WO2012018830A1

WO2012018830A1 - Dynamic barrier for thermal rock cutting

Info

Publication number: WO2012018830A1
Application number: PCT/US2011/046286
Authority: WO
Inventors: Nicholas Sazdanoff; Robert M. Potter; Jared M. Potter; Donald S. Dreesen; Thomas W. Wideman; Ed. Mccullough
Original assignee: Potter Drilling, Inc.
Priority date: 2010-08-02
Filing date: 2011-08-02
Publication date: 2012-02-09

Abstract

The invention relates to methods and apparatus for providing a fluid exclusion barrier between fluid regions of a thermal rock cutting system. An example method includes directing a rock cutting system having a distal portion down a borehole, and isolating a first fluid within a proximal portion of an annulus formed between the rock cutting system and a wall of the borehole by generating a fluid exclusion barrier within the annulus upstream of the distal portion of the rock cutting system and substantially preventing the flow of the first fluid through the fluid exclusion fluidic barrier toward the distal end of the borehole. The method may also include directing substantially all material from a distal end of the borehole to pass through the fluid exclusion barrier towards a proximal end of the borehole while

Description

DYNAMIC BARRIER FOR THERMAL ROCK CUTTING

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of, and incorporates herein by reference in its entirety, U.S. Provisional Patent Application No. 61/369,935, which was filed on August 2, 2010.

FIELD OF THE INVENTION

[0002] In various embodiments, the invention relates to methods and apparatus for conducting processes capable of spalling, cutting, or penetrating a material, such as rock. More particularly, the disclosed methods and apparatus may be used for isolating fluid regions in a borehole during the creation or expansion of a borehole for use in a geothermal energy system.

BACKGROUND OF THE INVENTION

[0003] Mechanical drilling, such as rotary or slide drilling, used for the creation of boreholes in, for example, resource mining, oil and gas, or geothermal applications, can be difficult in hard rock and high temperature environments. In these environments, rates of penetration (ROP) may be as little as 2-15 ft/hr. Furthermore, the extreme wear on the drill bit and drill string can necessitate removing the hardware from the hole, a process called

"tripping". In some cases, more time may be spent "tripping" than drilling the well.

[0004] Just as challenging is expanding the diameter of an existing borehole in hard rocks or in high temperature environments. While hole opening has been shown to significantly increase the productivity or injectivity of boreholes, current methods may not be effective in hard rocks or high temperature environments. For example, expandable mechanical reamers tend to be very slow and prone to breakage in the hard rocks and high temperatures of geothermal wells, and have very limited depth of cut. Fluid and abrasive jetting may be used for relatively soft or poorly consolidated rock common in petroleum wells, but may be relatively ineffective against hard rocks.

[0005] Thermal spallation drilling and hole opening, which use a high temperature flame or fluid jet in a gas, liquid, or fluid filled borehole, has been proposed as a more effective means to produce or expand boreholes in hard rock, compared to mechanical processes. While thermal spallation drilling and hole opening systems theoretically present great promise, a number of difficulties must be overcome in order to deploy these systems in actual downhole environments. One of the greatest challenges facing the commercial use of thermal technologies is maintaining isolation of the hot, working fluids (flame, steam, supercritical water or other low density superheated working fluid, as well as laser, arc, plasma, and combined thermo-mechanical process fluids) in the rock cutting region at the borehole wall or distal end of the borehole, from the relatively cold liquids, gases or fluids in the rest of the borehole. The hot, rock cutting or working region may be filled with one or more hot fluids, e.g., a mixed-phase fluid, that has a lower density than the liquid water, "mud", multi-phase, steam, or other circulating fluid in the colder region above. This creates Rayleigh-Taylor (RT) instability at the boundary between the two fluids, which occurs when a less dense fluid is supporting a more dense fluid. This instability, combined with the turbulent flow of fluids around the spallation flame or jet, may pull the cooler fluid into the hot, rock cutting region, effectively quenching the rock cutting process. Typically, thermal rock cutting processes have not provided a boundary between these two fluids to allow cost-effective commercial use of this drilling or hole opening technology.

SUMMARY OF THE INVENTION

[0006] As such, there is a great need for methods and apparatus for isolating the cool region in the bulk of a borehole from the hot region required for thermal rock cutting processes localized at the bottom of the borehole or borehole wall. These methods and apparatus allow the heat from for the thermal rock cutting to be effectively transferred to the rock, thereby inducing rapid rock cutting, and enabling the cost-effective production or hole opening of boreholes under conditions needed to access alternative energy sources, such as geothermal resources or unconventional natural gas.

[0007] The present invention is directed towards novel methods and apparatus for use in creating boreholes or enlarging boreholes for, e.g., geothermal energy systems, unconventional gas, or other resource exploration, production, injection, or extraction through spalling or thermally cutting rock. More particularly, various embodiments of the invention relate to methods and apparatus for isolating different fluid regions of a thermal spallation drilling or hole opening system to prevent quenching of a thermal spalling process resulting from the undesirable introduction of cooler fluid into the rock cutting region. [0008] One aspect of the invention includes a method of providing a fluid exclusion barrier that overcomes the RT instability between fluid regions in a borehole, preventing the cooler fluid or mud from entering the rock cutting region and quenching the drilling or hole opening process. The method includes directing a drilling or hole opening tool or downhole rock cutting system having a distal portion down a borehole, and isolating a first fluid within a proximal portion of an annulus formed between the downhole system and a wall of the borehole by generating a fluid exclusion barrier within the annulus upstream of the distal portion of the rock cutting system and substantially preventing flow of the first fluid through the fluid exclusion barrier into the rock cutting region. The method may also include directing substantially all material from a distal end of the borehole to pass through the fluid exclusion barrier towards a proximal end of the borehole. The rock cutting system may be a drilling system, a hole opening system, and/or an air-based thermal spallation system.

[0009] The first fluid may include, or consist essentially of, at least one of water, drilling mud, or aerated foam. The at least one water or drilling mud or aerated foam, may contain oils, gels, thixotrops, viscosifiers, polymers, stabilizers, weighting agents, gases, and other additives typically used in the oil and gas and geothermal industries, and a combination thereof. The first fluid may also be substantially a gas or supercritical fluid, composed substantially of steam, air or nitrogen. The first fluid may also contain the products of the downhole heat generation system and rock cutting such as combustion gases, superheated water, steam, supercritical water, condensed water, rock cuttings, and added particles (added to the cutting stream or generated in situ by e.g. flame spray synthesis) and a combination thereof. Means for generating the fluid exclusion barrier may include, or consist essentially of, at least one fluid outlet for directing a second fluid within the rock cutting system into the annulus. The at least one fluid outlet may be located substantially flush with an outer wall of the rock cutting system. The second fluid may be substantially similar to the first fluid. The second fluid may also include at least one of a chemical additive, a thermally- sensitive foaming agent, a buffer, and a base.

