CN110869580A

CN110869580A - Hybrid roller cone mill bit and hybrid roller cone drag bit

Info

Publication number: CN110869580A
Application number: CN201880037833.1A
Authority: CN
Inventors: 马修·查尔斯·斯特罗埃维尔; 乔纳森·沃尔特·霍华德; 托马斯·加利费特; 帕特里夏·安·尼尔; 凯瑞·安德鲁·迈于斯塔
Original assignee: Weida Mining And Industry Co Ltd
Current assignee: Weida Mining And Industry Co Ltd
Priority date: 2017-06-08
Filing date: 2018-04-20
Publication date: 2020-03-06
Also published as: SE1930396A1; US20180355670A1; WO2018226319A1; RU2019144334A; CA3057152A1

Abstract

A roller cone mill drill bit for a wellbore, comprising: a body having a plurality of lower legs and a coupling formed at an upper end thereof; a plurality of roller disks, each roller disk being fixed to the support shaft of a corresponding leg to rotate relative to the support shaft; a row of breakers mounted around each roller disc; and a stationary mill mounted to the support shaft and including a backing plate for each roller disk. Each pad is loaded with a cermet material.

Description

Hybrid roller cone mill bit and hybrid roller cone drag bit

Technical Field

The present disclosure relates generally to hybrid roller mill bits (hybrid roller-mill bits) and hybrid roller drag bits (hybrid roller-drag bits).

Background

US 2,320,136 discloses a composite rotary drill bit having an outer side roller gauge or reamer tool for removing formation material from the bottom of a hole and also having an intermediate blade for removing a central portion of material from the bottom within the circular path traced by the side cutter.

US 5,853,055 discloses a rotary cone drill bit for drilling a borehole into an earth formation, having a body with a threaded pin end and a domed end from which three legs project. A cutter cone is rotatably mounted to each leg and is radially oriented about the central axis of the drill bit. Each cutter cone has a row of gage cutting elements extending from a cone surface closest to the mouth and a leading row of cutting elements extending closest to an apex of the cone. The central spout for ejecting the fluid or slurry is located on the dome. The spout has a converging nozzle with an outlet orifice extending below a predetermined horizontal plane intersected by the cone or cutting element. The outlet orifice has a constant diameter over a length at least equal to its diameter to reduce the spread of the ejected fluid or slurry flow. The fluid or slurry ejected from the center nozzle travels substantially uninterrupted within the cylindrical spaces between the cones, which are not invaded by any cutting elements. This substantially uninterrupted flow of fluid that reduces diffusion strikes the bottom of the borehole (bore hole) with maximum impact energy to enhance removal of formation cuttings.

US 6,581,702 discloses a tri-cone rock drill bit which employs a non-plugging central jet nozzle having a plurality of staggered inlet apertures which open into side channels to reduce bit balling. The nozzles define a conical cavity through which the drilling mud flows and exits in streams (streams). The flow is directed from the nozzle through a main exit orifice large enough to avoid clogging, and from a side passage drilled through the side wall of the nozzle. The jet stream facilitates flushing of the voids and cutting surfaces within the drill bit. The nozzle uses staggered inlet orifices to the side channels and, together with the tapered shape of the central channel, facilitates maintaining drilling mud velocity within the central channel and, thus, flow rate to the target area of the drill bit.

US 7,845,435 discloses a hybrid drill bit with both roller cones and fixed blades and a method of drilling. The cutting elements on the fixed blades form a continuous cutting profile from the periphery to the axial center of the bit body. The roller cone cutting elements overlap the fixed cutting elements in a forward section and a shoulder section of the cutting profile between the axial center and the perimeter. The roller cone cutting elements fracture and pre-fracture or partially fracture the formation in the forward and shoulder sections that are confined and subject to high pressures.

US 8,678,111 discloses a hybrid earth-boring bit comprising a bit body having a central axis, at least one (preferably three) fixed blades depending downwardly from the bit body, each fixed blade having a leading edge, and at least one roller cutter, preferably three roller cutters, mounted for rotation on the bit body. The hob is located between the two fixed blades.

US 9,353,575 discloses a core cutter bit having a bit body with a central longitudinal axis defining an axial center of the bit body and configured at an upper portion thereof for connection into a drill string, at least one primary fixed blade extending downwardly from the bit body and inwardly toward, but not proximate to, the central axis of the bit; at least one auxiliary fixed blade extending radially outward from a location proximate a central axis of the drill bit; a plurality of fixed cutting elements secured to the primary and auxiliary fixed blades; at least one bit leg secured to the bit body; and a roller cutter mounted for rotation on the drill bit leg; wherein the fixed cutting elements on the at least one fixed blade extend outward from a center of the drill bit toward a gage of the drill bit, but do not include a gage cutting area, and wherein the at least one roller cone cutter portion extends substantially inward from the gage area of the drill bit toward the center of the drill bit, and an apex of the roller cone cutter is proximate a tip of the at least one auxiliary fixed blade, but does not extend to the center of the drill bit.

US 2016/0348440 discloses a drill bit comprising: a bit body having a longitudinal bit axis extending therethrough; a plurality of journals extending from the bit body, each journal having a journal axis extending from a base of the journal through a length of the journal; a cone rotatably mounted to each journal; and at least one blade projecting from a center of the bit body and extending radially outward to less than an outer diameter of the bit.

Disclosure of Invention

The present disclosure relates generally to a hybrid roller cone mill bit and a hybrid roller cone drag bit. In one embodiment, a roller cone mill drill bit for use in a wellbore comprises: a body having a coupler and a plurality of lower legs formed at an upper end thereof; a plurality of roller disks, each roller disk being fixed to the support shaft of a corresponding leg to rotate relative to the support shaft; a row of breakers mounted around each roller disc; and a fixed mill (fixed mill) mounted to the support shaft and including a backing plate for each roll disk. Each pad is loaded with a cermet material.

