U.S. patent application number 12/575839 was filed with the patent office on 2010-04-15 for methods and apparatus for thermal drilling.
This patent application is currently assigned to Potter Drilling, Inc.. Invention is credited to DONALD S. DREESEN, JARED M. POTTER, ROBERT M. POTTER, THOMAS W. WIDEMAN.
Application Number | 20100089576 12/575839 |
Document ID | / |
Family ID | 41728337 |
Filed Date | 2010-04-15 |
United States Patent
Application |
20100089576 |
Kind Code |
A1 |
WIDEMAN; THOMAS W. ; et
al. |
April 15, 2010 |
Methods and Apparatus for Thermal Drilling
Abstract
Methods and apparatus for spalling a geological formation, for
example to thermally drill a wellhole, are provided. Such methods
may include providing a housing comprising a reaction chamber and a
catalyst element held within the reaction chamber, providing at
least one jet nozzle, contacting one or more unreacted fluids or
solids with the catalyst element, wherein the unreacted fluid or
solid is adapted to react over the catalyst element, thus
generating a reacted fluid, and emitting the reacted fluid through
the at least one nozzle, wherein the at least one nozzle is
directed to an excavation site within or on the geological rock
formation, thereby creating spalls and/or a reacted rock
region.
Inventors: |
WIDEMAN; THOMAS W.; (MILTON,
MA) ; POTTER; JARED M.; (REDWOOD CITY, CA) ;
DREESEN; DONALD S.; (LOS ALAMOS, NM) ; POTTER; ROBERT
M.; (RIO RANCHO, NM) |
Correspondence
Address: |
GOODWIN PROCTER LLP;PATENT ADMINISTRATOR
53 STATE STREET, EXCHANGE PLACE
BOSTON
MA
02109-2881
US
|
Assignee: |
Potter Drilling, Inc.
Redwood City
CA
|
Family ID: |
41728337 |
Appl. No.: |
12/575839 |
Filed: |
October 8, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61103859 |
Oct 8, 2008 |
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61140477 |
Dec 23, 2008 |
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61140489 |
Dec 23, 2008 |
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61140512 |
Dec 23, 2008 |
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61236958 |
Aug 26, 2009 |
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Current U.S.
Class: |
166/272.6 ;
175/15 |
Current CPC
Class: |
E21B 7/18 20130101; E21B
41/0078 20130101; E21B 10/60 20130101; E21B 10/00 20130101; E21B
7/14 20130101 |
Class at
Publication: |
166/272.6 ;
175/15 |
International
Class: |
E21B 43/241 20060101
E21B043/241; E21B 7/14 20060101 E21B007/14 |
Claims
1. A method for spalling a geological rock formation, comprising:
providing a housing comprising a reaction chamber and a catalyst
element held within the reaction chamber, and at least one jet
nozzle; contacting one or more unreacted fluids or solids with the
catalyst element, wherein the unreacted fluid or solid is adapted
to react over the catalyst element, thus generating a substantially
flameless reacted fluid; and emitting the reacted fluid through the
at least one nozzle, wherein the at least one nozzle is directed to
an excavation site within or on the geological rock formation,
thereby creating spalls and/or a reacted rock region in said
geological rock formation.
2. The method of claim 1, wherein the unreacted fluid or solid is
at a temperature of about 350.degree. C. or less.
3. The method of claim 1, wherein the reacted fluid is about
500.degree. C. to about 1100.degree. C. when formed.
4. The method of claim 3, wherein the reacted fluid is about
800.degree. C.
5. The method of claim 1, wherein the contacting occurs at a
pressure of about 1 to about 200 MPa.
6. The method of claim 1, wherein the unreacted fluid is
substantially a liquid.
7. The method of claim 1, wherein the unreacted fluid has a density
of about 1 g/cm.sup.3.
8. The method of claim 1, further comprising introducing a flow of
water or drilling mud into the excavation site.
9. The method of claim 8, wherein the flow of water or drilling mud
at least partially forms an ascending fluid stream.
10. The method of claim 9, wherein the ascending fluid stream at
least partially removes the spall.
11. The method of claim 1, further comprising heating the unreacted
fluid or solid.
12. (canceled)
13. The method of claim 1, wherein said method is capable of
producing an about 1 inch diameter borehole in said geological
formation at about 0.5 inches per minute of reacted fluid flow.
14. The method claim 1, wherein the method is capable of producing
an about 8 inch diameter borehole in said geological formation at a
rate of penetration of about 20 feet per hour or more.
15. The method of claim 1, wherein the catalyst element comprises a
transition metal chosen from: platinum, lead, silver, palladium,
nickel, iron, cobalt, copper, chromium, manganese, iridium, gold,
ruthenium and rhodium, or mixtures or oxides or nitrides or salts
thereof.
16. The method of claim 1, wherein the catalyst element comprises a
transition metal disposed on a support.
17. The method of claim 16, wherein the support comprises
alumina.
18. The method of claim 1, wherein the catalyst element is disposed
on spheres, pellets, or grains comprising alumina.
19. The method of claim 1, wherein the catalyst element has at
least about 10 m.sup.2/g surface area of catalyst.
20. The method of claim 1, wherein the catalyst element is
platinum.
21-22. (canceled)
23. The method of claim 1, wherein the unreacted fluid or solid
comprises an oxidant.
24. (canceled)
25. The method of claim 1, wherein the unreacted fluid or solid
comprises a fuel.
26-31. (canceled)
32. The method of claim 25, wherein the fuel comprises an alcohol,
an alkyl, alkenyl, alkynyl, an alkoxyalkyl, or combinations
thereof.
33. (canceled)
34. The method of claim 32, wherein the unreacted fluid comprises
an alcohol fuel chosen from methanol, ethanol, propanol, or
butanol.
35. The method of claim 33, wherein the fuel is methanol.
36. The method of claim 23, wherein the oxidant is chosen from
oxygen, peroxide, peroxy compounds, permanganate and combinations
thereof.
37. The method of claim 36 wherein the oxidant is hydrogen peroxide
or metal peroxide.
38. The method of claim 1, wherein the unreacted fluid comprises
hydrogen peroxide.
39. The method of claim 1, wherein the unreacted fluid comprises an
aqueous solution comprising about 2% to about 50% by weight
hydrogen peroxide.
40. The method of claim 1, wherein the unreacted fluid comprises
about 10% to about 20% by weight methanol or ethanol.
41. The method of claim 1, wherein the unreacted fluid comprises an
aqueous solution comprising about 20% to about 50% by weight
hydrogen peroxide and about 10% to about 20% by weight methanol or
ethanol.
42. The method of claim 1, wherein the unreacted fluid comprises an
aqueous solution comprising about 38% by weight hydrogen peroxide
and about 12% by weight methanol.
43. The method of claim 1, further comprising transporting the
unreacted fluid to the housing through one conduit.
44. The method of claim 23, wherein fuel and oxidant are
transported to the housing through the same conduit.
45. The method of claim 1, wherein the reaction generating the
substantially flameless reacted fluid is substantially
self-energized.
46-63. (canceled)
64. An apparatus for excavating a borehole in a geological
formation, comprising: a housing; a reaction chamber within the
housing; a catalyst element held within the reaction chamber; and
at least one jet nozzle in fluid communication with the reaction
chamber.
65-66. (canceled)
67. The apparatus of claim 64, wherein the catalyst element
comprises a metal catalyst bed.
68. The apparatus of claim 64, wherein the catalyst element
comprises a transition metal.
69. The apparatus of claim 64, further comprising a plurality of
jet nozzles.
70-72. (canceled)
73. The apparatus of claim 64, wherein the jet nozzle has a
diameter ranging from approximately 0.01 inches to approximately
two inches.
74. The apparatus of claim 64, wherein the jet nozzle is a center
jet nozzle or a non-rotating peripheral gap ring nozzle.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Ser. No.
61/103,859, filed Oct. 8, 2008; U.S. Ser. No. 61/140,477 filed Dec.
23, 2008; U.S. Ser. No. 61/140,489, filed Dec. 23, 2008; U.S. Ser.
No. 61/140,512, filed Dec. 23, 2008; and U.S. Ser. No. 61/236,958,
filed Aug. 26, 2009, each of which is hereby incorporated by
reference in its entirety.
FIELD
[0002] In various embodiments, this disclosure relates to methods
and apparatus for conducting processes capable of spalling or
penetrating a material such as rock. For example, the disclosed
methods may be used for preparing boreholes for geothermal energy
systems.
BACKGROUND
[0003] Drilling very deep boreholes or enhancing existing wells in
hard rock far below the earth's surface, e.g. 10,000 feet deep or
more, is inherently incompatible with traditional mechanical or
contact drilling or rock removal technologies. Low rates of
penetration, extreme bit and drill string wear, and excessive time
spent "tripping" to replace damaged or worn bits and drill string
make conventional rotary and coiled tubing drilling economically
non-viable for many deep, hard rock applications.
[0004] Several non-contact techniques have been developed for hard
rock drilling but may be effective only in shallow and/or air
filled boreholes. Most notably, air or flame jet spallation
drilling uses a hot gas or flame directed against a rock surface to
cause spalling and removal of the rock. This technique, however, is
only feasible in shallow, air-filled boreholes. To drill deeper, a
borehole must be filled with water or "mud" to provide mechanical
stability. In this environment, flames are not viable in part
because of the difficulty in generating or maintaining the required
flame under the high pressure water column. For example, the high
pressures at the bottom of deep, fluid-filled boreholes make
behavior of the flames extremely unstable and difficult to
maintain. Further, initiating combustion under these conditions is
extremely challenging and typically requires an energy source to be
provided at the bottom of the borehole. However, using an energy
source such as a spark or glow plug would require, e.g., a power
cable to be run from the surface, which is not feasible in deep
applications. Other energy sources such as flame holders are
inherently unstable, especially at such depths.
[0005] Further, most combustion reactions produce very high
temperature flames, typically 1800-3000.degree. C. or more. Such
temperatures can destroy drilling components and require careful
addition of cooling water to maintain a temperature that can be
withstood by downhole tools. In addition, such high temperatures
can melt rock (e.g., into an amorphous glass) so that the rock is
then unspallable. Even a momentary interruption in cooling water
can transform rock so that it can no longer be spalled and/or
destroy downhole components, even if a cooler temperature is
recovered. Small changes in the stand-off distance, or distance
from the combustion to the rock surface, can result in dramatic
changes in the nature of the high temperature flame impingement,
which may result in a temperature too low for spallation, or
temperatures high enough to soften or melt the rock. Such tight
tolerances for stand-off distances are difficult to control at the
bottom of a deep borehole.
[0006] Further, flame-based combustion systems require multiple
conduits for fuel, oxidant and cooling or circulating water. Other
approaches to spallation drilling such as the use of electrical
heating require sufficient power down hole. In deep drilling
operations, multiple conduits or supply of sufficient power through
cables from the surface or through transformation of energy by
hydraulic flow may not be feasible, or may be simply
impossible.
[0007] Combustion systems that require the use of gaseous oxidants,
such as air or oxygen, are also unsuitable for deep fluid filled
borehole conditions, in part because the pressures required to pump
these gases against a hydrostatic column of a fluid filled borehole
are sometimes impossible to achieve, and even if possible, have
associated safety risks.
[0008] While thermal spallation has promised to provide a solution
to deep, hard-rock drilling, no methods have been able to
adequately or feasibly provide the heat required for viable
spallation drilling deep into a water filled borehole. If the
challenge of drilling deep boreholes in hard rock is not solved,
EGS may not become the much needed clean alternative to meeting our
current and future global energy needs.
SUMMARY
[0009] The present disclosure relates, at least in part, to a
method of reducing near wellbore impedance, or reducing the
restriction to fluid flow in the immediate vicinity (e.g. 1 inch to
about 3 feet) of an existing borehole wall) by providing a
spallation system to e.g. increase the diameter of a section of an
existing borehole or well, for example a geothermal well.
[0010] For example, one aspect of the invention includes a method
for spalling a geological rock formation. The method includes
providing a housing comprising a reaction chamber and a catalyst
element held within the reaction chamber, providing at least one
jet nozzle, contacting one or more unreacted fluids or solids with
the catalyst element, wherein the catalyst element facilitates the
reaction of the unreacted fluid, thus generating a reacted fluid,
and emitting the reacted fluid through the at least one nozzle. The
at least one nozzle may be directed to an excavation site within or
on the geological rock formation, thereby creating spalls and/or a
reacted rock region.
[0011] In one embodiment, the unreacted fluid or solid is at a
temperature of about 350.degree. C. or less. In one embodiment, the
reacted fluid is about 500.degree. C. to about 1100.degree. C. when
formed. The contacting may occur at a pressure of about 1 to about
200 MPa. The unreacted fluid may be substantially a liquid.
[0012] One embodiment further includes introducing a flow of water
or drilling mud into the excavation site. One embodiment further
includes heating the unreacted fluid or solid. The reacted fluid
may interact with a heat exchanger disposed in a position capable
of heating the unreacted fluid or solid.
[0013] In one embodiment, the method is capable of producing an
about 1 inch diameter borehole in said geological formation at
about 0.5 inches per minute of reacted fluid flow. In one
embodiment, the method is capable of producing an about 8 inch
diameter borehole in said geological formation at a rate of
penetration of about 20 feet per hour or more. The flow of water or
drilling mud may at least partially form an ascending fluid stream.
The ascending fluid stream may at least partially remove the
spall.
[0014] In one embodiment, the catalyst element may include a
transition metal, such as a transition metal chosen from: platinum,
lead, silver, palladium, nickel, cobalt, copper, chromium,
manganese, iridium, gold, ruthenium and rhodium, or mixtures or
oxides or salts thereof. The transition metal may be disposed on a
support. The catalyst element may be disposed on spheres, grains,
pellets, or other appropriately configured elements comprising
alumina. The catalyst element may have at least about 10 m.sup.2/g
surface area of catalyst. The catalyst element may be heated.
[0015] In one embodiment, the unreacted fluid includes an aqueous
solution. The unreacted fluid may be a miscible fluid mixture or a
non-miscible fluid mixture. The unreacted fluid or solid may
include an oxidant. The unreacted solid may include an encapsulated
oxidant.
[0016] In one embodiment, the unreacted fluid or solid includes a
fuel. The fuel may be a carbonaceous fuel. The fuel may include
hydrocarbons. The fuel may be a liquid fuel at room temperature.
The fuel may be a hydrocarbon gas, such as methane, ethane,
propane, butane (e.g. natural gas (NG) and/or liquefied natural gas
(LNG)) at room temperature. In one embodiment, the fuel is
gasoline, diesel, kerosene, biodiesel, or alcohol. In one
embodiment, the fuel includes an alcohol, an alkyl, alkenyl,
alkynyl, an alkoxyalkyl, or combinations thereof. In one
embodiment, the fuel is an alcohol fuel. In one embodiment, the
unreacted fluid may include an alcohol fuel chosen from methanol,
ethanol, propanol, or butanol.
[0017] In one embodiment, the oxidant may be chosen from oxygen,
peroxide, permanganate and combinations thereof. In one embodiment,
the oxidant may be hydrogen peroxide or metal peroxide. In one
embodiment, the unreacted fluid may include hydrogen peroxide or
metal peroxide. The unreacted fluid may include an aqueous solution
comprising about 2% to about 35% by weight hydrogen peroxide. The
unreacted fluid may include about 10% to about 20% by weight
methanol or ethanol. The unreacted fluid may include an aqueous
solution including about 10% to about 20% by weight hydrogen
peroxide and about 10% to about 20% by weight methanol or ethanol.
In one embodiment, the unreacted fluid may have a density similar
to water.
[0018] The method may further include transporting the unreacted
fluid to the housing through at least one conduit. The fuel and
oxidant may be transported to the housing through separate
conduits, or through the same conduit.
[0019] Another aspect of the invention includes a method for
flameles sly penetrating or reacting rock. The methods includes
contacting a composition comprising an oxidant with a catalyst to
flamelessly form a reacted fluid, and directing said reacted fluid
to said rock, thereby effecting penetration of the rock and/or
forming a reacted rock region.
[0020] In one embodiment, the contacting step occurs in the
presence of a fuel. In one embodiment, the composition includes an
alcohol fuel, such as ethanol or methanol. The oxidant may include
oxygen or hydrogen peroxide.
[0021] In one embodiment, the method further includes drilling the
reacted rock region with a drill bit. The contacting may occur at
about 5,000 ft to about 40,000 ft below a surface of the earth.
[0022] Another aspect of the invention includes a method for
producing a reacted fluid flow capable of spallation of rock. The
method includes contacting an unreacted fluid with a catalyst
element in the presence of an oxidant thereby generating a reacted
fluid, and emitting the reacted fluid through a nozzle, thereby
producing the reacted fluid flow capable of spalling rock.
[0023] In one embodiment, the reacted fluid is at a temperature of
about 500.degree. C. to about 900.degree. C. In one embodiment, the
reacted fluid produces a heat flux of about 0.1 to about 10
MW/m.sup.2 when said reacted fluid is in contact with the rock. The
unreacted fluid may be substantially a liquid. The reacted fluid
may be substantially a gas or a supercritical fluid. The unreacted
fluid may include a fuel. The unreacted fluid may further include
an aqueous solution. The unreacted fluid may be a miscible fluid
mixture. The unreacted fluid may include an alcohol, such as an
alcohol chosen from methanol, ethanol, propanol or butanol. In one
embodiment, the oxidant may be oxygen. In one embodiment, the
oxidant may be a peroxide. In one embodiment, the oxidant is
hydrogen peroxide. In one embodiment, the unreacted fluid comprises
the oxidant. In one embodiment, the catalyst comprises a transition
metal, such as a transition metal chosen from silver, lead, gold,
platinum, palladium, or nickel. The reacted fluid may include
water.
