[0001] This invention relates to drilling bits for use in drilling operations, such as in
the oil and gas industry and, in particular, to a bit suitable for alleviating problems
associated with running of the drilling bit into a well hole and pulling of the cutter
bit from the hole.
[0002] Conventional drilling bits comprise a generally tubular drilling bit body provided
at the bottom end thereof with a plurality of cutters for cutting the well formation.
Normally, the drilling bit is forged and provided at its bottom end with three legs
having attached to their bottom portions, known as shirt tails, mounting pins for
securing cone cutter elements made of a durable material. These cutter elements may
be conical and are provided with hard cutting teeth, made, for example, from tungsten
carbide, for cutting a formation. Through the centre of the drilling bit body is usually
provided a bore through which drilling fluids are delivered at high velocity via three
conduits to areas adjacent to the cutters to assist in cutting and cuttings removal.
However, the central bore is not itself directly open to the cutting face and, for
this reason, a number of problems can arise when a drilling bit is being run into
the hole, pulled from the hole or simply being used in cutting operations.
[0003] Firstly, it is to be appreciated that the drilling bit body will be in gauge with
the walls of the hole and, therefore, as the drilling bit is run into the hole it
acts as a piston which compresses material below the bottom end of the drilling bit
body. The only relief from the increasing pressures is leakage through zones where
the drilling bit body has lesser diameter than the gauge of the hole. However, as
these zones only have very small area for flow of cuttings and fluids, the flow is
substantially restricted and little pressure relief is obtained. The consequence of
such increasing pressures is "surge" or the generation of stresses on the rock formations
along the open hole section below the drilling bit. It is known in the oil and gas
industry that these stresses or surge pressures cause major damage to weak formations
and, more importantly, to productive reservoir sands. In particular, the formation
may be damaged by fracturing of the formation beneath the cutter bit during running
into the hole. This problem is worsened by increasing running speeds and higher viscosity
drilling fluids that cause higher pressure drop across the drilling bit. Clearly,
damage to the formation, with consequential reductions in oil and gas recovery, is
unacceptable to the industry for cost reasons.
[0004] Secondly, upon pulling of the drilling bit from the hole a reverse problem known
to the industry as "swabbing" occurs. In the worst cases, swabbing, which results
from fluid flow into the reduced pressure area caused by pulling of the drilling bit
and drillstring from the hole can cause blowouts which are extremely hazardous. In
addition, swabbing may result in contamination of the drilling fluids by formation
fluids necessitating costly treatment processes and/or increased drilling fluid cost.
Swabbing is most pronounced when the drilling bit or drilling stabilisers are encrusted
or packed with formation cuttings. In these cases, it becomes increasingly more difficult
to maintain an even hydrostatic pressure on both sides of the cutter bit because the
already restricted fluid flow area past the outer circumference of the cutter bit
is restricted even further. Other factors that contribute to swabbing include variable
viscosity drilling fluids and variation in hole diameter.
[0005] A yet further problem with conventional cutters is poor hole cleaning due to a poor
efficiency of cuttings removal from the centre of the cutting area at the bottom of
the hole. Conventional drilling bits rely on the delivery of drilling fluid to the
bottom of the hole for effective hole cleaning. In a typical design, as discussed
above, there are three cone cutters and, therefore, three nozzles, each adjacent to
each cutter cone, are provided for the jetting of cooling and cleaning fluid to the
bottom of the hole. Jetting occurs at high velocity with fluid impacting the bottom
of the hole at or near its outer edges close to the hole walls. This action effectively
washes the outer zone of the hole to remove cuttings. However, cleaning from the centre
of the hole is much less efficient because cuttings become trapped in recesses between
the cutters and the bottom end of the drilling bit body. In conventional bits, cutting
accumulation in this area can create what is called in the industry bit balling, where
the trapped cuttings restrict the rotation of the cutting cones. Bit balling has been
a major problem in the industry. Thus the overall cleaning and cutting efficiency
of the drilling bit is reduced.
