WO2012051648A1

WO2012051648A1 - A drill bit

Info

Publication number: WO2012051648A1
Application number: PCT/AU2011/001325
Authority: WO
Inventors: Brian Thomas Sanfead; Rober Gordon Brand Walters
Original assignee: Drilling Tools Australia Pty Ltd
Current assignee: Drilling Tools Australia Pty Ltd
Priority date: 2010-10-19
Filing date: 2011-10-19
Publication date: 2012-04-26
Anticipated expiration: 2013-04-19
Also published as: AU2011318230A1

Abstract

A drill bit (110) comprises: (a) a body (112) having a drill stem attachment end and a working end opposite the attachment end; (b) a means (130, 136a, 136b) for conveying working fluid extending through the body (112); (c) a plurality of planar wings (122) connected to the body (112) and provided with cutting edges (124) extending from the body (112); and (d) a working end (116) disposed about the cutting edges (124) of the planar wings (122). The means (130, 136a, 136b) for conveying fluid comprises a plurality of fluid flow passages (136a, 136b) for directing fluid towards the working end (116) of the drill bit (110), each fluid flow passage (136a, 136b) directing fluid in a selected direction. The planar wings (122) are advantageously mechanically fixed to the drill bit body (112), wing plates (122) being located in, and fixed by mechanically keying to, the drill bit body (110) in recesses (226) with final fixing being by welding.

Description

A DRILL BIT

This invention relates to drill bits.

US 5735360 describes drills for use in mining operations. Various types of drill bits have been developed in the past, including drag bits, claw bits, conical bits and so on, all in attempts to increase drilling efficiency and drill bit durability.

A problem which occurs frequently in drilling operations is management of drilling through soft and viscous material formations such as clay, mud or other material which may include grit and such like. Most drills include a hollow stem portion and one or more passages through the drill bit providing for the delivery of air or other fluid, including liquids, to the working face of a hole to cool the bit and flush debris from the hole. However, the relatively small diameter passages provided in most drill bits tend to clog with mud and debris limiting drilling speed (as referenced in US 5735360).

In an attempt to address these difficulties, a drill bit has been developed which is configured with a plurality of radially disposed "wings" extending from a conical centre body. Such a winged bit design, which is suitable for drilling of softer formations (such as coal seams) is distinct from drill bits used in reverse circulation ("RC") drilling which are typically used for hard rock drilling. Conventional designs of RC drill bits therefore do not comprise such wings, which would likely be quickly destroyed in service. Each wing is provided with sockets, having cutting teeth, called picks, disposed in them. The pick sockets have different spacing along each wing so that the central teeth along each wing are cutting along different paths, as the drill bit is rotated, for greater efficiency. At the same time, there is provided a relatively large passage between the wings and into the hollow conical body of the drill bit. This relatively large passage allows a greater flow of air and/or liquid coolant and/or lubricant therethrough, the aim being to allow a more rapid advance of the drill bit with less clogging with soft drill cuttings during drilling.

The relatively large passage is centrally located in the body of the bit and provides a non-directional exhaust portal or opening through which fluid flows without any particular direction. Despite some reduction of clogging experienced with exhaust face circuit designs, such a drill bit may be 'buried' to some extent in a relatively soft formation, such as a coal seam, during the drilling operation, causing rapid wear on the picks. Such wear may be experienced at the tip or leading cutting edge of the wings but abrasion also occurs on portion(s) of cutting teeth rotating in the above mentioned sockets due to the presence of grit between the mating surfaces.

International Patent Publication No. WO2008/069863 describes an earth boring bit, of similar type to that described in US 5735360, and designed to bore an angular non-vertical hole into underlying strata. In this design, the exhaust passage remains non-directional and wear problems as above described may continue to be experienced. The interchangeable flow restrictor that may be included in the exhaust passage, internally of the drill bit body, allows some tuning over velocity of fluid through the exhaust passage but does not fully address the problem of clogging and those wear problems mentioned above.

It is therefore an object of the present invention to provide a drill bit with one or more of reduced wear, improved drilling speed and service life over the above discussed drill bits.

With this object in view, the present invention provides a drill bit comprising:

a) a body having a drill stem attachment end and a working end opposite the attachment end;

b) means for conveying working fluid extending through the body;

c) a plurality of planar wings connected to the body and provided with cutting edges; and

d) a working end disposed about the cutting edges of said planar wings

wherein said means for conveying fluid comprises a plurality of fluid flow passages for directing fluid towards the working end of the drill bit, each fluid flow passage directing fluid in a selected direction. The working fluid is the fluid used to operate a drilling apparatus comprising the drill bit and is typically compressed air supplied by a suitably sized air compressor included in a drill rig in which the drill bit is used.

Each fluid flow passage is advantageously oriented, that is directed at an angle to direct fluid through respective discharge ports for each fluid flow passage towards zones - for example close to the cutting edges of the drill bit - where grit, clay, mud and other material, particularly soft viscous material may collect, adversely impacting on drilling operations. Different fluid flow passages in the same drill bit may be oriented toward different zones including the centre of the working end of the drill bit or the periphery of the working end of the drill bit. It is most advantageous for one or more of the fluid flow passages to be oriented at an angle towards the centre of the working end of the drill bit and one or more of the fluid flow passages to be oriented at an angle towards the periphery of the working end of the drill bit. The number of fluid flow passages may, without this being essential, correspond with the number of planar wings provided in the drill bit. For example, where four planar wings are provided, four fluid flow passages may be provided, such arrangement allowing for zones located between each of the wings to be flushed with the working fluid.

