[0001] The object of the invention is a drilling tool for maintaining a borehole and for
cutting rock material.
[0002] Obtaining hydrocarbons by means of directional holes consists of a series of complex
operations. The first of them is to drill a hole. This phase is followed by geophysical
research on geometry condition of the raw borehole. Then, casing pipes are introduced
into the borehole, which ensure stability and sealing of the borehole. Because of
the forces inside the hole, present under the ground, and diversity of drilled rocks,
the borehole begins to change its geometry immediately after the withdrawal of the
drill. Therefore, there is a risk of capturing the casing pipes by rock layers tightening
around and reducing the diameter of the hole. In addition, a swelling packet clay
material is deposited on the surface of the casing pipes and prevents conducting a
proper cementing operation. To prevent such a scenario, a number of methods are used:
- forcing a reciprocating movement and/or rotational movement of the cemented casing
string,
- selection of optimal parameters of fluid,
- use of leading, buffering and washing fluids,
- use of packers,
- use of mud cake scrapers and centralisers,
- tools such as guide-shoe, reamer-shoe.
[0003] From the point of view of the invention, the latter are important. These tools are
placed at the beginning of a casing string and have a drillable, substantially conical
nose and abrasive elements which are made of materials highly resistant to abrasion
processes, for example sintered carbides. Usually, they have, in their lower part,
openings to allow proper execution of cementing and to ensure a steady flow of drilling
fluid. The tool is intended to cut or abrade the rock material from the walls of the
hole in places where the hole has a diameter smaller than the designed one. After
introducing the pipes together with the tool and cementing the space between the hole
wall and the casing string, a nose cone of the tool is drilled in order to allow subsequent
steps of the hole exploration. These tools are produced by international concerns,
such as Weatherford, Downhole Products or Halliburton.
[0004] From British patent specification no.
GB 2482703, a tool in a form of a bit for maintaining or expanding a borehole is known. This
tool has a form of a hollow pipe which is placed in the borehole in which this tool
is moved along this hole. The tool further comprises means constituting blades and
openings which are connected to the interior of the tool in the form of a pipe and
are located axially in the front of the blade. The removed material can be directed
to the interior of the pipe, and the openings can have a form of slots and have an
edge which constitutes a blade.
[0005] US 5 199 511 A discloses a drill bit and method in which polycrystalline diamond cutters mounted
on a bit crown cut formation chips akin to the manner in which a grater cuts cheese.
Chips in impermeable or plastic formations are extruded by the cutters into cavities
internal to the bit via slots adjacent each cutter. Drilling fluid circulates internally
of the bit from the drill string and into the annulus above that portion of the bit
bearing cutters. In one embodiment, the portion of the bit body upon which the crown
is formed is made of an elastomer which is pressurized into sealing engagement with
the bottom of the borehole thereby further sealing freshly cut formation from drilling
fluid.
[0006] US 6 527 065 B1 discloses cutting elements for use in a rotary drill bit, that are configured to
facilitate positioning of the cutting elements at a positive rake angle with respect
to the formation to enhance compressive stresses in the cutting element and to reduce
cutting loads on the cutting elements. The cutting element generally comprises a three-dimensional
superabrasive cutting member having a leading edge and a three-dimensional arcuate
scoop-like surface which conveys formation cuttings away from the cutting element.
The cutting element may also be formed to a substrate or backing. A drill bit suitable
for use of the cutting elements is also disclosed which includes passageways and internal
fluid passages for enhancing the conveyance of formation cuttings away from the leading
edge of the cutting element.
[0007] US 2002189863 A1 discloses a drill bit for drilling casing in a well bore. The drill bit is constructed
from a combination of relatively soft and relatively hard materials. The proportions
of the materials are selected such that the drill bit provides suitable cutting and
boring of the well bore while being able to be drilled through by a subsequent drill
bit. Methods of applying hard materials to a soft material body are provided.
