drill a borehole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bottom view of a monolithic self sharpening rotary drill bit having three each welded mechanically pre-stressed metal components comprised of material having tungsten carbide rods and a hardened metal scraper embedded in steel.

FIG. 2 is a side view of a monolithic self sharpening rotary drill bit having three each welded mechanically pre-stressed metal components comprised of material having tungsten carbide rods and a hardened metal scraper embedded in steel.

FIG. 3 is a perspective view of one of the components comprised of material having tungsten carbide rods and a hardened metal scraper embedded in steel before the component is assembled and welded in place into the drill bit shown in FIGS. 1 and 2 .

FIG. 4 is a bottom view of three each of the mechanically pre-stressed welded steel components during assembly that are held in place and which are subjected to mechanical stress during the fabrication process of the drill bit shown in FIGS. 1 and 2 .

FIG. 5 is a bottom view of another monolithic self sharpening rotary drill bit that is comprised of tungsten carbide rods and a total of 6 hardened metal scrapers that are embedded into steel as one solid unit during the fabrication process.

FIG. 6 is a bottom view of another monolithic self sharpening rotary drill bit that is comprised of tungsten carbide rods and a total of 6 hardened metal scrapers that are embedded into steel alloy matrix materials that has been heat treated and/or has composition variations in the steel alloy materials that produce internal lateral mechanical stresses within the drill bit.

FIG. 7 is a side view of another monolithic self sharpening rotary drill bit that is comprised of tungsten carbide rods, hardened metal scrapers, and other materials that are embedded into steel alloy matrix material that provides compensation for longitudinal bit wear and compensation for lateral bit wear.

FIG. 8 is side view, rotated 90 degrees about the longitudinal axis of the drill bit, of the view shown in FIG. 7 which shows lateral mud flow compensation channels.

FIG. 9 is the bottom view of the drill bit corresponding to FIGS. 7 and 8 that shows various tungsten carbide rods cast in steel alloy matrix material, hardened metal scrapers that become exposed during bit wear, and a longitudinal mud flow compensation channel.

FIG. 10 is a side view of another monolithic self-sharpening rotary drill bit that has hardened metal scrapers protruding below the bottom of the bit that provides a self-actuating formation hardness compensation means within said bit triggered by bit wear that is responsive to the hardness of the geological formation.

FIG. 11 is side view, rotated 90 degrees about the longitudinal axis of the drill bit, of the view shown in FIG. 10 which shows additional hardened metal scrapers protruding below the bottom of the bit that provides a self-actuating formation hardness compensation means within said bit triggered by bit wear that is responsive to the hardness of the geological formation.

FIG. 12 is the bottom view of the drill bit corresponding to FIGS. 10 and 11 that shows the positions of several hardened metal scrapers protruding below the bottom of the bit that provides a self-actuating formation hardness compensation means within said bit that is responsive to the hardness of the geological formation.

FIG. 13 is a section view of another preferred embodiment of the invention that shows another type of self-actuating formation hardness compensation means within said bit controlled by bit wear that is responsive to the hardness of the geological formation.

FIG. 14 is a section view of another preferred embodiment of the invention that is a long lasting rotary drill bit for drilling a hole into variable hardness geological formations that has a compensating mechanism controllable from the surface of the earth to change the mechanical configuration of the bit in the well to minimize the time necessary to drill a borehole.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a bottom view of a preferred embodiment of the invention that is a monolithic self sharpening rotary drill bit having three each welded mechanically pre-stressed metal components comprised of material having tungsten carbide rods and a hardened metal scraper embedded in steel. The assembled drill bit 2 is comprised of the first, second, and third each separate mechanically pre-stressed metal components labeled respectively as elements 4 , 6 , and 8 in FIG. 1 . The three each separate mechanically pre-stressed metal components are welded together respectively by welds 10 , 12 , and 14 . A typical tungsten carbide rod 16 (viewed end-on) is embedded within steel in metal component 4 . Similarly, tungsten carbide rods are embedded in steel in the other metal components 6 and 8 that have similar shading shown in FIG. 1. A hardened metal scraper 18 is embedded in steel within metal component 4 ; a hardened metal scraper 20 is embedded in steel within metal component 6 ; and a hardened metal scraper 22 is embedded in steel within metal component 8 . The steel alloy matrix material in which the tungsten carbide rod 16 and the hardened metal scraper 18 are embedded in metal component 4 is labeled as element 24 in FIG. 1 . The tungsten carbide rods and the hardened metal scrapers of metal components 6 and 8 are also similarly embedded into steel. A radial flow watercourse is comprised of central hole 26 and waterpassages 28 , 30 , and 32 respectively in metal components 4 , 6 , and 8 . Junk slots 34 and 36 have been fabricated into first metal component 4 . Junk slots 38 and 40 have been fabricated into second metal component 6 . Junk slots 42 and 44 have been fabricated into third metal component 8 .

FIG. 2 is a side view of the monolithic self sharpening rotary drill bit described in FIG. 1 . Elements 6 , 8 , 12 , 16 , 20 , 22 , 40 , and 42 have already been defined above and are shown in FIG. 2 for illustrative purposes. A side view of metal component 6 is shown on the right-hand side of FIG. 2. A side view of metal component 8 is shown on the left-hand side of FIG. 2 . Metal components 6 and 8 are jointed with weld 12 . The leading edge of hardened metal scraper 20 in metal component 6 is identified in FIG. 2 . The leading edge of hardened metal scraper 22 in metal component 8 is identified in FIG. 2 . Junk slot 40 in metal component 6 and junk slot 42 in metal component 8 are identified in FIG. 2 . The bottom of tungsten carbide rod 16 is shown emerging from the bottom of the drill bit in FIG. 2 that is darkly shaded in that figure. Bit shank 45 (also called the “pin”) has the usual mechanical threads appropriate to be screwed into the drill collar (please refer to the section entitled “Tool Joints” beginning on page 9 of the book entitled “The Drill Stem”, Unit 1, Lesson 3, of the “Rotary Drilling Series”, Second Edition, published by the Petroleum Extension Service, Division of Continuing Education, The University of Texas at Austin, Austin, Tex., hereinafter defined as “Ref. 2”, and an entire copy of “Ref. 2” is included herein by reference). For the application herein, the Glossary of Ref. 2 defines several terms as follows. The “drill collar” is “a heavy, thickwalled tube, usually steel, used between the drill pipe and the bit in the drill stem . . . ” The “drill stem” is comprised of “all members in the assembly used for drilling by the rotary method from the swivel to the bit, including the kelly, drill pipe and tool joints, drill collars, stabilizers and various specialty items.” The “drill string” is “the column, or string, or drill pipe with attached tool joints that transmits fluid and rotational power from the kelly to the drill collars and bit.” Bit shank 45 and bit shank support 46 are manufactured from one piece of steel. The bottom portion of the bit shank support 46 is welded to the top portions of metal components 4 , 6 , and 8 by weld 48 . After welds 48 , 12 , 14 , and 16 have been completed, the drill bit is then in one-piece, or is a “monolithic drill bit”. The construction of the bit as defined in FIGS. 1 and 2 results in a “flared” or “bell shaped” bottom of the bit in the region labeled as element 50 in FIG. 2 .

