Replaceable drill bit assembly

Information

  • Patent Grant
  • 6454024
  • Patent Number
    6,454,024
  • Date Filed
    Friday, October 27, 2000
    23 years ago
  • Date Issued
    Tuesday, September 24, 2002
    21 years ago
Abstract
In a retrievable drill bit assembly, a standard drill pipe or casing pipe has a sub threaded into its lower end which forms a seat coupling for upper rounded pivotal ends of a pair of drill bits which are pivotally mounted between a pair of lift plates. The drill bits have blades extending from the pivotal ends with hardened cutter elements in staggered relation along or adjacent to the leading edge and a fluid passage leading into a series of nozzles in the blades which together with the rotational force of the drill pipe and the frictional force of the blades on the material to be bored will cause the blades to assume and maintain a mutually perpendicular position. The blades or cutters can be retrieved by a retrieval apparatus for the purpose of removal and replacement with a new set of blades.
Description




P BACKGROUND AND FIELD OF INVENTION




This invention relates to rotary drill bits and more particularly relates to a novel and improved drill bit assembly which can be retrievably mounted at the lower end of a conventional drill string and has pivotal blade arms which can be expanded radially outwardly by fluid pressure combined with the rotational force of the drill string and the frictional force of the drill string weight on the material being bored.




Numerous types of retrievable drill bit assemblies have been devised for downhole or earth boring operations but in the past have been costly to manufacture and operate, time-consuming and not capable of performing different types of boring operations, such as, milling operations. Representative patents are U.S. Letters Patent Nos. 2,203,998 to D. J. O'Grady, 2,814,463 to A. W. Kammerer, Jr., 3,196,961 to A. W. Kammerer, 3,552,509 to C. C. Brown, 3,554,304 to H. D. Link et al, 3,656,564 to C. C. Brown, 3,684,041 to A. W. Kammerer et al and 5,271,472 to R. E. Leturno.




There is a continuing demand and need for drill bit assemblies which are highly versatile as well as efficient and durable in use and specifically are conformable for use as a drill bit tool, mill section tool or combinations thereof and can be utilized, with or without fluid assist, with retrievable or stationary bits, with or without jet kerf cutting, with or without a pilot nose, and with or without tungsten carbide buttons, cutting teeth, cutting rollers or polycrystalline diamond inserts. Most desirably, the drill bit assembly of the present invention incorporates a unique combination and arrangement of cutters and fluid passages along one or more blade arms of a drill bit assembly; and which is further characterized by being easily and quickly retrievable and replaceable.




SUMMARY OF THE INVENTION




It is therefore an object of the present invention to provide for a novel and improved drill bit assembly which is highly versatile and conformable for use in performing various earth boring operations.




It is another object of the present invention to provide for a novel and improved method and means for mounting a drill bit assembly or other tooling at the lower end of a conventional drill string or casing string to carry out various downhole operations.




It is a further object of the present invention to provide for a novel and improved method and means for mounting drill bits and other tools at the lower end of a conventional drill or casing string wherein the tools are quickly retrievable and replaceable.




It is a further object of the present invention to provide for a novel and improved drill bit assembly which employs a unique combination of cutting inserts and fluid passages to carry out downhole cutting operations; and specifically wherein the cutting elements may be employed alone or in combination with fluid pressure to perform different cutting and kerfing operations.




It is a still further object of the present invention to provide for a novel and improved drill bit assembly in which cutting inserts are immovably positioned along a leading edge of the blade arm forming a part of each drill bit; and in an alternate but preferred form to provide for a series of rotatable cutter disks spaced along an undersurface of each blade arm to carry out cutting operations.




The present invention resides in a drill bit assembly to be lowered on a drill or casing string into a subsurface formation in which a sub is connected to a lower end of the drill string, and a drill bit has a pair of blades arranged in juxtaposed relation to one another including pivotal ends mounted in the sub about a common pivot member and blade arms extending tangentially from the pivotal ends between a position extending substantially in an axial direction downwardly from the sub and a cutting position extending in opposed perpendicular directions with respect to the rotational axis of the drill string, and the blade arms have a series of cutting elements along one edge thereof.