[0024] Another aspect of the invention includes an apparatus for
excavating a borehole in a geological formation. The apparatus
includes a housing, a reaction chamber within the housing, a
catalyst element held within the reaction chamber, and at least one
jet nozzle in fluid communication with the reaction chamber.
[0025] In one embodiment, the apparatus further includes at least
one conduit in fluid communication with the reaction chamber and
adapted to transport an aqueous solution to the reaction chamber.
In one embodiment, the apparatus further includes a heat exchanger
positioned above the reaction chamber, wherein the heat exchanger
is adapted to transfer heat between the aqueous solution being
transported within the at least one conduit and a fluid passing
around the heat exchanger. In one embodiment, the catalyst element
may include a metal catalyst bed. The catalyst element may include
a transition metal.
[0026] In one embodiment, the apparatus may further include a
single jet nozzle, or a plurality of jet nozzles. The at least one
jet nozzle may be directed substantially along an elongate axis of
the apparatus. At least one of the plurality of jet nozzles may be
directed at an acute angle to an elongate axis of the apparatus.
The at least one jet nozzle may have a diameter ranging from
approximately 0.01 inches to approximately two inches. The single
jet nozzle may be a center jet nozzle or a non-rotating peripheral
gap ring nozzle.
[0027] These and other objects, along with advantages and features
of the present invention herein disclosed, will become more
apparent through reference to the following description, the
accompanying drawings, and the claims. Furthermore, it is to be
understood that the features of the various embodiments described
herein are not mutually exclusive and can exist in various
combinations and permutations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] In the drawings, like reference characters generally refer
to the same parts throughout the different views. Also, the
drawings are not necessarily to scale, emphasis instead generally
being placed upon illustrating the principles of the invention. In
the following description, various embodiments of the present
invention are described with reference to the following drawings,
in which:
[0029] FIGS. 1A-1E are schematic views of a spallation process, in
accordance with one embodiment of the invention;
[0030] FIG. 2A is a schematic top view of a drill head for a
thermal spallation system, in accordance with one embodiment of the
invention;
[0031] FIG. 2B is a sectional side view the drill head of FIG.
2A;
[0032] FIG. 2C is a schematic bottom view of the drill head of FIG.
2A;
[0033] FIG. 2D is an end view of the drill head of FIG. 2A
positioned against a rock interface;
[0034] FIG. 2E is a side view of the drill head of FIG. 2A
positioned against a rock interface;
[0035] FIG. 3A is a schematic side view of a thermal-abrasive
reaming system, in accordance with one embodiment of the
invention;
[0036] FIG. 3B is a schematic sectional side view of the nozzle and
reamer of the thermal spallation-abrasive reaming system of FIG.
3A;
[0037] FIG. 4A is a schematic side view of a composite thermal
spallation and tricone roller bit drill system, in accordance with
one embodiment of the invention;
[0038] FIG. 4B is a sectional side view of the nozzle and tricone
drill bit for the thermal spallation and tricone roller bit drill
system of FIG. 4A;
[0039] FIG. 4C is an end view of the nozzle and tricone drill bit
of FIG. 4B;
[0040] FIG. 5 is a schematic sectional perspective view of a
spallation system and PDC drag drill bit, in accordance with one
embodiment of the invention;
[0041] FIG. 6A is a schematic sectional side view of a thermal
spallation system and a milling/abrasive drill bit, along with an
induction type heater system, in accordance with one embodiment of
the invention;
[0042] FIG. 6B is an end view of the thermal spallation system and
a milling/abrasive drill bit of FIG. 6A;
[0043] FIG. 7A is a schematic side view of a spallation system and
hammer drill bit, in accordance with one embodiment of the
invention;
[0044] FIG. 7B is an end view of the spallation system and hammer
bit of FIG. 7A;
[0045] FIG. 8 is a graphical representation of thermal effects on
the strength of plagioclase feldspar, in accordance with one
embodiment of the invention;
[0046] FIG. 9 is a graphical representation of differential stress
vs. strain on natural quartz crystals at various temperatures both
dry and water saturated, in accordance with one embodiment of the
invention;
[0047] FIG. 10 is a graphical representation of an experimentally
determined melting curve for water saturated granite mixture vs.
pressure, in accordance with one embodiment of the invention;
[0048] FIG. 11 is a sectional side view of the convergent radial
flow reactor;
[0049] FIGS. 12A and 12B are schematics of convergent and divergent
radial flow reactors;
[0050] FIGS. 13A, 13B, and 13C show views of a rock core
confinement system for laboratory drilling demonstrations;
[0051] FIG. 14 is an image of a cross section of a
24''.times.24''.times.36'' Sierra White Granite block after being
drilled, in accordance with one embodiment of the invention;
[0052] FIG. 15 shows a graph of wear rates of PDC and TSP cutters
against hard granite as a function of temperature;
[0053] FIG. 16 shows a graph of the relative shear strength as a
function of the ultimate temperature for two example granites;
[0054] FIG. 17 is an image of a 4'' diameter, 6'' long, rock core
with a drill head therein, in accordance with one embodiment of the
invention;
[0055] FIG. 18 is an image of a 4'' diameter, 6'' long rock core
where an initial predrilled borehole (represented by the dotted
line) is opened, increasing the borehole diameter and producing a
thermally affected zone, in accordance with one embodiment of the
invention;
[0056] FIG. 19 A-D show schematic views of a fracture intersecting
a wellbore: (A) with high near wellbore impedance; (B) globally
opened; (C) to reduce the near wellbore impedance; and (D) with the
fracture preferentially opened to produce to reduce near wellbore
impedance;
[0057] FIG. 20 is an image of a slabbed Granodiorite sample
subjected to spallation drilling followed by a dye penetrant which
indicates a zone of microfracturing and several distinct linear
fracture zones emanating perpendicular to the borehole region, in
accordance with one embodiment of the invention; and
[0058] FIG. 21 shows a graph of spalled particle size distribution
for an example thermal spallation drilling system.
DESCRIPTION
[0059] The present disclosure relates, at least in part, to methods
and systems for use in spallation, fracturing, loosening, or
excavation of material such as rock, for example, methods of making
or excavating boreholes, and/or enlarging existing boreholes. Such
methods include using a disclosed working fluid or reacted fluid,
e.g. a working fluid capable of producing a heat flux of about 0.1
to about 50 MW/m.sup.2 when in contact with rock.
Methods
[0060] For example, provided herein are systems and methods that
may be capable of creating 20 feet of an e.g., 8 inch borehole in
about hour, or 20 feet of a 4 inch borehole in about an hour or
less, or about a 0.2 inches of .about.1 inch borehole in about 4
minutes. Also provided herein are systems or methods for opening a
length of existing borehole, e.g. with an original diameter of that
may be as small as 4 inches, to a final diameter of about 36 inches
or more, which in some embodiments may be accomplished in 12-24
hours, or days. Contemplated systems and methods may be used to
create boreholes, shafts, caverns or tunnels in a target material
such as crystalline rock material, silicate rock, basalt, granite,
sandstone, limestone, peridotite, or any other rocky material.
Disclosed systems and methods may also be used for producing
multilaterals from an existing borehole, which in turn may be
opened. In certain embodiments, disclosed systems and methods may
be used, for example, to create vertical boreholes, horizontal
boreholes, deviated boreholes, angled boreholes, larger diameter
boreholes, curved boreholes, or any combination thereof. Also
provided herein are systems and methods that may spall rock at a
rate of about 100 ft.sup.3/hour or more, which may be useful for
example for the creation of tunnels, caverns, mineshafts, and the
like.
[0061] For example, also provided herein are methods to reduce
existing wellbore impedance and/or improve production of existing
wells (e.g. EGS wells). Such methods may include, for example,
increasing the diameter of at least portions (e.g. a working,
producing, or production zone or portion--one or more sections that
are typically significantly downhole, may be uncased, or cased with
slotted or perforated casing, and where substantially most of the
energy output or fluid production occurs, for example, in an EGS
well) of an existing wellbore.
[0062] The systems and methods disclosed herein may include sensors
such as gyroscopes, magnetometers, and/or inclinometers, for
monitoring the orientation of the drilling systems. Systems and
methods may also include at least one of temperature and/or
pressure sensors, flow sensors, natural rock gamma ray sensors,
resistivity/conductivity sensors and rock and/or pore space density
sensors, to identify rock properties and hydrologic conditions that
may influence the desired trajectory, for example, of the
borehole/drill hole. For example, sensors may be provided to
selectively monitor flow entry points and/or temperature changes of
fluids that will influence the target which influences desired
direction of drilling or hole opening. In one embodiment, the
methods and systems described herein provide for deep borehole
drilling, for example from approximately 1,000 feet to about 50,000
feet, or 5,000 feet to about 50,000 feet, or about 10,000 feet to
approximately 50,000 feet below the surface, or more. In other
embodiments, methods and systems described herein provide for hole
openings in e.g. production zones of a wellbore. One or more
wellbore diameters may be increased by about 0.1 to 10 feet or
more. In other embodiments, for example, substantially
perpendicular holes relative to a production zone of an existing
well can be formed that may be about 1 to about 1,000 feet or more
in length. Also contemplated herein are the formation of
parallel/collinear slots, multilaterals (similar to branching of a
tree) or horizontal deviations, which may be used to increase
production from e.g. a single, substantially vertical wellbore.
These multilaterals may be further hole opened.
[0063] For example, provided herein are systems and/or methods that
may be configured for drilling boreholes in hard rock for
geothermal, enhanced or engineered geothermal systems (EGS), and/or
oil and gas applications, natural gas production or enhanced oil
recovery or unconventional oil production, using a disclosed
working fluid to spall rock. However, the systems and methods
described herein may also be used for other applications such as,
but not limited to, exploratory boreholes, test boreholes,
boreholes for scientific study or resource assessment, quarrying,
ground source heat pumps, water wells, resource mining
(conventional or solution mining), combined HDR (hot dry rock)
solution mining, gas or liquefied natural gas (LNG) applications,
CO.sub.2 sequestration capture or storage, storage of water or
other resources, nuclear waste disposal, thermal or supercritical
oxidations of wastes, downhole chemical processing and/or tunnel or
cavern creation (new or in conjunction with an existing well).
[0064] For example, methods are provided herein for increasing the
diameter along a section of an existing geothermal well or
borehole, for example, methods are provided for creating
substantially axial (i.e. substantially parallel/collinear with the
wellbore) slots along the length of a working portion or production
zone of an existing borehole, methods of perforating an existing
borehole (e.g. creating holes substantially perpendicular to the
wellbore); methods for creating radial branches off of and/or
stemming from an existing borehole (e.g. intersecting a production
zone); and/or methods of creating one, two, or a plurality of
substantially axial slots along a length of an existing borehole,
wherein the methods include using a disclosed working fluid. The
axial slots or radial branches may be oriented, in some
embodiments, so as to intersect the greatest number of fractures or
to be facing the injection well. Also contemplated herein are
methods for substantially expanding the diameter of a wellbore
along a given length, or for removing a portion of material by
spallation, whereby the spallation induces further fracturing,
collapse or break-out of the rock wall.
[0065] Methods contemplated herein also include hydrothermal
reactions, explosions or detonations, which take place in the
wellbore or fractures for only a finite period. For example, an
unreacted fluid may be pumped into the wellbore and/or allowed to
penetrate the fractures. A reaction may then be initiated by e.g. a
catalyst "pill" sent down the drill string or by exposing a sample
of catalyst in a downhole tool, initiating a hydrothermal reaction
and causing spallation in fractures and macrofracturing in
wellbore.
[0066] Alternatively, the wellbore may be cooled by traditional
means of circulating fluids. An unreacted fluid which has a Self
Accelerating Decomposition Temperature (SADT)--a temperature at
which reaction runs away and propagates--that is below the
formation temperature may then be injected into the wellbore and
fractures. As the formation is allowed to recover from the cooling
treatment, the reaction may initiate, with or without the use of a
catalyst.
[0067] In some embodiments, two or more components of the unreacted
fluid, e.g. fuel and oxidant may be delivered through the conduit
in "slugs" so that there is no chance of a premature reaction in
the conduit. Once the desired mixture of e.g. fuel and oxidant have
been created in the wellbore, the reaction can be initiated by e.g.
a catalyst pill, exposing a catalyst in the tool, auto-initiated,
or by allowing the wellbore to warm. Since high concentrations of
e.g. fuel and oxidant can be delivered by this "slug" flow, it may
be possible to produce an unreacted fluid mixture e.g. above the
detonation limits which allows for propagation of the reaction and
shockwave throughout the producing zone and/or fractures, creating
spallation and fracturing.
[0068] In general, as discussed herein, "spallation" refers to the
breaking away of surface fragments of a material, e.g. rock "spall"
refers to the fragments of material formed by a process of
spallation. A thermal spallation process can refer to a spallation
process that uses a working fluid other than air, such as working
fluid that includes water (e.g., hydrothermal spallation resulting
from the creation of high temperature water from hydrothermal
oxidation reaction as disclosed herein), water or oil based
drilling muds, supercritical fluids, and the like.
[0069] Disclosed herein, in an embodiment, is a spallation method
that may use a means, for example, a hydrothermal means, a
flameless means and/or a self-energized means, e.g., a means that
does not use a separate energy source to initiate or generate a
chemical reaction to produce a heated, working fluid and/or a means
that does not include a flame. For example, a flameless chemical
means may include a reaction such as a hydrothermal oxidation
reaction, or a reaction that includes a physical change in the
reacting fluids, e.g., a phase change and/or solvation. An
exemplary hydrothermal oxidation reaction is the catalyzed reaction
of aqueous methanol and aqueous peroxide. It is understood by a
person skilled in the art that a flameless hydrothermal reaction
refers to an exothermic reaction that produces heat but does not
produce a flame. A flameless reacted fluid is the product of a
flameless hydrothermal reaction. For example, a contemplated
hydrothermal oxidation reaction may produce visible light through
diffuse ionization, but does not produce light from a flame, as
does combustion. In some embodiments, contemplated reactions are
aqueous and flameless. Such reactions are substantially stable in
the presence of water or increased temperature or pressure.
Contemplated reactions are distributed through water so the reacted
temperature may be produced at a desired temperature (e.g., below
the limits of tool construction or at a desired jet temperature)
without e.g. requiring mixing of cooling water. In some
embodiments, contemplated fuel and/or oxidant may be delivered to
the drill head down a single conduit at e.g., near pressure balance
with the fluid in the borehole.
[0070] Such means may allow the application of a working fluid to a
surface zone of a target material such as a hard and/or crystalline
rock with substantially high heat flux. Provided herein, for
example, are means to form a working fluid for e.g. borehole
creation or borehole enlargement which may produce a heat transfer
capability of about 0.1 to about 20 MW/m.sup.2, or about 1.0 to
about 30 MW/m.sup.2, about 0.5 MW/m.sup.2 to about 8 MW/m.sup.2,
about 0.1 MW/m.sup.2 to about 8 MW/m.sup.2, or about 2 MW/m.sup.2
to about 7 MW/m.sup.2, when in contact with the material. For
example, provided herein are means to form a working fluid may
produce a heat flux of about 0.1 to about 10 MW/m.sup.2, or about
1.0 to about 10 MW/m.sup.2, about 0.5 MW/m.sup.2 to about 8
MW/m.sup.2, or about 1 to about 8 MW/m.sup.2 or about 2 MW/m.sup.2
to about 7 MW/m.sup.2, when in contact with the material.
[0071] In an alternative embodiment, provided herein are means for
producing a working fluid having a heat flux of about 0.01 to about
10 kW/m.sup.2 when in contact with material. Such a heat flux may
be used to form e.g., caverns, tunnels and mineshafts, or for
enlarging the diameter of an existing borehole, for example, using
a lower heat flux process.
[0072] In some embodiments, the disclosed methods, means, and
apparatus are capable of achieving and/or maintaining (in for
example, a reaction chamber) or directing a reacted fluid towards
e.g. a rock surface at a temperature that is not substantially
higher than a certain desired temperature (for example not
substantially higher that the desired working fluid or the limits
of materials of construction of the system and/or apparatus), e.g.
to achieve and/or maintain a reacted fluid temperature between
about 500.degree. C. (or about 500.degree. C. above the ambient
rock temperature), and about 900.degree. C., or about the
temperature of rock fusion and/or brittle ductile transition. In
some embodiments, maintaining such a reacted fluid temperature may
be more advantageous as compared to known techniques such as air
spallation and/or flame spallation, which can use high combustion
temperatures that can induce melting or fusing of rock or can
damage downhole hardware. For example, FIG. 8 depicts brittle
ductile measurements on feldspar samples under no loading and with
overburden pressure applied to the material. It will be appreciated
that the temperature that induces melting or fusing of rock, or the
brittle/ductile transition may vary with the type and/or nature of
rock. For example, FIG. 9 depicts the relationship between
differential stress and strain on natural quartz crystals for
variations in temperatures and water content, while FIG. 10 shows
how the melting curve for water saturated granite is affected by
pressure. Furthermore, it can be appreciated that using a heat
source which exceeds this temperature may lead to undesirable
transformation of the rock, such as melting or softening. For
example, if it occurred, such undesired melting or softening may
impede further spallation.
[0073] In some embodiments, such a temperature and/or heat flux is
necessary for the spallation of rock by e.g. creating enough heat
flux to remove spalls while e.g. substantially maintaining a
temperature that does not e.g. degrade materials of construction
and/or fuse or soften rock, minerals or grain boundaries which may
make rock substantially more difficult to spall. For example,
applying a working fluid having substantially high heat flux when
in contact with rock may cause grains within the rock to expand and
thereby produce microfractures within the rock. The growth of such
microfractures may result in a fractured region that spalls,
buckles and/or separates from the surface of the rock or material.
