US2140417A

US2140417A - Core taker for rotary drills

Info

Publication number: US2140417A
Application number: US182122A
Authority: US
Inventors: Conklin Ancil Brooks
Original assignee: Individual
Current assignee: Individual
Priority date: 1937-12-28
Filing date: 1937-12-28
Publication date: 1938-12-13
Anticipated expiration: 1955-12-13

Description

Dec. 13, 1938. A. B. coNKLlN CORE TAKER FOR ROTARY DRILLS 2 Sheets-Sheet l Filed Dec. 28, 1 937 H-Blyon? Dec. 13, 1938. A. B, CONKLlN 2,140,417

CORE TAKER FOR ROTARY 'DRILLS Filed Deo. 28, 1957 2 Sheets-Sheet 2 56 WIW/11,10%

5.6107ZZZ '7l l mama ose. 13, 193s UNI-'raos'rA'rss PATENT OFFICEl 15 claims.

'rms invention relates to rotary weil arming mechanism using a tubular drill and drill pipe and particularly to means for drilling and taking cores as samples of the stratum in which the d rill isv working and by means of a wire line. In wire lln'e retractible core drills known to me, this core is rotated with the drill,y thus causing great friction on the core and burning and crystaillzing the core. An object of my invention is, therefore, to provide core taking means removable or retractible by a lwire line which includes an idling core barrel, that is, one which will not rotate with the drill and, therefore, not lrotate around the core being cut, but will permit the core to slip up into the barrel with a minimum of friction and thus provide means whereby to cut long uncontaminated cores which will reveal the true condition of theformation being drilled.

A further object is to so construct the core barreland allied parts that the core will reveal the true condition of the formation being drilled and provide means whereby the polarity of the core can be immediately determined upon the arrival oi the core on the derrick iloor.

A still further oblect is to provide a divided core barrel which greatly simplies ythe removal of the core, the barrel being so constructed that when it is withdrawn from the drill pipe it may be separated into two longitudinal halves permitting the removal-oi the core without any destruction or injury to the core itself and doing away with the necessity of pounding the core barrel onthe derrick floor in order to shake the core out and preventing the core from being otherwise deformed or injured in order to secure its removal from the barrel.

-A still further object is to provide a core catcher mounted upon the core drill, the core catchervor catchers being so formed that they will be operative either in soft or hard formations and iurther being so constructed as to greatly reduce the l number oi parts.

A further object in this connection is to pro- 0 Ividel core catchers which will nearly completely close the bore of the core barrel and which will out 'the core oil adjacent the bottom oi the main drill so that the operator will know :lust what the drill has penetrated. f

v ,'Still another object is to provide a water channel ,or duct in each blade of the main drilling bit so arranged and constructed as tojet the drilledy mud out through the rearside vof the blade and against the cutting edge oi the succeeding blade, thus keeping the blades at all times free from cut- (Cl. Z-72) tings, lengthening the life of the bit and preventing sticky formation from balling up on it.

Other more detailed objects will appear in the course of the following description.

My invention is illustrated in the-accompany- 5 ing drawings whereinz- Fig. 1 is a vertical section of a rotary well drilling and core taking mechanism constructed in accordance with my invention. 1 l Fig. 2 is an elevation oi the core bit and barrel, 10

the clamps being in section.

Fig. 3 is an elevation partly in section of the collar whereby rotary motion iscommunicated from the drilling bit tothe core bit.

Fig. 4 is an underside plan view of the collar l5 shown in Fig. 3. l

Fig. 5 is a section on the line 5-5 f Fig. 1.

Fig. 6 is a section on the line 6--8 of Fig. 1.

Fig. 7 is a side elevation of one of the core catchers.

Fig. 8 is a front elevation thereof.

Fig. '9 is a section on the lines-9 oi' Fig. 8.

Fig. 10 is a section on the line Ill-III oi Fig. 1.

Fig. 11 is a fragmentary sectional view through one of the blades oi' the main drill bit showing 25 the spraying; nozzle thereon.

