U.S. patent application number 15/108842 was filed with the patent office on 2016-11-10 for a method for energy efficient and fast rotary drilling in inhomogeneous and/or hard rock formations.
The applicant listed for this patent is SINTEF TTO AS. Invention is credited to Odd-Geir LADEMO, Are LUND, Dirk NOLTE.
Application Number | 20160326806 15/108842 |
Document ID | / |
Family ID | 53524167 |
Filed Date | 2016-11-10 |
United States Patent
Application |
20160326806 |
Kind Code |
A1 |
LUND; Are ; et al. |
November 10, 2016 |
A METHOD FOR ENERGY EFFICIENT AND FAST ROTARY DRILLING IN
INHOMOGENEOUS AND/OR HARD ROCK FORMATIONS
Abstract
It is described a rotary drilling system (10) for drilling a
borehole (12) in inhomogeneous and/or hard rock formations. The
system (10) comprising: a rotary drill bit (20; 50), and at least
two electrodes (21, 22, 23, 51, 52, 53) arranged for pulsing
between said electrodes of at least one high voltage electro pulse
(41), wherein said at least one high voltage electro pulse (41) is
generated in response to a detected resistance on the drill bit
(20) from a rock formation (40) in front of the drill bit (20)
while rotating, in order to create small/micro-cracks (45) in the
rock formation (40).
Inventors: |
LUND; Are; (Trondheim,
NO) ; LADEMO; Odd-Geir; (Trondheim, NO) ;
NOLTE; Dirk; (Trondheim, NO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SINTEF TTO AS |
Trondheim |
|
NO |
|
|
Family ID: |
53524167 |
Appl. No.: |
15/108842 |
Filed: |
January 13, 2015 |
PCT Filed: |
January 13, 2015 |
PCT NO: |
PCT/NO2015/050006 |
371 Date: |
June 29, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61926527 |
Jan 13, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21C 37/18 20130101;
E21B 10/00 20130101; E21B 47/007 20200501; E21B 3/00 20130101; E21B
7/15 20130101 |
International
Class: |
E21B 7/15 20060101
E21B007/15; E21C 37/18 20060101 E21C037/18; E21B 3/00 20060101
E21B003/00; E21B 10/00 20060101 E21B010/00; E21B 47/00 20060101
E21B047/00 |
Claims
1-25. (canceled)
26. A rotary mechanical drilling system for mechanical drilling of
a borehole in inhomogeneous and/or hard rock formations, the system
comprising: a rotary drill bit, and at least two electrodes
arranged for pulsing between said electrodes of at least one high
voltage electro pulse, wherein said at least one high voltage
electro pulse is generated in response to a detected resistance on
the drill bit from a rock formation in front of the drill bit while
drilling, in order to create small-cracks/micro-cracks in the rock
formation, wherein said at least one high voltage electro pulse is
generated only when the detected resistance on the drill bit
exceeds a predetermined limit under drilling.
27. The rotary drilling system according to claim 26, further
comprising at least one sensor arranged in the drill bit for
detecting the resistance on the drill bit from the rock
formation.
28. The rotary drilling system according to claim 26, further
comprising at least one sensor arranged in the drilling system for
detecting the resistance on the drill bit from the rock
formation.
29. The rotary drilling system according to claim 26, further
comprising a radar or sonar for pre-detecting the resistance on the
drill bit from the rock formation.
30. The rotary drilling system according to claim 26, wherein the
detected resistance is in the form of a detected torque on the
drill bit from the rock formation.
31. The rotary drilling system according to claim 30, wherein said
at least one high voltage electro pulse is generated when the
detected torque on the drill bit exceeds a predetermined torque
limit under rotary drilling.
32. The rotary drilling system according to claim 26, wherein at
least two electrodes are incorporated in the drill bit.
33. The rotary drilling system according to claim 26, further
comprising an electro pulse device connected to said electrodes and
adapted for generating said at least one high voltage electro
pulse.
