(19)
(11) EP 0 230 129 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication:
29.07.1987 Bulletin 1987/31

(21) Application number: 86309813.3

(22) Date of filing: 16.12.1986
(51) International Patent Classification (IPC)4E21B 10/24
(84) Designated Contracting States:
AT BE CH DE ES FR GB GR IT LI LU NL SE

(30) Priority: 13.01.1986 US 818326

(71) Applicant: DRUMCO
Jasper Alabama 35501 (US)

(72) Inventors:
  • Johnsey, Walter F.
    Birmingham Alabama 35201 (US)
  • Drummond, Donald D.
    Jasper Alabama 35501 (US)
  • Wood, Roy W.
    Birmingham Alabama 35214 (US)

(74) Representative: Newby, John Ross et al
J.Y. & G.W. Johnson Furnival House 14/18 High Holborn
London WC1V 6DE
London WC1V 6DE (GB)


(56) References cited: : 
   
     
    Remarks:
    The title of the invention has been amended (Guidelines for Examination in the EPO, A-III, 7.3).
     


    (54) Drill bit lubrication system


    (57) A drill bit for drilling into underground formations is disclosed, the drill bit having one or more first conduits (18) for supplying gaseous drilling fluid to the cutting cone bearings (14), one or more second con­duits (19) for supplying lubricant to the cutting cone bearings (14), which conduits (18, 19) combine the gaseous drilling fluid with the lubricant in order to supply a mixture of gaseous fluid and lubricant to the bearings (14).




    Description

    FIELD 0F THE INYENTION



    [0001] The present invention relates to a drill bit for drilling into earth formations, and more particularly to a driIl bit having means for providing a controlled flow of lubricant or combining liquid lubricant with gaseous driIling fluid to supply a lubricant and gaseous fluid mixture to the cutting cones for lubrication and cooling of the cutting cone bearings.

    DESCRIPTION OF THE PRIOR ART



    [0002] Typical drill bits are used in combination with, for example, a rotary drill pipe system, for drilling deep holes into underground formations, such as into rock, coal, or the like. In a drilling system of this type, a drill string is formed by connecting a number of hollow extension pipes through which a drilling fluid, which may be either a drilling mud or a gaseous drilling fluid such as air, is supplied by way of the extensions to the drill bit to be exhausted at the surface being drilled. The drill bit contains suitable openings, such as nozzles, for discharging the drilling fluid from the drill bit onto the surface being drilled to clear dust and cuttings and scavenge them away from the area of the cutting cones. The drill bit of the present invention is for use in connection with drilling systems using a gaseous drilling fluid.

    [0003] ln the above-described system, a subassembly may be located on the dri)l string between the drill bit and the extension pipe line. A subassembly structure is known in the art and generally includes a central conduit, or plenum chamber, which extends from the rotary drill extension pipe to the vicinity of the drill bit. Pressurized air or other gasous drilling fluid from the rotary drill flows through the plenum chamber and is discharged downwardly through the drill bit, either through a central opening, or through nozzles positioned between the cutting cones.

    [0004] A source of major concern in the drilling art is protection of the cutting cones from excess wear and heat. It is desirable to lubricate or cool the cutting cone bearings and shafts which increases the useful life of the cutting cones and avoids the necessity of frequent drill bit replacement during a drilling operation. In the prior art, various systems have been employed to supply lubricant to the cutting cone bearings for lubrication during operation. In these systems, lubricant may be supplied from a storage means which is located either in the subassembly structure or in the drill bit itself. For example, in U.S. Patent No. 3,029,88l, a system is disclosed wherein a lubricant storage means is provided in the subassembly. The pressure of the gaseous fluid in the subassembly plenum chamber acts upon an expandable liner to force lubricant from the storage means, and into a lubricant supply conduit provided in the subassembly. The subassembly conduit communicates with a drill bit conduit to supply lubricant to the bearings. A major disadvantage which may arise in this system is that lubricant accumulates in the area of the bearings, and may break down due to the heat of the cutting cones. It is desirable, therefore, to provide means to continually flush lubricant from the bearings before such breakdown occurs.

    [0005] Another approach in the prior art has been to use the gaseous drilling fluid itself to cool the cutting cone bearings. For example, in U.S. Patent No. 4,080,09l, a drill bit is disclosed which provides a conduit communicating between the hollow interior of the drill bit and the cutting cone bearings, to allow passage of drilling air to the bearings. In this arrangement, relatively cool drilling air is intro­duced to cool the cutting cone bearings and shafts, as they become heated during the drilling operation. U. S. Patent No. 3,l25,l75 also discloses a structure which provides a conduit communicating between the hollow interior of the drill bit and the cutting cone bearings. In this structure, a ring member is provided in the drill bit, which reduces the quantity of air which enters the conduit, as compared to the quantity of air which exits in the vicinity of the cutting cones. Both of these systems suffer from the disadvantage that, although the bearings are cooled, they are not lubricated.

