US3406769A

US3406769A - Reverse circulation rotary expansible drill bits

Info

Publication number: US3406769A
Application number: US588947A
Authority: US
Inventors: Jr Archer W Kammerer
Original assignee: Individual
Current assignee: Individual
Priority date: 1966-10-24
Filing date: 1966-10-24
Publication date: 1968-10-22
Anticipated expiration: 1985-10-22

Description

Oct. 22, 1968 A. W. KAMMERER, J 3,406,769

REVERSE CIRCULATION ROTARY EXPANSIBLE DRILL BITS 7 A s s Filed OCT'. 24, 1966 Oct. 22, E968 A. W. KAMMERER, ,m 3,406,769

REVERSE CIRCULATION ROTARY EXPANSIBLE DRILL BITS 2 f F @4% w Q w M@ w..

IN veA/T012 2 Sheets-Sheet 2 @Jeez/E@ MC a lOl veA/ey.-

ters expanded outwardly.

United States Patentl O ABSTRACT OF THE DISCLOSURE A rotary drill bit for use in a well bore and having cutters expandable outwardly in response to fluid pressure in the well bore annulus surrounding the drill string, the cuttings passing upwardly through the the top of the well bore. i

l The present invention relates to rotary `drill bits, and more particularly to rotary drill bits of the expansible type `capableof drilling a ,bore hole of enlarged diameter, of

enlarging a borehole below a string of casing to a greater diameter than the inside diameter of the casing through which the drill bits are capable of passing, or of severing and milling away a section of well casing located in the bore hole. 4 d

Certain bore holes are drilled in formations by reversely circulating the drilling iiuid; that iS, the drilling fluid is pumped down the bore hole through the annular space surrounding the string of drill pipe to the drilling region, to ilush the cuttings from such region and upwardly through the drill bit and drill pipe to the top of the hole `or drilling rig. An object of the present invention is t provide rotary drill bits of the expansible type, in which the circulating fluid pumped downwardly through the annulus around the drill pipe string effects outward expansion of the drill bit cutters, such cutters bein-g of the type to drill the formation, or of the type to mill away a casing section. v 1 K Another object of the invention is to provide a rotary drill bit having cutters expandable outwardly by the pressure of fluid reversely circulated within the bore hole, in which the cutters are retained in their, fully outwardly expanded position despite cessation in the circulation of fluid through the bore hole. More specifically, the application of drilling weight to the drill bit retains the cut- This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of several forms in which it may be embodied. Such forms are shown inthe drawings accompanying and forming part of the present specification. These forms will now be described in detail for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense, since the scope of the invention is best deiined by the appended claims.

Referring to the drawings:

FIGURE 1 is a longitudinal section through a rotary expansible drill bit disposed within a bore hole, with the cutters and other parts occupying a retracted position;

FIG. 2 is a longitudinal section similar to FIG. 1, disclosing the relative position of the parts of the drill bit with its cutters in their fully expanded position;

FIG. 3 is a longitudinal section through another speciiic rotary expansible drill bit disposed in a well bore, and with its cutters and other parts occupying a retracted position;

FIG. 4 is a view similar to FIG. 3 disclosing the relative positions of parts of the bit with the cutters in their outwardly expanded position.

drill string toward Y As shown in the drawings, a rotary expansible drill bit A is secured to the lower end of a string of drill pipe B extending to the top of a bore hole C, and by means of which the drill bit is lowered through the bore hole to a location therein at which its diameter is to be enlarged. In the form of invention, illustrated in FIGS. l and 2, the upper portion of the rotary drill bit consists of a mandrel 10 having an upper pin'114 threadedly connected to the lower end of the string of drill pipe B. This mandrel includes an upper kelly or drill lstern member 12 slidably splinedto the main body 13 of the drill bit. The exterior 14 of the lower portio'npof the kelly is non-circular in Ishape, being telescopically received in a companionnoncircular socket 15 formed in the main bit body' 13. vAs an Vexar'nple,'the kelly exterior 14 and the socket 15 maybe of hexagonal shape to enable the kelly 12 to be moved `longitudinally with respect to the body, while still being capable of transmitting rotary motionto the body 13.

