[0001] The present invention relates generally to a rock bit of the type as described in
the preamble of claim 1.
[0002] Earth boring rock bits for drilling oil and gas wells typically have three rotatable
cutters that roll over the bottom of a borehole as the bit rotates. Each cutter is
generally conical and has a frustoconical heel surface that passes near the borehole
sidewall as the cutter rotates. One type of rock bit, known as a tungsten carbide
insert bit or TCI bit, has wear resistant inserts secured in holes formed in the cutters.
Such inserts are usually made of tungsten carbide.
[0003] For each cutter, the inserts are arranged in circumferential rows on the conical
surface of the rotatable cutter at various distances from the heel surface. The row
nearest, but not on the heel surface is known as the gage row. The gage row of inserts
cuts rock at the gage of the hole. The heel surface extends upwardly along the wall
of the hole drilled by the gage row.
[0004] In the types of bits as defined in the preamble of claim 1, such as shown in US-A-3,727,705,
certain cutters have gage row structure that includes staggered rows located thereon.
The staggered rows comprise two rows of inserts alternately spaced so that the grip
portion of the inserts do not interfere.
[0005] In this and other prior art bits (see FIGURE 4), the inserts on the gage row are
oriented in such a manner to cause the cutting elements to cut both the borehole bottom
and sidewall. This combined cutting action compromises the insert because the cutting
action operating on the borehole bottom is usually a crushing and gouging action while
the cutting action operating on the sidewall is a scraping action. Ideally, the crushing
action calls for a tough insert while the scraping action calls for a hard insert.
As a result, one grade of tungsten carbide cannot ideally perform both functions.
[0006] These bits obviated this problem by having the heel row of inserts provided with
a flat cutting surface parallel to the heel surface, and basically contact the sidewall
while the gage row of inserts contacts the borehole bottom. However, it has been found
that these rows are separated by such a distance as not to allow optimization of each.
[0007] U.S. Patent Nos. 2,774,570 and 2,774,571 show such arrangements. In each instance,
the heel row of inserts is still physically compromised because the lower portion
of each insert must still engage the borehole bottom while only the outside portion
scrapes the sidewall. In addition, because the heel row is separated from the gage
row, there is still a large portion of the sidewall that the gage row must scrape
against as it passes through the hole bottom and continues up the sidewall.
[0008] As a result, the inserts of the heel rows of these prior art bits cannot be as hard
as that recommended for the sidewall scraping action because they must be tough enough
to crush the bottom hole formation. In like manner, the gage row of inserts cannot
be as tough as the interior rows of inserts because they must perform a large portion
of scraping action on the borehole sidewall.
[0009] The present invention as defined in claim 1 minimizes the above-mentioned shortcomings
by providing a rolling cone rock bit with a plurality of cutters each mounted on the
body of the bit to rotate about an axis. Each cutter has a generally frusto-conical
support surface for rolling contact with the bottom of a borehole, and a heel surface
at the base of the cutter adjacent to the sidewall of the borehole. A plurality of
wear resistant inserts positioned on the support surface are arranged in circumferential
rows, each insert being generally cylindrical with a projected crown area profile
and having a central axis. One of the rows of inserts next to the heel surface is
a row of gage inserts, with each gage insert being oriented to have its axis extend
partiallly radially outward to enable the gage insert to engage the borehole bottom.
Each gage insert defines a cutting surface projected crown area profile taken through
a section through the centerline of the cone. A plurality of heel inserts located
near the gage inserts are at an acute angle with respect to the gage inserts in a
direction away from the apex of the cone. Each insert defines a cutting surface projected
crown area profile taken through a section through the centerline of the cone. The
crown area profile of a heel insert, when rotated around the cone to the same plane
as a gage insert crown area profile, overlaps the gage insert crown area profile to
enable the heel inserts to slidably engage the borehole sidewall.
[0010] Since the heel row inserts scrape against the wall, they are made of a harder grade
of tungsten carbide than the gage row inserts, and the gage row inserts are tougher
than the heel row inserts. Preferably, the heel row insert crown area profiles are
located up the borehole sidewall within three millimeters of the gage row insert crown
area profiles.
