FLUID DRILLING HEAD NOZZLE DESIGN

CONCEPTION DE BUSE DE TETE DE FORAGE A FLUIDE

English Abstract

A fluid cutting head (8) of the type having a plurality of nozzles in a rotatable nozzle assembly (9) for cutting a bore hole in rock, has nozzles being arranged to be supplied with high pressure drilling fluid, forming jets positioned to cut adjacent rock. The nozzles include one or more generally axially facing pilot nozzles (1 and 2) and one or more generally radially facing reaming nozzles (3, 4, 5 and 6), at least the pilot nozzles being characterised by a non-tapering outlet section such that the jet issuing therefrom is of substantially constant cross-section in a zone immediately adjacent the outlet section. The pilot nozzles are located in a leading part (26) of the rotatable nozzle assembly (9), having a minimised diameter, while the reaming nozzles are located in the following part (27) of the rotatable nozzle assembly (9), formed in a step-wise fashion to keep the reaming nozzles close to the rock face.

French Abstract

L'invention concerne une tête de coupe à fluide (8) du type équipé de plusieurs buses dans un ensemble de buses rotatif (9) destiné à découper un trou de forage dans une roche; ladite tête de coupe à fluide est dotée de buses qui sont disposées de manière à être alimentées par un fluide de forage à haute pression, formant des jets positionnés pour découper la roche avoisinante. Les buses comportent une ou plusieurs buses pilotes (1 et 2) se regardant généralement axialement et une ou plusieurs buses d'alésage (3, 4, 5 et 6) se regardant généralement radialement, au moins les buses pilotes se caractérisant par une section sortie non conique de sorte que le jet qui en sort est de section transversale sensiblement constant dans une zone jouxtant immédiatement la section sortie. Les buses pilotes sont situées dans une partie avant (26) de l'ensemble de buses rotatif (9), ayant un diamètre réduit, tandis que les buses d'alésage sont situées dans la partie suivante (27) de l'ensemble de buses rotatif (9), formée graduellement afin de maintenir les buses d'alésage proches de la face rocheuse. Figure 3

Claims

9
CLAIMS
Claims
1. A fluid cutting head of the type having a plurality of nozzles in a
rotatable
nozzle assembly for hydraulically cutting a bore hole in rock, said nozzles
being
arranged to be supplied with high pressure drilling fluid, forming jets
positioned to cut
adjacent rock, said nozzles including one or more generally axially facing
pilot nozzles
and one or more generally radially facing reaming nozzles, at least the pilot
nozzles
being characterised by a non-tapering outlet section such that the jet issuing
therefrom
is of substantially constant cross-section in a zone immediately adjacent the
outlet
section, and wherein the leading part of the rotatable nozzle assembly
incorporating
the pilot nozzles is of significantly lesser diameter than the following part
of the
rotatable nozzle assembly incorporating the reaming nozzles.
2. A fluid cutting head as claimed in claim 1, wherein the reaming nozzles
are
also characterised by a non-tapering outlet section such that the jet issuing
therefrom is
of substantially constantly cross-section in a zone immediately adjacent the
outlet
section.
3. A fluid cutting head as claimed in claim 2 wherein the reaming nozzles
are
orientated such that the jets issuing therefrom are angled rearwardly relative
to the
direction of travel of the cutting head.
4. A fluid cutting head as claimed in any one of the preceding claims,
wherein
the following part of the rotatable nozzle assembly is formed in a stepwise
fashion of
steps of progressively increasing diameters, there being at least one reaming
nozzle
located in each step such that the jet issuing from each reaming nozzle is
located close
to the adjacent bore hole surface.

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5. A fluid cutting head as claimed in any one of the preceding claims
wherein
one or more of the nozzles have an inlet portion of inwardly tapering section
upstream
of the non-tapering outlet section.
6. A fluid cutting head as claimed in any one of the preceding claims
wherein
the pilot nozzles have an internal diameter less than 1.0 mm.
7. A fluid cutting head as claimed in any one of the preceding claims
wherein
the reaming nozzles have an internal diameter less than 1.3 mm.
8. A fluid cutting head as claimed in claim 7 wherein the reaming nozzles
have
an internal diameter between 0.5 mm and 1.3 mm.
9. A fluid cutting head when constructed arranged and operable
substantially as
described herein with reference to the accompanying drawings.