[0010] In one embodiment, the fluid outlet comprises, or consists essentially of, at least one of a fluid directing jet nozzle and a fluid directing slot. The second fluid may exit the at least one fluid directing jet nozzle at a flow rate, for example, of at least about 37 gallons/minute and, in some embodiments, at least about 50 to 75 gallons/minute (for a 4 inch borehole with an annulus of ½" between the rock cutting system and the borehole wall). In certain embodiments, larger boreholes and/or smaller drill strings a may require higher mass flows of the second fluid.

[0011] The at least one fluid outlet may be adapted to direct the second fluid from the outer wall of the drilling or hole opening system towards a proximal end of the borehole at an acute angle to an elongate central axis of the borehole. The acute angle may, for example, be an angle between about 5° and about 60°, or between about 10° and about 45°.

[0012] The at least one fluid outlet may be adapted to direct adjustably the second fluid from the outer wall of the rock cutting system. In one embodiment, the method further includes directing the second fluid from the outer wall of the rock cutting system towards the bottom of the borehole at an acute angle to an elongate central axis of the distal end of the rock cutting system during other operations that require, for example, that the high temperature jet must be cooled, that the bottom of the hole must be clear of debris, or that the tool must be pushed out of a section of hole. The at least one fluid outlet may direct the first fluid against the borehole wall to stop the rock cutting process, either by dropping the temperature of the below the spallation temperature of the rock, or by cooling the rock face. The flow of the second fluid may be distributed or separated in various positions along the length of the tool. For example, one portion of the second fluid may be added close to the thermal rock cutting process to cool the hot, rock cutting fluid below the onset of spallation, and the remainder of the second fluid added closer to the proximal end of the tool to provide a fluid exclusion barrier and assist in rock cuttings transport to the surface.

[0013] The means for generating a fluid exclusion barrier may include, or consist essentially of, a plurality of fluid outlets arranged symmetrically around the outer wall of the drill or hole opening system upstream of the distal portion thereof. In one embodiment, the plurality of fluid outlets are adapted to rotate around an elongate central axis of the drilling or hole opening system. In one embodiment, the plurality of fluid outlets may be at an acute angle relative to an elongate central axis of the borehole and offset radially to produce a swirling or vortex pattern.

[0014] In another embodiment, flutes in, for example, a stabilizer, accelerate the fluid through the barrier to reduce the RT instability. The stabilizer can also serve as a bore wall wiper to scrape off wall jet softened formation that is inside the specified hole diameter, and may be combined with mechanical processes. It can also serve as a "no-go" in drilling applications to assure that the drill can advance only after the rock cutting produces the required minimum hole diameter. The vertical position of the bottom of the blades may serve as a standoff contact such that a very low constant weight applied to the drill bit may be sufficient to advance the stabilizer and scrape the soft wall to shape a round hole, while at the same time producing an optimum, or near-optimum, nozzle standoff distance at the bottom of the hole.

[0015] In one embodiment, a stabilizer may include flow ports that produce a fine spray of a small fraction of the total second fluid onto the hot wall of the recently spalled rock to quench the spallation process and flash a liquid second fluid to a gas to produce a large volume from a small mass flow. Reducing the temperature of the initial fluid in stages by the introduction of small amounts of the secondary fluid can also produce a gradient in fluid density reducing the tendency for a RT instability. In one embodiment, the quenching jets may drive the fluid at a high pressure, resulting in the production of a high pressure within fluid exclusion barrier. This high pressure will have the effect of driving fluid both up and down the flutes of the stabilizer and to spill over onto the surface of the blades to produce separation between the first fluid above the fluid exclusion barrier and the hotter rock cutting fluid below the barrier. Jets pointed at an acute angle relative to an elongate central axis, exiting the tool above an upset in the tool outer diameter (such as a stabilizer) can have synergistic effects. The method may include pumping the second fluid through at least one fluid conduit in the drilling or hole opening system to the at least one fluid outlet, and/or controlling a volumetric flow rate of the second fluid.

[0016] The dynamic barrier properties for thermal drilling or opening of boreholes may be regulated through controlling various parameters. For a given hole size, tool size, fluid exclusion barrier size, open area, gap size, hydraulic diameter, borehole and tool surface roughness, pore pressure, and working fluid temperature, the distance of the fluid exclusion barrier to the rock cutting jets, length of the fluid exclusion barrier, density of fluids, viscosity of fluids, mass flow of fluids, velocity of fluids, spacing and angle of second fluid jets, Reynolds Number of fluids, frictional pressure drop along the fluid exclusion barrier, dynamic pressure in the fluid exclusion barrier, momentum in fluid exclusion barrier, dynamic pressure / open area, dynamic pressure / hydraulic diameter, dynamic pressure / gap size, thermal cutting power, thermal cutting power / open area, thermal cutting power / hydraulic diameter, velocity / open area, velocity / hydraulic diameter, and/or volume of non-condensable gas may be modified for the fluid exclusion barrier to separate the first fluid from the working or rock cutting region.

[0017] The fluid exclusion barrier may, for example, have a dynamic pressure of at least about 50 Pa for one specific set of conditions. In other embodiments, different conditions and control parameters may result in higher or lower dynamic pressures. In one embodiment, the fluid exclusion barrier has a dynamic pressure that is greater than the Raleigh-Taylor instability at the fluid exclusion barrier.

[0018] In one embodiment, the distal portion of the drilling or hole opening system includes at least one thermal spallation jet nozzle. The material directed to pass through the fluid exclusion barrier may include at least one of an output of the thermal spallation jet nozzle and material excavated from the distal end of the borehole or borehole walls. The output of the thermal spallation jet nozzle may include, or consist essentially of, a reacted fluid. The reacted fluid may include steam or supercritical water. The reacted fluid may include particles added to improve the rock cutting or generated in-situ by (e.g. flame spray synthesis). The reacted fluid may also include a base, such as a hydroxide. The reacted fluid may exit the thermal spallation jet nozzle at a temperature of approximately 400-1200°C, 600-1000°C, up to, or greater than, about 800°C, and/or, for example, at a flow rate of up to about 70 grams/second for a 4" hole drilled at 20-30'/h or 2800 grams/sec for a hole opened at ΙΟ'/h. In general, flow rate scales with the square surface area of the exposed rock and the Rate of Penetration (ROP), or by the volume of rock removed. As such, higher or lower flow rates may be achieved for different conditions and control parameters. In one embodiment, the temperature of the thermal spallation jet nozzle may be higher or lower than 800°C, if required. In one embodiment, at least one of the output of the thermal spallation jet nozzle and the material excavated from the distal end of the borehole creates a dynamic pressure in the annulus between the rock cutting system and the wall of the borehole that assists in maintaining the fluid exclusion barrier.