In FIG. 2 , the bottom of weld 12 is labeled as element 52 . As the bit wears due to the abrasiveness of the rock and under the influence of the erosion of the drilling mud, the position of weld 52 moves vertically upward in the drill bit from the bottom of the drill bit by the distance labeled with legend “X” in FIG. 2 . (Here, the “bottom of the drill bit” means the hypothetical plane that “best fits” the “average position” of the tungsten carbide rods and steel emerging from the bottom of the bit, which may or may not be planar.) The distance from the bottom of weld 48 to the bottom of the drill bit is identified by the legend Z in FIG. 2 . When the drill bit is new, the distance Z=L, where L is the original length of the new drill bit. Therefore, Z is the usable length of the drill bit remaining after longitudinal wear. FIG. 2 shows the extreme flared position of hardened metal scraper 20 at the bottom of the drill bit and that extreme position is labeled as element 54 . FIG. 2 shows the extreme flared position of hardened metal scraper 22 at the bottom of the drill bit and that extreme position is labeled element 56 . The width between the extreme positions 54 and 56 is labeled with legend WI that establishes one limitation on the minimum inside diameter of the hole. The width between hardened metal scrapers 20 and 22 in a standard, non-flared, portion of the drill bit is labeled with legend W 2 in FIG. 2 . The inside diameter of the hole is only indirectly related to the dimensions WI and W 2 . A geometric parameter better related to the dimensions of the hole to be drilled is the vector radius that points to the outer portion of the drill bit at a given azimuthal direction with respect to the axis of the drill bit, and that radius is labeled with legend T in FIG. 2 . The “magnitude of that vector radius T” is the distance in any one chosen direction from the center of the drill bit to the outer edge of the drill bit in that particular chosen direction. Various radii may be measured in different azimuthal directions such as T 1 , T 2 , T 3 , etc. Those radii are measured at a distance from the bottom of weld 48 and that distance is labeled with legend Y in FIG. 2 . Different particular positions of Y may be specified respectively identified as Y 1 , Y 2 , Y 3 , etc.

In FIG. 2 , the position of the watercourse through the interior of the drill bit is figuratively identified by dashed line 58 . Various different tungsten carbide rods 60 , 62 , and 64 are shown protruding below the steel alloy matrix of the tool bit that are shaded solid for clarity. The positions of the steel alloy matrix material between the three previously identified tungsten carbide rods are labeled respectively as elements 66 and 68 in FIG. 2 .

FIG. 3 is a perspective view of metal component 6 before weldment into the drill bit shown in FIGS. 1 and 2 . Junk slots 38 and 40 are shown at several positions on metal component 6 for illustrative purposes. Watercourse passage 30 is repetitively shown at several positions along metal component 6 for illustrative purposes. Hardened metal scraper 20 is identified in FIG. 3. A tungsten carbide rod 70 is identified that is located within the steel alloy matrix 72 of metal component 6 . Metal component 6 is fabricated having an arc shape using various possible processes. The arc shaped component 6 and the orientation of the arc is specified by the radius identified in FIG. 3 with the legend “R”. The radius R is contained in the hypothetical geometric plane having the watercourse passage 30 and the line along the tip of the hardened metal scraper 20 , where that line is identified as element 74 in FIG. 3 . The arc shaped component 6 can be directly cast in this form. Alternatively, component 6 can be cast having an initially straight form, which can thereafter be bent under stress into the desired arc shape. Numerous other fabrication techniques can produce metal component 6 with the suitable arc shape shown in FIG. 3 .

FIG. 4 is a bottom view of a particular cross section of the drill bit at one stage of the fabrication process at a particular chosen value of Y. Three each of the mechanically pre-stressed welded steel components are held in place and are subjected to mechanical stress during the fabrication process of the drill bit shown in FIGS. 1 , 2 , and 3 . Here, metal components 4 , 6 , and 8 are held in place for welding a portion of the assembly. Guide 76 holds metal component 4 in place with a force labeled with legend F 1 in FIG. 4 . The force F 1 from guide 76 is transmitted to junk slots 34 and 36 . At this stage of assembly, bit shank 45 and bit shank support 46 are held in place with a vise or clamp during assembly, although that vise is not shown in FIG. 4 . Other guides holding the assembly in place for welding are not shown for simplicity. Not shown is guide 78 that holds metal component 6 in place with a force F 2 applied to junk slots 38 and 40 ; and similarly, not shown is guide 80 that holds metal component 8 in place with a force F 3 applied to junk slots 42 and 44 .

Several steps in the fabrication of the drill bit shown in FIG. 4 have already been completed. Weld 48 has been completely finished prior to the fabrication step shown in FIG. 4 . Initially, metal component 6 as shown in FIG. 3 , and similarly shaped metal components 4 and 8 , are welded in their final orientations at their attachment to bit shank support 46 by weld 48 . Metal components 4 , 6 , and 8 at that stage of fabrication will be separated at the bottom of the bit because each of those parts have their respective radii R. However, a jig having guides 76 , 78 , and 80 respectively force metal components 4 , 6 , and 8 in place so that portions of welds 10 , 12 , and 14 can be made sequentially. Element 82 in FIG. 4 points to a portion of weld 10 during the process of fabrication shown in FIG. 4 . At this particular position Y 1 along the length of the drill bit, guides 76 , 78 , and 80 positively force metal components 4 , 6 , and 8 in place for weldment. At this position Y 1 , the distance of separation between metal components 4 and 6 is labeled with legend Dl in FIG. 4 ; the distance of separation between metal components 6 and 8 is labeled with legend D 2 in FIG. 4 ; and the distance of separation between metal components 8 and 4 is labeled with legend D 3 in FIG. 4 . Prior to weldment of the drill bit at position Y 1 , the forces F 1 , F 2 , and F 3 are adjusted until the distances D 1 , D 2 , and D 3 all become approximately equal to D(AVERAGE). Thereafter, a bead-weld is made joining metal components 4 , 6 , and 8 at position Y 1 . This process is repeated for various different positions Y 2 , Y 3 , etc., until the monolithic drill bit is welded together.

By the time that welds 10 , 12 , and 14 in FIG. 1 are completed, metal components 4 , 6 , and 8 are under considerable stress. This preferred embodiment of the invention provides pre-stressed mechanical elements welded together to form a monolithic drill bit that expands radially in the well producing a flair on the bottom of the bit. That flair determines the inside diameter of the well and is used to prevent jamming of the bit in the well. The welds 4 , 6 , and 12 tend to hold the bottom of the drill bit in line. Wearing those welds allows the bottom of the tool bit to expand as shown in FIG. 2 . The fact that as the welds wear, that the bottom of the tool bit automatically flares outward radially in the well is an example of a lateral compensation means to compensate for lateral wear of the drill bit during drilling operations.

Therefore, FIGS. 1 , 2 , 3 , and 4 describe a preferred embodiment of the invention that is a monolithic drill bit possessing lateral compensation means to compensate for lateral wear of the drill bit during drilling operations so that the drill bit makes a relatively constant gauge hole as the bit undergoes lateral wear.

As the bit rotates under weight, the relatively soft steel alloy matrix material surrounding the tungsten carbide rods wears away. Therefore, the continual erosion of the relatively soft steel alloy matrix results in the progressive uncovering of the rods resulting in the appearance of the bottom of the tool bit as shown in FIG. 2 . Such erosion of steel surrounding the tungsten carbide inserts of the tungsten carbide insert roller cone bits is known to naturally occur during drilling with such bits (Ref. 1, page 21). The bit described herein will undergo similar wear. Until the length Z becomes very small, there is a continuous supply of tungsten carbide rods sticking out the bottom of the tool bit that drills the well. As the tungsten carbide rods dull, or their ends break off, more will become available as the steel alloy matrix material naturally wears away. The process of the gradual wearing of the steel alloy matrix material that exposes additional portions of the tungsten carbide rods is an example of a longitudinal compensation means that compensates for the longitudinal wear of the drill bit during drilling operations.

