US 3656564 A
A drilling system employing casing as drill pipe and a bit assembly which is bodily insertible and removable through the casing and releasably attachable thereto for rotation with the casing.
Claims available in
Description (OCR text may contain errors)
United States Patent Brown [151 3,656,54 [451 Apr. 18, 197
 APPARATUS FOR ROTARY DRILLING OF WELLS USING CASING AS THE DRILL PIPE  Inventor: Cicero C. Brown, c/o Brown Oil Tools, Inc. P.O. Box 19236, Houston, Tex. 77024  Filed: Dec.3, 1970 21 Appl. No.: 94,909
Related 0.8. Application Data Continuation-impart of Ser. No. 778,509, Nov. 25, 1968, Pat. No. 3,552,507, and a continuation-in-part of Ser. No. 803,911, Mar. 3, 1969, Pat. No. 3,552,508, and a continuation-in-part of Ser. No. 857,046, Sept. 11, 1969, Pat. No. 3,552,509, and a continuation-in-part of Ser. No. 864,747, Oct. 8, 1969, Pat. No. 3,552,510.
Primary Examiner-James A. Leppink Attorney-R. Werlin  ABSTRACT A drilling system employing casing as drill pipe and a bit assembly which is bodily insertible and removable through the casing and releasably attachable thereto for rotation with the casing.
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PATENTEDAPR 18 m2 SHEET 1 [IF 4 WWW ATTORNEY PATENTEDAPMBIQIE sum 20F 4 A TTOENEY PATENTEDAPR 18 I972 sum u 0F 4 A TToe/vsy APPARATUS FOR ROTARY DRILLING OF WELLS USING CASING AS THE DRILL PIPE RELATED APPLICATIONS This application is a continuation-in-part of my co-pending applications, Ser. No. 778,509, filed Nov. 25, 1968 now U.S. Pat. No. 3,552,507; Ser. No. 803,911, filed Mar. 3, 1969 now U.S. Pat. No. 3,552,508; Ser. No. 857,046, filed Sept. 11, 1969 now U.S. Pat. No. 3,552,509; and Ser. No. 864,747, filed Oct. 8, 1969 now U.S. Pat. No. 3,552,510.
In the drilling of wells for oil and gas, for example, by the rotary method, the drilling is conventionally done by the employment of relatively small diameter string of drill pipe to which a bit is secured, the entire string being rotated to drill the bore hole. After a suitable internal has been drilled, sometimes only a short distance but at other times for the full depth of the well, casing larger in diameter than the drill pipe will be run into the bore hole and subsequently cemented to seal off the formations through which the bore hole extends. This necessarily involves the series of operations in which the drill string must be extended as the hole deepens, as by the addition of sections to the drill pipe, and also the entire drill string must be withdrawn whenever it becomes necessary to replace the bit and then re-insert it to resume drilling. Thus making of such so-called round trips are not only time-consuming but also create hazards of blowouts and other undesirable conditions in the well. After the appropriate drilling of the hole has been completed, the drill string must be withdrawn and easing run to the desired depth. This, too, may present hazards because with the drill string out of the well, control of the well becomes more difficult.
Heretofore numerous efforts have been made to provide a system employing the casing itself as the drill pipe in order to overcome some of the hazards enumerated, as well as time loss. However, these prior efforts have not proven satisfactory for various reasons well-known to those skilled in the art.
The present invention, therefore, is directed to an improved arrangement by which the casing may be employed as the drilling string and when used in combination with a retractable or removable bit section will perform all of the functions of drilling and casing of a well in a sequence of series of operations which thereby greatly facilitates drilling operations.
In accordance with the present invention a bit assembly is provided which includes both the primary bit and a plurality of radially extendible and retractable underreamers, the entire bit assembly being arranged and constructed to be insertible bodily through the bore of the casing and moved to the lower end of the casing either on a wire line tool string or by simply dropping it into the casing, where, either by gravity alone or supplemented by pumped fluid pressure, the bit assembly will be forced to the bottom of the lower end of the casing string, which is provided with a landing shoe to receive the bit assembly. The bit assembly is provided with anchor or latch means engageable with appropriate latch grooves or other anchor-engaging structure in the landing shoe. The latter, in the illustrative embodiments, includes a landing shoulder on which the bit assembly is landed and appropriate spline slots to receive the extended underreamer arms to lock the bit assembly to the casing against relative rotation whereby rotation of the casing string will be effective to rotate the bit for purposes of drilling the well.