In one preferred form, the cutting elements are inserted in recesses along the entire length of each blade arm and include an arcuate surface portion which protrudes from an undersurface of the blade arm. In addition, the cutting elements have flat surface portions substantially flush with the leading edge of the blade arm. In a second preferred form, the cutting elements are in the form of cutter disks which are journaled about individual roller shafts on the undersurface of each blade arm, the axis of rotation of each cutter disk being such that the disk rotates along a line which is tangential to the radius of curvature of the drill bit at that location.




In either preferred form, each of the blades has a fluid passage extending at least along the length of the blade arm and a plurality of fluid discharge bores communicating with the fluid passage for discharge of fluid under pressure from the passage in the form of high velocity streams cutting into the formation. Most desirably, the discharge means extend transversely of the passage through an undersurface of each blade and is defined by nozzles extending through the blade behind the cutting element. For most efficient cutting and removal of the formation being drilled, the nozzle locations are staggered with respect to the cutting element location so that the cutting elements break up the material between the kerf lines formed by the nozzles. For example, if the nozzles are disposed only along one of the blades and the cutting elements disposed only along the other of the blades, the cutting elements will break up that formation material between the kerf lines formed by the nozzles on the one blade. If the cutting elements are positioned on both blades, they are preferably staggered with respect to one another so as to engage different radial distances in the formation between the kerf lines, and correspondingly if the nozzles are positioned along both blades should be offset with respect to one another to form kerf lines at different radial distances and thereby achieve enhanced cutting action. The number and spacing of cutting elements and nozzles will of course vary with the hardness of material being drilled, hole size and velocity of the fluid discharged.




From the foregoing, the method of drilling into a subsurface formation comprises the steps of discharging a high velocity stream of fluid through a plurality of nozzles in at least one of a pair of rotating blades whereby a series of kerf lines are formed in concentric circles, and placing a series of cutting elements on at least one other of the blades to break up the formation material between the kerf lines formed by the jet streams through the nozzles. Whether the nozzles and cutting elements are positioned along one or both blades, most desirably the cutting elements are offset with respect to the path of the nozzles so as to break up the formation between the kerf lines formed by the nozzles. When rotating cutter disks are employed as the cutting elements, the disks are oriented to follow or track the kerf lines formed by the nozzles to assist in breaking up the rock or other material between the kerf lines.




As an added feature of the present invention, the pivot member for the blades is removably seated in the sub and lift plates extend upwardly from the sub having a latching device which is engageable by a retrieval bar so as to effect latching engagement between the retrieval bar and latching member for the purpose of lifting the drill bit out of the hole for replacement.




There has been outlined the salient features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. In this regard, the term “drill string” is employed herein to interchangeably refer to a rotating string of drill pipes or casings. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a view partially in section of a preferred form of drill bit assembly in accordance with the present invention with the drill bits shown in their operating position;





FIG. 2

is an elevational view of the assembly shown in

FIG. 1

;





FIG. 3

is another view similar to

FIG. 1

but illustrating the assembly at right angles to that shown in FIG.


1


and with the drill bits in their operating position;





FIG. 4

is a view partially in section of the preferred form of drill bit assembly shown at rest in further combination with a preferred form of bit retrieval apparatus;





FIG. 5

is an elevational view of the assembly shown in

FIG. 4

with the drill bits shown at rest;





FIG. 6

is a view partially in section of the assembly illustrated in

FIGS. 4 and 5

but taken at right angles to that of

FIGS. 4 and 5

;





FIG. 7

is a cross-sectional view enlarged of the preferred form of drill bit assembly and seal employed therein;





FIG. 8

is a cross-sectional view taken about lines


8





8


of

FIG. 7

;





FIGS. 9 and 10

are enlarged views in detail of each of the drill bits employed in the drill bit assembly of the present invention;





FIG. 11

is a cross-sectional view of the drill bit shown in FIG.


