GB2072243A - Earth boring drill bit - Google Patents

Abstract

A fluid jetting system for a rolling cone drill bit is provided in which a pressurized fluid spray (46) is directed tangentially across the main cutting inserts (22) and against the formation face so that when the drill bit is used in its most advantageous areas, such as the soft, medium-soft and plastic formations, the jetting system prevents "balling-up" of the cutters and greatly increases the drilling efficiency of the bit. <IMAGE>

Description

SPECIFICATION Rolling cutter drill bit This invention relates to a rolling cone drill bit for drilling through underground formations.

In the drilling of boreholes through underground formations for the purposes of locating and producing oil and gas, and for the purposes of mining and production of steam energy through thermal wells, the most common type of drilling apparatus used today is the tri-cone rolling cutter drill bit. This bit generally comprises a central body section having three legs extending downwardly therefrom. Each leg has an inwardly projecting bearing journal upon which is rotatably mounted a frustoconical cutter. Generally, the most prevalent type of cutting structure utilized in the tri-cone bit is the tungsten carbide insert cutting structure. Tungsten carbide cutting elements are press-fit in holes drilled in the frustoconical cutters and protrude outwardly to provide a digging, crushing and gouging action on the bottom of the borehole as the bit is rotated.

The tungsten carbide insert bit has generally been known and used for approximately the last 30 years. For the first 20 years (1950 to about 1 970), those in the art felt that the cutting structure of the insert bit should be of the nonoffset or "true rolling cone" type. The offset, which is defined as the amount by which the rotational axes of the rolling cutters is offset from the rotational axis of the main bit, was a feature found in milled tooth bits but believed to be detrimental to insert bits because of the breakage problem in the tungsten carbide inserts when the additional drag forces were introduced through the use of offset.

In February, 1970, a new bit design was patented in U.S. Patent No. 3,495,668 (P. W.

Schumacher, Jr.) in which, for the first time, an insert bit successfully incorporated offset axis cutters to achieve greater gouging and scraping action in the borehole. A subsequent U.S.Patent No. 3,696,876, (Ott) in October, 1972, also disclosed a similar invention wherein offset axis cutting elements were incorporated into an insert bit.

Drilling bits incorporating the combination of offset cutters and tungsten carbide inserts were successfully introduced by the applicants for the present invention, Reed Rock Bit Company, in 1970, and have become the most prevalent type of drill bits in the drilling industry over the past ten years. This second generation of drill bits utilizing offset axes and tungsten carbide inserts are particulariy advantageous in soft to medium-soft formations by reason of their introduction of a gouging and scraping action which enhances the drilling efficiency and rate of penetration of the bit in these formations. The amount of offset utilized in these bits ranges on the order of from about 1/64 to about 1/32 inch offset per inch of drill bit diameter. For instance, a 7-7/8 inch bit having offset would have from 1/8 inch to 1/4 inch total offset in the cutters.

Conventional drilling bits currently on the market are limited in the amount of offset introduced into the cutters to about 1/32 inch of offset per inch of diameter. Thus, the maximum amount of offset utilized in these soft formation bits currently runs about 1/4 inch in a 7-7/8 inch diameter bit. During this ten year period when offset axis insert bits have been made commerically successful, those skilled in the art of drill bit technology generally have followed the principle that any additional offset in the cutters above about 1/32 inch per inch of bit diameter would not add any significant efficiency or increased drilling rate to the bit to justify the increased breakage that such increased offset would introduce.In fact, drilling tests conducted utilizing insert bits with offset somewhat greater than 1/32 inch per inch of bit diameter have indicated insignificant gains in rate of penetration, but larger incidences of insert breakage. Thus, those skilled in the art have restricted their insert bit designs to having an offset range of from zero to 1/32 inch per inch of bit diameter.

The arrangement described hereinafter utilizes a unique insert bit design having great amounts of offset in the cutting structure far exceeding those ranges utilized in conventional offset-axis insert bits. It was found by this inventor that when offset equal to or greater than 1/16 inch per inch of bit diameter was introduced into a tri-cone insert bit, that greatly significant increases in rate of penetration and bit performance can be obtained.

