AU608014B2 - Release coupling - Google Patents

Description

W1§~7~ /1 L i i- 1< 3 00 r- 0f I i^'s 0t 00 09 a o 0 00 0 00 e a 0 0 0 o0 00 00 0 9o 000 0900 a a 9« 00 «C1 44 «i S F Ref: 61406 FORM COMMONWEALTH OF AUSTWALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Complete Specification Lodged: Accepted: Published: Priority: Related Art: Class Int Class This document contains the amendments Made under Section 49 and is correct for printing.

Name and Address of Applicant: Desmond Edward Beswick 1-3rd. Avenue Cloverdene cenoni REPUBLIC OF SOUTH AFRICA Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Address for Service: Complete Specification for the invention entitled: Release Coupling The following statement is a full description of this invention, including the best method of performing it known to me/us 5845/4 i FIELD OF THE INVENTION: This invention relates to a releasable or breakable coupling device o particularly, though not necessarily exclusively, for use in drill strings for core, or so called "diamond", drillinr operations.

0 4 0 S 5 RACKGROUND OF THE INVENTION 0 0 NormJlly the drill string or drill equipment comprises a plurality of drill rods (wire-line or conventional rod-line), a core barrel

B

assembly, a reaming shell, and a drill bit, though designs vary and *o 1 several components may be combined or integrated. The drill string o 10 components are usually connected by threaded couplings.

4*4 During drilling, the equipment may become stuck in the hole, eg. the bit may become "burnt-in" or the drill rods may be snagged or otherwise stuck. "Burning-in" is common and arises from insufficient supply of 0 o04* lubricant, such as water or slurry, to the bit which causes excessive friction resulting in melting of the bit body and matrix. Thus the bit fuses with the rock or deforms outwardly to become mechanically locked against longitudinal movement.

When equipment has become stuck or "lost" do;ni a hole, the drilling operator has a choice of .abandoning the hole or "fishing" for as much of the drill string as possible and thereafter "wedging" past the remaining equipment. With "deep holes", such as more than 1000m and up page 2

I:

I i

I

3to 5000m or more, both the cost if the abandoned equipment and the cost of re-drilling a hole or portions of a hole are very high, so that the -operator has little choice but to fish out as much as possible. Much time and money is spent on such fishing, which may last as long as six months.

Also, while a large portion of the hole may be recovered, little of the equipment recovered may still be useful as fishing tends to damage the drill rods by belling the ends.

It is known to use a quick release coupling that includes a multistart thread in the drill string, but this has not proved successful at all times especially at greater depths. In use, because of high axial loading, locking torque of several tonnes and hydraulic pressure of several hundred bar, the coupling also becomes locked, so that the drill rods frequently uncouple much higher up the drill string when it is rotated in the reverse direction to release the coupling. The drill rods uncouple whei; the axial '5I loading has been lower, where there has been less torque wind-up and release, and where lower friction on the rods does not prevent the transmis-ion of uncoupling torque. Also hole deviation and consequent wind-up play a great part, requiring several turns at the surface to start movement at the bottom of the hole.

SUMMARY OF THE INVENTTON ft 4'

V,

ft Vo

V

iii *I1 ft 94 I 49 .4~

V

I,

I I IIr 30 I t

LI

It is the object of the present invention to overcome or substantially ameliorate the above disadvantages.

There is disclosed herein coupling means for core drilling equipment including first and second tubular members one of which is an inner member that has i portion that fits into the other member which is an outer member; torque means connecting the members to each other to transmit torque from one to the other; and shear means connecting the members longitudinally to one another and comprising frangible pin member, with the pin member extending substantially radially with respect to the tubular members between the interfitted portions of the tubular members, being constructed to shear to allow the members to separate longitudinally when a predetermined tensile force applied to the coupling means is exceeded, and being welded to the outer member.

There is further disclosed herein drillirg equipment including:a drill bit having a body and a matrix of drilling material at its forward end; ;/26351 3A a core barrel assembly having a core barrel shell, a core cage and a core cage seat on the core cage; and a coupling means as claimed in claim 1, with the first member being immediately adjacent to the drill bit, the second mrmber being adjacent to and being connected to the core barrel shell, and the coupling means including a cage load seat constructed to engage the core cage seat of the core barrel assembly.