[0008] The stability of the borehole is affected by parameters such as:
- weight of the drilling fluid,
- ECD (Equivalent Circulating Density) during the circulation of the hole,
- salinisation of the drilling fluid, and stabilisers of swelling clays,
- pH of the drilling fluid,
- hydrodynamic and dynamic effect of the nozzles of the drill bit and underreamer,
- presence of swelling clays.
[0009] In the drilling technology, there is a phenomenon of stability changes (swelling
of smectite/illite clays) of the hole as a function of time. This translates into
the quality of the cemented sections of the piping. The situation requires solving
encountered problems by means of new techniques and technologies. One of the risks,
to which too little attention has been paid so far, is the phenomenon of directional
expansion of swelling clays.
[0010] In the course of exploration and development activities, openings drill through different
types of rock with varying physical and chemical properties. Argillaceous rocks (mudstones,
claystones, shales) composed of different kinds of clay minerals are among the most
frequent rocks. The percentage of mixed packet minerals and illites increases with
depth, usually gradually, and the amount of smectites decreases. The Silurian, Ordovician
and Cambrian deposits are dominated by illites. Also mixed packet minerals, often
containing smectites. Their main structural unit is a film comprising two inwardly
facing tetrahedral plates with a central octahedral plate containing aluminum. The
layers may extend in two directions but bonds between the films are weak and have
a perfect cleavage allowing water and other molecules to be absorbed between the films,
resulting in directional expansion. Based on existing information, the occurrence
of swelling clays in the Ordovician, Silurian, Devonian, Carboniferous and Jurassic
profiles was found. In many situations, the borehole is relatively stable, i.e. its
dimensions remain substantially unchanged for several hours. However, this is largely
dependent on geological conditions. The main obstacle during drilling and cementing
processes are geological conditions prevailing in the holes. One of the main problems
is related to the swelling of clay formations, as indicated above. This leads to narrowing
of the hole clearance, and consequently to its occlusion.
[0011] The main problem with devices enlarging the hole diameter used so far in the oil
drilling industry, is cutting the excavated rock material. Attempts to completely
wash it out prove to be ineffective, and additionally lead to escalating changes in
geometry of the hole.
[0012] The rock material, exhibiting a high viscosity, is deposited on the surface of the
pipes, thereby preventing correct bonding of cement. Accumulation thereof leads to
formation of local blockages, which causes formation of channels in the introduced
cement paste.
[0013] The aim of the invention is to develop a drilling tool without the disadvantages
of known tools.
[0014] The invention is defined by the appended claims.
[0015] According to the invention, a drilling tool for maintaining a borehole and for cutting
rock material, comprises a hollow elongated body in the form of a pipe, the body having
a longitudinal axis and being provided with a plurality of cutting blades arranged
around the body in such a way that they protrude from the external surface of the
body, the drilling tool having an upper end,
wherein the cutting blades are grouped into sets arranged on the periphery of the
body,
- wherein in each set, the cutting blades are shaped as bands, the ends of which are
connected to the body, and the central parts of the cutting blades between the ends
protrude from the body, and in each set the cutting blades are placed one upward of
the other and are angularly offset relative to each other,
- wherein in each set, each cutting blade in the set is spaced from the axis of the
body of the drilling tool by a dimension larger than the dimension of the distance
from the axis of the body of the cutting blade located directly downward of it,
- wherein the body is provided with slots connecting the interior of the body to its
external surface and arranged radially under the cutting blades, and not connected
to the cutting blades, and, in use, drilling fluid flows through the interior of the
body,
- wherein in each set, the bands of the cutting blades form, in their central part,
a lateral channel extending in parallel to the longitudinal axis substantially on
the external surface of the body and under the bands of the cutting blades, and, in
use, the drilling fluid along with cut rock material flows through the lateral channel,
- and wherein, in use, a zone of lower pressure under the cutting blades in lateral
channels is obtained, allowing suction of the cut rock material, and then its fragmentation
through transverse flow of the drilling fluid.