[0011] The above noted features and advantages of the present invention will be more fully
understood upon a study of the following description of a preferred embodiment in
conjunction with the detailed drawings wherein:
FIGURE 1 is a perspective view of a three cone rock bit utilizing gage row cutters
made in accordance with the present invention;
FIGURE 2 is an enlarged perspective view of one of the cones shown in FIGURE 1;
FIGURE 3 is a fragmentary sectional view of the cone through the centerline of the
cone located in a borehole; and
FIGURE 4 is a fragmentary sectional view of a prior art cone showing the location
of a conventional heel row insert.
[0012] FIGURE 1 illustrates a drill bit or rock bit, generally indicated by an arrow 10,
having a threaded pin section 11 for securing to the bottom end of a drill string.
The rock bit further includes a main body 12 having a plurality of legs 13, 14 and
15 extending downwardly therefrom. Each leg includes a bearing pin (not shown in FIGURE
1) extending toward the center of the bit. Three cone shaped cutters 16 are rotatably
mounted on the bearing pins and are adapted to roll along the bottom of a borehole
as the bit is rotated.
[0013] The cutters 16 tend to roll along the hole bottom much like a wheel except that because
the axes of the bearing pins are offset from the axis of the bit, and because of the
geometry of the cones, a true roll of the cones is not possible. Therefore, in addition
to the rolling motion, a small sliding motion is imparted thereto which would be analogous
to the movement of an automobile tire that is out of alignment.
[0014] Each cutter cone 16 has a plurality of wear resistant inserts 20 interferingly secured
by the insert grip 90 in mating holes drilled in the support surface of the cutter
cone. Preferably the inserts 20 are constructed from sintered tungsten carbide.
[0015] The inserts 20 are located in rows that extend circumferentially around the generally
conical surface of each cutter. Certain of the rows are arranged to intermesh with
other rows of the other cutters so that the entire bottom of the hole is drilled.
[0016] Referring now to FIGURE 2, as mentioned previously, each cutter is generally conically
shaped with a nose area 21 at the apex of the cone and a heel surface 22 at the base
of the cone. The heel surface 22 is frustoconical and is adapted to pass near the
wall of the borehole as the cutters rotate about the borehole bottom. The row of inserts
20 closest to the heel surface 22 is called the gage row 23. In practice of this invention,
the gage row inserts are further separated into a first row of gage inserts 24 and
a second row of heel inserts 25.
[0017] As shown in FIGURE 3, which is a fragmentary cross section through the centerline
of a cutter 16, each of the gage inserts 24 is oriented with its axis extending radially
outwardly and downwardly to engage the borehole bottom. The cutting profiles of the
inserts are illustrated in a cross section as seen in FIGURE 3. Each of the heel inserts
25, on the other hand, is with its axis oriented outwardly and downwardly at a greater
angle from the centerline of the cone. The heel inserts are oriented at an acute angle
to the gage inserts in a direction away from the apex of the cutter cone to more closely
face the sidewall of the borehole.
[0018] During drilling operations, a tremendous amount of weight from the drill string is
applied to the bit 10 as it is rotated. As the inserts 20 of the first three rows,
beginning with the nose row, rotated with the cutter, they eventually come in contact
with the rock formation on the bottom of the hole. The imprint made on the formation
is created by the insert contacting the formation with its trailing side, rolling
on the formation about its apex, and then exiting with the last contact being made
by its leading side. During this rolling movement, the offset of the cone axis causes
each insert 20 to slide a small amount which causes the imprint to become somewhat
elongated. This combined rolling and sliding motion along with extreme loads involved
causes the formation contacted by the insert to be crushed, with little chips being
broken off thereby.
[0019] Because of the high loads involved with this crushing action, the inserts 20 must
be made of an extremely tough grade of tungsten carbide.
[0020] The gage row of inserts 24 also contact the hole bottom in a similar manner. However,
prior to the present invention, these inserts 24 also performed a scraping action
along the borehole sidewall before they make their imprint on the borehole bottom
(see FIGURE 4). As mentioned previously, this necessitated making the gage row inserts
harder to accommodate the scraping function and minimize wear which can cause the
hole to be drilled under the desired gage or diameter. Unfortunately, when one makes
a tungsten carbide insert harder, it necessarily becomes less tough.