Typically, the torque means is constructed such that insignificant shearing ferces are applied to the shear means when the drill string is rotated or compressed, i.e. a load is applied to the bit, in use.

r i t* 0 0 0 00 S0 0 0 0 o 9**i I tt 26351

I

Preferably the interfitted portions of the members are substantially cylindrical. Preferably they are a sliding fit for at least a portion of their interFitted portions.. Preferably they are sealed to each other to prevent liquid from passing between the inside and outside of the members.

Preferabliy the first and second members have longitudinally opposed mating shoulders for transmitting compressive forces between the members.

The coupling means may include a third cylindrical member and a second shear means, with the members being arranged in at least two pairs relatively to one another and with the shear means being arranged such that there is one shear means between each pair of the members. Either of the shear means may be sheared to allow the respective pair or the members to be separated. The characteristics of the shear means can be 15 selected or tailored as desired to ensure separation of the coupling means when different criteria ara met.

o o The three members may consist of a sliding member and two torque transmitting members, the sliding member being a sliding fit in the torque members with one shear means being provided between each torque 0 0 20 member and the sliding member. The torque m'cns may couple the torque members directly to each other or indirectly via the sliding member.

The torque means may be mating longitudinally extei,ding dogs, splines or fingers on the members, he rein generally referred to as "dogs"; or *may be at least one and preferably a plurality of pins each of which is fixed to one of the members and engages in a longitudinal slot in the other member with the slot intersecting the end of the member. The torque means may also be a suitable combination of dogs and pins and may include a suitable bonding medium.

The dogs may extend in opposed radial directions from one member to the other or may extend longitudinally from one member into the other.

page 4 The torque means may be constructed, either alone or with the shear means depending on the configuration of the coupling means, to have a predetermined maximum torque shear strength. This allows the coupling to shear when, say, the bit burns in to prevent shearing of the rods higher up the drill string. This maximum torque shear strength is selected to be at safe limits between the expected drilling torque and the torque shear strength of the drill rods.

As a guide drill rods will shear in torsionally at the rod joints at about 5 to 8 kNm depending on diameter and age or condition. Also a pre-torque to lock the rod joints of 0,9 to 2,3 kNm is normally used, while drilling torque is approximately ikNm depending on type of tV t Imachine, core diameter and rock type. Within these parameters the predetermined torque shear strength of the coupling is preferably in *44 0 the range 2 to 3,5 kNm, more preferably 2,5 to 3 kNm.

*o* o 15 The shear means may comprise a frangible member extending between the 4 904440 members and constructed to shear when a pre-determined tensile force acting between the members is exceeded. The frangible member may be at least one substantially radially extending pin, an arcuate key or an

SOI

oO ainulus. The frangible member may be of brass, non-ferrous alloy, a a 0 ZO0 mild steel, or a steel alloy.

Q0 4 ooor Additionally or alternatively, the shear means may comprise at least one annular weakened zone in one or both of the members formed to shear when a pre-determined tensile force acting between the members is Earo exceeded. The weakened zone is conveniently an annular groove.

The pre-determined tensile force or shearing force depends on where the coupling means is positioned, the rock type, core diameter, and the condition of the drill rods. The shearing force is preferably selected to be at least 1,5 to 2 tonnes greater than the force required at any selected position along the drill string to "break-out" the drilled core, which normally ranges from 1 to 1,5 tonnes, but may be higher.

page i Preferably the coupling means is provided at or near the drill bit, with the shearing for.ce being selected to be at least 3 tonnes, preferably in the range 3,2 to 9,6 tonnes.

The shearing force is also selected to allow for decreases in strength of the shearing means due to fatigue in use, while not being so high as to cause breakage further up the drill string owing to the combined effect of the mass of the equipment and the restraining force of a burnt-in drill bit.