[0016] Preferably, the cutting blades are grouped into two levels of arranged on the periphery
of the body, and arranged one upward of the other and offset from each other by an
angle of 0
0 to 45
0.
[0017] Preferably, each set on one level comprises four cutting blades, wherein the sets
of cutting blades are arranged on the periphery of the drilling tool every 90
0.
[0018] Also preferably, each set on one level comprises six cutting blades, wherein six
sets of cutting blades on one level are arranged symmetrically on the periphery of
the drilling tool.
[0019] Also preferably, the cutting blades in each set are offset from the cutting blades
located directly under it by an angle of 5
0 to 25
0.
[0020] Also preferably, the upper end of the drilling tool is provided with a thread for
connecting the drilling tool to casing pipes.
[0021] Also preferably, the drilling tool ends in a base made of a cuttable material.
[0022] Also preferably, directional channels are made in the base for optimal flow of the
drilling mud.
[0023] Also preferably, inlet openings are made in the base for the flow of the drilling
mud.
[0024] The object of the invention is presented in embodiments in the drawing, in which:
- Fig. 1 shows a drilling tool in a side view,
- Fig. 2 shows a drilling tool in a partial cross-section,
- Fig. 3 shows a drilling tool in its frontal view,
- Fig. 4 shows a drilling tool in a side view of a portion showing the cutting blades,
- Fig. 5 shows the flow of drilling fluid and excavated material during the operation
of a drilling tool,
- Fig. 6 shows a schematic diagram of a drilling tool operating as an ejector,
- Fig. 7 shows computer simulations of drilling fluid flowing through a drilling tool.
[0025] As shown in an embodiment of the invention in Fig. 1, Fig. 2 and in Fig. 4 of the
drawing, a drilling tool 1 for maintaining a borehole and for cutting rock material
comprises an elongated body 2 in a form of a pipe. The external surface of the body
2 of the drilling tool 1 is provided with a series of cutting blades 3 arranged around
the body 2 in such a way that the cutting blades 3 protrude from the external surface
of the body 2.
[0026] The cutting blades 3 are shaped as bands 4 connected to the body 2 of the drilling
tool 1 in such a way that the ends of the bands 4 are connected to the body 2, and
in the central part between the ends of the bands 4 they protrude from the body 2
so that they are at a larger distance from the axis of the drilling tool 1 than the
external surface of the drilling tool 1.
[0027] The cutting blades 3 are grouped into sets 5 of cutting blades 3 so that in each
set 5, the cutting blades 3 are placed one upward of the other, and the sets 5 can
be angularly offset relative to each other. This angular offset of the cutting blades
3 can vary within a range of 0
0 to 45
0, wherein the offset value depends on many factors, such as, for example, size of
the drilling tool 1 generally meant as its diameter, type of rock material in which
the borehole is drilled, depth of the borehole, and many others. In an embodiment
of the invention shown in Fig. 1, this offset does not occur, i.e. it equals zero.
[0028] Each cutting blade 3 in the set 5 is spaced from the axis of the body 2 of the drilling
tool 1 by a dimension larger than the dimension of the distance from the axis of the
body 2 of the cutting blade 3 located directly downward of it. Such a solution causes
that the cutting blade 3 located upward, collects a further layer of rock material
the cutting blade 3 located downward was unable to collect.
[0029] In the body 2 of the drilling tool 1, elongated slots 6 are made, extending radially
relative to the body 2, connecting the interior of the body 2 of the drilling tool
1 to its external surface. The slots are not connected to the cutting blades 3 but,
as shown in Fig. 5, they are located under the bands 4 of the cutting blades 3.
[0030] The bands 4 of the cutting blades 3, in their central part extending between the
ends connecting the bands 4 to the body 2 of the drilling tool 1, form, in each set
5 of the cutting blades 3, a lateral channel 11 extending in parallel to the axis
of the drilling tool 1 substantially on the external surface of the body 2 and under
the bands 4 of the cutting blades 3.