The body 13 has alimited range of longitudinal relatife movement along the mandrel 10, its upward movement being determined by engagement of an inwardly directed body shoulder 16 with the lower end 17 of the kelly, and its downward movement being limited by engagement of a stop device 18, secured within the upper portion of the body, with a piston structure 19 secured to the mandrel. As specifically shown in the drawings, the piston structure includes an annular piston 20 encompassing the cylindrical portion 21 of the kelly of the mandrel substantially above its hexagonal portion 14, the lower end of the piston resting upon a lower split, snap retainer ring 22 located in a'peripheral groove 23 in the kelly, its upper end engaging an outwardly directed flange portion 24 of a two-piece retainer` ring 25 disposed in a peripheral groove 26 in the mandrel, the piston 20 encompassing the two-piece upper retainer ring below its flange 24. Leakage of fluid between the kelly 12 and piston 20 is prevented by a suitable side seal ring 27 on'the kelly engaging the inner surface of the piston 20, vthe piston having a suitable piston ring 28 mounted thereon slidably sealing against the inner cylindrical wall 29 of the drill bit body, which wall extends upwardly from a shoulder 30 marking the upper vend ot the non-circular body socket 15.

The upper stop device 18 includes a stop ring 31 insert able downwardly within an upper body counterbore 32 and bearing against an upwardly directed body shoulder 33, this stop ring 31 extending across the two-piece retainer ring 25 and being held in a downward position v against the body shoulder by one or a plurality of split,

When the body 13 is disposed in a downward position with respect to the lmandrel 10, as disclosed in FIG. 1, the upper stop ring 31 may rest upon the two-piece retainer ring 25. At this time, a lower cylinder head 36, secured within the body 13 and which surrounds the upper Ikelly or drill stem member 12, is spaced substantially below the piston structure 19. This cylinder head 36 is annular in shape, being secured to the body by a plurality of circumferentially spaced screws 37 threaded in the body and extending into a peripheral groove 38 in the cylinder head. The cylinder head has an inner seal ring 39 slidably and sealingly engaging the cylindrical periphery 21 of the kelly above its hexagonal portion 14, and also an external seal ring 40 sealing against the inner cylindrical wall 29 of the cylinder portion 41 of the main body 13 of the drill bit.

The -body 13 has a plurality of expansible parts mounted on it. These include cutter supporting members 42 pivotally mounted in one or more body slots 43 on hinge pins 44 which are suitably secured to the body to prevent loss therefrom. Each cutter supporting member depends from the hinge pin and carries a suitable cutter 45 onfits lower end. As specifically illustrated, the cutters 45 are of the toothed l'roller type, beingV designed for drilling upon relatively hard formations. However, the cutters could be constituted as drag cutters, or as milling1 cutters, in the event the e-xpansible drill -bit is to be employed for severing and milling away a section of well casing or for drilling a soft formation.

The cutter supporting members 42 and the cutters 45 themselves tend to occupy a retracted position substantially entirely within the contines of the main body 13 of the bit. These cutter supporting members and the cutter structures are expandable outwardly to enlarge the diameter of an existing bore hole, or, if milling cutters are employed, to sever and mill away a length of casing disposed in the bore hole. To accomplish the expansion, each cutter supporting member 42 has an inclined expander surface 46 on its inner portion below its hinge pin 44, which tapers in a downward and inward direction, each expander surface terminating in a lock surface 47 formed on a lock portion 48 of the cutter supporting member. The outward expansion is accomplished by relatively elevating the body 13 along the mandrel 10, as described specically hereinbelow. which will produce relative longitudinal movement between the cutter supporting members 42 and the tubular member 49 of the mandrel 10. This tubular member includes a lower portion 50 slidable within a guide bushing 51 `mounted in a bridge 52 secured to the body and extending across the body slot or slots 43. The guide bushing 51 is disposed below the lock portions 48 of the cutter supporting members 42 and is secured in place by a lower contractible split retainer ring 53 disposed in a groove 54 in the bushing and engaging the lower end of the bridge 52, an upper flange 55 on the bushing engaging the upper end of the bridge.

