Note: Descriptions are shown in the official language in which they were submitted.
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PULSED ELECTRIC ROCK DRILLING, FRACTURING,
AND CRUSHING METHODS AND APPARATUS
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is related to U.S. Provisional Patent Application Serial No.
60/603,509,
entitled "Electrocrushing FAST Drill and Technology, High Relative
Permittivity Oil, High
Efficiency Boulder Breaker, New Electrocrushing Process, and Electrocrushing
Mining
1.0 Machine", filed on August 20, 2004.
This application is also related to U.S. utility application entitled "Pulsed
Electric Rock
Drilling Apparatus", filed August 19, 2005 under application serial number
11/208,671; U.S.
utility application entitled "High Permittivity Fluid", filed August 19, 2005
under application serial
number 11/208,766; U.S. utility application entitled "Electrohydraulic Boulder
Breaker", filed
August 19, 2005 under application serial number 11/208,579; and U.S. utility
application entitled
"Virtual Electrode Mineral Particle Disintegrator" under application serial
number 11/208,579,
filed August 19, 2005 now issued as United States Patents 8,083,008 and
9,010,458.
BACKGROUND OF THE INVENTION
zo Technical Field:
The present invention relates to pulse powered drilling apparatuses and
methods. The
present invention also relates to insulating fluids of high relative
permittivity (dielectric constant).
Background Art:
Processes using pulsed power technology are known in the art for breaking
mineral
lumps. Fig. 1 shows a process by which a conduction path or streamer is
created inside rock to
break it. An electrical potential is impressed across the electrodes which
contact the rock from
the high voltage electrode 100 to the ground electrode 102. At sufficiently
high electric field, an
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arc 104 or plasma is formed inside the rock 106 from the high voltage
electrode to the low voltage
or ground electrode. The expansion of the hot gases created by the arc
fractures the rock. When
this streamer connects one electrode to the next, the current flows through
the conduction path, or
arc, inside the rock. The high temperature of the arc vaporizes the rock and
any water or other
fluids that might be touching, or are near, the arc. This vaporization process
creates high-
pressure gas in the arc zone, which expands. This expansion pressure fails the
rock in tension,
thus creating rock fragments.
The process of passing such a current through minerals is disclosed in U.S.
Patent No.
4,540,127 which describes a process for placing a lump of ore between
electrodes to break it into
monomineral grains. As noted in the '127 patent, it is advantageous in such
processes to use an
insulating liquid that has a high relative permittivity (dielectric constant)
to shift the electric fields
away from the liquid and into the rock in the region of the electrodes.
The '127 patent discusses using water as the fluid for the mineral
disintegration process.
However, insulating drilling fluid must provide high dielectric strength to
provide high electric fields
at the electrodes, low conductivity to provide low leakage current during the
delay time from
application of the voltage until the arc ignites In the rock, and high
relative permittivity to shift a
higher proportion of the electric field into the rock near the electrodes.
Water provides high
relative permittivity, but has high conductivity, creating high electric
charge losses. Therefore,
water has excellent energy storage properties, but requires extensive
deionization to make it
sufficiently resistive so that it does not discharge the high voltage
components ,by current leakage
through the liquid. In the deionized condition, water is very corrosive and
will dissolve many
materials, including metals. As a result, water must be continually
conditioned to maintain the
high resistivity required for high voltage applications. Even when deionized,
water still has such
sufficient conductivity that it is not suitable for long-duration, pulsed
power applications.
Petroleum oil, on the other hand, provides high dielectric strength and low
conductivity, but
does not provide high relative permittivity. Neither water nor petroleum oil,
therefore, provide all
the features necessary for effective drilling.
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Propylene carbonate is another example of such insulating materials in that it
has a high
dielectric constant and moderate dielectric strength, but also has high
conductivity (about twice
that of deionized water) making it unsuitable for pulsed power applications.
In addition to the high voltage, mineral breaking applications discussed
above, Insulating
fluids are used for many electrical applications such as, for example, to
insulate electrical power
transformers.
There is a need for an insulating fluid having a high dielectric constant, low
conductivity,
high dielectric strength, and a long life under industrial or military
application environments.
Other techniques are known for fracturing rock. Systems known in the art as
"boulder
breakers" rely upon a capacitor bank connected by a cable to an electrode or
transducer that is
inserted into a rock hole. Such systems are described by Hamelin, M. and
Kitzinger, F., Hard
Rock Fragmentation with Pulsed Power, presented at the 1993 Pulsed Power
Conference, and
Res, J. and Chattapadhyay, A, "Disintegration of Hard Rocks by the
Electrohydrodynamic Method"
Mining Engineering, January 1987. These systems are for fracturing boulders
resulting from the
mining process or for construction without having to use explosives.
Explosives create hazards
for both equipment and personnel because of fly rock and over pressure on the
equipment,
especially in underground mining. Because the energy storage in these systems
are located
remotely from the boulder, efficiency is compromised. Therefore, there is a
need for improving
efficiency in the boulder breaking and drilling processes.
Another technique for fracturing rock is the plasma-hydraulic (PH), or
electrohydraulic (EH)
techniques using pulsed power technology to create underwater plasma, which
creates intense
shock waves in water to crush rock and provide a drilling action. In practice,
an electrical plasma
is created in water by passing a pulse of electricity at high peak power
through the water. The
rapidly expanding plasma in the water creates a shock wave sufficiently
powerful to crush the
rock. In such a process, rock is fractured by repetitive application of the
shock wave.
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DISCLOSURE OF INVENTION
According to one aspect of the invention, there is provided an assembly for
creating
pressure waves in a liquid-filled cavity within a material, said assembly
comprising: a transducer
comprising a transducer case having a plurality of openings and at least one
electrode set, said
openings for enabling a pressure wave created within said transducer case to
expand into said
cavity; and an energy storage component disposed directly adjacent to said
transducer, said
energy storage component disposed in a module, said module having a larger
diameter than
said transducer case; wherein said electrode set comprises at least one high
voltage electrode
and at least one low voltage electrode separated by an electrode gap.
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An electrical current passes through the electrode gap to create pressure
through
expansion of the liquid as the liquid undergoes a phase change to gas and/or
plasma.
A switch preferably connects the energy storage component to the electrode
set.
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The energy storage component preferably comprises an inductive energy storage
component.
More than one set of electrodes are preferably arranged in parallel allowing
parallel
current flow.
More than one set of electrodes may also be arranged in series.
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More than one set of electrodes may also be arranged in a geometric
configuration.
The geometric configuration preferably comprises a configuration selected from
the
group consisting of a straight line, a curve, a circle, a spiral, and a
combination thereof.
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The material preferably comprises a boulder.
A primary electrical power source is connected to the energy storage component
for
charging the energy storage component, the primary electrical power source
located away from
the material.
A cable preferably connects the primary electrical power source to the energy
storage
component.
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The primary electrical power source preferably comprises an inductive energy
storage
apparatus to provide a high voltage pulse via the cable to charge the energy
storage
component.
The primary electrical power source may also comprise an electrical power
supply to
provide a high voltage via the cable to charge the energy storage component.
The primary electrical power source may also comprise a high voltage capacitor
bank to
provide a high voltage via the cable to charge the energy storage component.
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The capacitor bank preferably comprises at least one switching component
selected
from the group consisting of a spark gap, a thyratron, a vacuum gap, a pseudo-
spark switch, a
mechanical switch, a solid state switch, and a combination thereof.
At least one electrode set is preferably disposed in the transducer so that
capacitance is
provided between an electrode and a ground structure of the transducer.
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The capacitance is preferably formed via a liquid disposed between the
electrode and
the ground structure.
The capacitance may also be formed via a capacitor disposed between the
electrode
and the ground structure.
A liquid or capacitor between the at least one electrode to another electrode
in the
electrode set to preferably form said capacitance.
The energy storage component is preferably disposed directly into a hole in
the material.
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According to a further aspect of the invention, there is provided a method for
creating
pressure waves in a liquid-filled cavity within a material, the method
comprising: providing a
transducer assembly, the transducer assembly comprising a transducer case
having a plurality
of openings and at least one electrode set comprising at least two electrodes;
providing an
energy storage component directly adjacent to said transducer case; said
energy storage
component disposed in a module, said module having a larger diameter than said
transducer
case; disposing the transducer assembly but not the energy storage component
within a hole in
the material; passing an electrical current through a gap formed between the
at least two
electrodes; converting electrical energy to pressure energy, thereby forming a
pressure wave;
and the pressure wave expanding via the openings into the cavity.