[0021] Because of these compromises, the gage rows of inserts in prior art rock bits suffered
from breakage problems. As a result, inserts 26 had to be placed on the heel surfaces
of the cones to ensure the heel surface integrity after the gage inserts broke or
wore down. Since such inserts were separated a relatively large distance D
2 from the gage inserts (FIGURE 4), they do not come into play and do not contact the
sidewall until after the gage inserts break or wear to a certain point, the problems
concerning gage insert breakage continued.
[0022] The present invention minimizes such a problem by having the heel row inserts 25
interleaved between the the gage inserts with their cutting surface profiles being
overlapped. The crowns of the gage row inserts and heel row inserts are separated
by only a distance D
1 in the cutting surface profile as illustrated in FIGURE 3. This enables the heel
inserts 25 to engage the borehole sidewall at points much lower in the borehole and
much sooner in the cutting cycle than previous heel inserts. The distance D
1 is preferably within four millimeters in a 20 cm diameter rock bit.
[0023] The crown of the insert is the part of the projected area of the insert that contacts
the intact rock formation, as illustrated in FIGURE 3. By scraping away the borehole
sidewall in those lower areas before the gage inserts have the opportunity to engage
the sidewall, the gage inserts 24 are spared from having to do a large amount of scraping.
As a result, there would be a much smaller amount of gage insert scraping compared
to the prior art, and this amount does not require the gage inserts to make any compromises
from a toughness standpoint. Since the vast majority of the cutting action of the
gage inserts is the crushing and gouging action occurring on the borehole bottom,
the gage row inserts 24 can now be made of the same tough grade of tungsten carbide
as the inner rows of inserts.
[0024] If one were to isolate attention on a single cutting insert as the bit rotates within
a borehole, its path would be seen to be a modified planetary motion. The cutter cone
rotates about the journal which is slightly offset from the axis of the bit. As the
bit rotates, the cone rolls on the borehole bottom with a small sliding motion imparted
thereto because of the geometry of the cones and the journal offset. During this motion,
the insert eventually moves down into engagement with the borehole bottom. As it touches
down on a particular location, the insert rotates on that spot but with a small sliding
motion. For the most part, the insert acts on the formation spot in a crushing action
in addition to a small scraping action. As a result, such inserts have to be tough
to resist the comprehensive forces acting on the insert. This greatly overrides the
need to be hard to resist the small abrasive forces acting on the insert because of
the small sliding.
[0025] If the insert is a gage insert, the same planetary motion occurs except that the
planetary orbit is the largest. As the gage insert touches down on the hole bottom,
the same type of movement is involved, i.e. the insert rolls over the spot with a
small sliding motion. However, because of the journal offset, the gage insert would
also contact a portion of the sidewall during a portion of its travel. This, of course,
results in almost pure scraping, and the gage insert normally would have to be harder
than an inner row insert because of the large abrasive forces acting thereon.
[0026] As a result, conventional gage inserts had the problem of having to resist the high
compressive forces encountered with the hole bottom, and the high abrasive forces
encountered with the sidewall of the borehole. Unfortunately, compromises had to be
made because tungsten carbide inserts cannot have a maximum toughness and maximum
hardness at the same time. Because of this, the gage inserts usually always wore faster
than the inner rows of inserts.
[0027] Prior bits sometimes avoid any sliding motion because of the true roll aspects of
the cone, i.e. zero journal offset and zero oversize angle. However, this was not
always the case, even for hard formation bits. Usually for such bits, only one row
of inserts would become the "drive row" and assumed the true roll condition. All other
rows would have some sliding associated with them. Therefore, unless the outer gage
row would become the drive row, a certain amount of sliding would occur and the sliding
forces acting on the sidewall would have to be dealt with.
[0028] In today's drilling, the vast majority of rock bits are soft and medium formation
bits that have journal offset and do not have any "true roll" capabilities.