When such spall is ejected from the rock surface, it exposes fresh
material below the spall, and the spall process may continue. An
exemplary spallation process is shown in FIG. 1. Such spallation
processes may be easier when, for example, pre-existing stress in
rock, e.g. lithostatic loading or deviatoric (non-uniform) loading,
is present.
[0074] In the thermal spallation process of FIG. 1, a rock 1 has an
exposed surface 3 which contains, near the surface, a small flaw 2
in the mineral structure. Heat is applied to the rock surface 3 by
a high temperature source, such as a supersonic flame jet or
hydrothermal jet. The rock 1 may be subjected to the natural stress
found in the ground which acts on the grain in all directions, but
is typically lowest in a direction perpendicular to the exposed
mineral surface. As the mineral starts to expand from the applied
heat, stresses parallel to the exposed surface increase, so the
flaw 2 starts to grow 5 to relieve the stress. The flaw may expand
to a size 6 where the grain or portion of the grain 7 is separated
from the rock 1, thereby leaving a void 8 and a fresh surface for
further heat transfer and spallation.
[0075] In some embodiments, the heat flux and/or temperature of the
working fluid may be adjusted to produce or facilitate rock removal
processes such as macrofracturing, dissolution, partial melting,
softening, change in crystalline phase, decrystallization, or the
like. For example, removal of large volumes of rock such as in the
creation of caverns, mine shafts or tunnels, or larger hole opening
processes, such as reducing near wellbore impedance, may require
lower heat fluxes.
[0076] Substantially high heat fluxes may produce small spalls,
which in turn may improve lift (and removal) from the borehole. For
example, spalls produced by methods disclosed herein are, in some
embodiments, approximately less than or about 0.1 mm to about 2.0
mm thick and may have diameters less than or about 1-20 times, or
about 1 to about 5 times, their thickness. In some embodiments,
spalls may be produced that are less than or about 0.1 mm to about
2.0 mm in all dimensions. In some embodiments, spalls as large as
10 mm may be formed; these spalls have significant thermal damage
and microfracturing which may cause them to be broken down further
in the flow streams or by mechanical forces in the wellbore during
drilling.
[0077] In some embodiments, such as hole opening using lower heat
fluxes, created spalls may be on the order of inches to several
feet; these spalls may be left in place, allowed to fall into an
existing cavern or "rat hole" (existing below the production zone),
or may be reduced and/or removed by a secondary process such as
mechanical drilling. Non-removal of such formed spalls may be
advantageous, e.g. smaller conduits may be needed to transport
fluids to and from the bottom of the hole. Substantial non-removal
of spalls may be particularly advantageous if larger spalls are
generated by lower heat fluxes. In other embodiments, any rock that
is removed may intentionally makes the hole less stable, resulting
in break-out or cave-ins, further expanding the diameter without
requiring the complete spallation of all of the loosened
material.
[0078] In some embodiments, seismic or acoustic monitoring of the
fracturing or the sound in the section of the borehole may provide
information as to the size and extent of spalling and the size or
shape of the resulting borehole. In other embodiments, the methods
and apparatus disclosed herein also provide for an additional down
hole fluid, which may improve buoyancy or lift of cuttings (for
example, improved buoyancy in aerated foams, liquid water or
drilling mud as compared to air used in flame jet spallation) and
may, in some embodiments, assist in transport of particles to the
surface of the wellbore where they can be separated from e.g.,
water using standard oilfield (or geothermal) drilling technologies
such as, but not limited to, shaker screens, mud pits, and
hydro-cyclone de-sanders, and de-silters. In some embodiments, the
methods of spallation disclosed herein produce substantially
smaller cuttings or spall in comparison to conventional rotary
drill cuttings. In another embodiment, the methods of spallation
disclosed herein provide for substantial control over the size of
spalls formed, by e.g. controlling heat flux and/or temperature
e.g. of a heated or reacted fluid.
[0079] In another embodiment, application of a high heat flux (e.g.
using a reacted or working fluid) on the surface of the target
material may result in a thermally affected zone or reacted rock
region. For example, a thermally-affected zone having reduced
mechanical strength (due to e.g. microfracturing, macrofracturing,
softening, and/or annealing), which may extend as much as about 1/4
inch or more below the rock surface, may be created by a disclosed
reacted or working fluid inducing e.g. a substantially high heat
flux. Provided herein is a method for penetrating or reacting rock,
e.g. a method for forming a reacted rock region, which may be
suitable for penetration using conventional mechanical rock drills.
(For example, such reacted rock region may be easier to drill using
mechanical rock drills as compared to a rock region that has not
been reacted). Such a method may therefore further include
mechanically drilling, reaming, or otherwise removing the reacted
rock, as described below. For example, removing the reacted rock
may increase the diameter or improve the shape of the well.
[0080] Near wellbore impedance may occur where fractures intersect
a wellbore, as shown, e.g., in FIG. 19A. In one embodiment, a
method of fracture enlargement is provided, e.g. to reduce wellbore
impedance, by using a provided working fluid in a wellbore.
Pressure in an existing well may be controlled, in some
embodiments, by e.g., "shutting in the well", "zonal isolation" or
by "packing off" the length of the borehole being treated such that
the working fluid is forced into or near fractures (e.g. identified
fractures or fractures along an isolated zone), inducing spallation
or geomechanical changes at the surface of the fracture, enlarging
the fracture, and thereby resulting in an improvement in the flow
of fluids through the fracture, as shown, e.g., in FIG. 19D. In
other embodiments, the pressure in an existing well may be
controlled to prevent flow of the fluid into the fractures, by
either maintaining neutrally or "underbalanced" conditions. In
other embodiments, the pressure may be varied or cycled; this may
assist in blowing produced spalls or fractured rock out of the
fractures or away from the borehole wall. Pressure or flow may also
be cycled to allow for the measurement of flow and temperature from
the borehole to determine how effective the treatment has been, or
if additional treatment is necessary. In other embodiments, the
wellbore may be expanded more globally, by removing the rock in and
around the fracture, also leading to a reduction in wellbore
impedance, as shown, e.g., in FIGS. 20B and 20C. In other
embodiments, the walls of the borehole can be spalled to create
features such as slots or perforations that may be designed to
better intersect the existing fractures or to weaken the walls of
the wellbore in that location so as to induce further collapse and
expansion of the wellbore, leading to a further reduction in
impedance. In some embodiments, the reacted fluid may comprise
other chemicals which may assist in the process of reducing
wellbore impedance, e.g. chemicals which increase or decrease the
solubility of certain minerals. Incorporation of these chemicals
either from the unreacted fluid or from a separate stream, may be
used to prevent minerals from being dissolved by the high
temperature fluid jet and/or or being redeposited in the cooler
fractures, or may be used to facilitate dissolution of the minerals
in either the spalls or along the fracture walls. These chemicals
may include alcohols e.g. methanol, or bases e.g. hydroxides, or
combinations of the two, such as alcoxides. Alternatively, these
chemicals may include acids, such as HCl, HF or the like.
[0081] The disclosed methods and apparatuses of e.g., spalling
rock, can be applied to any formation of rock, for example, can be
applied to a subterranean formation in which the hydrostatic head
of fluid in the borehole produces a pressure at the bottom of the
borehole that does not exceed the fracture pressure of the
formation. In some embodiments, during operation of the disclosed
methods, the pressure of a borehole may be maintained below the
formation's fracture pressure or above the pressure of exposed
permeable formations to prevent inflow. For example, a drilling mud
may be used to vary the hydrostatic pressure in the borehole or to
create partial isolation of the working zone.
[0082] The methods described herein may further include monitoring
properties (e.g. size, shape, temperature and/or chemical
composition) of the formed spalls and/or may include adjusting or
monitoring e.g. a working fluid temperature and/or heat flux, to
e.g., optimize rate of penetration or maintain a pre-determined or
desired range of spall sizes. Such measurements may be performed by
e.g., an optical measurement, seismic measurement, an acoustic
measurement, a chemical measurement, and/or a mechanical
measurement. For example, fluid flow and temperature sensors
coupled with computational models may be used to determine heat
flux at e.g. the bottom of the borehole. In some embodiments,
chemistry of the returning fluid (e.g. fuel, oxidant or combustion
products) may be monitored to e.g. adjust the downhole reaction
conditions or as an indicator of system, e.g., combustion or
oxidation catalyst efficiency. For example, CO, CO.sub.2,
formaldehyde, formic acid, NO.sub.x, oxygen, fuel (e.g. alkanes,
methanol or ethanol), or oxidant may be detected in returning
fluids as e.g. indicators of condition of a catalyst used for
oxidation reactions. In another embodiment, fluid chemistry (e.g.
pH, dissolved minerals, suspended minerals, and agglomerates) may
be monitored in the returning fluid, which may allow for adjusting
additives in the working or cooling-lift fluid to reduce or enhance
solid or mineral precipitation, agglomeration, dissolution.
Downhole monitoring of temperature, heat flux, stand-off, and/or
borehole geometry by e.g. temperature sensors, flow sensors,
acoustic monitors, or calipers may allow for optimization of the
drilling conditions. In other embodiments, standard oilfield and
geothermal drilling methods and equipment for the measurement of
the formation, orientation, and borehole conditions, e.g.
measurement while drilling (MWD) or logging while drilling (LWD)
systems may be used, as well as directional drilling and drilling
with casing or casing while drilling technologies.
[0083] For example, in a disclosed method for hole opening of
existing wellbores, a drill string deploying the heating system
(e.g. the catalyst or combustion chamber for producing the reacted
fluid) may also contain instrumentation to help identify and locate
the areas of the working portions to be treated. Once the
instrumentation identifies the regions or fractures, a drill string
can then be pulled up the wellbore to align the jets or nozzles
with the areas to be treated. A packer or heat shield may be used
to separate the instrumentation from the heat of the spallation
process and to isolate the zone of the borehole to be treated.
Working Fluids and Apparatus
[0084] In some embodiments, the working fluid includes a
substantially aqueous fluid, e.g. water. Other exemplary fluids
include oil or water based drilling mud. The fluids may be selected
for optimum heat capacity and/or heat transfer properties. In
alternate embodiments, a working fluid may include a gas such as
neon or nitrogen. Contemplated working fluids may include by
appropriate additives, e.g. viscosifiers, thermal stabilizers,
density modifying additives such as barite, and those common in
oil, gas and/or geothermal drilling.
[0085] The working fluid may be directed through one or more
nozzles, for example, a nozzle disposed in a drilling system. Such
nozzles may be adapted to direct the fluid substantially along an
elongate central axis, for example, in a pulsing (e.g. cyclically
pulsing) flow or a substantially continuous flow. For example, in
some embodiments, a single, centrally located, non-rotating thermal
spallation system may have a reduced number of moving parts and
reduced mechanical complexity that may result in a substantially
simplified and/or cost effective system. Minimizing the moving
parts within a thermal spallation system, may allow stronger and
more robust materials to be used in construction of the system, and
therefore the resulting structure may be better adapted to
withstand the high pressures, temperatures, and mechanical wear and
impact that is generated at the bottom of a borehole during
operation. In another embodiment, a combination of centrally
located and peripheral nozzles can be used to optimize heat flux
across the surface of the rock, drilling rates, spall size or
borehole geometry.
[0086] For example, such as in hole opening applications provided
herein, the shape of the openings may be controlled to make
features in the walls of existing boreholes such as channels,
perforations, slots, or multilaterals (multiple branches drilled
out from the existing wellbore). For example, the shape of the
openings may be controlled by controlling spall size, or may be
controlled by the orientation of the nozzles. For example, an
apparatus with at least one substantially perpendicular nozzle may
be slowly run along the length of a production zone of an existing
borehole, creating a slot. Alternatively, a single substantially
perpendicular jet may sit on one position in the existing borehole
creating a perforation. An apparatus with multiple perpendicular
jets (within the same or different apparatus) or if the tool or
apparatus is rotated, a series of holes or parallel slots can be
created. The pressure from the surface pumps and/or reaction may be
used to move the nozzle e.g., towards the rock face to maintain a
small stand-off. A ring or peripheral gap nozzle can create
disc-like openings if stationary (as shown, e.g., in FIG. 19B), or
open the diameter along the length of the wellbore if translated. A
less directed or more even heat flux may be applied to open the
hole more evenly in all areas, or in the areas of greatest existing
stress. In an embodiment, methods of reducing wellbore impedance
are provided that include the use of less focused or directed jets,
jets substantially axial with the wellbore or with greater
stand-off distances or lower heat fluxes, to produce more global
spalling of the area of a production zone. In some embodiments,
"packers" or plugs (e.g., cement or ceramic plugs) may be used to
isolate the areas of a production zone to be treated.
[0087] Also provided herein are apparatuses for spalling rock, such
as an apparatus that includes a fluid heating means adapted to heat
a fluid to a temperature greater than about 500.degree. C. above
the ambient temperature of a surrounding material and less than
about the temperature of the brittle-ductile transition temperature
of the material; and at least one nozzle adapted to direct the
heated fluid onto a target location on the surface of the material,
wherein the fluid produces a heat flux of about 0.1 to about 20
MW/m.sup.2 at an interface between the fluid and the target
location, and thereby creating spalls of the material. The nozzles
of the disclosed apparatuses and systems may include a high
temperature resistant material, e.g. a ceramic or ceramic
composites, metal-ceramic composites, stainless steels, austenitic
steels and superalloys such as Hastelloy, Inconel, Waspaloy, Rene
alloys (e.g. Rene 41, Rene 80, Rene 95), Haynes alloys, Incoloy,
MP98T, TMS alloys, and CMSX single crystal alloys, metal carbides,
metal nitrides, alumina, silicon nitride, and the like. The
materials may also be coated to improve their performance,
oxidative and chemical stabilities, and/or wear resistance.
Chemical Heating
[0088] For example, a disclosed spallation system or apparatus that
is capable of producing a fluid for use in the disclosed methods
and apparatuses may include at least one jet nozzle, and a housing
including a reaction chamber and, optionally, a catalyst element
held within the reaction chamber. In operation, unreacted fluids or
solids can be contacted with the catalyst element within the
housing, resulting in the unreacted fluid or solid reacting, with
the catalyst element and generating a reacted fluid. This reacted
fluid may then be emitted through the at least one jet nozzle and
directed to an excavation site within the geological rock
formation, thereby creating spalls and/or a reacted rock region. In
some embodiments, contemplated unreacted fluid or solids react in
the presence of a catalyst substantially self-energized, e.g., does
not require an additional energy or heat source such as e.g., a
spark, flame holder, flame, or glow plug to initiate or maintain
the reaction and produce the reacted fluid.
[0089] For example, one or more unreacted fluids or solids (e.g.
one or two unreacted fluids (e.g. liquids) (which may be the same
or different), or one unreacted fluid and one unreacted solid, or
one or two unreacted solids (which may be the same or different),
may be contacted with the catalyst element, thereby forming or
generating a reacted or working fluid. Such reacted fluid may be
emitted through at least one nozzle (e.g. one center nozzle, a ring
or peripheral gap nozzle, or a plurality of nozzles), where the at
least one nozzle is directed to an excavation site (e.g. bottom
hole or against the borehole wall) within or on the geological rock
formation. The directed reacted fluid may create spalls which may
or may not then be transported to the top of the hole and/or may
create a reacted rock region e.g., down hole. It will be recognized
by one skilled in the art that discrete spots on the catalyst may,
at times, exceed the final temperature of the working fluid due to
localized heating on the catalytic surface, but the reaction is
self-energizing and does not require an additional heat source to
be provided by e.g. a power cable from the surface or an unstable
flame holder.
[0090] The unreacted fluid may, in one embodiment have a density
similar to water. This may be advantageous, for example, in
minimizing any pressure differences between the unreacted fluid and
the fluids in the wellbore. For example, if the density of the
unreacted fluid is slightly greater than the fluids in the
wellbore, any required pumping pressures for the unreacted fluid
may be reduced.
[0091] Contacting unreacted fluids or solids with the catalyst may
occur at a pressure of for example, about 1 to about 200 MPa or 1
to about 400 MPa. The unreacted fluid or solid may be at a
temperature of about 20.degree. C. to about 350.degree. C. In some
embodiments, at least one of the unreacted fluids is substantially
liquid.
[0092] Contemplated catalysts include catalysts comprising
transition metals and/or noble metals, e.g. lead, iron, silver,
platinum, palladium, nickel, cobalt, copper, iridium, gold,
samarium, cerium, vanadium, manganese, chromium, ruthenium, zinc,
and/or rhodium, and or mixtures and/or alloys or salts thereof,
and/or complexes, e.g. carbonyl complexes thereof. Contemplated
catalysts include oxides and/or nitrides of e.g. metals. The
catalyst may, in one embodiment, include lanthanum, zirconium,
aluminum or cerium (e.g. lanthanum cerium manganese hexaaluminate,
Zr--Al-oxides and Ce-oxides) or other mixed metal oxide catalysts.
The catalyst may include promoters (e.g. cerium and/or
palladium).
[0093] In some embodiments, the catalyst may be provided on a
non-reactive support, and/or on a substantially porous support, or
a support with channels (e.g. a honeycomb structure). Such supports
may include alumina, sol-gels such as sol-gel derived alumina,
aerogels, carbon supports, solid oxides, solid nitrides,
oxidatively stable carbides, silica, magnesium and/or oxides
thereof, titanium zirconium, and/or zeolites, metals, ceramics,
intermetallics, corrosion resistant metals (e.g. iron chromium
alloys), or alloy or composites thereof, or other materials
commonly used in catalytic supports. The supports can be but are
not limited to powdered, granular, or fixed bed. In some
embodiments, the catalyst or catalytic bed may further include
inhibitors that inhibit e.g. plating or poisoning on the surface of
the catalyst or catalytic support. In other embodiments, the
catalyst may include cation salts and/or promoters such as ionic
promoters or tin, nickel, silver, gold, cerium, platinum, manganese
oxides, or salts. A contemplated catalyst may include other
components such as boron, phosphorus, silica, selenium or
tellurium. Catalysts or their supports may be comprised of
nanoparticles.
