Roller cone drill bit with cuttings evacuator

An earth boring drill bit having an alternate path to allow cuttings to be ejected or evacuated from the drill bit and up the bore hole is disclosed. The evacuation hole of the present disclosure allows larger sized cuttings to evacuate from the bit without having to be continually ground by rolling cone cutters until the cuttings are small enough to follow a path around the edge of the shirttail of the bit and up the borehole. A cuttings restrictor is disposed at the inlet of the evacuation hole. The cuttings restrictor ensures that only cuttings that are sized to move completely through the evacuation hole and exit the drill bit are allowed to enter the evacuation hole.

TECHNICAL FIELD

The present invention relates generally to earth boring drill bits for drilling a wellbore, and more particularly to a roller cone rock bit with a cuttings evacuator.

BACKGROUND

Roller cone or rotary cone bits are well known in the art of earth boring drilling operations. The most common design of a roller cone bit consists of three roller cones, each rotatably mounted on a downwardly and radially inwardly extending bearing pin. Each roller cone supports a plurality of cutting elements, which are referred to as cutters. Each of the bearing pins is spaced approximately 120 degrees apart with the three pins formed as a part of a bit body. The entire structure is rotated at the end of a drill string. Boring is accomplished by applying weight to the drill bit and rotating the drill string, thereby causing the roller cones to roll and crush the rock formation beneath the bit. As the bit is rotated and moves through a formation, the cutter elements contact and disintegrate portions of the formation in order to form the desired bore hole. The earth separated from the formation become cuttings that are removed from the bottom and sides of the bore hole and washed away by a drilling fluid, such as air or drill mud, that is supplied to the drill bit from the surface through the hollow rotating drill string. The cuttings are suspended in the drilling fluid and carried to the surface in the space between the bore hole and the drill string.

The cuttings produced by the drilling operation are abrasive and with continued use will erode the cutters and other portions of the bit. The grinding and re-grinding of the cuttings produced by the drilling operation slows the formation penetration rate of the bit and shortens the life of the bit. The re-ground cuttings tend to dull the cutters and the finely ground particles may enter the bearing surfaces formed between the roller cones and the journals supported by the bit, restricting cutter cone rotation and further limiting bit life.

Reference is made to U.S. Pat. No. 6,082,473 to Dickey, which is incorporated herein by reference and discloses a self-cleaning polycrystalline diamond compact (PDC) bit.

Reference is also made to U.S. Pat. No. 5,462,128 to Gray, which is incorporated herein by reference and discloses a cutter bit having a passageway for cuttings to escape to the surface of the hole.

Further reference is made to U.S. Pat. Nos. 2,692,117 and 3,099,324 each to Kucera which disclose drill bits having passageways through the bit for the evacuation of cuttings.

SUMMARY

An earth boring drill bit having an alternate path to allow cuttings to be ejected or evacuated from the drill bit and up the bore hole is disclosed. The evacuation hole of the present disclosure allows larger sized cuttings to evacuate from the bit without having to be continually ground by rolling cone cutters until the cuttings are small enough to follow a path around the edge of the shirttail of the bit and up the borehole. A cuttings restrictor is disposed at the inlet of the evacuation hole. The cuttings restrictor ensures that only cuttings that are sized to move completely through the evacuation hole and exit the drill bit are allowed into the evacuation hole.

In certain embodiments, the drill bit may include a drilling fluid hole that extends from an inner plenum of the bit and intersects the evacuation hole. Drilling fluid may flow from the inner plenum, through the drilling fluid hole, and into the evacuation hole. This fluid flow may enhance the evacuation and ejection of cuttings from the evacuation hole.

Other embodiments of the drill bit of the present disclosure may include an excluder disposed at the outlet of the evacuation hole. The excluder may include features that partially block an opening leading to the outlet, and thus prevent debris and flushed cuttings from reentering the evacuation hole through the outlet.