[0029] In this invention, to optimize drilling with a bit having offset and no true rolling,
there is a single substantially overlapping row of inserts near the heel of the cutter
cone with each alternate gage row insert 24 oriented toward the hole bottom to cut
the hole bottom while the other of each alternate heel row insert 25 being oriented
to the sidewall to cut the sidewall.
[0030] Since sidewall scraping is going to exist a set of heel row inserts is oriented to
do substantially all of the scraping and leave very little scraping for the other
set of gage row inserts which are left to attack the hole bottom. As a result, the
first set can be made of a hard material and the second set of a tough material.
[0031] Basically, this is accomplished by two means, i.e. the orientation of the two inserts
(one toward the hole bottom and the other toward the sidewall) and the close proximity
of the insert projection profiles. The closeness is shown by dimension D
1 in Figure 3, which is preferably less than four millimeters.
[0032] Moreover, since the heel row inserts 25 are restricted to mostly scraping, they can
be made of a very hard tungsten carbide or they can also be coated with super hard
abrasives such as polycrystalline diamond.
[0033] Although the inserts 24 are shown as hemispherical, they can also be constructed
of different conventional shapes such as chisels. In addition, the heel row inserts
25 can have their abrasive surfaces be slightly spherical, flat, or some other configuration
and still come within the invention.
[0034] It will of course be realized that various other modifications can be made in the
design and operation of the present invention. Thus, while the principal preferred
construction and mode of operation of the invention have been illustrated and described
in what is now considered to represent its best embodiments, it should be understood
that within the scope of the appended claims, the invention may be practiced otherwise
than as specifically described and illustrated.
1. A rock bit (10) for drilling a borehole, having a bit body (12), a plurality of cutters
(16) each mounted on the bit body (12) to rotate About an axis, each cutter (16) having
a generally frusto-conical support surface for rolling contact with the bottom of
a borehole, each cutter (16) further having a heel surface (22) at the base thereof
adjacent to the sidewall of the borehole, and a plurality of wear resistant inserts
(20,24) positioned on the support surface and being arranged in circumferential rows,
each insert (20,24) being generally cylindrical with a projected crown area profile
and having a central axis, one of the rows of inserts being positioned next to the
heel surface (22) defining a row (23) of gage inserts, with each gage insert (24)
oriented to have its axis extend partially radially outward to enable the gage insert
(24) to engage the borehole bottom, each gage insert (24) further defining a cutting
surface projected crown area profile taken through a section through the centreline
of the cone, and a plurality of heel inserts (25) located near the gage inserts (24)
at an acute angle with respect to the gage inserts (24) in a direction away from the
apex of the cone, characterised in that each heel insert (25) further defines a cutting surface projected crown area profile
taken through a section through the centreline of the cone, the crown area profile
of the heel insert (25), when rotated around the cone to the same plane as a gage
insert crown area profile, overlapping the gage insert crown area profile to enable
the heel inserts (25) to slidably engage the borehole sidewall.
2. The rock bit of claim 1 wherein the heel inserts (25) are interleaved between the
gage inserts (24).
3. The rock bit of any of the preceding claims wherein the inserts (20,24,25) are made
of tungsten carbide.
4. The rock bit of claim 3 wherein the heel row inserts (25) are made of a harder grade
of tungsten carbide than the gage row inserts (24).
5. The rock bit of claim 4 wherein the gage row inserts (24) are made of the same tough
grade of tungsten carbide as the other rows of inserts (20).
6. The rock bit of any of the preceding claims wherein the heel row insert crown area
profiles are located up the borehole sidewall within four millimetres of the gage
row insert crown area profiles.
7. The rock bit of any of the preceding claims wherein the heel inserts (25) are coated
with an outer layer of polycrystalline diamond.
8. The rock bit of any of the preceding claims wherein the rotational axes of the cutters
(16) are each offset from the axis of the bit body (12).
9. The rock bit of any of the preceding claims wherein the cutters (16), when rotating,
define a substantially flat surface corresponding to the bottom of a borehole, and
a generally cylindrical surface corresponding to the side wall of a borehole.