[0006] The present invention provides a drilling bit comprising:
(a) a body adapted to be connected to a tubular drill string and being rotatable about
its axis, said body having a full diameter portion and an upper portion which has
at least a circumferential segment which is positioned radially inwardly with respect
to the axis of the full diameter portion;
(b) a plurality of leg members extending downwardly from the body and defining a zone
therebetween and below the body;
(c) cutting means mounted on each leg member and extending inwardly into the zone
for cutting a formation; and
(d) a return passage extending upwardly through the body from said zone and exiting
at the upper portion opposite the circumferential segment whereby a portion at least
of the fluid delivered from the tubular drill string to said zone, i.e. to the cutting
face, flows from said zone through the return passage in the body, bypassing the full
diameter portion of the body.
[0007] The return passage provides a route for cuttings to escape to the surface of the
hole.
[0008] Conveniently, the return passage exists the body of the drilling bit at an opening
which extends in a plane substantially normal to a central axis extending in the same
direction as the tubular drill string. In addition, it may be found desirable for
the return passage to communicate with at least one further passage which by-passes
the full diameter portion of the body such that the aforesaid portion at least of
the fluid exits from the body through a number of openings. The openings to the further
passages need not be located at the same level and can be orientated at a variety
of different angles corresponding to the trajectory of the first or further passages
which ranges between 0° and 90° to the central axis of the cutter bit body, that is
the return passage exits from said body at an opening which extends in a plane having
an axis extending at an angle not being perpendicular to the central axis of said
body.
[0009] Preferably, flow of cutting through the return passage is assisted by jetting drilling
fluid through at least one nozzle communicating a drilling fluid supply and the return
passage, and having a trajectory the same as the return passage. The same applies
to the further passage. Further, the drilling bit body may be provided with one or
more supply passages communicating a drilling fluid supply with an opening or openings
of the cutter bit body located adjacent to the cutting means for supply of drilling
fluids, such as cooling and cleaning fluids, thereto.
[0010] Preferably, the first passage opening in the bottom portion of the cutter bit body
is located in a recess defined by a plurality of cutting means to readily allow transfer
of cuttings and fluids from the recess to the second zone of the hole.
[0011] In a particularly advantageous embodiment of the invention at least one said nozzle
is located at a point adjacent and above the uppermost point of the path of rotation
of said cutting means, said nozzle having a trajectory the same as said return passage.
In one arrangement a second passage and nozzle communicates a filling fluid supply
for the cutter bit with the first passage. Preferably, at least one said nozzle is
located at a point adjacent and above the uppermost point of the path of rotation
of said cutting means, said nozzle having a trajectory approximately tangential to
the path of rotation of said cutting means.
[0012] For a better understanding of the invention, and to show how the same may be carried
into effect, reference will now be made, by way of example, to the accompanying drawings,
in which:-
Figure 1 is a sectional view of a drilling bit made in accordance with a first embodiment
of the invention;
Figure 2 is a sectional view of a drilling bit made in accordance with a second embodiment
of the invention; and
Figure 3 is a sectional view of a drilling bit made in accordance with a third embodiment
of the invention.
Figure 4 is a sectional view of a drilling bit made in accordance with a fourth embodiment
of the invention.
Figure 5 is a sectional view of a drilling bit made in accordance with a fifth embodiment
of the invention.
[0013] As can be seen from Figure 1 of the drawings, a drilling bit 10 embodying the invention
for use in drilling operations comprises a body 10 having a top portion 11 and a bottom
portion 12, the bottom portion 12 being provided with cutting means (not shown) for
cutting a formation to which the cutter bit is exposed. Within an outer circumference
13 of the bottom portion 12 of the body 10, there is provided a first opening 14 to
a first passage 15 through the body 10 to communicate a first zone 20 of a hole located
below the bottom portion 12 of the body with a second zone 21 of the hole located
above the bottom portion 12 of the body. In this way, cuttings and fluids located
below the bottom portion of the cutter bit can be transferred from the first zone
20 to the second zone 21.