The bit assembly also includes connector means pivotally connected by crank means to the underreamers which will be actuatable from the upper end of the casing string by a suitable running tool by mechanical means or by hydrostatic force, as by drilling fluid circulating through the system, for purpose of extending or actuating the underreamers so as to enlarge the bore hole drilled by the pilot bit sufficiently to allow free downward movement of the casing behind the bit as the hole is being drilled.
Additionally, the bit assembly includes a fluid circulation passageway controlled by a by-pass valve means which is normally open to allow by-passing of fluid while the bit section is being inserted through the casing into the landing shoe or being withdrawn therefrom but which is closeable in response to the movement of the connector means to the underreamerextending positionto direct and confine fluid flow to the bit discharge passages while drilling. This valve arrangement assures high velocity wash fluid and minimizes wash fluid requirements.
Novel lock means are provided to lock the underreamers in extended position contemporaneously with the closing of the y-pass valve means and additional lock means are provided to actuate and release the anchor elements employed to anchor the bit assembly to the landing shoe.
To withdraw the bit assembly a conventional fishing tool or spear is run into the casing on a wire line and connected to anchor-releasing elements of the bit assembly, whereby an upward pull applied to the fishing tool will be effective to retract the underreamers and release the bit assembly from the landing shoe to which it has been anchored. The spacing arrangement between the underreamers and anchor elements is so designed as to assure that the underreamers are fully retracted before the bit section is released, thereby avoiding damage to the underreamers which might otherwise occur if they were not completely retracted when they pass through the lower end of the landing shoe.
Other and more specific objects and advantages of this invention will become more readily apparent from the following detailed description when read in conjunction with the accompanying drawing which illustrates a useful embodiment and modification thereof in accordance with the present invention.
In the drawing:
FIG. 1 is a longitudinal, sectional view showing the bit assembly run on a wire line tool and inserted into the landing shoe preparatory to anchoring the bit assembly to the landing shoe;
FIG. 2 is a partial view generally similar to FIG. 1 showing an intermediate stage in the operation of anchoring the bit assembly to the landing shoe and with the underreamers in their extended position;
FIG. 3 is a partial view generally similar to FIG. 2 showing the bit assembly in drilling position with the running tool being withdrawn from the casing;
FIG. 4 is a view similar to FIG. 3 showing a retrieving tool inserted in the bit assembly preparatory to withdrawing the latter from the landing shoe;
FIG. 5 is a view similar to FIG. 4 showing the parts in released position for withdrawal by the retrieving tool;
FIG. 6 is a cross-sectional view taken on lines 6-6 of FIG.
FIGS. 7 and 8 are cross-sectional views taken on lines 7-7 and 8-8, respectively, of FIG. 2;
FIG. 9 is a cross-sectional view taken on line 99 of FIG. 3;
FIGS. 10, 11 and 12 are partial sectional views illustrating modifications of the pilot bit portion of the bit assembly;
FIG. 13 is a cross-sectional view taken along line 13l3 of FIG. 10;
FIG. 14 is a cross-sectional view taken along line 14-14 of FIG. 12; and
FIG. 15 is a detail of an underreamer cutter seal.
Referring to the drawing, the landing shoe 10 and bit assembly B comprise the basic drilling structure which is secured to the casing. Shoe 10 is provided with an internally threaded socket 12 by which it is threadedly secured to the lower end of casing C. Adjacent its lower end shoe 10 is provided with an internal shoulder 11 on which the bit assembly will land initially when lowered through the casing.
Bit assembly 13 comprises a generally tubular body 16 having a bore 17 and is dimensioned to be freely insertible bodily through the bore of casing C into the bore of shoe 10. Body 16 is provided about an intermediate portion thereof with an external shoulder 18 adapted to seat initially on shoulder 11 when the bit assembly is lowered into the shoe. An annular seal ring 20 is disposed about the exterior of body 16 above shoulder 18 to seal with the bore wall of shoe 10.