    [0006] U. S. Patent No. 2, 8l4,464 discloses a drill bit structure provide a conduit between the drill bit interior and the cutting cone bearings, and suggests that the drilling fluid may consist of an air stream containing a fine spray of lubricant such as oil, to lubricate the cutting cone bearings. Of course, when oil is injected into the drilling air, oil is also contained in the air which exits at the drilling surface in the vicinity of the cutting cones. This is undesirable since it results in oiling the drilling surface and oiling of the dust and cuttings arising from the drilling operation.

    [0007] Another gaseous fluid drilling system employing lubricant entrained in the gaseous drilling fluid is disclosed in U. S. Patent No. 3,924,695. The drill bit structure disclosed includes a separator assembly, which acts to remove lubricant from the gaseous drilling fluid before it is discharged onto the drilling surface. The lubricant, removed from the gaseous stream is then directed to the cutting cone bearings by way of a conduit provided in the drill bit.

    [0008] A drill bit structure providing for an internal storage source of liquid lubricant is disclosed in U.S. Patent No. 4,375,242. In the drill bit, an air conduit is provided between the drill bit interior and a sealing o-ring, which supports the cutting cone on the bit. The pressure from the air conduit also acts to urge lubricant from the internal storage source, and supply the lubricant by way of a separate conduit to the cutting cone bearings for lubrication.

    [0009] With the foregoing in mind, it is an object of the present invention to provide for an improved drill bit structure which enables lubricant, which may be supplied, for example, from a storage means in a drill subassembly, to be combined with gaseous drilling fluid in a conduit means which communicates between the interior of the drill bit and the cutting cone bearings. A gaseous fluid and lubricant mixture or at the normal operating pressure, lubricant is supplied through the conduit means at a controlled rate to the cutting cone bearings to provide both cooling and lubrication.

    SUMMARY OF THE INVENTION



    [0010] The present invention provides for a drill bit for use in a rotary drill system utilizing a source of gaseous fluid under pressure. The drill bit is provided with at least one rotary cutting cone for drilling into an earth formation, such as rock or coal. The bit is provided with a first conduit means, in the form of an air passage which extends from the hollow interior of the drill bit to the cutting cone bearings. A second conduit means is provided in the drill bit for receiving lubricant from an external storage source, which may be contained in a drilling subassembly. The second conduit means is in the form of a lubricant passage which intersects with and provides lubricant to the first conduit means, whereby a lubricant and gaseous fluid mixture may be formed beyond the intersection. The resulting mixture or lubricant flow is directed, through the first conduit means, to the cutting cones for cooling and lubrication of the cutting cone shafts and bearings. Additionally, the second conduit means may contain replaceable orifice elements which regulate the amount of lubricant entering the second conduit means for combining with the gaseous fluid in the first conduit means.

    DESCRIPTION OF THE DRAWINGS



    [0011] 

    Figure l is a cut-away perspective view of a drill bit of the present invention;

    Figure 2 is cross-sectional view taken across line 2-2 in Figure l; and

    Figure 3 is a cross-sectional view of a drill bit of the present invention attached to a subassembly having an internal storage supply of lubricant.


    DESCRIPTION OF THE INVENTION



    [0012] The drill bit of the present invention is intended to be attached to a drill string or drilling subassembly, the drill string or subassembly having a lubricant storage means and means for supplying the lubricant to the drill bit.

    [0013] The drill bit of the present invention comprises a main body portion l0 as shown in Figure l. An upper nipple ll attaches the drill bit to a drilling subassembly, or to the extension pipes forming a drill string. The nipple of the drill bit is threaded, so as to threadedly engage the tapered socket of a subassembly and form a firm connection therebetween. One or more leg portions l2 extend downwardly from the body portion l0 of the drill bit at circumferencially spaced intervals. Mounted for rotation in each leg portion l2 is a rotary cutter l3. It is generally preferred in the industry to use a drill bit having three cutting cones. Cutting cones l3 are rotatably mounted to the leg portion of the drill bit by bearings l4 and bearing shafts l5.

    [0014] The drill bit contains a hollow interior portion l6 forming a chamber for receiving gaseous drilling fluid from the subassembly plenum chamber. The gaseous drilling fluid from chamber l6 is exhausted from the drill bit into the area of the cutting cones to pick up and remove the dust and cuttings which result from the drilling operation. The gaseous drilling fluid may be ejected through nozzles l7 located between the cutting l0cones. Alternatively, the nozzles may be omitted and the gaseous fluid ejected through a central orifice located between the cutting cones, as is known in the art. In the present case, the orifice must have sufficient restriction to provide an elevated pressure within the chamber l6.