Drawings

So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings, it being noted, however, that the drawings illustrate only typical embodiments of the disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.

Fig. 1 illustrates a hybrid roller cone mill drill bit positioned for drilling through a fracture plug disposed in a wellbore according to one embodiment of the present disclosure. Figures 2A-3B illustrate a roller cone mill bit. Fig. 4A to 4C show a cutter of a fixed mill of a roller cone mill bit. Fig. 4D-4F illustrate mounting the cutters to the mill backing plate of the hybrid drill bit.

Figure 5 illustrates drilling a wellbore using a hybrid roller cone drag bit according to another embodiment of the present disclosure. Figures 6 and 7A show a roller cone drag bit. Figure 7B illustrates mounting of a fixed cutting structure to a roller cone drag bit.

Figures 8 and 9A illustrate a second hybrid roller cone drag bit according to another embodiment of the present disclosure.

Figure 9B illustrates a third hybrid roller cone drag bit according to another embodiment of the present disclosure.

Detailed Description

Fig. 1 illustrates a hybrid roller cone mill drill bit 1 positioned for drilling through a fracture plug 2 disposed in a wellbore 3 according to one embodiment of the present disclosure. For hydraulic fracturing operations, the fracture plug 2 is set against a casing or liner string 4 to isolate a zone of the formation (not shown) adjacent the wellbore 3. To set the frac plug 2, a setting tool (not shown) and frac plug 2 may be deployed down the casing or liner string 4 using a wireline (not shown). The frac plug 2 may be set by supplying power to the setting tool via a cable to activate the setting tool. The piston of the setting tool may move the exterior of the frac plug 2 along the mandrel 5 of the frac plug while the cable constrains the mandrel of the setting tool and the plug mandrel, thereby compressing the packing element 8 and driving the slips 6 along the corresponding slip cone 7 of the frac plug. The packing element 8 may be radially expanded to engage the casing or liner string 4 and the slips 6 may be wedged to engage the casing or liner string 4.

The casing or liner string 4 may then be perforated above the set frac plug 2 and the isolated zone may be hydraulically fractured by pumping a ball 9 and then pumping fracturing fluid (not shown) down the casing or liner string 4. The ball 9 may fall into the mandrel seat of the plug mandrel 5 thereby forcing the fracturing fluid into this region via the perforations. Another frac plug (not shown) may then be placed over the fractured zone and the casing or liner string 4 may be re-perforated over the plug to hydraulically fracture another zone. This process may be repeated a number of times, such as ten or more or twenty times, until all zones adjacent the wellbore 3 have been fractured.

After all zones have been fractured, the production valve at the wellhead may be opened to produce fluid from the wellbore in an attempt to retrieve the ball 9. However, such attempts often fail. Roller cone mill drill bit 1 (only partially shown) may be deployed down a casing or liner string 4 using coiled tubing (not shown). A drilling motor (not shown), such as a mud motor, may connect roller cone mill bit 1 to coiled tubing. Roller cone mill bit 1, drilling motor and coiled tubing may be collectively referred to as a mill string. Milling fluid may be pumped down the coiled tubing to drive the drilling motor to rotate the roller cone mill bit 1, and the roller cone mill bit may be advanced to engage the frac plug 2 to drill through the frac plug. Once drilled through, the mill string may be advanced to drill through the next frac plug 2 until all frac plugs have been drilled through.

Alternatively, the mill string may comprise a drill pipe string with or without a drilling motor instead of coiled tubing. Alternatively, roller cone mill drill bit 1 may be used to drill through other types of downhole tools, such as packers, bridge plugs, float collars, float shoes, stepped collars, guide shoes, reamer sleeves, and/or casing bits.

Figures 2A to 3B show a roller cone mill bit 1. Roller cone mill drill bit 1 may include a body 10, a plurality of roller discs 11a-c, a plurality of breakers 20, and a stationary mill 12. The roller discs 11a-c, the breakers 20 and the stationary mills 12 may form the lower cutting face of the roller cone mill bit 1. The roller discs 11a-c and the breakers 20 may be located at the outer part of the cutting face, while the stationary mill 12 may be located at the inner part of the cutting face.

The body 10 may have an upper coupling 13, a lower leg 14a-c for each roller disk 11a-c and a dome 15 formed between the legs. The body 10 and the roller discs 11a-c, respectively, may be made of a metal or an alloy, such as steel. The body 10 may be made by attaching three forgings together, such as by welding. The legs 14a-c may be evenly spaced around the body, for example three legs at one hundred twenty degrees. The upper coupling 13 may be a threaded pin for connection to a drilling motor or a drill pipe. A hole may be formed through the coupler 13 and extend to a plenum (not shown) formed adjacent the dome 15.

Each leg 14a-c may have an upper shoulder 16s, an intermediate skirt 16h, a lower support shaft 16b, and a perforated boss 16 p. The shoulder 16s, skirt 16h, apertured boss 16p and support shaft 16b of each leg 14a-c may be interconnected, such as by being integrally formed and/or welded together. Each perforated boss 16p may be in fluid communication with the plenum via a respective port formed in the coupling 13 and may have a nozzle (not shown) secured therein for discharging milling fluid onto the respective roll discs 11 a-c. Each support shaft 16b may extend from a respective skirt 16h in a radially oblique direction toward the center of the roller cone mill bit 1.

Alternatively, roller cone mill bit 1 may include a flow channel formed through dome 15 for each roller disk 11a-c, rather than perforated boss 16 p. Each fluid passage may be in fluid communication with a plenum and may have a nozzle (not shown) secured therein for discharging milling fluid onto a respective roll disk 11 a-c. The flow channel may be disposed about the center of roller cone mill bit 1.