Additionally or alternatively the shear means may comprise a suitable bonding medium connecting the members together and which shears, melts ,or deteriorates when a pre-determined criterion is met. The bonding medium may be a suitable metal or metal alloy, such as a soft or brazing solder, with a suitable low melting point or an appro'priate 0, plastics, such as an epoxy resin. The bonding medium may coit the opposed surfaces of the members or may be provided as a frangible member as described above. In this event, the preferred pre-determined criterion is temperature, so that the members separate when a pre-determined temperature is exceeded, such as by the bit heating up o owhen it'burns-in.

So0, 20 In use, when the drill bit burns in, it heats up considerably, such as 600 to 800"C, this heat is conducted to the coupling device and to the bonding medium. Above a certain temperature, eg. 150 to 200°C for epoxy resin and 200 to 600 0 C for selected alloys, the bonding medium will deteriorate irreversibly. The members can then separate longitudinally. Alternately, the bit can be run for an extended time without lubricant to cause it to heat up sufficierrly to melt or soften the bonding medium so that pulling on tht drill string will cause the members to separate longitudinally.

The coupling means may be constructed as an end portion of an item of the drill string, with one of the members having a suitable threaded formation for connection into a drill string and the other being integral with the end region of the item, such as the distal end of a page 6 -7drill rod, the core barrel shell or the reaming shell or the proximal end of the drill bit.

Alternatively the coupling means may be constructed as a separate device connectable into a drill string at a suitable location. Suc, device may be connected between the drill and the reaming shell; the rearling shell and the core barrel shell; the core barrel shell and the rod line; and between selected drill rods. Several such devices having differing shearing criteria may be provided at desired locations along the drill string.

Preferably the coupling device is constructed as a reaming shell, with matrix slugs being provided on the outer surface of at least one of the members. This constructions makes the device an item that must be replaced at regular intervals, so minimising the possibility of the device becoming defective through fatigue, deformation or corrosion.

Another aspect of the invention provides a drill string for core Sdrilling including at least one coupling means of the invention.

,o Preferably the drill string includes a plurality of coupling means at o 6 selected spaced locations along its length, the shear means of the respective coupling means having relative shear strengths that increase :2d sequentially from the distal to the proximal end of the drill string, e.g.

upwardly when drilling downwardly.

Yet another aspect of the invention provides a drill string component including a coupling means of the invention.

Yet another aspect of the invention provides a method of facilitating the recovery of drilling equipment comprising a drill string at the distal end of which is a core barrel assembly and a drill bit including the steps of:coupling the core barrel assembly to the drill bit by coupling means comprising two members connected by shear means adapted to shear when a predetermined criterion is met and by torque means to transmit torque between the members; applying a tensile force to the drill string to cause the shear means to shear when the bit becomes burnt in; withdrawing the drill string above the coupling means by separating the members of the coupling device, with a portion of one of the two members of the coupling means remaining in a hole being drilled; r r 8 connecting another coupling means and drill bit to the end of the withdrawn drill string; replacing the drill string in the hole being drilled; and drilling through the remaining portion of the original coupling device and the burnt in drill bit and thereafter continuing drilling operations.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: Fig. 1 shows an axial section of a lower portion of a drill string including an embodiment of reaming shell formed as a coupling device; Fig. 2 shows an axial section of a variant of coupling device; Fig. 3 shows an axial section of a portion of yet another embodiment of coupling de'ice; ,i"1T Fig. 4 shows an axial exploded section of another embodiment of coupling device; SI"" Fig. 5 shows, partly in section, a portion of a core drilling bit connected by an embodiment of coupling means to a core barrel assembly; Sor Fig. 6 shows, partly in section, a core drilling bit connected to a %°,oZe core barrel assembly by a yet another embodiment of coupling means; and Fig. 7 shows, partly in section yet another variant of reaming shell coupling of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Figure 1 shows a b-ttom region of a core drill string 10 in a hole 12 which has been bored in ec -h to extract a core, the drill string comprising a core barrel 14 (only a portion being shown), a coupling device 16 and a diamnd drilling bit 18.

1 /2,6351

Q

r 'I I The core barrel 14 is conventional and has a pin thread portion 20 of standard dimensions for coupling core drill equipment at its lower end.

