US2966949A - Full hole permanent drill bit - Google Patents

Description

Jan. 3, 1961 Filed July 16, 1958 G. B. WEPSALA, JR

FULL HOLE PERMANENT DRILL BIT 4 Sheets-Sheet 1 FlG.-5

George B. Wepsulu,Jr. inventor ByuMQ7 M Attorney Jan. 3, 1961 (5.13. WEPSALA, JR 2,966,949

FULL nous PERMANENT DRILL BIT Filed July 16, 1958 4 Sheets-Sheet 2 I IIIIII George B. Wepsula, Jr. Inventor v B11019. 7 Attorney Jan. 3, 1961 G. B. wEPsALA, JR 2,966,949

FULL HOLE PERMANENT DRILL BIT Filed July 16, 1958 4 Sheets-Sheet I5 FIG.'3

George B. Wepsalo, Jr. Inventor Attorney Jan. 3, 1961 s. B. WEPSALA, JR 1 2,966,949

FULL HOLE PERMANENT DRILL BIT Filed July 16. 1958 4 Sheets-Sheet 4 llj l I L25 4 IIS reeeeeet I e e e e e m 1 igigigifigigi 5 I3 ll IO FIG. 6

George B. Wepsol'a, Jr. 7 Inventor FULL HOLE PERMANENT DRILL BIT George B. Wepsala, Jr., Caracas, Venezuela, assignor, by mesne assignments, to Jersey Production Research Company Filed July 16, 1958, Ser. No. 748,868

10 Claims. (Cl. 175329) This invention relates to drill bits. It relates particularly to drill bits which effect cutting by a plurality of hard particles dispersed in a matrix of relatively softer material. It relates more particularly to such bits for drilling holes in the earths substrata, and it relates more particularly still to such bits for drilling full or bore holes in the earths substrata as contrasted to annular or core holes.

In present day practice the drilling of a large proportion of bore holes in the earth for the production of crude petroleum from underlying oil-bearing strata is accomplished by what is known as rotary drilling. In this method a drill pipe string provided with a bit at its lower end is run into the full length of the bore hole. The drill bit is rotated to accomplish drilling by a combination of scraping, grinding, and percussive forces which break up rocky strata ahead of the drill. A drilling fluid is circulated down through the drill pipe, around and across the cutting elements of the drill bit, and back through the annulus between the drill pipe and the wall of the hole to remove heat and and flush debris generated in drilling, and to seal the hole.

It has been observed that certain types of hard sand and chert are of such a nature that ordinary rock bits tend to wear out in a relatively short time upon encountering them. It has been found also that such formations can be drilled much more effectively if the cutting elements of the drill bit comprise particles of very hard materials such as industrial diamonds. These hard particles are retained in a drill head or body which may be attached to a shank member suitable for coupling to the lower end of a drill pipe string, and the bit so formed is known as a diamond drill bit.

Diamond drill bits have been made for drilling holes of two kinds. One is an annular or core hole. The other is a full or bore hole. In either case the forward cutting face of the drill bit usually comprises a single layer of hard particles or diamonds. Diamonds may appear also on the lateral surfaces of a bit as reaming cutters. Circulation of drilling fluid from the inside to the outside of the drill pipe for purposes stated already may be provided by grooves across the forward and lateral faces between clusters of diamonds.

Wear of a diamond drill bit, while not rapid, will take place. The cutting particles will be eroded and possibly cracked away. The material of the drill head which comprises the retaining means for the diamonds will be torn away on its bottom surface to reduce the security of its grip on the diamonds with the result that some of them may be pulled out altogether. The life of a diamond drill bit of conventional design will be terminated when the stones in its forward face have been worn to the point that they are no longer of a satisfactory size and shape for the drilling speeds and pressures required to penetrate the strata in question, or else so many have been torn away that the full area of the hole being drilled is not swept by cutting particles.

It is apparent that the useful life of a diamond drill bit could be increased greatly if fresh diamonds could become exposed to continue the drilling action as the initial cutters are worn or cracked away or become dislodged from the drill head. The process of exposing United States Patent fresh cutting particles as the result of wear and withdrawal of those ahead of them might be continued indefitntely providmg that adequate circulation of drilling fluid across the cutting face were assured at all times.

'lhese problems have been solved to some extent in the case of d.amond drill bits for core holes. A part.cular construction in this connection known as an impregnated bit is illustrated and described by J. D. Cumming: Diamond Drill Handbook, Toronto, 1956, pp. 123-4. This bit comprises a plurality of fragmented bortz (generally any diamond structure other than carbon or ballas and not suited for gems) of selected screen size, and small whole diamonds mixed with a metal powder as a matrix which is pressed and sintered into an annular shape of some length. The matrix material is often a tungsten carbide alloy bonded with cobalt and other metals with a flow point lower thantungsten caib.de (W C). The bit so formed is characterized by a number of relatively deep radial grooves for circulation of drilling fluid from the inside to the outside of the drill pipe string.