[0014] The drilling bit body 10 above described could be a three cone drilling bit familiar
to the drilling industry with the additional provision of the first passage 15. The
body 10 is connected to the rest of a drillstring run into the hole by a connecting
thread portion 16 provided on the top portion 11 of the body 10. However, other connecting
means may also be used.
[0015] The body 10 is constructed of a suitable durable material such as steel and the cutting
means is comprised, for example, of three rotatable conical cutting elements which
are rotatably secured by bearings on pins 30 located on leg members 31 of the drilling
bit 1, two of which are shown in Figure 1. Though not necessary for the practice of
the invention, the cutting elements may be fabricated from a hard material such as
steel or tungsten carbide and be provided with teeth of the same material to provide
a cutting action. The cutting elements are rotatable in response to the revolution
of the drillstring and lubricated by oil or grease supplied through port 46, one of
which is shown in each of Figures 1 to 4.
[0016] It may also be readily seen from Figure 1 that a recess 26 is definable by the cutter
elements. During use of the drilling bit 1, cuttings accumulate therein, in the absence
of the first passage 15, reducing both the hole cleaning and cutting efficiency of
the drilling bit 1. It will also be apparent that if the first passage 15 is not present,
the drilling bit 1 will be an almost solid structure acting as a piston with little
pressure relief and increasing the problems of surge and swab. These problems are
alleviated to an appreciable extent by provision of the first passage 15. It is also
desirable, for the purposes of avoiding plugging of the passage 15 with cuttings,
to coat the passage 15 with a non-stick material such as Teflon (Registered Trade
Mark).
[0017] The trajectory of the passage 15 may also be a matter of some importance in practice.
The opening 24 through which cuttings and fluids exit the first passage 15 and enter
the second zone 21 may be either parallel or perpendicular to a central axis 23 of
the central bore 25 of the drilling bit 1. However, it will be appreciated that if
the first passage 15 and its opening 24 to the second zone 21 are perpendicular to
the central axis 23, erosion of the hole walls may occur, where jetting of drilling
fluids is conducted in accordance with the embodiment described with reference to
Figure 3. This would be undesirable.
[0018] However, the trajectory of the first passage 15 is not critical to the drilling bit
in its broadest aspect and it is therefore to be understood that the first passage
15 may be oriented at any angle in the range 0° to 90° to the central axis 23, i.e.
not have its axis perpendicular to the central axis of the body 10. In the embodiments
shown, the passage opening 24 is parallel to the central axis 23.
[0019] The first passage 15 is separated by wall 27 from the central bore 25 through which
drilling fluids travel via conduit 36 and nozzle 37 to a location adjacent the cutting
elements.
[0020] In the embodiment shown, only one such conduit and nozzle arrangement is shown. However,
in a conventional three cone bit it will be understood that there are present three
such arrangements. In this way drilling fluids are jetted at high velocity to the
cutting face where they assist with cutting operations by cooling and cleaning of
the drilling bit 1.
[0021] Additionally, it will be seen that, in contrast to the situation where the first
passage 15 is absent, the flow of drilling fluids passes through the recess 26 and
into the first passage 15 thereby enhancing cuttings removal and hole cleaning. In
addition, the restricted flow area of the conventional drilling bit has been increased
by the flow area of the first passage 15 thereby increasing pressure relief and allowing
a reduction in surge and swab pressures on running into the hole or pulling from the
hole of the drilling bit and drillstring.
[0022] Figure 2 shows a further embodiment of the invention in which the flow area for communication
between the first zone 20 and the second zone 21 of the hole is increased still further
by the provision of a plurality of openings, two of which openings 24 and 24a are
shown. However, any desired number of openings can be employed. Opening 24a communicates
with first passage 15 through a further passage 33. This arrangement, by increasing
the flow area and improving the distribution of drilling fluid flow into the annulus
between the drilling bit body 10 and the hole walls, gives additional assistance in
relieving the surge and swab pressure problems. The further passage 33 may likewise
be coated with Teflon to improve flow properties and reduce the risk of plugging with
cuttings. There is no requirement that openings 24 and 24a be at the same level of
the drilling bit body 10 or at the same trajectory as each other, though this may
be found convenient for the purposes of manufacture and uniform flow distribution.