The drill bit 18 is also conventional and includes a coupling part 22 with an internal or box thread, a body part 24 and a matrix 26, such as diamonds embedded in a hinder of tungsten carbide. Flow passages 28 are formed through the matrix 26 for lubricating and cooling water to flow through the bit, eg. down the drill string and then upwardly between the drill string and the walls of the hole 12. Blocking of these passages or a split in a drill rod above the drill bit results in an insufficient supply of water to tVie bit which causes it to burn-in.

,t t The coupling device 16 comprises a first memher 30 coupled to an second P member 32 by torque means and shear means as described below.

o ,o The first member 30 has an upper coupling portion 34 with a box thread to engage the pin thread 20 of the core barrel. Likewise the second member 32 has a pin thread 36 to engage the box thread 22 of the drill bit. The standard threads of the portions 34 and 36 are provided to o +connect the coupling 16 into conventionally threaded drill equipment and at any suitable position along the drill string.

The first member 30 ha a lower reduced diameter sleeve portion 38 that is a tight, telescopic fit in a countersunk sleeve portion 40 of the member 32. The engaged sleeve portions form utipper and lower sets of longitudinally abutting annular shoulders 42 and 44 for transmitting compressive forces between the members in normal drilling and for accommodating shock loading when the bit impacts on the bottom of the hole.

Two steel pins 46 welded to sleeve portion 40 extend radially inwardly for approximately the thickness of the inner sleeve portion 38. Each pin 46 is snugly received in the base of a slot 48 in the sleeve 38, each slot intersecting or being open at the end of the member 30. The pins 46 transmit mainly torque and some compressive forces between the coupling members. The pins fit tightly fit in the slots 48 to ensure minimal backlash in the coupling. The pins 46 do not transmit tensile forces or prevent longitudinal separation of the members 30 and 32.

page 9 In an example, a coupling for 76msn outer diameter drill strings has two 14mm diameter pins of EN3A steel hardened to 430MPa to provide a torque coupling of about 4000 Nm.

Two further, smaller diameter pins 50 connect, the members 30 and 32 longitudinally to each other. The pins 50 are externally threaded and engage in tapped registering bores in the overlapping sleeve portions.

The pins 50 are designed to shear when a pre-determined tensile force applied to the drill string is exceeded. In the above example, each of the pins 50 is of 10mm diameter Naval brass to provide an axial shear strength of approximately 3 tonnes. For ensuring reliable shearing and water sealing, the holes for the screws 50 are drilled and tapped after the coupling members have been engaged and clamped to make the shoulders 42 and 44 abut firmly.

0 09 oo Diamond matrix slugs provided externally on the member 30 make the 15 coupling 16 function as a rriming shell to keep the hole 12 "on gauge".

In practice, the end region of a drill string is assembled conventionally with standard threaded components, other than the reaming shell which is replaced with the coupling 16 of the invention.

Drilling is performed in the normally, with the coupling 16 transmitting downward pressure to the face of the bit via the shoulders 42 and 44 and torque via the pins 46. When the bit 18 must be replaced, such as every 100m or so, then the drill string is withdrawn while the shear pins 50 hold the coupling members 30 and 32 together.

For reliable use, the coupling is replaced with every fourth bit, ie.

after about 400m has been drilled. T6 this end the matrix slugs 52 are constructed to wear at a rate suitable to ensure the operator notices the wear and replaces the coupling 16 at appropriate times.

Should the bit 18 burn in, it is then necessar ioe withdraw the drill string, or as much of it as possible, quickly to avoid down-time. If this happens, upwardly directed force or tension is applied to the page i drill string to exceed the 3 tonnes shear strength of the pins 50. The pins chus shear and the drill string including the core barrel 14 and the member 30 of the coupling disengage from the drill bit 18 and may be withdrawn from the hole. Only the drill bit, which is no longer useable in any event, and the lower member 32 r-iain down the hole.