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The at least two electrodes preferably comprise at least one high voltage
electrode and
at least one low voltage electrode.
The at least one high voltage electrode or the at least one low voltage
electrode
preferably comprises an intermediate electrode.
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Capacitance between each intermediate electrode and a ground structure of the
transducer assembly is preferably provided by disposing the at least one
electrode set in the
transducer assembly.
The capacitance is preferably formed by disposing a liquid between the
intermediate
electrode and the ground structure.
The capacitance may also be preferably formed by disposing a capacitor between
the
intermediate electrode and the ground structure.
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The capacitor preferably comprises a solid or liquid dielectric material.
The capacitance is preferably formed by disposing a liquid or capacitor
between the at
least one electrode set from electrode to electrode.
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Electrical energy is preferably supplied to the energy storage component.
A cable is preferably connected to an energy storage device located away from
the
material.
A pressure energy is preferably created through expansion of the liquid as the
liquid
undergoes a phase change to gas or plasma.
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More than one set of electrodes is preferably arranged in parallel.
More than one set of electrodes may also preferably be arranged in a line or
series of
straight lines.
More than one set of electrodes may also preferably be arranged in a geometric
configuration.
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The geometric configuration is preferably selected from the group consisting
of a straight
line, a curve, a circle, a spiral, and a combination thereof.
The material may preferably comprise a boulder.
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Other objects, advantages and novel features, and further scope of
applicability of the
present invention will be set forth in part in the detailed description to
follow, taken in
conjunction with the accompanying drawings, and in part will become apparent
to those skilled
in the art upon examination of the following, or may be learned by practice of
the invention. The
objects and advantages of the invention may be realized and attained by means
of the
instrumentalities and combinations pointed out in the appended claims.
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BRIEF DESCRIPTION OF DRAWINGS
The accompanying drawings, which are incorporated into and form a part of the
specification, illustrate one or more embodiments of the present invention
and, together with the
description, serve to explain the principles of the invention. The drawings
are only for the
purpose of illustrating one or more preferred embodiments of the invention and
are not to be
construed as limiting the invention. In the drawings:
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Fig. 1 shows an electrocrushing process of the prior art;
Fig. 2 shows an end view of a coaxial electrode set for a cylindrical bit of
an embodiment
of the present invention;
Fig. 3 shows an alternate embodiment of Fig. 2;
Fig. 4 shows an alternate embodiment of a plurality of coaxial electrode sets;
Fig. 5 shows a conical bit of an embodiment of the present invention;
Fig. 6 is of a dual-electrode set bit of an embodiment of the present
invention;
Fig. 7 is of a dual-electrode conical bit with two different cone angles of an
embodiment
of the present invention;
Fig. 8 shows an embodiment of a drill bit of the present invention wherein one
ground
electrode is the tip of the bit and the other ground electrode has the
geometry of a great circle of
the cone;
Fig. 9 shows the range of bit rotation azimuthal angle of an embodiment of the
present
invention;
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Fig. 10 shows an embodiment of the drill bit of the present invention having
radiused
electrodes;
Fig. 11 shows the complete drill assembly of an embodiment of the present
invention;
Fig. 12 shows the reamer drag bit of an embodiment of the present invention;
Fig. 13 shows a solid-state switch or gas switch controlled high voltage pulse
generating
system that pulse charges the primary output capacitor of an embodiment of the
present
invention;
Fig. 14 shows an array of solid-state switch or gas switch controlled high
voltage pulse
generating circuits that are charged in parallel and discharged in series to
pulse-charge the output
capacitor of an embodiment of the present invention;
Fig. 15 shows a voltage vector inversion circuit that produces a pulse that is
a multiple of
the charge voltage of an embodiment of the present invention;
Fig. 16 shows an inductive store voltage gain system to produce the pulses
needed for the
FAST Drill of an embodiment of the present invention;
Fig. 17 shows a drill assembly powered by a fuel cell that is supplied by fuel
lines and
exhaust line from the surface inside the continuous metal mud pipe of an
embodiment of the
present invention;
Fig. 18 shows a roller-cone bit with an electrode set of an embodiment of the
present
invention;
Fig. 19 shows a small-diameter electrocrushing drill of an embodiment of the
present
invention;
Fig. 20 shows an electrocrushing vein miner of an embodiment of the present
invention;
Fig. 21 shows a water treatment unit useable in the embodiments of the present
invention;
Fig. 22 shows a high energy electrohydraulic boulder breaker system (HEEB) of
an
embodiment of the present invention;
Fig. 23 shows a transducer of the embodiment of Fig. 22;
Fig. 24 shows the details of the an energy storage module and transducer of
the
embodiment of Fig. 22;
Fig. 25 shows the details of an inductive storage embodiment of the high
energy
electrohydraulic boulder breaker energy storage module and transducer of an
embodiment of the
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present invention;
Fig. 26 shows the embodiment of the high energy electrohydraulic boulder
breaker
disposed on a tractor for use in a mining environment;
Fig. 27 shows a geometric arrangement of the embodiment of parallel electrode
gaps in a
transducer in a spiral configuration.
Fig. 28 shows details of another embodiment of an electrohydraulic boulder
breaker
system;
Fig. 29 shows an embodiment of a virtual electrode electrocrushing process;
Fig. 30 shows an embodiment of the virtual electrode electrocrushing system
comprising a
vertical flowing fluid column;
Fig. 31 shows a pulsed power drilling apparatus manufactured and tested in
accordance
with an embodiment of the present invention; and
Fig. 32 is a graph showing dielectric strength versus delay to breakdown of
the insulating
formulation of the present invention, oil, and water.
MODES(S) FOR CARRYING OUT THE INVENTION
The present invention provides for pulsed power breaking and drilling
apparatuses and
methods. As used herein, "drilling" is defined as excavating, boring into,
making a hole in, or
otherwise breaking and driving through a substrate. As used herein, "bit" and
"drill bit" are defined
as the working portion or end of a tool that performs a function such as, but
not limited to, a
cutting, drilling, boring, fracturing, or breaking action on a substrate
(e.g., rock). As used herein,
the term "pulsed power" is that which results when electrical energy Is stored
(e.g., in a capacitor
or inductor) and then released into the load so that a pulse of current at
high peak power is
produced. "Electrocrushing" ("EC") is defined herein as the process of passing
a pulsed electrical
current through a mineral substrate so that the substrate is "crushed" or
"broken".
Electrocrushina Bit
An embodiment of the present Invention provides a drill bit on which is
disposed one or
more sets of electrodes. In this embodiment, the electrodes are disposed so
that a gap is formed
between them and are disposed on the drill bit so that they are oriented along
a face of the drill bit.
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In other words, the electrodes between which an electrical current passes
through a mineral
substrate (e.g., rock) are not on opposite sides of the rock. Also, in this
embodiment, it is not
necessary that all electrodes touch the mineral substrate as the current is
being applied. In
accordance with this embodiment, at least one of the electrodes extending from
the bit toward the
substrate to be fractured and may be compressible (i.e., retractable or
depressible) into the drill bit
by any means known in the art such as, for example, via a spring-loaded
mechanism.
Generally, but not necessarily, the electrodes are disposed on the bit such
that at least one
electrode contacts the mineral substrate to be fractured and another electrode
that usually
touches the mineral substrate but otherwise may be close to, but not
necessarily touching, the
mineral substrate so long as it is in sufficient proximity for current to pass
through the mineral
substrate. Typically, the electrode that need not touch the substrate is the
central, not the
surrounding, electrode.
Therefore, the electrodes are disposed on a bit and arranged such that
electrocrushing
arcs are created in the rock. High voltage pulses are applied repetitively to
the bit to create
repetitive electrocrushing excavation events. Electrocrushing drilling can be
accomplished, for
example, with a flat-end cylindrical bit with one or more electrode sets.
These electrodes can be
arranged in a coaxial configuration.
Fig. 2 shows an end view of such a coaxial electrode set configuration for a
cylindrical bit,
showing high voltage or center electrode 108, ground or surrounding electrode
110, and gap 112
for creating the arc in the rock. Variations on the coaxial configuration are
shown in Fig. 3. A
non-coaxial configuration of electrode sets arranged in bit housing 114 is
shown in Fig. 4. Figs. 3-
4 show ground electrodes that are completed circles. Other embodiments may
comprise ground
electrodes that are partial circles, partial or compete ellipses, or partial
or complete parabolas in
geometric form.