The Lmitations of this construction for a coring bit, or, as it might be extended in modified form, for a full hole or boring bit are evident and have to do principally w.th the drilling fluid passages in the bit. While the matrix and diamond particle structure might be made indefinltely long, there will be a definite and not very great upper limit on the depth of the aforementioned radial grooves because of considerations of strength of the prong-like segments of the drill bit defining the walls of the groove. Furthermore, even if fairly deep grooves could be provided and strength requirements satisfied at the same time, disadvantages might well be incurred in the continuously decreasing size of groove cross section for fluid passage as the drill bit wore. This would at least impose a new variable in the regulation of drilling fluid supply pressure.

It is a general object of the present invention to provide a full hole drill bit capable of such extended service that it may be considered an indefinitely wearing or permanent drill bit. j

Within the aforestated general object it is a particular object of the present invention to provide means for conveying drilling fluid across the working face of this bit whereby the flow of fluid is continuous and regulated to fluctuate only within predetermined limits within the consumable working length of the bit.

Within the aforestated general object it is a particular object of the present invention to provide for dynamic balance of the drill bit without any external adjustment as the bit is worn through its consumable working length.

Within the aforestated general object it is a particular object of the present invention to provide conveniently renewable protection against erosion for those regions of the bit through which drilling fluid may be expected These and other objects may be perceived and a fuller 1 understanding of the present invention obtained by referring to the following description and claims taken in conjunction with the following drawings in which;

Hg. 1 represents a bottom plan view of the full hole drill bit of this invention showing the working face thereof and particularly illustrating a representative array of hard particles for advance cutting and also reaming; internal trunk, bottom branch, and external flute passages wherethrough drilling fluid is supplied to, circulated across, and conveyed away from the working face, and

erosion protective liners for these passages.

Fig. 2 represents an elevation view in section along line 2--2 of Fig. 1 showing the full hole drill bit of this invention attached to the lower end of a drill pipe string in place at the bottom of a bore hole extending to the earths surface, and particularly illustrating a representa--' tive array of hard particles dispersed throughout the body of the drill, the path of circulation of drilling fluid through and around the drill bit, and means of attachment of renewable rigid liners for protecting the internal trunk and external flute passages of the bit against erosion by drilling fluid.

Fig. 3 represents a limited view on the same plane as Fig. 2 particularly illustrating means of attachment of renewable non-rigid liners for protecting the internal trunk and external flute passages of the full hole drill bit of this invention against erosion by drilling fluid.

Fig. 4 represents a developed elevation view of limited height along line 4-4 of Fig. 1 showing one of the flute regions and small amounts of adjacent land regions of the full hole drill bit of this invention, and particularly illustrating a representative array of the external ends of branch passages for conveying drilling fluid from the internal trunk passage to external flute passages.

Fig. 5 represents a limited view on the same plane as Fig. 2 particularly illustrating means for plugging the external end of a branch passage for conveying drilling fluid at a level above that of the Working face of the full hole drill bit of this invention.

Fig. 6 represents an elevation view of the bit shown in Figure 1 taken along the line 66.

trunk passage 12 to the edges of the drill body is a pattern of open-bottomed, open-ended branch fluid passages 13. Liners 14, 15, and 16 are provided for trunk passage 12, branch passages 13, and the flute regions of the drill body respectively. Liners 14 and 16 are perforated corresponding to the inside and outside end openings of branch fluid passages 13. Liners 15 are fully contained in the branch fluid passages. They terminate against liner 14 at one end, and slightly short of liners 16 at the other. This shortness, representative of a standard liner form, is to accommodate branch passage plugs, and will be more fully understood after reading the desc'ription of Fig. 5.

The function of liners 14 and 16 is to prevent trunk passage 12 and the flute regions from being cut out by erosive drilling fluid with consequent premature loosening of diamonds and end plugs for the branch fluid passages. Thes plugs, not shown in Fig. 1, will be pointed out in Figs. 2 and 4, and particularly discussed in connection with Fig. 5 and the operation of the drill bit ofthis invention. The problem of damage to matrix material by drilling fluid is cited by Cumming, p. 151. The function of liners 15 in branch passages 13 is likewise to prevent cutting out of these passages by drilling fluid, but this function is not as important as those of liners 14 and 16 since branch passages 13 will have drilling fluid flowing through them fairly briefly because they are intended to be destroyed in the course of normal use of the drill bit. Accordingly, liners 15 may very likely be omitted in many cases without harm, and indeed will have value only if abrasive fluid flowing through unlined passages 13 in normal drill operation would so erode surrounding matrix material that nearby diamonds would be noticeably loosened, or, perhaps, the bottom of an adjacent branch passage higher up in the drill body be prematurely opened.