[0023] Figure 3 shows a further embodiment of the invention in which the flow of cuttings
through first passage 15 is enhanced by jetting of drilling fluids upward through
the first passage 15 to create a venturi effect that further assists in cuttings removal
from the first zone 20. In this embodiment, the conduit 36 communicates through conduit
41 and nozzle 42 with the first passage 15 thereby ensuring flow of drilling fluids
into the first passage. Control over jetting velocity can be obtained by suitable
sizing of the conduit 41 and nozzle 42. The trajectory of the jet is preferably angularly
upward and in the embodiment shown is at 75° to the central axis 23 of the central
bore 25 of the drilling bit 1. Although in the embodiment described only one such
jet has been provided there could be provided a plurality of such jets to further
enhance cuttings removal and hole cleaning.
[0024] It is of some importance in this embodiment that the first passage 15 be designed
to avoid erosion damage caused by impingement of high velocity drilling fluids on
the walls 15a of the passage. With this end in view, hard facing of a portion of the
first passage 15 may be required.
[0025] Figure 4 shows a still further embodiment of the invention which is identical in
many respects to that of Figure 3 described above. However, in this embodiment, the
nozzle 37 is absent with conduit 36 being blanked off by blank 47 at the position
previously occupied by nozzle 37. Therefore, a jet of higher pressure through conduit
41 and nozzle 42 can be achieved. This facilitates removal of cuttings through the
first passage 15 to the surface of the hole.
[0026] Figure 5 shows a still further embodiment in which conduit 36 extends downwardly
a sufficient distance that the nozzle 42 is located to cause a jet of drilling fluid
above and adjacent, preferably immediately adjacent, the uppermost point, A, of the
path of rotation, B, of each cutter element (not shown). The jet is directed along
the trajectory of the first passage 15 to obtain the above described advantages.
[0027] There are also additional advantages to the arrangement shown in Figure 5. Firstly,
by extending the nozzles of the bit closer to the bottom of the hole and orientating
the jets across the recess 26, jetting of the drilling fluid achieves a valuable cleaning
effect which assists in the alleviation of balling-up or accumulation of cuttings
between the cone teeth or inserts of the cutter elements.
[0028] Secondly, and importantly the location of nozzle 42 is in close proximity to a cutting
face to which the drilling bit is exposed. As the jet of drilling fluid is directed
along passage 15 or approximately tangential to the path of rotation, A, a venturi
effect is obtained, creating a suction pressure at the cutting face which greatly
assists hole cleaning.
[0029] Using one, two or three such jets at the above described position and orientation
will create a reduced bottom hole pressure under the bit. This jetting action produces
a venturi effect under the bit such that the reduced bottom hole pressures allow formation
of an artificial drilling break.
[0030] Lower pressures at the bottom of the hole are desirable in that hole pore pressures
and bottom hole pressure become equalised which is desirable at the bit tooth and
rock contact. Consequently, the "chip hold down" which is always greater when drilling
with heavier mud weights can also be reduced allowing for an equally substantial increase
in the rate of penetration.
[0031] It is to be understood that the invention is in no way limited by the foregoing description
and different means of effecting the invention may be apparent to those skilled in
the art who have read the above description. For example, the invention is not limited
in its application to three cone cutter bits. Such differences, however, do not depart
from the scope of the invention.
1. A drilling bit comprising:
(a) a body adapted to be connected to a tubular drill string and being rotatable about
its axis, said body having a full diameter portion and an upper portion which has
at least a circumferential segment which is positioned radially inwardly with respect
to the axis of the full diameter portion;
(b) a plurality of leg members extending downwardly from the body and defining a zone
therebetween and below the body;
(c) cutting means mounted on each leg member and extending inwardly into the zone
for cutting a formation; and
(d) a return passage extending upwardly through the body from said zone and exiting
at the upper portion opposite the circumferential segment whereby a portion at least
of the fluid delivered from the tubular drill string to said zone, i.e. to the cutting
face, flows from said zone through the return passage in the body, bypassing the full
diameter portion of the body.