For some reason unknown to the inventor, the penetration rate and drilling efficiency of an offset insert bit does not increase significantly from about 1/32 inch offset per inch of bit diameter (upper range of conventional insert offset bits) up to about 1/1 6 inch offset per inch of bit diameter.

It was discovered though that beginning at about 1/1 6 inch offset per inch of bit diameter a significant jump in the rate of penetration and drilling efficiency was noted.

The use of large amounts of offset in milledtooth rolling cutter drill bits may not in itself be a novel concept. For instance, see U.S. Patent No.

1,388,456 to H. W. Fletcher, dated August 23, 1921, in which a two-cone rolling cutter drill bit having milled tooth cutters apparently incorporated a large amount of offset in the two cutters. The patent discloses no specific amount of offset to be utilized and, as far as this inventor is aware, no commercial embodiment of the Fletcher design ever became successful. The conventional milled tooth drill bits which have been available for the last 40 years have generally utilized offset in the range of 1/64 to 1/32 inch per inch of bit diameter and have been tri-cone bits. It was not until 1970, and the issuance of U.S. Patent No.

3,495,668, that the industry was introduced to the use of insert type bits utilizing the offset already present in milled tooth bits. The reason that the high offset cutters were not thought practical was that increases in offset above the 1/32 inch iimit previously mentioned would gain very little in cutting efficiency, but increased the amount of breakage of tungsten carbide inserts in the insert type bits. Also, increasing the offset necessarily requires reducing the size of the cutter cones to prevent interference between the inserts on adjacent cones. Smaller cones mean smaller bearing areas and/or thinner cone shells, both of which add to earlier bit failure. Also, greater offset means less efficient intermeshing of inserts on adjacent cones which in turn reduces the amount of self-cleaning of the inserts and increases "balling-up".

Conventional jetting systems are generally made up of two different types. The oldest type is the regular drilling fluid system where large, relatively unrestricted fluid openings are provided in the bit body directly above the cutter cones to allow a low pressure flow of the drilling fluid to fall on the cones and move around the cones to the bottom of the borehole. By necessity, this is a low volume, low-velocity flow since the fluid stream impinges directly upon the cutter face, and abrasion of the cones is a serious problem under these circumstances. The second type of conventional bit fluid system comprises the "jet" bits. In a jet bit a high pressure jet of fluid is generated from the bit body directly against the formation face without impinging on any cutting elements or any portion of the bit.In some instances, the so-called jet bits have fluid nozzles extending from the bit bodies all the way downward to a point only a fraction of an inch above the formation face to maximize hydraulic energy of the fluid stream impinging on the formation face. The conventional jet bits do not emit fluid against any cutting elements because of the adverse effect of erosion from the high pressure drilling fluid.

An object of the present invention is to provide a drill bit incorporating an improved jetting system.

According to the present invention there is provided a rolling cone drill bit for drilling through underground formations and having a hollow bit body, a plurality of downwardly extending legs on said body, and a rolling cone cutter rotatably mounted on each said leg; each said cutter having protruding hard metal cutting elements inserted therein; characterised in that there is provided a directed fluid jetting system having fluid jet means associated with said bit body and in fluidic communication with the hollow portion of said bit body, said jet means being arranged to receive pressurized fluid from said hollow body and direct a pressure stream of fluid across at least one of said hard metal cutting elements.

The present invention differs from the foregoing two conventional types in that it uses a directed jet spray which impinges directly upon the cutter inserts.

An insert type bit, as opposed to a milled tooth bit is described hereinafter, which insert bit utilizes rolling cone cutting elements rotatably mounted on lugs having rotational axes with large offset from the rotational axis of the drill bit. The amount of offset ranges between 1/16 and 1/8 inch per inch of bit diameter. The resulting arrangement produces greatly increased rates of penetration and drilling efficiency when utilized in soft to medium soft formations. It should be noted that the drill bit as herein described, when embodied in a tri-cone oilwell drilling bit, suffers a greater amount of erosion and breakage of the hard metal cutting inserts in the cones, but the total gain in drilling efficiency and rate of penetration far offsets the increased wear and breakage of the cutting elements.