The planar wings may be mechanically fixed to the drill bit body. Preferably, planar wings or wing plates are located in, or mechanically keyed to, the drill bit body in recesses provided for the purpose. Final fixing may be by welding. A number of wing plates may be fixed to the drill bit body. However, a stronger drill bit design may be achieved by minimizing the number of wing plates and including an assembly of wing plates, for example an assembly of interlocking wing plates. Use of keying is advantageous from the perspective of drill bit strength and durability and it reduces the frequency of repair or replacement of the drill bit in service. In one particularly advantageous embodiment, wing plates are interlocked and keyed to the drill bit body in recesses provided for the purpose. Interlocking of wing plates may take place following keying of one wing plate into position on the drill bit body. Final locking of wing plates into position on the drill bit body may involve welding in addition to keying. For example, four individual wing plates could be replaced with two interlocking wing plates providing four distinct planar wing portions.

Cutting edges are advantageously provided with cutting teeth or picks. A holder, termed a crown block, may hold a number of cutting picks respectively located within a series of pick sockets provided in a crown block rather than a planar wing. A typically less durable construction in which individual picks are held in individual sockets is advantageously avoided. The crown block, typically one being correspondent to each planar wing of the drill bit, may be fixed to the drill bit, and more particularly a planar wing thereof by keying, welding, other techniques or a combination of these techniques. Such a construction is more durable in service. It follows that the planar wings are not provided with cutter elements along all of their outward surfaces and it may be possible to exclude use of abrasion elements over the entire outer surfaces of the wings as well.

Each fluid flow passage most advantageously includes a nozzle or restrictor which will provide increased pressure (particularly above fluid pressure in the primary fluid passage if the fluid flow passages are supplied with fluid from this primary fluid passage) of fluid discharged through a discharge port provided for each fluid flow passage. Such nozzles and restrictors, such as orifice plates, have size and working fluid discharge pressure selected to provide a fluid pressure that is sufficient to avoid or significantly reduce clogging, or bogging of the drill bit, under expected drilling conditions. This assists to minimize inconvenient and potentially costly clogging of drill bits by direction of sufficiently high pressure fluid to remove debris and formation material causing such clogging. In addition, this clogging also results in wear - particularly in zones including the tip or leading cutting edge of the wings but also on portion(s) of cutting teeth rotating in the above mentioned sockets due to the presence of grit between the mating surfaces. Therefore, direction and localisation of high pressure working fluid, or compressed air, into these zones results in increased flushing of debris or formation solids away from the zones and reduced wear. Jet nozzles are particularly useful for inclusion in the fluid flow passage(s).

The nozzle or restrictor is to be located at or proximate the discharge port of each fluid flow passage. A nozzle is to be oriented toward a zone such as the centre of the working end of the drill bit (centre zone) or the periphery of the working end of the drill bit (periphery zone) where risk of clogging occurs. Where the drill bit has a plurality of fluid flow passages, conveniently diverging from the primary fluid passage, at least one fluid flow passage and its associated nozzle or restrictor will be oriented at an angle towards the centre zone and at least one passage and its associated nozzle or restrictor will be oriented at an angle towards the periphery zone. Nozzles are preferably recessed a distance, or set back, within fluid flow passages but otherwise nozzles, preferably such as jet nozzles, may be fitted into a fluid flow passage in any convenient manner for example interference fitting. Snap rings, O-rings or circlips may also be used for fixing or locking nozzles into position. Such connections may also allow for quick and efficient field replacement of nozzles to increase drilling efficiencies.

A fluid flow passage is conveniently cylindrical/circular cross-section in shape. Alternatively, the fluid flow passage may have cylindrical/circular cross section towards its discharge port end. A convenient form of nozzle, such as a jet nozzle, therefore has a cylindrical body and an internal bore suitably configured to increase pressure of working fluid as it passes through the internal bore. To that end, the internal bore is designed to obstruct or throttle fluid flow passing towards the discharge port. While inclusion of an orifice plate would achieve this objective, a preferred internal bore has an inward tapering portion, reducing the cross-sectional area of the fluid flow passage in a gradual manner, before terminating in a cylindrical discharge passage or port. The tapering portion may have constant slope or may have an inwardly curving or cusp-like shape. Orifice size or dimension for a nozzle is advantageously selected to optimize working fluid discharge pressure with reference to parameters including working fluid compressor capacity and nature of the formation to be drilled.

Nozzles and restrictors may be used in combination to ensure that the fluid pressure in the fluid flow passages is sufficient to avoid or minimize clogging. Restrictor(s) may also be located in the primary fluid passage of the drill bit to achieve the same object.

The discharge ports are set back or located a distance away from the working end of the drill bit and not at the bit or cutting face itself. This distance is to be sufficient, without wishing to be bound by any theory, to allow a higher velocity, and greater cleaning effect, as working fluid exhausted from the discharge ports expands to a lower pressure within the bore hole. This pressure may be atmospheric pressure. In addition, the setting back of the discharge ports from the cutting edges reduces the probability of clogging with formation solids. This probability further decreases with decreasing acute angle for arrangement of the cutting edges to a longitudinal axis of the drill bit.

Each fluid flow passage is conveniently supplied with pressurized working fluid from a primary fluid passage extending through the body of the drill bit. The fluid is the working fluid for a drilling apparatus including the drill bit and is typically compressed air.