[0019] In one embodiment, the fluid exclusion barrier includes at least one of a brush and/or a shim. The shim may include a hydraulically activated bladder and/or a pressure or flow actuated flapper. The brush may include a plurality of elements (arranged, for example, in rows or randomly), wherein the plurality of elements may be selected from the group consisting of high temperature or corrosion resistant metal wires, ceramic fiber sheets, braided wires, high temperature polymers, and combinations thereof. A small amount of a cooling fluid, such as a second fluid, may be added directly below the fluid exclusion barrier to improve the longevity and performance of the elements. The fluid exclusion barrier may form a bypass path adapted to allow material from the distal end of the borehole to pass therethrough. In one embodiment, a fluid exclusion barrier may include at least one fluid outlet for the second fluid combined with a brush, shim, or fluted stabilizer.

[0020] Another aspect of the invention includes an apparatus for providing a fluid exclusion barrier between fluid regions in a borehole. The apparatus includes a rock cutting system having a distal portion adapted for insertion down a borehole, and means for generating a fluid exclusion barrier within an annulus formed between the drilling system and a wall of the borehole, or between the hole opening system and existing borehole, upstream of the distal portion of the drilling or hole opening system. The fluid exclusion barrier may be adapted to substantially prevent the flow of a first fluid through the fluid exclusion fluidic barrier toward the distal end of the borehole under certain operating conditions. In some embodiments, the fluid exclusion barrier may allow substantially all material from the distal end of the borehole, such as reacted fluids or fluids produced from the wellbore, to be directed through the fluid exclusion barrier towards a proximal end of the borehole. In other embodiments, under other operating conditions, such as highly fractured rock, a significant amount of the reacted fluid or rock cuttings may not return through the fluid exclusion barrier, but first fluid is still prevented from entering the rock cutting region. In one embodiment, when the steam jet turns off, the barrier may not entirely hold back the fluid in the annulus, resulting in some back-flow of the first fluid. In one embodiment, the first fluid includes, or consists essentially of, at least one of drilling mud, aerated foam, water, air, steam or a combination thereof.

[0021] The means for generating the fluid exclusion barrier may include at least one fluid outlet for directing a second fluid within the drilling or hole opening system into the annulus. The at least one fluid outlet may be located flush, or substantially flush, with an outer wall of the rock cutting system. The at least one fluid outlet may include, or consist essentially of, at least one of a fluid directing jet nozzle or a fluid directing slot. The at least one fluid directing jet nozzle may direct the second fluid at a flow rate of at least about 37 gallons/minute.

[0022] The at least one fluid outlet may be adapted to direct a second fluid from the outer wall of the rock cutting system towards a proximal end of the borehole at an acute angle to an elongate central axis of the distal end of the rock cutting system. The acute angle may be between about 5° and about 60°, or between about 10° and about 45°. The second fluid may be selected from the group consisting of a superheated water, steam, supercritical water, combustion gases, rock cuttings, particles (from e.g. flame spray synthesis) and a combination thereof. The second fluid may also include at least one of a chemical additive, a thermally- sensitive foaming agent, a buffer, and a base

[0023] The at least one fluid outlet may be adapted to direct adjustably the second fluid from the outer wall of the rock cutting system. In one embodiment, the fluid outlet directs the second fluid from the outer wall of the rock cutting system towards a distal end of the borehole at an acute angle to an elongate central axis of the distal end of the rock cutting system during insertion of the rock cutting system into the borehole. A plurality of fluid outlets may be arranged symmetrically around the outer wall of the rock cutting system upstream of the distal portion thereof. The plurality of fluid outlets may be adapted to rotate around an elongate central axis of the rock cutting system.

[0024] The apparatus may include means for pumping the second fluid through at least one fluid conduit in the rock cutting system to the at least one fluid outlet and/or means for controlling a volumetric flow rate of the second fluid. The fluid exclusion barrier may have a dynamic pressure of at least about 50 Pa.

[0025] In one embodiment, the distal end of the rock cutting system includes at least one thermal spallation jet nozzle. The material directed to pass through the fluid exclusion barrier may include at least one of an output of the thermal spallation jet nozzle and material excavated from the distal end of the borehole. The output of the thermal spallation jet nozzle may include, or consist essentially of, a reacted fluid such as, but not limited to, steam. The reacted fluid may exit the thermal spallation jet nozzle at a temperature of up to about 800°C and/or at a flow rate of up to about 70 grams/second. In one embodiment, at least one of the output of the thermal spallation jet nozzle and the material excavated from the distal end of the borehole creates a dynamic pressure in the annulus between the rock cutting system and the wall of the borehole assists in maintaining the fluid exclusion barrier.

[0026] The fluid exclusion barrier may include at least one of a brush and a shim. The fluid exclusion barrier forms a bypass path adapted to allow material from the distal end of the borehole to pass therethrough. The shim may include, or consist essentially of, a hydraulically activated bladder and/or a pressure or flow actuated flapper. In one embodiment, the flapper may be pushed out against the borehole wall during periods when the dynamic seal is required. The brush may include a plurality of elements, including, but not limited to, fibers, braided wires, and combinations thereof.

[0027] In one embodiment, the rock cutting system includes at least one of a thermo- mechanical drilling system and a hole opening system. The barrier may also be used with other thermal excavations in a wellbore, including reaming, slotting, perforating, and side-tracking. The jets of the barrier may also be used to assist in the "clean out" of the hole, and to assist in the axial translation of the pipe in the hole, especially important in horizontal sections with slide drilling, by providing thrust, lift, and vibrations.

[0028] The barrier may, in one embodiment, be combined with a heat recovery system, such as a heat exchanger, to improve the thermal efficiency of the drill. For example, the reacted fluid can find a path of least resistance through an annulus between the 3.0" OD returns shroud and the 2 - 1/2" OD heating sub. The top of the annulus may connect to the hot side of the heat recovery (heat exchanger) sub just above the final heating sub. The inlet to the annulus inside the returns shroud may be located just below the fluid exclusion barrier that is attached to the outside of the bottom of the shroud. The outlet of the returns shroud may connect to the hot side inlet of the heat recovery sub. The returns shroud may be insulated from the heat recovery sub and from the cooler fluids outside the shroud just above the fluid exclusion barrier.