The stationary mill 12 may include a backing plate 12a-c for each roller disk 11a-c and a plurality of cutters 17 mounted to the backing plate. Each of the mill backing plates 12a-c can have the shape of a conical polyhedron including a circular base 23b and a plurality of sides converging toward a truncated apex. The sides of each mill mat plate 12a-c may include one or more mounting faces 23m adjacent its apex to mate with one or more complementary mounting faces of adjacent mill mat plates 23 m. The mill backing plates 12a-c may be attached together at the mounting face 23m, such as by welding. Each of the mill backing plates 12a-c can be made of a metal or alloy, such as steel.

Each support shaft 16b and corresponding roller disk 11a-c may have one or more pairs of aligned grooves, and each pair may form a raceway for receiving a set of roller bearings 18. Thrust washers 19 may be disposed between the inner side of each roller disk 11a-c and the respective seat 23b, such as in a groove formed in the seat. Roller bearings 18 and thrust washers 19 may support the rotation of each disk 11a-c relative to the respective leg 14a-c and mill backing plate 12 a-c. The roller bearings 18 and thrust washers 19 may be lubricated by milling fluid discharged from the respective apertured bosses 16 p.

Each mill backing plate 12a-c can have a receptacle formed therein and extending from the base. The ends of the respective support shafts 16b may be received in the receptacles to mount the mill backing plates 12a-c to the body 10 once the mill backing plates 12a-c have been welded together. Each roller disk 11a-c may be secured to a respective leg 14a-c by being entrained between the base of the respective mill backing plate 12a-c and a respective skirt 16 h. Each of the roller disks 11a-c may have a tapered portion formed at the periphery of the inner side surface, and each of the seats 23b may have a complementary lip portion formed at the periphery thereof.

Alternatively, each leg 14a-c may have a lubricant reservoir (not shown) formed therein and lubricant passages (not shown) extending from the reservoir to the respective sets of roller bearings. Lubricant may be retained within each leg 14a-c by a pair of seals (not shown), such as O-rings, each positioned in a respective gland (not shown) formed in the inside surface of a respective roller disk 11 a-c. The first gland of each pair may be positioned adjacent the skirt 16h and the second gland of each pair may be positioned adjacent the respective thrust washer 19, thereby preventing lubricant from leaking from the roller bearing 18 into the wellbore 3. A pressure compensator (not shown) may be provided in each reservoir to regulate the lubricant pressure therein. A balancing channel may extend from each reservoir and through the dome 15 to operate the respective pressure compensator to adjust the lubricant pressure to be slightly greater than the bottom hole pressure. In this alternative, the thrust washers 19 may still be lubricated by the milling fluid discharged from the respective perforated bosses 16 p. In a variant of this alternative, a second gland may be located in the inner side of each roller disk 11a-c, so that the thrust washer 19 is also lubricated by the lubricant.

Alternatively, the upper and lower edges of each skirt 16h may be protected from corrosion and/or wear by case hardening with a ceramic material or a cermet material, respectively. The outer surface of each skirt 16h may also be protected from corrosion and/or wear by a protective insert secured (such as by interference fit or brazing) in its socket. Each protective blade may be made of cermet. Each of the roll discs 11a-c may be treated to resist corrosion and/or wear by surface hardening, such as carburization.

Each roller disk 11a-c may have a plurality of shoulders formed therein, such as heel shoulders and gage shoulders. Rows of gauge breakers 20 may be mounted around each of the roll discs 11a-c at the respective gauge shoulders. Each breaker 20 may be a blade that is mounted by interference fit in a respective socket formed in a respective roller disk 11 a-c. Each breaker 20 may be made of a cermet, such as cemented carbide, and may have a cylindrical or conical portion mounted in the respective roll disk 11a-c and a conical or chisel shaped portion protruding from the respective shoulder of the respective roll disk.

Rows of heel protectors 21 may be mounted around each roller disk 11a-c at the respective heel shoulders. Each heel protector 21 may be a blade that is mounted by interference fit in a respective socket formed in a respective roller disk 11 a-c. Each protector 21 may be made of cermet (such as cemented carbide), and may be cylindrical.

Alternatively, the disruptor 20 and/or the heel protector 21 may be covered with polycrystalline diamond (PCD). Alternatively, each breaker 20 may be a hardfaced milling tooth, or each row of breakers may include both a blade and a milling tooth.

Roller cone mill bit 1 may also have junk slots 22 formed between the shirttail 16h of each adjacent leg 14 a-c. Each flute 22 may be formed into the body 10, such as by milling and/or forging. Each apertured boss 16p may be located in a respective flute 22. Each junk slot 22 may be sized to allow passage of debris (not shown) generated during milling of the frac plug 2 into the annulus formed between the mill column and the casing or liner column 4.

Fig. 4A to 4C show one of the typical mill cutters 17. To form a stationary mill 12, each mill backing plate 12a-c may be fitted with a mill cutter 17. The mill cutters 17 may be blocks, such as cubic blocks, made of cermet material. The cermet material may be a cemented carbide comprising a binder and a carbide, such as cobalt tungsten carbide. The cermet material may be formed into a block by sintering, such as hot pressing.

The mill cutter 17 may have a pair of opposing rectangular sides and four profiled sides connecting the rectangular sides. Each profiled side may have a rectangular end portion located adjacent the respective rectangular side and a profiled intermediate portion connecting the respective end portions. Each rectangular end may have chamfered corners adjacent to the respective rectangular sides. Each profile may have a pair of opposing trapezoids converging from the respective end towards the centre of the mill cutter 17. Each profiled portion may further have a chamfered (thinned) rectangular central portion connecting the ends of the trapezoidal portion remote from the respective end. Each rectangular side surface may have a convex peripheral portion and a concave inner portion. A tapered wall may connect the peripheral portion of each projection to the respective inner portion. Each corner of the tapered wall may be scraped off.