Drill body may be made of a number of materials, the selection being influenced by the nature of the included cutting particles, the method chosen to fabricate the matrix and particle structure, and the service to which the finished drill bit is to be applied. These problems are reviewed by Cumming, pp. l22- 3 and 127-30. A general requirement is that the matrix material wear at least as fast as the particles which it retains so that new sharp particle edges will be exposed as the initial cutting elements are consumed. The matrix must, of course, be sufficiently tough and abrasion resistant that its hold on the particles will not be lost before the latter have been worn extensively in useful service. Suitable matrix materials include copper-tin bronzes, aluminum bronze, manganese bronze, beryllium-copper alloys, tungsten-cobalt alloys, cobalt-chromium-tungsten alloys, copper-nickel alloys, and the like. Such matrix materials and techniques for casting or sintering them in fabricating diamond bits are.described in the literature and will be familiar to those skilled in the art.

The cutting particles 11 will comprise industrial diamonds in most applications. Drill bits of the nature in question may, however, have cutting and reaming particles of other materials such as tungsten carbide cemented into chips in a matrix of cobalt. In this connection see Cumming, pp. -6. Throughout this description cutting particles 11 will be referred to frequently as diamonds, but it should be understood that so long as matrix and cutting particle materials are properly matched in respect of requirements noted already the question of whether the cutting particles used are actually diamonds or any particular grade thereof does not afiect the spirit and scope of this invention.

The material of liners 14 and 16 for trunk passage 12 and the flute regions will desirably be the superior of the material of drill body 11) in respect of resistance to erosion by drilling fluids and such fluids entraining drilling debris and hence liners of alloy steel, tungsten car bide and similar materials will preferably be used. The use of rubber as a liner for diamond drill bit fluid pas sages is suggested by Cumming, p. 130. It is, however, contemplated that liners 14 and 16 will be so afiixed tothe drill body or other drill bit structure to be easily replaceable. Accordingly, whatever the fluid erosion resistance of the materials of liners 14 and 16 may be com pared with that of drill body 10, the purpose of these liners will be served if they be inspected for erosion from time to time and replaced as necessary. Note that liners 16 are dovetailed in the drill body. This arrangement serves to locate the liners, and to restrain them from be;- ing thrown off the drill body by centrifugal force.

Liners 14 and 16 will, of course, be shortened alongwith the drill body by earth strata being drilled in the course of normal usage of the drill bit of this invention. It is desirable that whatever the fluid erosion resisting qualities of the liner materials may be, their abrasion resisting qualities be no better than those of materials of drill body 10 with which they are used. Should they be better, the drill body will be worn preferentially to the liners, and an excessive vertical thrust from drilling pressures be exerted on the latter elements. Such excess pressure will at least tend to buckle and shift the liners and so upset register of the perforations therein with the inner and outer ends of branch passages 13.

The material of branch passage liners 15 should be substantially the superior of the material of drill body it) in respect of fluid erosion resistance if these liners be used at all. While it would be possible to replace a liner 15 it is not contemplated that this will be done, and if the material of liners 15 be no more erosion resistant than that of drill body 10 the space given over to accommodating these liners had as well be occupied by matrix material, and construction of the drill bit simplified accordingly. Liners of alloy steel, tungsten carbide and the like will generally be suitable.

Liners 15, if used, will be open-bottomed, open-ended members wherever employed. All top and lateral wall surfaces 015 these liners contiguous With material of drill body should be securely cemented or otherwise bonded thereto across their wholearea. This is not only to prevent endwise shifting of liners by centrifugal force, but also to make sure that the entire material of any liner 15 will be consumed by either erosion or abrasion in the course of normal drill operation; that is, that no liner 15 nor any substantial piece thereof will be crumpled or torn bodily away from the walls of its passage 13 by shearing or bending action of earth strata in the course of drilling and then act to block flow of fluid through this passage or a flute region, or get in way of any diamonds 11 and break them or otherwise impede their cutting action. The firmness with which all liners 15 are to be aflixed to the surfaces of their accommodating passages 13 is a major reason for avoiding consideration of replacement of these liners once installed.

