Note: Descriptions are shown in the official language in which they were submitted.
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CUTTING ELEMENT ARRANGEMENT FOR SINGLE ROLLER
CONE BIT
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority, pursuant to 35 U.S.C. ~ 119(e), of
U.S. Provisional Patent Application No. 60/484,172 filed July 1, 2003. That
Application is incorporated by reference in its entirety.
Background of Invention
Field of the Invention
[0002] The invention relates generally to the field of roller cone ("rock")
bits
used to drill wellbores through earth formations. More specifically, the
invention is related to an arrangement of cutting elements ("inserts") used in
roller cone bits having a single roller cone.
Background Art
[0003] Roller cone bits are one type of drill bit used to drill wellbores
through
earth formations. Roller cone bits include a bit body adapted to be coupled
to a drilling tool assembly or "drill string" which rotates the bit as it is
pressed axially into the formations being drilled. The bit body includes one
or more legs, each having thereon a bearing journal. The most commonly
used types of roller cone drill bits include three such legs and bearing
journals. The roller cone is rotatably mounted to the bearing journal. During
drilling, the roller cones rotate about the respective journals while the bit
is
rotated.
[0004] The roller cones include a number of cutting elements (also referred to
and known as "inserts" or "teeth"), which may be press fit cutting elements
made from tungsten carbide and other materials, or may be milled steel teeth.
The cutting elements engage the formation in a combination of crushing,
gouging, and scraping or shearing action that removes small segments of the
formation being drilled.
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[0005] The cutting elements on a cone of a three-cone bit are generally
classified as inner-row cutting elements and gage-row cutting elements.
Inner row cutting elements engage the bore hole bottom, but not the well
bore wall. Gage-row cutting elements engage the well bore wall and
sometimes a small outer ring portion of the bore hole bottom. 'fhe direction
of motion of cutting elements engaging the rock on a two or three-cone bit is
generally in one direction or a very small limited range of direction, i.e.,
10
degrees or less.
[0006] One particular type of roller cone drill bit includes only one leg,
bearing journal, and roller cone rotatably attached thereto. The drilled hole
and the longitudinal axis of this type of bit are generally concentric. This
type of drill bit has generally been preferred for drilling applications when
the diameter of the hole being drilled is small (e.g., less than about 4 to 6
inches [10 to 15 cm]) because the bearing structure can be larger relative to
the diameter of the drilled hole when the bit only has one concentric roller
cone. This is in contrast to the typical three-cone rock bit, in which each
journal must be smaller relative to the drilled hole diameter.
[0007] Similar to roller cones of a two-cone or three-cone rock bit, cutting
elements are disposed around a surface of a single roller cone bit for
penetrating into a formation. One type of cutting element that has been
disposed around the surface of a roller cone is a substantially planar cutting
element. Flat crested cutting elements are examples of substantially planar
cutting elements. Figure 1 shows a flat crested cutting element 10.
Properties of the flat crested cutting element 10 include a relatively large
surface area 12 for engaging a formation and sharp corners 14 for shearing
action. Although substantially planar cutting elements 10 are effective in
maintaining a gage of a bore hole, they are not effective in penetrating into
hard formations.
[0008] Another type of cutting element that has been disposed around the
surface of a roller cone is a substantially non-planar cutting element (also
referred to as "non-flat crested cutting elements"). Conical cutting elements
and chisel cutting elements are examples of substantially non-planar cutting
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elements. Figure 2 shows a substantially non-planar cutting element 20.
Properties of the substantially non-planar cutting element 20 include a
relatively more pointed surface area 22 for engaging a formation.
[0009] Such substantially non-planar cutting elements may be characterized,
or otherwise defined, as having a particular tip radius to extension ratio.
For
example, Figure 3 shows how a conical cutting element 23 may be
characterized in terms of a ratio of its tip radius 24 to its tip extension
26.
Similarly, Figures 4a and 4b, which show front and side views of a chisel
insert 25, show how the chisel insert 25 may be characterized in terms of a
ratio of its tip radius 27 to its tip extension 28. Those skilled in the art
will
understand that the tip radius to extension ratio of a particular cutting
element allows for the characterization of the "aggressiveness" of the cutting
element in a general manner.