1. Gesteinsbohrmeißel (10) zum Bohren eines Bohrloches mit einem Meißelkörper (12), einer
Vielzahl von Schneidköpfen (16), die jeweils am Meißelkörper (12) zum Drehen um eine
Achse montiert sind, wobei jeder Schneidkopf (16) eine im allgemeinen kegelstumpfförmige
Tragfläche für einen rollenden Kontakt mit dem Boden eines Bohrloches aufweist, jeder
Schneidkopf (16) ferner eine rückwärtige Oberfläche (22) an seiner Basis benachbart
der Seitenwand des Bohrloches sowie eine Vielzahl von verschleißfesten Einsätzen (20,
24) aufweist, die an der Tragfläche positioniert und in Umfangsreihen angeordnet sind,
wobei jeder Einsatz (20, 24) im wesentlichen zylindrisch mit einem vorstehenden, gewölbten
Flächenprofil ausgebildet ist und eine zentrale Achse aufweist, wobei eine der Einsatzreihen
benachbart der rückwärtigen Oberfläche (22) angeordnet ist und eine Reihe (23) von
Kalibereinsätzen definiert, wobei jeder Kalibereinsatz (24) so ausgerichtet ist, daß
seine Achse teilweise radial nach außen weist, damit der Kalibereinsatz (24) mit dem
Boden des Bohrloches in Eingriff treten kann, wobei jeder Kalibereinsatz (24) ferner
ein vorstehendes, gewölbtes Flächenprofil einer Schneidfläche definiert, bezüglich
eines Schnitts durch die Mittellinie des Kegels, und mit einer Mehrzahl von rückwärtigen
Einsätzen (25), die nahe den Kalibereinsätzen (24) unter einem spitzen Winkel bezüglich
der Kalibereinsätze (24) in einer Richtung weg vom Scheitelpunkt des Kegels angeordnet
sind, dadurch gekennzeichnet, daß jeder rückwärtige Einsatz (25) ferner ein vorstehendes, gewölbtes Flächenprofil
der Schneidfläche im Schnitt durch die Mittellinie des Kegels aufweist, wobei das
gewölbte Flächenprofil der rückwärtigen Einsätze (25), wenn sie um den Kegel zur gleichen
Ebene wie ein gewölbtes Flächenprofil des Kalibereinsatzes gedreht wird, das gewölbte
Flächenprofil des Kalibereinsatzes überlappt, so daß die rückwärtigen Einsätze (25)
gleitend mit der Seitenwand des Bohrloches in Eingriff treten können.
2. Gesteinsmeißel nach Anspruch 1, wobei die rückwärtigen Einsätze (25) zwischen die
Kalibereinsätze (24) eingefügt sind.
3. Gesteinsmeißel nach einem der vorangegangenen Ansprüche, wobei die Einsätze (20, 24,
25) aus Wolframcarbid hergestellt sind.
4. Gesteinsmeißel nach Anspruch 3, wobei die Einsätze (25) der rückwärtigen Reihe aus
einem Wolframcarbid eines höheren Härtegrades als die Einsätze (24) der Kaliberreihe
hergestellt sind.
5. Gesteinsmeißel nach Anspruch 4, wobei die Einsätze (24) der Kaliberreihe aus dem gleichen
Hochleistungs-Wolframcarbid wie die anderen Reihen der Einsätze (20) hergestellt sind.
6. Gesteinsmeißel nach einem der vorstehenden Ansprüche, wobei die gewölbten Flächenprofile
der Einsätze der rückwärtigen Reihe bezüglich der Seitenwand des Bohrloches innerhalb
von 4 mm höher angeordnet sind als die gewölbten Flächenprofile der Einsätze der Kaliberreihe.
7. Gesteinsmeißel nach einem der vorstehenden Ansprüche, wobei die rückwärtigen Einsätze
(25) mit einer äußeren Schicht aus polykristallinem Diamant beschichtet sind.
8. Gesteinsmeißel nach einem der vorstehenden Ansprüche, wobei die Drehachsen der Schneidköpfe
(16) jeweils gegenüber der Achse des Meißelkörpers (12) versetzt sind.
9. Gesteinsmeißel nach einem der vorstehenden Ansprüche, wobei die Schneidköpfe (16)
bei ihrer Drehung eine im wesentlichen flache Oberfläche, die dem Boden eines Bohrlochs
entspricht, und eine im wesentlichen zylindrische Oberfläche definieren, die der Seitenwand
eines Bohrlochs entspricht.