The nozzle jetting system embodied in the present invention for delivering drilling fluid to the cutting elements and the face of the formation as it is being drilled utilizes directed nozzles which create a spray of pressurized drilling fluid and directs this spray across the protruding tungsten carbide inserts and against the formation face. The new jetting system provides a dual function of cleaning material from the inserts and also sweeping the cuttings from the borehole face. This system is particularly advantageous when drilling through those certain types of formations which, because of their softness or ductility, become very plastic during drilling operations, and tend to "ball up" in the spaces between the inserts on the cutters.This "balling up" greatly reduces the rate of penetration and the cutting efficiency of drill bits when penetrating such plastic formations. The jetting system incorporated in the present invention provides a plurality of fluid jets directed at preselected angles to spray drilling fluid across the inserts without impinging the cutter cone surfaces, with the spray also being directed against the formation face to further flush and clean the cuttings as they are gouged and scraped out of the formation.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a side view of one embodiment of the present invention comprising a three-cone bit: Fig. 2 is an axial bottom view of the three-cone bit of 1; Fig. 3 is a schematic representation of the three cutter cones of the bit of Figs. 1 and 2, showing the concept of offset cutter axes; Fig. 4 is a diagram of the cutter configuration in one embodiment of the invention illustrating the location and placement of the inserts in the cutter and also indicating the offset of the cutters; Fig. 5 is a schematic diagram showing an overlay of the insert pattern of all three cutters of Fig. 4 to show bottom hole coverage of the bit; ; Fig. 6 is a schematic illustration of one embodiment of this invention indicating the directed nozzle system and its interaction with the cutter and the formation; Figs. 7 and 8 are illustrations of a particular embodiment of the directed nozzle system shown schematically in Fig. 6; Fig. 7 is an axial end-view of a central nozzle system, and Fig. 8 is a partial cross-sectional side view of the nozzle of Fig. 7: Figs. 9 to 11 are different views of a second embodiment of the directed nozzle system utilizing an intermediate jet; and Figs. 12 to 14 illustrate axial bottom views of a third embodiment of the present invention which utilizes a peripheral directed nozzle system.

Referring to Fig. 1, a first embodiment of the invention, shown in isometric view, comprises a tri-cone drilling bit 10 having a central main body section 1 2 with an upwardly extended threaded pin end 14. The threaded pin 14 comprises a tapered pin connection adapted for threadedly engaging the female end of a section of drill stem.

The body section 1 2 has three downwardly extending legs 1 8 formed thereon, each of which contains a rotatably mounted frustoconical cutter 1 6. A plurality of nozzles 20 may be located in the periphery of the body section 12 aimed downward past cutters 16. In Fig. 2, which is an axial view looking up from the borehole toward the bottom of the bit, the cutters 1 6 of bit 10 are shown with hard metal cutting elements 22 projecting from raised lands 24 formed on the surfaces of the cones. In a typical embodiment the inserts generally would comprise three different categories, gauge row inserts 26, intermediate row inserts 28, and nose inserts 30.As is well known in the industry, the inserts are secured in the cones by drilling a hole in the cone for each insert with the hole having a slightly smaller diameter than the insert diameter, thus resulting in an interference fit. The inserts are then pressed under relatively high pressure into the holes and the press fit insures that the inserts are securely held in the cones.

Although not shown in the drawings, each cutter 1 6 is rotatably mounted on a cylindrical bearing journal machined on each leg 8, as is well known in the art. As is also well known in the art, bearings such as roller bearings, ball bearings, and/or sleeve bearings are located between the cutter and the bearing journal to provide the rotational mounting. In one preferred embodiment, cutters were mounted on bearing journals with sleeve bearings and ball bearings therebetween as illustrated in U.S. Patent No.

3,990,751 and U.S. Patent No. 4,074,922 in the name of Henry W. Murdoch granted November 9, 1 976 and February 21, 1 978, respectively, and assigned to Reed Tool Company of Houston, Texas.

In Fig. 3, the cutters 1 6 are illustrated schematically as simple frustoconical figures. Each cutter cone 1 6 has an axis of rotation 32 passing substantially through the centre of the frustoconical figure. The central rotational axis of the bit 10 is illustrated as point 34 in Fig. 3 since Fig. 3 is taken from a view looking directly along the rotational axis of the bit. From Fig. 3, it can be seen that because of the offset of axes 32, none of the axes intersect axis 34 of the bit. In this flat projection, the intersection of the axes 32 forms an equilateral triangle 36. The amount of offset measured in a linear distance for any particular bit can be determined from a full scale diagram similar to Fig. 3 for that bit by measuring the distance from axis 34 to the mid-point of any side of triangle 36.