Referring now particularly to Figs. 1 and 2, III designates generally the drilling bit. 'I'his drilling bit is of the box type having four blades II, as shown in Fig. 10, and in each o! these blades there is a vertical water duct I2. Two of these water ducts are shown in Fig. 1 and each water duct at its upper end is inwardly and upwardly inclined, as at I3, and opens upon the inner i'ace of the annular bit I Il. Each water duct I2 below 85 the root of the blade I I is extended rearward relative to the direction oi rotation oi' the bit and opens upon the rear face of the blade. Within this rearwardly extended'portion I4 there is disposed a nozzle I5 having a plurality of apertures 40 by means of which the liquid is directed to two different points along the cutting edge oi' the rear blade. (See Fig.`11.) While in Fig. 1, I have illustrated a four-blade, drag-type drilling bit, it is intended that there may be a hard-for- 46 mation roller type bit which will be interchangeable with the bit shown in Fig. 10. I have not illustrated this roller type of bit as this type of bit is well known and forms no part ci my invention in itself. The bit I0 at its upper end is in- 50 teriorly screw-threaded, as at I6, and coacting with this outwardly iiared screw-threaded portion is the tubular joint or section I1 which is approximately 10 ft. or more in length and which at its upper end is tapered and exteriorly screw- 55 pipe section |1 is formed with a plurality of 1ongitudinally extending grooves or channels I9 in order to permit of an increased quantity of liquid which is being pumped to the drilling bit by increasing the unobstructed area inside oi' this drill collar or pipe section I1. 'I'he utility of Athese grooves will appear more fully hereinafter. It will be seen that the drill collar I1 has a slightly tapered bore which will permit the passage of the core barrel assembly and that the interior diameter of the drill I0 is slightly greater than that of the drill collar but that at its lower end the drill I0 has an inwardly extending shoulder 2|). Just below the upper ends of the ducts |3, the interior face of the drill III is screw-threaded at 2 I, and disposed within the lower portion of the drill I9 and resting upon the shoulder 20 is a sleeve or bushing 22 which at its upper end is screwthreaded for engagement with the screw-threads 2 I. A clearance groove 23 is formed in the inner face of the drill I0 just below the screw-threads 2|. The bushing 22 at its lower end is formed at lopposite points with inwardly projecting thickened portions or

lugs

24 and 25, each of these lugs or thickened portions` being undercut, as at 28. The

spaces

21 and 28 between these lugs are of different widths, as shown clearly in Fig. 4, the space 21 being much wider than the space 28. These

lugs

24 and 25 constitute bayonet joints for a purpose to be laterstated. It may be remarked also that the threads 2| are left-hand threads.

Adapted to operate through the drill collar I1 and the drill I0 and through the tubular sections of the drilling string is the core barrel and core cutting mechanism shown particularly in Fig. 2 as removed from the drill.

This comprises the core cutter 29 which at its lower end is provided with the usual teeth 39.

.These teeth on this core cutter head 29 are slightly turned in at the cutting tip so that they will cut a core justa little smaller than the uniform interior diameter of the core cutter head which extends up to a point approximately even with the cutting edge of the blades of bit I0. This cutter head 29 has an exterior diameter slightly less than the interior diameter of the bit I 0 below the shoulder 2li, so that it may move easily through the central aperture in the lower end of the bit I0. The upper end of the cutter 29 is exteriorly screw-threaded at 30. Having screw-threaded engagement with threads 30 is a collar 3| formed, as shown in Fig. 2, with oppol sitely disposed downwardly extending

lugs

32 and 34. Each of these lugs has an angular extension 33 at its lower end. These

parts

32 and 34 constitute, with the

lugs

24 and 25, a bayonet joint connection. As illustrated in Fig. 2 in dotted lines, the opposed lug 34 is much narrower than the lug 32. This lug 34 iits within the recess 28 of the bushing 22 while the lug 32 iits within the recess 21 of this bushing. The necessity of providing lugs of different widths and making the

spaces

21 and 28 of different widths will appear more fully` hereinafter.

As illustrated in Fig. 1, the upper end of the collar 3| is formed with an annular channel 35. From Fig. 1, it will be seen that the core cutting head 29 has a uniform interior diameter up to a point approximately even with the cutting edge of the blades of the drill bit I0 and that from there on, the interior of core cutter 29 gradually increases in diameter slightly and the internal diameter of the collar 3| is equal to the interior diameter ofthe upper end ofthe core cutting head 29.