    [0015] Communicating between chamber l6 and the cutting cone bearings l4 and bearing shafts l5, is first conduit means l8 forming passage for the gaseous drilling fluid. First conduit means l8 allows gaseous drilling fluid, such as air, to pass from the hollow interior of the drill bit through the first conduit means to cool the cutting cone bearings l4 and bearing shafts l5.

    [0016] The drill bit of the present invention is also provided with a circumferential groove 20 surrounding the drill bit, to form a reservoir for lubricant which is located in the surface of the drill bit surrounding the nipple ll. The circumferential groove, which preferably in both width and depth measures approximately 5 mm (3/l6"), receives lubricant from, for example, a supply conduit 34 in a drilling subassembly, as described hereinafter in connection with Fig. 3. Second conduit means or bore l9 connects circumferential groove 20 with first conduit means l8, and supplies lubricant from the groove 20 to the gaseous drilling fluid passing through the first conduit means l8 to the bearings. The precise point where second conduit means l9 intersects with first conduit means l8 is a choice of design.

    [0017] In one mode of operation, the lubricant supplied by second conduit means or bore l9 is picked up and combined with the gaseous drilling fluid in first conduit means l8, and is supplied to the cutting cone bearings l4. In this manner, a mixture of lubricant and gaseous drilling fluid is supplied to the bearings to achieve both a lubricating and a cooling effect. Also, lubricant build-up and heat breakdown at the bearings is avoided due to the continuous supply of fresh mixture provided to the bearings, the air in the mixture acting to flush out lubricant before it accumulates.

    [0018] Means is provided to regulate the amount of lubricant supplied to the bearings. To this end, second conduit means l9 may be fitted with replaceable orifices, in the present instance annular rings 2l. The diameter of the orifice in annular rings 2l may be varied to regulate the flow of lubricant supplied to the bearings. The annular rings 2l may be formed of metal, plastic, or any suitable material. The annular rings 2l are inserted into second conduit means l9 in the vicinity of circumferential groove 20, for example in a counter bore 22 at the mouth of the bore l9. When it is desired to modify the rate at which lubricant is supplied to the bearings, the user simply removes the drill bit from the subassembly, and replaces each annular ring 2l with an annular ring having a different sized orifice, to provide the desired lubricant flow.

    [0019] Referring to Figure 3, the drill bit of the present invention is shown attached to a drilling subassembly. The drill bit of the present invention is designed to work in combination with a subassembly having a supply of lubricant contained therein. A subassembly of this type is shown, for example, in applicant's co-pending European Patent Application 0106700, filed October 18, 1982. Another subassembly having lubricant storage is shown in U. S. Patent No. 3,029,88l.

    [0020] A representative subassembly comprises a housing 30 and a hollow plenum chamber 3l. Gaseous drilling fluid from the drill line is supplied to plenum chamber 3l, and then to drill bit interior chamber l6. The subassembly structure additionally contains lubricant storage means in the form of, for example, annular chamber 32 surrounding the housing. The flow of lubricant from the storage means may be effected in various ways. For example, a passageway 35 may be provided to allow communication between the pressurized gaseous fluid in the plenum chamber and the lubricant storage area, to act as a pressure source forcing lubricant downward and into lubricant supply conduits 34, at spaced intervals around the circumference of the subassembly. A piston (not shown) may be provided in the annular chamber 32 to force lubricant from the chamber. It should be apparent that other types of pressure means are equally suitable to force lubricant from the storage means, for example, an expandable liner.

    [0021] The lubricant forced through supply conduit 34 accumulates in the circumferential groove 20 on the drill bit. In the preferred embodiment, illustrated in Figure 2, the circumferential groove extends entirely around the drill bit. This obviates the need to align supply conduit(s) 34 on the subassembly with individual bores or second conduit means l9 in the drill bit in order to supply lubricant to the second conduit means.

    [0022] It has been found beneficial to the operation of the present invention for an orifice ring 36 to be placed in the plenum chamber of the subassembly in order to somewhat reduce the flow of gaseous fluid. The orifice should be located downstream from the pressure means acting on the lubricant storage in the subassembly, and upstream of the entrance to first conduit means l8 in the hollow interior chamber l6 of the drill bit. By varying the pressure as controlled by orifice ring 36, the flow of lubricant to the bearings can be varied or controlled. In this manner, a greater pressure of gaseous fluid is acting upon the lubricant storage means, while a somewhat reduced fIow acts upon the first conduit means l8. Sufficient force to achieve continuous lubricant flow from the chamber 32 is thereby maintained. One expedient arrangement is to place an orifice ring directly at the connection between the subassembly and the drill string below passageway 35. This allows the orifice ring to be removed or replaced simply by removing the subassembly from the drill string.