Figures 4D-4F illustrate the mounting of mill cutters 17 to one of the typical mill backing plates 12 a-c. The sides of each mill backing plate 12a-c can also include one or more, such as three, working faces 23 w. Each working face 23w may have a plurality of grooves 24 formed therein for mounting a respective mill backing plate 12a-c with a mill cutter 17. Each of the flutes 24 may be V-shaped to facilitate a desired orientation of the mill cutter 17 therein. The desired orientation may be the orientation shown in fig. 4E or the orientation shown in fig. 4F.

Each mill cutter 17 may occupy only a small portion of the surface of the respective mill backing plate 12a-c, such that the surface needs to be populated with a number of mill cutters, such as greater than or equal to ten, fifteen, twenty, or thirty mill cutters. The mill cutters 17 may be mounted in respective recesses 24, such as by brazing. To facilitate the brazing operation, several mill cutters 17 may be incorporated in a bar (not shown) with a tinned adhesive that allows the welder (human or robot) to quickly braze the cutters to the surface.

Alternatively, each working surface 23w may be non-profiled and the cutters may be mounted on the working surface in random orientations. Alternatively, each mill backing plate 12a-c may be case hardened with a ceramic or cermet material rather than mounting the mill cutters 17 to the mill backing plate.

When drilling through the frac plug 2 using a chip removal mill, excessive torque is applied to the drilling motor, causing the motor to stall, which adversely affects operating efficiency and shortens the useful life of the motor, compared to the prior art. When using a roller cone drill bit to drill through the frac plug 2, the bit may need to be replaced due to bearing failure before all of the frac plug has been drilled through. Advantageously, roller cone mill bit 1 achieves the advantages of a pin tumbler mill and a roller cone bit without suffering from the disadvantages of both. The roller discs 11a-c reduce the torque while still providing stability against the sleeve or bushing column 4. The attachment of the mill backing plates 11a-c together provides additional support for the roller disks 11a-c, thereby reducing the load on the roller bearings 18 and thrust washers 19 and extending their useful life. Additionally, the fixed mill 12 may be replaced by grinding through the weld points attaching the mill backing plates 12a-c together to remove the worn fixed mill while a new mill backing plate is disposed on the support shaft and the new mill backing plate is welded together.

Figure 5 illustrates drilling a wellbore 25 using a hybrid roller cone drag bit 26 according to another embodiment of the present disclosure. The wellbore 25 may be drilled using a drilling system 27. The drilling system 27 may include a drilling rig 27r, a fluid handling system 27f, a blowout preventer (BOP)27b, a drill string 28, and a controller, such as a Programmable Logic Controller (PLC)27 p. Rig 27r may include a derrick 29d, a top drive 30, a drawworks 31, and a bedplate 29f at a lower end of the rig, the bedplate 29f having an opening through which a drill string 28 extends down into a wellbore 25 via a wellhead 32. Blowout preventers 27b may be connected to wellhead 32.

The drill string 28 may include a Bottom Hole Assembly (BHA)28b and a tubular string 28 p. The tubing string 28p may comprise joints of drill pipe, such as joined together by threaded couplings. BHA28b may be connected to tubing string 28p, such as by a threaded coupling, and includes roller cone drag bit 26 and one or more drill collars 33.

BHA components

26, 33 may be connected to each other, such as by threaded couplings. Top drive 30 may rotate 34r roller cone drag bit 26 via tubing string 28 p.

Alternatively, BHA28b may include a drilling motor for rotating roller cone drag bit 26 instead of or in addition to top drive 30. Alternatively, the drill string may include coiled tubing instead of the tubing string 28 p. Alternatively, the BHA28b may further include a steering tool, such as a bent sub or rotary steering tool, and a telemetry uplink for communicating with the PLC27 p.

The upper end of the tubing string 28p may be connected to the mandrel of the top drive 30. The top drive 30 may include a motor for rotating 34r the drill string 28. The top drive motor may be electric or hydraulic. The frame of top drive 30 may be coupled to rails (not shown) of derrick 29d to prevent top drive frame rotation during rotation 34r of drill string 28 and to allow vertical movement of the top drive with travel block 31t of drawworks 31. The frame of the top drive 30 may be suspended from the derrick 29d by a travelling trolley 31 t. The travelling block 31t may be supported by a wire rope 31r which is braided through the sheave wheels of the blocks 31c, t and extends to a winch 31w for winding up the wire rope, thereby raising or lowering the travelling block 31t relative to the rig floor 29 f.

The wellhead 32 may be mounted on a casing string 35 that has been deployed into the wellbore 25 and cemented 36 therein. The lower section of wellbore 25 may be vertical (shown) or deviated (not shown), such as inclined or horizontal.

Fluid handling system 27f may include a mud pump 37, a drilling fluid reservoir (such as a sump 38 or storage tank), a solids separator (such as a shale shaker 39), a pressure sensor 40, one or more flow lines, such as return line 41r, supply line 41s and feed line 41f, and a stroke counter 42. A first end of return line 41r may be connected to a flow junction 43 mounted on wellhead 32, and a second end of the return line may be connected to an inlet of shaker 39. The lower end of supply line 41s may be connected to the outlet of mud pump 37, and the upper end of the supply line may be connected to the inlet of top drive 30. The pressure sensor 40 may be assembled as part of the supply line 41 s. A first end of feed line 41f may be connected to an outlet of sump 38 and a second end of the feed line may be connected to an inlet of mud pump 37.