Therefore, FIGS. 1 , 2 , 3 , and 4 describe a preferred embodiment of the invention that is a monolithic rotary drill bit having longitudinal compensation means to compensate for the longitudinal wear of the drill bit during drilling operations.

The cutting action of this type of bit provides cutting action similar to that provided by a diamond bit. Diamond bits provide the following three types of basic cutting actions: compressive action; abrasive action; and plowing action (Ref. 1, page 33). In compressive action, the exposed tungsten carbide rods create stresses that result in the fracturing of the rock. In abrasive action, the exposed tungsten carbide rods and the relatively softer steel alloy matrix material simply grind through the formation. In plowing action, the exposed tungsten carbide rods actually penetrate the formation and the formation is gouged out in front of the penetrating tungsten carbide rods as the bit rotates. In most cases, the rock fragments will be carried away by the action of the mud flow.

Hardened metal scrapers 18 , 20 , and 22 act like the blades of modern drag bits when the bit is under load. The “flared” or “bell shaped” bottom region of the bit is labeled as element 50 in FIG. 2 . That “flared” or “bell shaped” region acts like the lower flared taper on some modern drag bits. That flared taper determines the inside diameter of the hole and prevents the sticking or jamming of the bit. Therefore, this method of operation of the bit results in a flared portion of the bit that prevents “undergauging” of the hole which can result in jamming of the bit. This flared portion of the preferred embodiment of the invention provides the analogous function to that provided by the oversize lower portion of a diamond bit which, by design, is used to prevent jamming (See FIGS. 37 , 38 , and 39 in Ref. 1). Therefore, the hardened metal scrapers 18 , 20 , and 22 acting on the walls of the well determine the minimum inside diameter of the hole. The sharp edges of the hardened metal scrapers 18 , 20 , and 22 become progressively more available to abrade the wall of the well as the steel alloy matrix material of the bit erodes. This process of additional exposure of the hardened metal scrapers provides additional lateral compensation means to compensate for lateral bit wear during drilling operations.

The portions of hardened metal scrapers facing down in the well also play a role in drilling the well at the bottom of the bit. Modern day drag bits have portions of their blades facing downward to the hole (See FIGS. 45 and 46 in Ref. 1). The portions of hardened metal scrapers 18 , 20 , and 22 that face downward functionally act similarly to the downward facing blades of drag bits. The exposed portions of these hardened metal scrapers facing downward provide additional longitudinal compensation means to compensate for longitudinal bit wear.

Therefore, FIGS. 1 , 2 , 3 , and 4 describe a monolithic rotary drill bit having longitudinal compensation means to compensate for the longitudinal wear of the drill bit during drilling operations. FIGS. 1 , 2 , 3 , and 4 further describe a monolithic drill bit possessing lateral compensation means to compensate for lateral wear of the drill bit during drilling operations.

FIG. 5 shows a bottom view of another preferred embodiment of the invention. It is similar to the invention described in FIGS. 1 through 4 . However, here there are no analogous welds 10 , 12 , 14 or 48 . Instead, a bit looking similar to the side view in FIG. 2 is cast in one piece and the threads fabricated on the top of the bit thereafter. Tungsten carbide rod 16 ; hardened metal scrapers 18 , 20 , and 22 ; and central hole 26 of the waterpassages have already been defined. The junk slots in the bit are shown in FIG. 5 but are not numbered. Different varieties of hardened metal scrapers 84 , 86 , and 88 are also cast into the steel alloy matrix material. The points of the different hardened metal scrapers facing outward are set-back into the steel alloy matrix material by a distance from the lateral wall of the bit which is labeled with the legend “S” in FIG. 5 . Therefore, by design, hardened metal scrapers 84 , 86 , and 88 do not become exposed until the bit undergoes substantial lateral bit wear. Larger tungsten carbide rods typified by the one labeled with legend 90 in FIG. 5 are also present. In this case, all of the tungsten carbide rods and hardened metal scrapers are cast at one time into steel alloy matrix material 92 . The progressive exposure of the downward facing scrapers and rods as the bit undergoes longitudinal wear provide compensation for longitudinal bit wear thereby producing a long-lasting bit. The progressive exposure of extra scrapers 84 , 86 , and 88 after substantial lateral bit wear provides compensation for lateral bit wear that makes a substantially constant gauge hole. The invention in FIG. 5 is simpler and less expensive to fabricate than that shown in FIGS. 1-4 and therefore is of importance.

FIG. 6 shows another preferred embodiment of the invention. Like that shown in FIG. 5 , it is a monolithic bit that is cast as one unit. All of the numbered items are the same through element 90 . However, the composition of steel alloy matrix materials and their heat treatments are chosen to result in internal stresses within the drill bit. Those internal stresses result in the flaring of the bottom portion of the drill bit upon wear. First steel alloy matrix material 94 is cast and heat treated with a first heat treatment to the radius labeled with legend “M” in FIG. 6 . Second steel alloy matrix material 96 is then cast and heat treated with a second heat treatment from radius M to the outer lateral portions of the drill bit. The steel alloy matrix material 96 is chosen to be of higher tensile strength and more resistant to wear than steel alloy matrix material 94 . The heat treatments and alloy steels are chosen such that internal stresses are built up in the drill bit pointing outward, or toward the lateral portions of the drill bit. When steel alloy matrix material 94 inside the radius M is worn away during drilling, the drill bit tends to flair outward at the bottom. The progressive exposure of extra scrapers 84 , 86 , and 88 after substantial lateral bit wear, and the additional flaring of the bit at its bottom after substantial lateral bit wear, provide compensation for lateral bit wear that makes a substantially constant gauge hole. The progressive exposure of downward facing scrapers and rods as the bit undergoes longitudinal bit wear provides compensation for longitudinal bit wear that provides a long-lasting bit. The bit in FIG. 6 is more complex and more expensive to fabricate than that in FIG. 5 . However, the bit in FIG. 6 has extra lateral compensation for lateral bit wear and will tend to produce a more constant gauge hole than will the bit in FIG. 5 .

FIG. 7 shows a cross sectional view of another preferred embodiment of the invention that is a monolithic rotary dill bit. The cross sectional view is identified with legends “A” and “C” that are shown in FIG. 9 . Tungsten carbide rods 98 , 100 , 102 , 104 , 106 , 108 , 110 , and 112 are cast into steel alloy matrix material 114 . Hardened metal scraper 116 is exposed on the left of the drill bit in FIG. 7 . Hardened metal scraper 118 is exposed on the right of the drill bit in FIG. 7 . Watercourse 120 exits at the bottom of the bit that has a mud channel encapsulated by a hardened metal tube 122 to prevent wear inside the bit due to the abrasive mud flow. Watercourse 124 exits at the bottom of the bit that has a mud channel encapsulated by hardened metal tube 126 to prevent wear inside the bit due to the abrasive mud flow. Hardened metal mud blocking part 128 is installed to prevent wear due to the mud flow through main mud flow channel 130 . The following are all cast as one unit together at the same time in steel alloy matrix material 114 : tungsten carbide rods 100 , 102 , 104 , 106 , 108 , 110 , and 112 ; hardened metal scrapers 116 and 118 ; hardened metal tubes 122 and 126 ; and hardened metal mud blocking part 128 . Standard steel alloy casting methods are used to align the parts and to fabricate the monolithic drill bit. The wall 132 of main mud flow channel 130 does not have hardened metal tube reinforcement in FIG. 7 . (However, hardened metal tube wall reinforcement to main mud flow channel 130 may be added and cast into place with the rest of the parts—although that is not shown in FIG. 7 ). The main mud flow channel 130 is connected to watercourse 120 and watercourse 124 and provides mud to the bottom of the bit through those watercourses and others not shown in FIG. 7 . Bit shank 134 (also called the “pin”) has the usual mechanical threads appropriate to be screwed into the drill collar (described in FIG. 2 ). Mating shoulder 136 is to “bottom-out” solidly against the drill collar. The bit shank 134 and mating shoulder 136 may be machined into the bit after casting as shown in FIG. 7 . (Alternatively, bit shank 134 and mating shoulder 136 can be a separate part that is cast into place with the rest of the rods, tubes, and scrapers—although that separate part is not shown in FIG. 7 for simplicity.)