Certain matters of form of the drill bit shown in Fig. 1 are not to be considered critical for purposes of this invention. For example, the drill body may have either more or less than three flutes or exterior longitudinal passageways. Likewise, neither is the illustrated array of diamonds 11 controlling. Some information regarding distribution of diamonds in drill bits is given by Cumming, pp. 135-7. In general it may be said that the diamonds should be so arrayed that the entire bottom surface of the hole being drilled will be swept by at least one cutting particle, except that in full hole bits there is usually no diamond in the absolute center of the cutting face. There should be enough space between cutting particles to allow passage of drilling debris, and, correspondingly, suflicient matrix material should be allowed between the particles to insure their firm retention therein. For purposes of this invention the areas between diamonds 11 on the bottom surface of the drill bit shown in Fig. 1 should be thought of as regions where other cutting particles will appear as the bit is worn in service. This effect will be understood more clearly after reading the description of Fig. 2 and of the operation of the drill bit of this invention. Any desired arrangement of diamonds can readily be attained if a sintering technique is used to fabrcate the bit. The diamonds can be spaced in successive layers of powdered metal to form the desired pattern and the entire body section can then be sintered. A molten bonding metal such as copper or a copper-nickel alloy can also be cast into voids between particles of matrix metal and diamonds arranged in a suitable pattern. Both techniques are well known in the diamond bit industry.

Additionally, neither is the particular pattern of branch fluid passages 13 appearing in Fig. 1 an invariable. The function of these passages is to convey drilling fluid from the trunk passage 12 to the outside of the bit for sure maintenance of fluid circulation in keeping with the cooling and flushing purposes stated earlier. Some fluid will, of course, get across the face of the bit by a multitude of paths between the diamonds. On the subject of fluid passages or waterways see Cumming, pp. 150-151. A more or less uniformly distributed flow of fluid across the drill face is considered desirable, and branch passages 13 at any particular level in drill body 10 may be of any cross section and configuration needed to obtain such fluid distribution, consistent always with diamond arrangement and strength requirements of the drill bit and the principles of this invention. These principles, as they affect arrangement of branch passages 13 with respect to trunk passage 12 and to each other, will be understood more clearly after reading the description of Figs. 2 and 4 and of the operation of the drill bit of this invention.

Finally, the Y-cross section of trunk passage 12 asit appears in Fig. 1 is not by itself a controlling feature of this invention. This configuration is, however, to' be considered as possessing particular properties to be stated following a discussion of certain problems which will arise in designing an actual drill bit intended to embody the present invention.

Since the drill bit of this invention is intended for the boring of full holes, no earth surface at the bottom of, a hole being bored may be continuously in line with any part of an opening extending through the drill bit, otherwise a core will be generated as drilling progresses. This means that any internal longitudinal passage or passages such as trunk passage 12 must avoid the axis of rotation of the bit. Such avoidance, however, can lead to problems of rotational unbalance. Considering that diamond drills turn at speeds as high as 4000 r.p.m. (Cumming, p. 146), a dynamic side thrust of considerable magnitude may be generated on a drill bit if the center 'of gravity of the bit be only slightly offset from its axis of rotation, especially in the case of a bit of extended working length and correspondingly great mass as contemplated by this invention. Among its harmful effects, such side thrust will cause undue wear on a drill bit, a decreased rate of advance of the bit, and irregular enlargement of the hole being bored.

If a full hole diamond drill bit he provided with a plurality of internal longitudinal or trunk passages for flow of drilling fluid these may be of uniform length and cross section, and be arranged symmetrically around the center of the bit with any accompanying branch passage patterns to avoid rotational unbalance. In such an arrangement, however, there is the danger that the branches which interconnect the trunk passages to sweep the region lying between the endings of the latter passages will ,be stagnant due to pressure balance, and serve neither to cool nor flush. For this reason, which relates back, to 'the aforementioned desirably uniform fiow of fluid across the drill face, a single trunk passage from which all branch passages radiate without any possibility of dead flow regions is considered an optimum arrangement. Y

Obviously, considering flow and balance conditions alone, it-would be most convenient to provide a simple round trunk passage located on the drill axis. This would, however, cause the drill to be of the coring rather than of the full hole variety. If the round trunk were made fully eccentric of the axis the drill could cut a full hole, but balance conditions would not be satisfied unless special adjustment of the branch passages were made in compensation. Of course, if a drill bit does nothave balanced internal passages net rotational side thrust may still be avoided by adding or removing material in noncritical areas. However, since it is contemplated that the drill bit of this invention will change considerably in length and weight during its working life, any initial compensation for unbalanced fluid passages might not be satisfactory on a permanent basis. While such devices as balance screws could be adjusted from time to time, the most desirable condition will be to have the internal passages balanced with respect to themselves not only initially but also for all conditions of wear of the bit.