Located initially substantially above the guide bushing 51 and below the hinge pins 44, and in cutter supporting member recesses 56, is a mandrel lock and expander 57 which has outer surfaces 58 adapted to engage the expander surfaces 46 and the lock surfaces 47. The lock and expander may be formed integral with the tubular member 49, the upper portion 90 of the latter being piloted within a socket 91 formed in the lower portion of the kelly. This upper portion 90 is in enlarged boss engaging a downwardly facing shoulder 60 of the kelly, the tubular member being held against the shoulder by a suitable split retainer or lock ring 61 expanded into an internal groove 62 encompassing the kelly socket 91 and engaging the lower end of the tubular member boss 90.

As described hereinbelow, a suitable tiuid medium is provided, which is pumped downwardly in the bore hole around the exterior of the drill string B, such tiuid passing around the exterior of the drill bit A to the drilling region to flush the cuttings inwardly through the slot or slots 43 of the body and toward a flow bean 65 mounted within a counterbore 66 in the lower end of the tubular member 49, the tiuid passing upwardly through the central orifice or passage 67 of the ow bean and through the central passage 68 of the tubular member 49 into the central passage 69 through the kelly 12, from where the fluid and cuttings pass upwardly through the drill pipe string B to the top of the bore hole. The iiuid can also pass through the slots 43 around the exterior of the mandrel and into the hexagonal portion 15 of the body 13, leakage of this fluid upwardly around the tubular member yboss 58 being prevented by a suitable seal ring 70 in the upper kelly sealingly engaging the periphery of the enlarged boss.

Assuming the'body 13 of the tool to be elevated relatively along the tubular mandrel 10, the inclined expander surfaces 46 of the cutter supporting members shift upwardly along the lock and expander portion 57 of the tubular member 49. During such upward shifting, the cutter supporting members 42 and the cutters 45 carried thereby will pivot about the hinge pins 44 and be urged in an outward direction. The upward movement of the body 13 with respect to the mandrel can continue until the cutters 45 have been shifted outwardly to their fullest extent, as determined by engagement of stop shoulder 71 on the cutter supporting members with companion shoulders 72 formed in the body 13 on opposite sides of the body slot or slots 43. When such expansion occurs, the body shoulder 16 will engage the lower end 17 of the kelly portion 12 of the tubular mandrel 1t), and the lock and expander 57 on the tubular member will be disposed 4behind and in engagement with the lock portions 48 of the cutter supporting members 42.

The relative upward movement of the body 13 of the tool along the tubular mandrel 10 is accomplished by the action of fluid pressure being pumped downwardly through the annulus D surrounding the drill pipe string B. This pressure will be greater than the pressure within the

passages

68, 69 of the tubular mandrel 10, in view of the pressure drop occasioned by the orifice 67 formed in the lower bean 65 secured within the tubular member 49. The pressure within the central passage 69 will be the same pressure as exist in the cylinder space 75 defined between the lower cylinder head 36 and piston 20, and between the periphery 21 of the kelly portion 12 of the mandrel and the inner wall 29 of the cylindrical portion 41 of the main body of the drill bit, communication between the central passage 69 and the annular cylinder space 75 being provided by bleeder ports 76 in the kelly extending between the central passage and the annular cylinder space immediately below the piston structure.