9


and illustrating the disposition of fluid passages in the drill bit;





FIG. 12

is an end view partially in section of the drill bit shown in

FIG. 11

;





FIG. 13

is a cross-sectional view of the drill bit illustrated in

FIG. 10

;





FIG. 14

is an end view partially in section of the drill bit illustrated in

FIG. 13

;





FIG. 15

is a bottom plan view of the one preferred form of drill bit assembly illustrated in

FIGS. 9

to


14


;





FIGS. 16 and 17

are enlarged views in elevation of each of the drill bits of a second preferred form of invention;





FIG. 18

is a bottom plan view of the second preferred form of drill bit assembly;





FIG. 19

is an elevational view of a portion of the retrieval apparatus shown with the latch member in a closed position;





FIG. 20

is an elevational view of the apparatus shown in

FIG. 19

with the latch member in the open position; and





FIG. 21

is an enlarged fragmentary view of the latching device as shown in FIG.


19


.











DETAILED DESCRIPTION OF PREFERRED EMBODIMENT




Referring in more detail to the drawings, there is shown in

FIGS. 1

to


3


a preferred form of invention in which a conventional drill pipe


10


is threadedly attached to a sub in the form of a seat coupling


11


for a pair of drill bits or blades


12


. Each drill bit includes an upper rounded pivotal end or collar


14


and a blade arm


16


, the collars


14


being journaled on a common pin


18


which extends transversely of the drill pipe


10


and supports the bits


12


for pivotal movement between a position extending substantially in a lengthwise direction of the drill pipe


10


when at rest and, when in operation, a transverse direction as illustrated in

FIGS. 6 and 1

, respectively. In this relation, the bits


12


are mounted on the pin


18


between a pair of lift plates


20


which extend upwardly from the pin


18


, the plates


20


having vertically spaced lift plate bolts


22


. Opposite ends of the pin


18


are slidable in grooves G in diametrically opposed sides of the coupling


11


and are shown seated at the lower ends of the grooves G. An annular seal


24


, shown in detail in

FIGS. 7 and 8

, is positioned above the bits


12


with the lift plates


20


extending upwardly through slots


25


in the seal


24


so as to confine the flow of fluid through the central opening


26


of the seal into fluid passages in the bits


12


in a manner to be hereinafter described.




Considering in more detail the mounting and construction of the bits


12


, as shown in FIGS.


9


to


15


, each of the blade arms


15


and


16


extends tangentially away from the collar


14


and has inserts


28


of a hardened cutting material inserted in circular recesses along a leading edge


30


of each blade arm


15


and


16


. The inserts


28


are in the form of cylindrical pins having their longitudinal axes extending perpendicular to the length of the arm


16


. Further, the greater diameter of each insert


28


is inserted into the thickness of the arm so that only a limited arcuate surface


28


′ protrudes from the undersurfaces


31


of the arms


15


and


16


. Additional inserts


29


extend transversely of the blade arm over a limited distance of the collar


14


as well as along a free terminal edge


32


of each blade arm


15


and


16


, as illustrated in

FIGS. 9 and 10

. More specifically,

FIGS. 9 and 10

illustrate the offset relationship between the inserts for the respective blade arms


15


and


16


as hereinafter described in more detail.




As shown in

FIGS. 11

to


15


, each of the blade arms


15


and


16


is preferably of generally rectangular cross-section and includes fluid passages made up of a first bore


34


which extends chordally through the collar


14


of the blade and a second bore


35


which extends substantially at right angles to the first bore


34


in a lengthwise direction throughout the full length of the blade arms


15


and


16


but at a gradual angle extending away from the inserts


28


. A series of nozzles or jets


38


communicate with the bore


35


and extend transversely therefrom to pass through the thickness of the blade arms


15


and


16


and discharge fluid as a high velocity stream at spaced intervals along the undersurfaces


31


of the blade arms


15


and


16


immediately behind the inserts


28


. Preferably, each nozzle or jet is in the form of a cylindrical body


39


provided with an inner tapered bore


40


which converges toward its discharge end, and the body is mounted within a discharge passage


41


by a suitable retainer ring


42


. A plug


37


at the extreme outer or free end of the blade arm


16


may similarly be defined by one of the nozzles


38


as described or, if desired to completely plug off the discharge end of the bore


35


may insert the solid cylindrical plug


37


as shown.