The fluid flow passages may diverge from a primary fluid passage extending through part of the length of the drill bit. In such case, each fluid flow passage may extend towards the working end of the drill bit at an acute angle to an axis of the primary fluid passage, this angle being selected to flush the working end of the bit to minimize clogging and wear. The axis of the primary fluid passage is also an axis, typically the central axis, of the drill bit. The diameter of fluid flow passage(s) will typically be less than the diameter of the primary fluid passage. The primary fluid passage is desirably to be located centrally of the body, perhaps co-axial with an axis of the body. The primary fluid passage may have a terminal wall towards the working end of the drill bit with fluid flow passage(s) diverging, through aperture(s) formed in the terminal wall, from the primary fluid passage towards the working end of the drill bit body.

The drill bit may be described as a claw bit. An advantageous design of drill bit has the planar wings extending radially outwardly at an acute angle to an axis of the drill bit in contrast to other drill bits in which the planar wings have edges parallel to a longitudinal axis of the drill bit. Drill bits may be used in vertical and angled drilling applications. The selected acute angle is greater for an angled drilling application of the drill bit than a vertical drilling application. It may be possible, however, to select an acute angle which is suitable for both vertical and angled drilling applications. A preferred such angle would be in the range 50 to 70 degrees, with a most preferred angle being about 60 degrees.

The planar wings may extend beyond a truncated conical portion of the body of the drill bit, this conical portion having a base wall extending transverse to a longitudinal axis of the drill bit and side walls convergent towards the base wall. The discharge ports for the fluid flow passages are formed in the truncated conical portion. Advantageously, the discharge ports are formed either in a side wall of the truncated conical portion in the case of a fluid flow passage oriented towards the periphery zone of the working end of the drill bit or in the base wall of the truncated conical portion in the case of a fluid flow passage oriented towards the centre zone of the working end of the drill bit. In an alternative embodiment, the body of the drill bit has a generally cylindrical portion with a planar base wall. The drill bit of the present invention may be more fully understood from the following non-limiting description of a preferred embodiment thereof made with reference to the accompanying drawings in which:

Fig. 1 is a perspective view of an earth boring bit according to the prior art. Fig. 2 is a top perspective view of a drill bit in accordance with one embodiment of the present invention.

Fig. 3 is a bottom perspective view of a drill bit in accordance with one embodiment of the present invention.

Fig. 4 is a view of the drill bit of one embodiment of the present invention from its working end and shown in Figs. 2 and 3 of the drawings.

Fig. 5 is a side view of a drill bit in accordance with one embodiment of the present invention as shown in Figs. 2 to 4 of the drawings.

Fig. 6 is a view of the drill bit from its bottom end as shown in Figs. 2 to 5 of the drawings and without the fixturing/mounting of the cutting edges.

Fig. 6a is a side view of a drill bit in accordance with a further embodiment of the present invention.

Fig. 6b is a view of the drill bit of Fig. 6a from its bottom end.

Fig. 6c is a top view, on a reduced scale, of the drill bit of Figs. 6a and 6b.

Fig. 6d is a side view of a drill bit in accordance with a second further embodiment of the present invention.

Fig. 6e is a view of the drill bit of Fig. 6c from its bottom end.

Fig. 6f is a top view, on a reduced scale, of the drill bit of Figs. 6d and 6e.

Fig. 7 is a part sectional view of the drill bit as shown in Figs. 2 to 6 of the drawings and taken along a first section line to show the bit body and primary fluid passage.

Fig. 8 is a part sectional view of the drill bit as shown in Fig. 7 of the drawings and taken along a second section line to show bit body and divergent fluid flow passages disposed at a first angle.

Fig. 9 is a part sectional view of the drill bit as shown in Figs. 7 and 8 of the drawings and taken along a third section line to show bit body and divergent fluid flow passages disposed at a second angle.

Fig. 10 is a detailed section view of a fluid flow passage with jet nozzle showing the seating arrangement. Fig. 1 1 is a detailed section view of the fluid flow passage of Fig.10 without jet nozzle showing the seating arrangement.

Fig. 12 is a view from a working end of one jet nozzle which may be used in the drill bit shown in Figs. 2 to 1 1 .

Fig. 13 is a view of the jet nozzle of Fig. 12 taken from its other end.

Fig. 14a shows a first interlockable wing plate for use in a drill bit in accordance with a further embodiment of the present invention.

Fig. 14b shows a second interlockable wing plate, for interlocking with the wing plate of Fig. 14a, for use in the drill bit of the further embodiment of the present invention.

Fig. 15a shows an end view of two wing plates assembled by interlocking.

Fig. 15b shows a side view of two wing plates prior to assembly.

Figs. 15c and 15d show isometric views of two interlockable wing plates prior to assembly.

Fig. 15e shows a further isometric view of two interlockable wing plates prior to assembly.

Fig. 15f shows a first isometric view of the two wing plates after assembly. Fig. 15g shows a top view of the two wing plates after assembly.

Fig. 15h shows a side view of the two wing plates after assembly.

Fig. 15i shows a second isometric view of the two wing plates after assembly.

Fig. 15j shows a third isometric view of the two wing plates after assembly. Fig. 1 6 shows an isometric view of a drill bit prior to assembly of the wing plates.

Fig. 17 shows an isometric view of the drill bit of Fig. 16 after assembly of the wing plates.

Fig. 18a shows an exploded isometric view of the drill bit of Fig. 16 showing the jet nozzles included within the drill bit.

Fig. 18b shows a detail of Fig. 18 showing a jet nozzle included within the drill bit.