34. The rotary drilling system according to claim 26, further
comprising a torque sensing device arranged for detecting the drill
bit torque from the rock formation in front of the drill bit under
drilling.
35. The rotary drilling system according to claim 26, further
comprising an electronic switch for electro pulsing.
36. The rotary drilling system according to claim 26, wherein the
electro pulse device comprises at least one of: a capacitor, a
rectifier and a transformer of low to high voltage and/or
current.
37. The rotary drilling system according to claim 26, wherein the
system further comprises an electrical source comprising at least
one of: a battery pack or batteries, a mud driven generator, a
water driven generator, a compressed air driven generator, a rotary
drill string driven generator, and cables to surface.
38. The rotary drilling system according to claim 26, further
comprising a drilling assembly.
39. The rotary drilling system according to claim 38, wherein the
rotary drill bit is arranged in the drilling assembly.
40. The rotary drilling system according to claim 38, wherein the
electro pulse device is arranged in the drilling assembly.
41. The rotary drilling system according to claim 26, wherein the
drill bit comprises at least one of: teeth, scrapers and cutter
disks, and wherein said at least two electrodes are incorporated in
at least one of: the drill bit itself, the teeth, the scrapers and
the cutter disks.
42. The rotary drilling system according to claim 26, wherein the
system is adapted for tunneling, and the drill bit is a rotary
tunnel excavator.
43. A method for rotary mechanical drilling of a borehole in
inhomogeneous and/or hard rock formations, comprising: rotary
mechanical drilling a borehole using a rotary drill bit, pulsing
between at least two electrodes of at least one high voltage
electro pulse, wherein said at least one high voltage electro pulse
is generated in response to a detected resistance on the drill bit
from a rock formation in front of the drill bit while rotating,
creating small cracks/micro-cracks in the rock formation, wherein
said at least one high voltage electro pulse is generated only when
the detected resistance on the drill bit exceeds a predetermined
limit under rotary drilling.
44. Method according to claim 43, further comprising detecting the
resistance by detecting a torque on the drill bit from the rock
formation.
45. Method according to claim 43, further comprising detecting by
using a radar or sonar for pre-detecting the resistance on the
drill bit from the rock formation.
46. The rotary drilling method according to claim 43, wherein at
least two electrodes are incorporated in the drill bit.
47. The rotary drilling method according to claim 43, further
comprising excavating the micro-cracked rock lattice or matrix.
48. The rotary drilling method according to claim 43, wherein the
method is adapted for tunneling, and the drill bit is a rotary
tunnel excavator.
Description
INTRODUCTION
[0001] The present invention concerns a rotary drilling system and
a method for drilling a borehole in inhomogeneous and/or hard rock
formations.
BACKGROUND OF THE INVENTION
[0002] Rotary drilling is generally used today for drilling of deep
wells for e.g. oil, gas, mining and geothermal energy exploration
and excavation. In the resent year, PDC (Polycrystalline Diamond
Compact) bits have been the fastest developing drilling bit
technology, delivered in a large variety of different shapes and
sizes, mainly optimized to rock types and well diameter size.
Whenever possible it is the preferred bit choice for any drilling.
For high temperature and/or high pressure environments they also
have a clear benefit to many other drill bit concepts due to no
moving parts. However, a major disadvantage by PDC bits is their
inability to drill efficiently in inhomogeneous (soft-hard) rock
formations, due to large wear from dysfunctional vibrations (bit
impact wear) and abrasive wear. Due to similar stability issues,
they have neither been suited for large well diameters. When
drilling in rock formations, the friction between the drill bit
under rotation and the rock formation will vary also depending on
the rock properties, e.g. hardness, porosity etc. This friction is
experienced as a resistance on the drill bit by the rock formation.
Drilling in inhomogeneous or hard rock formation results in highly
varying resistances experienced by the drill bit during drilling. A
PDC bit tends to create stick-slip, caused when cutters teeth are
stalling in hard rock due to excessive depth of cut when coming
from a softer to a harder rock formation. The consequent vibrations
are potentially severe when the drill string has accumulated enough
torque to break the cutters loose and the drill string up-winds.