As best seen from

FIG. 15

which illustrates the undersurfaces


31


of the drill bits


12


, the inserts


28


on one blade arm are offset with respect to the inserts


28


on the other blade arm; and similarly, the jets


38


on the one blade arm


15


are offset or staggered with respect to the nozzles


38


on the other blade arm


16


. It is the primary function of the nozzles to form the kerf lines as illustrated in dotted form in

FIG. 15

, and thus the nozzles


38


on one blade arm will form the kerf lines K


1


, and the nozzles


38


on the other blade arm will form kerf lines K


2


between the kerf lines K


1


. It is the primary function of the cutter inserts


28


to break up the rock between the kerf lines K


1


and K


2


and therefore are aligned between the nozzles of their respective blade arms or, in other words, to break up the rock between the kerf lines formed by the nozzles. Accordingly, as seen from

FIG. 15

, as viewed from the bottom of the well bore or underside of the drill bits


12


, the cutting inserts or cutters


28


on the lefthand blade arm will traverse the rock or other material between the kerf lines K


1


formed by the jets


38


on the righthand blade


16


, assuming that the blades are rotating in a clockwise direction as viewed from above the blades. Conversely, the cutters


28


on the righthand blade will traverse the rock or other formation material between the kerf lines K


2


formed by the jets


38


on the lefthand blade


15


. Specifically, the cutting inserts


28


will operate to scrape or shear off the rock or formation material.




In the other preferred form of invention as shown in

FIGS. 16

to


18


, cutter disks


44


are mounted for rotation about individual roller shafts


45


which are affixed in recesses in the undersurface of the blade arms


15


′ and


16


′ immediately ahead of the nozzles or jets


38


. As best seen from the bottom view,

FIG. 18

, the axis of rotation for each disk


44


is such as to correspond to the radius of curvature which that disk


44


follows or, in other words, the shaft


45


for each bearing is oriented to be perpendicular to the radius of curvature at that point on the undersurfaces of the blade arms


15


′ and


16


′. The individual disks


44


are of a hardened material, such as, tungsten carbide or polycrystalline diamond material similar to that of the inserts


28


and have tapered surfaces which intersect or terminate in a cutting edge


46


which will follow the kerf line of the nozzle jet streams from the opposed blade at that particular point or radius as illustrated in FIG.


11


. In addition, cutting inserts


29


corresponding to the inserts


29


shown in

FIG. 15

may be positioned along the undersurface of the collar portion


14


of each drill bit


12


. The fluid is expelled from the circulation channels under sufficient pressure to kerf and remove the cuttings or at least weaken it for ease of removal by the disks


44


, after which the fluid and cuttings will move upwardly between the drill pipe


10


and face of the bore until expelled at the surface. It will be apparent that the term “fluid” as employed herein is intended to refer to any liquid, gas or mixture thereof which is customarily employed in earth boring or kerfing operations.




In order to retrieve and replace the bits


12


, such as, when the bits


12


or their inserts


28


become dull or worn, they may be removed by a retrieval bar


50


which is attached to the lower end


52


of a wireline W extending from a conventional surface block and tackle, winch or similar device to run tools in and out of the hole. The retrieval bar


50


is suspended from the lower looped end of the wireline W and includes centralizers