Drilling can then proceed substantially immediately thereafter by fitting a fresh coupling device 16 and a drill bit suitable for drilling steel and re-inserting the drill string down the hole. The drill is operated first to drill out the remaining portion of the coupling and the old drill bit and then a small way, eg. 100 400mm, through rock again to ensure the metal is drilled away. Finally the drill string is removed, a fresh bit 18 attached, and normal drilling a 6 continued.

a a Alternatively, the operator may use a fresh bit 18 not adapted for 15 drilling steel. While there might be some additional wear, the such wear will not be excessive, whereas the savings in time, equipment and capital costs will be considerable.

o o °o It is expected that the operation described above will.at most take about one day and the already drilled hole will be saved. Also the S 20 necessity of wedgii j past at some position much higher up the drilled hole, which could be anywhere from 100 to a few thousand meters from the burnt in bit, will be avoided.

*Figure 2 shows an embodiment of drill coupling 100, comprising three members, namely a first coupling member 102 wiith a standard box thread portion 104, a second coupling member 106 with a standard pin thread portion 108 and an internal unthreaded third member 110.

The members 102 and 106 have mating splines or dogs 112 and 114, respectively, that interfit one another with close tolerances, ie. less than 0.1mm, whereby when engaged torque can be transmitted between the two members without significant backlash. The ends of each of the dogs form shoulders through which compressive forces are transmitted between the members.

page 11

L,

The shell 110 is a tight sliding fit, ie less than 0,1mm tolerance, inside both of the members 102 and 106 and is connected to each of them separately by sets of two shear pins 116 and 118.

In use, this embodiment functions similarly to that described above, except either of the two sets of shear pins may shear to release the core barrel from the drill bit.

A feature of this embodiment is that the construction, ie. thickness and material, of the shell 110 can be tailored as desired as it is not load-bearing. For example, it may be formed of a suitable plastics or epoxy resin that will deteriorate should the bit burn in. Also, it may o* o be made of a ductile material that will allow at least one set of the o pins 116 and 118 to be drawn through it when sufficient tansile force 9o'o" is applied between the members 102 and 106. The shell 110 can also be of a relatively thin material which is press fitted into the members 15 102 and 106 to act as a shock absorbing member or damper to inhibit 999*o0 backlash which may arise in the coupling after extended use. Moreover, one set of pins may be of metal and the other of suitable plastics or epoxy resin, so that the coupling can be released either when a oo predetermined tensile force is exceeded or when the coupling has been heated above a predetermined temperature.

Figure 3 shows an embodiment of coupling device 200 in which a shear ring 206 of suitable epoxy resia is received in opposed circumferential grooves 202 and 204 formed in the opposed faces of two telescoped parts 0, C 208 and 210 of the coupling member. The ring 206 provides a longitudinal connection between the members preventing them from being pulled apart during normal use, while allowing such separation either when a pre-determined tensile force is applied between the members or when the epoxy deteriorates through being heated.

Instead of an epoxy material, the ring 206 may be of an appropriate polyurethane which provides the required shear characteristics and which has the benefit of damping backlash between the coupling members.

The ring may also be of a suitable metal, such as brass or aluminium.

page 12 Figure 4 shows a coupling device 60 comprising a first member 61 and a second member 62. The first member 61 has a box thread portion 64 and an unthreaded externally reduced diameter coupling portion 66. An external shoulder 68 is formed at the interface of the portion 64 and 66. The shoulder is stepped to form a dog 70 defining forward 72 and rearward 74 shoulders.

The second member 62 has a pin thread portion 76 and a countersunk coupling portion 80 having an inner bore 82 that is a close fit, ie.

less than 0,1mm tolerance, over the coupling portion 66. The free end of the coupling portion 80 forms a stepped shoulder 84 forming a dog 86 defining forward 88 and rearward 90 shoulders. The outer corners of the dog 86 is rounded to facilitate assembly, while the corresponding corner between the risers 70 and rearward shoulder portion 74'of the member 61 is complementally rounded.

t S 15 In practice the device is assembled by applying a thin coating of silicone sealant in liquid or jell form to the coupling portion 66 and shoulder 68, fitting and clamping the members 61 and 62 together with °o the shoulders abutting, drilling two or four holes at substantially equal spacing around the member through the portions 66 and 80, tapping the holes .nd screwing shearable steel studs (not shown) into them, and then welding ,he outwardly exposed ends of the studs tc ensure they are firmly held 'n position.