[0094] In other embodiments, the catalyst may be configured as a
bed over which (or through which) the unreacted fluid is flowed. In
some embodiments, the catalyst bed may be sized and shaped to fit
within an appropriate drill head housing, or the catalyst bed may
be disposed in a different housing separate from the nozzle. In one
embodiment, the catalyst bed may be substantially cylindrical, less
than approximately three inches in diameter and two feet in length.
In an alternative embodiment larger or smaller catalyst beds may be
used. For example, in one alternative embodiment a catalyst bed of
approximately 0.5 inches in diameter and 1-2 inches in length may
be used. In other embodiments, axial or radial flow reactors may be
used. In other embodiments, multiple catalyst beds may be used of
the same or different designs. The catalyst bed may include a
catalyst on a substantially non-reactive support and/or a porous
support.
[0095] A catalytic support may include for example, a zeolite
molecular sieve of porous extrudate, piece, pellets, powder, or
spheres, and/or porous alumina, silica, alumino-silicate extrudate,
pieces, pellets, powder, or spheres. Catalytic supports may be
chemically resistant to any unreacted or reacted fluid. In one
example embodiment, the catalyst bed includes about 0.5% platinum
on 1/16'' alumina spheres having a surface area of at least
approximately 10 m.sup.2/g, or at least 100 m.sup.2/g (e.g. a
surface area of about 5 m.sup.2/g to about 15 m.sup.2/g or more).
In one embodiment, the catalyst bed may be about 5% platinum with a
promoter on alumina grains e.g., with a high surface area. In some
embodiments, the catalyst or catalyst bed may have plates or
sheets. In an alternative embodiment, other forms of catalysis are
contemplated (for example using a hot surface or a slug of hydrogen
peroxide to initiate the reaction or bring the catalyst bed up to
temperature that may produce a substantially self-sustaining
reaction) may be used in place of, or in addition to, catalytic
reactions. In one embodiment, the decomposition of a peroxide over
a catalyst generates free oxygen and heat which raises the
temperature of the unreacted fluid to initiate or help initiate the
reaction; the pressure of the unreacted fluid may be increased to
raise the boiling point of the decomposed fluid to initiate or
assist initiation of the reaction.
[0096] In an alternative embodiment, a catalyst bed can be used in
conjunction with a heat exchanger to initiate the reaction and
raise the temperature of a down flowing unreacted fluid, wherein
once the system has an appropriate temperature and/or the reaction
is self-sustaining, the catalyst bed may be by-passed and/or
isolated by e.g. a thermally-actuated mechanical valve, which may
improve catalytic longevity. A higher activity catalyst bed may
also be used to "light off" the reaction, after which lower
activity beds may be used to maintain its high activity. The use of
higher pressures in the catalyst bed through e.g. choked flow
across the nozzle, mud weight in the borehole, or back pressure at
the wellhead, may increase the reaction rates per unit catalyst and
decrease the pressure drops across the catalyst bed which may allow
for smaller catalyst bed volumes and e.g. axial reactor beds.
[0097] In some embodiments, the catalyst may be disposed on a
moving rotating element, such as blades or screens on a
hydraulically driven turbine, which may increase the contact
between the catalyst and fluid. In another embodiment, the catalyst
may be on a support that can be e.g., mechanically, thermally, or
chemically removed, e.g. without having to pull a drill string out.
For example, if the catalyst performance decreases or the catalyst
is poisoned, the catalyst can be removed (e.g. by dissolution of
alumina in hydrofluoric acid) and a fresh catalyst may be sent down
in, e.g. in the form of a pill. The catalyst may be supported on
carbon that is combusted once the reaction reaches full
temperature.
[0098] The catalyst may be regenerated, by for example, passing an
oxidant, hydrogen or a hydrogen source over the catalyst at
temperature, by acid or base washes, or any other technique
commonly used in catalytic combustion systems. Hydrogen or
additional oxidant may be added continuously to the unreacted fluid
to prevent e.g. coking while also reducing the light-off
temperature.
[0099] A catalyst chamber may be a water cooled reactor. In another
embodiment, the catalyst chamber may be a transpiring wall reactor
from a porous material tube that includes metal or ceramics.
[0100] The catalyst chamber may have distinct zones. For example,
different zones may be responsible for different chemical
reactions, destruction or binding of catalyst poisons, or for
different temperatures or to reduce the amount of the most
expensive catalyst (e.g. noble metal) that is needed, or to provide
zones of less expensive, sacrificial catalysts. The relative flow
through different zones may be changed depending on the temperature
of the catalyst chamber or over time. Different zones, for example,
may have substantially the same catalyst and geometry or different
catalyst and geometry. For example, sending the unreacted fluid
over one bed at a time until the bed is no longer active can extend
the working life of a tool before it needs to be pulled from the
hole to replace the catalyst.
[0101] In one embodiment, the unreacted fluid is an aqueous fluid.
In other embodiments, an unreacted fluid may be liquid and may
include water, oil, water or oil based drilling muds, aerated
fluids, and/or supercritical CO.sub.2, or any other appropriate
liquid for use as e.g. the working fluid. In one embodiment water
can be separated downhole from the unreacted fluid by cyclone
separators or other appropriate fluid separation systems and
methods. For example, an unreacted fluid may be liquid, gaseous, or
a supercritical fluid (e.g. H.sub.2O at temperatures above about
375.degree. C. and 3200 PSI (approximately 7400' water column).
[0102] For example, the unreacted fluid may include water and/or an
oxidant and/or a fuel. In operation, the unreacted fluid may be,
e.g., pumped to a drill head assembly of a disclosed spallation
system. In the drill head, the unreacted fluid can be, for example,
passed over a catalyst configured (or otherwise put in contact with
the catalyst) to e.g., cause the flameless reaction with an oxidant
and/or a fuel that may be present in e.g. the unreacted fluid. Such
a reaction may produce a reacted fluid, e.g. a fluid at an elevated
temperature, that may then be directed out of an e.g., distal jet
nozzle of the spallation drill head assembly and impinge upon a
target rock surface, creating thermally damaged rock and/or spalled
rock. The reacted fluid, in some embodiments, may include water in
gaseous (steam) or supercritical form, for example, may be a gas
when in first contact with rock. After contacting the rock, the
expelled water, gas or supercritical fluid can then, in some
embodiments, flow up the borehole, carrying the spalled rock with
it. In some embodiments, the reacted (hot) fluid is allowed to
travel up the borehole to further spall the borehole walls and
expand the diameter of the borehole. In other embodiments, the
reacted fluid is cooled e.g. just above the drilling assembly by a
heat exchanger and/or cooling-lift fluid, thereby substantially
stopping the spallation reaction. In other embodiments, the reacted
fluid is directed through a "shroud" which may reduce its
interaction with the sides of the rock wall, and also substantially
stopping the spallation reaction. In an alternative embodiment,
some of the reacted fluid does not travel up the wellbore but
rather enters the rock or formation through e.g. fractures. In some
embodiments, the spalls or rock fragments are not carried up the
wellbore but are allowed to fall further into the hole or remain on
the borehole wall.
[0103] In one embodiment, a non-reacted or unreacted fluid includes
a fuel and/or oxidant. For example, the unreacted fluid may include
two or more components that are miscible with each other. In
another embodiment, an unreacted fluid and/or an unreacted solid is
present, for example, an unreacted solid may include an oxidant
(e.g. a solid encapsulated oxidant), or an unreacted substantially
solid fuel, e.g. a wax. An unreacted solid may be dispersed,
dissolved, undissolved or encapsulated within a solid. In one
embodiment at least one of the fuel and/or oxidant may change state
or dissolve, decompose, or otherwise react during its transport
along the borehole to the drill head, or upon reaching a drill
head. A catalyst or accelerant may be added to the unreacted fluid,
wherein the catalyst can be activated at the bottom of the hole by
heat or mechanical force, with or without the use of a secondary
permanent catalyst. The working fluid may also contain an inhibitor
to prevent the reaction from occurring along the length of a drill
string.
[0104] In certain embodiments, a nonreacted fluid is pumped down
hole to a drill head at the distal end of the borehole at
approximately 1-50 or 5-50 gallons per minute, e.g. about 20
gallons/minute. In one embodiment, an unreacted fluid may be pumped
down one or more small diameter tubes that may be nested inside of
a traditional steel coiled tubing system. Such small diameter tube
or tubes may have one or more periodic check valves so as to
prevent the unreacted fluid from back-flowing and to limit
uncontrolled reactions from propagating up the nested tube.
[0105] In an alternative embodiment, any appropriate tubing system
for transporting the aqueous solution to the catalyst or drilling
head assembly may be utilized. In some embodiments, the fuel and
oxidant are transported to the catalyst or drilling head assembly
through one conduit, or in separate conduits. For example,
fuel/oxidant mixtures which are stable at desired concentrations
can be transported together in one tube. This may, for example,
have advantages over transporting the fuel and oxidant separately
in that it would require one less conduit to pass material to the
distal end of the borehole. It may also simplify storage, mixing,
or handling procedures on the surface. Fuels or oxidants which may
be carried in the bulk cooling-lift water (and separated at the
bottom of the hole) to also reduce the number of conduits.
[0106] In one embodiment, the fuel and oxidant may be combined in a
number of different ways to allow for transportation of the fuel
and oxidant down the same conduit. For example, fuel and oxidant
may be transported down a single conduit through use of a single
molecule ("single-source") or network/complex. The chemical heat
source can be a monopropellant, such as hydrogen peroxide, nitrous
oxide, or hydrazine. Alternatively, fuel and oxidant may be
transported down a single conduit through use of methods including,
but not limited to, slug flow (i.e. gases and/or liquids sent one
after another), dissolved gases, or bubble flow (i.e. small bubbles
suspended in a fluid and transported along with the fluid). In an
alternative embodiment, the fuel and oxidant may be transported
down the same conduit as two solid materials in one or more
"pills". In a further alternative embodiment, one or more of the
fuel and/or oxidant may be transported in an encapsulated form such
as, but not limited to, a material, such as a peroxide,
encapsulated by e.g., wax.
[0107] In some embodiments, fuel and oxidant may be sent down one
conduit in two separate fluid phases. For example, the fuel may be
carried in an oil-based phase, and the oxidant in the water based
phase. At the bottom of the hole, the two phases can be, for
example, homogenated, or the fuel and/or oxidant can be separated
from its respective phase by means of a hydrocylcone or other
separation device and then combined with its reactant.
[0108] Contemplated fuels include carbonaceous fuel, such as a
fossil fuel (e.g. coal, biomass), gasoline, natural gas (e.g.
liquefied natural gas) diesel, biodiesel or kerosene. For example,
fuels contemplated for use in the disclosed methods include
alcohols, alkyls, cycloalkyls, alkenes, alkynyls, ethers,
alkoxyalkyls, (e.g. CH.sub.3CH.sub.2O CH.sub.2CH.sub.3,), dioxanes,
glycols, diols, ketones, acetone, aldehydes and/or aromatic organic
compounds such as benzene or naphthalene, or combinations thereof.
Hydrocarbons may be used as fuel, and include alkanes (e.g.
C.sub.1-C.sub.20 alkanes) such as methane, ethane, propane, butane,
pentane, hexane, heptane, octane, and higher alkyl fuels such as
naptha, kerosene, paraffin, hydrocarbon oligomers, and/or other
waxes. Other contemplated fuels include ethylene vinyl acetate
(EVA), polyvinyl chloride (PVC), boranes (such as B.sub.2H.sub.6 or
B.sub.5H.sub.9), carboranes, ammonia, kerosene, diesel, fuel oil,
bio-based oils, such as biodiesel, starch, sugars, carbohydrates,
or other oxyhydrocarbons. A fuel may be, or include, hydrogen,
hydrogen generating compounds, or hydrogen containing polymers such
as polyethylene, polypropylene, or paraffin polymers. A fuel may
also be, or include, reactive metals such as aluminum, beryllium,
and coated or encapsulated sodium.
[0109] For example, contemplated fuels include alcohol fuels (e.g.
C.sub.1-C.sub.8 alcohols) such as methanol, ethanol, propanol,
and/or butanol, or mixtures thereof, which in some embodiments may
be optionally substituted by one or more halogens. In certain
embodiments, the fuel may be substantially miscible in water, e.g.
methanol, ethanol or benzene.
[0110] Contemplated oxidants include air, oxygen, peroxides, (e.g.,
hydrogen peroxide or methyl ethyl ketone peroxide) percarbonates,
permanganates, permanganate salts, as well as combinations thereof.
For example, contemplated oxidants include inorganic and/or organic
peroxides such as peroxides of alkali metal peroxides, e.g.
lithium, sodium, and/or potassium peroxides, e.g. sodium peroxide
and/or barium peroxide. Alkyl peroxides such as t-butyl peroxide
and benzoyl are contemplated. Oxidants contemplated herein may
include hypochlorite and/or hypohalite compounds, halogens such as
iodine, chlorite, chlorate or perchlorate compounds, hexavalent
chromium compounds, sulfoxides, ozone, nitric acid, N.sub.2O,
and/or persulfuric acid. Other possible oxidants include F.sub.2,
OF.sub.2, O.sub.2/F.sub.2 mixtures, N.sub.2F.sub.4, CIF.sub.5,
CIF.sub.3, N.sub.xO.sub.y, IRFNA IIIa: 83.4% HNO.sub.3, 14%
NO.sub.2, 2% H.sub.2O, 0.6% HF: IRFNA IV HAD: 54.3% HNO.sub.3, 44%
NO.sub.2, 1% H.sub.2O, 0.7% HF, RP-1, C.sub.10H.sub.18, and
CH.sub.3NHNH.sub.9.
[0111] As disclosed herein the peroxide may be in e.g. aqueous
form, or may be in a solid form e.g. pellets that may include urea.
An unreacted fluid that includes an e.g. oxidant, e.g. hydrogen
peroxide, may also include corrosion inhibitors and/or passivating
agents and/or anti-foaming agents and/or surfactants and/or surface
tension modifying agents. For example, an unreacted fluid may
include stabilizers such as phosphoric or phosphonic acid or sodium
pyrophosphate or tin compounds. In an embodiment, an oxidant, e.g.
high pressure or liquid oxygen may be metered into a fuel stream
(e.g. methane or methanol stream); mixing can take place either at
the surface or in the drill head. The mixture may then travel into
the drill head. In one embodiment the drilling head is configured
to withstand bottom hole pressures of upwards of about 100 to 4000
PSI, 1000 to about 4000 PSI, or about 1000 to about 30000 PSI (e.g.
about 1 to about 200 MPa), e.g. the pressures present at the bottom
of a deep wellbore.
[0112] In some embodiments, a provided unreacted fluid may include
an aqueous solution comprising by weight of about 5% to about 52%
oxidant, e.g. hydrogen peroxide, or about 30% to about 40% oxidant,
or about 5% to about 50% oxidant, and may include about 5% to about
20% fuel, e.g. methanol, or about 10% to about 20% fuel, e.g. 10%
to about 15% fuel, or even about 5% to about 50% fuel. For example,
an unreacted fluid may include about 2% to about 40% by weight
hydrogen peroxide. In another embodiment, the unreacted fluid may
include about 10% to about 20% by weight methanol or ethanol. In an
exemplary embodiment, the unreacted fluid includes about 15%
methanol or ethanol and about a stoichiometric amount of air,
oxygen, or peroxide (e.g. hydrogen peroxide). In another exemplary
embodiment, the unreacted fluid includes 38% by weight hydrogen
peroxide and about 12% by weight methanol, or e.g. about a 4:1
weight ratio of hydrogen peroxide/methanol, e.g. about a 5:1 to
about a 1:1 weight ratio of hydrogen peroxide/methanol.
[0113] In an exemplary embodiment, the unreacted fluid is slightly
oxidant rich to assure complete combustion of the hydrocarbons to
reduce the amount of by-products caused by incomplete combustion,
such as carbon monoxide, formaldehyde, and/or formic acid. In other
embodiments, the unreacted fluid may be T-Stoff (80% hydrogen
peroxide, H.sub.2O.sub.2 as the oxidizer) and C-Stoff (methanol,
CH.sub.3OH, and hydrazine hydrate, N.sub.2H.sub.4.nH.sub.2O) as the
fuel); nitric acid (HNO.sub.3) and kerosene; inhibited red fuming
nitric acid (IRFNA, HNO.sub.3+N.sub.2O.sub.4) and unsymmetric
dimethyl hydrazine (UDMH, (CH.sub.3).sub.2N.sub.2H.sub.2), nitric
acid 73% with dinitrogen tetroxide 27% (AK27), and
kerosene/gasoline mixture, hydrogen peroxide and kerosene;
hydrazine (N.sub.2H.sub.4) and red fuming nitric acid; Aerozine 50
and dinitrogen tetroxide, unsymmetric dimethylhydrazine (UDMH) and
dinitrogen tetroxide; or monomethylhydrazine (MMH,
(CH.sub.3)HN.sub.2H.sub.2) and dinitrogen tetroxide. In another
embodiment, the unreacted fluid may include 50-98% hydrogen
peroxide. The products from decomposing the 50-98% peroxide (e.g.
H.sub.2O and/or O.sub.2) over a catalyst (e.g. platinum, silver, or
palladium), may then be allowed to react with a fuel (e.g.
methanol). The heat from the decomposition of the hydrogen
peroxide, combined with downhole temperatures and pressures and/or
the use of a heat exchanger, may auto-initiate or sustain the
reaction of fuel and oxidant, such as peroxide and/or oxygen with
methanol and/or ethanol.