54


attached at vertically spaced intervals by suitable fasteners, such as, bolts


53


. A retrieval slot


55


at the lower end


51


of the bar


50


receives an upper one of the lift plate bolts


22


, all as illustrated in

FIGS. 4 and 6

. As illustrated in more detail in

FIGS. 19

to


21


, a latch assembly is mounted at the lower beveled end of the retrieval bar


50


and comprises a latch


56


which is pivotally connected alongside the slot


55


by latch pin


58


in a support block


60


which is welded to the lower end of the retrieval bar


50


. Anchor pins


61


and


62


are positioned at upper and lower ends of the support block


60


and a spring element


64


affixed to the latch


56


may be releasably attached to either one of the anchor pins


61


or


62


. For example, when blades


12


are to be retrieved from the hole, the spring


64


is attached so as to springload the latch


56


in a direction extending across the slot


55


so that when the latch


55


is lowered against the upper lift plate bolt


22


, the spring force will be overcome to pivot the latch upwardly until the bolt


22


clears the latch and the latch is then free to return to its original closed position. The wireline W is then lifted to pull the blades


12


out of the hole.




In lowering a new set of blades


12


into the hole, the spring


64


is released from the upper anchor


61


and attached to the lower anchor


62


so as to bias the latch


56


toward the open position away from the slot


55


. The upper lift plate bolt


22


for the new set of blades is positioned in the slot


55


and the latch


56


manually pivoted back into the closed position and the blade assembly then lowered until the weight of the bolt


22


is bearing against the latch


22


and the new blades then lowered by wireline into the drill pipe


10


until seated in the seat coupling


11


. Once the blade assembly is properly seated in the coupling


11


, continued lowering of the latch assembly to remove the weight of the upper bolt


22


from the latch


56


will permit the latch


56


to be pivoted upwardly under the urging of the spring


64


into the open position and the retrieval bar


50


can then be removed from the hole.




In use, the drill bits


12


are assembled with the lift plates


20


on the pin or shaft


18


and placed in the seat coupling


11


which is then threadedly attached to the drill pipe


10


. The lower lift plates


20


and pin are slidable through groove G in the seat coupling


11


until firmly seated in the lower end of the groove. The drill pipe


10


is then lowered into the formation to be bored and with rotational force applied to the drill pipe


10


, the blade arms


12


are swung outwardly into the drilling position as shown in FIG.


3


. Fluid is supplied under pressure into the circulation channels or bores


34


and


35


of the drill bits


12


and converted into high velocity jet streams by the nozzles


38


. The delivery of fluid under a high degree of force through the blades


12


will cooperate in maintaining the blades in a perpendicular position with respect to the drill pipe. Further, under frictional force applied by the material to be bored, the blade arms


12


will be maintained in the perpendicular position as described. The fluid which is pumped through the jet channels or nozzles


38


will form the kerf lines K


1


and K


2


except in extremely hard rock materials. In certain formations, the jet force will be sufficient without additional cutting elements to kerf and remove the material to be bored, or at least weaken the material for ease of removal by the blades


12


.




With the assistance of either form of the staggered or offset cutting elements


28


or


44


as described any remaining material is removed between the kerf lines, and the fluid will operate to carry any of the cuttings between the drill pipe


10


and face of the bore up to the surface.




When it is desired to retrieve the drill bits


12


resulting from becoming worn or broken or as a result of the nozzles


38


becoming enlarged and less effective, the retrieval apparatus is lowered by wireline W through the drill pipe


10


as illustrated in

FIGS. 4

to


6


. Centralizers


54


keep the retrieval bar


50


centered in the drill pipe


10


until the lower beveled end of the retrieval bar


50


contacts the upper lift plate bolt


22


. Continued downward movement will cause the latch


55


to open until the bolt


22


clears the latch


55


and is returned to a closed position by the spring


64


. The entire lift assembly is then drawn out of the seat coupling and lifted upwardly through the drill pipe by the wireline until completely removed from the drill pipe


10


.




Once the drill bits


12


are replaced or refurbished, the spring


64


is then reversed and attached as described so as to cause the latch


55


to be in a normally open position. Once the upper lift plate bolt


22


for the new or refurbished drill bit assembly is positioned in the slot


55


, the latch


56


is manually returned to the closed position and the bit assembly can then be lowered until seated in the seat coupling


11


. Once the weight of the drill bit At assembly is removed from the latch


56


, the spring


64


will open the latch to permit the wireline W and retrieval from the drill pipe so that boring can be resumed.