Fig. 19 shows a bottom view of the drill bit of Figs 17, 18a and 18b.

Fig. 20 shows a section view taken along section line D-D of the drill bit as shown in Fig. 19. Fig. 21 shows a detail section view of a discharge port included in Fig. 20, the discharge port having a jet nozzle with orifice size A.

Fig. 22 shows a detail section view of a discharge port with an alternative jet nozzle with orifice size B for use in the discharge port shown in Figs. 20 and 21 .

Fig 23 shows an exploded bottom view of the drill bit of Fig. 19 showing the jet nozzles included within the drill bit.

Fig. 24 is an exploded section view taken along section line E-E of the drill bit as shown in Fig. 23.

Fig. 25 shows a detail exploded section view of a discharge port and its associated jet nozzle.

Fig. 26a is a top view of a holder, in the form of a crown block, for four picks for a planar wing of the drill bit.

Fig. 26b is a left side view of the crown block of Fig. 26a.

Fig. 26c is a front view of the crown block of Figs. 26a and 26b.

Fig. 26d is a right side view of the crown block of Figs. 26a to 26c.

Fig. 26e is a bottom view of the crown block of Figs. 26a to 26d.

Fig. 26f is an isometric view of the crown block of Figs. 26a to 26e.

Fig. 26g is an isometric view of the crown block of Fig 26f and taken from the opposite side of Fig. 26f.

Fig. 27a is a top view of a holder, in the form of a crown block, for three picks for a planar wing of the drill bit.

Fig. 27b is a left side view of the crown block of Fig. 27a.

Fig. 27c is a front view of the crown block of Figs. 27a and 27b.

Fig. 27d is a right side view of the crown block of Figs. 27a to 27c.

Fig. 27e is a bottom view of the crown block of Figs. 27a to 27d.

Fig. 27f is an isometric view of the crown block of Figs. 27a to 27e.

Fig. 27g is an isometric view of the crown block of Fig 27f and taken from the opposite side of Fig. 27f.

Figs. 28a and 28b are two respective isometric views of the crown block of Figs. 26a to 26f showing a pick located within one of its four pick sockets.

Fig. 29a is a view illustrating a pick and crown block pre-assembly.

Fig. 29b is a section view taken along section A-A of Fig. 29a. Fig. 29c is a detail section view B taken from Fig. 29b.

Fig. 30a is a view illustrating a pick and crown block pre-assembly.

Fig. 30b is a section view taken along section A-A of Fig. 30a.

Fig. 30c is a detail section view B taken from Fig. 30b.

Referring now to Fig. 1 , there is shown a perspective view of an earth boring bit 10 - as described in WO 2008/069863 - having relatively steeply angled cutting faces so that the apex 32 of the bit 10 makes initial contact with the surface and/or any underlying hard strata when the bit 10 is driven at other than a vertical angle to the surface or strata S. The bit 10 includes a truncated, generally conical body portion 12 having a relatively wide base 14 and a relatively narrow working end 16 opposite the base 14. A drill stem attachment end 18 extends from the base 14, with the drill stem attachment end 18 including a tapered, externally threaded portion 20 for removable attachment to a drill stem.

A series of radially disposed cutting faces or wings 22 extend outwardly from the conical body portion 12. Each of the faces has a working or leading edge 24. with each of the edges 24 forming an acute angle relative to the axial centerline of the bit 10. Each working or cutting edge 24 includes a series of separate cutting tooth or pick sockets 26 disposed along the working edge 24 of each wing 22. A pick 28 is removably and individually installed in each of the sockets 26. The picks 28 may be punched or pressed out of the sockets 26 when worn or broken, with new replacement picks being pressed into the sockets 26 as needed. The provision of separate pick sockets 26 provides a weak point in drill bit 10 and failure may occur too frequently at the pick sockets 26. Such failure is disruptive to drilling operations and has an undesirable cost.

Earth boring bit 10 includes a single fluid passage extending axially through the body portion 12 and threaded portion 20 for conveying fluid from the hollow drill stem through the bit 10 to flush debris from the hole being drilled during drilling operations. The working fluid, compressed air supplied from a compressor, is discharged through a single opening 16a at the working end 16 of bit 10.

The opening 16a, of relatively large diameter, is centrally located at the apex 32 of body portion 12 of the bit 10 and provides a non-directional exhaust portal or opening through which compressed air flows without any particular direction. Despite some reduction of clogging, bit 10 tends to be 'buried' or bogged to some extent in a formation during the drilling operation, causing rapid wear on the picks 28. Such wear is particularly experienced at the tip or leading cutting edges 24 of the wings but also on portion(s) of cutting teeth rotating in the above mentioned sockets due to the presence of grit between the mating surfaces. Even when an orifice plate is included to increase pressure of compressed air directed at the working end of the drill bit 10, these problems still occur. There is insufficient directionality for working fluid flow to avoid or sufficiently reduce extent of clogging, the relief portions of the wings not providing such directionality.

Referring now to Figs. 2 to 1 1 , there is shown a drill bit 1 10, which may be termed a claw bit, comprising a body 1 12. The body 1 12 includes a drill stem attachment end 1 18 and a working end 1 16. The drill stem attachment end 1 18 includes a tapered, externally threaded portion 120 for removable attachment to a drill stem (not shown).