Referring now to Fig. 4, in which a cutter layout is illustrated, the profiles or cross-sections of each of the cutters on the tri-cone bit of the preferred embodiment are laid out in relation to each other to show the intermesh of the cutting elements or inserts 22. Generally, each cutter in a tri-cone bit is of a slightly different profile in order to allow optimum spacing of the inserts for the entire bit. In Fig. 4, the three cutters are labelled A, B, and C.

The C cutter has been divided to illustrate its intermesh with both cutters A and B. It should be noted that the projections have been flattened out, and because of the two-dimensional aspect of this relationship, a distortion in the true three dimensional relationship of the cutters is necessary. In Fig. 4, the central axis of rotation 34 of the bit is indicated. Each cutter A, B and C, has a rotational axis 32 which is offset by a distance Y from an imaginary axis 32' which is parallel to the actual axis 32 and passes through point 34 which is the bit rotational axis.

Fig. 5 is a cutter profile which is an overlay of one-half of each of the cutters A, B and C to indicate the placement of all of the inserts with respect to bottom hole coverage. Each insert in the profile of Fig. 5 is labelled according to the particular cutter cone in which the insert is located. The angle X is indicated to show the journal angle of the bit. The journal angle is the angle that the bearing journal axis, which coincides with the rotational axis 32 of the cutter, makes with a plane normal to the bit rotational axis 34.

In this particular embodiment it was found that the preferred range of insert protrusion above the cutter surface should be greater than or equal to about one-half the diameter of the insert. Any protrusion significantly less than one-half the diameter would make the gouging and scraping action resulting from the large amount of offset ineffective. The preferred range of insert protrusion is from one-half to one times the insert diameter. The preferred shape of the protruding portion of the insert is conical or chisel.

Acceptable alternative shapes are hemispherical and sharpened hemispherical inserts.

Whereas the insert can be made of any hard metal alloy such as titanium carbide, tantalum carbide, or chromium carbide, in a suitable matrix, one particular range of embodiments utilizes tungsten carbide in a cobalt matrix. The cobalt content ranges from about 5% to about 20% by weight of the insert material, with the remainder of the metal being either sintered or cast tungsten carbide, or both. The hardness of the inserts is controlled by varying the cobalt content and by other well-known methods. The hardness ranges from about 85 Rockwell A to about 90 Rockwell A. In one particular embodiment, conical inserts having a protrusion greater than one-half of their diameter were used, with the inserts being made of tungsten carbide-cobalt alloy, having a cobalt content of around 12% by weight and a hardness of about 86.5 Rockwell A.

Referring now to Fig. 6, a schematic sketch of the directed nozzle fluid system of the invention is illustrated. In Fig. 6, a generally cylindrical jet nozzle 40 is shown connected to bit body 12 and communicating with a high pressure drilling fluid passage 42 passing therethrough. Nozzle 40 has an exit jet 44 from which high pressure drilling fluid 46 is emitted in a tight directed spray. Bit leg 18 is illustrated having conical cutter 1 6 located thereon. A direction arrow 48 is drawn on leg 1 8 to indicate the direction of movement of the bit leg in the borehole as the drill bit is rotated. Likewise, a second rotation arrow 50 is drawn on cutter 1 6 to indicate the simultaneous rotation of cutter 1 6 with movement of bit 10 in the borehole.The high-pressure drilling fluid stream 46 is directed in a closely controlled direction such that the fluid stream is either exactly tangent with the surface of cutter 1 6 or slightly displaced therefrom as shown in the drawing. The placement of stream 46 is a tangential relationship with cutter 1 6 allows effective cleaning of inserts 22 as they move through stream 46, but also prevents abrasive erosion of the cutter shell 1 6 which would occur if 46 impInged squarely thereon. Although the preferred embodiment is to have stream 46 either tangential to or slightly displaced from cutter shell 16, a slight impingement of stream 46 with cutter shell 16 would not be highly detrimental due to the very slight angle of incidence of stream 46 against the cutter surface.As fluid stream 46 passes over inserts 22 and close to cutter shell 16, it dislodges material built up between inserts 22 and drives it downward with the motion of the cutter 1 6. After the fluid passes the inserts it impinges on bottom 52 of the borehole and travels along the bottom picking up cuttings as they are chipped and gouged from the formation by inserts 22. The drilling fluid then passes below the cutter 16 and moves back upward outside the drill bit and up through the borehole in the conventional manner.