For drilling larger holes, a conical bit is preferably utilized, especially if
controlling the
direction of the hole is important. Such a bit may comprise one or more sets
of electrodes for
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creating the electrocrushing arcs and may comprise mechanical teeth to assist
the
electrocrushing process. One embodiment of the conical electrocrushing bit has
a single set of
electrodes, preferably arranged coaxially on the bit, as shown in Fig. 5. In
this embodiment,
conical bit 118 comprises a center electrode 108, the surrounding electrode
110, the bit case or
housing 114 and mechanical teeth 116 for drilling the rock. Either, or both,
electrodes may be
cornpressible. The surrounding electrode preferably has mechanical cutting
teeth 109
incorporated into the surface to smooth over the rough rock texture produced
by the
electrocrushing process. In this embodiment, the inner portion of the hole is
drilled by the
electrocrushing portion (i.e., electrodes 108 and 110) of the bit, and the
outer portion of the hole is
drilled by mechanical teeth 116. This results in high drilling rates, because
the mechanical teeth
have good drilling efficiency at high velocity near the perimeter of the bit,
but very low efficiency at
low velocity near the center of the bit. The geometrical arrangement of the
center electrode to the
ground ring electrode is conical with a range of cone angles from 180 degrees
(flat plane) to about
75 degrees (extended center electrode).
An alternate embodiment is to arrange a second electrode set on the conical
portion of the
bit. In such an embodiment, one set of the electrocrushing electrodes operates
on just one side
of the bit cone in an asymmetrical configuration as exemplified in Fig. 6
which shows a dual-
electrode set conical bit, each set of electrodes comprising center electrode
108, surrounding
electrode 110, bit case or housing 114, mechanical teeth 116, and drilling
fluid passage 120.
The combination of the conical surface on the bit and the asymmetry of the
electrode sets
results in the ability of the dual-electrode bit to excavate more rock on one
side of the hole than
the other and thus to change direction. For drilling a straight hole, the
repetition rate and pulse
energy of the high voltage pulses to the electrode set on the conical surface
side of the bit is
maintained constant per degree of rotation. However, when the drill is to turn
in a particular
direction, then for that sector of the circle toward which the drill is to
turn, the pulse repetition rate
(and/or pulse energy) per degree of rotation is increased over the repetition
rate for the rest of the
circle. In this fashion, more rock is removed by the conical surface electrode
set in the turning
direction and less rock is removed in the other directions (See Fig. 9,
discussed in detail below).
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Because of the conical shape of the bit, the drill tends to turn into the
section where greater
amount of rock was removed and therefore control of the direction of drilling
is achieved.
In the embodiment shown in Fig. 6, most of the drilling is accomplished by the
electrocrushing (EC) electrodes, with the mechanical teeth serving to smooth
the variation in
surface texture produced by the EC process. The mechanical teeth 116 also
serve to cut the
gauge of the hole, that is, the relatively precise, relatively smooth inside
diameter of the hole. An
alternate embodiment has the drill bit of Fig. 6 without mechanical teeth 116,
all of the drilling
being done by the electrode sets 108 and 110 with or without mechanical teeth
109 in the
surrounding electrode 110.
Alternative embodiments include variations on the configuration of the ground
ring
geometry and center-to-ground ring geometry as for the single-electrode set
bit. For example,
Fig. 7 shows such an arrangement in the form of a dual-electrode conical bit
comprising two
different cone angles with center electrodes 108, surrounding or ground
electrodes 110, and bit
case or housing 114. In the embodiment shown, the ground electrodes are tip
electrode 111 and
conical side ground electrodes 110 which surround, or partially surround, high
voltage electrodes
108 in an asymmetric configuration.
As shown in Fig. 7, the bit may comprise two or more separate cone angles to
enhance
the ability to control direction with the bit. The electrodes can be laid out
symmetrically in a sector
of the cone, as shown In Fig. 5 or in an asymmetric configuration of the
electrodes utilizing ground
electrode 111 as the center of the cone as shown in Fig. 7. Another
configuration is shown in Fig.
8A in which ground electrode 111 is at the tip of the bit and hot electrode
108 and other ground
electrode 110 are aligned in great circles of the cone. Fig. 8B shows an
alternate embodiment
wherein ground electrode 111 is the tip of the bit, other ground electrode 110
has the geometry of
a great circle of the cone, and hot electrodes 108 are disposed there between.
Also, any
combination of these configurations may be utilized.
It should be understood that the use of a bit with an asymmetric electrode
configuration
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can comprise one or more electrode sets and need not comprise mechanical
teeth. It should also
be understood that directional drilling can be performed with one or more
electrode sets.
The EC drilling process takes advantage of flaws and cracks in the rock. These
are
regions where it is easier for the electric fields to breakdown the rock. The
electrodes used in the
bit of the present invention are usually large in area in order to intercept
more flaws in the rock
and therefore improve the drilling rate, as shown in Fig. 5. This is an
important feature of the
invention because most electrodes in the prior art are small to increase the
local electric field
enhancement.
Fig. 9 shows the range of bit rotation azimuthal angle 122 where the
repetition rate or
pulse energy is increased to increase excavation on that side of the drill
bit, compared to the rest
of the bit rotation angle that has reduced pulse repetition rate or pulse
energy 124. The bit rotation
is referenced to a particular direction relative to the formation 126, often
magnetic north, to enable
the correct drill hole direction change to be made. This reference is usually
achieved by
instrumentation provided on the bit. When the pulsed power system provides a
high voltage pulse
to the electrodes on the side of the bit (See Fig. 6), an arc is struck
between one hot electrode
and one ground electrode. This arc excavates a certain amount of rock out of
the hole. By the
time the next high voltage pulse arrives at the electrodes, the bit has
rotated a certain amount,
and a new arc is struck at a new location in the rock. If the repetition rate
of the electrical pulses
is constant as a function of bit rotation azimuthal angle, the bit will drill
a straight hole. If the
repetition rate of the electrical pulses varies as a function of bit rotation
azimuthal angle, the bit will
tend to drift in the direction of the side of the bit that has the higher
repetition rate. The direction
of the drilling and the rate of deviation can be controlled by controlling the
difference in repetition
rate inside the high repetition rate zone azimuthal angle, compared to the
repetition rate outside
the zone (See Fig. 9). Also, the azimuthal angle of the high repetition rate
zone can be varied to
control the directional drilling. A variation of the invention is to control
the energy per pulse as a
function of azimuthal angle instead of, or in addition to, controlling the
repetition rate to achieve
directional drilling.
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Fast Drill System
Another embodiment of the present invention provides a drilling
system/assembly utilizing
the electrocrushing bits described herein and is designated herein as the FAST
Drill system. A
limitation in drilling rock with a drag bit is the low cutter velocity at the
center of the drill bit. This is
where the velocity of the grinding teeth of the drag bit is the lowest and
hence the mechanical
drilling efficiency is the poorest. Effective removal of rock in the center
portion of the hole is the
limiting factor for the drilling rate of the drag bit. Thus, an embodiment of
the FAST Drill system
comprises a small electrocrushing (EC) bit (alternatively referred to herein
as a FAST bit or FAST
Drill bit) disposed at the center of a drag bit to drill the rock at the
center of the hole. Thus, the EC
bit removes the rock near the center of the hole and substantially increases
the drilling rate. By
increasing the drilling rate, the net energy cost to drill a particular hole
is substantially reduced.
This is best illustrated by the bit shown in Fig. 5 (discussed above)
comprising EC process
electrodes 108 and 100 set at the center of bit 114, surrounded by mechanical
drag-bit teeth 116.
The rock at the center of the bit is removed by the EC electrode set, and the
rock near the edge of
the hole is removed by the mechanical teeth, where the tooth velocity is high
and the mechanical
efficiency Is high.
As noted above, the function of the mechanical drill teeth on the bit is to
smooth off the
tops of the protrusions and recesses left by the electrocrushing or plasma-
hydraulic process.
Because the electrocrushing process utilizes an arc through the rock to crush
or fracture the rock,
the surface of the rock is rough and uneven. The mechanical drill teeth smooth
the surface of the
rock, cutting off the tops of the protrusions so that the next time the
electrocrushing electrodes
come around to remove more rock, they have a larger smoother rock surface to
contact the
electrodes.