In use the coupling is connected into a drill string as described above, with compressive forces being transferred through the mating shoulders and torque forces through th dogs 70 and 86. If a drill bit or other component of a drill string becomes jammed, then the coupling can be broken or released by tensioning the drill string sufficiently to shear the steel studs. Instead of welding the outside of the pins they may be locked using a suitable epoxy sealer or a locking compound such as that sold under the trade name Locktite(TM).

The number of pins will depend on the ground being drilled and the force .,equiled to break the core. In areas where there is a sticky core which requires a considerable breakout force, then the number of page 13 5845/4 pins is increased, say to four, to ensure that the pins do not shear when breaking the core.

Figure 5 shows a variant adapted primarily for use with a standard length core barrel assembly and for those situations where the core is difficult to break, ie. requires considerable force.

In thi: event there is a modified core bit 300 having a matrix 302 and a round cylindrical body 304 with a smooth inner wall 306; a coupling member 308 having a reduced diameter portion 310 received in the body portion 304 of the bit; and a core barrel.assembly 312 including a core barrel 314 with a pin thread end engaged with the coupling member 308, a core cage 316 supported on bearings (not shown) in the shell 314, and ti a truncated conical core spring 318 within the end of the cage 316.

The bit 302 is mod'ified from a conventional bit in two respects. First it does not have a box thread for connectior to the core shell 314, but instead forms part of a release coupling means of the invention. The bit and coupling member are connected axially in tension by pins 320, in compression by shoulders 322 and 323, and in torque by dogs 324 of o44 °the type 'shown in Figure 4.

Second, the bit 300 is not formed with a seat to carry the load of the core cage. Instead a conical seat 330 is formed internally on the coupling member 308 and positioned to engage a complemental seat 332 at the lower end of the core cage 316.

In use, a core is broken for subsequent extraction to the surface, by forcing the cage 316 (downwardly) towards the hit to cause the seats 330 and 332 to engage and force the spider end of the cage 316 and thus the core spring 318 to grip the core. The bit and core barrel shell are then pulled upwardly to break the core.

When the core is broken the vertical load is supported by the seat 330 on the coupling member 308 and no load bears on the pins 320. On the other hand should the bit 300 burn in, then pulling on the drill string causes the pins 320 to shear axially.

page 14 Figure 6 shows another embodiment of coupling device 400 comprising two coupling members 402 and 404 having telescoped coupling sleeve portions 406 and 408 respectively. The members are coupled in compression and in torque by mating cogs 410 and 412. The base of the female sleeve 408 is a shrink fit over the male sleeve 406; this is achieved by making the external diameter of the male sleeve slightly greater than the internal diameter of the base region of the female sleeve and heating the female sleeve to expand it sufficiently before it is fitted over the male sleeve. On cooling the shrink fit regions of the sleeves form a water tight seal. The male sleeve is formed with two external annular grooves 414 and 416 constituting we.kaiied shear zones above the shrink fit region.

S<o In use, the male sleeve can be sheared at either of the zones 414 and 416 by applying sufficient tension to the device.

15 This construction is designed to facilitate accurate and less costly assembly as follows. The two members can each be machined on a S. computer controlled lathe and no further machining is thereafter S* requirea, eg. for fitting shear pins. The shear zones are formed at the same time as the male sleeve is formed. The two members need only S 20 be fitted to each other and pressed or driven home after the female sleeve has been heated to ensure they are adequately couple in tension for normal use. The shrink fit ensures effective water sealing without having to resort to clamps, to polish off any burrs on the mating 5 shoulders, to use sealants. And the shrink fit ensures there is no S" 25 backlash in the device.

As a development of this embodiment pins may still be provided between the sleeve portions to reinforce the strength of the the shrink fit.

The pins will be positioned between at least one of the weakened zones and the base of the female sleeve so as n.ot to affect shearing of the device.