At a point above seal ring 20, body 16 is enlarged in internal diameter defining an upwardly facing internal shoulder 19. The enlarged diameter portion 21 forms a cage which is provided with a plurality of angularly spaced generally rectangular radial windows or openings 22 in which are mounted anchor dogs 24 corresponding generally in shape to openings 22 and adapted when projected outwardly to be received in an annular anchoring groove 26 formed in the bore wall of shoe 10. The inner end faces of the anchor dogs are stepped downwardly to define upwardly facing shoulders 25 intermediate the upper and lower ends of the anchor dogs.
Groove 26 is formed at the upper end of an elongate annular recess 27 into which the anchor dogs are initially projectible before entering groove 26 as will be described more fully hereinafter. The anchor dogs are positioned in body 16 so that they will be in registration with recess 27 and below groove 26 when body 16 is seated on shoulder 11 (FIG. 1). The upper end of cage 21 is screwed into a cap ring 28 which overhangs the upper end of the body to define a downwardly facing annular shoulder 30 spaced from and opposing shoulder 19.
A setting sleeve 32, having an axial bore 33, is coaxially slidably disposed in bore 17 and is provided a short distance below its upper end with an external annular enlargement 31 defining upwardly facing annular shoulder 34 adapted to abut shoulder 30 in the running position of the tool (FIG. 1) and a downwardly facing annular shoulder 35 for purposes to be more fully described hereinafter.
At a point spaced below enlargement 31 setting sleeve 32 is provided with a second external enlargement 37 defining upwardly facing and downwardly facing shoulders 38 and 39, respectively.
A keeper ring or latching collar 36 is slidably mounted about setting sleeve 32 for longitudinal movement thereon between enlargements 31 and 37, the ring being shorter in length than the distance between the enlargements. Keeper ring 36 has a downwardly and inwardly stepped outer face complementing the stepped inner end faces of anchor dogs 24 and defining spaced shoulders 40 and 41 successively engageable with the upper inner edges of dogs 24 and with shoulders 25 on the anchor dogs in the course of projecting the anchor dogs as seen in FIGS. 1, 2 and 3. Shoulder 41 of the keeper ring rests on shoulder 38 of enlargement 37 in the running position of the tool (FIG. 1). A coil spring 42 surrounds sleeve 32 and is mounted in compression between shoulder 30 and the upper end of keeper ring 36 biasing the latter downwardly. The setting sleeve is provided wit a downwardly facing internal shoulder 43 which projects into bore 33 at a point generally opposite enlargement 37 for purposes to be described subsequently.
At a short distance below enlargement 37, sleeve 32 is provided with a plurality of radial windows or openings 44 in which are mounted lock dogs 45 which at a certain stage of operation of the tool, as will be described hereinafter, are adapted to be projected into an annular lock recess 46 provided in the wall of bore 17.
A lock sleeve 47 having an axial bore 48 is coaxially slidably disposed in bore 33 of the setting sleeve and is provided at an intermediate point with an external upwardly facing annular shoulder 49 adapted to abut shoulder 43 during retraction of the tool (FIG. 5). Lock sleeve 47 is provided with an external annular lock recess 50 adjacent its lower end spaced to be in registration with lock dogs 45 in the running position (FIG. 1) so as to allow lock dogs 45 to be in retracted position during running of the tool. Bore 48 of the lock sleeve is provided with an annular recess 48a intermediate its ends which is adapted for engagement by a retrieving tool as will appear subsequently.
The lower end of body 16 carries a downwardly facing internally threaded tubular socket 50a adapted to receive the externally threaded shank 51 of a bit 52 which constitutes the primary or pilot bit and may be of any conventional design for drilling a bore hole to any desired nominal diameter determined by the dimensions of the bit. Between shoulder 18 and socket 50a, body 16 is provided with a plurality of longitudinally extending radially opening slots 53 in which are mounted underreamers 54 of any suitable and known design mounted to arms 55. The latter are pivotally mounted on pivot pins 56 which extend transversely of the respective slots for enabling the underreamers to be angularly moved so as to be radially projected and retracted with respect to the slots 53. A tubular nozzle 57, having a bore 58 is secured to the lower end of lock sleeve 32 by means of an annular piston head 58a having a sliding sealed fit in bore 17. Nozzle 57 projects downwardly centrally of the tool. The lower end of nozzle 57 is provided with lateral ports 59 to define a sleeve valve which extends through a coaxial bore 60 in socket 50a fitted with an O-ring seal 61 arranged to control fluid flow from nozzle 57, when noule 57 is moved axially relative to socket 50a, as will be described subsequently.