Milling and other operations as described can be carried out with the preferred forms of drill bit assemblies. In all wells, particularly those where the conventional changing of downhole tools is costly and time-consuming, or where varying different diameters of borehole are desired, the bit assemblies of the present invention are especially effective.




It is therefore to be understood that while preferred forms of invention are herein set forth and described, the above and other modifications and changes may be made without departing from the spirit and scope of the present invention as defined by the appended claims and reasonable equivalents thereof.



Claims
  • 1. In a drill bit assembly to be lowered on a drill string into a subsurface formation, the improvement comprising:a sub connected to a lower end of said drill string; and a drill bit having a pair of blades arranged in juxtaposed relation to one another including pivotal ends mounted in said sub about a common pivot member, and blade arms extending outwardly from said pivotal ends between a position extending substantially in an axial direction downwardly from said sub and a cutting position extending substantially in a perpendicular direction with respect to the rotational axis of said drill string, said blade arms having a series of cutting elements along a cutting edge thereof; and means for imparting a centrifugal force to said blade arms to cause said blade arms to swing outwardly in a perpendicular direction with respect to the rotational axis of said drill string.
  • 2. In an assembly according to claim 1, each of said cutting elements inserted in recesses along the substantial length of each said blade arms and along a free terminal edge of each of said blade arms.
  • 3. In an assembly according to claim 2 wherein each of said cutting elements includes an arcuate surface portion protruding from an undersurface of said blade arm.
  • 4. In an assembly according to claim 3 wherein each said blade arm is of generally rectangular cross-section and terminates in a squared end portion, at least one of said cutting elements being mounted in said squared portion.
  • 5. In an assembly according to claim 1, said centrifugal force-imparting means including means for rotating said drill string, a fluid passage extending at least along the length of said blade arm, and a plurality of fluid discharge means communicating with said fluid passage for discharging fluid under pressure from said fluid passage outwardly from said blade arm.
  • 6. In an assembly according to claim 5 wherein said discharge means extend transversely of said passage through an undersurface of said blade arm.
  • 7. In an assembly according to claim 6 wherein said discharge means is in the form of nozzles extending through said blade arm adjacent to said cutting elements, said nozzles on each said blade arm being disposed in offset relation to said cutting elements, said cutting elements on one of said blade arms aligned to engage said formation between kerf lines formed by said nozzles.
  • 8. In an assembly according to claim 1 wherein said pivot member is removably seated in said sub, lift plates extending upwardly from said sub having a latch release member at their upper ends, a retrieval bar including latch means at its lower end and arranged for downward extension through said drill string into latching engagement with said latch engaging member whereby to lift said drill bits out of said sub and through said drill string to the surface.
  • 9. In an assembly according to claim 8 wherein said latch means includes a slot in a lower end portion of said bar, a pivotal latch member mounted for extension across said slot, and means for yieldingly urging said latch member between a latching position extending across said slot and a released position away from said slot.
  • 10. In an assembly according to claim 9 wherein said urging means is reversibly mounted to selectively bias said latch either toward or away from said latching position.
  • 11. In an assembly according to claim 1 wherein said cutting elements are defined by cutter disks journaled for rotation independently of said blade arm.
  • 12. In a drill bit assembly to be lowered on a drill string into a subsurface formation, the improvement comprising:a sub connected to a lower end of said drill string; and a drill bit having a pair of blades arranged in juxtaposed relation to one another including pivotal ends mounted in said sub about a common pivot member, and blade arms extending tangentially from said pivotal ends between a position extending substantially in an axial direction downwardly from said sub and a cutting position extending substantially in a perpendicular direction with respect to the rotational axis of said drill string, said blade arms having a series of cutting elements, said cutting elements each defined by a cutter disk journaled for rotation independently of said blade arm along a surface of said blade arm engaging said formation.