[0114] An unreacted fluid or solid, when contacted with the
catalyst, may generate a reacted fluid, e.g. a fluid for use in the
thermal systems disclosed herein. The reacted fluid may include
water and may also include nitrogen, carbon dioxide and/or carbon
monoxide, as well as smaller amounts of unreacted fuels and/or
oxidants and/or side products. For example, an unreacted fluid that
includes methanol and hydrogen peroxide, reacting with a catalyst,
produces exothermically water and carbon dioxide. In some
embodiments, little or no heat, and/or other initiator (e.g. spark,
glow plug, or flame holder), is required to initiate the reaction.
In some embodiments, contacting the unreacted fluid and catalyst
produces substantially continuously reacted fluid.
[0115] In some embodiments, the reacted or working fluid, e.g., hot
water, is focused out of the jet nozzle of the drill head assembly
and directed against the target rock surface. In one embodiment,
the jet temperature (reacted fluid temperature) and/or heat flux
may be controlled by adjusting the mixture of the aqueous solution
(for example, by increasing the methanol and/or oxygen
concentration to increase the jet temperature). In another
embodiment, the jet temperature and/or heat flux may be controlled
by increasing the flow rate of the unreacted and e.g., hence
reacted fluid. In another embodiment, the jet temperature and/or
heat flux may be controlled by adjusting the flow rate of the
unreacted fluid to adjust for complete or incomplete reaction. The
jet temperature and/or heat flux may also be controlled by, for
example, adjusting the flow rate of the unreacted fluid to reduce
the amount of heat exchange between the reacted and unreacted
fluids.
[0116] A drill assembly may include a drill head with a nozzle. An
exemplary drill head may have a diameter of approximately 3/4
inches with a 0.1 inch center nozzle through which the reacted
fluid is expelled. In alternative embodiments, nozzles with
different configurations and/or geometries may be utilized, such as
a larger or smaller nozzle diameter. For example, the drill head
may be about 5 to about 15, or 4 to about 29 times the diameter of
the nozzle. In one embodiment, the drill head assembly may include
a plurality of jet nozzles directed in either the same or different
directions from a distal portion of the drill head assembly. In
another embodiment, the drill head assembly includes one center jet
nozzle. Rock "spalls" (e.g. grains or platelets of less than about
0.025 inch to about 0.1 inch) can be ejected and may be swept up
the borehole by the reacted fluid (after the reacted fluid contacts
the rock). In one embodiment, a larger flow of cooling-lift water
(e.g., traveling in the annulus between the nested tube and coiled
tubing), can be introduced after the heat exchanger (if used), to
cool the fluid and help transport the spalls to the surface.
[0117] In one embodiment, a heat exchanger is placed above the
catalyst bed so that some of heat of the upflowing (e.g. reacted)
fluid is transferred to the down flowing (e.g. unreacted) fluid,
both conserving energy and preheating the solution prior to the
e.g. the catalyst bed, heater, or drill head. In an exemplary
embodiment, a nested drill string may act as a heat exchanger. In
some embodiments, the catalyst may be preheated by sending some
chemical, e.g. an oxidant (e.g. peroxide) in the down-flowing
fluid, with or without fuel, which may in some embodiments,
initiate a reaction, for example heating the catalyst. For example,
heat provided by a heat exchanger to a down flowing fluid may
provide enough heat to initiate the combustion reaction without the
need for a catalyst, which may allow flow to be directed away from
the catalyst bed (and thus may preserve or prolong the useful
lifetime of the catalyst). In some embodiments, hot gas may be used
to dry the catalyst bed prior to contact with the fuel and
oxidant.
[0118] In another embodiment, approximately 0.12 gallons per minute
of a 15-20% aqueous solution, such as, but not limited to an
aqueous methanol solution, is pumped through a preheater to bring
the temperature up to 290.degree. C. In an alternative embodiment,
a greater or lesser volume of aqueous solution may be pumped. In
further alternative embodiments the preheater may bring the
temperature of the aqueous solution up to a greater or lesser
temperature, as required. In a further alternative embodiment, no
preheater is required
[0119] In one embodiment spallation takes place with stand-off
distances (i.e. the distance from the nozzle exit at which the
target surface is placed) ranging from approximately 0.2-10.0
inches. In an alternative embodiment, stand-off distances of less
than 0.2 inches or greater than 10 inches may be achieved. This
may, for example, allow a one inch diameter hole to be drilled at a
rate of greater than 0.5 inches per minute. In one embodiment, the
standoff distance is varied, either periodically or randomly, in a
controlled or relatively uncontrolled manner, or in response to a
downhole measurement or physical, mechanical, electrical thermal,
or chemical condition. This variation in standoff may improve the
tools ability to reliably under ream or to produce a borehole of
consistent or desired geometry. Standoff distance, for example, may
be controlled by acoustic monitoring, e.g. analysis of the sound of
the jet can be used to determine the shape of the bottom of the
hole and distance between the nozzle and the bottom. Parameters of
the jet, (e.g., nozzle geometry, flow, temperature, stand-off) can
be adjusted to optimize drilling, either through communications to
the surface or by downhole processors or actuators. The
backpressure of the flow through the nozzle may also be used for
feedback to adjust e.g., the geometry of the nozzle, the flow rate,
the stand-off, and/or the rate of drill string displacement.
[0120] An example drill head assembly, a small scale axial flow
reactor, for a spallation system is shown in FIGS. 3A to 3C. In
this embodiment, a catalytic heater drilling spallation system 31
may be used to create high temperature high pressure fluids in a
reaction chamber or cell 26, initiated by a stream of hot water
mixed with 20% methanol to which gaseous oxygen is added. In
alternative embodiments, a higher or lower percentage methanol may
be used. This stream of fluid flows into the cell 26 through an
inlet fitting 18. In one embodiment, the cell body 26 is
constructed with an insulating gap 24 filled with an insulating
material, such as, but not limited to, nitrogen gas at the same, or
substantially the same, pressure as the fluid flowing into the cell
26. This gap 24 may assist in preventing heat loss from the
reaction chamber within the cell 26 into the cooling water
surrounding the cell 26, and also helps maintain the cell integrity
at the high temperatures of the reaction occurs. The nitrogen
enters the gap through a tube fitting 19 and into a collar 20. A
replaceable o-ring seal 21 allows the inner region to thermally
expand without loss of the nitrogen pressure blanket. A threaded
nut 22 secures the o-ring in place. In alternative embodiments,
alternative insulating materials and systems may be utilized in
place of, or in addition to, the nitrogen gas layer.
[0121] The reaction chamber within the central region of the cell
26 is filled with a catalyst, such as, but not limited to, platinum
coated alumina spheres 25, that are held in place by two stainless
steel filter screens 23. In an alternative embodiment, other
appropriate materials and/or means of positioning and holding the
catalyst may be used. In operation, the reacted fluid passes out of
the reaction chamber, after reacting with the catalyst 25, at an
elevated temperature. A nozzle body 27, such as a threaded nozzle
body, focuses the high temperature jet 28 of reacted fluid out of a
nozzle exit 29 onto a target location on a rock surface. The nozzle
body 27 may be, for example, screwed into place on the distal end
of the system 31 using the two drilled holes 30 and a spanner
wrench.
[0122] FIGS. 3D and 3E show the system 31 in operation. Prior to
starting the system 31, a granite block 39 is predrilled with a
small borehole 40. A seal-interface block 36 isolates the nozzle 27
from the coolant fluid, and provides a means for venting spalls and
oxidation fluids/gases from the borehole. The interface block 36
may, for example, have a cap 33 which is held in place using a
number of screws 34. The cap retains in place a thin metal washer
and ceramic felt pad 35 which makes a sliding seal for the system
31, thereby preventing inflow of coolant. The interface block 36
may be sealed to the outside using, for example, an o-ring 38. A
jet 37 of hot reacted fluid exits the nozzle exit 29 and enters the
predrilled borehole 40, where it spalls the rock at the distal end
of the borehole and flows upward and out of the interface block
through the chimney tube 32.
[0123] Another example, as depicted in FIG. 11, is a convergent
radial flow reactor housed within a 27/8'' OD drill head for
producing 4'' holes in granite using the laboratory test system or
deployed on a coiled tubing unit. This system is comprised of a
steam generation assembly 132 containing a catalyst bed 135, a
drill head 136, and a connector 134 that couples the unit to other
downhole subassemblies and the drill string. Unreacted fluid is
pumped down a single capillary in the drill string, through 133,
and into the steam generation assembly 132 where it flows through a
catalyst bed and reacts producing reacted that exits out a nozzle
136. Pressures and temperatures inside the steam generation
assembly 132 are measured at specific locations 137, 138 which can
be used to monitor the performance of the system. Flow schematics
of this steam generation assembly 140, 144 for a thermal spallation
drilling system are shown in FIG. 12A and FIG. 12B. A converging
flow design is shown in FIG. 12A. Fuel and oxidant enter the cell
141 and flow across a catalyst bed 142 where they react producing
the working fluid which exits down a tube 143 to the drill nozzle
(not shown). A diverging flow design is shown in FIG. 12B. Fuel and
oxidant enter the cell 145 and flow across a catalyst bed 146 where
they react producing working fluid which exits down and annulus
which converges to a tube 147 that leads to a drill nozzle (not
shown). For surface demonstrations of the drill head shown in FIG.
11, an example of a spallation drilling test system rock core
confinement apparatus 148 is shown in FIG. 13A, FIG. 13B, and FIG.
13C. The system can be used to simulate spallation drilling at the
surface where there is low stress on the rock. The system is
comprised of a steel concrete mold 149 that encases a rock sample
156 which is surrounded by concrete 157. A wellhead 151 is secured
to the rock sample prior to the sample being encased in concrete.
The entire system rests on a pallet 150 for ease of transportation.
Bolts 153 on the side on the concrete mold 149 can be tightened
after the concrete has hardened in order to induce a compressive
stress on the rock sample. A drill 158 enters as shown. Cooling
water or drilling mud is pumped through injection tubes 152 and
enters the wellbore at injection points 154. A flow barrier 155
prevents the cooling water from entering the hot thermal spallation
region downhole while the drill is in operation. Unreacted fluid is
pumped into the drill through a tube 159 and reacted fluid exits
the drill nozzle 160.
Thermochemical
[0124] In an alternative embodiment, a working fluid including an
aqueous fluid comprising water and hydroxides of Group I elements
of The Periodic Table of Elements, and mixtures thereof, may be
used. For example, an aqueous fluid may include a hydroxyl ion
concentration of the hydroxides of Group I elements of The Periodic
Table of Elements and mixtures thereof at ambient conditions is in
the range of about 0.025 to 30 moles of hydroxyl ion per kilogram
of water. In some embodiments, an upper limit of the range can be
determined by the solubility of the Group I hydroxide. For example,
a fluid may include about 0.1 to about 52 grams sodium hydroxide
per 100 grams of solution at room temperature (but may include more
at higher temperatures). In some embodiments, the fluid may
comprise alcohols such as methanol or ethanol with hydroxides,
which produce alkoxides. Such alkoxides may help solubilize
minerals in rock.
[0125] In some embodiments, concentrated aqueous or alcohol
solutions of hydroxides of alkali metals can react with subsurface
rock formations and may be capable of forming one or more water
soluble complexes with at least one of Si or Al. For
aluminosilicate rocks, the high alkoxide or hydroxyl ion
concentration in the fluid may provides the dual benefit of (i)
enhancing the dissolution rate by fully ionizing the chemical
surface groups on the formation rock, thus maximizing the density
of surface sites vulnerable to hydrolysis, and (ii) enhancing
solubility of reaction products by forming thermally stable soluble
complexes. Such fluids may dissolve rock and consume hydroxide
stoichiometrically until e.g., the hydroxyl ion concentration drops
to near 0.01 moles of hydroxyl ion per kilogram of water or
alcohol. Materials to achieve hydroxyl ion concentration above 0.01
moles of hydroxyl ion per kilogram of water include, but are not
limited to alkali metal and alkaline earth metal components such as
hydroxides, silicates, carbonates, bicarbonates, mixtures thereof
and the like. In example material is sodium hydroxide. Other
solutes may be added in any desired quantity to achieve other
objectives, as long as the hydroxyl ion concentration is
maintained
Coupled Thermal and Mechanical Systems
[0126] One aspect of the present invention relates, at least in
part, to drilling systems, and associated methods of use, that
includes a heat source to thermally affect a target material and a
mechanical drilling system. The drilling systems may be used to
create boreholes or increase the diameter of existing boreholes in
any of the target materials described herein including, but not
limited to, crystalline rock material, silicate rock, basalt,
granite, sandstone, limestone, or any other rocky material. The
drilling systems may be used to create vertical boreholes,
horizontal boreholes, angled boreholes, curved boreholes, as well
as slots, perforations, fracture enlargement, or other forms of
hole opening, or any combination thereof. In one embodiment, the
methods and systems described herein provide for improved deep
borehole drilling, for example from approximately 10,000 feet to
approximately 50,000 feet below the surface, or more.
[0127] A borehole may be created, for example, through the combined
use of a heated fluid and a mechanical drilling and/or reaming or
milling system. Combining a mechanical drilling system with e.g. a
thermal drilling system such as those described above may overcome
certain limitations of thermal systems alone, by, for example, the
combination may provide for controlling stand-off and/or rate of
penetration or bit advancement, penetrating unspallable or
thermally-insensitive or unspallable zones, comminuting larger
pieces of rock that may be produced or fall from the borehole wall,
penetrating fractures which have inflowing or potential for
outflowing fluids. Combining the use of a heat source to thermally
affect a target material with a mechanical drilling system may
overcome certain limitations of conventional mechanical drilling
systems alone by, for example, preventing the wear and fatigue to
the drill bit that is produced through traditional mechanical
drilling technologies. More particularly, by utilizing one or more
heat sources to thermally affect a rock portion in advance of one
or more conventional drilling and/or milling systems, the
mechanical and physical strength of the rock to be drilled and/or
milled can be reduced forward of, and/or simultaneously with, the
mechanical drilling process. This may allow for increased
penetration rates with reduced bit wear, vibration and drill string
fatigue, and uncontrolled trajectory deviations compared to
conventional drilling processes. For example, new cutter materials
such as TSP can operate at temperatures above 1000.degree. C., as
shown, e.g., in FIG. 15, where hard rocks such as granites are
significantly softened, as shown, e.g., in FIGS. 8, 9, 10, and 16.
Therefore, a thermal jet which reduces the rock strength by, e.g.
partially spalling and/or microfracturing and/or softening combined
with a mechanical drilling process using a high temperature bit
material, has the possibility of a corresponding ROP exceeding that
of either process along. As a result, the efficiency of
conventional mechanical drilling methods may be significantly
increased by the use of a heat source to modify the properties of
the rock in advance of the mechanical drilling system.
[0128] In one embodiment, the mechanical drilling and/or reaming
system may, for example, include a traditional mechanical,
chemical, or other appropriate drilling and/or reaming mechanism.
Embodiments of the invention may, for example, incorporate any
appropriate mechanical bit design, including, but not limited to,
roller cone bits, tricone bits, polycrystalline diamond compact
(PDC), reaming bits, milling bits, hammer drill bits or coring
bits, or other appropriate drilling bits. The design of these bits,
including cutting and rock reduction surfaces, can be optimized so
that the depth-of-cut and rate-of-penetration can be maximized
while keeping the wear, vibration, and trajectory deviations within
acceptable limits. Materials and novel designs, including high
temperature metals and alternative methods for inclusion of cutting
surfaces, may be optimized for use under these relatively high
temperature conditions. The use of high temperatures may also allow
for the use of ultra-hard materials that tend to be brittle at
lower temperatures. In an alternative embodiment, the drilling
system may include other physical or chemical processes such as,
but not limited to, sonication, sonic drilling, laser drilling,
arc/plasma, particle assisted drilling, chemical dissolution, or
other appropriate physical or chemical processes of use in drilling
applications in addition to, or in place of, a mechanical drilling
system.
[0129] In order to thermally affect the rock to be drilled and/or
reamed or milled by the mechanical drilling system, one or more
heat sources may additionally be incorporated into the system. This
heat source may include any appropriate heat source adapted to
thermally affect a rock through spallation, microfracturing,
macrofracturing, dissolution, partial melting, softening,
modification of grain boundaries, change in crystalline phase,
decrystallization, erosion, or the like. For example, certain
materials such as shales and clays may be modified (e.g.,
dehydrated at high temperatures) to reduce or eliminate bit
baling.
[0130] In one embodiment of the invention, a combined thermal and
mechanical borehole creation system may include a spallation
drilling mechanism, such as, but not limited to, any of the thermal
spallation systems described herein, with mechanical drilling
mechanism such as, but not limited to, a drilling, reaming,
milling, and/or hole opening process. A downhole chemical reaction
(e.g. hydrothermal oxidation of methanol and peroxide over a
catalyst) may provide both thermal energy as well as the mechanical
energy (e.g. expansion of the hot fluid to e.g. drive a
hammer).
[0131] In one embodiment, a small pilot borehole may be formed,
e.g. with the thermally produced pilot borehole being substantially
smaller than the target diameter of the final borehole. The pilot
borehole may thereafter be milled, drilled, or otherwise enlarged,
by a mechanical system such as a reaming system, or other
appropriate hole opening system, to form the final borehole of the
required diameter. This method may, for example, allow for more
precise control of borehole geometry, and provide substantial cost
and time benefits for producing the final reamed borehole. The
pilot hole may serve as a guide, stay, or centralizer for the
reaming bit. In addition, removal of rock from the circumference of
a lead borehole (that has been created by spallation system)
through a reaming process may be, for example, faster, easier,
and/or produce less bit wear than traditional drilling of the
entire borehole. The spallation drilling mechanism and reaming
mechanism may be part of a single device, or be separate devices.