2. A drilling bit as according to claim 1 wherein said return passage exits from said
body at an opening which extends in a plane substantially normal to a central axis
extending in the same direction as said tubular drill string.
3. A drilling bit as according to claim 1 wherein said return passage communicates with
at least one further passage bypassing the full diameter portion of the body such
that said portion at least of the fluid exits from said body through a plurality of
openings.
4. A drilling bit as according to claim 1 wherein said return passage exits from said
body at an opening which extends in a plane having an axis extending at an angle not
being perpendicular to a central axis of said body.
5. A drilling bit according to claim 1 wherein flow of cuttings through said return passage
is assisted by jetting drilling fluid through at least one nozzle communicating a
drilling fluid supply and the return passage, and having a trajectory the same as
the return passage.
6. A drilling bit according to claim 3 wherein flow of cuttings through at least one
said further passage is assisted by jetting drilling fluid through a nozzle communicating
a drilling fluid supply and said further passage and having a trajectory the same
as said further passage.
7. A drilling bit according to claim 5 or 6 wherein at least one said nozzle is located
at a point adjacent and above the uppermost point of the path of rotation of said
cutting means, said nozzle having a trajectory the same as said return passage.
8. A drilling bit according to claim 5 or 6 wherein at least one said nozzle is located
at a point adjacent and above the uppermost point of the path of rotation of said
cutting means, said nozzle having a trajectory approximately tangential to the path
of rotation of said cutting means.
1. Bohrmeißel, enthaltend
a) einen Korpus, der für ein Verbinden mit einem rohrförmigen Bohrgestänge geeignet
und um seine Achse drehbar ist, wobei der Korpus einen Volldurchmesserbereich und
einen oberen Bereich mit mindestens einem Umfangssegment aufweist, welches radial
einwärts in bezug auf die Achse des Volldurchmesserbereiches angeordnet ist;
b) eine Vielzahl von Beinteilen, die sich vom Korpus abwärts erstrecken und zwischen
sich und unterhalb des Korpus eine Zone definieren;
c) Schneidmittel, die an jedem Beinteil befestigt sind und sich einwärts in die Zone
erstrecken, um eine Formation zu schneiden; und
d) einen Rückführungsdurchlaß, der sich aufwärts durch den Korpus erstreckt und im
oberen Bereich gegenüber dem Umfangssegment austritt, wobei zumindest ein Teil der
von dem rohrförmigen Bohrgestänge zu der Zone, d. h. zu der Schneidfläche herbeigeführten
Flüssigkeit aus der Zone durch den Rückführungsdurchlaß in den Korpus fließt und den
Volldurchmesserbereich des Korpus umgeht.
2. Bohrmeißel nach Anspruch 1, wobei der Rückführungsdurchlaß über eine Öffnung aus dem
Korpus austritt, die sich in einer Ebene im wesentlichen senkrecht zu einer zentralen
Achse erstreckt, welche in gleicher Richtung wie das rohrförmige Bohrgestänge verläuft.
3. Bohrmeißel nach Anspruch 1, wobei der Rückführungsdurchlaß mit mindestens einem weiteren
den Volldurchmesserbereich des Korpus umgehenden Durchlaß kommuniziert, so daß mindestens
der Teil der Flüssigkeit aus dem Korpus durch eine Vielzahl von Öffnungen austritt.
4. Bohrmeißel nach Anspruch 1, wobei der Rückführungsdurchlaß über eine Öffnung aus dem
Korpus austritt, die sich in einer Ebene mit sich unter einem nicht rechtwinkligen
Winkel zu einer zentralen Achse des Korpus verlaufenden Achse erstreckt.
5. Bohrmeißel nach Anspruch 1, wobei der Fluß an Bohrmehl durch den Rückführungsdurchlaß
mittels Ausspritzen von Bohrflüssigkeit aus mindestens einer Düse unterstützt wird,
die mit einer Bohrflüssigkeitszuführung und dem Rückführungsdurchlaß kommuniziert
und eine gleiche Trajektorie wie der Rückführungsdurchlaß aufweist.