[0029] 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

[0030] 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:

[0031] FIG. 1 is a schematic cutaway perspective view of a thermal spallation rockcutting system including a dynamic barrier, in accordance with one embodiment of the invention; [0032] FIG. 2A is a schematic perspective view of a distal portion of a thermal spallation rock cutting system having a dynamic barrier assembly, in accordance with one embodiment of the invention;

[0033] FIG. 2B is a schematic partial cutaway view of the thermal spallation cutting system of FIG. 2A;

[0034] FIG. 2C is a schematic cross- sectional side view of a section of a distal working portion for a thermal spallation cutting system, in accordance with one embodiment of the invention;

[0035] FIG. 2D is a cross-sectional end view of a section of another distal working portion for a thermal spallation cutting system, in accordance with one embodiment of the invention;

[0036] FIG. 3 is a partial cross-sectional side view of a thermal spallation cutting system having a spall filter, in accordance with one embodiment of the invention;

[0037] FIG. 4A is a schematic cross-sectional side view of a thermal spallation cutting system having a dynamic barrier assembly in combination with a brush or shim barrier, in accordance with one embodiment of the invention;

[0038] FIG. 4B is a schematic perspective view of the thermal spallation cutting system of

FIG. 4A;

[0039] FIG. 4C is a partial cross-sectional side view of a thermal spallation cutting system having a stabilizer with embedded flutes, in accordance with one embodiment of the invention;

[0040] FIG. 4D is an end view of the stabilizer of FIG. 4C;

[0041] FIG. 5 is a chart indicating the relationship between dynamic pressure from a spalling fluid in an annulus of a borehole and borehole pressure, in accordance with one embodiment of the invention;

[0042] FIG. 6A is a schematic cross-sectional side view of a thermal spallation cutting system and dynamic barrier assembly test cell, in accordance with one embodiment of the invention;

[0043] FIG. 6B is an exploded cross-sectional side view of portions of the thermal spallation cutting system test cell of FIG. 6A;

[0044] FIG. 7A is an image of an example thermal spallation cutting system in operation in the test cell of FIG. 6A, in accordance with one embodiment of the invention;

[0045] FIG. 7B is an image of the dynamic barrier region of the thermal spallation cutting system of FIG. 7A in operation; [0046] FIG. 8A is a downhole image of a simulated roughened borehole for a thermal spallation cutting system test cell, in accordance with one embodiment of the invention;

[0047] FIG. 8B is an image of a thermal spallation cutting system in operation in the test cell of FIG. 8A;

[0048] FIG. 9 is a schematic cross- sectional view of a spallation hole opening system in a borehole, in accordance with one embodiment of the invention;

[0049] FIG. 10A is a schematic top view of a barrier supporting structure in accordance with one embodiment of the invention;

[0050] FIG. 10B is a schematic sectional view of the barrier supporting structure of FIG. 10A taken along the line A-A;

[0051] FIG. IOC is a schematic perspective view of the barrier supporting structure of FIG. 10A;

[0052] FIG. 11 A is a schematic top view of a barrier supporting structure in accordance with one embodiment of the invention;

[0053] FIG. 1 IB is a schematic side view of the barrier supporting structure of FIG. 11A;

[0054] FIG. 11C is a schematic perspective view of the barrier supporting structure of FIG. 11 A;

[0055] FIG. 12A is a schematic cross-sectional view of a spallation hole opening system with a barrier supporting structure in an expanded sealing position, in accordance with one embodiment of the invention;

[0056] FIG. 12B is a schematic cross- sectional view of the spallation hole opening system of FIG. 12A with the barrier supporting structure in a collapsed position;

[0057] FIG. 13A is a schematic cross-sectional view of a spallation hole opening system with a barrier supporting structure in an expanded configuration, in accordance with another embodiment of the invention;

[0058] FIG. 13B is a schematic cross- sectional view of the spallation hole opening system of FIG. 13 A with the barrier supporting structure in a collapsed position;

[0059] FIG. 14A is a schematic cross-sectional view of a spallation hole opening system with a flexible membrane barrier supporting structure in an expanded position, in accordance with one embodiment of the invention;

[0060] FIG. 14B is a schematic side view of the flexible membrane barrier supporting structure of FIG. 14A in the expanded position; [0061] FIG. 14C is a schematic perspective view of the flexible membrane barrier supporting structure of FIG. 14A in expanded position;

[0062] FIG. 15 is a schematic cross-sectional view of a movable packer in a borehole, in accordance with one embodiment of the invention;

[0063] FIG. 16A is a schematic cross-sectional side view of a spinning bladed educator, in accordance with one embodiment of the invention;

[0064] FIG. 16B is a schematic cross- sectional perspective view of the spinning bladed educator of FIG. 16A in accordance with one embodiment of the invention :

[0065] FIG. 17A is a schematic side view of a barrier supporting structure with shims in an expanded sealing position, in accordance with one embodiment of the invention;

[0066] FIG. 17B is a schematic side view of the barrier supporting structure of FIG. 17A in a closed position;

[0067] FIG. 17C is a schematic perspective view of the barrier supporting structure of FIG. 17A in the expanded sealing position;

[0068] FIG. 18A is a schematic cross-sectional view of a spallation hole opening system in a borehole, in accordance with one embodiment of the invention;

[0069] FIG. 18B is a schematic cross- sectional view of a spallation drilling system in a borehole, in accordance with one embodiment of the invention; and

[0070] FIG. 19 is a table of exemplary value ranges for various parameters of a thermal spallation rock cutting system, in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

[0071] For convenience, certain terms employed in the specification, examples and appended claims are collected here. These definitions should be read in light of the remainder of the disclosure and understood as by a person of skill in the art. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by a person of ordinary skill in the art.

[0072] The term borehole includes any opening that is created in the ground that is substantially longer than it is wide, such as a well, a wellbore, a well hole, and other terms commonly used or known in the art to define these types of narrow long passages in the earth. Although boreholes are generally oriented substantially vertically, they may also be oriented on an angle from vertical, to and including horizontal. Thus, using a level line as representing the horizontal orientation relative to the surface, a borehole can range in orientation from 0° (i.e., a horizontal borehole), to 90° (i.e., a vertical borehole) and greater than 90° (e.g., such as a heel and toe). Boreholes may further have segments or sections that have different orientations, they may be arcuate, and they may be of the shapes commonly found when directional drilling is employed. Thus, as used herein, unless expressly provided otherwise, the "bottom" of the borehole, the "bottom" surface of the borehole and similar terms refer to the end of the borehole, i.e., that portion of the borehole farthest along the path of the borehole from the borehole's opening, the surface of the earth, or the borehole's beginning. As used herein, unless expressly provided otherwise, the term borehole wall refers to the surfaces of the well substantially perpendicular to the orientation of the borehole.