The cylinder head 36 itself is subject to the relatively high pressure of the fluid surrounding the bit body 13, and which is capable of passing upwardly through the slots 43 and around the kelly portion 12 of the body for action in an upward direction on the cylinder head 36 over the annular area R. Thus, the cylinder head 36 is subject to the relatively high pressure of tiuid acting upon it in an upward direction; whereas, the pressure of the uid in the cylinder space 75 above the cylinder head is at a relatively low pressure, a pressure differential being provided which is capable of shifting the body 13 upwardly along the mandrel 10 until the cutters 45 have been expanded outwardly to their fullest extent, as disclosed in FIG. 2. The fluid under pressure, as has been noted above, is developed by restricting the ow of fluid through the orifice 67 of the mandrel. As a result of such restriction of flow, the pumping of a compressed gas or drilling mud at an adequate rate downwardly through the annulus D around the drill pipe and around the drill bit A will result in a relatively high pressure of iiuid being present in the well bore for upward action on the cylinder head 36 surrounding the exterior of the kelly 12.

The tluid pressure in the annulus D is also acting in a downward direction upon the piston structure 19, and will force, or tend to force, the mandrel 10 downwardly within the body 13 and shift the expander 57 down along the surfaces 46 to expand the cutters 45 outwardly. Such action can occur upon contact of the cutters against the wall of the hole C, which resist upward movement of the cutters and body along the wall of the hole, the drill pipe B stretching downwardly or elongating, or the drill pipe being slacked ott sufiiciently at the top of the wall bore, to permit its lowering for the purpose of enabling the mandrel 10 to lower within the body 13 and along the supporting members 42.

In the use of the apparatus disclosed in FIGS. 1 and 2, the cutters 45 are initially in their retracted position, as disclosed in FIG. 1, the body 13 of the tool and the cutter members being located in their initial lower position with respect to the mandrel 10. The drill bit A is lowered on a string of drill pipe B to the desired location in the well bore at which the cutters are to be expanded outwardly. When such position is reached, the drilling uid is pumped downwardly through the annulus D sur- J rounding the string of drill pipe B, passing upwardly through the orifice 67 and developing a back pressure below the cylinder head 36, which will shift the |body 13 and cutters 45 upwardly along the mandrel 10. During such upward shifting, the drill pipe and bit A are rotated at the proper speed, the cutter supporting members 42 shifting upwardly along the mandrel lock and expander 57 and progressively enlarging the well bore, until the cutters 45 have been expanded to their fullest extent, as determined by engagement of the body shoulder 16 with the lower end 17 of the kelly, and the engagement of the stop shoulders 71 on the cutter supporting members with the companion shoulders 72 formed in the body on opposite sides of its slot or slots.

Appropriate drilling weight can now be imposed downwardly through the drill pipe string B on the drill Bit A, which will be transmitted directly from the kelly 12 to Vthe body `13 of the tool, and through its shoulders 72 to the cutter supporting members 42 and to the cutters 45, the cutters being urged against the transverse shoulder E produced in the formation by the expanded cutters. The rotation of the drill pipe string and drill bit continues with the circulating or drilling fluid being pumped down through the -annulus D, such duid passing around the expanded cutters 45 to cool them and clean them of cuttings, and to carry the cuttings inwardly toward the orilice 67 and upwardly therethrough into the

passages

68, 69 through the mandrel 10, and then upwardly through the drill pipe string B to the top of the bore hole or to the top of the drilling rig. Because of the relatively small cross-sectional area through the drill pipe B, as compared to the diameter of the enlarged well bore F, the cuttings will be conveyed by the drilling fluid at relatively high velocities through the drill pipe to the top of the latter. This becomes of importance in the event that a greatly `enlarged bore F is drilled by the cutters, since the circulation of uid in the normal direction, that is, downwardly through the drill pipe B and upwardly around the drill bit A and through the annulus D `surrounding the string of drill pipe, would result in a rather low velocity of fluid passing upwardly through the annulus, such velocity oftentimes being insufficient to carry the cuttings upwardly to the t-op of the bore hole.