A further development involves brazing the two sleeve portions to each other, either with or without shrink fitting. In this event'a ring of brazing material may be positioned in the groove 416, the members page fitted together, and the device heated in an oven or inductively sufficiently to cause the brazing material to flow and bond the members. This technique is particularly suitable for an example of the type shown in Figure 5, in which the diamond matrix is braze welded to the bit body by inductive heating while the matrix is accommodated in a carbon mould.

Figure 7 shows a shearable reaming shell 500 comprising a first member 502 with a box thread portion 504 and an inner sleeve portion 506, a second member 508 with a pin thread portion 510 and an outer sleeve portion 512 fitted over the inner sleeve portion 506, d'ive dogs 514 engaged in slots or keyways 516, axial shear pins 518, and reaming slugs 520. The dogs 514 are formed at the end of the outer sleeve 512 I and are dimensioned to shear torsionally when a predetermined torque is I exceeded, say 2,7kNm. The many relatively smaller arc slots and dogs 15 facilitates machining in that the slots can be milled in an axial direction without having to rotate the milling head to cater for radial deviations at the edges of the slots to maintain tolerances. The first .and 'econd members are sealed to each other by an 0-ring 522 seated in a triangular cross-section annular space formed .etween an inner 20 shoulder at the base of the sleeve 512 and an external bevel at the end of the sleeve 506. This arrangement ensures the 0-ring will not be extrrded by hydraulic forces to enter between and lock the sleeves 506 and 512 axially.

It is to be understood that the invention is not limited to the precise constructional details shown in the drawings and described above and modifications may be made thereto as well as will other embodiments become apparent without departing from the spirit of the invention.

For example in the embodiment of Figure 1 radially extending splines on the opposed faces of the coupling members.30 and 32 may be used for transmitting torque instead of the pins 46 and slots 48. Similarly, with the embodiment of Figure 2 the internal faces of the coupling members 102 and 108 can have radially extending splines to mate with corresponding splines on the shell 110.

page 16 Also the shear strength of, say, the pins 46 of the example of Figure 1 may provide a torque coupling of about IkNm, so that the combined torque coupling of the pins 46 and 50 provide a maximum torque coupling of about 3kNm. Thus, the coupling will shear torsionally before the rod joints in the event of the bit burning in, being unnoticed by the operator, and causing a rod to shear at a rod joint higher up the drill string.

Another modification for any embodiment is that the mating faces may be coated with a suitable sealant of epoxy resin or silicone to hold the 10 parts together, ensure effective water sealing, and absorb backlash.

000 The sealant may deteriorate when heated and be selected such that, in **combination with shlear pins of lower shear strength, it provides the 0o oo, required longitudinal shear strength. In this event the !shear strength ooa is maintained during normal use, but decreases because of deterioration of the epoxy resin when the bit becomes heated. However, the decrease Sis such that force is still required to break the coupling device longitudinally whereby an attempt can still be made to withdraw the ,oO drill bit. Should the drill bit burn in to such an extent that it 0 0 cannot be extracted, then the coupling device will break.

0 0o oo 20 While not shown in the drawings, a plurality of coupling devices can be used along the length of the drill string, with the shear strength of each of the coupling devices increasing upwardly. For example the lower- ':oo most coupling may have a shear strength of 3 tonnes, the next 4 tonnes, o O 5 the next 5 tonnes and so on, with the couplings being spaced at 200m.

intervals. This construction permits the drill string to be broken at the lowest point possible consistent with where the drill string has become jammed. For example if it has jammed a few hundred metres above the drill bit, then the coupling at, say, 400m will break while the couplings above it will not break. The remaining portion of the drill string may be left in the hole with wedging taking place immediately above the break, since it .is known that the drill str'ing below the break is jammed and little purpose would to be served in trying to fish for the remaining section.

The appended claims are to be regarded as an integral part of the present disclosure.

page 17

Claims (15)

1. Coupling means for core drilling equipment including first and second. tubular members one of which is an inner member that has a portion that fits into the other member which is an outer member; torque means connecting the members to each other to transmit torque from one to the other; and shear means connecting the members longitudinally to one another and comprising a frangible pin member, with the pin member extending substantially radially with respect to the tubular members between the interfitted portions of the tubular members, being constructed to shear to allow the members to separate longitudinally when a predetermined tensile force applied to the coupling means is exceeded, and being welded to the outer member.