  • 13. In an assembly according to claim 12, said cutting elements disposed along an undersurface of each said blade arm.
  • 14. In an assembly according to claim 13, wherein each said cutting element has a cutter disk provided with a tapered cutting edge.
  • 15. In an assembly according to claim 14 wherein each said blade arm is of generally rectangular cross-section and terminates in a squared end portion, said cutting elements being mounted in recesses in said blade arm.
  • 16. In an assembly according to claim 12, each of said drill bits including a fluid passage extending at least along the length of said blade arm, and a plurality of discharge means communicating with said passage for discharging fluid under pressure from said passage outwardly from said blade arm.
  • 17. In an assembly according to claim 16 wherein said discharge means extend transversely of said passage through an undersurface of said blade arm.
  • 18. In an assembly according to claim 17 wherein said discharge means is in the form of nozzles extending through said blade arm between said cutting elements.
  • 19. In an assembly according to claim 12 wherein said pivot member is removably seated in said sub, lift plates extending upwardly from said sub having a latch release member at their s upper ends, a retrieval bar including latch means at its lower end and arranged for downward extension through said drill string into latching engagement with said latch engaging member whereby to lift said drill bits out of said sub and through said drill string to the surface.
  • 20. In an assembly according to claim 19 wherein said latch means includes a slot in a lower end portion of said bar, a pivotal latch member mounted for extension across said slot, and means for yieldingly urging said latch member between a latching position extending across said slot and a released position away from said slot.
  • 21. In an assembly according to claim 20 wherein said urging means is reversibly mounted to selectively bias said latch either toward or away from said latching position.
  • 22. In an assembly according to claim 18 wherein said nozzles on each said blade arm are disposed in offset relation to said cutting elements, said cutting elements on one of said blade arms aligned to engage said formation between or along kerf lines formed by said cutting elements on the other of said blade arms.
  • 23. The method of drilling a subsurface formation comprising the steps of:discharging high velocity streams of fluid through a plurality of nozzles in at least one of a pair of pivotal drill bits and rotating said drill bits to cause said bits to form a series of concentric circular kerf lines in the formation; and providing a series of cutting elements on at least another of said drill bits to break up any formation material between said kerf lines.
  • 24. The method according to claim 23 wherein said cutting elements are offset with respect to said nozzles.
  • 25. The method according to claim 23 wherein said nozzles and said cutting elements are disposed along formation-engaging surfaces of each of said drill bits.
  • 26. The method according to claim 23 including the step of imparting a centrifugal force to said drill bits to cause said bits to swing outwardly into operating position and to maintain said drill bits in the operating position.
  • 27. The method according to claim 25 wherein said cutting elements on one of said drill bits are offset with respect to said cutting elements on another of said drill bits.
  • 28. The method according to claim 23 including the step of discharging said fluid through said nozzles under sufficient force to cause said drill bits to swing radially outwardly into operating position.
  • 29. The method according to claim 23 including the step of maintaining said drill bits in the operating position by virtue of the frictional engagement between said drill bits and the material being bored.
US Referenced Citations (13)
Number Name Date Kind
1044598 Sullivan Nov 1912 A
1585540 Dougherty May 1926 A
2203998 O'Brady Jul 1940 A
2814463 Kammerer, Jr. Nov 1957 A
2893693 Clark Jul 1959 A
3196961 Kammerer Jul 1965 A
3552509 Brown Jan 1971 A
3554304 Link et al. Jan 1971 A
3656564 Brown Apr 1972 A
3684041 Kammerer, Jr. et al. Aug 1972 A
5148875 Karlsson et al. Sep 1992 A
5271472 Leturno Dec 1993 A
5494121 Nackerud Feb 1996 A
Non-Patent Literature Citations (1)
Entry
History of Oil Well Drilling (Brantley, J.E.) (1971) pp. 1114-1120; 1160-1167; 1171; 1175-1176; 1180-1185.