The EC bit preferably comprises passages for the drilling fluid to flush out
the rock debris
(i.e., cuttings) (See Figs. 6). The drilling fluid flows through passages
inside the electrocrushing
bit and then out] through passages 120 in the surface of the bit near the
electrodes and near the
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drilling teeth, and then flows up the side of the drill system and the well to
bring rock cuttings to
the surface.
The EC bit may comprise an insulation section that insulates the electrodes
from the
housing, the electrodes themselves, the housing, the mechanical rock cutting
teeth that help
smooth the rock surface, and the high voltage connections that connect the
high voltage power
cable to the bit electrodes.
Fig. 10 shows an embodiment of the Fast drill high voltage electrode 108 and
ground
electrodes 110 that incorporate a radius 176 on the electrode, with electrode
radius 176 on the
rock-facing side of electrodes 110. Radius 176 is an important feature of the
present invention to
allocate the electric field into the rock. The feature is not obvious because
electrodes from prior
art were usually sharp to enhance the local electric field.
Fig. 11 shows an embodiment of the FAST Drill system comprising two or more
sectional
components, including, but not limited to: (1) at least one pulsed power FAST
drill bit 114; (2) at
least one pulsed power supply 136; (3) at least one downhole generator 138;
(4) at least one
overdrive gear to rotate the downhole generator at high speed 140; (5) at
least one downhole
generator drive mud motor 144; (6) at least one drill bit mud motor 146; (7)
at least one rotating
interface 142; (8) at least one tubing or drill pipe for the drilling fluid
147; and (9) at least one cable
148. Not all embodiments of the FAST Drill system utilize all of these
components. For example,
one embodiment utilizes continuous coiled tubing to provide drilling fluid to
the drill bit, with a cable
to bring electrical power from the surface to the pulsed power system. That
embodiment does not
require a down-hole generator, overdrive gear, or generator drive mud motor,
but does require a
downhole mud motor to rotate the bit, since the tubing does not turn. An
electrical rotating
interface is required to transmit the electrical power from the non-rotating
cable to the rotating drill
bit.
An embodiment utilizing a multi-section rigid drill pipe to rotate the bit and
conduct drilling
fluid to the bit requires a downhole generator, because a power cable cannot
be used, but does
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not need a mud motor to turn the bit, since the pipe turns the bit. Such an
embodiment does not
need a rotating interface because the system as a whole rotates at the same
rotation rate.
An embodiment utilizing a continuous coiled tubing to provide mud to the drill
bit, without a
power cable, requires a down-hole generator, overdrive gear, and a generator
drive mud motor,
and also needs a downhole motor to rotate the bit because the tubing does not
turn. An electrical
rotating interface is needed to transmit the electrical control and data
signals from the non-rotating
cable to the rotating drill bit.
An embodiment utilizing a continuous coiled tubing to provide drilling fluid
to the drill bit,
with a cable to bring high voltage electrical pulses from the surface to the
bit, through the rotating
interface, places the source of electrical power and the pulsed power system
at the surface. This
embodiment does not need a down-hole generator, overdrive gear, or generator
drive mud motor
or downhole pulsed power systems, but does need a downhole motor to rotate the
bit, since the
tubing does not turn.
Still another embodiment utilizes continuous coiled tubing to provide drilling
fluid to the drill
bit, with a fuel cell to generate electrical power located in the rotating
section of the drill string.
Power is fed across the rotating interface to the pulsed power system, where
the high voltage
pulses are created and fed to the FAST bit. Fuel for the fuel cell is fed down
tubing inside the
coiled tubing mud pipe.
An embodiment of the FAST Drill system comprises FAST bit 114, a drag bit
reamer 150
(shown in Fig. 12), and a pulsed power system housing 136 (Fig. 11).
Fig. 12 shows reamer drag bit 150 that enlarges the hole cut by the
electrocrushing FAST
bit, drag bit teeth 152, and FAST bit attachment site 154. Reamer drag bit 150
is preferably
disposed just above FAST bit 114. This is a conical pipe section, studded with
drill teeth, that is
used to enlarge the hole drilled by the EC bit (typically, for example,
approximately 7.5 inches in
diameter) to the full diameter of the well (for example, to approximately 12.0
inches in diameter).
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The conical shape of drag bit reamer 150 provides more cutting teeth for a
given diameter of hole,
thus higher drilling rates. Disposed in the center part of the reamer section
are several passages.
There is a passage for the power cable to go through to the FAST bit. The
power cable comes
from the pulsed power section located above and/or within the reamer and
connects to the FAST
drill bit below the reamer. There are also passages in the reamer that provide
oil flow down to
the FAST bit and passages that provide flushing fluid to the reamer teeth to
help cut the rock and
flush the cuttings from the reamer teeth.
Preferably, a pulse power system that powers the FAST bit is enclosed in the
housing of
the reamer drag bit and the stem above the drag bit as shown in Fig. 11. This
system takes the
electrical power supplied to the FAST Drill for the electrocrushing FAST bit
and transforms that
power into repetitive high voltage pulses, usually over 100 kV. The repetition
rate of those pulses
is controlled by the control system from the surface or in the bit housing.
The pulsed power
system itself can include, but is not limited to:
(1) a solid state switch controlled or gas-switch controlled pulse generating
system with a
pulse transformer that pulse charges the primary output capacitor (example
shown in Fig. 13);
(2) an array of solid-state switch or gas-switch controlled circuits that are
charged in
parallel and in series pulse-charge the output capacitor (example shown in
Fig. 14);
(3) a voltage vector inversion circuit that produces a pulse at about twice,
or a multiple of,
the charge voltage (example shown in Fig. 15);
(4) An inductive store system that stores current in an inductor, then
switches it to the
electrodes via an opening or transfer switch (example shown in Fig. 16); or
(5) any other pulse generation circuit that provides repetitive high voltage,
high current
pulses to the FAST Drill bit.
Fig. 13 shows a solid-state switch or gas switch controlled high voltage pulse
generating
system that pulse charges the primary output capacitor 164, showing generating
means 156 to
provide DC electrical power for the circuit, intermediate capacitor electrical
energy storage means
158, gas, solid-state, or vacuum switching means 160 to switch the stored
electrical energy into
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pulse transformer 162 voltage conversion means that charges output capacitive
storage means
164 connecting to FAST bit 114.
Fig. 14 shows an array of solid-state switch or gas switch 160 controlled high
voltage pulse
generating circuits that are charged in parallel and discharged in series
through pulse transformer
162 to pulse-charge output capacitor 164.
Fig. 15 shows a voltage vector inversion circuit that produces a pulse that is
a multiple of
the charge voltage. An alternate of the vector inversion circuit that produces
an output voltage of
about twice the input voltage is shown, showing solid-state switch or gas
switching means 160,
vector inversion inductor 166, intermediate capacitor electrical energy
storage means 158
connecting to FAST bit 114.
Fig. 16 shows an inductive store voltage gain system to produce the pulses
needed for the
FAST Drill, showing the solid-state switch or gas switching means 160,
saturable pulse
transformers 168, and intermediate capacitor electrical energy storage means
158 connecting to
the FAST bit 114.
The pulsed power system is preferably located in the rotating bit, but may be
located in the
stationary portion of the drill pipe or at the surface.
Electrical power for the pulsed power system is either generated by a
generator at the
surface, or drawn from the power grid at the surface, or generated down hole.
Surface power is
transmitted to the FAST drill bit pulsed power system either by cable inside
the drill pipe or
conduction wires in the drilling fluid pipe wall. In the preferred embodiment,
the electrical power is
generated at the surface, and transmitted downhole over a cable 148 located
inside the
continuous drill pipe 147 (shown in Fig.11).
The cable is located in non-rotating flexible mud pipe (continuous coiled
tubing). Using a
cable to transmit power to the bit from the surface has advantages in that
part of the power
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conditioning can be accomplished at the surface, but has a disadvantage in the
weight, length,
and power loss of the long cable.
At the bottom end of the mud pipe is located the mud motor which utilizes the
flow of
drilling fluid down the mud pipe to rotate the FAST Drill bit and reamer
assembly. Above the
pulsed power section, at the connection between the mud pipe and the pulsed
power housing, is
the rotating interface as shown in Fig. 11. The cable power is transmitted
across an electrical
rotating interface at the point where the mud motor turns the drag bit. This
is the point where
relative rotation between the mud pipe and the pulsed power housing is
accommodated. The
rotating electrical interface is used to transfer the electrical power from
the cable or continuous
tubing conduction wires to the pulsed power system. It also passes the
drilling fluid from the non-
rotating part to the rotating part of the drill string to flush the cuttings
from the EC electrodes and
the mechanical teeth. The pulsed power system is located inside the rigid
drill pipe between the
rotating interface and the reamer. High voltage pulses are transmitted inside
the reamer to the
FAST bit.