[0010] Although substantially non-planar cutting elements 20 are effective in
penetrating into hard formations, they wear quickly relative to substantially
planar cutting elements 10 and are not effective in maintaining a gage of a
bore hole.
[0011] Accordingly, in situations in which the maintenance of bore hole gage
is important, roller cones having all substantially planar cutting elements
are
used, and in situations in which penetration into hard formations is
important, roller cones having all substantially non-planar cutting elements
(including combinations of conical cutting elements and chisel cutting
elements) are used.
Summary of Invention
[0012] According to one aspect of one or more embodiments of the present
invention, a roller cone drill bit comprises a bit body adapted to be coupled
to a drill string, a bearing journal depending from the bit body, and a single
roller cone rotatably attached to the bearing journal, where the single roller
cone has a plurality of cutting elements disposed at positions selected such
that a majority of cutting elements adapted to engage a bottom of a bore hole
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are substantially non-planar cutting elements and a majority of cutting
elements adapted to engage a wall of the bore hole are substantially planar
cutting elements.
[0013] According to one aspect of one or more embodiments of the present
invention, a roller cone drill bit comprises a bit body adapted to be coupled
to a drill string, a bearing journal depending from the bit body, and a single
roller cone rotatably attached to the bearing journal, where the single roller
cone has at least one inner row of cutting elements comprising at least one
substantially non-planar cutting element and at least one outer row of cutting
elements comprising at least one substantially planar cutting element.
[0014] According to one aspect of one or more embodiments of the present
invention, a roller cone drill bit comprises a bit body adapted to be coupled
to a drill string, a bearing journal depending from the bit body, and a single
roller cone rotatably attached to the bearing journal, where the single roller
cone has at least one substantially planar cutting element and at least one
substantially non-planar cutting element.
[0015] Other aspects and advantages of the invention will be apparent from
the following description and the appended claims.
Brief Description of Drawings
[0016] Figure 1 shows a substantially planar cutting element.
[0017] Figure 2 shows a substantially non-planar cutting element.
[0018] Figure 3 shows a conical cutting element.
[0019] Figure 4a shows a front view of a chisel cutting element.
[0020] Figure 4b shows a side view of a chisel cutting element.
[0021] Figure 5 shows a generalized cut away view of a single roller cone bit.
[0022] Figure 6 shows a single roller cone bit in accordance with an
embodiment of the present invention.
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Detailed Description
[0023] As discussed above, typical roller cones have either all substantially
planar cutting elements or all substantially non-planar cutting elements
depending on whether gage maintenance or formation penetration is more
important. What is needed, however, especially with the use of a single
roller cone bit, is a design that facilitates both gage maintenance and
effective formation penetration.
[0024] A general structure for a single roller cone bit which can be made
according to various embodiments of the present invention is shown in cut
away view in Figure 5. The bit includes a bit body 1 made of steel or other
high strength material. The bit body 1 includes a coupling 4 at one end
adapted to join the bit body 1 to a drill string (not shown) for rotating the
bit
during drilling. The bit body 1 may include gage protection pads 2 at
circumferentially spaced apart positions about the bit body 1. The gage
protection pads 2 may include gage protection inserts 3 in some
embodiments. The gage protection pads 2, if used, extend to a drill diameter
13 of the bit.
[0025] The other end of the bit body 1 includes a bearing journal lA to which
a single, generally hemispherically shaped roller cone 6 is rotatably mounted.
In some embodiments, the cone 6 may be locked onto the journal lA by
locking balls 1B disposed in corresponding grooves on the outer surface of
the journal lA and the interior surface of the cone 6. The means by which
the cone 6 is rotatably locked onto the journal lA is not meant to limit the
scope of the present invention. The cone 6 is formed from steel or other high
strength material and may be covered about its exterior surface with a
hardfacing or similar material intended to reduce abrasive wear of the cone 6.
In some embodiments, the cone 6 will include a seal 8 disposed to exclude
fluid and debris from entering the space between the inside of the cone 6 and
the journal lA. Such seals are well known in the art.