Technical advantages of the disclosed drill bit include features that allow larger sized cuttings to be evacuated from the drill bit, as opposed to being reground by the cutter cones. By reducing the amount of regrinding that occurs in the drilling operation, penetration efficiency may be improved, fewer cutters may be lost, and bits may last longer.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is made toFIG. 1, which shows a rotary cone bit including a bit body10having at one end a threaded shank12for attachment to a drill string member (not shown). The threaded shank12is adapted to be threadably engaged with a drill string in accordance with conventional drill bit operation. Extending from the bit body10are three leg portions14(only two of which are shown), each providing support for a rotatable roller cutter cone16. Both the bit body10and the shank12have an axially extending passageway defining an internal plenum (seeFIG. 2). Drilling fluid is directed through the plenum and exits at nozzles20(only one shown). The drilling fluid may be air, liquid (water or mud), foam, or any combination thereof. For example, a liquid such as drilling mud may be employed to flush the bore hole of debris during the drilling operation. A nozzle20is positioned between each pair of cones. Each of the nozzles may be surrounded by a hard facing ring for improved wear resistance against debris circulating around the drill bit during a drilling operation in a bore hole. The nozzles20may be interchangeable jet nozzles, which may be sized to achieve a desired pressure drop of the drill fluid.

As illustrated inFIG. 1, the roller cutter cones16each have substantially the same base diameter to permit cutting teeth22on each cone to project between cutting22teeth of the other cutter cones. The cutting teeth22on each of the cutter cones16are arranged in rows. The cutters may be any material suitable for removing and crushing an earth formation and such material may depend on the composition of the formation being drilled. In the embodiment shown, the cutter teeth22comprise tungsten carbide inserts press fit into the cone surface and projecting therefrom. An evacuation hole38is illustrated by broken lines inFIG. 1. The evacuation hole38extends at an angle through the leg of the bit and provides a passageway between a central region of the bit between the cones16and an external surface of the bit leg14. Embodiments of the present disclosure may include an evacuation hole38through each leg14of the bit. Thus, a bit may have three legs14where each leg defines an evacuation hole38. However, one evacuation hole38for a single bit may be sufficient. Cuttings separated from the formation by the roller cones16flow through the evacuation hole38, past a flushed cuttings excluder, and into the space between the bit body10and the borehole wall.

Reference is made toFIG. 2, which is a cross section of a portion of the rotary cone bit ofFIG. 1. The cross section shows one leg14and one pin30extending from the leg14. The pin30provides the bearing and sealing surfaces that interface with corresponding surfaces of the roller cone16, which has been removed for clarity. The cutter cones rotate about the axis of the pin30. This axis of rotation is inclined with respect to the vertical axis of the bit. An exterior portion of the leg14is known as the shirttail32.

Drilling fluid is directed through the drill string and reaches the plenum of the bit, which is defined by an interior plenum surface18. From the plenum the fluid is received by one or more discharge ports34. Drill bits usually have one discharge port34per roller cone. Fluid flows through the discharge ports34and exits to the bit cavity36located in a central region of the bit among the cones and between the cones and a surface of a throat area39.

The drilling fluid serves to keep the bit cool. For example, roller cone bits often have non-sealed rolling element bearings that support the roller cones16as they rotate. Some of the drilling fluid may be directed to flow through channels internal to the bit body10to these bearings in order to keep them cool during down hole operation.

The drilling fluid also functions to flush earth cuttings out of the bit cavity36, around the shirttail32, and up the borehole. For cuttings to be flushed out through this path, they must be sufficiently small to fit between the shirttail32and the wall of the borehole. Larger cuttings may not be immediately flushed from the bit cavity36. Rather, they may be reground by the cutters until the cuttings are small enough to flow with the drilling fluid between the shirttail32and the borehole wall. This regrinding reduces bit efficiency and accelerates bit and cutter wear. Also, the drilling fluid is susceptible to recirculation in the cavity36near the discharge nozzles20, which can cause erosion and coring problems with the bit near the nozzles20. In addition, continuous grinding of larger cuttings may lead to loss of cutter inserts, may reduce bit life, and may reduce bit penetration.