When the enlarged bore hole F has been produced to the desired length, or upon the cutters 45 becoming dull, the drill bit can be removed simply by ceasing the circulation of fluid downwardly through the annulus D surrounding the drill pipe, 4and by elevating the string of drill pipe, which will elevate the mandrel within the body 13 of the tool, and replace the mandrel lock and expander 57 above the lock surfaces 47 and within the cutter member recesses 56, the piston structure 19 engaging the stop ring 31 to raise the body 13 of the tool. The cutter supporting members 42 and cutters 45 are then free to shift inwardly back substantially within the confines of the `body 13 of the tool, allowing the entire drill bit A to be elevated in the bore hole to the top thereof, or to the drilling rig. In the event the cutters 45 do not shift inwardly by gravity upon elevation of the mandrel 10 within the body 13 ofthe tool, such elevation will cause a shoulder 80 on the tubular member 49 to engage the inwardly extending fingers 81 on the cutter supporting members 42 and swing them upwardly, -causing the cutter supporting members and cutters below the hinge pins 42 to swing inwardly back within the confines of the drill bit body 13, permitting the string of drill pipe B, with the drill bit A thereon, to be elevated within the bore hole and removed entirely therefrom.

In the vform of invention illustrated in FIGS. 3 and 4, the string of drill pipe B is connected directly to the main body 13a of the drill bit, and the mandrel 10a is shifted downwardly hydraulically by the pressure of fluid surrounding the main body to expand the cutter supporting members 42 and cutters 45 outwardly. The mounting of the cutter supporting members and cutters in the main body 13a and the coaction -between the mandrel 10a, and particularly its expander and lock 57 and the cutter supporting members 42 to effect outward expansion of the latter, is substantially the same as in the form of invention disclosed in FIGS. 1 and 2.

The main body 13a is elongate, including a lower cylinder head above the upper end of its slot or slots 43, extending inwardly toward the mandrel or plunger 10a above the mandrel lock and expander 57, and having a suitable rod seal 101 slidably and sealingly engaging the periphery of the lower rod portion 49a of the mandrel or plunger, which extends upwardly within a cylinder 41a formed by the upper portion of the body of the tool. This cylinder includes an upper cylinder head 102 threadedly secured to the upper cylindrical sleeve portion of the cylinder 41a, and having a threaded pin 103 threadedly secured to the lower end of the drill pipe string B. The mandrel 10a has a piston` 104 slidable along the Vinner cylindrical wall 105 of the cylinder, there being a suitable piston seal ring 106 mounted thereon for sealing against the cylinder wall. The mandrel `10a further includes an upper rod portion 107 extending upwardly from the piston 104 and slidable within a central bore 103 extending through the upper cylinder head 102, there being a suitable rod seal 109 on the upper head slidably and sealingly engaging the upper rod portion.

Initially, the mandrel 10a is retained in an upward position within the body by a helical compression return spring 110 disposed in a low pressure cylinder space 111 provided between the piston 104 and lower cylinder head 100, the lower end ofthe spring bearing against the lower cylinder head, and its upper end against the piston and urging the piston upwardly, and consequently the mandrel or plunger 10a upwardly to a position in which the cutter supporting members 42 and cutters 45 are retracted, the piston being spaced a short distance below the upper cylinder head 102. The mandrel is urged downwardly within the cylinder and body of the tool by fluid under pressure in the annular space D surrounding the drill pipe and the body of the tool. Such fluid under pressure passes through inlet ports 111a in the upper portion of the cylinder skirt into a high pressure cylinder space 112 between the upper cylinder head 102 and the piston 104, urging the piston 104 downwardly against the force of the return spring 110, and the entire mandrel 10a downwardly to shift the expander and lock 57 downwardly along the expander surfaces 56 of the cutter supporting members 42 to expand the cutters 45 outwardly, the mandrel moving downwardly until the expander and lock 57 engages the upper end of the guide bushing 51, at which time the expander and lock is disposed behind the lock surfaces 47 on the cutter supporting members, as disclosed in FIG. 4. Fluid within the low pressure cylinder space 111 can pass through the bleeder ports 76a in the lower rod portion 49a of the mandrel into the central passage 69a through the mandrel, which opens upwardly into the cylinder head 102 and the string of drill pipe B, the lower portion of the central mandrel passage communieating with the body slots 43 through the orifice or the ow restricting bean 65 mounted within the lower end of the mandrel 10a.