Each of the underreamer arms 55 is fixedly connected to an angularly extending crank arm 62 having its free end secured to a crosshead pin 63 mounted in a crosshead groove 64 formed in the exterior of noule 57 at a point below piston 58a. With this arrangement it will be seen that the movement of nozzle 57 downwardly will act through crank arms 62 to rotate the underreamers outwardly and upwardly while reverse movement of the nozzle will act to retract the underreamers. The same movement of nozzle 57 will simultaneously function to open the valve means formed by sleeve valve ports 59 and the upper end of socket 50a. The intermediate portion of the latter is conically tapered to form sloping walls 61b which are provided with a plurality of jet nozzles 61a positioned to direct a spray of high pressure wash fluid against the underreamer cutters when the latter are in extended position (FIG. 2) to clean the surfaces of the cutters. The lower end of landing shoe 10 is provided with downwardly tapering spline slots 11a shaped to cooperate with arms 55 to limit the outward movement of the underreamers to the extent desired and to form a rotary drive connection between the shoe and the underreamers.
The device is designed to be run on a suitable running tool, designated generally by the letter R, which may, in turn, be run on a conventional sand or wire string, or on a string of tubing P. As illustrated tool R includes a tubular body 70 connectible at one end to the running string and having its other end abutting the upper end of lock sleeve 47. A collet ring 71 is slidably mounted about body 70 and is split to provide a plurality of spring collet fingers 72 terminating in enlarged heads 73 which initially are adapted to be latched in an annular recess 74 provided in the bore of setting sleeve 32 adjacent its upper end and to be held therein by the upper end of lock sleeve 47. A spacer ring 75 surrounds fingers 72 and extends between collet ring 71 and the upper end of setting sleeve 32. A keeper collar 76 surrounds the abutting end portion of spacer ring 75 and setting sleeve 32 and is pinned to spacer ring 75 by means of a shear pin 77. In this position the lower end of collar 76 bears against the upper end of cap 28 (FIG. 1). Cooperating shoulders 78 and 79 are provided on spacer ring 75 and collar 76 to retain the collar on the ring when shear pin 77 has been broken (FIG. 2) and the running tool is being withdrawn (FIG. 3). Setting sleeve 32 has an expansible split latch ring 80 mounted in the bore thereof just below recess 74 and lock sleeve 47 is provided with a matching latch recess 81 in its exterior adjacent its upper end to enable securing lock sleeve 47 to setting sleeve 32 upon relative downward movement of the lock sleeve as will be described subsequently.
In operation, the bit section secured to running tool R will be inserted into the upper end of casing C and will be lowered through the bore of the casing until the bit section is brought to a stop by the engagement of shoulder 18 on shoulder 11 in the landing shoe. At this stage, as the bit section is lowered into place, sleeve valve 59 will be above sea] 61 in the bit socket, permitting free by-passing of well bore fluids through the bore of bit section which might otherwise hinder the movement of the bit section through the casing. The parts of the bit section will be positioned as illustrated in FIG. 1 in which the setting sleeve is held in its retracted position by collet fingers 73 and shear pin 77. Anchor dogs 24 will thus be free to retract, whereby to allow the free movement of the bit section through the casing and into landing shoe 10. At the same time, lock dogs 45 will be in their retracted positions, as seen in FIG. 1.
Wlth the bit section thus in place in the landing shoe, downward jarring force is applied through the running string to break shear pin 77. Thereupon the downward force will be transmitted to setting sleeve 32, as well as to lock sleeve 47. The resulting downward movement of both sleeves will move latches 45 into recess 46 and latch ring 80 into recess 81, while shoulder 35 will contact the upper edge of keeper ring 36 to drive anchor dogs 24 into recess 27.
The downward movement of the setting sleeve will also be transmitted via nozzle 57 through the crosshead pins 63 and crank arms 62 to underreamer arms 55 to swing the underreamers outwardly toward their extended positions (FIG. 2).
Now, running tool R may be pulled upwardly while casing C is rotated and lowered to align slots 11a in the casing shoe with the underreamer arms to receive the latter and form therewith a rotary drive connection between casing C and the bit section (FIG. 3). This additional downward movement of the casing relative to the bit section will bring anchor recess 26 in registration with anchor dogs 24 which will then be projected outwardly into the recess by the pressure of spring 42 acting on keeper ring 36. As a result the bit section will now be effectively locked to the landing shoe in position to be rotated by rotation of the casing string.