The body 1 12 of drill bit 1 10 has a series of planar wings 122 fixed to body 1 12. Importantly, the planar wings 122 are mechanically keyed to body 1 12, in recesses or grooves provided for the purpose, and then welded to it. This use of keying and welding provides a stronger construction less subject to damage than the earth boring bits of the prior art. The planar wings 122 extend beyond a truncated conical portion 1 13 of the body 1 12 of drill bit 1 10 as conveniently shown in Figs. 2, 3 and 5. This conical portion 1 13 has a base wall 1 14 extending transverse to a longitudinal axis L of the drill bit 1 10 and side walls 1 15 convergent towards the base wall 1 14. Side walls 1 15 face in the direction of a periphery of the working end 1 16 of the drill bit 1 10. Base wall 1 14 faces downward toward the centre of the working end 1 16 of drill bit 1 10.

The working end 1 16 of drill bit 1 10, disposed about planar wings 122, is relatively wide in comparison with the drill stem attachment end 1 18 due to series of four radially disposed wings 122 extending radially outwardly at an acute angle to the longitudinal axis L of the drill bit 1 10 from the body 1 12. The wings 122 are otherwise planar in geometry as this assists cutting action. Each of the wings 122 has, fixed to it, an angled, slightly serrated, cutting or leading edge or crown block 124, each including a series of cutting tooth or pick sockets 126 within a single block. The crown block 124 is treated, for example by hardening, to provide required strength and durability. Location of all pick sockets 126 within a single crown block 124, rather than within the structure of a planar wing 122, provides a more robust construction than for the drill bit 10 of Fig. 1 . Use of crown blocks 124 avoids need for picks to be directly fixed into the planar wings 122. During use of drill bit 1 10, wear is likely to occur on the crown blocks 124 but it is easier, and less costly to replace a crown block 124, if required, than a planar wing 122 of the drill bit 1 10. Crown blocks 124 may also be made of strongly wear resistant material to reduce wear.

Crown blocks 124, which are illustrated throughout Figs. 2 to 6f and further in Figs. 26a to 30c may be welded, mechanically fixed or keyed (for example by dovetailing or square keying) to each planar wing 122 at surface 124a as shown in Figs. 26f and 27f in a manner allowing flexibility for re-adjustment and replacement as a drilling operation proceeds. Crown blocks 124 are modular and different forms of crown block 124 may be used for different drilling applications and formations.

Picks 128 are fitted into the pick sockets 126 of crown blocks 124 in the following manner. Sleeves 127, of hardened steel or tungsten carbide, are first press fitted or shrink fitted (with the assistance of a liquefied gas such as nitrogen) of sleeves 127 into the pick sockets 126 of each crown block 124 as shown in the pre-assembly state shown in Figs. 29a to 29c. Picks 128 are then located within the sleeves 127, being seated in facets 126b, in the manner as shown in Figs. 30a to 30c with illustrative isometric views being provided as Figs. 28a and 28b. The pick 128 shown in the drawings is located towards the longitudinal axis, L, of the drill bit 1 10 and is, in this sense, the innermost pick located on crown block 124. The gauge pick 128a or the pick located outermost on the crown block 124 is located in pick socket 1260. Four such gauge picks 128a are shown in the drawing. Gauge picks 128a are located radially outward of planar wings 122, as especially conveniently seen in Fig. 6f.

Picks 128 are relatively elongated, in comparison with a button construction, and have conical geometry at their tips 129 and are, as with sleeves 127, of tungsten carbide or hardened steel. Picks 128 are located within the sleeves 127, being seated on facets 126b, in a manner allowing them to rotate during operation of the drill bit 1 10.

Picks 128 may be located within sleeves 127 and removed from them in straightforward operations. Removal is assisted by the pick sockets 126 extending through the crown block 124 to openings 126a allowing for the picks 128 to be punched out of the pick sockets 126 when required for maintenance or other purposes.

It will be noted that two of the crown blocks 124 are provided with three picks 128 and two of the crown blocks 124 are provided with four picks 128. It is not essential that each crown block 124 used in drill bit 1 10 have the same number of picks 128 located within them. Indeed, use of crown blocks 124 with differing number of picks 128 may facilitate assembly of the drill bit 1 10. The differing crown blocks 124 for four picks 128 and three picks 128 are shown in Figs 26a to 24g and 27a to 27g respectively.

Wings 122 may be arranged in an angled or vertical configuration as shown in Figs. 6a to 6c (angled) and Figs. 5, 6, 6d to 6f (vertical). In the angled configuration, wings 122 have a lesser acute angle to the longitudinal axis, L, of the drill bit 1 10 than for the vertical configuration. In addition, the base wall 1 14 is located at a greater distance D, from the leading cutting picks 128d for the angled configuration, than the corresponding distance F for the vertical configuration. It may be noted that the drill bit body portion 1 13 of the drill bit 1 10 shown in Figs. 6a to 6d is generally cylindrical and not in the shape of a truncated cone.

Drill bit 1 10 includes a means for conveying working fluid through it and towards the working end 1 16 comprising a primary fluid passage 130 and fluid flow passages 136a, 136b opening through discharge ports 137. Fluid flow passages 136a, 136b diverge at respective angles A and B from the primary fluid passage 130 extending part of the length of the drill bit 1 10 as shown in Figs. 8 to 1 1 . Selection and function of angles A and B is described below. The working fluid used to operate the drilling apparatus comprising the drill bit 1 10 is compressed air supplied by a suitably sized air compressor.