[0031] The cutting blades 3 on the body 2 of the drilling tool 1 are configured so that
their operation causes fragmentation and discharging the cut rock material towards
the heel of the borehole.
[0032] In the preferred embodiment of the invention, shown in Fig. 1, Fig. 2, Fig. 3 and
in Fig. 4, the cutting blades 3 are grouped into sets 5 arranged on the periphery
of the body 2 of the drilling tool 1 and placed one upward of the other, wherein in
each set, there are six cutting blades 3, and and on one level around the body 2 of
the drilling tool 1, six sets 5 of the cutting blades 3 are arranged. The sets 5 of
the cutting blades 3 are therefore arranged every 60
0. Of course, in other embodiments, the number of sets 5 of the cutting blades 3 both
horizontally and on the periphery of the body 2 of the drilling tool 1, depending
on the destination, can vary.
[0033] Also, the angular offset of the cutting blades 3 in the set 5 in relation to the
cutting blades 3 located directly downward of them can vary and amount 5
0 to 25
0, wherein in the embodiment shown in Fig. 1, it amounts to 6
0.
[0034] In order to connect to a set of pipes used to maintain the borehole, the drilling
tool 1 is provided with a thread 7 at its upper end. In an embodiment shown in Fig.
2, the thread 7 is an internal thread but it is obvious that in other embodiments
the thread may be formed outside the drilling tool 1.
[0035] The drilling tool 1 ends in a base 8 made of a cuttable material. In the base 8,
directional channels 9 are made for optimal flow of the drilling fluid. The base 8
also has inlet openings 10 for the drilling fluid. After completion of its task, the
base 8 of the drilling tool 1 may be drilled.
[0036] The principle of operation of the drilling tool 1, according to the invention, is
based on a solution innovative on a global scale, which allows cutting the rock material,
and then fragmentising it and discharging it onto the surface out of the borehole.
The very idea of operation can be compared to the calibrator known from the engineering
industry, which, however, uses the principle of operation of the ejector for removing
the cut material from the cutting zone. It is this innovation that provides the developed
tool with significant advantages over analogous structures.
[0037] Fig. 6 schematically shows the principle of operation of the ejector, relating to
the drilling tool, according to the invention. In Fig. 6, it can be seen that in the
negative pressure zone, formed in the narrowing of the space into which a fluid, in
this case a drilling fluid, is forced, the sucked rock material, cut by the cutting
blades 3 of the drilling tool 1, is captured and accelerated.
[0038] This phenomenon is shown in more detail in Fig. 5 in relation to the drilling tool
1 according to this embodiment. The slots 6 connecting the interior of the body 2
of the drilling tool 1 to its external surface correspond to the negative pressure
zone of Fig. 6. Directly upward the slots 6 the bands 4 of the cutting blades 3 are
arranged, thereby forming, in each set 5 of the cutting blades 3, lateral channels
11 in which the rock material cut by the cutting blades 3 in the resulting borehole
is accelerated. This capturing and accelerating of the rock material leads to its
further fragmentising at the edges of the cutting blades 3 and preventing formation
of deposits on the casing pipes which could disturb the process of their cementing.
[0039] The proposed solution allows the use of high velocity gradients in the vicinity of
the cutting blade 3 for precise fragmentation of the cut material and discharging
it up the hole along with the drilling fluid. Appropriate fragmentation of the cut
material is essential as it prevents formation of so-called mud cakes. This translates
into proper cementing of the hole and into environmental safety and return on investment.
It is worth noting that the drilling tool 1, according to the invention, does not
have any moving parts, which contributes to its reliability.
[0040] In relation to the drilling tool 1, according to the invention, computer simulations
with the use of CFD (Ansys Fluent) tool were conducted, which showed that the flow
of the drilling mud in appropriately profiled openings and channels inside the cutting
blades 3 induces the occurrence of pressure anomalies, as illustrated in Fig. 7. A
special form of the so-called hydrodynamic paradox was used herein. Thereby, a zone
of lower pressure under the cutting blades 3 in lateral channels 11 was obtained,
allowing suction of the cut rock material, and then its fragmentation through transverse
flow of the drilling fluid.