(0026] The cone 6 includes a plurality of cutting elements thereon at selected
positions, which in various embodiments of the invention are cutting
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elements 5, 7 generally fit into corresponding sockets (not shown separately)
in the outer surface of the cone 6.
(0027) The journal lA depends from the bit body 1 such that it defines an
angle a between the rotational axis 9 of the journal lA and the rotational
axis
11 of the bit body 1. The size of this angle a will depend on factors such as
the nature of the earth formations being drilled by the bit. Nonetheless,
because the bit body 1 and the cone 6 rotate about different axes, the motion
of the cutting elements 5, 7 during drilling can be roughly defined as falling
within a wall contacting zone 10, in which the cutting elements 7 located
therein at least intermittently contact the outer diameter (wall) of the
wellbore, and a bottom contacting zone 12, in which the cutting elements 5
located therein are in substantially continuous contact with the earth
formations, and generally do not contact the outer diameter (wall) of the
wellbore during drilling. The cutting elements 7 in the wall contacting zone
therefore define the drill diameter 13 of the bit.
[002$] The cutting elements 5, 7 may be made from tungsten carbide, other
metal carbide, or other hard materials known in the art for making drill bit
cutting elements. The cutting elements 5, 7 may also be made from
polycrystalline diamond, boron nitride, or other super hard material known in
the art, or combinations of hard and super hard materials known in the art.
[0029] Various embodiments of the present invention have a cutting element
arrangement that uses substantially planar cutting elements having a range of
motion falling within a bore hole wall contacting zone and substantially non-
planar cutting elements (e.g., conical and/or chisel cutting elements) having
a
range of motion falling within a bore hole bottom contacting zone.
[0030] Figure 6 shows an exemplary single roller cone bit 40 in accordance
with an embodiment of the present invention. As shown in Figure 6, an
angular position of a cutting element of a single roller cone bit 40 may be
defined as follows. A first angle a 60 is defined as a journal angle from a
horizontal plane 62. A second angle 8 64 is defined as the angle between an
axis 66 of a single roller cone 54 and an axis of a cutting element. The sum
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of the first angle a 60 and the second angle B 64 can then be used to describe
the angular position of a particular cutting element. Those skilled in the art
will appreciate that the foregoing cutting element angular position
description is applicable to describing an arrangement of cutting elements in
all three dimensions. In other words, an angular position of a cutting element
defined as the sum of the journal angle 60 from a horizontal plane 62 and an
angle between an axis 66 of the single roller cone 54 and an axis of a cutting
element applies to a three dimensional layout of the single roller cone bit
40.
[0031] With respect to the definition of cutting element angular position
discussed above, substantially non-planar cutting elements (e.g., conical and
chisel cutting elements) 48 may be selected and disposed at an angle
preferably anywhere substantially between 0 degrees and 120 degrees.
Substantially planar cutting elements (e.g., flat crested cutting elements) 50
may be selected and disposed at an angle anywhere substantially between
120 degrees and 175 degrees. Note that Figure 6 is not to scale with respect
to the indications of the angle measurements.
[0032] Accordingly, a single roller cone bit 40 is provided that has a cutting
element arrangement for penetrating into hard formations while maintaining
a full gage of a bore hole. In this arrangement, the substantially non-planar
cutting elements 48 are selected and positioned so as to support most of the
weight of the single roller cone bit 40. The shape of the substantially non-
planar cutting elements allows them to penetrate a hard formation
effectively.
[0033] The substantially planar cutting elements 50 are selected and
positioned so as to maintain a substantially full gage of the bore hole. The
shape of the substantially planar cutting elements 50 provides greater carbide
volume for increased wear resistance necessary to maintain bore hole gage.
Moreover, the sharp corners of the substantially planar cutting elements 50
allow the substantially planar cutting elements 50 to cut with an efficient
shearing action.
[0034] In one or more embodiments of the present invention, a region for
disposition or placement of the substantially planar cutting elements 50 may
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be at an angle anywhere substantially between about 125 degrees and about
165 degrees.
[0035] In one or more embodiments of the present invention, a region for
disposition or placement of the substantially planar cutting elements 50 may
be at an angle anywhere substantially between about 135 degrees and about
155 degrees.