In the use of the particular expansible drill bit disclosed in FIGS. 3 and 4, the parts initially occupy the relative positions illustrated in FIG. 3, the return spring 110 tending to retain the mandrel 10a in its upper position within the body 13a, the cutters 45 and cutter supporting members 42 being retracted substantially completely within the confines of the body. The apparatus is lowered on the drill pipe B in the bore hole C to a location in which the cutters 45 are to be expanded outwardly, and the drill bit is then rotated by rotating the string of drill pipe, while circulating fluid is pumped downwardly through the annullus D surrounding the drill pipe. The fluid will pass upwardly through the orice 67 into the central passage 69a through the mandrel, the pressure in the low pressure cylinder space 111 then being less than the pressure in the high pressure cylinder space 112, the high pressure fluid passing through the inlet ports 111a into the upper cylinder space 112 and acting downwardly on the piston over its annular area S, as shown in FIG. 4, shifting the mandrel 10a downwardly and causing the expander and lock portion 57 of the mandrel to engage the expander surfaces 46 on the cutter supporting members 42, to shift them outwardly and to force the cutters 45 against the wall of the bore hole C.

The cuttings produced by the cutters are flushed by the circulating fluid inwardly through the body slots 43 and upwardly through the bean 65 into the central passage 69a, where they will flow upwardly through the drill pipe B to the top of the bore hole or drilling rig. The downward force of the fluid on the piston 104 and the mandrel progressively shifts the cutters 45 outwardly to a greater extent, forcing them against the wall of the well bore, until the cutters have been expanded outwardly to their maximum extent, as determined by engagement of the shoulders 71 on the supporting members with the companion body shoulders 72 on opposite sides of its slots 43.

Rotation of the drill pipe B can now continue while appropriate drilling weight is imposed thereby upon the body 13a of the tool and the cutters 45, forcing the cuters against the annular shoulder E which they form in the bore hole between the enlarged bore diameter F and the original bore hole diameter C, the cutters acting upon the shoulder E to drill it away, and the cuttings continually being flushed by wardly through the annulus D around the drill pipe, and around the drill bit A, inwardly toward its axis and upwardly through the mandrel 10a into the drill pipe B to be conveyed to the surface.

After the hole enlarging operation has been completed, or the cutters 45 become dull, circulation of fluid is discontinued which will reduce the pressure in the high pressure cylinder space 112 and allow the spring 110 to shift the mandrel or plunger 10a upwardly to its initial position disclosed in FIG. 3, the expander and lock 57 being again located within the supporting member recesses 56, the cutters 45 shifting inwardly within the confines of the body. If the cutters do not move inwardly of their own accord, then the shoulder 80 on the mandrel 10a will engage the inwardly directed fingers 81 on the upper portions of the cutter supporting members 42 and swing them upwardly about their hinge pins 44, and the pendent portions of the cutter supporting members and cutters inwardly substantially entirely within the confines of the bit body. The drill bit A can now be elevated in the bore hole by elevating the string of drill pipe B, and removed entirely from the bore hole.

I claim:

1. In a rotary drill bit adapted for attachment to a drill string to be rotated thereby in a bore hole: a main body; cutter means carried by said body; and means engaging said cutter means and responsive to fluid pressure in the bore hole annulus surrounding the `drill string for expanding said cutter means laterally outwardly of said body.