IDisposed above the collar 3| and extending upward within the pipe` sectior I1 and having a length of approximately 10 ft..is the'core barrel designated generally 36. This core barrel is formed in two interchangeable halves, lthe line of separation between the two halves of the core barrel being designated 31 in Fig. 1. as both halves are alike and inasmuch as both halves when placed together form a cylindrical core barrel, the core barrel will be described as a unit. This core barrel is formed at at least two, and preferably three, points along its length with annular grooves 38. One of these grooves is shown as being disposed adjacent the lower end of the core barrel, the other groove adjacent the upper end of the core barrel. These grooves are for the reception of split rings 39 shown in Fig. 5,

which rings act to hold the two sections of the core barrel in closed relation. The split rings are resilient so that they may be expanded and taken off the core barrel in order to permit the sections of the core barrel to be opened one from the other when the core barrel is taken out of the hole.

'I'he lower end of the core barrel has an external diameter less than and iitting loosely within the internal diameter of the bushing 22. At its lower end the core barrel is recessed so as to provide an inwardly extending annular flange 4|)v which extends into the groove 35 of collar 3|. The recess extends upward above the upper end of the collar 3| to provide for the reception of opposed raceways 4|, there being bearing balls disposed in these raceways. Thus thel collar 3| has xed engagement with the core cuter 29 (that is, it rotates with the cutter head 29) but has rotative 'engagement with the core barrel 38. The core barrel adjacent its upperend is annularly recessed at 42 and the upper extremity of the core barrel is upwardly and inwardly tapered at 43. Set within the upper end of the core barrel is the cylindrical valve cage 44 having a flange 45 at its lower end which nts within the annular recess 42. 'I'he exterior diameter of this cage is equal to the interior diameter of the upper end of the core barrel and the lower end of the cage is formed with a seat 46 for a ball valve 41. The

4upper end of the cage is closed' by a plug 48 having a plurality of longitudinally extending apertures 49 in it and having a central interiorly screw-threaded hub into which the spear head and pull bar 50 is screwed, this pull bar having at itsv upper end the usual tapering spear head wherewith the locking dogs of an overshot may be engaged to permit the core barrel and allied parts to be drawn to the surface. The exterior diameter of the core barrel is reduced between its upper end portion and the middle portion, as at 5|, and between this middle portion and the lower end portion of the core barrel there is a second reduction 52, these reduced portions being for the purpose of permitting the free passage of liquid.

It will be noted from Fig. l, that the .grooves I9 are disposed opposite the relatively large diameter of the upper end of the core barrel andthe `weightof the core barrel assembly from the bushing 22, and rotated approximately half a turn in a counterclockwise direction. 'Ihis will cause the collars 22 and 3l to become unlocked.- The overshot is then run on the wire line and the core barrel assembly withdrawn. When the assembly reaches the derrick floor, the overshot is released from the spear head 50 and the barrel 36 laid in ahorizontal position. The clamps 39 are then removed and one-half of vthe, idling inner barrel is removed from the core. This core may then be removed from the other half of the core barrel, if desired; if another core is desired, the assembly is made up as before and dropped into the well. Y

It is to be understood that where drilling is being done without coring, there is a center bit which is dropped into place within the drill I and takes the place of the core barrel assembly. This center bit fits into the main bit I0 in exactly the same manner as the core barrel does but instead of cutting a core,.it serves as a continuation of the cutting edges of the main drilling bit I0, closing the hole in the lower end of the bit. The center bit may be provided with a spear head so a's to be retrieved in the same manner as the core barrel.

'I'he advantages of this construction are many. The idling inner core barrel 36 which has swiveled engagement with the core cutter 29 eliminates the burning effect caused by the core barrel revolving around the corey and prevents the core from becoming crystallized. If the core is crystallized, this condition by no means represents a true sample of the formation from which the core was taken. In my construction, the only movement of the core barrel is to slip gradually over the core as the drilling progresses and the main drill bit I0 and the core cutter 29 move downward. With my arrangement, due to the posiy tion of the teeth in the core cutter, the 'gradual increase in diameter in the upper portion of the core cutter 29 and the downward taper at the lower end of the core cutter with the idling inner barrel, it is possible to cut long cores. 'I'he core being uninjured by burning or crystallization will reveal the true condition of the formation being drilled and the polarity of which can immediately be determined.