[0036] In one or more embodiments of the present invention, a region for
disposition or placement of the substantially planar cutting elements 50 may
be at an angle anywhere substantially between about 140 degrees and about
150 degrees.
[0037] In one or more embodiments of the present invention, a substantially
non-planar cutting element may be positioned such that a longitudinal axis of
the substantially non-planar cutting element 48 resides along the same path
as the vertical axis 65 of the single roller cone bit 40.
[0038] In a preferred embodiment of the present invention, the tip radius to
extension ratio of a substantially non-planar cutting element is substantially
equal to 0.3. However, in one or more other embodiments of the present
invention, the tip radius to extension ratio of a substantially non-planar
cutting element may be anywhere substantially between 0.2 and 0.5.
[0039] In one or more embodiments of the present invention, any of the
substantially non-planar cutting elements 48 and the substantially planar
cutting elements 50 may be arranged to extend greater than or equal to 7/16
inches from the outer hemispherical surface of the single roller cone 54.
[0040] In one or more embodiments of the present invention, any of the
substantially non-planar cutting elements 48 and the substantially planar
cutting elements 50 may be arranged to extend greater than or equal to 0.55
inches from the outer hemispherical surface of the single roller cone 54.
[0041] In one or more embodiments of the present invention, any of the
substantially non-planar cutting elements 48 and the substantially planar
cutting elements 50 may be arranged to extend greater than or equal to 1/2
inches from the outer hemispherical surface of the single roller cone 54.
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[0042] In one or more embodiments of the present invention, any of the
substantially non-planar cutting elements 48 and the substantially planar
cutting elements 50 may be arranged to extend less than or equal to 0.6
inches from the outer hemispherical surface of the single roller cone 54.
[0043] In one or more embodiments of the present invention, the substantially
non-planar cutting elements 48 may have a structure in which an exterior
material of the substantially non-planar cutting element 48 is softer than an
embedded region within the substantially non-planar cutting element 48. For
example, the substantially non-planar cutting element 48 may be embedded
with a diamond insert. Such a structure in which a core harder than an
exterior of a cutting element is embedded within the cutting element allows
the substantially non-planar cutting element 48 to be "self sharpening" in
nature, thereby increasing bit life and penetration effectiveness.
[0044] The differing ranges of degrees with respect to the placement of the
substantially non-planar cutting elements 48 and the substantially planar
cutting elements 50 may be defined by the regions on the single roller cone
46 designed to be the bore hole contacting zone and the wall contacting zone,
respectively. In other words, when the single roller cone 46 shown in Figure
6 is in operation, a majority of the cutting elements engaging a bottom of a
bore hole are substantially non-planar cutting elements and a majority of the
cutting elements engaging a wall of the bore hole (i.e., maintaining a gage of
the bore hole) are substantially planar cutting elements.
[0045] Moreover, the single roller cone 46 shown in Figure 6 may be
described as having inner rows of cutting elements and outer rows of cutting
elements. An inner row of cutting elements may be defined as a row of
cutting elements falling within a particular range of degrees. Like with an
inner row of cutting elements, an outer row of cutting elements may also be
defined as a row of cutting elements falling within a particular range of
degrees.
[0046] In one or more other embodiments, an inner row of cutting elements
may be defined as a row of cutting elements for penetrating into a formation,
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or cutting away from a bottom of a bore hole. In such embodiments, an outer
row of cutting elements may be defined as a row of cutting elements for
cutting away from a wall of the bore hole, or maintaining a gage of the bore
hole.
[0047] Advantages of the present invention may include one or more of the
following. In one or more embodiments, a single roller cone bit has a cutting
element arrangement effective in penetrating into hard formations and
maintaining full gage of a bore hole. The cutting element arrangement
includes substantially non-planar cutting elements positioned on a region of
the single roller cone intended to engage a bottom of a bore hole and
substantially planar cutting elements positioned on a region of the single
roller cone intended to engage a wall of the bore hole.
[0048] While the invention has been described with respect to a limited
number of embodiments, those skilled in the art, having benefit of this
disclosure, will appreciate that other embodiments can be devised which do
not depart from the scope of the invention as disclosed herein. Accordingly,
the scope of the invention should be limited only by the attached claims.