Stick-slip is the root cause of many costly and time consuming
problems in drilling operations; vibration related equipment
failure, drill string failure, bit impact damage and slow rate of
penetration (ROP). These technical obstacles are being
progressively addressed, e.g. by new bit designs, new hybrid bit
designs, shock-absorbers above the bit (mechanical decrease of bit
torque), or addition of a torsional impact hammer function to the
bit in order to provide additional torsional energy to assist in
fracturing the formation. Similar problems may more or less also be
experienced by other rotary drill bits as e.g. roller cone bits,
hybrid roller cone--PDC bits, and cutter disks in rotary tunnel
excavators. Drilling by an electro pulse boring (EPB) method is
well known and has been described by e.g. V. F. Vajor et. al. in
"Physics Vol. 4" of Tomsk Polytechnic University (Russia) 1996.
Different solutions for EPB drilling methods and equipment are
given in U.S. Pat. No. 7,784,563, U.S. Pat. No. 7,530,460 and U.S.
Pat. No. 8,109,345, including combinations of electrodes for
electro pulsing with mechanical cutters on the drill-head. However,
in the mentioned patents, the electro pulse boring (EPB) is set to
be the main excavation method throughout the drilling processes,
either by general fracturing (making cutter bits) of the rock in
front of the drill head or by fracturing the surrounding rock
material to facilitate drilling in the direction of the directed
electric energy.
SUMMARY OF THE INVENTION
[0003] The invention solves or at least alleviates the problems by
the prior art drilling systems.
[0004] In a first aspect, the present invention relates to a rotary
drilling system for drilling a borehole in inhomogeneous and/or
hard rock formations. The system comprises a rotary drill bit.
Furthermore, the system comprises at least two electrodes. Said
electrodes are arranged for pulsing therebetween of at least one
high voltage electro pulse. Said at least one high voltage electro
pulse is generated in response to a detected resistance on the
drill bit from a rock formation in front of the drill bit while
rotating, in order to create small/micro-cracks in the rock
formation.
[0005] The electrodes may be incorporated in the rotary drill bit.
The at least one high voltage electro pulse may be generated when
the detected resistance of the drill bit exceeds a predetermined
limit under rotary drilling. The predetermined resistance limit
under rotation is determined based on a number of parameters e.g.
the hardness of the rock formation, the drilling equipment and the
drill bit, and may vary when pre-detected devices are used. The
rotary drilling system may further comprise at least one sensor
arranged in the drill bit for detecting the resistance on the drill
bit from the rock formation. Alternatively, at least one sensor may
be arranged in the drilling system for detecting the resistance on
the drill bit from the rock formation. In a further embodiment, the
rotary drilling system may further comprise a radar or sonar for
pre-detecting the resistance on the drill bit from the rock
formation.
[0006] Further, an electro pulse device may be connected to said
electrodes and adapted for generating said at least one high
voltage electro pulse. A sensing device may be arranged for
detecting the resistance to a drill bit from the rock formation in
front of the drill bit under rotary drilling. The system may
include an electronic switch for electro pulsing. The system may
further include at least one of: a capacitor, a rectifier and a
transformer of low to high voltage and/or current. The system may
further include an electro pulse device for controlling and
generation of the high voltage electrode pulses. The electronic
switch may form part of the electro pulse device. The electro pulse
device may further comprise at least one of: a capacitor, a
rectifier and a transformer of low to high voltage and/or
current.
[0007] The rotary drilling system may further comprise an
electrical source comprising at least one of: a battery pack or
batteries, a mud driven generator, water driven generator, a
compressed air generator, a rotary drill string driven generator,
and cables to surface. The rotary drilling system may comprise a
drilling assembly. The rotary drill bit may be arranged in the
drilling assembly. In an embodiment, the electro pulse device may
be arranged in the drilling assembly. The drill bit may further
comprise at least one of: teeth, scrapers and cutter disks, and
wherein said at least two electrodes are incorporated in at least
one of: the drill bit itself, the teeth, the scrapers and the
cutter disks.