Four fluid flow passages 136a, 136b are provided in body portion 1 12 of the drill bit 1 10, a number correspondent with the number of planar wings 122. Each fluid flow passage 136a, 136b is oriented, that is directed at an angle to direct fluid through discharge ports 137 towards zones - for example close to the planar wings 122 and cutting edges 124 - where grit, clay, mud and other material, particularly soft viscous material could collect, adversely impacting on drilling operations through clogging. There are four such zones located in the spaces between the planar wings 122.

The fluid flow passages 136a, 136b are supplied with compressed air from primary fluid passage 130. Primary fluid passage 130 has a terminal wall 132 towards the working end of the drill bit 1 10 with fluid flow passages 136a diverging, through apertures 134 formed in the terminal wall 132, from the primary fluid passage 130 towards the working end 1 16 of the drill bit body 1 12 (as conveniently shown in Figs. 7 to 9). Apertures 134 are of ovoid shape contrasting with the generally cylindrical geometry of the fluid flow passages 136a, 136b.

Fluid flow passages 136 in the drill bit 1 10 are oriented at angles towards zones including the periphery of the working end 1 16 of the drill bit 1 10 and the centre of the working end 1 16 of the drill bit 1 10. One pair of fluid flow passages 136a, as shown in Figs. 2, 4, 6, 8, 10 and 1 1 diverge from primary fluid passage 130 at an angle A, an angle selected to ensure compressed air flow, in direction A, towards the periphery of the working end 1 16 of drill bit 1 10. Fluid flow passages 136a discharge through discharge ports 137 formed in beveled side walls 1 15 of the truncated conical portion 1 13 of body 1 12 of the drill bit 1 10. The other pair of fluid flow passages 136b, as shown in Figs. 3, 6 and 9 diverge from primary fluid passage 130 at an angle B, an angle selected to ensure compressed air flow, in direction B, towards the centre of the working end 1 16 of drill bit 1 10. Fluid flow passages 136b discharge through discharge ports 137 formed in the base wall 1 14 of the truncated conical portion 1 13 of body 1 12 of the drill bit 1 10.

The drill bit 1 10, as illustrated in Figs. 6a to 6d, differs in its arrangement of discharge ports 137. For this embodiment of drill bit 1 10, all discharge ports 137 are located in the planar base wall 1 14. Under many conditions, such arrangement of discharge ports 137 will be sufficient to achieve the desired cleaning effect. However, in softer formations, it is desirable for discharge ports 137 to be set back at a greater distance D from the cutting face C (see Figs. 6a and 6b) than the distance F from cutting face C (see Figs. 6c and 6d). In either case, however, the distance D or F is sufficient - given the nature of the formation - to allow a higher velocity as working fluid exhausted from the discharge ports 137 expands to a lower pressure within the bore hole.

Each fluid flow passage 136a, 136b includes a nozzle 160, recessed or set back within each flow passage 136a, 136b, to provide increased fluid pressure over pressure in the primary fluid passage 130 supplying working fluid to those fluid flow passages 136a, 136b. The increased working fluid pressure, achieved by location and design of the nozzles 160, is sufficient to avoid or significantly reduce clogging under expected drilling conditions thus assisting to minimize inconvenient and potentially costly clogging of drill bits by direction of sufficiently high pressure fluid to remove debris and formation material causing such clogging. Such clogging would otherwise result in unacceptable wear of the cutting edges 124 of the planar wings 122 but also on portion(s) of picks 128 rotating in the above mentioned sockets 126 due to the presence of grit in those sockets 126. Therefore, direction of high pressure working fluid, or compressed air, into these zones results in reduced wear. Jet nozzles are selected for the nozzles 160 of fluid flow passages 136a, 136b.

Each jet nozzle 160 is located at a position set back or recessed from the discharge port 137 of each fluid flow passage 136a, 136b as shown in Figs. 2 to 4, 6 and 7 to 10. Jet nozzles 160 are oriented with centre axis toward a zone being the periphery of the working end 1 16 of the drill bit 1 10 (periphery zone) or the periphery of the working end of the drill bit (centre zone) dependent on whether a jet nozzle 160 is located in fluid flow passage 136a or 136b. Recesses 164 are illustrated in a number of the drawings.

Each fluid flow passage 136a, 136b is conveniently cylindrical and has circular cross section towards its discharge port 137 end. Jet nozzles 160, as most conveniently illustrated in Figs. 10 to 13, therefore conveniently have a cylindrical body 163 and an internal bore 166 suitably configured to increase pressure of working fluid as it passes through the internal bore 166. To that end, the internal bore 166 is designed to obstruct or throttle fluid flow passing towards each discharge port 137. To this end, internal bore 166 has an inward tapering portion 168, reducing the cross-sectional area of the fluid flow passage in a gradual manner, before terminating in a cylindrical discharge passage 169. The tapering portion 168 has an inwardly curving or cusp-like shape. The degree of curvature of tapering portion 168 may be selected to achieve the desired increase in working fluid pressure.

Jet nozzles 160 are press fitted into fluid flow passages 136a, 136b and snap rings and/or O-ring components are conveniently used to make such fitting secure as schematically illustrated in Figs. 10 and 1 1 . O-ring or snap ring 162 is fitted into groove 161 following press fitting of the jet nozzle 160 to make the connection.

Jet nozzles 160 and restrictor 170 are used in combination to ensure that the fluid pressure in the fluid flow passages 130, 136a, 136b is sufficient to avoid or minimize clogging. To this end, orifice plate 170, having opening 171 with diameter less than the inner diameter of primary fluid passage 130 is fitted at the drill stem attachment end 1 18 of drill bit 1 10. This throttles compressed air flow through the primary fluid passage 130 and assists with increasing pressure and velocity of compressed air passing through the drill bit 1 10. This, in turn, reduces clogging and wear of the cutting edges 124 of the drill bit 1 10.

