Note: Descriptions are shown in the official language in which they were submitted.
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OIL WELI. DRILL:[:NG BIT
BACKGROUND OF THE INVENTIO~
In the drilling of a borehole through the earth's crusts
to penetrate oil or gas bearing formations several types of drill
bits are utilized. One category of drill bits is that of the roll-
ing cone or rolling cutter drill blt. Such a bit usually utilizes
three of such rolling cone cutters rotatably mounted on downward
extending journals each of which protrudes from one of three legs
-~ L0 extending downwardly at the lower end of the bit body. In the
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rolling cone bit category there axe basically two types of cutter
constructions. The ~lrst type is the "milled tooth" bit wherein the
conical cutters have prot2uding cutting elements or mllled teeth
formed on the surface thereof from the same basic piece of blank ;~
stock as the cone. The second category o~ rolling cone drill bits
involves the "insert" type of bits wherein the cones are made of
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one material and have drilled recesses in the surfaces for receiving
hard metal cutting elements termed inserts.
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Each type of ~olling cone drill bit has advanta~es and
~0 disadvantages. The milled tooth type of bit is advantageous in
that broad flat sharpened tooth shapes can be formed on the cutters
to provide a wide sharply penetrating cutting action on the bottom
~ hole. These broad flat sharp milled teeth are also tough and
- fracture resistant since they are made out of the same tough alloy
as the cone and are integral parts thereof. The disadvantage in
the milled tooth cutter type of bit is that the teeth are
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particularly suscept1ble to wear from abrasion and erosion of the
alloy in the extended tooth area.
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The second type of bit, the insert bit, offers the advantage of the hard -~
metal cutting elements or inserts which are tremendously resistant to such
abrasive forces. Usually the inserts are made of a very hard material such
as tungsten carbide sintered and compacted into a generally cylindrical-frusto
conical shape. Holes are usu~ally bored into the conical cutter to receive
the cylindrical end of the insert and the generally frusto conical portion
of the insert protrudes From the cutter surface. The disadvantage of the inserttype bits is that the inserts generally are not as fracture resistant as the
mil`led tooth cutting elements and therefore cannot be shaped as broad and flat
and sharp as the milled teeth. Thus the bottom hole coverage and penetration
rate of the insert is less desirable than that of the milled tooth although ~;the insert generally will wear many times longer than the milled tooth.
-- The conventional insert bits manufactured today generally utilize three
rolling cones having circumferential rows of inserts securely attached to the
cones by interference fit within the holes bored substantially perpendicular
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to the surface of the cone. These conventional cutter cones have rows of inserts
in circumferential rows around the conical surfaces of the conesO One of the
problems incurred in this conventional insert pattern is that because of the
deeply bored insert recesses in the conical surfaces a weakening of the cone
structure is effected. This weakening must be offset bX a thickening of the
cone resulting in a circumferential land passing around the cone in the area
of the insert locations. This adds to the weight and reduces the effective
size of the allowable bearing surface on which the cone is mounted. In additionto the problem of the weakening of the cone structure, which weakening is particularly
susceptible to hoop stresses in the cone structure, the insert type constructionalso suffers from an effect known as tracking and gyration.
Tracking and the resulting gyration occurs because of the circumferential
rows of inserts forming grooves in the rock face being drilled. These parallel
grooves leave a raised ridge of rock material called a kerf. When this kerf ?
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becomes high enough it causes these rows of inserts to track
down grooves formerly cut by the other cutter inserts and
results in the drill bit following a non-central axis of
rotation. When the drill bit begins to track, the action is an
orbital action termed "gyration" and is a destructive force on
the drill bit. Likewiser the gyration effect reduces the
cutting speed of the bi-t to a negligible amount. The kerf
buildup even-tually contacts the non-cutting surfaces of the
cones and totally stops any cutting action of the bit in the
hole. Likewise~ the gyration forc s introduced are not those
for which the bit is designed and as a result, unusual damage
usually occurs to the inserts, the cones and the bearings.
