Boring or penetrating the earth – Bit or bit element – Rolling cutter bit or rolling cutter bit element
Reexamination Certificate
2000-06-08
2002-04-23
Dang, Hoang (Department: 3672)
Boring or penetrating the earth
Bit or bit element
Rolling cutter bit or rolling cutter bit element
C175S426000, C175S376000
Reexamination Certificate
active
06374930
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates generally to roller cone drill bits for drilling earth formations, and more specifically to roller cone drill bit designs.
2. Background Art
Roller cone rock bits and fixed cutter bits are commonly used in the oil and gas industry for drilling wells.
FIG. 1
shows one example of a roller cone drill bit used in a conventional drilling system for drilling a well bore in an earth formation. The drilling system includes a drilling rig
10
used to turn a drill string
12
which extends downward into a well bore
14
. Connected to the end of the drill string
12
is roller cone-type drill bit
20
, shown in further detail in FIG.
2
.
Roller cone bits
20
typically comprise a bit body
22
having an externally threaded connection at one end
24
, and a plurality of roller cones
26
(usually three as shown) attached at the other end of the bit body
22
and able to rotate with respect to the bit body
22
. Disposed on each of the cones
26
of the bit
20
are a plurality of cutting elements
28
typically arranged in rows about the surface of the cones
26
. The cutting elements
28
may comprise tungsten carbide inserts, polycrystalline diamond compacts, or milled steel teeth.
Significant expense is involved in the design and manufacture of drill bits to produce drill bits with increased drilling efficiency and longevity. For more simple bit designs, such as fixed cutter bits, models have been developed and used to design and analyze bit configurations having optimally placed cutting elements, a more balanced distribution of force on the bit, and a more balanced distribution of wear on the cone. These force-balanced bits have been shown to be long lasting and effective in drilling earth formations.
Roller cone bits are more complex in design than fixed cutter bits, in that the cutting surfaces of the bit are disposed on roller cones. Each of the roller cones independently rotates relative to the rotation of the bit body about an axis oblique to the axis of the bit body. Because the roller cones rotate independent of each other, the rotational speed of each cone is likely different. For a given cone, the cone rotation speed can be determined from the rotational speed of the bit and the effective radius of the “drive row” of the cone. The effective radius of a cone is generally related to the radial extent of the cutting elements that extend axially the farthest from the axis of rotation of the cone. The cutting elements which extend axially the farthest from the axis of rotation of the cone are generally located on a so-called “drive row”. In some configurations, the cutting elements on the drive row are located to drill the fall diameter of the bit. In such cases, the drive row may be interchangeably referred to as the “gage row”.
Adding to the complexity of roller cone bit designs, cutting elements disposed on the cones of the roller cone bit deform the earth formation by a combination of compressive fracturing and shearing. Additionally, most modem roller cone bit designs have cutting elements arranged on each cone so that cutting elements on adjacent cones intermesh between the adjacent cones, as shown for example in FIG.
3
A and further detailed in U.S. Pat. No. 5,372,210 to Harrell. Intermeshing cutting elements on roller cone drill bits is desired to permit high insert protrusion to achieve competitive rates of penetration while preserving the longevity of the bit. However, intermeshing cutting elements on roller cone bits substantially constrains cutting element layout on the bit, thereby, further complicating the designing of roller cone drill bits.
Because of the complexity of roller cone bit designs, accurate models of roller cone bits have not been widely developed or used to design roller cone bits. Instead, roller cone bits have been largely developed through trial and error. For example, if its been shown that a prior art bit design leads to cutting elements on one cone of a bit being worn down faster that the cutting elements on another cone of the bit, a new bit design might be developed by simply adding more cutting elements to the faster worn cone in hopes of reducing wear on each of the cutting elements on that cone. This trial and error method of designing roller cone drill bits has led to roller cone bits with cutting elements unequally distributed between the cones, wherein the number of cutting elements on one cone of the bit differs by three or more from the number of cutting elements on another cone of the bit. In some cases, especially those involving cutting structures comprising intermeshing teeth, the difference between the number of cutting elements on each cone is significantly more than three. In some prior art bit designs, the unequal distribution of the number of cutting elements between the cones may result in an unequal distribution of force, strain, stress, and wear between the cones, which can lead to the premature failure of one of the cones. In other prior art bit designs, the unequal distribution of the number of cutting elements between the cones may result in an unequal distribution of contact with the formation between the cones or an unequal distribution of volume of formation cut between the cones.
One example of a prior art roller cone bit configuration considered effective in drilling well bores is shown in
FIGS. 3A-3D
. In
FIG. 3A
, the profiles of each of the cutting elements on each cone are shown in relation to each other to show the intermeshing of the cutting elements between adjacent cones. This drill bit comprises a bit body
100
and three roller cones
110
attached to the bit body
100
such that each roller cone
110
is able to rotate with respect to the bit body
100
about an axis oblique to the bit body
100
. Disposed on each of the cones
110
is a plurality of cutting elements
112
for cutting into an earth formation. The cutting elements are arranged about the surface of each cone in generally circular, concentric rows arranged substantially perpendicular to the axis of rotation of the cone, as illustrated in FIG.
3
C. In this example, the rows of cutting elements are arranged so that cutting elements on adjacent cones intermesh between the cones. In this example, the cutting elements
112
comprise milled steel teeth with hardface coating applied thereon.
As is typical for milled tooth roller cone bits with intermeshing teeth, the teeth in this example are arranged in three rows
114
a
,
114
b
, and
114
c
on the first cone
114
, two rows
116
a
and
116
b
on the second cone
116
, and two rows
118
a
and
118
b
on the third cone
118
. The first row
114
a
on the first cone
114
is located at the apex of the cone and is typically referred to as the spearpoint. Referring to
FIG. 3C
, the first row
114
a
of the first cone comprises four teeth spaced about the apex of the cone as shown in the table at
120
and illustrated in the spacing diagram at
134
. The second row
114
b
on the first cone
114
comprises nine teeth spaced apart as shown in the table at
122
and illustrated in the spacing diagram at
136
. The third row
114
c
on the first cone
114
comprises nine teeth spaced apart as shown in the table at
124
and illustrated in spacing diagram at
138
. The first row
116
a
on the second cone
116
comprises five teeth spaced apart as shown in the table at
126
and illustrated in the spacing diagram at
140
. The second row
116
b
on the second cone
116
comprises nine teeth spaced apart as shown in the table at
128
and illustrated in the spacing diagram at
142
. The first row
118
a
on the third cone
118
comprises seven teeth spaced apart as shown at
126
and illustrated in the spacing diagram at
144
. The second row
118
b
on the third cone
118
comprises eleven teeth spaced apart as shown at
128
and illustrated in the spacing diagram at
146
.
This prior art drill bit has a total of fifty-four teeth, wherein twenty-two teeth are disposed on the first cone, fourteen teeth are disposed on the seco
Huang Sujian
Singh Amardeep
Dang Hoang
Rosenthal & Osha LLP
Smith International Inc.
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