In the case of electrical power transmission through conduction wires in rigid
rotating pipe,
the rotating interface is not needed because the pulsed power system and the
conduction wires
are rotating at the same velocity. If a down hole gearbox is used to provide a
different rotation rate
for the pulsed power/bit section from the pipe, then a rotating interface is
needed to accommodate
the electrical power transfer.
In another embodiment, power for the FAST Drill bit is provided by a downhole
generator
that Is powered by a mud motor that is powered by the flow of the drilling
fluid (mud) down the
drilling fluid, rigid, multi-section, drilling pipe (Fig. 11). That mudflow
can be converted to
rotational mechanical power by a mud motor, a mud turbine, or similar
mechanical device for
converting fluid flow to mechanical power. Bit rotation is accomplished by
rotating the rigid drill
pipe. With power generation via downhole generator, the output from the
generator can be inside
the rotating pulsed power housing so that no rotating electrical interface is
required (Fig. 11), and
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only a mechanical interface is needed. The power comes from the generator to
the pulsed power
system where it is conditioned to provide the high voltage pulses for
operation of the FAST bit.
Alternatively, the downhole generator might be of the piezoelectric type that
provides
electrical power from pulsation in the mud. Such fluid pulsation often results
from the action of a
mud motor turning the main bit.
Another embodiment for power generation is to utilize a fuel cell in the non-
rotating section
of the drill string. Fig. 17 shows an example of a FAST Drill system powered
by fuel cell 170 that
is supplied by fuel lines and exhaust line 172 from the surface inside the
continuous metal mud
pipe 147. The power from fuel cell 170 is transmitted across the rotating
interface 142 to pulsed
power system 136, and hence to FAST bit 114. The fuel cell consumes fuel to
produce electricity.
Fuel lines are placed inside the continuous coiled tubing, which provides
drilling fluid to the drill
bit, to provide fuel to the fuel cell, and to exhaust waste gases. Power is
fed across the rotating
interface to the pulsed power system, where the high voltage pulses are
created and fed to the
FAST bit.
As noted above, there are two primary means for transmitting drilling fluid
(mud) from the
surface to the bit: continuous flexible tubing or rigid multi-section drill
pipe. The continuous
flexible mud tubing is used to transmit mud from the surface to the rotation
assembly where part
of the mud stream is utilized to spin the assembly through a mud motor, a mud
turbine, or another
rotation device. Part of the mudflow is transmitted to the FAST bits and
reamer for flushing the
cuttings up the hole. Continuous flexible mud tubing has the advantage that
power and
instrumentation cables can be installed inside the tubing with the mudflow. It
is stationary and not
used to transmit torque to the rotating bit. Rigid multi-section drilling pipe
comes in sections and
cannot be used to house continuous power cable, but can transmit torque to the
bit assembly.
With continuous flexible mud pipe, a mechanical device such as, for example, a
mud motor, or a
mud turbine, is used to convert the mud flow into mechanical rotation for
turning the rotating
assembly. The mud turbine can utilize a gearbox to reduce the revolutions per
minute. A
downhole electric motor can alternatively be used for turning the rotating
assembly. The purpose
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of the rotating power source is primarily to provide torque to turn the teeth
on the reamer and the
FAST bit for drilling. It also rotates the FAST bit to provide the directional
control in the cutting of
a hole. Another embodiment is to utilize continuous mud tubing with downhole
electric power
generation.
In one embodiment, two mud motors or mud turbines are used: one to rotate the
bits, and
one to generate electrical power.
Another embodiment of the rigid multi-section mud pipe is the use of data
transmitting
wires buried in the pipe such as, for example, the lntelipipe manufactured by
Grant Prideco. This
is a composite pipe that uses magnetic induction to transmit data across the
pipe joints, while
transmitting it along wires buried in the shank of the pipe sections.
Utilizing this pipe provides for
data transmission between the bit and the control system on the surface, but
still requires the use
of downhole power generation.
Another embodiment of the FAST Drill is shown in Fig. 18 wherein rotary or
roller-cone bit
174 is utilized, instead of a drag bit, to enlarge the hole drilled by the
FAST bit. Roller-cone bit
174 comprises electrodes 108 and 110 disposed in or near the center portion of
roller cone bit
174 to excavate that portion of the rock where the efficiency of the roller
bit is the least.
Another embodiment of the rotating interface is to use a rotating magnetic
interface to
transfer electrical power and data across the rotating interface, instead of a
slip ring rotating
interface.
In another embodiment, the mud returning from the well loaded with cuttings
flows to a
settling pond, at the surface, where the rock fragments settle out. The mud
then cleaned and
reinjected into the FAST Drill mud pipe.
Electrocrushinq Vein Miner
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Another embodiment of the present invention provides a small-diameter,
electrocrushing drill
(designated herein as "SED") that is related to the hand-held electrohydraulic
drill disclosed in
U.S. Patent No. 5,896,938 (to a primary inventor herein). However, the SED is
distinguishable
in that the electrodes in the SED are spaced in such a way, and the rate of
rise of the electric
field is such, that the rock breaks down before the water breaks down. When
the drill is near
rock, the electric fields break down the rock and current passes through the
rock, thus fracturing
the rock into small pieces. The electrocrushing rock fragmentation occurs as a
result of tensile
failure caused by the electrical current passing through the rock, as opposed
to compressive
failure caused by the electrohydraulic (EH) shock or pressure wave on the rock
disclosed in
U.S. Patent No. 5,896,938, although the SED, too, can be connected via a cable
from a box as
described in the '938 patent so that it can be portable. Fig. 19 shows a SED
drill bit comprising
case 206, internal insulator 208, and center electrode 210 which is preferably
movable (e.g.,
spring-loaded) to maintain contact with the rock while drilling. Although case
206 and internal
insulator 208 are shown as providing an enclosure for center electrode 210,
other components
capable of providing an enclosure may be utilized to house electrode 210 or
any other electrode
incorporated in the SED drill bit. Preferably, case 206 of the SED is the
ground electrode,
although a separate ground electrode may be provided. Also, it should be
understood that more
than one set of electrodes may be utilized in the SED bit. A pulsed power
generator as
described in other embodiments herein is linked to said drill bit for
delivering high voltage pulses
to the electrode. In an embodiment of the SED, cable 207 (which may be
flexible) is provided to
link a generator to the electrode(s). A passage, for example cable 207, is
preferably used to
deliver water down the SED drill.
This SED embodiment is advantageous for drilling in non-porous rock. Also,
this
embodiment benefits from the use concurrent use of the high permittivity
liquid discussed
herein.
Another embodiment of the present invention is to assemble several individual
SED drill
heads or electrode sets together into an array or group of drills, without the
individual drill
housings, to provide the capability to mine large areas of rock. In such an
embodiment, a vein of
ore can be mined, leaving most of the waste rock behind. Fig. 20 shows such an
embodiment of
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a mineral vein mining machine herein designated Electrocrushing Vein Miner
(EVM) 212
comprising a plurality of SED drills 214, SED case 206, SED insulator 208, and
SED center
electrode 210. This assembly can then be steered as it moves through the rock
by varying the
repetition rate of the high voltage pulses differentially among the drill
heads. For example, if the
repetition rate for the top row of drill heads is twice as high but contains
the same energy per
pulse as the repetition rate for the lower two rows of drill heads, the path
of the mining machine
will curve in the direction of the upper row of drill heads, because the rate
of rock excavation will
be higher on that side. Thus, by varying the repetition rate and/or pulse
energy of the drill heads,
the EVM can be steered dynamically as it is excavating a vein of ore. This
provides a very useful
tool for efficiently mining just the ore from a vein that has substantial
deviation in direction.
In another embodiment, a combination of electrocrushing and electrohydraulic
(EH) drill bit
heads enhances the functionality of the EVM by enabling the EVM to take
advantage of ore
structures that are layered. Where the machine is mining parallel to the
layers, as is the case in
mining most veins of ore, the shock waves from the EH drill bit heads tend to
separate the layers,
thus synergistically coupling to the excavation created by the EC electrodes.
In addition,
combining electrocrushing drill heads with plasma-hydraulic drill heads
combines the compressive
rock fracturing capability of the plasma-hydraulic drill heads with the
tensile rock failure of the EC
drill heads to more efficiently excavate rock.
