Note: Descriptions are shown in the official language in which they were submitted.
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ACKGROUND OF THE INVENTION
This invention relates in general to earth borlng
bits, and in particular to a solid head bit with a wear
resistant core containing a nozzle passaye and at least
one cutting element.
Most oil and gas wells are drilled with rolling
cutter bits. In some formations, however, solid head bits
have been found to be more efficient. These solid head
bits are of steel and have a lower face within which a
number of cutting elements are secured in holes. Each
cutting element has a cylindrical tungsten carbide stud
located in the hole, and a flat cutting edge bonded to the
stud and facing in the direction of rotation. The cutting
edge consists of polycrystalline diamond on a tungsten
carbide substrate.
Each drill bit has an axial drilling fluid passage
with one or more outlets. To reduce e~osion of the steel
body of the bit, a tungsten carbide nozzle is located at
the outlet. For good bottom hole coverage, it is
_ 20 desirable to place some of the cutting elements close to
the nozzles. How~ver, because of the hole required for
the stud, and the necessary supporting metal around each
stud hole, it is difficult to place the cutting elements
in the optimum positions. Erosion of the supporting metal
occurs if the cutting element is placed too close to the
nozzle, resulting in a loss of the element.
In U.S. Pat. 4,303,136, Harry N. Ball, December 1,
1981, a cutting element with a flat cutting edge is shown
with a passage formed through the base of the cutting
element. The purpose of the passage is to discharge
drilling fluid across the cutting edge. However, the
passage appears likely to be subject to plugging because
of its small diameter.
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S MMARY OF T~IE INVENTION
In this invention, a solid head bit is provided with
a core secured at an outlet of the drilling fluid passage.
This core is of hard, wear resistant material and has a
nozzle passage extending through it that is in
communication with the drilling fluid passage. Also, the
core has one or more cutting edges secured to its face.
Preferably the nozzle passage in the core is offset from
the axis of the drill bit. The cutting edges may be
optimally positioned close to the outlet of the nozzle
passage for providing good bottom hole coverage.
The -cutting edge is preferably secured to a stud or
base that is brazed in a hole in the core. The core
diameter allows a nozzle passage that is at least one half
the diameter of the cutting edge. The core is held by a
snap ring retainer and sealed with an O-ring.
BRIEF DESCRIPTION OF TIIE DRAWINGS
Fig. 1 is a vertical-sectional view of a drill bit
constructed in acco~dance with this invention.
Fig. 2 is a bottom view of the drill bit of Fig. 1.
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DESCRIP~ION OF T~IE PR~FER~F,D FMBODIMENT
Referriny to FigO 1, drill bit ll has a body 13 that
is forged from a single piece of steel. Threads 15 are
formed on the upper end for securing to a striny of drill
pipe. An enlarged head 17 is located on the lower end of
body 13. Head 17 has a plurality of cylindrical segments
19 that are spaced-apart and shown more clearly in Fig. 2.
Head 17 has on its lower end a face, which is made-up of a
central portion 21 and a frusto-conical portion 23. The
central portion 21 is flat and located in a plane
perpendicular to the axis of drill bit 11. The
frusto-conical portion 23 extends between the central
portion 21 and the cylindrical portion 19.
The cylindrical portion ~9 has a plurality of inserts
25 of hard metal such as tungsten carbide interferingly
secured in mating holes. Both the central portion 21 and
frusto-conical portion 23 of the face have a plurality of
holes 27 formed therein. Each hole receives a tungsten
carbide base or cylindrical stud 29 of a cutting element
31. Each cutting element 31 has a cutting edge 33 bonded
tb the stud 29. Cutting edge 33 is circular and faces
into the direction of rotation. Cutting edge 33 is a
laminated disk containing polycrystalline diamond on the
face backed by a tungsten carbide substrate. Cutting
edges 33 are conventional and marketed by the General
Electric Company. As shown in Fig. 1, holes 27 are
generally inclined with respect to the a~is of bit 11. As
shown in Fig. 2, holes 27 are widely dispersed about the
face of drill bit 11.
Body 13 has an axial passage 35. The lower end of
axia1 passage 35 is an enlarged counterbore section 37
centrally located on the axis of bit 11. Counterbore
section 37 has a cylindrical wall surface with a larger
diameter than the upper portion of passage 35. A
downwardly~facing annular shoulder 39 forms the base of
counterbore section 37. A small, cylindrical cavity or
hole 41 is formed at one point on shoul~er 39.
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A core 43 is adaptcd to bc secured in counterbore
sec-tion 37. Core 43 is constructed of ~ hard,
wear-resistant material of hardness considerably greater
than body 13, such as sintered tungsten carbide.
Typically body 13 may ha~e a ha dness o~ about 38 Rockwell
C, while tungsten carbi.de might be 87-90 Rockwell A. Core
43 has a cylindrical wall surface and a lower face with a
concave or depressed section 45. Concave section 45 is
circular, as shown in Fig. 2, with an axis that coincides
with the axis of the bit. Concave section 45 is about
one-fourth of a spherical surface and has a width that
extends almost completely across the diameter of core 43.
The face also includes a perimeter or circular rim 47 that
encircles concave section 4~. Rim 47 defines a corner
with a cylindrical sidewall o~ core 43.