2. In a rotary drill bit as defined in claim 1; said expanding means for said cutter means comprising a mandrel movable longitudinally Within and relative to said body, said body and mandrel providing cylinder and piston means having high pressure areas subject to the fluid under pressure in the bore hole annulus to effect expansion of said cutter means.

3. In a rotary drill bit as defined in claim 1; said expanding means for said cutter means comprising a mandrel movable longitudinally within and relative to said body, said body and mandrel providing cylinder and piston means having high pressure areas subject to the fluid under pressure in the bore hole annulus to effect expansion of said cutter means; said mandrel having a passage the drilling fluid pumped down- '8 through which fluid pumped down the bore hole annulus can flow upwardly and into the drill string.

4. In a rotary drill bit as defined in claim 1; said expanding means for said cutter means comprising a mandrel movable longitudinally within and relative to said body, said body and mandrel providing cylinder and piston means having high pressure areas subject to the fluid under pressure in the bore hole annulus to effect expansion of said cutter means; said mandrel having a passage through which fluid pumped down the bore hole annulus can flow upwardly and into the drill string; means for reducing the pressure of the fluid flowing upwardly through the mandrel passage; and means communicating the low pressure area of said cylinder and piston means with the reduced pressure region of said mandrel passage.

5. In a rotary drill bit as defined in claim 1; said expanding means for said cutter means comprising a mandrel movable longitudinally within and relative to said body, said body and mandrel providing cylinder and piston means having high pressure areas subject to the fluid under pressure in the Ibore hole annulus to effect expansion of said cutter means; said mandrel having a passage through which fluid pumped down the bore hole annulus can flow upwardly and into the drill string; said mandrel having flow restricting means in its passage for reducing `the pressure of the fluid flowing upwardly through the mandrel passage; and means communicating the low pressure areas of said cylinder and piston means with the reduced pressure region of said mandrel passage.

6. In a rotary drill bit as defined in claim 1; said expanding means for said cutter means comprising a mandrel movable within and downwardly of said body, said body and mandrel providing cylinder and piston means having high pressure areas subject to the fluid under pressure in the bore hole annulus to effect expansion of said cutter means.

7. In a rotary drill bit as defined in claim 1; said expanding means for said cutter means comprising a mandrel movable longitudinally within and relative to said body, said body having a cylinder portion, said mandrel having a piston portion within said cylinder portion, said portions having relatively high pressure areas subject to the fluid under pressure in the bore hole annulus to effect expansion of said cutter means.

8. In a rotary drill bit as defined in claim 1; said expanding means for said cutter means comprising a mandrel movable longitudinally within and relative to said body, said body having a cylinder portion, said mandrel having a piston portion within said cylinder portion, said portions having relatively high pressure areas subject to the fluid under pressure in the bore hole annulus to effect expansion of said cutter means; said mandrel having a passage through which fluid pumped down the drill string annulus can flow upwardly and into the drill string; means for reducing the -pressure of the fluid flowing upwardly through the mandrel passage; and means communicating the high pressure areas of said cylinder portion and piston portion with the reduced pressure region of said mandrel passage.

9. In a rotary drill bit adapted for attachment to a drill string to be rotated thereby in a bore hole: a main body; cutter means mounted on said body for expansion laterally outwardly of said body; a mandrel co-nnectible to the drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body; coengageable expander means on said mandrel and cutter means; and fluid operated means subject to the pressure of fluid in the bore hole annulus surrounding the drill string for elevating said body and cutter means with respect to said mandrel to cause said expander means to expand said cutter means laterally outward.

10. In a rotary `drill bit as defined in claim 9; said fluid operated means comprising a cylinder portion on said body having a cylinder head, a piston portion on said mandrel above said cylinder head and along which said cylinder portion is slidable, the uid under pressure i-n the bore hole annulus acting on said cylinder head to relatively elevate said cylinder portion and body along said mandrel.