[0008] The system may be adapted for tunneling, and the drill bit
may then be a rotary tunnel excavator.
[0009] In a further aspect, the invention provides a rotary
drilling method for drilling a borehole in inhomogeneous and/or
hard rock formations. The method comprising rotary drilling of a
borehole using a rotary drill bit, pulsing between at least two
electrodes of at least one high voltage electro pulse, wherein said
at least one high voltage electro pulse is generated in response to
a resistance on the drill bit from a rock formation in front of the
drill bit while rotating, creating small/micro-cracks in the rock
formation.
[0010] The at least two electrodes may be incorporated in the drill
bit. The method may further comprise generating said at least one
high voltage electro pulse when the detected resistance on the
drill bit exceeds a predetermined limit under rotary drilling. The
detected resistance may be in the form of a detected torque on the
drill bit from the rock formation. Detection of the resistance may
be pre-detected using a suited detecting device in the drill bit or
drilling assembly. The generation of said at least one high voltage
electro pulse may be performed or initiated when the detected
resistance on the drill bit exceeds a predetermined limit under
rotary drilling, or by a signal from the device pre-detecting
resistance. The predetermined resistance limit or torque limit
under rotary drilling may be determined based on a number for
factors, e.g. rock formation hardness, the equipment and drill bit
used, and may vary by pre-detecting the resistance from rock
formation. Said at least one high voltage electro pulse may have a
value of about 100 kV or more.
[0011] The method may further comprise excavating the
small/micro-cracked rock lattice or matrix. The method may further
be adapted for tunneling, and the drill bit may then be a rotary
tunnel excavator.
[0012] In general, the present invention provides a technology
system that "softens up" the rock in front of a rotary drill bit by
formation of small/micro-cracks in the rock lattice when the
resistance on the drill bit or drill bit teeth/cutters exceeds, or
are to exceed, a given limit while rotary drilling. The rock in
front of the rotary drill bit is "softened up" by one or more
short-duration, high voltage electro pulse(s) given through
separate electrodes in the rotary drill bit, causing
small/micro-cracks in the rock formation between and/or around the
electrodes. The small/micro-cracks in the rock lattice will avoid
stick slip, high torque and abrasive wear of any rotary drill bit,
while keeping an even and high rate of penetration. By "softening
up" the rock formation with the high voltage electro pulse(s) when
needed, the drill bit is experiencing almost the same resistance
from the rock formation all the time during drilling, regardless of
the properties of the rock formation. This enables maintaining a
constant or little varying rotational speed of the drill bit
resulting. This results in an efficient drilling process also
reducing risks for damage on drilling equipment. The "soften up" of
the rock formation in front of the rotary drill bit in the present
invention may only be activated when needed based on the detected
resistance on the drill bit. The electro pulsing in the present
invention is only used for forming small/micro-cracks in the rock
formation in front of the drill bit and not for cracking of the
rock formation for rock bits. Cracking of the rock formation for
rock bits are used when drilling with an electro pulse method as
the main drilling method. The present invention, which activates
the high voltage electro pulse(s) only when needed based on the
detected resistance on the drill bit, keeps the total energy demand
to a fraction of what is usually needed for either the rotary
drilling bit technology or electro pulsing drilling used
separately.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 illustrates a rotary drilling system according to an
embodiment of the present invention,
[0014] FIG. 2-4 are showing steps of the principle for "softening
up" the rock in front of a rotary drill bit by small
cracks/micro-cracks according to the present invention,
[0015] FIG. 5 illustrates another rotary drilling system according
to another embodiment of the present invention.