Description

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Title of the Invention
"FLUID DRILLING HEAD NOZZLE DESIGN"
[0001] This invention relates to the design of the nozzles and rotatable
nozzle
assembly for a fluid drilling head of the type generally described in our
earlier
international patent application PCT/AU02/01550 (international publication No.
WO
03/042491 Al), the content of which is incorporated herein by way of cross
reference.
Background of the Invention
[0002] In previously known forms of fluid drilling heads, it has been
common to use
a type of nozzle known as a "horn nozzle" having a diverging outlet portion
designed to
produce a powerful cavitation cloud for the cutting or breaking of rock in the
drilling
operation. Such a device is shown in Figure 2 of this specification.
[0003] Further research by the applicants has shown that while the
cavitation cloud
generated by horn nozzles of this type is indeed powerful, it is generated at
a position
remote from the nozzle outlet. The zone between the cavitation cloud and the
nozzle
outlet is a "dead zone" which is not effective in cutting rock adjacent to the
nozzle
outlet. Accordingly, placement of such nozzles to generate smooth and self-
advancing
geometry is very difficult due to the dead zone immediately in front of the
pilot jets at
the leading edge of the fluid cutting head, and effective design of the fluid
cutting head
is also difficult due to the physical size of the horn nozzles. Prior art
devices of the type
shown in Figure 2 need to be fed slowly into the bore hole to ensure the rock
being cut
stays remote from the front of the head. If the tool gets too close to the
rock, the rock
would be in the dead zone and a "stall" would result.

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Summary of the Invention
[0004] The present invention therefore provides a fluid cutting head of the
type
having a plurality of nozzles in a rotatable nozzle assembly for cutting a
bore hole in
rock, said nozzles being arranged to be supplied with high pressure drilling
fluid,
forming jets positioned to cut adjacent rock, said nozzles including one or
more
generally axially facing pilot nozzles and one or more generally radially
facing reaming
nozzles, at least the pilot nozzles being characterised by a non-tapering
outlet section
such that the jet issuing therefrom is of substantially constant cross-section
in a zone
immediately adjacent the outlet section.
[0005] Preferably, the reaming nozzles are also characterised by a non-
tapering
outlet section such that the jet issuing therefrom is of substantially
constantly cross-
section in a zone immediately adjacent the outlet section.
[0006] Preferably, the leading part of the rotatable nozzle assembly
incorporating
the pilot nozzles is of significantly lesser diameter than the following part
of the
rotatable nozzle assembly incorporating the reaming nozzles.
[0007] Preferably, the following part of the rotatable nozzle assembly is
formed in a
stepwise fashion of steps of progressively increasing diameters, there being
one
reaming nozzle located in each step such that the jet issuing from each
reaming nozzle
is located close to the adjacent bore hole surface.
Brief Description of the Drawings
[0008] Notwithstanding any other forms that may fall within its scope, one
preferred
form of the invention will now be described by way of example only with
reference to
the accompanying drawings, in which:
[0009] Figure 1 is side view of a fluid drilling head according to the
invention;

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[0010] Figure 2 is a diagrammatic representation of a prior art fluid
drilling head
showing the formation of cavitation clouds remote from the nozzle outlets;
[0011] Figure 3 is a right hand perspective view of the rotatable nozzle
assembly of
a fluid drilling head according to the invention;
[0012] Figure 4 is a left hand perspective view of the rotatable nozzle
assembly of a
fluid drilling head according to the invention;
[0013] Figure 5 is an end view of the rotatable nozzle assembly shown in
Figures 3
and 4;
[0014] Figure 6 is a side view of the rotatable nozzle assembly shown in
Figures 3
and 4, and
[0015] Figure 7 is a cross-sectional view through a nozzle of the type used
in the
fluid drilling head according to the invention.
Detailed description of the Preferred Embodiments of the Invention
[0016] In the preferred form of the invention, a fluid drilling head 8
typically has a
rotatable nozzle assembly 9 and may incorporate other features such as a
gauging ring
mounted at the leading end of a drill head body 11.
[0017] The more detailed configuration of the rotable nozzle assembly 9
will be
described below with reference to Figures 3 to 7, which demonstrate how the
nozzle
design and placement can be optimised to overcome the problems of a typical
prior art
fluid drilling head of the type shown at 12 in Figure 2.
[0018] In the typical prior art fluid drilling heads, the rotatable nozzle
assembly 13 is
provided with pilot nozzles 14 and reaming nozzles 15 which are typically of a
"horn
nozzle" design having a diverging outlet portion. Nozzles of this type
generate