[0073] The term hole opening refers to any process that increases the diameter of an existing borehole. This is sometimes referred to in the industry as "well enhancement", "reaming", or "under reaming". The increase in the diameter of the borehole does not need to be even around the circumference of the borehole. For example, hole opening can include the formation of slots into the borehole wall collinear with the orientation of the borehole, circumferential, or other geometries. It can also include irregular shapes, induced either by the cutting action of the tool, or by natural features in the rock, such as non-uniform stresses, differences in mineralogy, or fractures. Hole opening can include the process described in U.S. Patent Application Serial Nos. 12/575,857 and 13/048,405, each of which is incorporated herein by reference in its entirety.

[0074] The term rock generally refers to any coherent, naturally occurring substance generally composed of minerals. As used herein, a rock can also include any naturally occurring, subterranean solid, can be both homogeneous and heterogeneous, and composed substantially of minerals, metals, ores. Rocks can contain natural or hydraulic fractures, as well as liquids or gases within pore structures.

[0075] The term spallation refers to a rock cutting or material failure process that occurs when a high heat flux is applied to the surface of a hard or crystalline material. The thermal expansion and induced stress due to the heat flux causes surface materials to break away from the underlying layers. Existing stresses, flaws, or grain boundaries can assist in the spallation process. The term spall refers to fragments of material formed by the spallation process. [0076] The term tool or downhole tool refers to a piece of equipment or hardware which is deployed into a wellbore via a drill string, drill pipe, coiled tubing, wireline, or slick line.

[0077] The term fluid generally refers to a substance that has no fixed shape and yields easily to external pressure, or a continuous, amorphous substance whose molecules move freely past one another and that has the tendency to assume the shape of its container. Examples used herein include liquid (e.g. water, drilling muds), aerated liquid (e.g. aerated foams), gas (e.g. steam, nitrogen, air), or supercritical fluids (e.g. supercritical water).

[0078] The term working fluid refers to the high temperature fluid used to induce a heat flux on the rock surface and cause spallation. The working fluid may be composed of the reacted fluid.

[0079] Various embodiments of the invention relate to methods and apparatus for providing a barrier between different fluid regions of a cutting system such as, but not limited to, a thermal spallation drilling or hole opening system.

[0080] Thermal spallation cutting systems may be used in the spallation or excavation of material such as rock for the purpose of making, opening, or excavating boreholes. A thermal spallation process refers to a spallation process that uses an elevated temperature working fluid to facilitate removal rates. While gases (as part of a combustion process) may be used alone, a working fluid other than gas may be used, such as a working fluid that includes water (e.g., hydrothermal spallation), water or oil based drilling muds, oils, other supercritical fluids, other gases, and the like. Solids may also be entrained in the working fluid to improve the cutting process.

[0081] Example thermal spallation cutting systems may be capable, for example, of creating 20 feet of an 8 inch diameter borehole in about one hour, or 20 feet of a 4 inch borehole in about an hour or less, or about 0.2 inches of about 1 inch diameter borehole in about 4 minutes. Such systems 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 rock. The systems may be used to create vertical boreholes, horizontal boreholes, deviated boreholes, angled boreholes, curved boreholes, sidetracked boreholes, or any combination thereof. The cutting systems can also be used to modify the shape of a borehole, by for example, producing radial or vertical slots, perforating, expanding the diameter (reaming), as described in U.S. Patent Application Serial No. 12/575,857, or stabilizing the borehole by removing material that might otherwise "breakout", as described in U.S. Patent Application Serial No. 13/048,405, each of which was incorporated by reference above. An example thermal spallation cutting system may spall rock at a rate of about 100 ft /hour or more, which may be useful for example for the creation of tunnels, mineshafts, and the like. Example cutting systems including hydrothermal spallation jets are described in U.S. Patent Application Serial Nos. 12/575,823, 12/575,839, 12/575,852, 12/575,857, and

13/048,405, the disclosures of all of which are incorporated herein by reference in their entirety.

[0082] Thermal spallation cutting systems may include sensors, such as gyroscopes, magnetometers, and/or inclinometers, for monitoring the orientation of the cutting systems. Such systems and methods may also include temperature and/or pressure sensors, natural rock gamma ray sensors, spinners, resistivity/conductivity sensors, and/or 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. Sensors may be provided to selectively monitor flow entry points and/or temperature changes of fluids that influence the target and desired direction of cutting.

[0083] Example thermal spallation cutting systems may provide for both shallow cutting (e.g., up to about 1,000 feet or more) and deep borehole cutting (e.g., up to about 10,000 feet, 50,000 feet, or more, below the surface). This includes both drilling and hole opening operations.

[0084] Various thermal spallation rock cutting systems may be configured for drilling or opening boreholes in hard rock for geothermal, enhanced or engineered geothermal systems (EGS), and/or oil and gas applications for enhanced oil recovery or unconventional oil or gas production. Alternatively, the rock cutting systems 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, resource mining (conventional or solution mining), combined HDR (hot dry rock) solution mining, gas or liquefied natural gas (LNG) storage applications, C0₂ 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.

[0085] In general, thermal spallation methods may use, for example, hydrothermal, flameless, and/or sparkless systems to generate a heated, and/or reacted, working fluid. The thermal spallation methods may also use a combustion reaction tempered by the addition of additional gases or water to reduce the temperature of the jet, improving the longevity of the materials of construction and reducing the temperature of working fluid below the flame temperature of the neat combustion to prevent overheating of the rock surface. For example, a flameless chemical system may include a reaction including, but not limited to, a hydrothermal oxidation reaction, combustion, a thermite reaction, or an incendiary reaction. Such systems may allow the application of a heated working fluid to a surface zone of a target material such as a hard and/or crystalline rock with a substantially high heat flux. For example, various thermal spallation cutting systems may produce a working fluid for borehole creation that may produce a heat flux ranging from between 0.1 and 2 MW/m 2 (e.g., about 0.1 MW/m 2 , 0.5 MW/m², 1.0 MW/m², or 2 MW/m²) up to between 7 and 50 MW/m² (e.g., about 7 MW/m², 8

MW/m 2", 30 MW/m 2", or 50 MW/m 2") in various combinations, when in contact with the material. In alternative embodiments, thermal spallation rock cutting systems may produce a working fluid having a heat flux of about 0.01 to about 10 kW/m when in contact with the material to be removed. Such a heat flux may be used to form, for example, caverns, tunnels, mineshafts and other larger excavations.