    [0023] Instead of receiving lubricant from a supply conduit in a subassembly, the drill bit of the present invention may receive lubricant that is supplied by a conduit in the drill string from a surface-mounted supply, as shown in U.S. Patent No. 4,508,l83. In this arrangement, the drill bit may be attached directly to the extension pipe, and the circumferential groove 20 may receive lubricant directly from the drill string conduit.

    [0024] In actual operation of the aforesaid structure, it has been found that, at the operating pressures for the gaseous drilling fluid commonly employed in the drill string, the flow to the bearings through first conduit l8 is substantially entirely lubricant. The flow of lubricant to the bearings and the exclusion of any significant amount of gaseous fluid is believed to result from the generally higher pressure in passageway 35 delivering the lubricant to conduit l8, than the flow of gaseous fluid after it has passed through orifice ring 36. As noted previously, orifice ring 36 increases the back pressure above the orifice ring 36 and reduces the quantity of flow of gaseous fluid in plenum chamber 3l. Hence, a greater pressure is exerted upon the lubricant storage means 32 by way of supply conduit 35, than is present in the plenum chamber 3l and hollow bit interior l6 after the gaseous fluid has passed through orifice ring 36, which results in a lesser pressure gaseous fluid flow inside plenum chamber 3l and in hollow drill bit interior l6.

    [0025] Accordingly, at the intersection between first conduit l8 and second conduit l9 in the drill bit, the gaseous fluid from the bit interior portion l6 is substantially excluded from the lower portion of conduit l8 at the intersection of conduit l9. Hence, the flow reaching the cutting cone bearings, through the lower portion of first conduit means l8, is substantially entirely lubricant received at a higher pressure from conduit l9, with the general result that no substantial amount of gaseous fluid reaches the bearings during normal operation. It has been found most beneficial to have the pressurized lubricant metered to the bearings in a controlled manner. As noted earlier, the pressure for the lubricant flow can be controlled by varying the size of the orifice ring 36. In the preferred operation of the system, a limited quantity of lubricant is provided for packing the bearings, without having an excess lubricant flow from the bearings into the drill hole which may permit cuttings to float back to the bearing holders and bearings.

    [0026] It should also be appreciated that, in the preferred operation of the system, when the flow of lubricant of the present system is depleted, the flow of gaseous fluid acting on conduit means l8 will be such that a flow of gaseous fluid is provided to the bearings. Accordingly, in the event the supply of lubricant in storage means 32 is exhausted or interrupted, the bearings are nonetheless given some degree of protection by the cooling effect of gaseous fluid supplied to the bearings by first conduit means l8 until such time as the lubricant supply is replenished or reestablished.

    [0027] In a preferred embodiment of the present invention, a perforated member 40 in the form of a slotted tube is fitted into the mouth of the first conduit l8 and acts to filter dirt, stone, or other heavy material which may be present in the gaseous drilling fluid from entering the first conduit means l8.


    Claims

    1. An earth boring drill bit for use, in a gaseous fluid drilling system, in combination with a drill string having means for supplying lubricant to the drill bit, the drill bit comprising:

    a) a body portion (10) having a hollow interior (16);

    b) a shank portion (11) extending from said body portion for attachment of the drill bit to a drill string;

    c) at least one leg portion (12) extending from said body portion;

    d) one or more cutting cones (13) supported on said leg portion by bearings (14);

    e) one or more discharge openings (17) communicating with said hollow interior (16) for exhausting gaseous fluid from the hollow interior onto the surface being drilled;

    f) one or more first conduit means (18) providing gaseous passage means communicating between said hollow interior (16) and said cutting cone bearings (14);

    g) supply reservoir means (20) between the top of said body portion and said shank portion, for receiving lubricant; and

    h) second conduit means (19) providing lubricant passage means communicating between said supply reservoir means (20) and said first conduit means (18);
    whereby lubricant from said second conduit means (19) is combined with gaseous fluid in said first conduit means (18) to provide a mixture of lubricant and gaseous fluid to the cutting cone bearings.


     
    2. The drill bit set forth in claim 1 comprising three leg portions (12), three cutting cones (13) supported thereon, three first conduit means (18), and three second conduit means (19).
     
    3. The drill bit set forth in claim 1 or claim 2 wherein said one or more discharge openings consist of nozzles (17) connected to said hollow interior (16) and opening between adjacent cutting cones (13).
     
    4. The drill bit set forth in any preceding claim wherein said reservoir supply means consists of a circum­ferential groove (20) surrounding said body portion.
     
    5. The drill bit set forth in claim 4 wherein said circumferential groove (20) is provided with orifice rings (21) at the point of communication with said second conduit means (19) to control the amount of lubricant supplied to said second conduit means (19).
     
    6. The drill bit set forth in any preceding claim wherein the first conduit means (18) contain a perforated member (40) at the point of communication with the hollow interior (16).
     




    Drawing










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