Now consider trunk passage 12 of Fig. l whch is to be assumed as extending through the drill body parallel with the axis thereof. The surfaces of passage 12 from which branch passages 13 depart are to be assumed of equal radius centered on the axis of the bit, and of substantially equal circumferential length and angular spacing. Accordingly all branch passages 13, whether of constant or varying cross section, may be extended radially from the bit axis and be of equal length, and this will allow the pattern of branch passages at any level and throughout the working length of the drill body 10 to be balanced by itself. Without violating the foregoing limitations, it is evident that the cross section of trunk passage 12 may be configured to satisfy the two requirements of avoidance of the drill bit axis and balanced removal of material.

A Y-section is not the only one which may be configured to meet these requirements for branch passages running to three fluted regions or to more or less than thre e.-. It is shown for purposes ofexample only. The possibility exists also, as previously implied, of having a: branch passage pattern and a trunk passage of equal and opposite unbalance for all levels of wear of a drill bit to provide a net side thrust of zero. Unbalanced passage patterns, and indeed balanced ones if there be substantial variation in length of branch passage runs from the trunk passage, may, however, cause undesirable unevenness in distribution of drilling fluid across the working face of a. bit. In any case, whatever passage arrangement be used, achievement of dynamic balance for all degrees of wear should be sought in any drill bit constructed as an embodiment of this invention, although absence of such balance will not render ineflective any other inventive features here disclosed.

Refer now to Fig. 2. In this 17 represents a substrata of the earth through which a bore hole is being drilled. The drill bit assembly itself is attached to the lowest drill pipe string element 18 by a screwed connection. This assembly comprises the matrix and particle structure of drill body 10 and diamonds 11 joined to a threaded neck or, shank member 1 9 This joint may be made by brazing or any other appropriate means.

Thediamonds 11' are shown dispersed throughout and embedded in the. bottom, and side surfaces of drill body 10. For convenience of illustration and explanation the diamonds are shown having more or less uniform size, shape, orientation, and distribution. In an actual drill made as an embodiment of this invention probably none of these. conditions will obtain precisely, nor will considerable departure from these conditions render this invention ineffective. A reference concerning diamond distribution in actual bits has been given already. On the other features cited see Cumming, pp. 1202 (sze), and pp. 158-63 (shape and orientation). What should obtain inran actual bit to render this invention most effective is that the cutting particles overlap each other vertically as shown in Fig. 2 and horizontally as shown previously in Fig. 1 throughout the intended wearing length of drill body lllto present an array capable of sweeping a full hole at any level in this length.

The offset attitude of trunk fluid passage 12 and its liner 14 is apparent. Branch fluid passages 13 fitted with liners 15 appear at a number of levels in the drill body which is shown in suflicient length to allow a recurrence of branch passage patterns. A necessa-y condition for purposes'of this invention is that at least one pattern of branch passages 13 be present at any and every level of the wearing length of drill body 10. To satisfy this condition there must be vertical overlapping of branch passage patterns. Accordingly, succeedIng. patterns vary. in their angular relation to trunk passage 12. The method of satisfying the cited condition will be understood more clearly after reading the description of Fig. 4.

The external ends of all branch passages 13 except for those at the bottom working face of the drill bit are closed with plugs 20. The method and means of retention and release of plugs 20 will be more clearly understood after reading the description of Fig. 5 and of the operation of the drill bit of this invention. It may be said here, however, that no p'ug will be released until the working face of the bit has been worn up to the bottom edge of the. plug in question. This illustrates the reason Why there probably will not be as great need toprovide liners for branch passages 13 as for trunk passage 12 and the flute regions; namely, that there will be. no flow of fluid through any branch until its bottom edge and the level of the working face coincide.

In. Fig. 2 the drill bit is shown with a flat, horizontal working face. Such a face contour is not restrictive of this invention. Full hole or noncoring damond drill bits have been built with face contours ranging from semi-spherical convex to 120 or less included angle conn d (Q1 l ll l P1}. 1 3 ,4-6). In any actualfull hole drill magnitude likely to be encountered with only slight tie-- flection.

Trunk passage12 of drill body 10 is continued in un-' modified form through the full length of neck member 19 except for a region at the upper end of the neck which is bored to accommodate an externally circular flange integral with liner 14, and supporting and retaining elements therefor. Between the flange of liner 14 and the internal shoulder of drill neck 19 is at least one rigid spacer 21 which is circular externally, but perforated in Y-section to fit closely to the main body of liner lfl.

At least one spacer 21 may be of laminated constructionv to allow it to be peeled through a range of thicknesses. This will provide means of fine up and down adjustment of any liner 14.. with respect to the drill neck and drill body assembly of any bit whereby accurate vertical register of the perforations in the liner with the. ends of branch passages 13 may be obtained.