1. A drilling tool (1) for maintaining a borehole and for cutting rock material, comprising
a hollow elongated body (2) in the form of a pipe, the body (2) having a longitudinal
axis and being provided with a plurality of cutting blades (3) arranged around the
body (2) in such a way that they protrude from the external surface of the body (2),
the drilling tool (1) having an upper end,
wherein the cutting blades (3) are grouped into sets (5) arranged on the periphery
of the body,
- wherein in each set (5), the cutting blades (3) are shaped as bands (4), the ends
of which are connected to the body (2), and the central parts of the cutting blades
(3) between the ends protrude from the body (2), and in each set (5) the cutting blades
(3) are placed one upward of the other and are angularly offset relative to each other,
- wherein in each set (5), each cutting blade (3) in the set (5) is spaced from the
axis of the body (2) of the drilling tool (1) by a dimension larger than the dimension
of the distance from the axis of the body (2) of the cutting blade (3) located directly
downward of it,
- wherein the body (2) is provided with slots (6) connecting the interior of the body
(2) to its external surface and arranged radially under the cutting blades (3), and
not connected to the cutting blades (3), and, in use, drilling fluid flows through
the interior of the body (2),
- wherein in each set (5), the bands (4) of the cutting blades (3) form, in their
central part, a lateral channel (11) extending in parallel to the longitudinal axis
substantially on the external surface of the body (2) and under the bands (4) of the
cutting blades (3), and, in use, the drilling fluid along with cut rock material flows
through the lateral channel (11),
- and wherein, in use, a zone of lower pressure under the cutting blades (3) in lateral
channels (11) is obtained, allowing suction of the cut rock material, and then its
fragmentation through transverse flow of the drilling fluid.
2. The drilling tool, according to claim 1, wherein the cutting blades (3) are grouped into two levels of sets (5) arranged on the periphery
of the body (2), and arranged one upward of the other and offset relative to each
other by an angle of 0° to 45°.
3. The drilling tool, according to claim 1, wherein each set (5) on one level comprises four cutting blades (3), wherein the sets (5)
of the cutting blades (3) are arranged on the periphery of the drilling tool (1) every
90°.
4. The drilling tool, according to claim 1, wherein each set (5) on one level comprises six cutting blades (3), wherein six sets (5)
of the cutting blades (3) on one level are arranged symmetrically on the periphery
of the drilling tool (1).
5. The drilling tool, according to claim 1, wherein the cutting blades (3) in the set (5) are offset relative to the cutting blades (3)
located directly under them by an angle of 5° to 25°.
6. The drilling tool, according to claim 1, wherein the upper end of the drilling tool (1) is provided with a thread (7) for connecting
the drilling tool (1) to casing pipes.
7. The drilling tool, according to claim 1, wherein the drilling tool ends in a base (8) made of a cuttable material.
8. The drilling tool, according to claim 7, wherein directional channels (9) are made in the base (8)for optimal flow of the drilling
fluid.
9. The drilling tool, according to claim 7, wherein inlet openings (10) are made in the base (8) for the flow of the drilling fluid.