In FIG. 7 , near the center of the bottom of the bit, there is an inward recession into the bit shown generally as region 138 in FIG. 7 . This recession helps guide the bit in a manner similar to how a coring bit is guided by the core it makes as it travels through the rock. There is a bit guide radius, labeled with legend “G” in FIG. 7 , that is the radius that best approximates the curvature present in the steel alloy of the surface defining the inward recession 138 along cross section “A”-“C”. The definition of the phrase “bit guide recession” in this application shall generally refer to any inward recession present near the center of the drill bit. The lower right-hand surface of the steel alloy matrix material in exterior region 140 of the bit has portions that protrude or extend outward below than the center of the bit. This region can be specified by a lateral bit radius labeled with legend “H” in FIG. 7 . Lateral bit radius H is that radius that best approximates the curvature present in the steel alloy matrix of the surface in region 140 along cross section “A”-“C”. Similar comments apply to the lower left-hand side of the bit. The definition of the phrase “lateral bit protrusion” in this application shall mean a region of the bit having any outward extending portion that extends lower than the center of the bit.

FIG. 8 shows another cross sectional view of of the monolithic rotary drill bit shown in FIG. 7 . This cross sectional view is rotated 90 degrees (viewed from the bottom—see FIG. 9 ) from that shown in FIG. 7 . The cross sectional view is identified with legends “B” and “D” that are shown in FIG. 9 . Elements number 114 , 128 , 130 , 132 , 134 , 136 and 138 have already been defined in FIG. 7 . In this case, the bit guide radius G of the bit guide recession is the same along cross section “B”-“D” and along cross section “A”-“C”, although this is not always necessarily true. Tungsten carbide rods 142 , 144 , 146 , 148 , 150 , 152 , 154 , 156 , 158 , 160 and 162 are cast into steel alloy matrix material 114 . Watercourse 164 exits at the bottom of the bit that has a mud channel encapsulated by a hardened metal tube 166 to prevent wear inside the bit due to the abrasive mud flow. Another view of hardened metal mud blocking part 128 is shown that prevents wear due to the mud flow through main mud flow channel 130 . The main mud flow channel 130 is connected to watercourse 164 . The main mud flow channel 130 is also connected to watercourses 120 and 124 shown in FIG. 7 , and to others shown in FIG. 9 .

FIG. 8 also possesses lateral mud flow cavities that are sealed when the bit is new. Main mud flow channel 130 is connected to lateral mud flow compensation cavity 168 that is in turn connected to lateral mud flow compensation cavity 170 . Lateral mud flow compensation cavity 170 terminates into its sealed end 172 when the bit is new. The wall thickness of the metal from the end of the cavity 172 to the outer portion of the drill bit is labeled with legend “P” in FIG. 8 . As the bit undergoes lateral wear, eventually the dimension “P” is ground off the lateral wall of the drill bit. Eventually, the end of the cavity 172 opens to the hole. When that happens, mud flow squirts out laterally into the well. The cross sectional dimensions of the lateral mud flow compensation cavity 170 are chosen so that a controlled mud flow exits laterally out of the bit as the rotary bit rotates in the well. This extra mud flow will tend to increase the diameter or the gauge of the hole. This extra mud flow compensates for the lateral bit wear (that would otherwise cause the bit to drill a tapered hole). Such a channel that opens after lateral wear shall be defined herein as a “lateral mud flow compensation channel”. When the bit undergoes lateral wear, the opening of the lateral mud flow compensation channel tends to produce a relatively constant gauge hole. Therefore, FIGS. 7 and 8 describe a monolithic drill bit possessing lateral compensation means to compensate for the lateral wear of the drill bit during drilling operations that tends to make a relatively constant gauge hole. Similarly, FIG. 8 shows that main mud flow channel 130 is connected to lateral mud flow compensation cavity 174 that is in turn connected to lateral mud flow compensation cavity 176 . Lateral mud flow compensation cavity 176 terminates into its sealed end 178 when the bit is new. The wall thickness of the metal from the end of the cavity 178 to the outer portion of the drill bit is labeled with legend “Q” in FIG. 8 . Also shown is the lateral bit protrusion on the right hand side of the bit along cross section “B”-“D” that is labeled as region 180 in FIG. 8 .

FIG. 9 shows the bottom view of the preferred embodiments shown in FIGS. 7 and 8 . FIG. 9 shows the orientations of the cross sections. FIG. 7 showed the cross section “A”-“C”. FIG. 8 showed the cross section “B”-“D”. Tungsten carbide rods 98 , 100 , 102 , 106 , 108 , 110 and 112 have been identified in FIG. 7 . Hardened metal scrapers 116 and 118 have been identified in FIG. 7 . Watercourse 120 having hardened metal tube 122 and watercourse 124 were identified in FIG. 7 . Tungsten carbide rods 144 , 146 , 148 , 150 , 152 , 154 , 156 , 158 , 160 , and 162 have been identified in FIG. 8 . Watercourse 164 was identified in FIG. 8 . Additional hardened metal scrapers 182 and 184 are shown in FIG. 9 . Recessed hardened metal scrapers 186 and 188 are shown in FIG. 9 . Their outer edges are set back from the outer surface of the bit by a distance labeled with legend “J” in FIG. 9 . Their outer edges becomes exposed upon the lateral wear of the bit. The process of additional exposure of the hardened metal scrapers provides additional lateral compensation means to compensate for lateral bit wear during drilling operations.

FIG. 9 shows additional watercourses 190 and 192 exiting from the bottom of the bit. Element 194 is a sealed end to another watercourse. The wall thickness of the material to enter that new watercourse is chosen to be some predetermined dimension (0.20 inches thick for example). Therefore, as the bit undergoes longitudinal wear, another waterpassage opens up facing downward resulting in additional mud flow into the bottom of the well during drilling. This extra mud flow will tend to increase the drilling rate which therefore tends to compensate for longitudinal bit wear. Such a channel that opens after longitudinal bit wear shall be defined herein as a “longitudinal mud flow compensation channel”. Therefore, FIGS. 7 , 8 , and 9 describe a monolithic rotary drill bit having longitudinal compensation means to compensate for the longitudinal wear of the drill bit during drilling operations.

FIG. 9 also has a square shaped tungsten carbide “rod” labeled as element 196 . A triangular shaped tungsten carbide “rod” is identified as element 198 in FIG. 9 . An elliptically shaped tungsten carbide “rod” is identified as element 200 in FIG. 9 . An irregular shaped “rod” is identified as element 202 in FIG. 9 . Larger O.D. rods are respectively identified as elements 204 and 206 in FIG. 9 . The term “rod” has been used many times herein.