A concave depression 49 is also located on the upper
end of core 43. Concave section 49 is circular and
located on the axis of bit 11. Concave sect~on 49 is
somewhat more than one-fourth of a spherical surface, and
has a width that is equal or slightly greater than the
diameter of axial passage 35. The upper end of core 43
has a circular portion 51 that surrounds concave section
49 and intersects the sidewall of core 43. Circular
portion 51 is flat, located in a plane perpendicular to
the axis of core 43, and adapted to seat against shoulder
39. A cylindrical hole or cavity 53 is formed in the core
circular portion 51 for registering with hole 41 for~ed in
the shoulder 39. A cylindrical pin 55 fits tightly within
holes 41 and 53 for preventing rotation of core 43 with
respect to the bit 11. Pin 55 has a length that is
slightly less than the cumultive depths of the holes 41
and 53. The height of core 43 from rim 47 to circular
portion 51 is equal to the depth of counterbore section
37, making rim 47 flush with bit central portion 21.
A nozzle passage 57 is located in core 43, and
extends between the concave sections 45 and 49. The axis
of nozzle passage 57 is parallel to the axis of drilling
fluid passage 35, but noncoinciding or offset to one
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side. The diameter of no~zlc passage 57 is greater than
one-half the width or diameter oE thc cutting edge 33.
Preferably the diameter of nozzle passage 57 is greater
than the diameter of cutting edge 33 and also yreater than
the diameter of stud 290
In this embodiment, three cutting elements 59 are
located in the lower cnd or face of core 43. Each cutting
element 59 is identical to the cutting elements 31 Iocated
in the bit face portions 21 and 23. Each cutting element
59 is located in a cylindrical hole 61 formed in core 43.
10 The holes 61 are drilled for optimum positioning and may
be inclined, as shown in Fig. 1. As shown in Fig. 2, one
of the cutting elements 59 is located very close to nozzle
passage 57. Another cutting element 59 is placed slightly
further outward, and the third is located near the edge of
15 core 43. The cutting edges of the cutting elements 59 all
face generally into the direction of rotation, but are not
necessarily located on radial lines. The diameter of core
43 is at least twice the diameter of the cutting edge 33~
The core 43 diameter is also at least twice the diameter
20 of each hole 61.
Also, referring still to Fig. 2, channels 63 are
formed in -the face of core 43 for registering with
channels 65 formed in the bit face portions 19 and 21.
Each channel 63 begins in the concave section and extends
25 through the rim 47, where it merges with one of the
channels 65. Channels 65 are curved to direct ~rilling
fluid past the faces of the cutting edges 33 and to the
recessed portions or flutes between cylindrical segments
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Core 43 is retained in counterbore sectlon 37 by
retaining means that includes a snap ring 67. Snap ring~
67 is circular in transverse cross-section, and fits
within yrooves 69 and 71 formed in core 43 and counterbore
section 37, respectively. Groove 69 is of a dcpth greater
than the thickness of snap ring 67, to enable snap ring 67
to be compressed fully within groove 69. This allows the
core 43 to be inserted into counterbore section 37.
. .. . . . . ... ..... .
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Groove 71 is of a depth about half the thickness of snap
ring 67. A seal means comprising an O ring 73 i5 located
in a groove in counterbore section 37 to seal against
leakage.
Core 43 is manufactured by conventional powder
me~allurgy techniques. Tungsten carbide granules located
within a matrix of cobalt or the like are formed into the
desired shape, then sintered in a furnace. Some of the
features such as the groove 69, and holes 53 and holes Çl
may be machined after molding but before sintering. After
sintering, little or no machining work is required. To
assemble the bit, the snap ring 67, which is split, is
placed around and compressed into groove 69. Pin 55 is
positioned either in hole 41 or hole 53. The core 43 is
pushed into counterbore sec~ion 37. By rotating core 43
slightly, the pin 55 will register the two holes 41 and
53. Further depression results in the snap ring 67
springing radially outward and locking into groove 71.
The cutting elements 59 are brazed into holes 61 with a
material such as silver. The cutting elements 31 are
pressed into holes 27.
In operation, bit 11 will be secured to a string of
drill pipe and lowered into the hole. The drill pipe is
rotated, rotating the bit 11 with it. The cutting edges
of the cutting elements 31 and 59 scrape and disintegrate
the formation during rotation. Drilling fluid, normally a
liquid, is pumped down the drill string, through drilling
fluid passage 35 and nozzle passage 57 to discharge
against the borehole bottom. The drilling fluid flows
along channels 63, 65 and up between cylindrical segments
19. The fluid flushes cuttings from the borehole and
returns the cuttings to the surface. The elevations of~
cutting elements 59 in concave section 45 are chosen to
allow a conical portion to build up in the borehole bottom
to assist in centering the bit.
The invention has significant advantages. The core
of tungsten carbide allows cutting elements to be
positioned optimally around the nozzle outlet. The core
reduces erosion around the nearby cutting elements because
of its hardness and high resistance to wear.
While the invention has been shown in only one of its
forms, it should be apparent to those skilled in the art
that it is not so limited but is susceptible to various
changes and modifications without departi.ng from the
spirit of the invention.