Referring now to Figs. 7 and 8, one embodiment of the directed jetting system is disclosed. This embodiment utilizes a multi-orifice jet nozzle which protrudes downwardly from the central area of the bit body towards the central area between the three conical cutters. Fig. 7 is a partial axial end-view of the bit 10 partially illustrating two cutters 1 6 and the location of a multi-orifice jet 56. Jet 56 is generally cylindrical in nature having a bevelled edge or surface 58 at the downward projecting end thereof and having three nozzle openings 615 formed through the bevelled surface 52. A flat, closed end 62 is located at the bottom of the nozzle. A fluid spray 64 is shown emanating from one of openings 60.

This spray passes across the inserts in the cutters 1 6 without impinging on the actual cutter surfaces. The spray cleanses any packed cuttings which might be lodged between the various inserts and then moves outward and then downward to sweep the bottom of the borehole in front of the cutters as they roll into the formation surface. Fig. 8 is a partial side view of the bit of Fig. 7 showing a single cutter 1 6 and the multi-jet nozzle 56. In this figure, the nozzle 56 is shown in a cross-sectional diagram and it can be seen that the nozzle has a central passage 66 which communicates with the nozzle openings 60.

Nozzle 56 is securely located in a bore 68 formed in bit body 12. Bit body 12 has a fluid cavity 70 formed therein which communicates with threaded pin end 14 (Fig. 1) which also is tubular in nature. Thus, it can be seen that drilling fluid pumped down the drill string passes through threaded pin 14 into bit cavity 70, through nozzle bore 66 and out the nozzle opening 60 into a jet or spray 64 which impinges the major cutting inserts on cone 1 6 and then is directed either against the face of the borehole or, as shown in Fig. 8, may be directed against the wall of the borehole whereupon the fluid moves down the wall and across the formation face to pick up additional loose cuttings thereon.

Referring now to Figs. 9 to 11, a second embodiment of the directed nozzle system is disclosed in which the fluid jetting system is directed across the main cutting inserts and impinges directly upon the borehole face. In this embodiment, the projected nozzle arrangement is replaced by a slanted jet configuration formed through the wall of the bit body 12 and communicating with bit cavity 70. Fig. 9 is a partial axial view showing part of two cutter cones 16, the bit body 12 and a directed jet passage 74.

The drilling fluid is emitted from jet passage 74 in a stream 76 which impinges the major cutting inserts in cones 16 and passes downward to impinges the bottom of the borehole. In this embodiment three of the jet passages 74 are formed in bit body 12 so that each conical cutter 1 6 has one jet passage associated therewith for sweeping cuttings from the inserts and impinging the bottom of the borehole. Fig. 10 is a side view of one cutter looking from the central axis of the bit radially outward at the cutter. Jet passage 74 passes through bit body 12, communicating with the drilling fluid in the drill string by means of cavity 70 and pin 14. Fig. 11 is a partial side schematic view of the cutter 1 6 of Fig. 1 0 rotated approximately 90 degrees.In Fig. 11, one of the three jet passages 74 is shown in communication with cavity 70 and emitting a jet stream 60 of drilling fluid passing across the cutting inserts of cutter 1 6 and impinging the borehole bottom.

Referring to Figs. 1 2 to 14, two additional embodiments of the present invention with the directed nozzle system are indicated. In Fig. 12 a drill bit is shown in the axial view looking up from the bottom of the borehole. The bit has three conical cutters 16 having a plurality of tungsten carbide inserts 22 securely held in raised lands 24 on the cutters. A set of three peripherally directed nozzles 80 are located around the outer periphery of bit body 12, extending downward therefrom into the generally open areas between the outer rows of inserts on the conical cutters. The embodiment of Fig. 1 2 utilizes the three directed nozzles which are generally cylindrical in nature, each having a bevelled face 82 and a jet passage 84 formed through face 82 and communicating with a central bore passage in nozzle 80.Jet passage 84 is formed such that a directed spray of fluid 86 is emitted therefrom which impinges across the main cutting inserts of the conical cutters which are located clockwise from each nozzle 80. Each jet passage 84 is aimed in a generally circumferential direction with respect to bit body 1 2 and in a tangential direction to cutter cones 1 6 such that the fluid spray emitted therefrom does not impinge squarely on the cone 1 6. Each nozzle 80 having the single jet passage 84 is arranged to clean the inserts on the cutter located in a clockwise direction from the nozzle.