'Ihe divided core barrel 36 greatly simplifies the removal of the core. It eliminates the use of any sort of core removing device such as screws, jacks, rams or \hydrauli'c pumps. It does away with the necessity of pounding the core barrel on the derrick floor in-an attempt to get the core out and it. does'away with the necessity of washing out the core with water.

Since the core cutter 29 and the collar 3| will interlock with the drilling bit I0 in only one position of the collar '3| with relation to the bushing 22, it is possible, by noting the position of thebushing 22 in relation to the bit and by "orienting the drill pipe in the well, to determine the polarity of the core immediately on its arrival on the derrick floor.

It is common practice to orient a drill pipe,

that is, tokeep a check on the position of theA first joint of the drill pipe in order to control the direction of drilling to thus bring back or keep the drilling bit under the lease or control the direction of drilling where directionalrelief wells are Vbeing drilled. Inasmuch as it is possible to orient or keep a. check on the drill bit and since my core barrel will fit the drill bit in only one position, the operator will know by observing a mark on the last joint of the drill pipe the exact position of the core barrel at the time when the drill pipe is raised to cause the core catchers to shear off the core. After the core is sheared off, the lowest unbroken section of core in the barrel will not change its position in relation to the core catcher and core cutter head, that is, the core drill, and so by4 noting the position of the two locking extensions 'on the collar 3| which differ greatly in size, the operator will know, when the assembly is reeled to the surf ace, which side of the core is the north side. By this means, the polar-` ity of the core, that is, which part of the core was pointing toward the north before it was removed from the earth, may be readily determined.

At the present time, it is necessary to ship the core to a distant laboratory in order to obtain this information. Byproviding'means whereby the polarity of the core may be known, it is possible to determine the direction and approximate amount of dip or strike in the sub-surface formation in which the drilling is being done, and this information is particularly valuable in the case of Wildcat drilling or where the boundary of a newly discovered field has not been established.

'Ihe specially formed water-course in each blade of the drilling bit i0 serves to jet the drilling mud out through the rear face of the blade and against the cutting edge of the following.

blade. This keeps the blades at all times free of cuttings, lengthening the life of the bit and preventing sticky formation from balling the bit up.

In rotary drilling; the mud ywhich is pumped from the slush pit up through the swivel joint and down through the drill pipe to the drilling bit is caused to whirl by the rotation of the drill pipe. This motion is clockwise and it is in order to keep the mud from causing the idling inner barrel to revolve that the spiral fins 53 are provided, which are arranged so that the mud in its downward movement strikes the fins and this offsets the fluid friction between the mud and the exterior surface of the core barrel assembly, making it possible for the core barrel assembly to remain in a stationary position.

Particular attention is called to the fact that the core catchers 54 are combination hard and soft core catchers; that is, they are so hard, sharp and rigid that they will shear off the hardest cores and when they have moved down to a posi-` tion across the barrel and at right angles thereto, they practically completely close the core barrel so that the very softest and most unconsolidated cores will not sift or leak through between or around the catchers. In other core-taking structures known to me, the hard formation catchers by no manner of means close the barrel but would permit the escape of soft cores, while the soft formation catchers are in the form of easily exed springs which move asidevto permit the inward movement of the core and then wad up in the core to prevent the core from vdropping out. Such springs as these could not possibly cut into a hard core. 1

What is claimed is:-

1. A core taking assembly for rotary drills, including a core cutting bit, means constructed and arranged for detachably connecting the core cutting bit with the rotary drill for unitary rotary movementin one direction but disconnecting the core cutting bit from the drill upon a rotary movement of the drill in the other direction to .thereby permit the'litting of the core taking as- 75 and below the grooves I9. n the reduced portion 5| and disposed upon the exterior of the Acore barrel arethe two spiral ns 53 which extend spirally through 180 in the same direction to each other, there being a iin on each section of the core barrel. These fins serve to o'set the twist imparted -to the core barrel by the whirling column of mud which is being pumped down through the drill vpipe and through the section I1 and out through the ducts I2.