SUMMARY OF THE INVENTION
~`~ The present invention overcomes these disadvantages by
providing a drill bit cone structure having a unique insert -
- pattern which reduces failures from hoop stresses on the cone
structure and greatly prevents gyration and trackirg of the
conical cutters of the drill bit. Briefly this pattern of
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insert placement on the conical cutters is a series of non-
linear circumferential bands of inserts on the cutter surfaces.
More particularly the invention in one aspect pertains to a
rolling cutter for a tri-cone drill bit, which cutter comprises
a generally conical cutter body having a conical surface
adapted to carry protruding cutting elements thereon and which
is further adapted to be rotated in close proximity to an
underground formation borehole face. One or more non-gage
circumferential insert rows on the cutter conlcal surface are
arranged peripherally around the cu-tter body and a plurality of
hard metal inserts are in at least one of the non-gage rows,
the inserts being located in a staggered non-circular peripheral
relationship in the rows.
- The invention also pertains to an oil well drill bit of
~ the type having one or more downwardly extending legs, each
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having a downward projecting bearing journal with a generally
conical cutter rotatably mounted thereon. The improvement
comprises each conical cut-ter having a gage row of inser-ted
hard metal cutting elements pro-truding thererom and at least
one non-gage row o inserted hard metal cutting elements
protruding therefrom. At least one o the non gage rows o
inserted hard me-tal cutting elements is in at least one of the
cutters arranged in a staggered non-circular peripheral
relationship arouncl the cutter.
In a urther embodlment the invention contemplates a :
tricone roller cutter drill bit or drilling a well bore which -~
comprises a bit body having a threaded pin at its upper end
adapted to be detachably secured to drill pipe for rotating ;
the drill bit and three dependiny legs at its lower end with
each leg being spaced from the other legs and having an inwardly
extending bearing ~ournal, and a roller cutter mounted on each
kearing journal. Each of the roller cu-tter comprises a generally
frustoconical body, and a plurality of elongated cutting elements
of a tungsten carbide material mounted on the roller cutter body
with their longitudinal axes extending generally radially with
respect to the roller cu-tter body. Each cutting element tapers
toward its outer end to a tip engageable with the bottom of the
well bore, and the cutting elements are arranged in a plurality
of generally annular rows around the roller cutter bodyr one row
being adjacent the base of the roller cutter body and constitu-t-
ing a gage row and another row being between the gage row and
- the apex of the roller cutter body and constituting an in-ter-
mediate row. The cutting elements of the intermediate row are
spaced at generally equal inter~als around the roller cutter
body with each cutting element being offset from the cutting
.~ elements adjacent thereto in the direction of the longitudinal
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axis of the roller cu-tter body. The amount of offset between
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the longitudinal centerlines of adjacent cutting elements of the
intermediate row is less than the width of the -tip of a cuttiny
element. Thus, -the tips of the cutting elements o~ the inter-
mediate row overlap each other when the roller cutter is viewed
in longitudinal sec-tion, whereby, upon rota-tion o the drill bit,
the cutting elements of the intermediate row engage the bottom of
the well bore over a generally annuIar area having a thickness
greater than the width of the tip of a cutting element for in-
creased bottom hole coverage by the drill bit, with a resultant
reduction of the tendency of the drill bit to gyrate.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-sectional plan view of the three cutter
cones of a drill bit which embody the present invention.
Figure 2 is a partial cross-sectional view OL a cutter cone
illustrating the insert patterns of the present invention. ;
Figure 3 is a partial developed view of one of the cutter
cones showing the positioning of the inserts on the cutter cone.
Figure 4 is a view similar to Figure 3 showing the position-
ing of the inserts of a second embodiment of the drill bit.
DESCRIPTION OF THE PREFERRED E~BODIMENTS
Figure 1 is a typical cutter layou-t of -the three conical
cutters of a rolling cone drill bit. Because the cutters are
located in non-planar relationship the single dimensional layout
of the cutter relationship necessaxily requires the distortional
effects resulting from this projection. As a result one of the
cones must be split in half as i]lustrated in order -to show the
- intermeshing relationships of the inserts on one cone with thoseof the adjacent cones. In Fiyure 1 the three conical cutters 10,
11, and 12 are illustrated in schematic cross-sectional view.