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powerful cavitation clouds shown diagrammatically at 16 which are effective in
cutting
and breaking up rock. It has been found through careful laboratory testing
that while
the cavitation clouds 16 generated by the nozzles 14 and 15 are indeed
powerful, they
are remote from the nozzle outlets as clearly shown in Figure 2 resulting in a
"dead
zone" 17 between the cavitation cloud 16 and the nozzle outlets. Because of
the dead
zone, prior art tools of this nature need to be fed slowly into the hole to
ensure that the
rock being cut stays remote from the front surface 18 of the head. Once the
front
surface 18 advances too quickly into the rock face, the cavitation cloud 16 is
no longer
effective and the jet issues against the rock face in the dead zone 17.
[0019] The present invention overcomes this deficit by providing nozzles of
the type
shown in Figure 7 where the nozzle 18 is typically inserted into a hole 19
formed in the
rotatable nozzle assembly 20 and secured in place by a threaded engagement 21.
[0020] The nozzle is typically formed to sit in a counter bore 22 such that
the top of
the nozzle thread 23 sits flush with the base of the counter bore.
[0021] While the inlet portion 24 of each nozzle is typically tapered
inwardly to
increase the velocity of the high pressure water pumped through the nozzle,
the outlet
section 25 is formed of non-tapering section as is clearly seen in Figure 7
such that the
jet issuing therefrom is of substantially constant cross-section in the zone
immediately
adjacent the outlet section.
[0022] It has been found that the use of nozzles formed to this
configuration results
in a jet which is effective at cutting or breaking rock immediately adjacent
the outlet
from the nozzle, so avoiding the dead zone 17 typically found in the prior art
nozzle
configurations.
[0023] In order to maximise the rock cutting effect of nozzles of this
type, it has also
been found most effective to form the rotatable nozzle assembly in steps such
that the

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leading part 26 incorporating the pilot nozzles forming jet 1 and jet 2 is of
significantly
lesser diameter than the following part 27 of the rotatable nozzle assembly
incorporating the reaming nozzles.
[0024] The
reaming nozzles 3, 4, 5, and 6 are typically located to provide reaming
jers as shown in Figures 3 and 4 and are located at 29, 30, 31 and 32
respectively as
can be clearly seen in Figure 6.
[0025] In
this manner, the following part 27 of the rotatable nozzle assembly 9
is formed in a stepwise fashion of progressively increasing diameters, there
being one
reaming nozzle located in each step such that the jet issuing from each
reaming nozzle
is located close to the adjacent bore hole surface.
[0026] This
has been found to be most effective in maximising the operation of each
reaming jet, allowing the reaming jets to issue from their nozzles close to
the surface of
the bore hole to be reamed and enlarged until the final bore hole diameter is
achieved.
Ultimately, the bore hole diameter is controlled by the gauging ring 10.
[0027] This
effect is optimised by reducing the diameter of the leading part 26 as
much as physically possible so that the pilot jet rock cutting function is
reduced
compared with the progressive enlargement of the bore hole diameter from the
reaming jets in the following stepped parts 27.
[0028]
Combined with the use of nozzles of the type described above, this allows
the reaming jets to operate close to the rock face and increase the diameter
of the bore
in a step-wise manner. There rearward facing orientation of the reaming jets
also
allows much more efficient rock breaking at this close proximity.
[0029]
Laboratory testing has shown that the zone within about 5 mm of the outlet
from each reaming jet is very destructive, and much more so than the remote
cavitation
cloud of the horn nozzles used in prior art devices.

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[0030] The actual diameters of the nozzle outlets are selected depending on
the
nature of the rock to be cut, as is the pressure of the water supplied to the
nozzles
through the fluid drilling head. Testing has shown that drilling is effective
at pressures
of 48 MPa to 73 MPa. 48 MPa is better in bright coals, and 73 MPa is better in
claystone bands and sandstone.
[0031] Nozzle diameters vary depending on the material and nozzle location.
The
front pilot nozzles need be no greater than 0.7mm to 1.0 mm in diameter. It is
best to
minimise these sizes to improve net tool forward thrust, and a small change
makes a
big difference as they point virtually straight ahead. The reamers work well
in the
range between 0.5mm and 1.3mm, again depending on the coal conditions. The 310
m hole was drilled with 0.8 straight ahead, 0.9 forward angled, and 1.1 in the
three
reamers in this head. This, however, produced a penetration rate of around
1m/min.
[0032] In this manner, a rotatable nozzle assembly for a fluid drilling
head can be
provided which allows faster drilling rates than has previously been achieved
with prior
art drilling heads and further allows more accurate control of the bore hole
size, and the
effective location of the reaming nozzles.

Representative Drawing