2. The coupling means of claim 1, wherein the torque means is constructed such that insignificant shearing forces are applied tl to the shear means when the drill string is rotated or compressed in use.

3. The coupling means of either of claims 1 or 2, wherein the first and second members are substantially circular in cross-secti on. 4t4. The coupling means of any of claims 1 to 3, wherein means is provided to seal the interfitted portions of the tubular members Sto each other in a watertight mariner. The coupling means of any of claims 1 to 4, wherein the first and second members have longitudinally opposed mating shoulders for transmitting compressive forces between the each other.

6. The coupling means of any of claims 1 to 5, wherein the pin member is engaged by means of complementary screw thread formations with at least the outer member. 71 3A'R o: J~ page 6 I 19

7. The coupling means of any of claims 1 to 6, wherein the torque means comprises engaged, substantially mating profiles on the first and second members.

8. The coupling means of claim 7, wherein the torque means comprises longitudinally extending dogs.

9. The coupling mearis of any of claims 1 to 6, wherein the torque means comprises at ieat one pin which is fixed to one of the members and engages in a longitudinal slot in the other member with the slot intersecting the end of the member. The coupling means of any of claims 1 to 9, wherein the shear means further comprises at least one annular weakened zone in at least one of the members, the zone being formed to shear when a predetermined tensile force acting between the members is exceeded.

11. The coupling means of any of claims 1 to 10, wherein the 4 a predetermined tensile force is at least 3 tonnes.

12. The coupling means of any of claims 1 to 11, wherein the coupling means is constructed as an end portion of an element of a drill string, with one of the members of the coupling means having a suitable threaded f'ormation for connection into a further element of the drill string and the other of the member. of the coupling means being integral with the end region of the element of the drill string of which it forms a portion

13. The coupling means of any of claims 1 to 11, wherein the Scoupling means has for connecting the coupling means into a drill string. r

14. The coupling means of any of claims 1 to 13, wherein the coupling device is constructed as a reaming shell, with matrix slugs being provided on the outer surface of at least one of the members. Drilling equipment for core drilling including at least one coupling means as claimed in any of claims 1 to 14. i I /26351 I RA17\ 7 -v l

16. Drilling equipment including:- a drill bit having a body and a matrix of drilling material at its forward end; a core barrel assembly having a care barrel shell, a core cage and a core cage seat on the core cage; and a coupling means as claimed in claim 1, with the first member being immediately adjacent to the drill bit, the second member being adjacent to and being connected to the core barrel shell, and the coupling means including a cage load seat constructed to engage the c'ore cage seat of the core barrel assembly.

17. A method of facilitating the recovery of drilling equipment comprising a drill string at the distal end of which is a core barrel assembly and a drill bit including the steps of:- coupling the core barrel assembly to the drill bit by coupling a r means comprising two members connected by shear means adapted to shear when a predetermined criterion is met and by torque means to transmit torque between the members; applying a tensile force to the drill string to cause the shear means to shear when the bit becomes burnt in; withdrawing the drill string above the coupling means by 'y separating thie members of the coupling device, with a portion of one of the two members of the coupling means remaining in a hble being drilled; a, connecting another coupling means and drill bit to the end of #,si the withdrawn drill string; replacing the drill string in the hole being drilled; and drilling through the remaining portion of the original coupling device and the burnt in drill bit and thereafter continuing drilling operations. t i i i--r~l ~~~Ueri~r 0 .4 4t 21

18. A coupling means for core drilling equipment, the coupling means being substantially as hereinbefore described with reference to the -accompanying drawings.

19. A drilling equipment substantially as hereinbefore described with reference to the accompanying drawings. A method for facilitating the recovery of drilling equipment, the method being substantially as hereinbefore described with reference to the accompanying drawings. DATED this TWENTY-SEVENTH day of NOVEMBER 1990 Desmond Edward Beswick Patent Attorneys for the Applicant SSPRUSON FERGUSON I 49 4 4 06 4 I 0 4 6 t ;/26351