According to an embodiment of the present disclosure, drilling fluid may flush earth cuttings away from the roller cone cutters16and the bit through a passageway defined by an evacuation hole38. The evacuation hole38may be formed through the leg14and may be at any suitable angle. An evacuation hole38may be formed through a single leg14, all the legs14, or less than all the legs14. In certain embodiments, the evacuation hole38may be a constant diameter straight hole as shown inFIG. 2. In other embodiments, the evacuation hole38may be an increasing diameter tapered hole38′ (as shown inFIG. 3C), where the diameter of the tapered hole38′ increases toward the outlet. The evacuation hole38may also range in diameters. Thus, larger bits may support a larger diameter evacuation hole38. The evacuation hole38may be formed in the bit leg14by drilling, milling, plunge electro-discharge machining or any suitable process for removing material. A milled evacuation hole38may be generally slot-shaped, as opposed to cylindrical.

In certain embodiments, an interior surface of the evacuation hole38may support a sleeve. The sleeve may run the length of the evacuation hole38and may extend into the cavity36as further detailed below with respect to the description of the cuttings restrictor42. The sleeve may be employed to provide an abrasion/erosion resistant inner surface for the evacuation hole38, which may resist wear caused by cuttings being evacuated through the bit. The sleeve may comprise any suitable abrasion/erosion resistant material, such as tungsten carbide, a glass filled polymer, or a ceramic. The sleeve may have a tapered inner surface to assist in the prevention of clogging. The tapered surface may be an interior surface of the sleeve, while the exterior surface of the sleeve corresponds to the geometry of the evacuation hole38.

The outlet of the evacuation hole38may be formed in any portion of the backside surface of the leg14that is up hole of the bottom edge33of the shirttail32. For example, the outlet may be formed in a surface adjacent an upper shoulder surface35and may be on the leading or trailing side of the leg14. In other embodiments, it may be formed partially in the shoulder surface and partially in the outer (gage or shirttail surface) of the leg14. Still further, the outlet may be formed in the outer surface of the leg14.

The cuttings follow path37and enter the evacuation hole38from the bit cavity36and exit from the outlet into the space41between the bit body10and the borehole wall15.

The entry portion of the evacuation hole38may be through a surface of the bit generally in the throat area39. In certain embodiments, the evacuation hole38may include features at its inlet that prevent cuttings from becoming lodged in the evacuation hole38, and may include features at its outlet that prevent re-entry of flushed cuttings or other debris in the evacuation hole38.

According to one embodiment, the evacuation hole38may be in fluid communication with a drilling fluid hole40, which is connected to the plenum. The drilling fluid hole40may be smaller in diameter than the evacuation hole38. The drilling fluid hole40may be defined by the plenum at one end and an intersection with the evacuation hole38at the other end. Similar to the evacuation hole38, the drilling fluid hole40may be formed by drilling, plunge electro-discharge machining, or milling.

In certain embodiments, the drilling fluid hole40may intersect an up-hole portion of the evacuation hole38. Drilling fluid flowing through the plenum may also flow through the drilling fluid hole40and into the evacuation hole38. This flow will help draw cuttings into and completely through the evacuation hole38. In this manner, cuttings may be drawn through the evacuation hole38to be ejected away from the bit. Some embodiments of the present disclosure may effectively evacuate and remove cuttings from the cavity36without a drilling fluid hole40.

Reference is now made toFIG. 3A, which shows an isometric view of a portion of the drill bit ofFIGS. 1 and 2.FIG. 3Bshows the bit in cross-section.FIGS. 3A and 3Bshow, exploded from the bit, a cuttings restrictor42at the inlet of the evacuation hole38and a flushed cuttings excluder44exploded from the outlet of the evacuation hole38. The cuttings restrictor42and the flushed cuttings excluder44may be formed from any suitable abrasion or erosion resistant material including steel, tungsten carbide, a glass filled polymer, or a ceramic material. In certain embodiments, the restrictor and excluder features described herein may be formed integral with the bit body10. The cuttings restrictor42and the flushed cuttings excluder44may fit into respective countersunk holes formed in the bit. The restrictor42and excluder44may be press fit, glued, screwed or otherwise secured into the countersunk holes.