Next abovethe liner flange is a gasket ring 22 made of slightly compressible material such as hard rubber. Resting on gasket 22 is at least one rigid washer 23. In

its uncompressed state the stack comprising spacer 21,.

the flange of liner 14., gasket 22, and washer 23 should extend slightly above the top of neck member 12. This extension will be the amount of compression to betaken in. gasket 22. At least one washer 23 may be of laminated construction to allow it to be peeled through a range of thicknesses to obtain the desired extension with accuracy.

When the threaded connection of drill neck 19. and pipe string element 18. is made up, the drill neck will be run in to full depth to bear on the internal shoulder of the pipe string. Gasket 21 will be compressed, and the flange of liner 14 and its supporting spacer 21 will be held down hard on the internal shoulder of neck member 19 to maintain the afore-mentioned accurate vertical register of liner perforations and branch passage internal endings in the face of drilling loads tending to shift liner 14. upward with respect to drill body 10. Maintenance of angular register will be no problem because the cross section configuration of passage 12 will inhibit any relative rotation of a liner closely fitted therein.

Not only trunk passage liner 14 but aiso each flute region liner 16 is flanged at its upper end. The flange of each liner 16 will be in the form of a ring segment and will be characterized by at least one axial hole to pass a screw 24 which is accommodated further by a tapped hole in neck member 19. Note that screw 24 appears as a shoulder screw which is not fully seated. The utility of this shouldered design will appear presently. Between the flange and the outer shoulder of drill neck 19 is at least one plate 25 of form similar to the flange and with matching holes. At least one plate 25 may be of laminated construction to allow it to be peeled through a range of thicknesses. This will provide means of fine up and down adjustment of any liner 16 with respect to the drill neck and drill body assembly of any bit whereby accurate register of liner perforations with the external endings of branch passages 13 may be obtained.

A lock Washer 26 is interposed between the screw head and the linear flange. The threads of screw 24 are: of course. dressed with an appropriate anti-corrosion compound to permit easy removal of the screw from the neck member after the bit has; been immersed in drilling fluid. ad. i e screw 24 sdr llgd di m t aly to pass rubber.

erosion and corrosion by drilling fluid moving with considerable velocity and through which are dispersed rock cuttings and other hard, finely divided solids.

Circumferential or lateral alignment of flute region liners 16 is provided primarily by the dovetail arrangement illustrated in Fig. 1 which extends through neck member 19, and determines the angular register of liner perforations with the outer ends of branch fluid passages 13. The need of accurate register both vertically and angularly in respect of the method and means of retention and release of branch passage plugs 20 will be more v fully appreciated after reading the description ofFigs. 4 and 5 and of the operation of the drill bit of this invention.

An elevation view depicting the exterior of the bit shown in Figures 1 and 2 appears in Figure 6 of the.

drawing. This view is taken along the line 6-6 of Figure 1 and shows the arrangement of the outer surface of the bit.

Refer now to Fig. 3. It is contemplated that liners 14 and 16 may be made not only of substantially rigid materials, but also of relatively flexible materials such as Flexible liners may be made to precisely the same dimensions as rigid liners and used interchangeably in any drill bit assembly with substitutions for only a few small parts. Compressible gasket 22 is replaced by a rigid spacer 28. This spacer is circular externally, but is perforated in Y-section to correspond with the passage through liner 14. By means of spacer 28 a more or less uniform compression is taken across the flange of this liner. Lock washer 26 is replaced by at least one plate 25, and screw 24 is run in to seat on the external shoulder of drill neck 19, taking compression in the flange of liner 16.

Speaking generally in respect of Figs. 1, 2, and 3, it

is desirable that liners 14 and 16 of both the rigid and flexible species have close sliding fits in the trunk passage '12 and dovetailed flute regions which retain them. The

mechanical joints which must be broken and made up for removal of eroded liners and installation of new ones are obvious. It is conceivable that when flexible liners are used an epoxy resin or similar cement will need to be applied to their surfaces which are contiguous to surfaces of the drill neck and drill body to prevent these liners from being collapsed or pulled out of the dovetails by either shearing action of the earth strata being drilled, centrifugal force, or unbalanced hydraulic pressure due to fluid leakage between liner and body surfaces. When a flexible liner which has been cemented is to be replaced, care should be exercised in stripping out the remnants. A rigid liner pushed through the trunk passage and flutes may be used in clearing such remnants.

, Refer now to Fig. 4 which shows the endings of branch fluid passages 13 in one of the flute surfaces of the drill bit of this invention. Closure plugs 20 are in place in all branch passages except for those immediately adjacent the initial bottom surface of the drill bit in which liners 15 are shown. Plugs 20 are of substantially the same width as these liners, and are somewhat less wide than the horizontal dimension of the perforations in flute liner 16. Note the reaming diamonds 11 in the adjacent land surfaces.