In this application, the term “rod” shall mean any physical item possessing a geometrical shape that is relatively long compared to any other dimension perpendicular to its length. If the “rod” has a cylindrical shape, then the rod shall have a length that is at least N times its diameter where the number N is defined to be the aspect ratio of the rod. N can be chosen to be equal to a predetermined number (not necessarily an integer). For example, the aspect ratio N can be chosen to be the number 3.0. In this case, the “rod” would have a length at least 3 times its diameter. If the “rod” has a rectangular shape, then the rod shall have a length that is at least N times any of the dimensions perpendicular to its length. If the “rod” has a hollow cylindrical shape, then the rod shall have a length that is at least N times its outside diameter regardless of the inside diameter of the hole through it. If the “rod” has an irregular shape such as element 202 in FIG. 9 , then the meaning of “rod” shall mean that the length of the rod shall be equal to or exceed N times “the average dimension of the rod perpendicular to its length”. As the bit turns, any type of hardened “rod” as defined above shall become gradually exposed as the relatively softer matrix material becomes exposed. The process of the gradual wearing of the steel alloy matrix material that exposes additional portions of the tungsten carbide rods is an example of a longitudinal compensation means that compensates for the longitudinal wear of the drill bit during drilling operations. Therefore, FIGS. 7 , 8 , and 9 describe a preferred embodiment of the invention that is a monolithic rotary drill bit having longitudinal compensation means to compensate for the longitudinal wear of the drill bit during drilling operations.

FIG. 9 also identifies junk slot 208 and junk slot 210 in the monolithic dill bit. For future reference, the “azimuthal angle” is that angle subtended from the center of the bit to a given direction in relation to the line from the center of the bit to the direction “C”. However, for clarity, that angle is not identified in FIG. 9 . Similarly, “the vector radius” shall mean the radius along any azimuthal angle to the outer boundary of the drill bit (that is not shown for simplicity).

It is now appropriate to discuss in detail how the invention may be used to optimize the drilling rate in geological formations having variable hardnesses. This is the typical situation where the hardness of the geological formation is a function of depth from the surface of the earth. For example, in sedimentary basins, it is often the case that near the surface, the geological formations are relatively soft, but the formations generally become relatively harder with increasing depth from the surface of the earth. Typically, there are also abrupt changes in formation hardnesses at specific depths from the surface of the earth.

It is well known in the industry that drag bits, otherwise also called “fish tail bits”, are to be used in geological formations having hardnesses that are described as “Soft and Soft Sticky” and “Soft-Medium”. As described earlier, drag bits are also characterized in having blades, and depending upon their shape, those blades are sometimes also referred to as the “fish tails” by some authors.

The drag bits are not recommended in geological formations having hardnesses that are described as “Medium”, “Medium-Hard”, “Hard”, and “Extremely Hard”. Instead, in the relatively harder formations, tungsten insert roller cone bits and diamond bits are recommended. For the definitions of these terms relating to the hardness of geological formations, please refer to the document entitled “1995 Drill Bit Classifier” published by World Oil, Gulf Publishing Co., Houston, Tex., September, 1995, hereinafter defined as “Ref. 3”, an entire copy of which is included herein by reference.

The reason that the drag bits are not recommended in the harder formations is because the blades of the drag bits are known to wear rapidly and to break-off during drilling operations in such harder formations. So, for the purposes of this application, the term “relatively soft geological formations” shall be those formations having hardnesses of either “Soft and Soft Sticky” or “Soft-Medium” as defined in Ref. 3. For the purposes of this application, the term “relatively hard geological formations” shall be those formations having hardnesses of “Medium”, “Medium-Hard”, “Hard”, or “Extremely Hard” as defined in Ref. 3.

As previously mentioned, in sedimentary basins, it is often the case that near the surface, the geological formations are relatively soft, but become relatively hard with increasing depth from the surface of the earth. Suppose for logical purposes herein, from the surface of the earth to a particular depth, that the geological formation is relatively soft. Suppose that beyond that particular depth, the geological formation is relatively hard. So, there is a sharp transition from relatively soft to relatively hard at the particular depth. The preferred embodiment in FIG. 9 may be modified to optimize the drilling rate in such a formation. If elements 186 and 188 extend beyond the bottom of the bit, i.e., if they would “stick out beyond the bottom of the bit” by approximately ¼ inch in one preferred embodiment, then this bit would have interesting properties to be described shortly. For the purposes herein, this particular bit is described as having hardened metal scrapers protruding below the bottom of the bit. For a given rotary speed of the drill string, and in relatively soft formations, this bit would drill faster than the bit otherwise shown in FIG. 9 because it is known that drag bits, or fish tail bits, drill faster in relatively soft geological formations. However, when the particular depth is reached wherein the formation becomes relatively hard, then the protruding scrapers would wear very rapidly, and would otherwise break-off, leaving the invention as basically shown in FIG. 9 . The invention shown in FIG. 9 would then drill relatively rapidly in the relatively hard formation. The point is that the addition of protruding scrapers makes a rotary drill bit for drilling a borehole into a geological formation that has at least “one self-actuating formation hardness compensation means within the bit that is responsive to the hardness of the geological formation”, and this quote is a term defined herein. The rapid wear or the breakage of the protruding hardened scrapers is one example of a “self-actuating formation hardness compensation means within the drill bit”, a term that is also defined herein.

To further elaborate on this preferred embodiment having hardened metal scrapers protruding below the bottom of the bit, please refer to FIG. 5 . This embodiment described herein differs from that described in FIG. 5 in that hardened metal scrapers 18 , 20 , 22 , and 84 , 86 , and 88 in FIG. 5 would in this embodiment, protrude below the bottom of the bit. FIG. 10 shows a particular example of such hardened metal scrapers protruding below the bottom of the bit that is a preferred embodiment of this invention.

FIG. 10 shows a cross sectional view of another preferred embodiment of the invention that is a monolithic rotary drill bit. The cross sectional view is identified with legends “EE” and “FF” which are shown in FIG. 10 . This nomenclature is used so as not to be confused with other legends having single letters appearing elsewhere in the specification. Tungsten carbide rods 216 , 218 , 220 , 222 , 224 , and 226 are cast into steel alloy matrix material 228 . Hardened metal scraper 230 is exposed on the left of the drill bit in FIG. 10 . Hardened metal scraper 230 has bottom edge 231 . Hardened metal scraper 232 is exposed on the right of the drill bit in FIG. 10 . Hardened metal scraper 232 has bottom edge 233 . Watercourse 234 provides the mud channel for conducting drilling mud through the drill bit to the bottom of the bit. Bit shank 236 (also called the “pin”) has the typical mechanical threads appropriate to be screwed into the drill collar (as described in FIG. 2 ). The bit shank 236 and the mating shoulder 238 can be machined into the bit after the casting of the various elements together as described earlier in the case of FIG. 7 .

In FIG. 10 , near the center of the bottom of the bit, there is an inward recession into the bit generally shown as region 240 . This recession helps guide the bit in a manner similar to how a coring bit is guided by the core it makes as it travels through the rock. For additional details about this region of the bit, please refer to FIG. 7 .

FIG. 11 shows another cross sectional view of the monolithic rotary drill bit shown in FIG. 10 . This cross sectional view is rotated 90 degrees (viewed from the bottom—see FIG. 12 ). The cross sectional view is identified with legends “GG” and “HH” that are shown in FIG. 11 . Hardened metal scrapers 242 and 244 are shown in FIG. 11 . Hardened metal scraper 242 protrudes below the radial portion of the drill bit by a distance identified by legend “P1” in FIG. 11 . Similarly, hardened metal scraper 244 protrudes below the radial portion of the drill bit by a distance identified by legend “P2”, although P 2 is now shown in FIG. 11 for simplicity. Hardened metal scraper 242 has bottom scraper edge 246 . Hardened metal scraper 244 has bottom scraper edge 248 . Watercourse 234 is again shown in FIG. 11 . Various tungsten carbide rods cast in the steel allow matrix material could have been shown in FIG. 11 , but that was not done so for the purposes of simplicity.