With the EVM mining machine, ore can be mined directly and immediately
transported to a
mill by water transport, already crushed, so the energy cost of primary
crushing and the capital
cost of the primary crushers is saved. This method has a great advantage over
conventional
mechanical methods in that it combines several steps in ore processing, and it
greatly reduces the
amount of waste rock that must be processed. This method of this embodiment
can also be used
for tunneling.
The high voltage pulses can be generated in the housing of the EVM,
transmitted to the
EVM via cables, or both generated elsewhere and transmitted to the housing for
further
conditioning. The electrical power generation can be at the EVM via fuel cell
or generator, or
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transmitted to the EVM via power cable. Typically, water or mining fluid flows
through the structure
of the EVM to flush out rock cuttings.
If a few, preferably just three, of the EC or PH drill heads shown in Fig. 20
are placed in a
housing, the assembly can be used to drill holes, with directional control by
varying the relative
repetition rate of the pulses driving the drill heads. The drill will tend to
drift in the direction of the
drill head with the highest pulse repletion rate, highest pulse energy, or
highest average power.
This electrocrushing (or EH) drill can create very straight holes over a long
distance for improving
the efficiency of blasting in underground mining, or it can be used to place
explosive charges in
areas not accessible in a straight line.
Insulating Drilling Fluid
An embodiment of the present invention also comprises insulating drilling
fluids that may
be utilized in the drilling methods described herein. For example, for the
electrocrushing process
to be effective in rock fracturing or crushing, it is preferable that the
dielectric constant of the
insulating fluid be greater than the dielectric constant of the rock and that
the fluid have low
conductivity such as, for example, a conductivity of less than approximately
10-6 mho/cm and a
dielectric constant of at least approximately 6.
Therefore, one embodiment of the present invention provides for an insulating
fluid or
material formulation of high permittivity, or dielectric constant, and high
dielectric strength with low
conductivity. The insulating formulation comprises two or more materials such
that one material
provides a high dielectric strength and another provides a high dielectric
constant. The overall
dielectric constant of the insulating formulation is a function of the ratio
of the concentrations of
the at least two materials. The insulating formulation is particularly
applicable for use in pulsed
power applications.
Thus, this embodiment of the present invention provides for an electrical
insulating
formulation that comprises a mixture of two or more different materials. In
one embodiment, the
formulation comprises a mixture of two carbon-based materials. The first
material preferably
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comprises a dielectric constant of greater than approximately 2.6, and the
second material
preferably comprises a dielectric constant greater than approximately 10Ø
The materials are at
least partly miscible with one another, and the formulation preferably has low
electrical
conductivity. The term "low conductivity" or "low electrical conductivity", as
used throughout the
specification and claims means a conductivity less than that of tap water,
preferably lower than
approximately 10-5 mho/cm, more preferably lower than le mho/cm. Preferably,
the materials
are substantially non-aqueous. The materials in the insulating formulation are
preferably non-
hazardous to the environment, preferably non-toxic, and preferably
biodegradable. The
formulation exhibits a low conductivity.
In one embodiment, the first material preferably comprises one or more natural
or
synthetic oils. Preferably, the first material comprises castor oil, but may
comprise or include
other oils such as, for example, jojoba oil or mineral oil.
Castor oil (glyceryl triricinoleate), a triglyceride of fatty acids, is
obtained from the seed of
the castor plant. It is nontoxic and biodegradable. A transformer grade castor
oil (from
CasChem, Inc.) has a dielectric constant (i.e., relative permittivity) of
approximately 4.45 at a
temperature of approximately 22 C (100 Hz).
The second material comprises a solvent, preferably one or more carbonates,
and more
preferably one or more alkylene carbonates such as, but not limited to,
ethylene carbonate,
propylene carbonate, or butylene carbonate. The alkylene carbonates can be
manufactured, for
example, from the reaction of ethylene oxide, propylene oxide, or butylene
oxide or similar oxides
with carbon dioxide.
Other oils, such as vegetable oil, or other additives can be added to the
formulation to
modify the properties of the formulation. Solid additives can be added to
enhance the dielectric or
fluid properties of the formulation.
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The concentration of the first material in the insulating formulation ranges
from between
approximately 1.0 and 99.0 percent by volume, preferably from between
approximately 40.0 and
95.0 percent by volume, more preferably still from between approximately 65.0
and 90.0 percent
by volume, and most preferably from between approximately 75.0 and 85.0
percent by volume.
The concentration of the second material in the insulating formulation ranges
from
between approximately 1.0 and 99.0 percent by volume, preferably from between
approximately
5.0 and 60.0 percent by volume, more preferably still from between
approximately 10.0 and 35.0
percent by volume, and most preferably from between approximately 15.0 and
25.0 percent by
volume.
Thus, the resulting formulation comprises a dielectric constant that is a
function of the ratio
of the concentrations of the constituent materials. The preferred mixture for
the formulation of the
present invention is a combination of butylene carbonate and a high
permittivity castor oil wherein
butylene carbonate is present in a concentration of approximately 20% by
volume. This
combination provides a high relative permittivity of approximately 15 while
maintaining good
insulation characteristics. In this ratio, separation of the constituent
materials is minimized. At a
ratio of below 32%, the castor oil and butylene carbonate mix very well and
remain mixed at room
temperature. At a butylene carbonate concentration of above 32%, the fluids
separate if
undisturbed for approximately 10 hours or more at room temperature. A property
of the present
invention is its ability to absorb water without apparent effect on the
dielectric performance of the
insulating formulation.
An embodiment of the present invention comprising butylene carbonate in castor
oil
comprises a dielectric strength of at least approximately 300 kV/cm (I psec),
a dielectric constant
of approximately at least 6, a conductivity of less than approximately 105
mho/cm, and a water
absorption of up to 2,000 ppm with no apparent negative effect caused by such
absorption. More
preferably, the conductivity is less than approximately 10-6 mho/cm.
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The formulation of the present invention is applicable to a number of pulsed
power
machine technologies. For example, the formulation is useable as an insulating
and drilling fluid
for drilling holes in rock or other hard materials or for crushing such
materials as provided for
herein. The use of the formulation enables the management of the electric
fields for
electrocrushing rock. Thus, the present invention also comprises a method of
disposing the
insulating formulation about a drilling environment to provide electrical
insulation during drilling.
Other formulations may be utilized to perform the drilling operations
described herein.
For example, in another embodiment, crude oil with the correct high relative
permittivity derived
as a product stream from an oil refinery may be utilized. A component of
vacuum gas crude oil
has high molecular weight polar compounds with 0 and N functionality.
Developments in
chromatography allow such oils to be fractionated by polarity. These are
usually cracked to
produce straight hydrocarbons, but they may be extracted from the refinery
stream to provide
high permittivity oil for drilling fluid.
Another embodiment comprises using specially treated waters. Such waters
include, for
example, the Energy Systems Plus (ESP) technology of Complete Water Systems
which is
used for treating water to grow crops. In accordance with this embodiment,
Fig. 21 shows water
or a water-based mixture 128 entering a water treatment unit 130 that treats
the water to
significantly reduce the conductivity of the water. The treated water 132 then
is used as the
drilling fluid by the FAST Drill system 134. The ESP process treats water to
reduce the
conductivity of the water to reduce the leakage current, while retaining the
high permittivity of
the water.
High Efficiency Electrohydraulic Boulder Breaker
Another embodiment of the present invention provides a high efficiency
electrohydraulic
boulder breaker (designated herein as "HEEB") for breaking up medium to large
boulders into
small pieces. This embodiment prevents the hazard of fly rock and damage to
surrounding
equipment. The HEEB is related to the High Efficiency Electrohydraulic
Pressure Wave
Projector disclosed in U.S. Patent No. 6,215,734 (to the principal inventor
herein),
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Fig. 22 shows the HEEB system disposed on truck 181, comprising transducer
178, power
cable 180, and fluid 182 disposed in a hole. Transducer 178 breaks the boulder
and cable 180
(which may be of any desired length such as, for example, 6-15 m long)
connects transducer 178
to electric pulse generator 183 in truck 181. An embodiment of the invention
comprises first
drilling a hole into a boulder utilizing a conventional drill, filling the
hole is filled with water or a
specialized insulating fluid, and inserting HEEB transducer 178 into the hole
in the boulder. Fig.
23 shows HEEB transducer 178 disposed in boulder 186 for breaking the boulder,
cable 180, and
energy storage module 184.