1. Ein Bohrwerkzeug (1) zur Herstellung von Bohrungen und zum Abtragen vom Gestein, das
aus einem hohlen, länglichen Körper (2) in Form eines Rohrs besteht, wobei der Körper
(2) eine Längsachse aufweist und mit einer Vielzahl von Schneide (3) versehen ist,
die so rund um den Körper (2) angeordnet sind, dass sie von der Außenfläche des Körpers
(2) abstehen, wobei das Bohrwerkzeug (1) ein oberes Ende aufweist,
wobei die Schneide (3) in Form von Streifen (5) an der Begrenzungsfläche des Körpers
angeordnet sind,
- wobei in jedem Streifen (5) die Schneide (3) in Form von Bändern (4) herausgebildet
sind, deren Enden mit dem Körper (2) verbunden sind, und die mittleren Bereiche der
Schneide (3) zwischen den Enden von dem Körper (2) abstehen und in jedem Streifen
(5) die Schneide (3) übereinander angeordnet und um einen Winkel zueinander versetzt
sind,
- wobei in jedem Streifen (5) jeder Schneide (3) im Streifen (5) von der Achse des
Körpers (2) des Bohrwerkzeugs (1) um ein Maß entfernt ist, das größer ist als das
Maß der Entfernung von der Achse des Körpers (2) des Schneides (3), der sich direkt
unterhalb davon befindet,
- wobei der Körper (2) mit Schlitzen (6) versehen ist, die den Innenraum des Körpers
(2) mit dessen Außenfläche verbinden und radial unter den Schneide (3) angeordnet
und mit den Schneide (3) nicht verbunden sind, wobei im Betrieb der Vorrichtung die
Bohrflüssigkeit durch den Innenraum des Körpers (2) fließt,
- wobei die Bänder (4) der Schneide (3) in jedem Streifen (5) in dem zentralen Bereich
einen seitlichen Kanal (11) herausbilden, der parallel zur Längsachse an der Außenfläche
des Körpers (2) und unter den Bändern (4) der Schneide (3) verläuft und im Betrieb
die Bohrflüssigkeit zusammen mit dem abgetragenen Gestein durch den seitlichen Kanal
(11) befördert werden,
- und wobei im Betrieb eine Zone mit einem geringeren Druck unter den Meißeln (3)
in seitlichen Kanälen (11) entsteht, womit das abgebaute Gestein eingesaugt und anschließend
durch den Querstrom der Bohrflüssigkeit zerkleinert wird.
2. Ein Bohrwerkzeug nach Anspruch 1, wobei die Schneide (3) in zwei Ebenen von Streifen (5) an der Begrenzungsfläche des Körpers
(2) angeordnet sind und übereinander und um einen Winkel von 0° bis 45° zueinander
versetzt angeordnet sind.
3. Ein Bohrwerkzeug nach Anspruch 1, wobei jeder Streifen (5) auf einer Ebene vier Schneide (3) umfasst, wobei die Streifen
(5) der Schneide (3) an der Begrenzungsfläche des Bohrwerkzeugs (1) je 90° angeordnet
sind.
4. Ein Bohrwerkzeug nach Anspruch 1, wobei jeder Streifen (5) auf einer Ebene sechs Schneide (3) umfasst, wobei sechs Streifen
(5) der Schneide (3) auf einer Ebene symmetrisch an der Begrenzungsfläche des Bohrwerkzeugs
(1) angeordnet sind.
5. Ein Bohrwerkzeug nach Anspruch 1, wobei die Schneide (3) im Streifen (5) gegenüber den direkt unter ihnen liegenden Schneide
(3) um einen Winkel von 5° bis 25° versetzt sind.
6. Ein Bohrwerkzeug nach Anspruch 1, wobei das obere Ende des Bohrwerkzeugs (1) mit einem Gewinde (7) zum Anschluss des Bohrwerkzeugs
(1) an die Bohrrohre versehen ist.
7. Ein Bohrwerkzeug nach Anspruch 1, wobei das Bohrwerkzeug mit einer Sockel (8) endet, die aus einem schneidfähigen Material
besteht.
8. Ein Bohrwerkzeug nach Anspruch 7, wobei die Fließkanäle (9) an der Sockel (8) für eine optimale Führung der Bohrflüssigkeit
vorgesehen sind.
9. Ein Bohrwerkzeug nach Anspruch 7, wobei an der Sockel (8) Einlassöffnungen (10) für die Führung der Bohrflüssigkeit vorgesehen
sind.