1. Trépan de roche (10) pour percer un trou de forage, ayant un corps de trépan (12),
plusieurs dispositifs de découpe (16) chacun étant agencé sur le corps de trépan (12)
pour tourner autour d'un axe, chaque dispositif de découpe (16) ayant une surface
de support de manière générale tronconique pour venir en contact roulant avec le fond
d'un trou de forage, chaque dispositif de découpe (16) ayant en outre une surface
de talon (22) au niveau de la base de celui-ci adjacente à la paroi latérale du trou
de forage, et plusieurs éléments rapportés résistant à l'usure (20, 24) positionnés
sur la surface de support et étant agencés dans des rangées circonférentielles, chaque
élément rapporté (20, 24) étant de manière générale cylindrique en ayant un profil
de surface couronne en saillie et ayant un axe central, l'une des rangées d'éléments
rapportés étant positionnée après la surface de talon (22) définissant une rangée
(23) d'éléments rapportés de gabarit, chaque élément rapporté de gabarit (24) étant
orienté pour avoir son axe s'étendant partiellement radialement vers l'extérieur pour
permettre à l'élément rapporté de gabarit (24) de venir en contact avec le fond du
trou de forage, chaque élément rapporté de gabarit (24) définissant en outre un profil
de surface de couronne en saillie formant surface de découpe, pris dans une section
transversale traversant l'axe du cône, et plusieurs éléments rapportés de talon (25)
situés à proximité des éléments rapportés de gabarit (24) au niveau d'un angle aigu
par rapport aux éléments rapportés de gabarit (24) dans une direction s'éloignant
du sommet du cône, caractérisé en ce que chaque élément rapporté de talon (25) définit
de plus un profil de surface de couronne en saillie formant surface de découpe pris
dans une section transversale traversant l'axe du cône, le profil de surface de couronne
de l'élément rapporté de talon talon (25), lorsqu'il tourne autour du cône dans le
même plan qu'un profil de surface de couronne d'élément rapporté de gabarit, recouvre
le profil de surface de couronne d'élément rapporté de gabarit pour permettre aux
éléments rapportés de talon (25) de venir en contact coulissant avec la paroi latérale
du trou de forage.
2. Trépan de roche selon la revendication 1, dans lequel les éléments rapportés de talon
(25) sont intercalés entre les éléments rapportés de gabarit (24).
3. Trépan de roche selon l'une quelconque des revendications précédentes, dans lequel
les éléments rapportés (20, 24, 25) sont constitués de carbure de tungstène.
4. Trépan de roche selon la revendication 3, dans lequel les éléments rapportés de la
rangée de talon (25) sont constitués d'un carbure de tungstène de qualité plus dure
que les éléments rapportés d'une rangée de gabarit (24).
5. Trépan de roche selon la revendication 4, dans lequel les éléments rapportés d'une
rangée de gabarit (24) sont constitués de carbure de tungstène de même qualité de
dureté que les autres rangées d'éléments rapportés (20).
6. Trépan de roche selon l'une quelconque des revendications précédentes, dans lequel
les profils de surface de couronne d'éléments rapportés d'une rangée de talon sont
situés vers le haut de la paroi latérale du trou de forage, à moins de quatre millimètres
des profils de surface de couronne d'éléments rapportés d'une rangée de gabarit.
7. Trépan de roche selon l'une quelconque des revendications précédentes, dans lequel
les éléments rapportés de talon (25) sont revêtus d'une couche extérieure de diamant
polycristallin.
8. Trépan de roche selon l'une quelconque des revendications précédentes, dans lequel
les axes de rotation des dispositifs de découpe (16) sont chacun décalés de l'axe
du corps de trépan (12).
9. Trépan de roche selon l'une quelconque des revendications précédentes, dans lequel
les dispositifs de découpe (16) lorsqu'ils tournent, définissent une surface à peu
près plate correspondant au fond d'un trou de forage, et une surface de manière générale
cylindrique correspondant à la paroi latérale d'un trou de forage.