After the spray passes across the main cutting inserts, it is directed against the bottom of the borehole to further provide cleaning action during the drilling operation. In Fig. 13, a slightly different embodiment of the peripheral nozzle system is disclosed in which three double jet nozles 90 are located around the periphery of the bit bottom extending downwardly therefrom between the outer edges of the cones 1 6. Each nozzle 90 has two jet passages formed therein passing through opposed bevelled faces 92 and 94. Thus, each nozzle 90 has a jet passage directed at each cutter cone 1 6 located adjacent thereto. Fig. 14 is a diagrammatic sketch showing the nozzle 90 from the side and illustrating the two bevelled faces 92 and 94. Jet passages 96 pass through the two bevelled faces and communicate with an inner bore in nozzles 90.Pressurized drilling fluid passes through the drill bit and into the nozzles 90 in a manner similar to that of the embodiment shown in Fig. 12.

The nozzles utilized in the embodiments illustrated in Fig. 6 to 1 4 are preferably formed by casting, forging, and/or machining from a hard material such as steel or one of the hard metal alloys such as tungsten carbide in a cobalt matrix.

The tungsten carbide-cobalt alloy can be of the type using intered tungsten carbide, cast tungsten carbide, or a combination of both. Alternatively, the nozzles could be formed of any material which successfully resists erosion.

Thus, the present invention defines several unique features, including a fluid jetting system which provides a highly efficient cleaning of the protruding inserts as well as a cleaning of the formation face as it is being drilled.

This system directs the high-pressure fluid jet at or near a tangent to the cutter cones in a position to sweep the main cutting inserts, thereby cleaning the balled up material therefrom, and the fluid stream thereafter passes from the insert region to the formation face directly, or from the insert region to the borehole wall and then down the wall and across the formation face.

Although certain preferred embodiments of the present invention have been herein described in order to provide an understanding of the general principles of the invention, it will be appreciated that various changes and innovations can be effected in the described drill bit structure without departure from these principles. For example, whereas a tri-cone bit having three conical cutters is disclosed, it is clear that the bit structure could be of the four-cone type, and still embody the principles of the present invention.

Likewise, the number and location of the directed nozzles could be varied from those shown and still obtain equivalent operation, function, and results.

Claims (5)

1. A three-cone rolling cutter drill bit of the type having hard metal cutting elements inserted in generally frusto-conical cutters, characterised in that there is provided: fluid jet means on said drill bit extending downwardly therefrom to a point a substantial distance from the lowermost extreme of said bit: said jet means having at least one nozzle opening directed toward said cutting elements on the lower portion of each said cutter and adapted to spray pressurized fluid across a plurality of said lower elements in a generally tangential orientation of the bodies of said cutters; each of said nozzle openings being further arranged to spray a fluid across cutting elements on each cutter immediately prior to said elements contacting a borehole face during drilling operation of said bit.

2. A drill bit as claimed in Claim 1 wherein each said nozzle opening is directed toward and arranged to emit a spray impinging on the main cutting elements of each cutter including the gage row and at least one intermediate row thereof.

3. A drill bit as claimed in Claim 1 or 2, wherein each said nozzle opening is arranged to emit a fluid spray substantially tangential to each said cutter at an angle substantially greater than zero degrees and substantially less than ninety degrees from the bottom of the borehole.

4. A drill bit as claimed in any preceding claim, wherein each said nozzle opening is arranged to emit a fluid spray which impinges a plurality of hard metal cutting elements and thereafter impinges the borehole bottom face.

5. A three-cone roller cutter drill bit substantially as hereinbefore described with reference to Figs. 1 to 3; Figs. 4 and 5; Figs. 6 to 8; Figs.9 to 11; or Figs.12 to 14 of the accompanying drawings.