A washer 171 is fitted at the drill stem attachment end 1 18 of drill bit 1 10 to assist sealing and maintenance of required compressed air flow pressure through the drill bit 1 10 when connected to a drilling apparatus.

Referring now to Figs 14a to 25, there is shown a further embodiment of the drill bit in which the planar wings, provided with formation cutting faces, are formed by an assembly of interlocking wing plates 220 and 222.

Wing plate 220, as shown in Fig. 14a and clearly of planar design, is provided with a slot 221 and angled portions 225 generally configured in the shape of a truncated triangle with rounded apices and approximating the profile of the working end 216 of the drill bit body 212. Wing plate 220 is also provided with a beveled portion 219 on which picks (not shown) are to be located, the picks being provided in a crown piece (also not shown).

Wing plate 222, as shown in Fig. 14b and clearly of planar design, is of complementary design to wing plate 220, having a slot 223 for engaging with the slot 221 and also having a beveled portion 224 and angled portions 225.

Angled portions 225 of wing plates 220 and 222 are provided for engaging or 'keying' with grooves or recesses formed about the periphery of the body 212 of drill bit 210 as shown in Figs. 16 and 17. Figs. 15a to 15e indicate how the wing plates 220 and 222 are interlocked together by keying to form a single wing plate assembly, the wing plate assembly having four distinct planar wing portions 227. Wing plates 220 and 222 are moved into a position in which slots 221 and 223 are in alignment. Wing plate 220 is then slid or pressed over wing plate 222 until the slot portions 221 a and 223a engage. At that point, the wing plates 220 and 222 are interlocked and the wing plate assembly is complete, as shown in Figs. 15f to 15j, bar welding to lock the wing plates 220 and 222 together.

The wing plate assembly could be made prior to connection to the body of a drill bit. However, as indicated in Fig. 16, wing plate 222 may first be keyed into grooves 226, adapted to receive the angled portions 225 of that wing plate 222. To that end, grooves 226 have a complementary profile to the angled portions 225 of wing plate 222. Welding then follows to lock wing plate 222 into position on the body 212 of drill bit 210. This results in a stronger construction than if keying was not adopted. Wing plate 220 may then be assembled, by interlocking, to wing plate 222 in essentially the same manner as above described. Again, the angled portions 225 of wing plate 220 are keyed, for purposes of enhanced strength over other constructions, into grooves 226 which are adapted to receive these angled portions 225. Following welding to lock wing plate 220 into position on wing plate 222 and body 212 of drill bit 210, the finished drill bit 210 is shown in Fig. 17.

Figs. 18a to 25 show drill bit 210 with the interlocking wing plate assembly and with jet nozzles 260 fitted in discharge ports 237 of fluid flow passages 236, four of which are provided. Each discharge port 237 is located in a quadrant 229 of a base wall 214 of the drill bit body 212 formed by the assembly of interlocking wing plates 220 and 222. Base wall 214 extends perpendicular to axis N of drill bit 210 and has greater area than base wall 1 14 of drill bit 1 10 and the body 212 is of generally cylindrical shape with a beveled portion at the transition with base wall 214, a difference in shape from the truncated conical portion 1 13 for drill bit 1 10.

Each discharge port 237 discharges pressurized working fluid, compressed air, at an acute angle to the longitudinal axis N of drill bit 210. Again, the compressed air is directed towards zones where clay, grit, mud and other material, particularly soft viscous material could collect, adversely impacting on drilling operations through clogging. The location of each discharge port 237, in the corner 231 of each correspondent quadrant 229 is selected to promote this cleaning effect. Airflow direction in the drill bit 210 is shown by the airflow direction arrows in Figs. 20 to 22.

As with drill bit 1 10, fluid flow passages 236 are supplied with compressed air from primary fluid passage 230. Primary fluid passage 230 has a concave terminal wall 232 towards the working end 216 of drill bit 210 with fluid passages 236 diverging, through apertures 234 formed in the terminal wall 232, towards the working end 216. Apertures 234 are of ovoid shape and greater cross sectional area than other portions of the generally cylindrical fluid flow passages 236.

Jet nozzles 260 have a cylindrical body 263, the cylindrical shape allowing ready accommodation at the discharge port 237 end of each fluid flow passage 236. The internal bore 266 is suitably configured to increase compressed air pressure as it passes through the internal bore 266. To that end, the internal bore 266 is designed to obstruct or throttle compressed air passing towards each discharge port 237. To this end, jet nozzles 260 have an inward tapering portion 268, reducing the flow cross-sectional area in a gradual manner before terminating in a cylindrical discharge portion 266 having orifice size indicated by dimension A in Fig. 21 . For jet nozzles 260, the transition is more gradual than for jet nozzles 160 (and no cusp portion is included, the transition is more linear). This selection of jet nozzle design results from a selection process taking into account air compressor capacity and nature of the formation to be drilled.

Such selection process may result in various jet nozzles being selected. Further, as a drilling operation proceeds, an optimum drilling strategy may be to change jet nozzles 260 over in the field. Such change over of nozzles 260 is part of the drilling strategy and is to be distinguished from repair operations. Fig. 22 indicates a further jet nozzle 260a which is available to replace jet nozzles 260 as required. Jet nozzle 260a has a similar design to jet nozzles 160. However, the orifice size has a dimension B less than dimension A for jet nozzles 260 and this design would allow higher compressed air discharge pressures and a higher working end 216 cleaning effect to be achieved. Jet nozzles 260, 260a are press fitted into fluid flow passages 236 at their discharge port 237 ends. Circlips 262, located within grooves 261 of the cylindrical bodies 263 of jet nozzles 260, are conveniently used to make such fitting secure as schematically illustrated in Figs. 23 to 25.