Pressure sensor 40 may be in data communication with PLC27p and may be operable to monitor riser pressure. Stroke counter 42 may also be in data communication with PLC27p and may be operable to monitor the flow of mud pump 12. The PLC27p may also communicate with a hook-shaped weighing cell clamped on the wireline 31r, and with a position sensor of the winch 31w, for monitoring the depth of the BHA28 b. PLC27p may further communicate with a torque sensor and a tachometer of top drive 30.

Mud pumps 37 may pump drilling fluid 44 from the sump 38 through supply lines 41s and to the top drive 30. The drilling fluid 44 may include a base fluid. The base fluid may be refined or synthetic oil, water, saline or water/oil emulsion. The drilling fluid 44 may also include solids, such as organo-soils, lignite, and/or bitumen, dissolved or suspended in a base fluid to form a slurry.

Drilling fluid 44 may flow from the supply line 41s and into the bore of the tubular string 28p via the top drive 30. Drilling fluid 44 may flow down tubing string 28p through the bore of BHA28b and out of roller cone drag bit 26, where the fluid may circulate cuttings away from the bit and return the cuttings up to an annular space 45 formed between an inside surface of casing 35 or wellbore 25 and an outer surface of drill string 28. Returns 46 (drilling fluid 44 plus cuttings) may flow up annulus 45 to wellhead 32 and exit the wellhead through flow junction 43. The returns 46 may continue through return line 41r and into shale shaker 39 and be processed thereby to remove cuttings to complete a cycle. With circulation of the drilling fluid 44 and returns 46, the drill string 28 may be rotated 34r by the top drive 30 and lowered 34a by traveling the trolley 31t to extend the wellbore 25 to a hydrocarbon bearing formation or a depth sufficient for geothermal power generation.

Figures 6 and 7A show roller cone drag bit 26. Figure 7B illustrates the mounting of fixed cutting structures 47 to roller cone drag bit 26. Roller cone drag bit 26 may include a body 48, a plurality of roller disks 49a-c, a plurality of breakers 55g, n, and a fixed cutting structure 47. Roller disks 49a-c, breakers 55g, n, and fixed cutting structures 47 may form the lower cutting face of roller cone drag bit 26. The roller discs 49a-c and breakers 55g, n may be located outside the cutting face, while the fixed cutting structure 47 may be located inside the cutting face.

The body 48 may have an upper coupling 50, a lower leg 51 for each roller disk 49a-c, and a dome 52 formed between the legs. The body 48 and the roller discs 49a-c may each be made of a metal or alloy, such as steel. The body 48 may be made by attaching three forgings together, such as by welding. The legs 51 may be evenly spaced around the body, such as three legs at one hundred twenty degrees. The upper coupling 50 may be a threaded pin for connection to a drilling motor or drill pipe. A hole may be formed through the coupler 50 and extend to a plenum (not shown) formed adjacent the dome 52.

Each leg 51 may have an upper shoulder 51s, an intermediate skirt 51h, a lower support shaft 51b, and a perforated boss 51 p. The shoulder 51s of each leg 51, the skirt 51h, the apertured boss 51p and the support shaft 51b may be connected to one another, such as by being integrally formed and/or welded together. Each perforated boss 51p may be in fluid communication with the plenum via a respective port formed in the coupling 50, and may have a nozzle (not shown) secured therein for discharging drilling fluid 44 onto a respective roller disc 49 a-c. Each support shaft 51b may extend from a respective skirt 51h in a radially oblique direction toward the center of roller cone drag bit 26,

alternatively, roller cone drag bit 26 may include a flow channel formed through dome 52 for each roller disk 49a-c instead of perforated boss 51 p. Each flow passage may be in fluid communication with a plenum and may have a nozzle (not shown) secured therein for discharging milling fluid onto a respective roller disc 49 a-c. The flow channels may be disposed about the center of roller cone drag bit 26.

The fixed cutting structure 47 may include a central hub 47h, blades 47a-c for each roller disk 49a-c, and a plurality of shear cutters (shearcuters) 53 mounted to each blade and embedded in the hub. The hub 47h and blades 47a-c may be integral, and each blade may extend radially outward from the hub. Each blade 47a-c may have an outer surface 47f formed to mate with a complementary inner side surface 49f of an adjacent roller disk 49 a-c. The shear cutters 53 may be mounted, such as by brazing, in corresponding recesses formed along the leading edges of the blades 47 a-c. The shear cutters 53 may be inserted, such as by brazing, into corresponding receptacles formed in the bottom of the central hub 47 h.

In addition, the fixed cutting structure 47 may further include a plurality of spare shear cutters (not shown). The spare shear cutters may be mounted, such as by brazing, in pockets formed along the bottom of the blades 47 a-c. Each spare shearing tool may be aligned with or slightly offset from the corresponding (front) shearing tool 53. In addition, the fixed cutting structure 47 may further include a plurality of depth of cut (DOC) limiters (not shown). The DOC limiter may be mounted, such as by brazing or interference fit, in a socket formed in the bottom of the inserts 47 a-c. The DOC limiter may be bullet-shaped or oval-shaped and may be made of any of the materials described above for the fragmenter 20.

The central hub 47h and blades 47a-c may be made of a composite material, such as ceramic and/or cermet powder infiltrated with a metal binder, or may be metallic, such as steel, and may be hard-faced. Each shear cutter 53 may comprise a superhard cutting table, such as polycrystalline diamond, attached to a hard substrate, such as a cermet, to form a compact, such as a Polycrystalline Diamond Compact (PDC). The cermet may be a carbide bonded by a group VIIIB metal such as cobalt tungsten carbide. The substrate and the cutting table may each be solid and cylindrical, and the diameter of the substrate may be equal to the diameter of the cutting table.