Mounted within the core cutter 29 approximately opposite the extreme Vlower end of the main drill In are a plurality of core catchers which in a sense act as pawls in that they are so mounted that they permit the upward movement of the core within the drill but as soon as the drill is pulled upward and the tendency of the core is to move downward with relation thereto, the core catchers will turn upon their pivots and cut through the core and hold the upper portion of the core from any downward movement. These core catchers are shown in detail in Figs. 6 to 9.

As illustrated in Fig. 8, each core catcher 54 is approximately triangular in shape except that the lower edge 55 is curved on the same radius,l as the radius of the inside diameter of the core cutter, so that when they are swung downward to a horizontal position, this curved rear edge will fit closely against the inner face of the core cutter. The inside surface of each catcher 54 is also curved, as shown in Fig. 9, at 56, to the same radius as that of the inside diameter of the part 29 so that while in drilling position, except for the sharp inwardly extending' points51, each core catcher will t ilush into the wall of the core cutter, allowing the core to pass freely. The sharp chisel point 51 which forms the upper tip of the catcher does not recede into the wall but projects slightly inward and upward, as shown in Fig. 1, so that when the main bit I0 ls raised slightly, the points of the catchers will dig into the core. Each core catcher is so shaped that once it is started inward upon a lifting movement applied to the `rnain bit I0, the core catcher will swing readily toward the center of the core cutter, shearing off the core and closing the bore of the core cutter. The core catchers can only drop to a horizontal position due to the fact that the extreme right and left-hand portions of the curved back 55 will come in contact with the wall of core cutter 29 when the catchers have dropped to a horizontal position. Each core catcher is formed with a reinforcing rib 58 at its back and this rib is extended/downward to form a lug 59 having an elongated or elliptical passage 60 through it and through this passage passes the pivot pin 6I shown in dotted lines in Fig. 6. The passageways for these-pins. 6I are formed in the wall of the core bit 29, opening upon the outer face of the core blt so as to permit the insertion and withdrawal of these pivot pins. By forming the opening 60 elliptical, each core catcher will be free to move up or down slightly so that when the device is raised to close the core catchers, the downward pressure of the core on the sharp tip of the core catcher will not be supported on the pivot pin 6I but on the end of the core catcher and the seat Within which the core catcher rests, each seat being formed by a recess in the wall of cutter head 29, as shown best in Figs. l and 6.

Attention is again called to the fact that the

spaces

21 and 28 between the

lugs

24 and 25 in bushing 22 are considerably different in width and that the two extensions or lugs 32 and 34 differ in width and each can only llt in the

corresponding space

21 or 28 .'A'I'his is a'very important feature of my invention as this prevents the core barrel from bein" vinserted fully into the drill IIl except in onejposition of the parts. It will-be noted that the interior diameter of the collar 3| at the extensions -32 and k34 is slightly greater than`the external diameter of the threads Y3|! on the upper endof the core cutter 29, so that these

extensions

32 and 34 will slip down over the core cutter head 29 when the two parts are screwed together. i

In assembling the parts, the core catchers 5,4 are put in place in the wall of the core cutter and fastened by the small pins 6|. The collar 3| is then screwed upon the upper end of the core cutter. The shank of the spear head 50 is then screwed into place after the ball 41 has been put in place, of course. 'I'he sleeve 22 is screwed into the upper end of the drill I9 and its position is noted if the implement is to be oriented in the drill hole. The raceways 4I containing the bearing balls are placed on top of the collar 3| and the two sections of the core barrel are then put in place so as to engage the flange 45 and engage the recess 35 of collar 3| and are clamped in place by the clamps 39. The assembly is then ready to be dropped down through the drill pipe. These parts, as assembled in the manner shown in Fig. 2, constitute the core barrel assembly.