DETAILED DESCRIPTION
[0016] In the following description, details are set forth to
provide an understanding of the present invention. However, it will
be understood by those of ordinary skill in the art that the
present invention may be practiced without these details and that
numerous variations or modifications from the described embodiment
may be possible.
[0017] The present invention provides a system and a method for
softening up the rock formation in front of a rotary drill bit by
creation of small/micro-cracks in the rock lattice or matrix when
the resistance on the drill bit is to, or exceeds a predetermined
limit while rotary drilling. This enables efficient drilling with
approximately constant rotational speed on the drill bit as the
resistance experienced by the drill bit due to friction between the
rotating drill bit and the rock formation is maintained about a
same level throughout the drilling process.
[0018] A rotary drilling system 10 according to an embodiment of
the present invention, is shown in FIG. 1. The system 10 comprises
a drilling assembly 11 used to form a borehole 12, e.g. a wellbore.
The wellbore may be drilled in any direction but usually, but not
restricted thereto, from a surface into any desired formation. The
drilling assembly 11 may be based on any standard rotary drilling
technology. The rotary drilling assembly 11 and the rotary drilling
system 10 may be selected from any known rotary drilling system and
support systems including any known equipment, methods, and
procedures known to anyone skilled in the art of rotary
drilling.
[0019] In front of the drilling assembly 11 there is a rotary drill
bit 20. At least two electrodes are arranged for pulsing between
said electrodes of at least one high voltage electro pulse (41).
The at least two electrodes (21, 22, 23) may be incorporated in the
rotary drill bit (20). The body of rotary drill bit (20) may also
in itself be an electrode. The at least one high voltage electro
pulse (41) (illustrated in FIG. 2) is generated in response to a
detected resistance on the drill bit (20) from a rock formation
(40) in front of the drill bit (20) while rotating. The at least
one high voltage electro pulse (41) creates small/micro-cracks (45)
in the rock formation (40). The at least one high voltage electro
pulse (41) is generated when the detected resistance on the drill
bit (20) under rotary drilling exceeds a predetermined limit. The
predetermined resistance limit under rotation is determined based
on a number of parameters e.g. the hardness of the rock formation
to be drilled, the drilling equipment used and the drill bit
used.
[0020] The rotary drill bit 20 may be provided with drill bit teeth
21 and/or scrapers 22 for excavation of the rock formation in front
of the drill bit 20. The bit teeth 21 or scrapers 22 on the drill
bit 20 may also in an embodiment include the at least one
electrodes 21, 22 for high voltage electro pulsing. The drill bit
20 may also include separate electrodes 23 or be an electrode in
itself. The electrodes 21, 22 and/or 23 may be of any suited
material and placed at any suited place on the drill bit 20 in
order to efficiently "soften up" (create small/micro-cracks in) the
rock in front of the drill bit 20 by pulsing of high voltage
current between the at least two electrodes 21, 22, 23 and/or the
drill bit itself. The voltage used for the pulsing between said at
least two electrodes 21, 22, 23 and/or the drill bit itself, may be
of any high voltage. The at least one high voltage electro pulse
may have a value of about 100 kV or more. Drill bit 20 may contain
any device for injection of insulating drilling fluid for the
electro pulsing, if needed. Other drill-bits, equipped with or
without the present invention with drill-bit 20 in assembly 11 may
be used in other places along the drilling assembly system 10, as
e.g. reamers for widening the borehole 12.
[0021] Electrical connections to the electrodes 21, 22, 23, and or
the drill bit 20 itself, may be incorporated in the drill bit 20 in
any suitable way. The electrical connections may further be
connected to an electric switch 35 in the drilling assembly 11 by
any suitable means. The electric switch 35 for electro pulsing may
be of any kind e.g. an electronic switch or a mechanical switch,
generating high voltage electric pulses at given value and
frequency. The switch 35 will only be operating when needed for the
drilling purposes. The switch 35 may be engaged or triggered in
response to the measured or pre-detected resistance on the drill
bit (20) from a rock formation (40), from the resistance sensing
device 30 or detecting device 31. The resistance on the drill bit
(20) from a rock formation (40) may be detected by a resistance
sensing device (30), or pre-detected by a detecting device (31).