[0086] In some embodiments, the disclosed methods, means, and apparatus are capable of achieving, maintaining, and/or directing a high temperature working fluid (in, for example, a reaction chamber) at a target rock surface that is not substantially higher than a certain desired temperature (e.g., not substantially higher that 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 °C (or about 500 °C above the ambient rock temperature) and about 900 °C or about the temperature of rock fusion and/or brittle ductile transition. An example thermal spallation rock cutting system can maintain a working fluid (e.g., steam) temperature of about 800°C at a target location within a geological formation.

[0087] Generating such temperatures and/or heat flux at a target location may be necessary for the spallation of rock by creating enough heat flux to remove spalls while substantially maintaining a temperature that does not 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, fresh material is exposed below the spall, and the spallation process may continue. 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.

[0088] In operation, rock cutting systems including thermal spallation drilling or hole opening systems include a distal end having a drilling/spalling tip (e.g., a drill bit and/or thermal spallation nozzle), and a drill string (i.e., a tubing string for supporting the distal end and connecting it to various systems at the surface) extending upstream of the distal end, along the borehole up to, for example, a control system located at or near the surface. In various embodiments, the drill string may include fluid conduits for transporting fluids between the surface to and from the distal end, communication links for sending control signals to and receiving sensor data from control system components and sensors located at one or more locations along the drill string and/or in the drilling/hole opening tip, and/or power conduits for providing power to the drilling/hole opening tip and/or sensors located therein.

[0089] One or more fluids, e.g., drilling mud, may be pumped down the drill string and into the annulus formed between an outer surface of the drill string and the wall of the borehole to provide hydrostatic pressure to prevent the borehole from collapsing or breaking out, as well as controlling fluid ingress from the surrounding rock into the borehole. Drilling mud may include, or consist essentially of, water, compressed air or gases, polymers, foaming agents, aerated foams, water-based mud, oil-based mud, and/or synthetic -based fluid. The fluids within the annulus may also be used to transport cuttings and/or spalls from the distal end of the borehole to the surface and for cooling the high temperature working fluid before it contacts temperature- sensitive portions of the drilling or hole opening tool or causes secondary spallation along the wall of the borehole. These fluids are generally unheated.

[0090] While the use of this drilling mud is important in stabilizing the borehole and transporting cuttings/spalls from the bottom of the borehole to the surface, it is important to isolate this cold fluid to prevent it from entering the hot, rock-cutting region and quenching the spallation jet (or other thermal spalling or cutting systems) at or near the distal end of the rock cutting system. Further, drilling muds can decompose at the temperatures of the working fluids and should be separated from such high temperatures. As such, a system has been developed to substantially prevent the flow of the colder fluid (first fluid or drilling mud) down into rock cutting region of borehole, while still allowing other fluid (working fluid, reacted fluid, produced reservoir fluids) and cuttings/spalls to pass up the borehole for removal. [0091] Various embodiments of the invention therefore include a dynamic seal/barrier assembly (DSA) that functions as a fluid exclusion barrier between fluid regions (i.e., a hot working fluid region and the cooler region containing the drilling mud or first fluid upstream thereof) to inhibit the drilling mud within the cooler region from entering the rock cutting region and quenching a spallation process. In addition to preventing cooling fluid from entering the bottom of the borehole, the dynamic barrier assembly or fluid exclusion barrier allows cuttings and/or spalls to pass through the dynamic barrier so that they can be entrained in the cooling fluid or first fluid and lifted up the borehole. As such, certain embodiments of the invention meet both of these functional requirements (i.e., preventing the first fluid within the annulus between the drill string and the wall of the borehole from entering the rock cutting region and, also, allowing cuttings/spalls to pass from the rock cutting region into the drilling mud or first fluid). These functions are achieved in a dynamic environment that has variable properties related to overall diameter and variation of diameter of the borehole, type of rock, temperature between regions, borehole pressure, size of spalls, and borehole surface roughness, among others.

[0092] In various embodiments of the invention, several technologies or combinations of technologies can be implemented to achieve the functional requirements of the dynamic barrier assembly in a wide array of operating environments. For example, the systems and methods described herein may be used to provide a fluid exclusion barrier between fluid regions in any borehole drilling or hole opening system having fluid located within an annulus between the rock cutting system and the wall of the borehole. For example, various embodiments of the invention may be used in hydrothermal spallation rock cutting systems, air-based thermal spallation rock cutting systems, combined mechanical/spallation rock cutting systems, mechanical rock cutting systems, and/or chemical or thermo-chemical rock cutting systems. Such rock cutting systems may be directed down a borehole to cut, spall, and/or otherwise remove rock from the bottom of the borehole to create a borehole in a geological rock formation for use, for example, in geothermal energy systems, or may be directed down a borehole to remove rock from the wall of an existing borehole to increase the diameter and reduce skin damage.

[0093] The fluid exclusion barrier may be a flexible component or assembly that is both actuated and cooled by the flow of water or other fluid. Close contact with liquid water may help maintain the temperature of the barrier material at or below the saturation temperature of steam at the local pressure, which increases the longevity of the seal material and widens the range of materials which can be used, such as certain elastomers, plastics, ceramics, metal or other materials that can survive the operation conditions. It may also be desirable to have a flexible barrier which can be inserted in the well in a unexpanded or flattened position and then expanded to fill large gaps, if necessary. If cooling is adequate, a high temperature polymer can be used to make a flexible, compliant seal. Small perforations can be made into the polymer to improve cooling of the side of the material which is in contact with the second fluid. Alternatively, a woven metal fabric can be used which would have better temperature resistance and thermal conductivity. Non-standard mesh patterns, such as the straight or reverse twilled dutch weave, or herringbone weave, can be used to provide a less permeable barrier with improved mechanical strength. The weave can be made from material forms with various cross sections, such as round wire or flat strips, or a combination thereof. A number of cables or bundles with internal water flow can also be used to form the barrier. The barrier could be formed from a number of overlapping non-woven metal strips such that they could be expanded to obstruct a large portion of an annular gap. Any of these concepts could be used in conjunction with other embodiments in order to improve the function or durability or the barrier.

[0094] It may be desirable to move the tool and barrier into place in an unexpanded position such that the barrier is not damaged by contact with the wellbore and does not cause the downhole tools to bind in the borehole. Once in place, the barrier can be actuated by a number of different methods, such as hydraulic force from the water or fluid flow, pneumatic pressure from air or oxidant flow, steam pressure, compressive axial force on the tool or weight on bit (WOB), centripetal force from rotating components, a ball drop, or an electrically controlled actuator.