The pilot borehole may be used, for example, as an exploratory,
test, monitoring, or scientific borehole to e.g. determine the
quality of the resource and evaluate if a larger borehole should be
created.
[0132] The use of a working fluid for e.g., creation of a lead
borehole, may affect one or more properties (e.g. a thermal,
mechanical, chemical or physical property) of the material at the
surface of the pilot borehole wall. This may, in turn, make it
easier for the reaming system to ream the surface of the lead
borehole to create the final borehole. In one embodiment, the
reaming operation may also remove rock that is not structurally
stable. Such rock could, if not removed, fall into the hole, bridge
the hole, or form ledges that prevent the advance of casing or
stick the casing before it is on-depth. Bridges that form in the
casing annulus can e.g. divert or disrupt the placement of cement
which may jeopardize the success of well completion. The reduced
mechanical strength of the thermally affected zone, if not removed,
may also reduce the overall integrity of a completed well.
[0133] In each of the embodiments described above, a working fluid,
such as those described herein, may be used to weaken and/or remove
the rock at a distal end of a borehole prior to, or simultaneously
with, the drilling, reaming, and/or milling action of a mechanical
bit coupled to the thermal spallation system. In different
embodiments of the invention, a working fluid can be configured to
spall or thermally affect the entire bottom surface of the distal
end of the borehole. In an alternative embodiment, the
thermally-affected zone produced by a working fluid does not cover
the entire surface under the drill bit. Rather, the fluid stream
can be directed so as to target certain regions under the bit to be
weakened. Damage to or removal of these regions can cause
structural weakening of the remainder of the surface so that it may
be easily removed by a separate feature on the drill bit. In
another embodiment, a working fluid may be focused toward the sides
of the borehole, with or without additional working fluid being
focused toward the bottom of the borehole.
[0134] In various embodiments of the invention, the mechanical
drilling and/or milling or reaming operation may be carried out
concurrently with a thermal drilling operation, e.g. use of a
working fluid. For example, a mechanical drilling/reaming element
may be located either substantially close to the thermal treatment
operation and/or substantially offset along the drilling assembly,
thereby allowing the mechanical drilling process to be carried out
concurrently, or substantially concurrently, with a thermal
drilling operation. The mechanical drilling elements, (e.g. drill
bits or reaming bits) may therefore remove the thermally modified
portion of the geological formation and/or thermally unmodified
rock surrounding the thermally modified rock, thereby creating the
borehole and, in some embodiments, improving the geometry or
integrity of a wall of the borehole created by the spallation
system or other thermal treatment system.
[0135] The system may be adapted to remove both spalled or
thermally affected rock and non-spallable rock. In addition, the
system may be adapted to reduce the size of rock pieces that are
too large to be removed from the borehole in a circulating fluid.
As a result, the mechanical drilling system, in combination with
the thermal treatment system, may be used to create boreholes in a
number of different geological formations including a number of
different properties. For example, a coiled tubing deployed thermal
spallation drill head can be combined with a coiled tubing deployed
mud-motor drill; in formations where the thermal spallation process
is not effective, the mud motor may be used to turn a conventional
coiled tubing drill bit. Likewise, a drill pipe deployed
hydraulically driven turbo-generator can be used to produce
electricity for resistance heating elements used to initiate
thermal spallation or treatment of the rock. A thermally-stable
rotary drill bit serves to maintain proper stand-off of the jet
during pure spallation drilling, assist in some sections via
thermomechanical drilling, and be the sole mechanism for drilling
in others. This is particularly advantageous over prior, uncoupled,
systems, wherein, for example, a thermal treatment or thermal
drilling system may need to be removed from the borehole if
unspallable rock is found at the bottom of the borehole, or created
by over-heating the rock, and temporarily replaced by a mechanical
drilling system. This removal of a drilling system, and insertion
of another type of drilling system, whenever materials with
different properties are met may be extremely costly and time
consuming. By coupling a thermal system with a mechanical system
within a single drilling system, the need to replace the system
when different materials are met may be avoided.
[0136] In an alternative embodiment, the mechanical drilling
process may be performed as a secondary operation while some tubing
or pipe remains in the hole. In a further embodiment, the
mechanical drilling process may be performed as a secondary
operation after the thermal drilling assembly has been removed. In
one embodiment, different processes, such as a thermal drilling
process and a mechanical drilling and/or reaming process, may be
performed concurrently along different portions of a single casing
interval or wellbore.
[0137] In one embodiment, one or more thermal treatment nozzles can
be distributed throughout the front of a mechanical drill bit, or
through slots radially extending from an outlet port. The nozzles
can also be shrouded with a protective gas or fluid stream to
reduce cooling and mixing with the drilling fluid and/or increase
the potential for thermally damaging the rock surface. Gas shrouds,
fluid streams, solid insulation such as a ceramic or syntactic
ceramic, vacuum gaps, or gas or fluid filled gaps can also be used
to protect the materials of construction or mechanical drilling
equipment from high temperatures.
[0138] In one embodiment, the drilling process includes rotary or
coiled tubing drilling. As a result, a thermal jet, or a portion
thereof, may be configured to rotate. In an alternative embodiment,
one or more thermal jets, or a portion thereof, may be fixed, for
example, through either a center or peripheral ring jet.
[0139] In some of the embodiments described herein, a thermal
system including a single nozzle may be incorporated into a
mechanical drilling system. The single nozzle may be located
centrally along a central elongate axis of the system. As a result,
the thermal system may include a fixed, non-rotating, structure. A
mechanical drilling and/or reaming or milling mechanism may then by
positioned over or in the thermal system, and rotate around or in
the thermal system, to mechanically drill and/or ream the borehole
being created in conjunction with the thermal system. Providing a
single, centrally located, non-rotating thermal system may be
advantageous, for example, in simplifying the structure of the
system by reducing the number of necessary moving parts and
reducing the mechanical complexity of the overall system. This may,
for example, reduce the cost of the system while also allowing for
a more structurally sound and sturdy borehole creating tool. In one
embodiment, by minimizing the moving parts within the thermal
system, stronger and more robust materials may be used in the
construction of the thermal system, and the resulting structure may
therefore be better adapted to withstand the high pressures,
temperatures, impact, and mechanical wear that are generated at the
bottom of a borehole during drilling operations.
[0140] In one embodiment, a heat source may be incorporated into a
mechanical drilling system such that the distal end of the
mechanical drilling system extends a specified distance from the
distal end of the heat source. As a result, the impingement of the
distal end of the mechanical drilling system against the target
portion of the rock results in the substantially constant stand-off
distance between the rock surface and the heat source. This may be
advantageous, for example, in applications where a set distance is
required between the target surface and the distal end of the heat
source to ensure that the temperature, flow, and heat flux produced
at the surface of the target portion of the rock is within the
required limits for efficient spallation. Also provided herein are
methods that may achieve e.g., softening of rock at a radius
proportional to the wear rate of e.g. mechanical cutters such that
the life of the cutters is more uniform.
[0141] An example drilling system is shown in FIG. 3A and FIG. 3B.
In this embodiment, the drilling system 400 includes a pilot hole
thermal spalling system 54 and borehole reamer 55 in conjunction
with coiled tube drill rig system 410. The pilot hole thermal
spalling system 54 is powered by a fuel and oxidant fed through a
nested tube 42 contained in a motor driven shaft 41. The reactants
move through the assembly to a pilot drill reaction chamber 47. The
reaction chamber 47 is filled with a catalyst to initiate a thermal
reaction with the fluid passing therethrough to change at least one
property of the fluid such as, but not limited to, a temperature, a
pressure, or a state of the fluid. In one example, the reaction
between the fluid and the catalyst increases the temperature and
decreases the density of the fluid. As a result of the thermal
reaction, a jet 50 of hot gases/liquids is directed out of a nozzle
49 at the distal end of the chamber 47. The reaction chamber 47
may, in one embodiment, be thermally insulated from the main body
by, e.g. a gas filled cavity 48. The exit jet 50 spalls the rock at
the distal end of the borehole, thereby drilling a hole in the rock
52 and creating a damaged zone 51 around the bore.
[0142] The spalled rock can then be carried away from the target
location at the end of the borehole by the recirculating fluid or
drilling mud within the borehole. The nozzle portion 49 may, in one
embodiment, be constructed from a high temperature resistant
material such as, but not limited to, at least one of a ceramic,
ceramic composite, high temperature steel alloy, or the like.
[0143] The pilot spallation sub assembly 54 is attached to a
rotating reamer sub-assembly 55 which carves away the damaged rock.
The reamer 55 has multiple blades 43 having attached carbide or
diamond compacts 44 to cut away at the damaged rock zone 51.
Coolant, such as, but not limited to, a water or drilling mud, may
be introduced just below the reamer blades 43 with imbedded
compacts 44 through one or more outlets 45 to help cool the
assembly and remove cuttings.
[0144] In one embodiment, where the system is attached to a coiled
tube drill rig 410, the downhole assembly, or a portion thereof,
may need to be rotated through the use of a downhole motor 56
attached, for example, to a connector 57 and then to the nested
coiled tube 66 and powered by high pressure fluid supplied by
surface pumps 70.
[0145] The hard rock 58 found at depth can be effectively drilled
by this system. In one embodiment, shallow depth rock 59 can be
drilled, cased 61, and cemented 60 to prevent loss or introduction
of fluid during drilling. Drilling fluids including drilling mud
water and spalls are removed from the borehole through a flow line
62 to be separated and possibly recirculated. A rubber packoff in a
stripper head 63 diverts the returns into the flow line away from
the drill rig 410. On the surface, the coiled tube rig 400 contains
a coiled tubing injector 64a which is used to drive the coiled tube
within the borehole, a tube straightener 64b and a gooseneck 65
which is used to guide the tubing from the injector 64 into or off
of the reel 67. Fluid, including e.g. reactants, can be fed in from
a source 69 through a rotating coupling 68 into the reel assembly
67.
[0146] One example drilling system may include a drill string based
thermally assisted tricone drilling system. An example thermally
assisted tricone drilling system 500 is shown in FIGS. 5A-5C. In
this embodiment, heat to power a downhole spallation system such
as, for example, a hydrothermal spallation drill system, can be
provided by electrical resistance heating. A tricone bit 510 is
incorporated into a distal end of the drilling system 500. In one
embodiment, the tricone bit 510 has multiple rotating rollers 80a
which incorporate hard segments, constructed, for example, from
carbide, steel or ceramic segments, that are used to grind and wear
away at the rock and are held in place by sleeve or roller bearings
80b.
[0147] In one embodiment, electrical power may be generated using a
downhole turbine 83 in conjunction with an electrical generator 82.
Power from the generator 82 is carried to a heater 75 through one
or more power cables 71. Water 72 is pumped into the heater and
boiled producing superheated fluid at high pressure that is ejected
through one or more nozzles 79 in the drill bit. The heater 75 may
include an insulating gap 74, as described above. Drilling mud
and/or coolant is pumped down through an annular region 73 and into
the borehole through one or more conduits 78. A surface assembly 90
may be attached to the tricone bit 510. The surface assembly 90 may
include a conductor pipe and conductor casing 87 cemented in place
86 in a surface rock portion 85 to protect the potable water zones
and provide a high pressure seal to the earth. A segmented drill
string 88 is driven into the ground and rotated by the drill rig 90
and connected to a drilling fluid circulating pump 91.
[0148] In alternative embodiments of the invention, a drilling
system may include a spallation system, such as any of the
spallation systems described herein, coupled to other types of
mechanical drill bit, such as a PDC drill bit, diamond-impregnated
coring bit, or hammer drill bit. Example drilling systems including
a thermal spallation system coupled to various drill bits are shown
in FIGS. 6-8B.
[0149] For example, FIG. 5 shows a PDC bit 600 incorporating a
spallation system such as a hydrothermal spallation system. In this
embodiment, fluid, including water, fuel, and oxidant, is
introduced through an inlet tube 92 into a reaction chamber 95. The
reaction chamber 95 may be insulated by, e.g. a pressurized air gap
96. Upon passing into the chamber 95, the reactants within the
fluid contact a catalyst located within the chamber 95 and react,
producing high temperature reacted fluid. The reacted fluid exits
through one or more openings 100 as jets directed against a target
rock face. The spallation system is contained in the drill body 94
of the PDC bit 600 and connected to a drill string at a threaded
tool joint or threaded connection 93. Drilling mud or coolant is
pumped down through an annular gap 97 and down to one or more
outlet feeders 101 and vents 102 close to the bottom of the drill
bit 600. Rotation of the bit engages flutes 98 mounted on which the
compacts 99, such as, but not limited to carbide or PDC compacts,
cut away at the thermally affected target rock surface. The
compacts 99 are cutting elements set in the matrix of the bit body
on ridges, sometimes called blades, with flutes between the blades
for mud flow and cuttings passage to the annulus.
[0150] In an exemplary embodiment, nozzles 100 leading a PDC drill
bit 600 may be sized to soften the rock just ahead of each cutter
element (compacts) 99. Drilling through the presoftened rock will
reduce the wear on the tool 600, especially the compacts 99.
[0151] FIGS. 7A and 7B show a drilling system 700 including an
abrasive/grinding bit incorporating a hydrothermal spallation
system. In this embodiment, water is pumped downhole through an
opening 103 in a segmented drill string 104 into a downhole turbine
or motor 105 located within a subassembly 106. The motor 105 is
connected by a shaft to a water cooled rotating magnet assembly 107
contained within a housing 108. The magnet assembly 107 surrounds a
non-rotating metal core 109 having a series of holes to allow a
fluid to flow therethrough to remove heat generated by induction
from the rotating magnets 107. This resulting super-heated fluid
exits into a chamber 110 which may be insulated by an air gap 111
from a coolant fluid channel 112. The heated fluid exits through
one or more nozzles 113 to interact with a target rock surface.
Coolant is directed from coolant exit ports 114. An abrasive
material, such as, but not limited to diamond, are surface set into
or impregnated in a plurality of cutter segments (pads) 115. In
operation, the super-heated fluid exiting the nozzles 113 and
impinges upon the target rock surface, thereby damaging the rock
and assisting the cutting of the rock by the cutter segments (pads)
115.
[0152] FIGS. 8A and 8B show a drilling system 800 including a
thermal spallation system coupled to a hammer drill bit. In
general, a hammer drill is a drill with a hammering action. The
hammering action provides a short, rapid hammer thrust to pulverize
relatively brittle material and provide quicker drilling with less
effort. In one embodiment, the hammer drill may additionally
include a rotating motion that may be used separately or in
combination with the hammering motion. When used in the hammer
mode, the tool provides a drilling function similar to a
jackhammer.
[0153] In the embodiment of FIGS. 8A and 8B, coolant and/or
drilling fluid is introduced into a bit 800 through a drill string
connector 116 (e.g. a connection to a drilling assembly that
includes drill collars to provide a hammer with a large and stiff
inertial load to push off of.) The drill string connector 116
connects to the drill assembly. An upper valve plunger 118 and
return spring 119 is integrated into the hammer bit 800 to rapidly
press a driver 121 into an anvil 124, thereby driving the distal
end of the anvil 124 from a distal end 128 of the bit 800 to
transmit a blow to a target rock surface. The driver 121 may
include seals 120, 122, and a return spring 123. The anvil 124 is
attached to the body of the bit 800 through a guide nut 125, which
also prevents rotation of the bit. Integral to the anvil 124 is a
thermal combustion chamber 127 which is fed a fluid including a
fuel, water, and an oxidant from the surface through a separate
tube 117. The combustion chamber 127 may be thermally insulated
through, for example, a pressurized air gap 126. Hot fluid/gas
exits the chamber 127 through one or more jets 131 distributed
across the drill face. The distal end of the drill bit 128 is
cooled by water or drilling mud exiting through exit ports 129.
Stress to the thermally altered rock is created by the hammering
action combined with drill string rotation through the carbide
buttons 130.
[0154] In other embodiments, improved well control may also be
achieved through the use of a hydrostatic column of a fluid such
as, but not limited to, water or geothermal drilling mud, to
increase hydrostatic pressure e.g. to balance formation pressure in
exposed formation using, e.g., deep surface or intermediate casing
and high pressure blowout prevention equipment installed on a
wellhead. Thermal spallation, coupled with high velocity liquid
flow through nozzles, may produce high pressure jets, pulsating
jets or abrasive jets to produce a dual spallation/jet drilling
system. Such dual systems may include a combination of hot and cold
jets or include operating spallation jets at higher flow rates than
needed to produce spallation (and thus have a jet drilling process
substantially directly ahead of the nozzle and a spallation process
in the wall jet that forms beyond the radius of the jet produced
hole.). For example, the use of high temperature fluids may greatly
reduce the pressure required to achieve jet drilling in high
strength rock. Additionally, the use of fluids with temperatures
below the brittle-ductile transition of the rock may prevent the
rock from being overheated and becoming unspallable. Alternatively,
the rock may be heated above the ductile-brittle transition far
enough to soften the rock enough that it can be swept away or
drilled like soft to medium sediments. This may be advantageous,
for example, for materials, such as basalts, which are typically
less prone to spallation and not significantly damaged by heating
to a temperature below the ductile-brittle transition.
[0155] A thermal degradation process or spallation formation may
not be used continuously. Rather, certain embodiments of the
invention may include pulsed heat treatment, such as a cyclically
pulsed heat treatment. In a further alternative embodiment, the
heat treatment may be alternated with a cooling treatment. Such
alternation may increase the damage to the rock or may help
moderate the temperature of the drilling mechanism and materials of
construction while still imparting high temperature, at times,
against the rock surface. In one embodiment, the thermal spallation
jet(s), or other appropriate heat source, may be activated and
turned off as required, thereby allowing the use of the spallation
system to assist in the penetration through certain sections of a
target rock, while allowing the thermal spallation process to be
turned off when penetrating other sections or target rock, for
example where thermal spallation is either not required or
advantageous.