The operation of this structure is as follows:

After the core barrel assembly, as shown in Fig. 2, has been dropped into the drill pipe and has reached the drilling bit I0, a Kelly joint is screwed into the drill pipe and the mud pump started. If circulation is possible, it will be because the collar 22 and the collar 3| are properly matched and are in position such that the bayonet joint formed by these parts will become locked on rotation. Assuming that the bayonet joint of the bushing 22 has been properly matched with the bayonet joint of the collar 3|, the'n drilling is continued until the desired length of core has been cut. If the bayonet joints of the bushing 22 and collar 3| are not matched properly, circulation cannot be started because the core barrel will not have reached its lowest point in the bit I0 and the drill collar I1, consequently the lower shoulder on the core barrel 36 will not have passed out through the lower end of the drill collar I1 which tapers inwardly. Thus it will be known o that the core barrel assembly has not reached its lowest point in the drill` I0 and in the pipe section I1. This will be disclosed by the fact that circulation of the mud is not possible because the lower shoulder on the core barrel 36 has not passed through the lower end of the drill collar I1. In this case, it is necessary to raise the drill pipe a few feet bringing the drilling bit oi the bottom of the hole and then lower it slowly while.

rotating in a clockwise direction. This causes the collar 3| to change its position with relation to the bushing 22 and circulation is again attempted. This procedure is continued until the core drill and the vcore barrel have lowered sufiiciently so that the extensions or lugs 32 and 34 are in proper interlocking engagement with the bayonet joint at the lower end of the bushing 22.

When the core has been cut, the drill pipe is raised a foot or so, with the core barrel, which causes the triangular members 54 to dig into the core, shearing it off, these members 54 dropping to a horizontal position and closing the bore of the core cutter head 29. The drill pipe is then again lowered to drilling position which removes sembly from the rotary drill, and a core receiving barrel forming part of the assembly and disposed above the core cutting bit and having swiveledy connection therewith.

2. In a core taking assembly for rotary drills, a

core cutting bit, a core receiving barrel having above the bit, a collar having screw-threaded engagement with the upper end of the core cutting bit and having swiveled engagement with kthe lower end of the core receiving barrel, and antifriction bearings disposed between the upper end of the collar and an adjacent annular portion of the core receiving barrel.

4. In a core taking assembly for rotary drills, a core cutting bit, a core receiving barrel disposed above the bit, a collar having screw-threaded engagement with the upper end of the core cutting bit and having swiveled engagement with the lower end of the core receiving barrel, and antifriction bearings disposed between the upper end of the collar and an adjacent annular portion of the core receiving barrel, the core receiving barrel on its outer surface adjacent its upper end having -oppositely disposed ribs each extending spirally downward and around the barrel and the ribs extending in the same direction.

5. In a core taking assembly for rotary drills, a core receiving barrel formed in two longitudinal sections, and detachable split resilient rings embracing the two sections and holding the two sections of the barrel in engagement with each other to constitute a cylindrical barrel. 6. In combination with a tubular rotary drill, including an annular drilling bit, a core cutting bit disposed through the rotary drilling bit and projecting beyond the same, a core barrel swiveled to the upper end of the core cutting bit, the core cutting bit and the bar-rel being normally disposed within but being withdrawable from the main drilling bit, and coacting means on themain drilling bit and the core bit' constructed and arranged to secure interlocking engagement between the core cutting bit and the rotary drilling bit upon rotation of tlTe main drilling bit in one direction, said engagement being detachable upon a rotation of the main rotary drilling bit in the opposite direction to thus permit the bodily withdrawal of the core vcutting bit and barrel.

7. A core taking assembly for rotary drills, the rotary drill including an `annular main drilling bit, the assembly comprising a core cutting bit insertable through the main drilling bit, a core receiving barrel disposed above and operatively connected to the core cutting bit, and means constructed and arranged for detachably connecting the core cutting bit with the main drilling bitin only one predetermined position for unitary rotary movement in one direction but becoming disconnected therefrom upon a rotary movement of the main drilling bit in the other direction to thereby permit the lifting of the core taking assembly from the rotary drill by a wire line.