[0095] A mechanical spring may be used to deploy the compliant seal against the inside of the wellbore. Band centralizers are well suited for this purpose as their shape allows them to pass smoothly over obstacles in the well, they provide a smooth flow path for steam and particles travelling up the annulus, and they perform the function of centralizing the tool in the wellbore. The band centralizers could be used in conjunction with a flexible membrane, sheet, weave, or fabric made from polymer, metal or some other material in order to expand the material into position against the wellbore wall. If the flexible membrane is affixed to the inside of the band centralizers, they may help prevent the membrane from abrading against the inside of the hole on the way down. If desired, the outer diameter of the band centralizer assembly can be increased by shortening it axially using WOB, a piston-cylinder energized with one of the higher pressure fluids, an electrical actuator, or any other known method.

[0096] A convex tool with a conical, parabolic, elliptical, torispherical or other shape which complements the interior shape of the bottom of the hole may be used to control the width of the gap formed between the inside of the bore and the outside of the tool. The width of this gap will determine the flow path and velocity of the upward flowing reacting fluid and can be designed to maintain fluid exclusion. Protrusions, standoffs, inserts, flutes, or some other features can be employed with this design to maintain the desired gap between the drill and the rock across a variety of conditions. An added benefit of this design is that the increased velocity flow along the rock face can be used to induce controlled "secondary" spallation using the wall jet rather than the directly impinging jet, thereby reducing the specific energy and increasing the cutting efficiency. This approach can be used in conjunction with an inward flow path drill design such that distribution of flow across the entire bottom of the wellbore can be achieved.

[0097] The distal end of the tool can be designed with flutes, spacers, standoffs, or guides to ensure an even radial distribution of the second fluid out of the nozzle. Even distribution helps prevent perturbations from a straight path of the drill by forcing flow of the cutting fluid towards portions of the hole which have not yet been removed but are not in the direct path of the impinging jet or jets. This technique can be used in conjunction with the concept of a convex tool tip shape in order to further control the return flow.

[0098] The outside diameter of the tool can be designed to maintain a certain controlled annular gap in the flow path between the nozzle near the distal end of the tool and the inside wall of the bore. The gap size can be controlled to give a high enough velocity and dynamic pressure to exclude fluid from the cutting area. The risk of sticking the tool can be mitigated by maintain the outside diameter of the tool through the use of a spacer such that it can be released from the core of the tool and then removed by fishing or drilling. The material of the spacer can be designed to be drillable by conventional methods but protected from or impervious to the effects of steam and spall flow. Materials of construction of the spacer may include soft metals, ceramics, ceramic composites, ceramic foams, high temperature polymers, and combinations thereof. [0099] A peripheral ring can be used at the bottom of the tool to maintain a fluid exclusion region immediately beneath the end of the tool in the location of the rock removal. This may be designed with slots, teeth, holes or other perforations to allow a path for fluid and spalls to escape while maintaining a high enough velocity to exclude liquids. This style of barrier could be made from metal, ceramic, polymer, or a combination thereof.

[0100] A barrier can be maintained by using a device which is deployed in a stationary or semi-stationary position in the wellbore as the tool moves forward or backwards, such as a packer. The barrier can be moved forward in increments. This approach has the advantage in that the portion of the barrier which sees relative movement is between the outside of the tool and the inside of the packer-style barrier, which can have a more regular shape and surface finish than the inside of the rock.

[0101] In hole opening applications, the nozzle can be directed upwards such that the jet cuts a downward facing pocket adjacent to the borehole. By progressing the hole opening tool from the bottom to the top of the section of borehole to be opened, a pocket can be maintained where the steam in the cutting zone is physically above the borehole fluids and fluid exclusion will be aided by gravity.

[0102] A separator can be used down hole to remove spalls from the flow of steam and/or liquid water. The separator can be designed such that the spalls accumulate in the zone or zones where it is desired to maintain a fluid exclusion barrier. The accumulation of spalls can be used to enhance other barrier techniques by filling open gaps which could allow the influx of liquid water. The separator can be designed such that it reaches a steady state and spalls no longer accumulate once an adequate seal is achieved.

[0103] A pump, impeller, or compressor can be used to recirculate the down hole cutting fluid. This has the potential to significantly increase the flow rate and velocity of cutting fluid in the spallation region which can help prevent the influx of fluids into the region. The pump can be used in conjunction with a separator to remove some or all of the spalls and/or any fluids present at the pump inlet. Alternatively, the additional fluid can be vaporized upon

recirculation to increase the mass flow and aid in cooling. Spalls can be recirculated and used as an abrasive to help improve the removal of parent rock from the hole.

[0104] An example thermal spallation cutting system 100, including a dynamic barrier assembly 105 for generating a fluid exclusion barrier between different fluid regions of a borehole during drilling/hole opening, is shown in FIGS. 1 to 2D. The rock cutting system 100 includes a distal working portion 110 that is directed down a borehole 115 to spall rock from the distal end 120 of the borehole 115. An example distal portion 110 for a thermal spallation cutting system 100 is shown in FIGS. 1, 2A, and 2B. The working portion 110 may include a reaction chamber 112 housing a catalyst element. The working portion may also include elements such as, but not limited to, one or more combustion chambers, electric heaters, laser heaters, and/or friction heaters in addition to, or in place of, a catalyst element. In operation, a working fluid (e.g., a liquid such as water including at least one of an oxidant and/or a fuel) is pumped down at least one conduit in the drill string to the reaction chamber 112. The working fluid reacts with the catalyst in the reaction chamber 112, with the reacted fluid exiting from the spallation jet nozzle 125 at the distal end of the working portion 110. The dynamic barrier assembly 105 is positioned upstream of at least one nozzle 125 (e.g., one or more spallation jet nozzles) that directs a heated fluid (e.g., steam at about 800°C) towards the distal end 120 of the borehole 115 to spall rock therefrom. In operation, the dynamic barrier assembly 105 provides a fluid exclusion barrier within an annulus 130 formed between an outer wall 135 of the thermal spallation cutting system 100 and a wall 140 of the borehole 115. The fluid exclusion barrier may separate the heated fluid portion 145 (i.e., the fluid within the distal end 120 of the borehole 115) from the cold fluid portion 150 (e.g., drilling mud within the annulus 130), while allowing fluid from the heated fluid portion 145 (e.g., one or more reacted working fluids, such as steam or supercritical water, for a spallation process) and/or material from a distal end of the borehole (e.g., cuttings and/or spalls) to pass through the fluid exclusion barrier towards a proximal end of the borehole 115, while completely or substantially preventing the cold fluid from passing through the fluid exclusion fluidic barrier towards the distal end 120 of the borehole 115. In essence, the dynamic barrier assembly 105 acts as a one way valve.