The blades 47a-c may be equally spaced about the hub 47h, such as three blades at one hundred twenty degrees. A void may be formed between each adjacent blade 47a-c to accommodate drilling fluid discharged from the perforated boss 51 p. The bottom of each blade 47a-c may be contoured. The contoured bottom may be flush or nearly flush with the shoulders of the roller disks 49a-c at the outer surface 47 f. The contoured bottom may slope toward the dome 52 along the blades 47a-c proximate the hub 47h and may flatten as the bottom reaches the hub. The thickness of the blades 47a-c and hub 47h may correspond to (such as being equal or nearly equal to) the diameter of the roller disks 49a-c, thereby creating a gap between the top of the fixed cutting structure 47 and the dome 52. The diameter of each of the roller disks 49a-c may be equal. The width of each blade 47a-c may range from half the diameter of the roller disk 49a-c to the diameter of the roller disk.

Each support shaft 51b and corresponding roller disk 49a-c may have one or more pairs of aligned grooves, and each pair may form a raceway for receiving a set of roller bearings (not shown). Thrust washers (not shown) may be disposed between each inner face 49f and the respective outer face 47f, such as in grooves (not shown) formed in the outer faces. Roller bearings and thrust washers may support the rotation of each roller disk 49a-c relative to the respective leg 51 and fixed cutting structure 47. The thrust washer may be lubricated by drilling fluid 44 discharged from the perforated boss 51 p.

Each leg 51 may have a lubricant reservoir (not shown) formed therein and lubricant passages (not shown) extending from the reservoir to the respective sets of roller bearings. Lubricant may be retained within each leg 51 by a pair of seals (not shown), such as O-rings, each positioned in a respective gland (not shown) formed in the inside surface of a respective roller disk 49 a-c. The first gland of each pair may be located adjacent the skirt 51h and the second gland of each pair may be located adjacent the respective thrust washer, thereby preventing leakage of lubricant from the roller bearings into the bore 25. A pressure compensator (not shown) may be provided in each reservoir to regulate the lubricant pressure therein. A balancing channel may extend from each reservoir and through dome 52 to operate the respective pressure compensator to adjust the lubricant pressure to be slightly greater than the bottom hole pressure.

Alternatively, a second gland may be located in the inboard face of each roller disk 49a-c so that the thrust washers are also lubricated by the lubricant.

Roller cone drag bit 26 may further include a threaded fastener 54 for each roller disk 49a-c and blade 47a-c for mounting fixed cutting structure 47 to skirt 51 h. Each blade 47a-c may have a receptacle formed therein and extending from the respective outer face 47 f. Each blade 47 may also have a socket (not shown) formed therein and extending from one end of the respective receptacle. Each receptacle may be oversized relative to the corresponding support shaft 51b to facilitate positioning of the fixed cutter 47 structure thereon. Each of the skirt 51h and the support shaft 51b may have a hole formed therein for receiving the shaft of a corresponding threaded fastener therethrough. Each skirt 51h may have a countersunk or counter-sunk opening adjacent the corresponding hole for receiving the head of the corresponding threaded fastener 54. Each blade receptacle may be threaded to receive an end of the shaft of a respective threaded fastener 54 to mount a respective blade 47a-c to a respective support shaft 51b and secure each roller disk 49a-c to a respective leg 51 by trapping it between the outer face 47f of the respective blade and a respective skirt 51 h.

Alternatively, the upper and lower edges of each skirt 51h may be protected from erosion and/or wear as discussed above with respect to skirt 16 h.

Each roller disk 49a-c may have a plurality of shoulders formed therein, such as heel, gage and internal shoulders for roller disks 49a, b, and heel and gage shoulders for roller disk 49 c. Rows of gage breakers 55g may be mounted around each of the roller disks 49a-c at the respective gage shoulders. A row of inner breakers 55n may be mounted around each roller disk 49a, b at respective inner shoulders. Each breaker 55g, n may be a blade that is mounted by interference fit in a respective socket formed in a respective roller disk 49 a-c. Each breaker 55g, n may be made of a cermet, such as cemented carbide, and may have a cylindrical or conical portion mounted in the respective roll disk 49a-c and a conical or chisel shaped portion projecting from the respective shoulder of the respective roll disk.

Rows of heel protectors 56 may be mounted around each roller disk 49a-c at the respective heel shoulders. Each heel protector 56 may be a blade that is mounted in a respective socket formed in a respective roller disk 49a-c by an interference fit. Each protector 56 may be made of a cermet (such as cemented carbide) and may be cylindrical.

Alternatively, the breakers 55g, n and/or the heel protector 56 may be covered with polycrystalline diamond (PCD). Alternatively, each breaker 55g, n may be a hardfaced milling tooth, or each row of breakers may include both a blade and a milling tooth.

Figures 8 and 9A illustrate a second hybrid roller cone drag bit 57 according to another embodiment of the present disclosure. The second hybrid roller cone drag bit 57 may be assembled as part of the BHA28b in place of the hybrid roller cone drag bit 26. The second hybrid roller cone drag bit 57 may include a body 58, a plurality of roller disks 59a, b, breakers 55g, n, a retaining cap 80, a rod 63, and a plurality of shear cutters 53. Roller discs 59a, b, breakers 55g, n, retaining cap 60 and shear cutters 53 may form the lower cutting face of second roller cone drag bit 57. The roller discs 59a, b and breakers 55g, n may be positioned at the exterior of the cutting face, while the securing cap 60 and shear cutter 53 may be positioned at the interior of the cutting face.

The body 58 may have an upper coupling 50, a lower leg 61 for each

roller disk

59a, 59b, and a domed portion 62 formed between the legs. The body 58 and the roller discs 59a, b may each be made of a metal or alloy, such as steel. The body 58 may be made by attaching three forgings together, such as by welding. The legs 61 may be evenly spaced around the body, such as three legs at one hundred twenty degrees. A hole may be formed through the coupler 50 and extend through the dome 62. The hole may be centrally located around the second hybrid roller cone drag bit 57.