8. In combination, a tubular rotary drill string, including an annular main rotary drill at the lower end of the string,'a core cutting bit adapted to be disposed through the main drillingbit, a core receiving barrel operatively connected to the core cutting bit, coacting means on the confronting faces of the main drilling bit and'` the core cutting bit constructed and arranged to secure interlocking engagement between the core cutting bit and the main drilling bit upon a rotation of the main drilling bit in one direction, said engagement being detachable upon a rotation of the main drilling bit in the opposite direction to thereby permit the bodily lifting of the assembly through the rotary drill string, said means being constructed and arranged to prevent the interlocking of the core cutting bit with the main drilling bit except when the parts arein one predetermined position.

9. In combination, a tubular rotary drill string, including an annular main drill bit at the lower end of the string, a core cutting bit extending through the main drilling bit and having ,core' catching devices on its inner face, a core barrel operatively swiveled to the upper end of the core cutting bit and having an upwardly opening valve at its upper end, the inner face of the main drilling bit being formed to provide opposed angular inwardly projecting lugs spaced l from each other, the core cutting bit having complementary opposed angular lugs coacting with the iirst-named lugs to constitute'a bayonet joint, one of said last-named lugs having a width" greater than Ithe other of said lugs and the space between the like ends of the lrst-named lugs being wider thanthe space between the opposite ends of the first-named lugs whereby to prevent interlocking engagement between the said lugs on the 'main drill and core drill except when the parts are in predetermined position.

10. In combination, a tubular rotary drill string, including an annular main drilling bit at its lower end, the drilling bit having ducts leading from the interior of the drilling bit downward and discharging between the blades of the drilling bit, the interior face of the main drilling bit below said ducts being screw-threaded, a bushinghaving threaded engagement with said last-named threads and extending downward on the inside of the main drilling bit, the bushing at its lower end having opposed angular lugs projecting inward and spaced from each other, the space between the lugs at one end being wider than the space between the lugs at the other end and a core taking assembly insertable through said drill string and the bit, comprising an annular core bit having means on its inside face whereby to cut and retain a core within the bit upon an upward movement of the bit, a .collar having screw-threaded engagement with the upper end ofthe core cutting bit and having downwardly extending annular lugs constructed and arranged to have interlocking engagement with the lugs on the said bushing to form a bayonet joint connection, one of said lugs being narrower than the other lugy whereby to prevent the interlocking of the lugs on the main drill blt with the lugs on said bushing except when the parts are in one predetermined relation, the core receiving barrel having swiveled engagement at its lower end with said second-named collar, and anti-friction bearings disposed be ters disposed equi-'distantly around the inner 75 face of the drill, each cutter being aproximately triangular in facial elevation and the cutters together when lowered substantially closing the interior of the barrel and each cutter having its outer face formed with a longitudinally extending rib, the outer face on each side of said rib being transversely and longitudinally fiat and having its inner face transversely curved teilt ,the curvature of the annular barrel, the apex of each cutter being curved inwardly and longitudinally and the drill having recesses in which the cutters are normally disposed with their inner faces flush with the inner face of the core drill, each ,cutter being pivoted at its lower end to the walls of the corresponding recess.

12. In an annular core drill, a core cutting and supporting means, comprising a pluralityof cutters equi-distantly spaced around the inner face of the drill, each cutter being approximatelyV triangular in facial elevation and having a transversely curved inner face fitting the curvature of the annular drill, the apex of each cutter being longitudinally and inwardly curved, the drill having recesses in which the cutters are normally disposed, the lower edge of each cutter having a downwardly extending lug formed with a vertical Areceive said rings.

opening, and a.v pivot pin passi-ng through the opposed walls of each recess and Said opening.

13. In a core taking assembly for rotary drills, a core cutting bit, and a core receivingv barrel above the bit and having swiveied engagement at its lower end with the bit, the bit andV barrel helns withdrawable as a unit.

14. In a core taking assembly for rotary drills.

a core, cutting bit and a core receiving barrel.

rotary drill.

415. In a core taking assembly for rotary drills, ar core cutting bit and a core` receiving barrel having swiveied engagement with the bit, said barrel being longitudinally split throughout its ventire length to form two halves, andsplit resilient rings engaging around the barrel at separated points for holding said halves in ooaction with each other, the barrel being recessed'to y Anon.. Baooxs com iuml