FIG. 4Aillustrates a detailed view of the cuttings restrictor42secured to the bit. As shown inFIG. 4A, at least a portion of the cuttings restrictor42extends into the bit cavity36from the interior surface of the throat40of the bit. In certain embodiments, the restrictor may have an external annular portion43delimited by a flange45. The annular portion43may extend ⅛ inch, or ¼ inch, or up to approximately one-half inch into the cavity36. In other embodiments, the annular portion43may extend up to one inch into the cavity36. The restrictor42may extend into the cavity any suitable distance such that it does not interfere with the roller cutter cones16. Extension into the cavity allows the restrictor42to perform its function of restricting larger sized cuttings from entering the evacuation hole38. When a cutting that is sized too large to fit through the evacuation hole38contacts the restrictor42, it may be held in place by the restrictor42until the vibration of the bit or shutting off the flow of the drilling fluid allows the large sized particle to fall away from the restrictor42.

AlthoughFIG. 4Ashows only an up-hole perimeter of the annular portion43extending into the cavity36, in certain embodiments, the down-hole perimeter of the annular portion43may also extend into the cavity36. The cuttings restrictor42need not have a cylindrical opening. The restrictor42may be any suitable shape that restricts cuttings that are sized to clog the evacuation hole38from entering the evacuation hole38. In certain embodiments, the an inlet of the cuttings restrictor may have an asymmetrical shape.

A beveled surface46may be interior to the annular portion43. The beveled surface46transitions to a tapered inner surface48. The inner perimeter where this transition occurs may be a minimum diameter50of the restrictor42. This minimum diameter50ensures that if a cutting particle passes the minimum diameter50, then it will continue to move or flow through the portion of the restrictor42defined by the tapered inner surface48and on through the larger diameter evacuation hole38. In this manner, only cuttings that are sized to completely exit the bit through the evacuation hole38may enter through the restrictor42.

FIG. 4Billustrates an alternate embodiment of the present disclosure where a tapered surface similar to the tapered surface48of the cuttings restrictor42has been machined directly into the bit. As such, the evacuation hole38includes a tapered inlet portion56. Similar to the tapered surface of the cuttings restrictor42, the tapered inlet portion56has a minimum diameter that restricts cuttings that are not sized to pass completely through the evacuation hole38from entering the evacuation hole38.

Returning toFIGS. 3A and 3B, a cuttings excluder44is shown. The cuttings that flow through the evacuation hole38reach the flushed cuttings excluder44at the outlet of the evacuation hole38. The flushed cuttings excluder44comprises a ring52, which supports a prong54. An alternate embodiment comprises the prong54or similar excluding member that is supported by the bit body10, as opposed to a separate ring. The prong54ensures that cuttings that have already been flushed away from the bit and up the bore hole or any other debris, do not reenter the evacuation hole38through the outlet. Also, particles that become dislodged from the bore hole wall or are otherwise present in the bore hole may be prevented from entering the evacuation hole38through the outlet. In certain embodiments, the prong54may extend across the ring52less than the full diameter of the excluder44. The flushed cuttings excluder44may comprise a hinged steel prong which opens towards the exterior of the bit. In this manner, cuttings flowing through the evacuation hole38or the fluid pressure flowing through the evacuation hole38may open the prong to allow cuttings to exit through the flushed cuttings excluder44. However, when the drilling air/mud/foam pressure is removed and cuttings are no longer flowing through the evacuation hole38, the spring of the prong54may bias the prong54in its resting position where it can block cuttings from falling into the outlet of the evacuation hole38from the top side of the bore hole downward.

The flushed cuttings excluder44including the ring52and the prong54also may be positioned at the inlet of the evacuation hole in lieu of the restrictor42.

Thus, according to the teachings of the present disclosure, an alternate path for cuttings to be ejected or evacuated from a drill bit and up the bore hole is disclosed. The evacuation hole38of the present disclosure allows larger sized cuttings to evacuate from the bit without having to be continually ground by the rolling cone cutters16until the cuttings are small enough to follow the path around the edge of the shirttail of the bit and up the borehole. In this manner, cutter or bit failure may be prevented and drilling efficiency may be improved.

Embodiments of the invention have been described and illustrated above. The invention is not limited to the disclosed embodiments.