FIG. 12 shows the bottom view of the preferred embodiment shown in FIGS. 10 and 11 . FIG. 12 shows the orientations of the cross sections. FIG. 10 showed cross section “EE”-“FF”. FIG. 11 showed cross section “GG”-“HH”. The bottom view of tungsten carbide rods 216 , 218 , 220 , 222 , 224 and 226 are shown in FIG. 12 . Hardened metal scrapers 230 , 232 , 242 and 244 are shown in FIG. 12 Bottom edges of the respective scrapers 231 , 233 , and 246 are shown explicitly. However, bottom edge 248 is not shown for the purposes of simplicity. Watercourse 234 is also identified in FIG. 12 .

In addition in FIG. 12 , hardened metal scraper 230 has inward pointing angular structure 250 . Similarly, hardened metal scraper 232 has inward pointing angular structure 252 . Hardened metal scraper 242 also has inward pointing angular structure 254 and outer pointing angular structure 256 . Similar comments apply to hardened metal scraper 244 , although the respective pointed angular structures are not shown in FIG. 12 for simplicity. Hardened metal scraper 244 has a length, identified by legend “L244” in FIG. 12 , and a width, identified by legend “W244” in FIG. 12 . (Similarly, hardened metal scraper 230 has length L 230 and width W 230 ; hardened metal scraper 232 has length L 232 and width W 232 ; and hardened metal scraper 242 has length L 242 and width W 242 ; but these dimensions are not shown in FIG. 12 for simplicity.) Also not shown for simplicity in FIG. 12 are the junk-slots analogous to those described in many of the previous figures, including FIG. 1 and FIG. 9 .

The point of this is that the dimensions P 1 , P 2 , and the respective lengths and widths of the hardened metal scrapers are intentionally designed such that the drill bit will drill fast and efficiently in relatively soft geological formations. These dimensions are chosen such that the hardened metal scrapers will not wear unusually rapidly, nor will they break off in such relatively soft geological formations. However, upon entering a relatively hard geological formation, these dimensions are deliberately chosen such that the scrapers will wear rapidly or so that they will break off in relatively hard geological formations. Trial and error can be used to determine the appropriate dimensions if calculations prove somewhat unreliable, so that anyone with ordinary skill in the art can determine these dimensions with suitable effort.

In such a situation, the drill bit itself self-compensates for a change in the hardness of the geological formations. Hardened metal scrapers 230 , 232 , 242 and 244 are examples of “self-actuated formation hardness compensation means within the bit that are responsive to the hardness of the geological formations”, a term that has been previously defined.

Therefore, the preferred embodiment shown in FIGS. 10 , 11 and 12 is an example of a rotary drill bit for drilling a borehole into a geological formation having at least one self-actuating formation hardness compensation means within said bit that is responsive to the hardness of the geological formation.

The method of drilling a borehole using the drill bit shown in FIGS. 10 , 11 , and 12 is now described. The method of drilling a borehole into a geological formation that has variable hardness using a rotary drill bit attached to a rotary drill sting requires several simple steps. A rotary drill bit is chosen that has a self-actuating formation hardness compensation means within said bit that is responsive to the hardness of the geological formation. The drill bit is attached to the rotary drill string on the surface of the earth. The hole is drilled with the rotary drill bit attached to the drill string. The drilling rate is dependent upon the hardness of the geological formation at a specific depth. Here, the drilling rate is in inches per minute. Suppose that the geological formation changes from relatively soft to relatively hard at the one specific depth. The preferred embodiment herein provides for compensating one time for the change in hardness of the geological formation at the specific depth using said self-actuating formation hardness compensation means because at that depth the hardened metal scrapers protruding from the bottom of the bit will wear off rapidly leaving the remainder of the drill bit that will work well in relatively hard geological formations.

It is also evident that the preferred embodiment of the invention shown in FIGS. 10 , 11 and 12 also has the previously described virtues. The rotary drill bit described in FIGS. 10 , 11 , and 12 has the following minimum number of properties: (1) a first self-actuating longitudinal compensation means within said bit that is actuated by any longitudinal bit wear (for example, the tungsten carbide rods 216 , 218 , . . . ); (2) a second self-actuating longitudinal compensation means within said bit that is responsive to the hardness of the geological formation (for example, hardened metal scrapers 242 and 244 ); and (3) a self-actuating lateral compensation means within said bit that is actuated by any lateral bit wear (for example, hardened metal scrapers 230 and 232 ). It should be noted that because of the angles of the hardened metal scrapers 242 and 244 with respect to the vertical axis of the bit, these scrapers are also examples of self-actuating lateral compensation means within the bit that are responsive to the hardness of the geological formation. Other longitudinal and lateral compensation means previously described in FIGS. 1-9 could be added to any of the FIGS. 10 , 11 and 12 , but for simplicity, those additional longitudinal and lateral compensation means are not shown therein.

Many different geometries of elements protruding beyond the bottom of the bit could be cited that would provide further “longitudinal self-actuation formation hardness compensation means within the bit that are responsive to the hardness of the geological formations”, a term defined herein. Many different geometries of elements protruding laterally from the drill bit could also be cited that would also provide further “lateral self-actuation formation hardness compensation means within the bit that are responsive to the hardness of the geological formations”, a term that is defined herein.

As another example a preferred embodiment of the invention, please refer to FIG. 13 . This is a cross sectional view of another embodiment. For simplicity, only one view of this preferred embodiment is shown in FIG. 13 . Tapered hardened metal scraper 258 has one non-parallel edge 260 . Non-parallel edge 260 is not parallel to edge 262 . Therefore, there is a taper angle 264 related to non-parallel edge 260 . Tapered hardened metal scraper 258 is held in place between two parallel guide edges, namely, between inner guide edge 266 and outer guide edge 268 . Edges 262 , 266 and 268 are all parallel to one-another, but edge 264 is not parallel to any of those other edges. Because of the geometry chosen, FIG. 13 shows tapered hardened metal scraper 258 “jammed in place”, and it is in solid metal contact at “jam point 1 ” that is labeled with legend “JP 1 ” in FIG. 13 . Threaded ring retainer 274 has outer threads that seat against inner threads 276 of the bit shank 278 .

Second tapered hardened metal scraper 280 is similarly held in place against “jam point 2 ” that is labeled with the legend “JP 2 ” in FIG. 13 . The steel alloy matrix material 282 is so labeled. Tungsten carbide rods can be suitably placed into this steel alloy matrix material if desired, although no such tungsten carbide rods are shown in the section view in FIG. 13 for simplicity. Watercourse 284 is also shown in FIG. 13 .

The upper portion 286 of tapered hardened metal scraper 258 is in contact with the bottom of spring 270 . Similarly, the upper portion 288 of tapered hardened metal scraper 280 is in contact with the bottom of spring 270 . The force of the spring jams the two hardened metal scrapers into place at points JP 1 and JP 2 . The upper surface 286 of tapered hardened metal scraper 258 is a distance labeled with the legend D 286 below shoulder 290 . The upper surface 288 of tapered hardened metal scraper 280 is a distance labeled with the legend D 288 below shoulder 290 . Perhaps it is worth noting that shoulder 290 has cylindrical symmetry about the vertical axis along the center of the bit (which axis is not shown in FIG. 13 for simplicity).