[0156] One embodiment of the invention includes a drill bit design
for use with a thermally assisted mechanical drilling method. In
one embodiment, for example in very deep/hot formations, the
thermal treatment can be a cooling process, where a very low
temperature jet causes microfracture of the surface through a
reduction in temperature.
[0157] In one embodiment, the bulk of the fluid flow through the
drilling assembly--e.g. the portion used for cooling and cuttings
lift--may be relatively cool, while only a small portion--e.g. that
used for thermal degradation--is hot. As a result, some, or all, of
the cold fluid can be used to provide cooling to at least a portion
of the drilling device. For example, cold fluid may be sent through
or around the mechanical drilling structure to reduce its
temperature and improve survivability. In one embodiment, cold
water may be sent through flow channels in a traditional PDC or
tricone bit, while the hot portion of the fluid is insulated
directed substantially down against the rock. The channels
transporting the hot water may be isolated from the bit by a layer
of insulation, such as, but not limited to, a substantially solid,
liquid, gas, or vacuum insulation layer, or a combination of the
different insulation layers. In one embodiment, the relative ratio
of hot/cold can be adjusted to balance the performance of the two
drilling mechanisms.
[0158] One embodiment of the invention includes a spallation system
including control systems, and associated methods, adapted, for
example, to control the diameter of the wellbore produced by a
e.g., hydrothermal jet, maintain the desired well hole trajectory,
control the distance between the nozzle and the bottom of the hole
(i.e. the "stand-off"), and/or ensure a sufficient temperature
differential so as to induce spallation. These control systems may
include software and/or hardware based control elements designed to
ensure optimum performance of the thermal drilling system.
[0159] Disclosed methods may include introducing a flow of water
into the borehole. This flow of water may be used, for example, to
at least partially form an ascending fluid stream to carry loose
material such as, but not limited to, the spalled, drilled, or
otherwise loose rock from the bottom of the borehole. The returning
fluid may also travel up the borehole in reverse circulation, e.g.,
where the fluid can be directed upward through a separate tube or
annulus in the main drill string. The water flow may also be used
to provide cooling for one or more parts of the system and/or
surrounding rock. The provided cooling may be produced by at least
one of temperature cycling, thermal protection, and a circulated
cooling fluid.
[0160] In one embodiment, a heat exchanger may be coupled to a
portion of the system above the nozzle of the thermal spallation
system. This heat exchanger may be used, for example, to exchange
heat between a working or heating fluid (e.g. a reacted fluid),
spallation fluid, and loose material ascending through the borehole
and the fluid being pumped to the thermal spallation system, e.g.
an unreacted fluid, within a conduit extending from the surface to
the thermal spallation system.
[0161] In one embodiment, one or more of properties of working
fluid and jet may be selected to ensure that that the required
conditions are met for optimum spallation. These jet properties may
include, but are not limited to, a temperature, a heat flux, an
exciting jet velocity, a heat capacity, a heat transfer
coefficient, a Reynolds number, a Nusselt number, a density, a
viscosity, and/or e.g., a mass flow rate. For example, these
properties may be obtained through selection of the specific fluids
used, by mixing of multiple fluids, and/or by treatment of the
fluid through heating, cooling, pressurizing, chemically treating,
or otherwise adjusting the composition of the working fluid.
Exemplary ranges, without being limiting, for a thermal system for
borehole creation from 1,000-30,000 feet, using a working fluid,
may include those provided in Table 1 below. Such parameters may be
determined by using a disclosed working fluid in several different
or similar rock formations, as exemplified below, and assessing
preferable ranges.
TABLE-US-00001 TABLE 1 Example property ranges for Hydrothermal
Spallation drilling of boreholes. Property Borehole creation
Temperature (C.) 400-1200 Total Heat Output (MW/m 2) 0.1-100 (e.g.
about 1-10) Heat Flux (MW/m.sup.2) 0.1-100 Mass Flow (lbs/min)
0-500 Exiting Jet Velocity (m/s) 0-700 (e.g. about 400-700) Heat
Capacity of the Working Fluid 2.26-5 (kJ/kg*K) Heat Transfer
Coefficient of Working 38-56 Fluid (kW/m 2*K) Reynolds Number 0.5
.times. 10.sup.6-2.5 .times. 10.sup.6 (for 1'' hole) (for the
single, non-rotating center 12 .times. 10.sup.6-60 .times. 10.sup.6
(for 24'' hole) jet with round nozzle with diameter = 1/16 of hole
diameter) Nusselt Number 30-45 (for 1'' hole) 740-1040 (for 24''
hole) Density of working fluid at 0.01-0.1 temperature/pressure
(g/cm.sup.3) Viscosity of working fluid at 0.025-0.045
temperature/pressure (cp) Induced Strain in Rock (%) 0-30 Spall
Size, 80% of total mass (mm) 0.001-3
[0162] For example, a temperature at least that of the onset of
rapid thermal spallation but below the, e.g. brittle ductile
transition of the rock may be maintained.
[0163] The total heat output--the thermal power of the drill
divided by the cross sectional area of the borehole to be
drilled--may be kept, for example, between 0.1 and 100 MW/m2. The
heat flux--a product of the heat transfer coefficient and the
temperature difference between the wall jet and the rock
surface--may be kept, for example, between 0.1 and 100 MW/m.sup.2.
In certain embodiments, if too low a value of heat flux is used, a
thermal gradient may propagate and build in the rock, reducing the
relative strain of the surface rock to the underlying layer,
thereby reducing or preventing spallation. In one embodiment, it is
possible to increase the heat flux by increasing the Reynolds
number--a dimensionless number that gives a measure of the ratio of
inertial forces to viscous forces--in the nozzle exit. In certain
embodiments, the heat flux of a thermal jet for spallation drilling
may be increased without having the jet exceed the temperature e.g.
brittle-ductile transition of the rock, by increasing the mass
flow, and/or reducing the nozzle diameter (to increase the exiting
jet velocity). Increasing the velocity or mass flow of the jet may
also provide a mechanical or erosive means of removing material or
spalls from the rock surface, clearing and providing a freshly
exposed surface for further spallation, and/or help with spall and
cuttings lift.
[0164] The Nusselt number--a dimensionless ratio of convective to
conductive heat transfer across (normal to) the rock-fluid
boundary--may, in a non-limiting example, for a working fluid in
one or more of the disclosed systems, be between about 30 and 1040,
depending on hole size. In one embodiment, working fluid properties
can be optimized so as to produce an induced strain within the
grains of the rock of between about 0-30%, thereby generating
enough stress to cause structural failure, which may make use of
existing flaws, discontinuities, or grain boundaries in the rock
and/or in-situ stresses
[0165] Spall sizes may, in one embodiment, be optimized so that 80%
of the transported spalls maintain a range of 0.001-3 mm. If the
produced spalls are too large, they may not be lifted by the
drilling fluid and may plug small openings in heat exchangers and
internal returns tubes used in reverse circulation. If the produced
spalls are too small, it may be an indication that the heat flux is
too high, causing excessive microfracturing beyond what is needed
for drilling and cuttings lift, thereby wasting energy and
sacrificing efficiency, as well as increasing mineral dissolution.
Spall size may also be controlled to help plug fractures leading to
lost circulation or intrusion of fluids during drilling, or to
attempt not to plug fractures in producing zones during e.g. hole
opening for enhanced wellbore impedance.
[0166] In one embodiment, at least one property of the spalls
and/or working fluid (e.g. reacted fluid) may be monitored to
provide information relating to the spallation process. For
example, the spall size, shape, chemical composition, and/or number
of created spalls may be monitored to provide information on the
efficiency of a spallation process. In addition, or in the
alternative, one or more properties of the reacted fluid may be
monitored to provide information on the efficiency of the catalytic
reaction between the unreacted fluid and the catalyst. By
monitoring one or more of these properties, information on the
spallation process, such as, but not limited to, the efficiency of
the heating reaction, the rate of spallation, the composition of
the spalled rock, the temperature of the fluid leaving the nozzle,
and/or the heat flux at the target surface may be deduced.
[0167] In an embodiment, the properties of the fluids may be used
to inform the adjustment or addition of any additives into the
unreacted or cooling-lift water streams. Such additives may include
cleaning agents (e.g. to remove deposits from a catalyst, nozzle or
heat exchanger), and additives that increase or decrease tendencies
for materials in returning fluids to crystallize, precipitate, or
agglomerate. Contemplated cleaning agents may include solids that
are significantly abrasive to unwanted deposits but not to the
ceramic or metal of the nozzle. A cleaning agent may be added
continuously to a flow, or sent down periodically. Additives may
also assist in the opening of existing fractures in production
zones, or by preventing the produced spalls and minerals from
plugging the existing fractures by e.g. mineral redeposition.
[0168] The monitoring may be carried out using at least one of a
thermal measurement, an optical measurement, an acoustic
measurement, a chemical measurement, and a mechanical measurement
(e.g. a flow meter). For example, a laser-based optical system may
be used to measure one or more properties of the spalls exiting the
borehole. In alternative embodiment, any appropriate measurement
device may be used.
[0169] If a change in one or more properties is observed, a
property of the fluid and/or spallation system may be adjusted to
compensate for the observed change and ensure optimum spallation.
This adjustment may be made, for example, by adjusting one or more
properties of the unreacted fluid being sent down the borehole to
adjust the fluid temperature and/or heat flux created by the
spallation process to maintain e.g., a pre-determined spall size.
The unreacted fluid may be adjusted by changing a parameter such
as, but not limited to, a chemical composition, a fluid mixture, a
pressure, and/or a temperature.
[0170] In one embodiment, control of the Reynolds number of the
fluid jet at the exit of the nozzle by, e.g. controlling the mass
flow exiting the nozzle, controlling the nozzle size, and/or
controlling the viscosity of the fluid, may assist in controlling
the heat flux at the surface of the rock at the target
location.
[0171] The spalls and/or reacted fluid may be monitored at the
surface (i.e. after traveling from the distal end of the borehole
to the surface in the ascending fluid stream). In an alternative
embodiment, the spalls and/or reacted fluid may be monitored at a
location part way down the borehole and/or at the distal end of the
borehole. In one embodiment the spalls and/or reacted fluid are
monitored at a single location. In an alternative embodiment, the
spalls and/or reacted fluid are monitored at multiple
locations.
[0172] One embodiment disclosed herein includes a method for
excavation of a borehole in a geological formation by using a heat
source, such as, but not limited to, a thermal drilling system to
create a pilot borehole in a geological formation, measuring at
least one property of the geology of the pilot borehole, evaluating
the at least one measured property to determine whether to enlarge
the pilot borehole, and enlarging the pilot borehole if the at
least one measured property meets a set requirement. The pilot
borehole may be enlarged by inserting at least one of a spallation
drilling system and a mechanical drilling system into the pilot
borehole.
[0173] This method may be advantageous in situations where a pilot
borehole is to be formed in order to test the properties of the
geology to determine whether further drilling and completion is
warranted. The smaller pilot borehole is cheaper to drill than a
larger diameter borehole, but may still allow access to the
subterranean geology for testing. The pilot borehole may also be
used as a guide hole for the larger borehole drilling, and may
weaken the structure of the rock surrounding the pilot borehole to
facilitate easier drilling of the larger borehole.
[0174] The evaluating step may include evaluating whether the
geological formation is suitable for use as, for example, an
injection or production borehole for at least one of a geothermal
system, oil and gas, mining, excavation, or CO.sub.2 or nuclear
sequestration or storage. As discussed above, one or more
properties of the geology of the pilot borehole may be evaluated by
evaluating at least one property of spalls and/or the fluid (e.g.
the reacted spallation fluid, a cooling fluid, and a drilling mud)
exiting the borehole. In various embodiment, any of the drilling
systems described herein may be used to create the pilot borehole
and/or larger borehole
Self-Casing
[0175] The fluids used in the systems described herein, and/or the
loose materials created by the process described herein, can, in
one embodiment, strengthen and seal the walls against structural
collapse and wellbore fluid loss, thereby greatly extending time
interval between casing of the borehole. This may happen through
processes such as, but not limited to, precipitation of materials
on the surface walls of the borehole and/or depositing of loose
materials within cracks and other cavities on the walls of the
borehole.
[0176] In some applications, however, it may be desirable to
install casing in addition to any self-casing processes produced by
the systems and methods described herein. For larger diameter
borehole, for example, casing may be accomplished employing
conventional telescoping casing strings using methods familiar to
those skilled in the art. For small diameter boreholes, the slim
borehole can be cased, for example, using an expandable casing
string that is inserted into the borehole and then radially
expanded. The casing may be made of a malleable material, and when
it is placed in the borehole, it can be radially expanded against
the borehole wall upon application of an internal radial load.
[0177] The examples which follow are intended in no way to limit
the scope of this invention but are provided to illustrate the
methods and apparatus of the present invention. Many other
embodiments of this invention will be apparent to one skilled in
the art.
Example 1
[0178] An example method of testing the efficiency of a thermal
spallation system is described below. This method may be used to
test any appropriate spallation system on a material.
[0179] In the embodiment of Example 1, a Sierra White granite rock
core measuring 4'' in diameter and 6'' long was prepared by
pre-drilling a 0.75'' diameter hole 0.5'' deep on the top surface.
The core was then loaded into a stainless steel pressure vessel. A
preheater was assembled by winding a 20' long section of 0.125'' ID
stainless steel tubing in a machined groove around a 4'' brass
block in which contained a series of rod heaters.
[0180] The thermal spallation system included a 0.5'' ID.times.3''
long catalyst chamber which exits through a single, 0.09'' diameter
non-rotating nozzle located along the central axis. The catalyst
chamber is filled to a height of roughly 1.5'' with 0.5% platinum
on 1/16'' spheres having a surface area of 100 m.sup.2/g. A series
of stainless steel screens, spacers, and diffusers allow fluid to
pass through while holding the catalyst bed in place. The drill
head is insulated from surrounding cooling water by a 0.040'' gap
pressurized with nitrogen.
[0181] Before the start of a test, the drill head is driven to the
bottom of the predrilled hole and a depth is read off of a dial
indicator. The drill head is then retracted approximately 1.5''
from the bottom of the hole into a large cooling water chamber.
[0182] The hydrostatic pressure in the vessel is then raised to
1600 PSI by means of a back-pressure dome regulator. An axial load
of 6000 PSI and confining pressure of 3000 PSI are applied by
separate pumps acting upon the core to simulate deep geological
formation conditions. An air actuated pump is used to deliver 3 g/s
of a 20% by volume methanol in deionized water through the
preheater which raises the temperature of the unreacted fluid to
250-300.degree. C. A high pressure oxygen flow is metered into the
preheated aqueous methanol solution at sub-stoichiometric
ratios.
[0183] The thermal spallation system may use a methyl alcohol fuel,
and an O.sub.2 oxidant. The aqueous methanol/O.sub.2 solution
travels through the spacers, screens, and diffuser and over or
through the catalyst bed. The catalyst is not preheated and does
not need an additional heat source such as a glow plug, spark, or
flame for the reaction to initiated or maintained. The
substantially flameless catalytic oxidation of the methanol
produces heat within the water which raises the temperature of the
fluid to 800-900.degree. C.
[0184] The high temperature fluid exiting the nozzle into the
cooling chamber is initially diverted and cooled by a 4 GPM water
flow. The flow of aqueous methanol is increased to 9 g/s over 2
minutes while simultaneously adjusting the oxygen flow. The drill
head is then driven by a high pressure fluid pump at a rate of
1.0''/min through a stainless steel seal, isolating it from the
cooling water, and into the predrilled hole to a standoff of 0.25''
from the rock surface, as measured by the dial indicator. The
displacement of the drill head is then reduced to 0.5''/min. The
drill head penetrates into the rock until it reaches the full
stroke of the equipment, roughly 1.5'' below the predrilled rock
surface. In one embodiment, the drill head is then held at this
position to demonstrate the ability of the center jet nozzle to
drill in advance of the drill head and under ream. In an
alternative embodiment, the drill head need not be held
consistently at the bottom. Fluid and spalls exit the borehole into
the cooling water above the rock via a 0.189'' tube approximately
1.5'' in length. The bulk fluid then passes through a series of
screens which remove the bulk of the spalls before the bulk fluid
passes the back pressure dome regulator and then through a low
pressure hydrocyclone to remove very small size spalls. The spalls
from may be separated from the bulk fluid by filtering through a
200 mesh screen which retained approximately 88% of mass of the
excavated rock. Size analysis may be performed by laser light
scattering.
[0185] After being held for 10 minutes at this depth, the drill
head is rapidly retracted through the borehole seal, allowing
cooling water to fill the hole and the jet to be diverted,
quenching the spallation process. Aqueous methanol and oxygen flow
rates are gradually reduced and the preheater is turned off.
[0186] The sample may then be removed from the cell. The volume of
excavated rock may thereafter be determined from the mass of water
required to fill the volume of the new borehole, less the volume of
the predrilled hole. The rock core may then be dried and weighed. A
image of a rock core sectioned axially following the test with the
drill head that produced the borehole is shown in FIG. 17. A graph
showing spalled particle size distribution for the system of
Example 1 can be seen in FIG. 21.