The resistance sensing device 30 measures the resistance (force) on
the drill bit 20 from the rock formation in front of the drill bit
20, while the drill bit 20 is rotating. The resistance sensing
device 30 may e.g. be in the form of a mechanical (e.g. spring
compression), electronic or any combinations thereof sensor(s)
arranged in the drill bit itself, or as a mechanical or electronic
torque sensing device detecting the torque on the drill bit 20
arranged in the drilling assembly 11. The resistance sensing device
30 may be arranged on the drill bit 20, directly behind the drill
bit 20, or in other places on the drilling assembly 11, or rotary
drilling system 10. The resistance sensing device 30 may also be of
any other suitable kind. When the resistance sensing device 30
detects a resistance experienced by the drill bit 20 due to the
rock formation in front of the drill bit, exceeding a the
predetermined value/limit, the switch 35 is triggered or engaged,
and the electro pulsing between the electrodes 21, 22, 23, and or
the drill bit 20 itself, starts. The at least one high voltage
electro pulse 40 is generated in response to the detected torque on
the drill bit 20.
[0022] Resistance to drill bit 20 may alternatively, or in parallel
to resistance device 30, be pre-detected by a detecting device 31.
When pre-detecting resistance from the rock formation 40 in front
of the drill bit 20 exceeds a predetermined value/limit, electro
pulses 41 between the electrodes 21, 22, 23 and/or the drill bit 20
itself, may be engaged by electronic switch 35 shortly before or
simultaneously as the rotary drill bit 20 engage harder rock
formation. The detecting device 31 may be of any suited kind (e.g.
radar or sonar), and may detect rock properties in front of the
drill bit 20 by any suited means, e.g. by acoustic or electronic
signals or by electric resistance between electrodes 21, 22 and/or
23, and may be integrated in drill bit 20, directly behind the
drill bit 20, or in any other places on the drilling assembly
11.
[0023] The resistance sensing device 30 and/or detecting device 31,
and the electronic switch 35 may be arranged together as an
integrated unit.
[0024] The high voltage electro pulses supplied to the electrodes
21, 22, 23 and or the drill bit 20 itself, through switch 35 may
e.g. be energized from a capacitor(s) 36 in the drilling assembly
11. Energy may be supplied to the capacitor(s) 36 by an internal
energy supply in the drilling assembly 11 or trough electric cables
from the surface of the borehole 12. The drilling assembly 11 may
also include a rectifier or transformer of low to high voltage
and/or current. The internal energy supply may be provided by an
electrical source 37, including but not limited to e.g. batteries
or a battery pack. The batteries/battery pack 37 may also include
or be substituted by e.g. any of a mud driven generator, a water
driven generator, a compressed air generator, or a rotary drill
string generator.
[0025] In an embodiment a high voltage electro pulse device may
comprise the switch 35 for controlling and/or initiating the high
voltage electro pulsing. The high voltage electro pulse device may
further comprise at least one of: the capacitor 36, rectifier and
transformer of low to high voltage and/or current. All or some
parts of the high voltage electro pulse device can be arranged in
the drilling assembly 11.
[0026] In principle, the electro pulse devices 21, 22, 23, 30, 31,
35, 36, and 37 in the drilling assembly 11 of the present invention
operate independently of any other parts or operations of the
rotary drilling system 10 when needed for efficient drilling. In
any failure of the electro pulse functions in the system of the
present invention, the remaining rotary drilling system of the
drilling assembly system 10 will perform drilling as efficient as
an equal rotary drilling system without the present invention.
[0027] The principle of "soften up" the rock in front of a rotary
drill bit by small/micro-cracks in the rock lattice when the torque
of the drill bit teeth/cutters, detected by sensing device 30,
exceeds a given limit/value while drilling are illustrated in FIG.