6. Bohrmeißel nach Anspruch 3, wobei der Fluß an Bohrmehl durch mindestens einen weiteren
Durchlaß mittels Ausspritzen von Bohrflüssigkeit aus einer mit einer Bohrflüssigkeitszuführung
kommunizierenden Düse unterstützt wird und der weitere Durchlaß die gleiche Trajektorie
wie der Rückführungsdurchlaß aufweist.
7. Bohrmeißel nach Anspruch 5 oder 6, wobei mindestens eine der Düsen an einem Punkt
benachbart und oberhalb des höchsten Punktes des Rotationsweges der Schneidmittel
angeordnet ist und die Düse die gleiche Trajektorie wie der Rückführungsdurchlaß aufweist.
8. Bohrmeißel nach Anspruch 5 oder 6, wobei mindestens eine der Düsen an einem Punkt
benachbart und oberhalb des höchsten Punktes des Rotationsweges der Schneidmittel
angeordnet ist und die Düse eine annähernd tangentiale Trajektorie zum Rotationsweg
der Schneidmittel aufweist.
1. Trépan comprenant :
a)un corps apte à être raccordé à une colonne de forage tubulaire et pivotant autour
de son axe, ledit corps présentant une portion de diamètre plein et une portion supérieure
comportant au moins un segment circonférentiel qui est positionné radialement vers
l'intérieur par rapport à l'axe de la portion de diamètre plein ;
b)une pluralité de bras s'étendant vers le bas à partir du corps et définissant, entre
eux et sous le corps, une zone ;
c) des moyens de coupe montés sur chaque bras et s'étendant vers l'intérieur, dans
la zone, pour couper une formation ; et
d)un passage de retour traversant le corps vers le haut depuis ladite zone et débouchant
au niveau de la portion supérieure à l'opposé du segment circonférentiel, une partie
au moins de la boue délivrée depuis la colonne de forage tubulaire vers ladite zone,
c'est-à-dire la face de coupe, s'écoulant depuis ladite zone à travers le passage
de retour ménagé dans le corps, en dérivation avec la portion de diamètre plein du
corps.
2. Trépan selon la revendication 1, caractérisé en ce que ledit passage de retour débouche
dudit corps au niveau d'un orifice qui s'étend dans un plan sensiblement normal à
un axe central parallèle à ladite colonne de forage tubulaire.
3. Trépan selon la revendication 1, caractérisé en ce que ledit passage de retour communique
avec au moins un autre passage en dérivation avec la portion de diamètre plein du
corps, de telle sorte que cette partie au moins du fluide ressort dudit corps par
une pluralité d'orifices.
4. Trépan selon la revendication 1, caractérisé en ce que ledit passage de retour débouche
dudit corps au niveau d'un orifice qui s'étend dans un plan dont un axe forme un angle
non perpendiculaire avec un axe central dudit corps
5. Trépan selon la revendication 1, caractérisé en ce que l'écoulement de déblais à travers
ledit passage de retour est assisté par l'injection de boue de forage via au moins
une buse qui communique avec une source de boue de forage et le passage de retour
et dont la trajectoire est identique à celle du passage de retour.
6. Trépan selon la revendication 3, caractérisé en ce que l'écoulement de déblais à travers
le ou lesdits autres passages est assisté par l'injection de boue de forage via une
buse qui communique avec une source de boue de forage et ledit autre passage de retour
et dont la trajectoire est identique à celle dudit autre passage.
7. Trépan selon la revendication 5 ou 6, caractérisé en ce que la ou lesdites buses sont
situées à proximité et au-dessus du sommet de la trajectoire de rotation desdits moyens
de coupe, la ou lesdites buses ayant une trajectoire identique à celle dudit passage
de retour.
8. Trépan selon la revendication 5 ou 6, caractérisé en ce que ladite ou lesdites buses
sont situées à proximité et au-dessus du sommet de la trajectoire de rotation desdits
moyens de coupe, ladite buse ayant une trajectoire sensiblement tangentielle à la
trajectoire de rotation desdits moyens de coupe.