Testing of drill bits 1 10 and 210 having features as described above has demonstrated significantly greater endurance and service life than for conventional earth boring bits. Service life may be measured in terms of distance, typically metres drilled. Using this metric, the above described drill bits are typically drilling two, three and more times the distance drilled by conventional earth boring bits. At least part of the reason for this is the reduction of wear at the planar wings and destruction of cutting edges due to use of pick socket holders (crown blocks) which remove the need to form pick sockets in the planar wings, a construction more prone to wear.

Modifications and variations to the drill bit of the present invention may be apparent to skilled readers of this disclosure. Such modifications and variations are deemed within the scope of the present invention.

Claims

CLAIMS:

1 . A drill bit comprising:

(a) a body having a drill stem attachment end and a working end opposite the attachment end;

(b) a means for conveying working fluid extending through the body;

(c) a plurality of planar wings connected to the body and provided with cutting edges extending from the body; and

(d) a working end disposed about the cutting edges of the planar wings wherein said means for conveying fluid comprises a plurality of fluid flow passages for directing fluid towards the working end of the drill bit, each fluid flow passage directing fluid in a selected direction.

2. The drill bit of claim 1 wherein each fluid flow passage is oriented at an angle to direct fluid through respective discharge ports for each fluid flow passage.

3. The drill bit of claim 1 or 2 wherein a fluid flow passage is oriented at a different angle than another fluid flow passage.

4. The drill bit of claim 3 wherein one or more of the fluid flow passages is oriented at an angle towards the centre of the working end of the drill bit and one or more of the fluid flow passages is oriented at an angle towards a periphery of the working end of the drill bit.

5. The drill bit of any one of the preceding claims wherein said planar wings are mechanically fixed to the drill bit body.

6. The drill bit of claim 5 wherein said planar wings in the form of wing plates are located in, and fixed by mechanically keying to, the drill bit body in recesses with final fixing being by welding.

7. The drill bit of claim 6 wherein an assembly of interlocking wing plates is located in, and mechanically keyed to, the drill but body in recesses provided for the purpose with final fixing being by welding.

8. The drill bit of any one of the preceding claims wherein said cutting edges are provided with cutting picks respectively located within a series of pick sockets provided in a holder or crown block, one said crown block being correspondent to, and fixed to, each planar wing of the drill bit.

9. The drill bit of any one of the preceding claims wherein each fluid flow passage includes a nozzle or restrictor for increasing working fluid pressure for discharge through a discharge port provided for each fluid flow passage.

10. The drill bit of claim 9 wherein each said nozzle has an internal bore configured to increase pressure of working fluid as it passes through the internal bore by obstruction or throttling.

1 1 . The drill bit of any one of claims 2 to 10 wherein the discharge ports are set back or located a distance away from the working end of the drill bit.

12. The drill bit of any one of the preceding claims wherein said fluid flow passages diverge from a primary fluid passage extending through part of the length of the drill bit and each fluid flow passage, of less diameter than the diameter of the primary fluid passage, extends towards the working end of the drill bit at an acute angle to an axis of the primary fluid passage, this angle being selected to flush the working end of the bit to minimize clogging and wear.

13. The drill bit of claim 12 wherein said primary fluid passage has a terminal wall towards the working end of the drill bit with each fluid flow passage diverging, through aperture(s) formed in the terminal wall, from the primary fluid passage towards the working end of the drill bit body.

14. The drill bit of any one of the preceding claims wherein said planar wings each extend radially outwardly at an acute angle to an axis of the drill bit.

15. The drill bit of claim 14 wherein said acute angle is greater for an angled drilling application of the drill bit than a vertical drilling application.

16. The drill bit of any one of the preceding claims wherein said body of said drill bit has a truncated conical portion having a base wall extending transverse to a longitudinal axis of the drill bit and side walls convergent towards the base wall and each planar wing extends beyond said truncated conical portion of the body of the drill bit.

17. The drill bit of any one of claims 2 to 16 wherein said discharge ports for the fluid flow passages are formed in the truncated conical portion of the drill bit body.

18. The drill bit of claim 17 wherein said discharge ports are formed either in a side wall of the truncated conical portion in the case of a fluid flow passage oriented towards the periphery zone of the working end of the drill bit or in the base wall of the truncated conical portion in the case of a fluid flow passage oriented towards the centre zone of the working end of the drill bit.

A drilling apparatus including the drill bit of any one of the preceding claims.

A method of drilling a formation comprising drilling a formation with a drilling apparatus comprising drill bit comprising:

(b) a means for conveying working fluid extending through the body; (c) a plurality of planar wings connected to the body and provided with cutting edges extending from the body; and

(d) a working end disposed about the cutting edges of the planar wings wherein said means for conveying fluid comprises a plurality of fluid flow passages for directing fluid towards the working end of the drill bit, each fluid flow passage directing fluid in a selected direction and wherein each fluid flow passage includes a nozzle or restrictor for increasing working fluid pressure for discharge through a discharge port provided for each fluid flow passage and said nozzle or restrictor is changed in the field as drilling proceeds as part of a drilling strategy.