1. Outil de forage (1) pour maintenir un trou de forage et pour couper des matériaux
rocheux, comprenant un corps allongé creux (2) sous la forme d'un tuyau, le corps
(2) ayant un axe longitudinal et étant pourvu d'une pluralité de lames coupantes (3)
disposés autour du corps (2) de telle sorte qu'ils dépassent de la surface externe
du corps (2), l'outil de forage (1) ayant une extrémité supérieure,
dans lequel les lames coupantes (3) sont regroupées en ensembles (5) disposés sur
la périphérie du corps,
- dans lequel dans chaque ensemble (5), les lames coupantes (3) sont en forme de bandes
(4), dont les extrémités sont reliées au corps (2), et les parties centrales des lames
coupantes (3) entre les extrémités font saillie du corps (2), et dans chaque jeu (5)
les lames coupantes (3) sont placées l'une vers le haut l'une de l'autre et sont décalées
angulairement les unes par rapport aux autres,
- dans lequel dans chaque ensemble (5), chaque lame coupante (3) dans l'ensemble (5)
est espacée de l'axe du corps (2) de l'outil de forage (1) d'une dimension plus grande
que la dimension de la distance de la l'axe du corps (2) de la lame coupante (3) situé
directement en bas de celle-ci,
- dans lequel le corps (2) est pourvu de fentes (6) reliant l'intérieur du corps (2)
à sa surface externe et disposées radialement sous les lames coupantes (3), et non
reliées aux lames coupantes (3), et, en service, le fluide de forage s'écoule à l'intérieur
du corps (2),
- dans lequel dans chaque ensemble (5), les bandes (4) des lames coupantes (3) forment,
dans leur partie centrale, un canal latéral (11) s'étendant parallèlement à l'axe
longitudinal sensiblement sur la surface externe du corps (2) et sous les bandes (4)
des lames coupantes (3), et, en cours d'utilisation, le fluide de forage avec la matière
rocheuse coupée s'écoule à travers le canal latéral (11),
- et dans lequel, en utilisation, une zone de pression inférieure sous les lames coupantes
(3) dans les canaux latéraux (11) est obtenue, permettant l'aspiration de la matière
rocheuse coupée, puis sa fragmentation par écoulement transversal du fluide de forage.
2. Outil de forage selon la revendication 1, dans lequel les lames coupantes (3) sont regroupées en deux niveaux d'ensembles (5) disposés
sur la périphérie du corps (2), et disposés l'un au dessus de l'autre et décalés l'un
par rapport à l'autre par un angle de 0° à 45°.
3. Outil de forage selon la revendication 1, dans lequel chaque ensemble (5) sur un niveau comprend quatre lames coupantes (3), dans lequel
les ensembles (5) des lames coupantes (3) sont disposés sur la périphérie de l'outil
de forage (1) tous les 90°.
4. Outil de forage selon la revendication 1, dans lequel chaque ensemble (5) sur un niveau comprend six lames coupantes (3), dans lequel six
ensembles (5) des lames coupantes (3) sur un niveau sont disposés symétriquement sur
la périphérie de la outil de forage (1).
5. Outil de forage selon la revendication 1, dans lequel les lames coupantes (3) dans l'ensemble (5) sont décalées par rapport aux lames coupantes
(3) situées directement sous elles d'un angle de 5° à 25°.
6. Outil de forage selon la revendication 1, dans lequel l'extrémité supérieure de l'outil de forage (1) est munie d'un filetage (7) pour
connecter l'outil de forage (1) aux tubes de tubage.
7. Outil de forage selon la revendication 1, dans lequel l'outil de forage se termine par une base (8) réalisée en un matériau découpable.
8. Outil de forage selon la revendication 7, dans lequel des canaux directionnels (9) sont réalisés dans la base (8) pour un écoulement optimal
du fluide de forage.
9. Outil de forage selon la revendication 7, dans lequel des ouvertures d'entrée (10) sont réalisées dans la base (8) pour l'écoulement du
fluide de forage.