2, FIG. 3, and FIG. 4. Reference numbers referred to below, but not
shown in FIG. 2, FIG. 3, and FIG. 4, are shown in FIG. 1. FIG. 2
illustrates that the cutter teeth 21 or scrapers 22 of the drill
bit 20 hit a hard rock formation 40, resulting in a resistance
experienced by the cutter teeth 21 or scrapers 22 from the rock
formation that exceeds the limit for the sensing device 30. The
sensing device 30, thus engages the switch 35. One or more short
high voltage electro pulse(s) 41 is/are then generated through the
rock matrix 40 as illustrated in FIG. 2. After the electro
pulse(s), the lattice of the rock formation 40 will contain
internal small/micro-cracks 45 as illustrated in FIG. 3. The force
from the teeth 21 or scrapers 22 in the drill bit 20 that is now
required to excavate the rock matrix 40, which now contain
small/micro-cracks 45, will be less than the predetermined limit
set for the sensing device 30. The small/micro-cracked rock lattice
40 will then be excavated as shown in FIG. 4. When the rock lattice
with small/micro-cracks has been excavated, the electro pulse
process may be reinitiated as the teeth 21 or scrapers 22 of the
drill bit 20 again hit hard rock formation 40 resulting in a
detected resistance above the predetermined value for the formation
to be drilled, as illustrated in FIG. 2. During drilling, high
voltage electro pulses will be generated when resistance values
above the predetermined limit are sensed by the sensors or sensing
device 30. This enables efficient drilling with approximately
constant rotational speed on the drill bit as the resistance
experienced by the drill bit due to friction between the rotating
drill bit and the rock formation is maintained about a same level
throughout the drilling process. How often the high voltage electro
pulses are generated, depends e.g. on the predetermined limit set
and the properties of the rock formation.
[0028] The principle of "soften up" the rock in front of a rotary
drill bit by small/micro-cracks in the rock lattice when expected
increased resistance from rock formation 40 to the drill bit
teeth/cutters is pre-detected by detecting device 31, exceeds a
given limit/value while drilling are also illustrated in FIG. 2,
FIG. 3, and FIG. 4. Reference numbers referred to below, but not
shown in FIG. 2, FIG. 3, and FIG. 4, are shown in FIG. 1. FIG. 2
illustrates that the cutter teeth 21 or scrapers 22 of the drill
bit 20 is about to hit a hard rock formation 40. The detecting
device 31, thus engages the switch 35. One or more short high
voltage electro pulse(s) 41 is/are then generated through the rock
matrix 40 as illustrated in FIG. 2. After the electro pulse(s), the
lattice of the rock formation 40 will contain internal
small/micro-cracks 45 as illustrated in FIG. 3. The force from the
teeth 21 or scrapers 22 in the drill bit 20 that is now required to
excavate the rock matrix 40, which now contain small/micro-cracks
45, will be less than the predetermined limit set for the detecting
device 31. The small/micro-cracked rock lattice 40 will then be
excavated as shown in FIG. 4. When the rock lattice with
small/micro-cracks has been excavated, the electro pulse process
may be reinitiated as the teeth 21 or scrapers 22 of the drill bit
20 again are about to hit hard rock formation 40 having a
resistance above the predetermined value for the formation to be
drilled, as illustrated in FIG. 2. During drilling, high voltage
electro pulses may be generated when pre-detected resistance values
are above the predetermined limits sensed by detecting device 31.
This enables efficient drilling with approximately constant
rotational speed on the drill bit as the resistance experienced by
the drill bit due to friction between the rotating drill bit and
the rock formation is maintained about a same level throughout the
drilling process. How often the high voltage electro pulses are
generated, depends e.g. on the predetermined limits set from the
drilling equipment and the properties of the rock formation.