Main capacitor bank 183 (shown in Fig. 22) is first charged by generator 179
(shown in
Fig. 22) disposed on truck 181. Upon command, control system 192 (shown in
Fig. 22 and
disposed, for example, in a truck) is closed connecting capacitor bank 183 to
cable 180. The
electrical pulse travels down cable 180 to energy storage module 184 where it
pulse-charges
capacitor set 158 (example shown in Fig. 24), or other energy storage devices
(example shown in
Fig. 25).
Fig. 24 shows the details of the HEEB energy storage module 184 and transducer
178,
showing capacitors 158 in module 184, and floating electrodes 188 in
transducer 178.
Fig. 25 shows the details of the inductive storage embodiment of HEEB energy
storage
module 184 and transducer 178, showing inductive storage inductors 190 in
module 184, and
showing the transducer embodiment of parallel electrode gaps 188 in transducer
178. The
transducer embodiment of parallel electrode gaps (Fig. 25) and series
electrode gaps (Fig. 24)
can reach be used alternatively with either the capacitive energy store 158 of
Fig. 24 or the
inductive energy store 190 of Fig. 25.
These capacitors/devices are connected to the probe of the transducer assembly
where
the electrodes that create the pressure wave are located. The capacitors
increase in voltage from
the charge coming through the cable from the main capacitor bank until they
reach the breakdown
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voltage of the electrodes inside the transducer assembly. When the fluid gap
at the tip of the
transducer assembly breaks down (acting like a switch), current then flows
from the energy
storage capacitors or inductive devices through the gap. Because the energy
storage capacitors
are located very close to the transducer tip, there is very little inductance
in the circuit and the
peak current through the transducers is very high. This high peak current
results in a high energy
transfer efficiency from the energy storage module capacitors to the plasma in
the fluid. The
plasma then expands, creating a pressure wave in the fluid, which fractures
the boulder.
The HEEB system may be transported and used in various environments including,
but not
limited to, being mounted on a truck as shown in Fig. 22 for transport to
various locations, used
for either underground or aboveground mining applications as shown in Fig. 26,
or used in
construction applications. Fig. 26 shows an embodiment of the HEEB system
placed on a tractor
for use in a mining environment and showing transducer 178, power cable 180,
and control panel
192.
Therefore, the HEEB does not rely on transmitting the boulder-breaking current
over a
cable to connect the remote (e.g., truck mounted) capacitor bank to an
electrode or transducer
located in the rock hole. Rather, the HEEB puts the high current energy
storage directly at the
boulder. Energy storage elements, such as capacitors, are built into the
transducer assembly.
Therefore, this embodiment of the present invention increases the peak current
through the
transducer and thus improves the efficiency of converting electrical energy to
pressure energy for
breaking the boulder. This embodiment of the present invention also
significantly reduces the
amount of current that has to be conducted through the cable thus reducing
losses, increasing
energy transfer efficiency, and increasing cable life.
An embodiment of the present Invention Improves the efficiency of coupling the
electrical
energy to the plasma into the water and hence to the rock by using a multi-gap
design. A
problem with the multi-gap water spark gaps has been getting all the gaps to
ignite because the
cumulative breakdown voltage of the gaps is much higher than the breakdown
voltage of a single
gap. However, if capacitance is placed from the Intermediate gaps to ground
(Fig. 24), each gap
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ignites at a voltage similar to the ignition voltage of a single gap. Thus, a
large number of gaps
can be ignited at a voltage of approximately a factor of 2 greater than the
breakdown voltage for a
single gap. This improves the coupling efficiency between the pulsed power
module and the
energy deposited in the fluid by the transducer. Holes in the transducer case
are provided to let
the pressure from the multiple gaps out into the hole and into the rock to
break the rock (Fig. 24).
In another embodiment, the multi-gap transducer design can be used with a
conventional
pulsed power system, where the capacitor bank is placed at some distance from
the material to
be fractured, a cable is run to the transducer, and the transducer is placed
in the hole in the
boulder. Used with the HEEB, it provides the advantage of the much higher peak
current for a
given stored energy.
Thus, an embodiment of the present invention provides a transducer assembly
for creating
a pressure pulse in water or some other liquid in a cavity inside a boulder or
some other
fracturable material, said transducer assembly incorporating energy storage
means located
directly in the transducer assembly in close proximity to the boulder or other
fracturable material.
The transducer assembly incorporates a connection to a cable for providing
charging means for
the energy storage elements inside the transducer assembly. The transducer
assembly includes
an electrode means for converting the electrical current into a plasma
pressure source for
fracturing the boulder or other fracturable material.
Preferably, the transducer assembly has a switch located inside the transducer
assembly
for purposes of connecting the energy storage module to said electrodes.
Preferably, in the
transducer assembly, the cable Is used to pulse charge the capacitors in the
transducer energy
storage module. The cable is connected to a high voltage capacitor bank or
inductive storage
means to provide the high voltage pulse.
In another embodiment, the cable is used to slowly charge the capacitors in
the transducer
energy storage module. The cable is connected to a high voltage electric power
source.
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Preferably, the switch located at the primary capacitor bank is a spark gap,
thyratron,
vacuum gap, pseudo-spark switch, mechanical switch, or some other means of
connecting a high
voltage or high current source to the cable leading to the transducer
assembly.
In another embodiment, the transducer electrical energy storage utilizes
inductive storage
elements.
Another embodiment of the present invention provides a transducer assembly for
the
purpose of creating pressure waves from the passage of electrical current
through a liquid placed
between one or more pairs of electrodes, each gap comprising two or more
electrodes between
which current passes. The current creates a phase change in the liquid, thus
creating pressure
in the liquid from the change of volume due to the phase change. The phase
change Includes a
change from liquid to gas, from gas to plasma, or from liquid to plasma.
Preferably, in the transducer, more than one set of electrodes is arranged in
series such
that the electrical current flowing through one set of electrodes also flows
through the second set
of electrodes, and so on. Thus, a multiplicity of electrode sets can be
powered by the same
electrical power circuit.
In another embodiment, in the transducer, more than one set of electrodes is
arranged in
parallel such that the electrical current is divided as it flows through each
set of electrodes
(Fig. 25). Thus, a multiplicity of electrode sets can be powered by the same
electrical power
circuit.
Preferably, a plurality of electrode sets is arrayed in a line or in a series
of straight lines.
In another embodiment, the plurality of electrode sets is alternatively
arrayed to form a
geometric figure other than a straight line, including, but not limited to, a
curve, a circle (Fig. 25),
or a spiral. Fig. 27 shows a geometric arrangement of the embodiment
comprising parallel
electrode gaps 188 in the transducer 178, in a spiral configuration.
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Preferably, the electrode sets in the transducer assembly are constructed in
such a way as
to provide capacitance between each intermediate electrode and the ground
structure of the
transducer (Fig. 24).
In another embodiment, in the plurality of electrode sets, the capacitance of
the
intermediate electrodes to ground is formed by the presence of a liquid
between the intermediate
electrode and the ground structure.
In another embodiment, in the plurality of electrode sets, the capacitance is
formed by the
installation of a specific capacitor between each intermediate electrode and
the ground structure
(Fig. 24). The capacitor can use solid or liquid dielectric material.
In another embodiment, in the plurality of electrode sets, capacitance is
provided between
the electrode sets from electrode to electrode. The capacitance can be
provided either by the
presence of the fracturing liquid between the electrodes or by the
installation of a specific
capacitor from an intermediate electrode between electrodes as shown in Fig.
28. Fig. 28 shows
the details of the HEEB transducer 178 installed in hole 194 in boulder 186
for breaking the
boulder. Shown are cable 180, the floating electrodes 188 in the transducer
and liquid between
the electrodes 196 that provides capacitive coupling electrode to electrode.
Openings 198 in the
transducer which allow the pressure wave to expand into the rock hole are also
shown.
Preferably in the multi-electrode transducer, the electrical energy is
supplied to the multi-
gap transducer from an integral energy storage module.
Preferably in the multi-electrode transducer, the energy is supplied to the
transducer
assembly via a cable connected to an energy storage device located away from
the boulder or
other fracturable material.
1
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Virtual Electrode Electro-Crushing Process
Another embodiment of the present invention comprises a method for crushing
rock by
passing current through the rock using electrodes that do not touch the rock.