The vertical overlap of branch passages 13 from top to bottom of the drill body is apparent. A drill body of suflicient length to provide a recurrence of passage patterns is portrayed. As shown, the branch passages have rectangular cross sections. While such cross section is not critical for purposes of this invention, it is at least desirable that the branch passages be flat bottomed. With this configuration they will present wide areas into which drilling debris may be swept as soon as the bit is worn up to the bottom level of any particular pattern of branch passages.

Refer now to Fig. 5 in which details of closure means for a typical branch fluid passage 13 are shown. This passage may be any one above those adjacent the initial bottom of the drill bit; that is, those appearing in Fig. l.

Liner 15 stops slightly short of the external end of the branch passage, and beyond the end of this liner the bottom surface of the passage is stepped down slightly while the top surface is angled and stepped upward. Closure plug 20 is seated on the step in drill body 10 and on its upper surface conforms substantially with the contour of the branch passage. Plug 20 may be of material the same as or similar to that of drill body 10, and attachment of the plug to the drill body will be made along the bottom surface of the plug by an appropriate cement, solder, braze metal, or other joining material 29.

Flute region liner 16 with a perforation matching the branch passage is shown fitted closely to the drill body.

.The lower edge of the liner perforation should be about even with but no higher than the mainbottom of passage 13. In this way it can provide some protection against erosion for joining material 29, and at the same time not delay release of the plug. The upper edge of the aperture must overlap the upper edge of the plug so that liner 16 can act as a restraining means on the plug. The overlap must be enough, acting in combination with joining material 29, to be sure of holding the plug against the pressure diiferential existing between static fluid in passage 13 and fluid in flow in the flute region outside, but not so much to impede blowing out of the plug upon rupture of material 29. By reasonably precise fitting of parts shown in Fig. 5 an adequately tight seal of the passage ending maybe achieved.

The dimensions of parts shown in Fig. 5 should be such in relation to those of the flute passages of the drill body that once plug 20 has been released it will have no difiiculty in being flown fully clear of branch passage 13 and liner 16 into the flute passage with which the branch connects.

Operation of the drill bit of this invention will now be recapitulated. Drilling fluid flows downwardly through the drill pipe string as indicated by arrows in Fig. 2 to pass through the drill neck 19 and enter the trunk fluid passage 12 of drill body 10. From the trunk passage the drilling fluid radiates out into the branch passages 13. In all of these except those exposed at the bottom cutting face of the bit it will be blocked from traveling any further by the plugs 20 or by a plastic or soft metal plugging of 13. In the bottom passages 13, however, the fluid path will be clear. The drilling fluid will blow outwardly through the latter passages and across the cutting face of the drill bit generally, and then upwardly through the lateral diamonds and the flutes of the drill and into the annular space between the pipe string and the bore wall. Arrows indicate this upward flow in Fig. 2.

In the meanwhile the pipe string and the drill bit will be rotating with the diamonds 11 on the working drill face creating rock cuttings or other drilling debris ahead of the drill. These debris will be swept toward the wall of the hole. In part this will be done by drilling fluid flowing between the diamonds. More important, however, as the debris are overridden by and caught in the active branch passages 13 they will be ejected by the outwardly flowing fluid in these passages and by centrifiugal force. The debris will be delivered for the most part into the fluted regions of the drill and from there carried upward for eventual surface discharge by fluid rising as indicated. Once a depth of hole has been established, the diamonds extending from the lands of the same.

'11 drill. body will take a reaming cut on the bore. wall, and the debris from this cut will be discharged by the drilling fluid along with the debris from the main driLling cut.

With the progress of drilling. the diamonds 11 at the bottom of the drill bit as first used, the matrix material comprising drill body immediately surrounding them, and the leading edges of trunk and flute liners 1 4 and 16 will be worn away. Wearing of the matrix, however, will expose additional diamonds dispersed therein and partially overlapping those first used. Thus as the first used diamonds are consumed or torn away from the drill body due to weakening of the matrix bond on them, the particles next above them will come into action and continue the main drilling cut. A corresponding effect will be realized with the lateral diamonds for bore reaming. All of these are partially exposed from the start, but at rst the very lowest row of them may be expected to provide substantially all the reaming action. As this lowest row is consumed or torn out, the lateral cutters next higher will assume the major reaming duty. It may be seen, therefore, that as the drill bit wears in service new cutting particles for both main boring and reaming will come into action continuously. V

The same thing will be true of the patterns of branch fluid passages 13. The open-bottomed and open-ended branch passages 13 at the main drilling face of the bit as first used will be destroyed as matrix material which defines them is worn away. However, before the first pattern of branch passages is eliminated, the drill will have to wear past the joining materials 29 of the closure plugs Ztlof the next higher pattern. These joints will be ruptured; the plugs they retain will be blown out by fluid pressure, and at about the same time the bottoms of passages 13 which this next pattern comprises will be torn out by abrasion. Thus a whole new pattern of openbottomed and open-ended branch fluid passages will come into action maintaining a strong fluid circulation for cooling and flushing. Before the second pattern of branch passages 13 is itself eliminated due to matrix abrasion, the plugs and passage bottoms of the third pattern will be removed and so on.