The downward movement of nozzle 57 in effecting extension of the underreamers will move ports 59 of the sleeve valve below seal 61 and thereby direct wash fluid into the bit passages as well as to jets 61a.
With anchor dogs 24 locked into groove 27 and setting sleeve 32 and lock sleeve 47 in their respective locked positions as seen in FIG. 3, running tool R will be freed for withdrawal from its connection to the bit section and retrieval from the well.
The underreamers illustrated in FIGS. 1 to 5 employ a novel form of lubricant seal which has proven very useful in this portion of the bit structure heretofore described. As illustrated, each underreamer arm 55 carries a cylindrical shaft 85 on which the cutter 54 is rotably mounted by means of a central hub 86. A plurality of roller bearings 87 are appropriately arranged between hub 86 and shaft 85. A body of lubricant is introduced to the bearings through a duct 88 extending through the shaft. An outwardly opening one-way, lip-type seal 89 is mounted about shaft 85 between the inner end of hub 86 and the inner face of arm 55. As best seen in FIG. 15, seal 89 is mounted in a metal cup 90 which is dimensioned to provide a small amount of clearance about shaft 85 sufficient to allow the escape of lubricant expanding due to heat generated in the operation without causing destruction or blowout of the cutter seals which is a common occurrence in more conventional cutter designs.
When necessary to withdraw the bit section from the casing in order to replace or repair the pilot bit, underreamers or any other part of the bit section, a fishing tool, designated generally by the letter T, of the form illustrated and described in my co-pending application, Ser. No. 869,562, filed Oct. 27, 1969, or of any other generally conventional form, the details of which do not form a part of this invention, will be run into the casing bore on a wire line, or tubing string if desired, and will be latched into groove 48a of lock sleeve 47, as seen in FIGS. 4 and 5. n application of upward pull to the fishing string, the lock sleeve will be drawn upwardly bringing shoulders 49 and 43 in abutment (FIG. and placing lock recess 50 in registration with lock dogs 45, freeing the latter from recess 46. This same upward movement, now transmitted through abutting shoulders 37 and 46 will raise setting sleeve 32 a distance to raise keeper ring 36 sufiiciently to release anchor dogs 24 which will thus be free to retract from anchor groove 26. Additionally, the upward movement of the setting sleeve will be transmitted to nozzle 57 which will, in turn, raise sleeve valve 59 above seal 61 opening the by-pass valve to allow fluid to dump back into the well as the bit section is raised. Further the upward movement of nozzle 57 will rotate the underreamers back to their retracted position inside slots 53. The parts will now be in the same positions as when running into the casing (FIG. 1) and the entire bit section may now be withdrawn through the casing. I
When drilling is to be resumed, the bit section, with the parts in the original retracted positions, will be returned through the bore of the casing to its lodgment in shoe 10, the bit section anchored and the underreamers extended as described, and drilling will be resumed.
FIGS. 10 to 14 illustrate several modifications of the bit section, particularly in the mounting of the pilot bit to the bit body and in the lubricating systems for the pilot bits and underreamers.
In FIGS. 10 and 13 socket 50a is replaced by an annular plug having a bore 151 closed at its lower end by a wall 152. Three rotary cones 153 are releasably secured about plug 150 at 120? intervals by means of dovetail shanks 154 which are arranged to slide into longitudinally extending dovetail slots 155 formed in the exterior of plug 150 and are secured thereto by means of screws 156. Jets 157 mounted in end wall 152 are arranged to direct mud flush from nozzle 57 on cones 153.
Cutters 153 are mounted for rotation about shafts 158 integral with shanks 154. Anti-friction bearings 159 are provided between the cutters and the shafts and are lubricated through a duct 160 communicating with a lubricant reservoir 161 formed in shank 154 and closed by a sliding seal piston 162 which is exposed to the pressure of the mud flush in the bore of plug 150 by means of a duct 163 leading from bore 151 to the interior of reservoir outside piston 162.
When nozzle 57 is moved downwardly to close sleeve valve 159, fluid pressure from nozzle 57 will be directed through duct 163 against piston 162 thereby maintaining pressure on lubricant in reservoir 161 sufiicient to continuously force lubricant to the bearing surfaces. A portion of the fiuid will also be discharged through jets 157 against the cutting faces of cutters 153.