In this method, the
rock particles are suspended in a flowing or stagnant water column, or other
liquid of relative
permittivity greater than the permittivity of the rock being fractured. Water
is preferred for
transporting the rock particles because the dielectric constant of water is
approximately 80
compared to the dielectric constant of rock which Is approximately 3.5 to 12.
In the preferred embodiment, the water column moves the rock particles past a
set of
electrodes as an electrical pulse is provided to the electrodes. As the
electric field rises on the
electrodes, the difference in dielectric constant between the water and the
rock particle causes
the electric fields to be concentrated in the rock, forming a virtual
electrode with the rock. This is
illustrated in Fig. 29 showing rock particle 200 between high voltage
electrodes 202 and ground
electrode 203 in liquid 204 whose dielectric constant is significantly higher
than that of rock
particle 200.
The difference in dielectric constant concentrated the electric fields in the
rock particle.
These high electric fields cause the rock to break down and current to flow
from the electrode,
through the water, through the rock particles, through the conducting water,
and back to the
opposite electrode. In this manner, many small particles of rock can be
disintegrated by the
virtual electrode electrocrushing method without any of them physically
contacting both
electrodes. The method is also suitable for large particles of rock.
Thus, it is not required that the rocks be in contact with the physical
electrodes and so the
rocks need not be sized to match the electrode spacing in order for the
process to function. With
the virtual electrode electrocrushing method, it is not necessary for the
rocks to actually touch the
electrode, because in this method, the electric fields are concentrated in the
rock by the high
dielectric constant (relative permittivity) of the water or fluid. The
electrical pulse must be tuned to
the electrical characteristics of the column structure and liquid in order to
provide a sufficient rate
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of rise of voltage to achieve the allocation of electric field into the rock
with sufficient stress to
fracture the rock.
Another embodiment of the present invention, illustrated in Fig. 30, comprises
a reverse-
flow electro-crusher wherein electrodes 202 send an electrocrushing current to
mineral (e.g., rock)
particles 200 and wherein water or fluid 204 flows vertically upward at a rate
such that particles
200 of the size desired for the final product are swept upward, and whereas
particles that are
oversized sink downward.
As these oversized particles sink past the electrodes, a high voltage pulse is
applied to the
electrodes to fracture the particles, reducing them in size until they become
small enough to
become entrained by the water or fluid flow. This method provides a means of
transporting the
particles past the electrodes for crushing and at the same time
differentiating the particle size.
The reverse-flow crusher also provides for separating ash from coal in that it
provides for
the ash to sink to the bottom and out of the flow, while the flow provides
transport of the fine coal
particles out of the crusher to be processed for fuel.
Industrial Applicability
The invention is further illustrated by the following non-limiting example(s).
Example 1
An apparatus utilizing FAST Drill technology in accordance with the present
invention was
constructed and tested. Fig. 31 shows FAST Drill bit 114, the drill stem 216,
the hydraulic motor
218 used to turn drill stem 216 to provide power to mechanical teeth disposed
on drill bit 114, slip
ring assembly 220 used to transmit the high voltage pulses to the FAST bit 114
via a power cable
inside drill stem 216, and tank 222 used to contain the rocks being drilled. A
pulsed power
system, contained in a tank (not shown), generated the high voltage pulses
that were fed into the
slip ring assembly. Tests were performed by conducting 150 kV pulses through
drill stem 216 to
the FAST Bit 114, and a pulsed power system was used for generating the 150 kV
pulses. A
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drilling fluid circulation system was incorporated to flush out the cuttings.
The drill bit shown in
Fig. 5 was used to drill a 7 inch diameter hole approximately 12 inches deep
in rock located in a
rock tank. A fluid circulation system flushed the rock cuttings out of the
hole, cleaned the cuttings
out of the fluid, and circulated the fluid through the system.
Example II
A high permittivity fluid comprising a mixture of castor oil and approximately
20% by
volume butylene carbonate was made and tested in accordance with the present
invention as
follows.
1. Dielectric Strength Measurements.
Because this insulating formulation of the present invention is intended for
high voltage
applications, the properties of the formulation were measured in a high
voltage environment. The
dielectric strength measurements were made with a high voltage Marx bank pulse
generator, up
to 130 kV. The rise time of the Marx bank was less than 100 nsec. The
breakdown
measurements were conducted with 1-inch bails immersed in the insulating
formulation at
spacings ranging from 0.06 to 0.5 cm to enable easy calculation of the
breakdown fields. The
delay from the initiation of the pulse to breakdown was measured. Fig. 32
shows the electric field
at breakdown plotted as a function of the delay time in microseconds. Also
included are data from
the Charlie Martin models for transformer oil breakdown and for deionized
water breakdown
(Martin, T. H., A. H. Guenther, M Kristiansen "J. C. Martin on Pulsed Power"
Lemum Press,
(1996)).
The breakdown strength of the formulation is substantially higher than
transformer oil at
times greater than 10 sec. No special effort was expended to condition the
formulation. It
contained dust, dissolved water and other contaminants, whereas the Martin
model is for very well
conditioned transformer oil or water.
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2. Dielectric Constant Measurements.
The dielectric constant was measured with a ringing waveform at 20 kV. The
ringing high
voltage circuit was assembled with 8-inch diameter contoured plates immersed
in the insulating
formulation at 0.5-inch spacing. The effective area of the plates, including
fringing field effects,
was calibrated with a fluid whose dielectric constant was known (i.e.,
transformer oil). An
aluminum block was placed between the plates to short out the plates so that
the inductance of
the circuit could be measured with a known circuit capacitance. Then, the
plates were immersed
in the insulating formulation, and the plate capacitance was evaluated from
the ringing frequency,
properly accounting for the effects of the primary circuit capacitor. The
dielectric constant was
evaluated from that capacitance, utilizing the calibrated effective area of
the plate. These tests
indicated a dielectric constant of approximately 15.
3. Conductivity Measurements.
To measure the conductivity, the same 8-inch diameter plates used in the
dielectric
constant measurement were utilized to measure the leakage current. The plates
were separated
by 2-inch spacing and immersed in the insulating formulation. High voltage
pulses, ranging from
70-150kV were applied to the plates, and the leakage current flow between the
plates was
measured. The long duration current, rather than the initial current, was the
value of interest, in
order to avoid displacement current effects. The conductivity obtained was
approximately
1 micromho/cm [1X1(16 (ohm-cm)l].
4. Water Absorption.
The insulating formulation has been tested with water content up to 2000 ppm
without any
apparent effect on the dielectric strength or dielectric constant. The water
content was measured
by Karl Fisher titration.
5. Energy Storage Comparison.
The energy storage density of the insulating formulation of the present
invention was
shown to be substantially higher than that of transformer oil, but less than
that of deionized water.
Table 1 shows the energy storage comparison of the insulating formulation, a
transformer oil, and
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water in the 1 psec and 10 sec breakdown time scales. The energy density (in
joules/cm3) was
calculated from the dielectric constant (C,C0) and the breakdown electric
field (Ebd - kV/cm). The
energy storage density of the insulating formulation is approximately one-
fourth that of water at 10
microseconds. The insulating formulation did not require continuous
conditioning, as did a water
dielectric system. After about 12 months of use, the insulating formulation
remained useable
without conditioning and with no apparent degradation.
Table 1. Comparison of Energy Storage Density
Time = 1 psec Time = 10 psec
Dielectic kV/ Energy kV/c Energy
Fluid Constant cm Density m Density
Insulating 15 380 9.59E-02 325 7.01E-02
formulation
Trans. Oil 2.2 500 2.43E-02 235 5.38E-03
Water 80 600 1.27E+00 280 2.78E-01
Energy density =1/2* C * Cb*Ebd*Ebd¨ j/cmd
6. Summary.
A summary of the dielectric properties of the insulating formulation of the
present invention
is shown in Table 2. Applications of the insulating formulation include high
energy density
capacitors, large-scale pulsed power machines, and compact repetitive pulsed
power machines.
Table 2. Summary of Formulation Properties
Dielectric Strength = 380 kV/cm (1 psec)
Dielectric = 15
Constant
Conductivity = le-6 mho/cm
Water absorption = up to 2000 ppm with no apparent ill effects
The preceding examples can be repeated with similar success by substituting
the
generically or specifically described compositions, biomaterials, devices
and/or operating
conditions of this invention for those used in the preceding examples.
Although the invention has been described in detail with particular reference
to these
preferred embodiments, other embodiments can achieve the same results.
Variations and
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modifications of the present invention will be obvious to those skilled in the
art and it is intended
to cover all such modifications and equivalents.
10
20
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