Study of Fig. 4 will show that the cross section area of active branch passages 13 will not be a constant for all levels of wear of the drill bit in the working range but will vary between definite limits, being reduced gradualiy to a minimum value with wear of the bit, and then increased suddenly to a maximum value as a new passage pattern is activated. This variation will not affect the operability of the drill bit of this invention so long as the minimum cross section to which the active branch passages. can be reduced is kept high enough to accommodate suflicient fluid for flushing and cooling at the available supply pressure. The variation in total eflective flow area across the bit will not in fact be quite as pronounced as the variation in area of active branch passages 13 because of routes through which fluid can flow between the diamonds outside the passages 13 where matrix material has been preferentially abraded.

From this review of operating events it is apparent that as drilling pro resses and the drill bit is worn there will be no diminution of drilling efliciency nor need to provide new drill bits at predetermined intervals because of loss of either effective cutting members from or flow of drilling fluid across the bit surfaces in service. Indeed the working life of a drill bit made according to this invention so far as the number of feet of any particular class of earth substrata which it can penetrate is concerned is a function only of the length of bit which may be conveniently fabricated and thereafter handled in field service. Liners 1 and 16 may, of course, have to be changed from time to time before the drill bit is used up. Frequency of liner change will be determined by such factors as liner thickness, liner material, and nature of the drilling fluid.

Although this invention has been described with a certain degree of particularity, it is to be understood that the present disclosure has been made only by way of example, and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of this invention as hereinafter claimed.

What is claimed is:

1. An improved rotary drill bit comprising an upper body section provided with means for connecting said bit to the lower end of a rotary drill string and a lower body section attac ed to and depending from said upper body section, said lower body section comprising a matrix and a plurality of abrasion-resistant cutting elements dispersed within said matrix to form a lower bot tom hole contacting surface which extends radially from points near the axis of said bit to the periphery of said bit, said bit containing a vertical passageway which extends through said bit near the axis thereof, and said lower body section containing a plurality of verticallyspaced passageways extending laterally from said vertical passageway to openings in the side of said lower body section. i

2. A bit as defined by claim 1 wherein said particulate cutting elements are diamonds.

3. A bit as defined by claim 1 wherein said vertical passageway is displaced laterally from the axis of said bit.

4. A bit as defined by claim 1 wherein said verticallyspaced passageways are closed by plugs less resistant to abrasion than said cutting elements.

5. A bit as defined by claim 1 wherein said lower body section contains at least one external flute within which said openings in the side of said lower body section are located. 9'

6. An improved rotary drill bit comprising an upper shank section provided with means for connecting said bit to the lower end of a drill string and a generally cylindrical, externally fluted lower body section attached to and depending from said shank section, said lower body section comprising a matrix and a plurality of particulate cutting elements harder and more abrasionresistant than said matrix dispersed therein, said lower body section having a bottom hole contacting surface extending radially from points near the axis of 'said bit to. the periphery of said bit, said body and shank sections containing a vertical passageway extending through said bit near the axis thereof, and saidlower body section containing a plurality of vertically-spaced passageways extending from said vertical passageway to openings in the side of said lower body section within the flutes thereon.

7 A bit as defined by claim 6 wherein said vertical passageway is provided with a liner containing lateral openings which register with said vertically-spaced passageways.

8. A bit as defined by claim 6 wherein said verticallyspaced passageways are, provided with open-bottomed liners which are more resistant to erosion than said matrix.

9. A bit as defined by claim 6 wherein said lower body section is provided with liners in the flutes thereon which contain openings that register with said vertically-spaced passageways.

10. A bit asv defined by claim 6 wherein said verticallyspaced passageways are closed by plugs less resistant to abrasion than said cutting elements.

References Cited in the file of this patent UNITED STATES PATENTS 994,866 Muhleisen June 13, 1911 1,940,890 Stokes 7 Dec. 26, 1933 2,296,183 Richard Sept. 15, 1942 2,342,931 Fortune -i Feb. 29, 19.44 2,493,178 Williams Jan. 3 1950 2mm A stin June 10, .5

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