The lubricant system in the underreamers is also modified in that duct 88 is fed from a reservoir 188 fitted with a sliding seal piston 189 which is exposed to fluid pressure exteriorly of the bit section which produces a differential pressure across piston 189 sufiicient to feed lubricant slowly from reservoir 188 to the bearing surfaces of the underreamer.
FIG. 11 modifies the structure of FIG. 10 in that shank 254 which carries the cutters 253 is made integral with hollow plug 250 carried by the lower end of body 16. Lubricant reservoir 261 is formed in shank 254 and communicates with duct 260 leading to the cutter bearings. A differential area piston is mounted in reservoir 261 having its larger diameter section 262 disposed in reservoir 26] and its smaller diameter section 263 exposed to the fluid pressure in the bore of plug 250.
The lubricating system in the underreamers of this modification is the same as that in the modification illustrated in FIGS. 10 and 13.
FIGS. 12 and 14 illustrate a further modification of the cutter mountings of the pilot bit. In this instance the cutters are carried on shanks 354 which carry transverse dove-tail splines 355 which are received in complementary dove-tail grooves 356 which extend transversely of a plug 350 otherwise similar to plug 150 of FIGS. 10 and 13. The shanks are secured to the plugs by means of screws 357. The lubricating system in this modification is identical with'that shown in FIGS. 10 and 13, as is the lubricating system for the underreamers.
It will be understood that various changes and modifications may be made in the details of the illustrative embodiments within the scope of the appended claims but without departing from the spirit of the invention.
What I claim and desire to secure by Letters Patent is:
1. Apparatus for rotary drilling of wells using casing as the drill pipe, comprising:
a. a bit assembly bodily insertible and removable through the bore of a string of casing having a landing shoe on its lower end;
b. cooperating means on the bit assembly and said landing shoe for securing the bit assembly therein in non-rotative relation to the casing;
c. said bit assembly comprising:
i. a generally tubular body;
ii. radially movable anchor elements mounted on the body for releasably anchoring the body to said landing shoe;
iii. a sleeve member coaxially disposed in said body for reciprocation therein between upper and lower positions;
iv. a latching-collar longitudinally slidably mounted about said sleeve member cooperating with said anchor elements to respectively release and actuate the same in response to the movements of said sleeve member between said positions;
v. a main bit carried by the lower end of said body;
vi. a plurality of angularly spaced underreamers mounted on the body above said bit for radial movement between extended and retracted positions relative to said body;
vii. connector means pivotally connecting said sleeve member to said underreamers reciprocable with said sleeve member between said positions for respectively retracting and extending said underreamers; and
viii. releasable means initially securing said sleeve member to said body in said upper position.
2. Apparatus according to claim 1, wherein said bit section includes lock means carried by said sleeve member operable in response to movement of said sleeve member to said lower position to lock said sleeve member to said body in said lower position.
3. Apparatus according to claim 1 wherein said connector means includes sleeve valve means opening and closing fluid communication between the interior of said casing and said main bit.
4. Apparatus according to claim 1 including spring means normally biasing said latching collar toward the position actuating said anchor elements.
5. Apparatus according to Claim 1 wherein said cooperating means includes:
a. a tubular landing shoe secured to the lower end of the casing string;
b. radial slots in the lower end of said shoe spaced to receive the underreamers when moved to said extended positions.
6. Apparatus according to claim 1 wherein said underreamers include:
a. arm members pivotally secured to said body;
b. cutter shafts mounted to the outer end of said arm members;
c. frusto-conical cutters rotatably mounted on said shafts;
d. means for supplying lubricant between the related surfaces of said shafts and said cutters; and
e. outwardly opening uni-directional seal means between said surfaces.
7. In a bit assembly according to claim 1, means for securing said main bit to said body, comprising:
a. a hollow socket member carried by the lower end of said body;
b. a plurality of angularly spaced cutter-carrying shanks disposed about said socket member;
c. cooperating dove-tail spline means slidably connecting said shanks to said socket members; and
d. means for releasably securing said shanks to said socket member.
8. In a bit assembly according to claim 7:
a. toothed cutters rotatably supported by the outer ends of said shanks; I b. a self-contained lubricating system in each of said shanks operable in response to external fluid pressure to direct lubricant to the rotary surfaces of their respective cutters.