Example 2
Repeatability and Other Rock Types
[0187] An experiment as in Example 1 was been repeated on Sierra
White Granite, as shown in Table 2:
TABLE-US-00002 TABLE 2 Additional hydrothermal spallation drilling
of boreholes in Sierra White Granite run # 1 2 3 4 5 hole volume
(cc) 104.1 84.9 55.1 42.6 57.3 hole depth (cm) 10.26 8.27 6.016
6.49 6.16 final drill nozzle depth (cm) 4.66 4.47 3.67 4.33 4.655
final stand off (cm) 5.6 3.8 2.346 2.16 1.505 penetration rate(pump
setting) 200 400 600 800 990 run time(sec) 300 150 125 73 62 pen
rate (cm/min) 0.9525 1.905 2.8575 3.81 4.6736 quarrying rate
(cc/min) 20.82 33.96 26.448 35.0137 55.45161 avg hole area
(cm.sup.2) 10.1462 10.26602 9.15891 6.563945 9.301948 avg hole
diameter (cm) 3.594239 3.6154 3.414893 2.890931 3.441456 avg hole
diam (in) 1.415055 1.423386 1.344446 1.138162 1.354904 quarrying
rate (m.sup.3/hr) 0.001249 0.002038 0.001587 0.002101 0.003327
[0188] The process was conducted on other rock types including
Sioux Quartzite, Wausau Granite, Berea Sandstone, and
granodiorites, as shown in Table 3, as well as Barre, and Westerly
granites:
TABLE-US-00003 TABLE 3 Example results for hydrothermal spallation
drilling of boreholes in other rock types run # 6 7 8 9 10 rock
type wausau souix berea granodiorite granodiorite granite quartzite
sandstone hole volume (cc) 202.3 199.1 195.7 133.5 131.7 hole depth
(cm) 10.202 11.121 11.32 8.72 9.243 final drill nozzle depth (cm)
4.48818 4.445 4.572 3.62204 4.198 final stand off (cm) 5.71382
6.676 6.748 5.09796 5.045 penetration rate (pump setting) 9 18 27 9
9 run time (sec) 179 138 69 167 183 penetration rate (cm/min) 2.5 5
7.5 2.5 2.5 quarrying rate (cc/min) 67.81 86.57 170.17 47.96 43.18
avg hole area (cm 2) 19.83 17.90 17.29 36.86 14.25 avg hole
diameter(cm) 5.02 4.77 4.69 6.85 4.26 avg hole diam (in) 1.98 1.88
1.85 2.70 1.68
[0189] Other tests were conducted on Sierra White Granite while
independently varying a number of parameters including temperature,
mass flow, axial stress, confining stress, nozzle diameter, jet
velocity, heat flux, rate of drill head displacement. Table 1,
above, indicates determined parameters used to enable hydrothermal
spallation in one embodiment of the invention.
[0190] Other tests following Example 1 were conducted with
hydrostatic pressures including near ambient, 1500 PSI
(subcritical), and 3500 PSI (supercritical), to demonstrate the
viability of this system from shallow to deep wellbores.
Example 3
Borehole Drilling-4'' Diameter in Hard Rock
[0191] A 4'' diameter hole is pre-drilled to a depth of 5'' in
Sierra White granite rock block measuring 24.times.24'' square and
36'' tall. A drill head interface is placed in the pre-drilled hole
and sealed in place with high temperature cement. The block is
centered in cylindrical steel mold 38'' diameter, 44'' in length,
with a 0.375'' wall. This mold had been split down the side and
support railings were welded onto the outside edge. Bolts are used
to clamp the two halves of the mold together. Concrete is poured to
fill the empty volume between the rock block and mold. The concrete
is allowed to cure for 10 days, after which time the bolts are
tightened to provide 150 psi clamping pressure on the sample. A
diagram of the apparatus is shown in FIGS. 14A-C.
[0192] Approximately 450 g of Instant Steam catalyst obtained from
Oxford Catalyst PLC is loaded into a converging radial flow reactor
and placed inside a 27/8'' OD drill head, as shown in FIG. 11. The
drill head is slid into the drill head interface. Before the start
of a test, the drill head is driven to the bottom of the predrilled
hole and a depth is read off of the computer controls. The drill
head is then retracted approximately 10'' from the bottom of the
hole to allow cooling water from the drill head interface to enter
the bottom of the hole. A mixture of 38% hydrogen peroxide and 12%
methanol by weight is pumped into the catalyst bed at 3200 mL/min.
Neither the catalyst nor the fuel/oxidant fluid is preheated, and
no additional heat source such as a glow plug, spark, or flame for
the reaction is used. The mixture "lights off" over the catalyst
bed producing a 800.degree. C. jet of steam which exits a single,
0.189'' diameter non rotating nozzle located along the central
axis.
[0193] The drill head interface is advanced quickly through a
stainless steel seal in the drill head interface, isolating it from
the cooling water, and into the predrilled hole a to a distance of
5'' off the bottom of the hole; the advance rate is then reduced to
a setpoint drilling rate of 10'/h by a stepper motor, gear reducer,
drive screw, ball nut, and static and sliding support members. A
load cell is included to measure the drive force transmitted to the
drill assembly. The drill is advanced to its full stroke, roughly
13'' below the depth of the predrilled hole.
[0194] The reaction is immediately quenched by stopping the flow of
the reactants, and the drill is removed to reveal a hole that
extends 5'' past the final depth of nozzle exit. The sample is
removed from the concrete and sectioned to display the hole that is
created, as shown in FIG. 14.
Example 4
Field Drilling
[0195] A thermal spallation system can be deployed on a customized
AmKin 800 V track mounted coiled tubing unit. A 20' long
27/8-31/2'' OD bottom hole assembly is prepared from
instrumentation and controls subassembly (or "sub"), a release sub,
a dynamic barrier sub, stabilizers and centralizers, and an
iteration of the steam generation sub described in Example 4. The
steam generation sub houses an axial catalyst bed 21/2'' in
diameter and 12'' long filled with Oxford Catalysts Instant Steam
catalyst. The bottom hole assembly is attached to a Tenaris HS-90
2.00'' steel coiled tubing with a 0.134'' wall through a connector
sub. Inside of the coiled tubing, a 3/8'' OD nitric-acid passivated
stainless steel capillary is housed to transport the unreacted
fluid to the steam generation sub, and a 5/16'' 7-conductor
wireline cable is used for communication in the instrumentation
controls sub.
[0196] A starter well is drilled into competent rock and lined with
4'' ID casing. At the top of the casing is mounted a wellhead
diverter with stripper rubber. The bottom hole assembly and coiled
tubing is run through a wellhead diverter seal to the bottom of a
water-filled 300' hole.
[0197] The unreacted fluid is prepared at the surface by
continuously metering 52% high test peroxide, reagent grade
methanol, and deionized water into a mix tank to produce 38%
peroxide and 12% methanol. The mixture is pumped through the
capillary at 1 gallon per minute to the catalyst bed where it
self-energizes and reacts with the catalyst element without the
need for an external energy source (such as a spark, glow plug or
flame holder) thus generating a 800 C reacted fluid, without an
inherently unstable flame or the need for cooling water to protect
the materials of construction or overheating of the rock. This
reacted fluid is then emitting through a 0.189'' nozzle and
directed at the bottom of the hole, causing rapid spallation of the
rock. The coiled tubing is fed into the hole at a rate of 20'/h by
means of the coiled tubing injector on the AmKin 800 V continuously
drilling a 4'' borehole in the solid granite. Spalls are swept
through the dynamic seal assembly where they meet a 50 gallon per
minute flow of water flow, which has traveled down inside the 2''
coiled tubing and exited a series of upward pointing jets, to cool
the reacted fluid and carry the spalls to the surface. At the
surface, the spalls are removed by a series of "shakers", cyclones,
and filters, the water is cooled by a 200 kW mud cooler, and
continuously recirculated.
Example 5
Multilaterals with Hole Opening
[0198] A system as described in Example 4 can be used to create
multilaterals. At the desired depth, the bottom hole assembly is
deviated, the spallation jet is directed at the wall of the
borehole causing the drill to create a hole off-axis from the
existing borehole. The bottom hole assembly is advanced using the
coiled tubing injector and intersects additional fracture networks
which can provide flow to the main wellbore. When the final target
depth ("TD") is reached, the unreacted fluid is directed through a
second catalyst bed that is in fluid communication with 6 jets
oriented normal to the axis of the bottom hole assembly and spaced
60 degrees apart around the circumference of the tool. The
unreacted fluid is pumped again and reacted fluid exits the
circumferential jets, expanding the diameter of the wellbore as the
bottom of the hole assembly is withdrawn on the coiled tubing.
Periodically, this hole opening process is paused and the well is
allowed to produce fluid, blowing produced spalls and loose rock
from the fractures. Flow sensors including "spinners", and
thermocouples are used to infer the flow rate from a given
fracture. If additional hole opening is required, the hole opening
is restarted. In certain sections of the well where larger/global
hole opening is desired, the bottom hole assembly can be held in
place, causing extensive spallation, macrofracturing, breakout and
collapse of sections in the producing zone.
Example 6
Hole Opening of a 0.75'' Borehole
[0199] Using the procedure of Example 1, a Sierra White granite
rock core measuring 4'' in diameter and 6'' long was prepared by
pre-drilling a 0.75'' diameter hole 4'' deep on the top surface.
The core was then loaded into a stainless steel pressure vessel
described in Example 1.
[0200] The thermal spallation system includes a 0.5'' ID.times.3''
long catalyst chamber which exits through a single, 0.04'' diameter
non-rotating nozzle oriented perpendicular to the existing
predrilled hole. The catalyst chamber is filled to a height of
roughly 1.5'' with 0.5% platinum on 1/16'' spheres having a surface
area of 100 m.sup.2/g. A series of stainless steel screens,
spacers, and diffusers allow fluid to pass through while holding
the catalyst bed in place. The drill head is insulated from
surrounding cooling water by a 0.040'' gap pressurized with
nitrogen. The drill head is held in a large cooling water chamber
during start up.
[0201] The hydrostatic pressure in the vessel is then raised to
1600 PSI by means of a back-pressure dome regulator. An axial load
of 4500 PSI and confining pressure of 3000 PSI are applied by
separate pumps acting upon the core to simulate deep geological
formation conditions. An air actuated pump is used to deliver 3 g/s
of a 20% by volume methanol in deionized water through the
preheater which raises the temperature of the unreacted fluid to
250-300.degree. C. A high pressure oxygen flow is metered into the
preheated aqueous methanol solution at sub-stoichiometric
ratios.
[0202] The thermal spallation system uses methyl alcohol fuel, and
an O.sub.2 oxidant. The aqueous methanol/O.sub.2 solution travels
through the spacers, screens, and diffuser and over or through the
catalyst bed. The catalyst is not preheated and no additional heat
source is used. The catalytic oxidation of the methanol produces
heat within the water which raises the temperature of the fluid to
800-900.degree. C.
[0203] The high temperature fluid exiting the nozzle into the
cooling chamber is initially diverted and cooled by a 4 GPM water
flow. The flow of aqueous methanol is increased to 9 g/s over 2
minutes while simultaneously adjusting the oxygen flow. The drill
head is then driven by a high pressure fluid pump at a rate of 7.5
cm/min through a stainless steel seal, isolating it from the
cooling water, and into the predrilled hole. The reacted fluid
spalls the wall of the borehole until it reaches the full stroke of
the equipment, roughly 1.5'' below the predrilled rock surface.
Fluid and spalls exit the borehole into the cooling water above the
rock via a 0.189'' tube approximately 1.5'' in length. The bulk
fluid then passes through a series of screens which remove the bulk
of the spalls before the bulk fluid passes the back pressure dome
regulator and into a large collection tank.
[0204] The drill head is rapidly retracted through the borehole
seal, allowing cooling water to fill the hole and the jet to be
diverted, quenching the spallation process. Aqueous methanol and
oxygen flow rates are gradually reduced and the preheater is turned
off.
[0205] The sample is then removed from the cell. A large slot is
formed along the length of the predrilled hole in the same
orientation as the jet, increasing the diameter by roughly
2.times..
[0206] Effective experiments, following Example 5, holding the jet
stationary to open the hole globally; using axial jets, multiple
jets, and diffuse heating; and where rock is intentionally
fractured either or parallel or normal to either the existing
borehole or the jets have also been conducted. In one embodiment,
as shown in FIG. 18, using a vertical spallation jet in a
predrilled 7/8'' hole 1'' deep (shown as dashed lines) into a 4''
diameter rock core increased the diameter by roughly 2.times. and
created a thermally affected zone (shown by arrow) of highly
altered materials with reduced strength, as determined by SEM-EDAX,
thin sections, microscopy, punch and modified Chercar testing.
Example 7
Thermal and Mechanical Drilling
[0207] Spalls and/or a reacted rock region can be formed as
described above. A reamer element, including one or more reamer
elements mounted to the housing and located back from the distal
portion of the thermal spallation system, can then be used to ream
the thermally effected rock at the outer sides of the borehole
created by the thermal spallation system to enlarge and/or shape
the borehole, as required.
Example 8
Thermal Heating and TSP Drag Bit
[0208] Spalls and/or a reacted rock region can be formed as
described above. A drag bit with TSP cutters is then used to remove
the thermally effected rock from the borehole more easily than if
the rock was not heated.
Example 9
Rock Sample Tests
[0209] Thin sections: samples extracted from rocks in Examples 1-4
were cut into small sections using diamond blades and sent to a
thin section preparation laboratory. The samples were evacuated and
saturated with a blue epoxy to identify pores and fractures. The
samples were polished and then mounted to a glass slide and the
section ground down to a thickness required using a transmission
microscope with polarizing lens to determine mineral structure
alteration and other microscopic features.
[0210] Microscopic observations on the regions near the borehole
suggest thermal fracturing of grains especially quartz and
feldspars but little or no alteration of these minerals is apparent
in the micrographs.
[0211] Binocular microscope: samples were inspected with a
binocular microscope looking for evidence of alteration fractures
and other feature associated with changes in the physical or
chemical properties due to the rapid heating accompanying
hydrothermal spallation. Radial crack were identified in many of
the samples that have the appearance of being filled with small
quartz remnants (spalls). A general bleaching of the thermally
altered surface suggests removal of iron and other color generating
compounds.
[0212] Punch tests: a small spring loaded punch (pointed tool
steel) was used to remove small amounts of rock. The spring force
on each punch when triggered is approximately 15 pounds total. The
removed rock was collected and the total amount weighed. A series
of punches tests (20 ea) were used on each sample on the thermally
affected zone and on virgin rock, and results shown below:
TABLE-US-00004 Rock Removed (grams from 20 punches) Thermally- %
Rock Type Untreated Affected Zone Increase Sierra White 0.014 0.084
600% Granite Red Wausau 0.019 0.044 232% Granite Diorite 0.017
0.057 335% Souix Quartzite 0.017 0.027 159% Berea Sandstone 0.053
0.127 240%
Dye penetrant: a visual dye penetrant was applied to the surface of
the thermally altered rocks to see the extent and depth of the
fracturing/alteration. After application the rocks were visually
inspected with the binocular microscope. FIG. 20 shows an image of
an example diorite sample indicating the depth of penetration of
the dye into the altered zone and the flow of dye into two smaller
fracture zone perpendicular to the altered region. In various
embodiments of the invention, dye penetration from about 0.7 cm, at
the regions closest to where the jet is impacting the rock, to
approximately 1.5 cm further up the annulus, where the rock has
been exposed to the superheated fluid longer, may be achieved.
REFERENCES
[0213] All publications and patents mentioned herein, including
those items listed below, are hereby incorporated by reference in
their entirety as if each individual publication or patent was
specifically and individually incorporated by reference. In case of
conflict, the present application, including any definitions
herein, will control. [0214] U.S. Pat. No. 5,771,984; U.S. Pat. No.
7,742,603; U.S. Pat. No. 7,025,940; US2008/0093125 [0215]
"Feldspars and Feldspathoids, Structures, Properties, and
Occurrences: Structures, Properties and Occurrences," by William L.
Brown, North Atlantic Treaty Organization Scientific Affairs
Division, Published by Springer, 1983. [0216] "Hydrolytic weakening
of quartz and other silicates," by D. T. Griggs, Geo-phys. J. Roy.
Astron. Soc., 1967. [0217] "Origin of granite in the light of
experimental studies," by Tuttle, O. F. and N. L. Bowen, Geol. Soc.
Am. Mem. 74, 1958.
EQUIVALENTS
[0218] While specific embodiments of the subject invention have
been discussed, the above specification is illustrative and not
restrictive. Many variations of the invention will become apparent
to those skilled in the art upon review of this specification. The
full scope of the invention should be determined by reference to
the claims, along with their full scope of equivalents, and the
specification, along with such variations.
[0219] Unless otherwise indicated, all numbers expressing
quantities of ingredients, reaction conditions, and so forth used
in the specification and claims are to be understood as being
modified in all instances by the term "about." Accordingly, unless
indicated to the contrary, the numerical parameters set forth in
this specification and attached claims are approximations that may
vary depending upon the desired properties sought to be obtained by
the present invention.
[0220] The terms "a" and "an" and "the" used in the context of
describing the invention (especially in the context of the
following claims) are to be construed to cover both the singular
and the plural, unless otherwise indicated herein or clearly
contradicted by context. Recitation of ranges of values herein is
merely intended to serve as a shorthand method of referring
individually to each separate value falling within the range.
Unless otherwise indicated herein, each individual value is
incorporated into the specification as if it were individually
recited herein. All methods described herein can be performed in
any suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g. "such as") provided herein is intended
merely to better illuminate the invention and does not pose a
limitation on the scope of the invention otherwise claimed. No
language in the specification should be construed as indicating any
non-claimed element essential to the practice of the invention.
[0221] Having described certain embodiments of the invention, it
will be apparent to those of ordinary skill in the art that other
embodiments incorporating the concepts disclosed herein may be used
without departing from the spirit and scope of the invention.
Accordingly, the described embodiments are to be considered in all
respects as only illustrative and not restrictive.
* * * * *