[0029] The amount of electric current needed for drilling a given
amount of hard rock formation as illustrated in FIG. 2 is depending
on the properties of the rock lattice 40. This amount of electric
current is estimated to be considerably less than when drilled by
electro pulse drilling as the main drilling method. The use of
electro pulsing in the present invention only provides formation of
small/micro-cracks in a rock lattice upon mechanical
drilling/excavation and it does not require large cracks that chip
off large bits from the rock lattice as required when using single
electro pulse methods for excavating a borehole. The amount of
electric current is estimated to be in the order of 50% or less. A
considerable reduction of the amount of electric current/energy may
e.g. enable drilling assemblies having internal energy supplies
lasting the entire life time of the drill bit itself.
[0030] The principle of the present invention may in a similar way
be used in any other system for rotary drilling of inhomogeneous
and/or hard rock formations. An example, but not restricted
thereto, is for tunneling as shown in FIG. 5. Electrodes may be
incorporated in cutter disks 51 and/or scrapers 52, as separate
electrodes 53, and/or as the drill head of 50 itself, in a rotary
tunnel excavator 50. The electro pulses are only triggered when
needed due to the detected resistance (may be measured or
pre-detected) from the rock formation on the cutter disks 51 or
scrapers 52 at rotation of the rotary tunnel excavator 50. Electro
pulsing is provided by the electrodes in a similar manner as
explained for the embodiment shown in FIG. 1, and illustrated in
FIGS. 2, 3 and 4. Small/micro-cracks are thus formed in the rock
formation prior to excavation by the cutter disks 51 or scrapers
52.
[0031] The present invention concerns also a method for rotary
drilling of a borehole 12 in inhomogeneous or hard rock formations.
A rotary drill bit 20 us used for rotary drilling of the borehole
12. During drilling a resistance on the drill bit from the
formation is detected. When the detected resistance exceeds a
predetermined value, at least one high voltage electro pulse 41 is
generated between the at least two electrodes creating
small/micro-cracks 45 in the rock formation 40. Monitoring of the
resistance during drilling may be performed continuously, almost
continuously or at specific intervals.
[0032] The a least two electrodes 21, 22, 23, 51, 52, 53 may be
incorporated in the drill bit 20. One of the electrodes may also be
the drill bit itself. The rotary drill bit can also be a rotary
tunnel excavator 50 as shown in FIG. 5. Detecting the resistance
may be performed by detecting a torque on the drill bit 20 from the
rock formation. In an alternative embodiment, detecting the
resistance may be performed by a radar or sonar pre-detecting the
resistance on the drill bit 20 from the rock formation 40.
[0033] The drill bit, which is rotating at its intended rotational
speed during the measurement and high voltage pulse generation
procedure, excavates the small/micro-cracked rock lattice or matrix
40. When the measured or pre-detected resistance again exceeds the
predetermined value, this again results in the generation of the at
least one high voltage electro pulse 41. Monitoring of the
resistance during drilling and pulsing high voltage electro pulses
41 only when needed, ensures that the drill bit experiences about
the same resistance/force from the formation at all times during
drilling. This considerably improves and simplifies drilling in
inhomogeneous and/or hard rock formations, at the same time as the
energy consumption is considerably reduced.
[0034] The present invention may be used by any rotary drilling
method in inhomogeneous and hard rock formations. Primary use is
drilling of wellbores for oil, gas, mining and geothermal
exploration and excavation, and any tunneling with rotary equipment
for mining or any infrastructures, like but not restricted to, for
hydro power, electric cables, roads, train, and water.
[0035] Although a variety of examples and other information was
used to explain aspects within the scope of the appended claims, no
limitation of the claims should be implied based on particular
features or arrangements in such examples, as one of ordinary skill
would be able to use these examples to derive a wide variety of
implementations. Further and although some subject matter may have
been described in language specific to examples of structural
features and/or method steps, it is to be understood that the
subject matter defined in the appended claims is not necessarily
limited to these described features or acts. For example, such
functionality can be distributed differently or performed in
components other than those identified herein. Rather, the
described features and steps are disclosed as examples of
components of systems and methods within the scope of the appended
claims.
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