Tapered hardened metal scraper 258 is shown protruding a distance below the local circumference of the bottom of the dill bit by a distance labeled with numeral 292 in FIG. 13 . Similarly, tapered hardened metal scraper 280 is shown protruding a distance below the local circumference of the bottom of the dill bit by a distance labeled with numeral 294 in FIG. 13 . As the bottom of the bit wears, the material near jam points JP 1 and JP 2 will wear. This wearing will allow the distances 292 and 294 to increase in relatively soft geological formations. However, if a relatively hard geological formation is encountered instead, the bottom ends of tapered metal scrapers 258 and 294 will wear rapidly, or will otherwise break-off. Therefore, the preferred embodiment shown in FIG. 13 has many of the same functional features of the embodiment of the invention shown in FIGS. 10 , 11 and 12 .

As in the case of the earlier FIGS. 10 , 11 , and 12 , in FIG. 13 dimensions of the tapered hardened metal scrapers are intentionally designed such that the drill bit will drill fast in relatively soft geological formations. The drill bit will efficiently drill relatively soft geological formations, and the drilling rate will be relatively high. These dimensions are chosen such that the scrapers will not wear unusually nor will they break off in such relatively soft geological formations. However, upon entering a relatively hard geological formation, these dimensions are chosen such that the tapered hardened metal scrapers will wear rapidly or so that they will break-off in relatively hard geological formations. Trial and error can be used to determine these dimensions if calculations prove unreliable,, so that anybody with ordinary skill in the art can determine these dimensions with suitable effort.

In such a situation, the drill bit itself self-compensates for a change in the hardness of the geological formations. Tapered hardened metal scrapers 258 and 294 are examples of “self-actuated formation hardness compensation means within the bit that are responsive to the hardness of the geological formations”, a term that has been previously defined.

Therefore, the preferred embodiment shown in FIG. 13 an example of a rotary drill bit for drilling a borehole into a geological formation having at least one self-actuating formation hardness compensation means within said bit that is responsive to the hardness of the geological formation.

In summary FIGS. 10 , 11 , 12 and 13 describe long lasting rotary drill bit for drilling a hole into variable hardness geological formations that has at least one self-actuating compensation mechanism triggered by bit wear that is responsive to the hardness of the geological formation. The purpose of this bit responsiveness to the hardness of the geological formations is to minimize the time necessary to drill a borehole into the earth using rotary drilling techniques typically used in the oil and gas drilling industries.

Yet another preferred embodiment of the invention is responsive to force applied to the top of the bit. That force is called the “weight on bit”, otherwise called the “bit weight” hereinafter in this application. The bit weight can be readily determined by the weight indicator that is instrument located near the driller's position on the drilling rig. The bit weight can be determined from that instrument with the knowledge of the weight of the drill string including the drill collars, etc. Therefore, ordinary art in the industry is assumed herein. For example, please refer to Unit I, Lesson 1 of the Rotary Drilling Series entitled “The Rotary Rig and Its Components”, Third Edition, Petroleum Extension Service, The University of Texas at Austin, Austin, Tex., that is “Ref. 4” defined herein, and an entire copy of “Ref. 4” is included herein by reference.

As an example of a preferred embodiment of the invention responsive to bit weight, please refer to FIG. 14 . This is a cross sectional view of another embodiment of the invention. For simplicity, only one view of this embodiment is shown in FIG. 14 . Hardened metal scraper 296 is cylindrically symmetric above machining edge 298 in FIG. 14 . Below machining edge 298 , hardened metal scraper 296 is rectangular in shape. Similarly, hardened metal scraper 300 is cylindrically symmetric above machining edge 302 . Below machining edge 302 , hardened metal scraper 300 is rectangular in shape.

Spring 304 is captured between surface 306 and shoulder 308 on hardened metal scraper 296 . Threaded nut 310 screws into threads 312 in the body of the drill bit. Similarly, spring 314 is captured between surface 316 and shoulder 318 on hardened metal scraper 300 . Threaded nut 320 screws into threads 322 on the body of the drill bit.

The bit weight placed onto the top of the bit is shown by two downward pointing arrows in FIG. 14 and is labeled with the legend “BW”. With no bit weight, the extreme bottom portion of hardened metal scraper 296 is located a distance below the bottom of the bit that is labeled with the legend “D 296 ” in FIG. 14 . Similarly, with no bit weight, the extreme bottom portion of hardened metal scraper 300 is located a distance below the bottom of the bit that is labeled with the legend “D 300 ” in FIG. 14 . Clearances are designed so that the top end 324 of hardened metal scraper 296 will not bottom-out against hole surface 326 if the distance D 296 goes to zero. Similar comments may be made about hardened metal scraper 300 and the distance D 300 . The point is that relevant clearances in FIG. 14 are designed so that distances D 296 and D 300 can go to zero.

With the bit in the hole and in contact with the formation during drilling, if the bit weight is very large, then the distances D 296 and D 300 do go to zero. Therefore, the distances D 296 and D 300 are controllable from the surface of the earth with the bit weight applied to the top of the rotary drill bit that is in turn applied (or controlled) by the operator of the drilling rig.

Also shown in FIG. 14 are the metal alloy matrix material 328 . Not shown are tungsten carbide rods which may or may not be chosen to be present in another cross-sectional view of the drill bit in FIG. 14 . The bit shank 330 is also so labeled. No junk slots are shown in FIG. 14 for the sake of simplicity.

FIG. 14 shows an invention wherein the depth of the protrusions of the metal scrapers below the bottom of the bit are controlled by the bit weight. So, the operator on the surface of the earth can deliberately choose the dimensions D 296 and D 300 by choosing the bit weight applied to the drill bit. With little weight applied to the bit, then the hardened metal scrapers will be fully extended below the bottom of the bit. In this configuration, the bit will rapidly drill relatively soft geological formations. However, if great weight is applied to the bit, then the hardened metal scrapers will be forced back into the drill bit, and in this confirmation, the bit will rapidly drill relatively hard geological formations. Trial and error can be used to determine what bit weights are optimum for different formation hardnesses, so that anyone with ordinary skill in the art can determine these dimensions with suitable effort.

In such a situation, changes in the bit weight compensate for a change in the hardness of the geological formations. Hardened metal scrapers 296 and 300 are examples of “bit weight actuated formation hardness compensation means within the bit that are responsive to the hardness of the geological formations”, a term that has been previously defined.

Therefore, the preferred embodiment shown in FIG. 14 is an example of a rotary drill bit for drilling a borehole into a geological formation having at least one bit weight actuated formation hardness compensation means within said bit. Put another way, FIG. 14 shows a long lasting rotary drill bit for drilling a hole into variable hardness geological formations that has a mechanism controllable from the surface of the earth to change the mechanical configuration of the bit to minimize the time necessary to drill a borehole. Similarly, any means controllable from the surface of the earth to remotely change the configuration of the bit to optimize drilling is a preferred embodiment.

Because the hardened metal scrapers 296 and 300 point downward in FIG. 14 , i.e., they point in the longitudinal direction, it is evident that FIG. 14 shows a rotary drill bit for drilling a borehole into a geological formation having at least one longitudinal bit weight actuated formation hardness compensation means within said bit. However, it is evident that hardened metal scrapers do not necessarily have to point downward. Instead, hardened metal scrapers 296 and 300 could have instead been drawn in FIG. 14 to have a lateral component. I.e., it is evident that hardened metal scrapers can point in the lateral direction, which is merely a design choice. Therefore, it is evident that this preferred embodiment also describes a rotary drill bit for drilling a borehole into a geological formation having at least one lateral bit weight actuated formation hardness compensation means within said bit.

For the purposes herein, the phrase “automatically adjusts” may be used to mean the phrase “self-actuating”. In addition, the phrase “to optimize drilling” may be used to mean to minimize the time it takes to drill a well. Further, the phrase “to optimize the drilling rate” may be used to mean the concept of increasing the drilling rate in inches per minute to the maximum value possible. In some applications, the phrase “compensation means” may be used to mean the apparatus necessary “to optimize drilling”. In other applications, the phrase “compensation means” may be used to mean the apparatus necessary “to optimize the drilling rate”. Furthermore, the word “compensating” may be used to mean the phrase “to optimize drilling” or the phrase “to optimize the drilling rate” depending upon the connotation.