Each cutter comprises a generally conical body 13 upon which are
~ ~ circumferentially located raised insert lands 14 which pass cir-
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- cumferentially around the conical surface of cutter 10. A plur-
ality of hard metal cutting elements 15 commonly termed insexts
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are located in cylindrical bore~, 16 drilled into cone 10 per-
pendicular to the surace of land 14. Inserts 15 are yenerally
secured tightly in recesses 16 by means of an interference ~i-t.
The interference fit is achieved by boring holes 16 slightly
smaller in diame-ter -than the diameter of the cylirldrical portion
o~ inserts 15.
The present invention is distinc-tly illustrated in Figure 1 ~ ;~
by the offset pattern o~ inserts 15, 17 and 18 projecting upward-
: ly from land 14. In conventional designs all of the inserts in ~.
a land 14 would be located basically on -the same circumferential
circle on the cutter surface. In the present invention the
inserts in the land 14 are located in different concentric cir-
cum~eren-tial circles around the cutter. This new cut-ter profile
having offset or staggered inserts allows a greater bo-ttom hole
.~ coverage with the same number of inserts and greatly reduces the
tendency of the cutters to engage in tracking. This reduction
o the tracki.ng tendency serves to reduce bit gyration and
orbital action oE -the bit in the bottom of the bore hole.
Figure 2 illustrates an overlapping cutter profile showiny
20. the positioning of all of the inserts on the diferent cutters
o a single bit. The inserts 15a and 15b in Figure 2 represent
those inserts of cutter 11. Inserts 25a and 25b are those of
cutter 10 and inserts 35a and 35b are the inserts of cutter 12.
Inserts 45 are the inserts o cutters 10 and 11 and inserts 55
. are inserts on all three cutters. The inserts at 55 are normally
; termed gage row inserts.
~ Reerring to Figures 3 and 4 the staggered or offset inserts
pattern may be seen more clearly. In Figure 3 a sinusoidal insert
pattern is disclosed wherein the inserts have three basic
locations along the land 14. Each insert is ofset approximately
the same amount in a lateral direction from each adjacent insert
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and basically ends up with three closely associated rows of inserts
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in the same land. This pattern differs from the normal widely
spaced rows of inserts on the conven-tional cu-tters in that each
insert row in a single land is primarily overlapping each adjacent
row with only a slight amount of offset to one side or the other.
The amount of o~fset in -the land 14 has been exaggerated in order
to more clearly portra~ the pattern of inserts. Likewise, the
land has been flattened ou-~ to illustra-te the insert~pattern but
because of the circular conical shape of the cutter land 14 would ;-
normally no-t be a straight flat surface.
Figure 4 illustrates a second embodiment of the insert design
wherein the land 14 contains only two insert locations each sli~ht-
ly offset from the other and both overlapping each other sub-
stantially.
Thus, the present invention discloses a ne~ drill bit cutter
profile utilizing non-aligned cutter inserts in each insert land
on each oE the conical cutters. The non-aligned or staggered
inserts provide a better coverage of the bottom hole surface,
prevent tracking of following inserts, and thus greatly reduce
bit gyration and non-circular orbital motion. As a result,
breakage of inserts, destruction of cut-ter structures, and bearing
failure are greatly reduced without sacrificing the normal rate
of penetration of the drill bit.
Although a specific preferred embodiment of the ~resent in-
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vention has been described in the detailed description above, the
description is not intended to limit the invention to the part-
icular forms of embodiments disclosed therein since they are to
be recognized as illustrative rather than restrictive and it will
be obvious to those skilled in the ar-t that the invention is not
so limited. For instance, whereas the insert patterns as des-
cribed and illustrated in Figures 3 and ~ are of the sinusoidal
configura-tlon, it is clear that other offset or staggered patterns
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could also be utilized efficiently. Thus~ the invention is
declared to cover all changes and modifications or the
specific example of the invention herein disclosed for purposes
of illustration which do not constitute departure from the
spirit and scope of the invention.
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