Each leg 61 may have an upper shoulder 61s, an intermediate lower hem 51h, and a lower support shaft 61 b. The shoulder 61s, the skirt 61h and the support shaft 61b of each leg 61 may be connected to each other, such as by being integrally formed and/or welded together. Each support shaft 61b may extend from a respective skirt 61h in a radially oblique direction toward the center of the second hybrid roller cone drag bit 57. Each support shaft 61b and respective roller discs 59a, b may have one or more pairs of aligned grooves, and each pair may form a raceway to accommodate a set of roller bearings 64. Roller bearings 64 may support the rotation of each roller disc 59a, b relative to the respective foot 61 and retaining cap 60.

Each leg 61 may have a lubricant reservoir (not shown) formed therein and a lubrication passage (not shown) extending from the reservoir to the respective set of roller bearings. Lubricant may be retained within each leg 61 by a seal (not shown), such as an O-ring, located in a gland (not shown) formed in the inside surface of the respective roller disc 59a, b. A pressure compensator may be provided in each reservoir to regulate the lubricant pressure therein. A balancing channel may extend from each reservoir and through the dome 62 to operate the respective pressure compensator to adjust the lubricant pressure to be slightly greater than the bottom hole pressure.

Each roller disc 59a, b may be secured to a respective leg 61 by a plurality of balls (not shown) received in raceways formed by aligned grooves (not shown) in each roller disc and a respective support shaft 61 b. The balls may be fed to each raceway through a ball passage (not shown) formed in each leg 61 and retained therein by a corresponding ball plug (not shown). Each ball plug may be attached to a respective leg 61, such as by welding.

The rod 63 may be made of thick-walled pipe and metal or alloy such as steel. The upper end of the rod 63 may be threaded and may be received in a threaded socket formed in the dome 62 adjacent the bore to mount the rod to the body 58. The rod 63 may extend downward from the dome 62 and have a length corresponding to the diameter of the roller discs 59a, b. For each roller disc 59a, b, the rod 63 may have a port formed through the rod wall of the rod. Each port may discharge drilling fluid 44 onto a respective roller disc 59a, b. The second hybrid roller cone drag bit 57 may also include a nozzle 65 for each port. Each nozzle 65 may be mounted to the stem, such as by engaging threads formed on an outer surface of the nozzle with corresponding threads formed in a stem wall of the stem adjacent a corresponding port. Each nozzle 65 may be made of a corrosion resistant material such as a cermet.

The securing cap 60 may be made of any of the materials discussed above for the blades 47a-c and hub 47 h. The locking cap 60 may have a threaded receptacle formed in an upper portion thereof to engage the threaded lower end of the rod 63 to mount the locking cap to the rod. The securing cap 60 may have a recessed bottom and the shear cutters 53 are nested, such as by brazing, in corresponding receptacles formed therein.

Each roller disk 59a, b may have a plurality of shoulders formed therein, such as a heel shoulder, a gage shoulder, and an internal shoulder. Rows of gage breakers 55g may be mounted around each of the roller disks 49a-c at the respective gage shoulders. A row of inner breakers 55n may be mounted around each roller disk 59a, b at the respective inner shoulders. Rows of heel protectors 56 may be mounted around each roller disk 59a, b at the respective heel shoulders.

FIG. 9B illustrates a third hybrid roller cone drag bit 66 according to another embodiment of the present disclosure. Third cone drag bit 66 may be similar to second cone drag bit 66 except for having a bladed cap 67 instead of a retaining cap 60 and having adaptations to the bladed cap to accommodate rod 63 and dome 62. The bladed cap 67 may be made of any of the materials discussed above with respect to the blades 47a-c and hub 47 h.

The modified dome may have a receptacle formed therein adjacent the hole for receiving the upper end of the modified stem. Once the dome and stem socket have been engaged, the modified stem may be mounted to the dome by welding (not shown). The bladed cap 67 may have a receptacle formed in an upper portion thereof to engage the lower end of the modified rod. Once the cap and stem sockets have been engaged, the bladed cap 67 may be oriented and then mounted onto the stem socket by welding (not shown).

The bladed cap 67 may be made of any of the materials discussed above with respect to the blades 47a-c and hub 47 h. The bladed cap 67 may include a central hub 67h, blades 67a-c for each

roller disk

59a, 59b, and a plurality of shear cutters 53 mounted to each blade and embedded in the hub. The hub 67h and blades 67a-c may be integral, and each blade may extend radially outward from the hub. The shear cutters 53 may be mounted, such as by brazing, in respective pockets formed along the leading edges of the blades 67 a-c. The shear cutters 53 may be inserted, such as by brazing, into corresponding receptacles formed in the bottom of the central hub 67 h. The bottom of each blade 67a-c may be contoured. The contoured bottom may slope toward the dome 62 along the blades 67a-c near the hub 67h and may flatten as the bottom reaches the hub.

In addition, the bladed cap 67 may also include a backup shear knife and/or DOC limiter (not shown) as discussed above for the fixed cutting structure 47.

The blades 67a-c may be equally spaced about the hub 67h, such as three blades at one hundred twenty degrees. The roller disks 59a, b may be sized such that a cavity is formed between each adjacent roller disk. The bladed cap 67 may be oriented such that each blade 67a-c extends into a respective cavity. Blades 67a-c may extend into the cavity to create an overlap in the cutting profile of third cone drag bit 66. The blades may extend to an effective diameter that is greater than or equal to one-third, one-half, or two-thirds of the gage diameter of third cone drag bit 66. A space may be formed between each adjacent blade 67a-c to accommodate roller discs 59a, b.

Alternatively, the dome and the upper part of the rod may not be modified and connected together by a threaded connection.