It is evident that the basic functions of spring 270 in FIG. 13 could be replaced with suitable hydraulic means. Such hydraulic means can include the use of hydraulic fluid, a piston, another spring, etc. Therefore, by reference herein, FIG. 13 also describes a rotary drill bit for drilling a borehole into a geological formation having at least one hydraulic self-actuating formation hardness compensation means within said bit that is responsive to the hardness of the geological formation. By reference herein, FIG. 13 also describes a rotary drill bit for drilling a borehole into a geological formation having at least one self-actuating formation hardness compensation means within said bit operating by any physical principle that is responsive to the hardness of the geological formation.

It is evident that the basic functions of springs 304 and 314 in FIG. 14 could be replaced with suitable hydraulic means. Such hydraulic means can include the use of hydraulic fluid, a piston, another spring, etc. Therefore, by reference herein, FIG. 14 also describes a rotary drill bit for drilling a borehole into a geological formation having at least one hydraulic bit weight actuated formation hardness compensation means within said bit. Further, by reference herein, FIG. 14 also describes a rotary drill bit for drilling a borehole into a geological formation having at least one hydraulic bit weight actuated formation hardness compensation means within said bit, which bit weight activated compensation means operates by any known physical principle.

For additional information on hydraulic compensation means, please refer to the above defined U.S. Disclosure Document No. 445,686 mentioned earlier in the application. It is now useful to review other definitions that have been used herein.

The term “hardened rod” has been used many times herein. The term “hardened rod” shall be defined to include rods fabricated from tungsten carbide materials that are shaped into the form of a “rod” defined above. The term “hardened rod” shall also be defined to include any type of material having a rod shape possessing a hardness exceeding the hardness of the surrounding steel alloy matrix material.

The term “hardened steel scraper” has been used repeatedly herein. A hardened steel scraper as herein used is a long hardened steel object having a number of different shapes as described in the text. As defined above, the term “hardened rod” includes many objects that are described as “hardened steel scrapers”. In general, any “hardened metal scraper” described herein may be replaced with a suitably shaped piece of tungsten carbide material for the purposes of many embodiments of the invention.

The term “matrix material” has been used herein. The term “matrix” material shall be defined to include any material that is made to surround the hardened rods that comprise the monolithic drill bits described herein. However, the term “matrix material” shall be defined to specifically include tungsten carbide binder alloys, any known steel alloy material, crushed or powdered or sintered tungsten carbide materials or other suitable materials, any type very tough ceramic material that can bind to any hardened rod, any type of very tough ceramic material that can be glued to any hardened rod, or any other type of suitable binder material of any type produced by any process that can mechanically hold and surround the hardened rods and otherwise handle the stresses typical of materials used in drill bits. The term “matrix material” shall be defined to be any material whatsoever that surrounds the hardened rods that comprise the monolithic drill bits described herein. For the purposes herein, the word “steel” and “steel alloy” can be used interchangeably and mean any type of steel made suitable for the purpose. While the term “steel alloy matrix material” has often been explicitly used, that term may be replaced anywhere in the text with simply “matrix material” to rigorously define the preferred embodiments of the invention herein.

Many of the preferred embodiments described herein possess at least one hardened rod that is surrounded by matrix material that comprises the monolithic drill bit. If drill bits were instead fabricated having relatively short pieces of tungsten carbide materials cast into a steel matrix, then these relatively short pieces of tungsten carbide inserts could fall out of the bit into well as the drill bit wears thereby permanently damaging the drill bit. It would not matter if the relatively short pieces of tungsten carbide material were cylindrical shaped, rectangular shaped, or irregular in shape. Here, short can be operationally defined as follows. For any “short piece”, determine the longest dimension of the “short piece” along its “length”. Then determine “the average dimension of the short piece perpendicular to its length”. Therefore, the definition of “short piece” herein shall mean that the short piece shall have a length that is less than N times the average dimension of the short piece perpendicular its length where N is the aspect ratio defined above. For example, the aspect ratio N can be chosen to be equal to the number 3.0. In this case, the short piece would have a length less than 3 times the average dimension perpendicular to its length. The advantage of the preferred embodiments disclosed herein is that as they wear in the well during drilling operations, the relatively long pieces of tungsten carbide rods do not tend to fall out of the bits into the well. Instead, the hardened rods tend to be supported by the matrix material until they are ground off during the wear of the bit during drilling operations.

It is necessary to further state that the preferred embodiments of the invention herein can undergo substantial longitudinal wear before the bit becomes unusable. In many cases, many of the preferred embodiments herein provide a bit that can wear down to less ½ its original overall length when new—and yet remain functional. The various lateral compensation means provide a bit that can undergo substantial lateral wear before the bit becomes unusable.

The terms “longitudinal compensation means” and “lateral compensation means” have been described herein. As used herein, and unless otherwise explicitly stated, in many embodiments these compensation means are passive, or “self-actuating”, in that no external commands or controls are required from the surface to cause the desired compensation processes to occur. Instead, in such cases, these processes naturally occur within the bit as the rotary bit undergoes wear during drilling operations. In other words, these particular compensation processes are “triggered by bit wear”. Many other designs and physical principles of operation may be used to design different specific types of longitudinal compensation means to compensate for longitudinal bit wear and lateral compensation means to compensate for lateral bit wear. For example, certain pistons contained in hydraulic chambers may be used to implement changes in mud flow channels to implement longitudinal compensation means and lateral compensation means that are triggered by bit wear. Other physical processes can be used to alter mud flow to implement longitudinal compensation means and lateral compensation means that are triggered by bit wear. Put simply, any physical process that is triggered by bit wear that results in compensation for longitudinal bit wear and compensation for lateral bit wear is an embodiment of the invention herein. Many of the preferred embodiments herein merely suggest certain types of longitudinal compensation means and lateral compensation means that are triggered by bit wear and the invention should not be limited to specific means described herein.

While the above description contains many specificities, these should not be construed as limitations on the scope of the invention, but rather as exemplification of preferred embodiments thereto. As have been briefly described, there are many possible variations. Accordingly, the scope of the invention should be determined not only by the embodiments illustrated, but by the appended claims and their legal equivalents.

Claims

1. A method of drilling a relatively constant diameter borehole into a geological formation that has a variable hardness using a rotary drill bit attached to a rotary drill string including at least the following steps:(a) providing a rotary drill bit, whereby said rotary drill bit has a first self-actuating longitudinal compensation means within said bit that is actuated by any longitudinal bit wear, and whereby said rotary drill bit has a second self-actuating longitudinal compensation means within said bit that is responsive to the hardness of the geological formation, and whereby said rotary drill bit has self-actuating lateral compensation means within said bit that is actuated by any lateral bit wear, (b) attaching said bit to the rotary drill string on the surface of the earth; (c) drilling the borehole with said rotary drill bit attached to the rotary drill string, whereby the drilling rate at a specific depth from the surface of the earth is dependent upon the hardness of the geological formation at said specific depth; (d) compensating for any longitudinal bit wear of the drill bit by using said first self-actuating longitudinal compensation means; (e) compensating for any lateral bit wear of the drill bit by using said self-actuating lateral compensation means; and (f) compensating for the change in hardness of the geological formation using said second self-actuating longitudinal compensation means at a minimum of one particular depth from the surface of the earth to increase the drilling rate during the drilling of the borehole.