11. In a rotary drill bit as defined in claim 9; said fluid operated means comprising a cylinder portion on said body having a cylinder head, a pi-ston portion on said mandrel above said cylinder head and along which said cylinder portion is slidable, the fluid under pressure in the bore hole annulus acting on `said cylinder head to relatively elevate said cylinder portion and body along said mandrel; said mandrel having a passage through which fluid pumped down the -bore hole annulus can ow upwardly into the drill string; and means establishing fluid communication between said passage and the region of the cylinder portion located between said cylinder head and piston portion.

12. In a rotary drill bit as delined in claim 9; said uid operated means comprising a cylinder portion on said body having a cylinder head, a .piston portion on said mandrel above said cylinder head and along which said cylinder portion is slidable, the fluid under pressure in the bore hole annulus acting on said cylinder head to relatively elevate said cylinder portion and body along said mandrel; said mandrel having a passage through which uid pumped down the bore hole annulus can flow upwardly into the drill string; said mandrel having ow restricting means in its passage for lreducing the pressure of fluid flowing from Ithe bore hole annulus upwardly through the mandrel passage; and means establishing fluid communication between said passage above said tlow restricting means and the region of the cylinder portion located between said cylinder head and piston portion.

13. In a rotary drill bit adapted for attachment to a drill string to be rotated thereby in a bore hole: a main body connectible to the drill string; cutter means mounted on said body for expansion laterally outwardly of said body; a mandrel movable longitudinally in said body; coengageable expander means on said mandrel and cutter means; and fluid operated means subject -to the pressure of iluid in the bor-e hole annulus surrounding the drill string for shifting said mandrel longitudinally in said body and along said cutter means to cause said expander means to expand said cutter means laterally outward.

14. In a rotary drill bit as defined in claim 13; said fluid operated means comprising a cylinder portion on said body, a piston portion on said mandrel slidable in said cylinder portion, the uid under pressure in the bore hole annulus acting on said piston portion to shift said mandrel in said body and along said cutter means to expand said cutter means.

1S. In a rotary drill bit as delined in claim 13; said fluid operated means comprising a cylinder portion on said body, a piston portion on said mandrel slidable in said cylinder portion, said cylinder portion having Ian inlet for fluid under pressure in the bore hole annulus to enter said cylinder portion and act on a relatively high pressure side of said piston portion to shift said mandrel in said body and along said cutter means -to expand said cutter means.

16. In a rotary drill bit as defined in claim 13; said iluid operated means comprising a cylinder portion on said body, a piston portion on said mandrel slidable in said cylinder portion, said cylinder portion having an inlet for fluid under pressure in the bore hole annulus t0 enter said cylinder portion and `act on a relatively high pressure side of said piston portion to shift said mandrel in said body and along said cutter means to expand said cutter means; said mandrel having a passage through which fluid pumped down the bore hole annulus can ow upwardly into the drill string; and means establishing fluid communication between said passage and the cylinder portion on the low pressure side of said piston portion.

17. In a rotary drill bit as delined in claim 13; said iluid operated means comprising a cylinder portion on said body, a piston portion on said mandrel slidable in said cylinder portion, said cylinder portion having an inlet for fluid under pressure in the bore hole annulus to enter said cylinder portion and act on a relatively high pressure side of said piston portion to shift said mandrel in said body and along said cutter means to expand said cutter means; said mandrel having a passage through which iluid pumped down the bore hole annulus can ilow upwardly into the drill string; said mandrel having flow restricting means in its passage for reducing the pressure of uid flowing from the bore hole annulus upwardly through the mandrel passage; and means establishing fluid communication between said passage above said flow restricting means and the cylinder portion on the low pressure side of said piston portion.

References Cited UNITED STATES PATENTS 1,805,515 5/1931 Denney 166--55.8 2,699,921 l/ 1955 Garrison -267 2,859,943 ll/ 1958 Chadderdon 175-269 X 3,126,065 3/ 1964 Chadderdon 175-269 DAVID H. BROWN, Primary Examiner.