As used herein, reference to a wellbore may relate to a cased or lined section of the wellbore or to an open hole section of the wellbore.

While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A roller cone mill drill bit for a wellbore, comprising:

a body having a coupler formed at an upper end thereof and a plurality of lower legs;

a plurality of roller disks, each roller disk being fixed to the support shaft of a corresponding leg to rotate relative to the support shaft;

a row of breakers mounted around each roller disk; and

a stationary mill mounted to the support shaft and including a backing plate for each roller disk,

wherein each pad is loaded with a cermet material.

2. The roller cone mill drill bit of claim 1, wherein:

the roller disc, the breakers and the fixed mill form a lower cutting face of the roller cone mill bit, and

the roller disk and the disruptor are positioned at an exterior of the cutting face, while the stationary mill is positioned at an interior of the cutting face.

3. The roller cone mill drill bit of claim 2, wherein:

each leg also has a skirt, an

Each bearing shaft extends from a respective skirt in a radially oblique direction toward a center of the roller cone mill bit.

4. The roller cone mill drill bit of claim 1, wherein:

each mill mat plate has a circular base and a plurality of sides converging towards a truncated apex,

at least one of the sides of each mill backing plate is a mounting surface, an

The mill backing plates are attached together at the mounting face.

5. The roller cone mill drill bit of claim 4, further comprising:

a set of roller bearings disposed between each support shaft and the respective roller disc; and

a thrust washer disposed between each roller disk and the respective seat.

6. The roller cone mill drill bit of claim 5, wherein:

each leg also has a skirt and a perforated boss,

flutes are formed between the skirt of each adjacent leg and each apertured boss is located in a respective flute.

7. The roller cone mill drill bit of claim 6, wherein the roller bearing and thrust washer are configured to be lubricated by fluid discharged from the perforated boss.

8. A roller cone mill drill bit according to claim 5, wherein each leg has a lubricant reservoir formed therein and lubricant passages extending from the reservoir to the respective set of roller bearings.

9. The roller cone mill drill bit of claim 4, wherein:

each mill backing plate has a receptacle formed therein and extending from the base, an

One end of a respective support shaft is received in the receptacle to mount the mill backing plate to the body.

10. The roller cone mill drill bit of claim 9, wherein:

each leg also has a skirt, an

Each roller disk is secured to the respective leg by being entrained between the base of the respective mill backing plate and the respective skirt.

11. A roller cone mill drill bit according to claim 9, wherein each roller disc has a tapered portion formed at the periphery of its inner face and each seat has a complementary lip portion formed at its periphery.

12. The roller cone mill drill bit of claim 1, wherein the roller cone mill drill bit comprises three legs and three roller discs.

13. The roller cone mill drill bit of claim 1, wherein the body further has a dome formed between the legs, a bore formed through the coupler and extending to a plenum formed adjacent the dome, and a channel formed through the dome for each roller disc.

14. The roller cone mill drill bit of claim 1, wherein the cermet material is a plurality of cutter blocks brazed to the backing plate.

15. The roller cone mill drill bit of claim 14 wherein the cutter blocks are brazed into grooves formed in the backing plate in a desired orientation.

16. The roller cone mill drill bit of claim 14, wherein:

each cutter block has a pair of opposing rectangular sides and four profiled sides connecting the rectangular sides,

the profiled sides each having rectangular end portions located adjacent the respective rectangular side and a profiled intermediate portion connecting the respective end portions, and

each rectangular side has a convex perimeter portion and a concave interior portion.

17. A method of drilling through a plug using the roller cone mill drill bit of claim 1,

assembling the roller cone mill drill bit as part of a mill column;

deploying the mill string into a casing or liner string disposed in the wellbore and then into a plug disposed in the casing or liner string; and

injecting a grinding fluid through the mill string, rotating the roller cone mill bit, and engaging the roller cone mill bit with the plug to thereby drill through the plug.

18. A roller cone mill drill bit for drilling a wellbore, comprising:

a plurality of roller disks, each disk being fixed to the support shaft of a corresponding leg to rotate relative to the support shaft;

a row of breakers mounted around each roller disk; and

a fixed cutting structure mounted to the support shaft and comprising:

a central hub;

a blade for each roller disk, an

A plurality of shear cutters mounted to each blade.

19. The roller cone mill drill bit of claim 18, wherein the fixed cutting structure further has a plurality of shear cutters embedded in the hub.

20. The roller cone mill drill bit of claim 18, wherein:

each of the legs also has a skirt that,

the roller cone mill drill bit further includes a threaded fastener for each roller disc and blade,

each of the skirt and the support shaft having a bore formed therein for receiving the shaft of a respective said threaded fastener therethrough,

each skirt has an opening adjacent to the respective hole to receive the head of the respective threaded fastener, and

each blade has a threaded receptacle formed therein and receiving an end of the shaft of the respective threaded fastener to mount the respective blade to the respective support shaft and to secure each roller disk to the respective leg.

21. A roller cone mill drill bit for drilling a wellbore, comprising:

a body having a coupler formed at an upper end thereof, a plurality of lower legs, a dome formed between the legs, and a hole formed through the coupler and the dome.

A plurality of roller discs, each disc being fixed to the support shaft of a respective leg for rotation relative thereto;

a row of breakers mounted around each roller disk; and

a rod mounted to the dome adjacent the aperture and having a port formed through a rod wall of the rod for each roller disk;

a fixing cap mounted to a lower end of the rod; and

one or more shear cutters embedded in or mounted to the retaining cap.

22. The roller cone mill drill bit of claim 21, wherein:

the fixing cap has a central hub and a blade for each roller disk,

a cavity is formed between each adjacent roller disk, and

the retaining cap is oriented such that each blade extends into a respective cavity.