[0105] In one embodiment, the dynamic barrier assembly 105 includes one or more fluid directing elements 155 (e.g., jet nozzles and/or slots) formed in the outer wall 135 of the rock cutting system 100 for directing one or more fluids into the annulus 130 between the rock cutting system 100 and the wall 140 of the borehole 115. Openings of the fluid directors 155 may be located flush with, or substantially flush with, the outer wall 135. Alternatively, openings of one or more fluid directors 155 may extend out a set distance from the outer wall 135 of the rock cutting system 100. [0106] The fluid directors 155 may be configured to direct the fluid into the annulus 130 towards a proximal end of the borehole 115 at an acute angle (a) to an elongate central axis of the rock cutting system 100 (see FIG. 2C). In one embodiment, the angle between the elongate central axis of the borehole 115 and the direction of the fluid exiting the fluid directors 155 may be between 5° and 60°, or more particularly between 10° and 45° and, for example, from about 15° to about 20°. In general, the vertical (lifting) component of the dynamic pressure of a DSA fluid jet (water/mud jet) decreases with increasing angle (a). The fluid directions may each be oriented in a vertical plane, or may be canted with a circumferential component to provide a swirling flow. In one embodiment, an acute angle (β) to a radial axis of rock cutting system 100 may be between 0° and 60°, or more particularly between 0° and 45° and, for example, from about 10° to about 30° (see FIG. 2D). In one example embodiment, an acute angle (β) to a radial axis of rock cutting system 100 may be about 15°.

[0107] In an example embodiment, the fluid may exit the fluid directors 155 at a flow rate of at least 37 gallons/minute, with the fluid flow from the one or more fluid directors 155 producing a dynamic pressure of at least 50 Pa. In alternative embodiments, higher or lower flow rates, creating higher or lower dynamic pressures, may be used. In general, the required flow rate may depend on a number of factors such as, but not limited to, the hole size and the geometry and/or size of the drill string. For example, parameters of importance in determining the required volumetric flow rate from the one or more fluid outlets include, but are not limited to, the density and/or viscosity of first and/or second fluid, the dynamic pressure and/or velocity of the second fluid at the exit of the fluid outlet, the diameter of the fluid outlets, the spacing ration of the fluid outlets, the velocity of the fluid in the annular region of the barrier, the size of the annular gap between the drill string and the wall of the borehole, the dynamic pressure within the annular gap, and/or the angle of the fluid outlets to the elongate central axis of the borehole. For example, in one embodiment a flow rate of between 30 and 100 gallons/minute, and more particularly between 50 and 75 gallons/minute, may be used for a 4 inch borehole. In alternative embodiments, larger or smaller flow rates may be used, as appropriate. For example, in one embodiment, larger boreholes and/or smaller drill strings and/or higher mass flows of the jet may require more cooling/cutting lift water which, in turn, results in higher flow rates from the jet nozzle.

[0108] In operation, one or more fluids (e.g., water) are pumped from a remote location (e.g., at or near the surface) through one or more fluid conduits 160 in a drill string 165 and down to the fluid directors 155. The fluid directors 155 then inject the fluid into the annulus 130 at an angle, velocity, and volumetric flow-rate sufficient to create a dynamic pressure capable of supporting the annular column of drilling mud, thereby impeding the flow of cold fluid down into the distal end 120 of the borehole 115. In one embodiment, the dynamic pressure may be sufficient to prevent completely, or substantially completely, fluid from the cold region 150 passing into the hot region 145. In an alternative embodiment, the dynamic pressure may be sufficient to limit the flow of fluid from the cold region 150 into the hot region 145 to any extent necessary to prevent quenching of the heat source in the hot section 145. The dynamic pressure produced by the fluid directors 155 may be controlled, for example, by controlling the pumping rate of the fluid through the conduit 160, controlling the cross- sectional area of the exit of the one or more fluid directors 155, controlling the exit angles of the one or more fluid directors 155, and/or controlling the properties of the fluid being pumped (e.g., by selectively mixing various materials to produce the fluid to be pumped). The fluid may include, or consist essentially of, water and/or drilling mud. The fluid may also include additional elements including, but not limited to, one or more chemical additives, thermally- sensitive foaming agents, thioxotrops, gels, gums, viscosifiers, densifiers, lost-circulation control materials, corrosion inhibitors, chelating agents, buffers, acids and/or bases or other materials typically found in conventional drilling muds. Components that increase the viscosity of the annular fluid substantially upon initial contact with the high temperature fluid could be added in a small stream just before ejection from the canted outlet ports.

[0109] In one embodiment, where the reacted fluid exiting the spallation jet nozzle 125 includes steam at a temperature of approximately 800°C, the steam may condense within the region of the fluid exclusion barrier. In one embodiment of the invention, the dynamic barrier assembly 105 has a dynamic pressure margin sufficient to counteract any effect of this condensation on the effectiveness of the fluid exclusion barrier in preventing the flow of fluid from the cold fluid portion 150 to the heated fluid portion 145 of the annulus 130.

[0110] In one embodiment, the fluid exiting the fluid directors 155 includes water, with the fluid directors 155 configured to cause the water to flash to steam before or upon exiting the fluid directors 155, thereby potentially increasing the volume of the exiting fluids to assist in lifting the fluid through the annulus 130 away from the fluid exclusion barrier. In one embodiment, the fluid exiting the fluid directors 155 includes one or more combustion or hydro thermal oxidation products, with the fluid directors 155 configured to produce

combustion of the fluid exiting the fluid directors 155.

[0111] The drill string 165 may be coupled, at a proximal end, to a surface mounting system located at or near a surface of the rock formation being penetrated. The surface mounting system may include inlets for injection of one or more fluids (such as, but not limited to, water) into a first fluid conduit that is fluidically coupled to one or more of the fluid directors 155 (e.g., jet nozzles). The first fluid conduit may be coupled to a pumping system adapted to pump fluid to the fluid directors 155 at any required flow rate and pressure. A second inlet may be coupled to a second fluid conduit within the drill string 165 to provide a fluid conduit for the working fluid (e.g., water) for the spallation rock cutting system 100. The surface mounting system may also include one or more borehole outlet ports allowing for the removal of fluid from within the annulus 130 as it travels upstream away from the bottom of the borehole 115. Additional, separate conduits in the drill string 165 may include

communication and/or powering conduits for various elements of the system.

[0112] Each of a plurality of fluid directors 155 may direct fluid at the same acute angle to the elongate central axis of the borehole 115. Alternatively, one or more fluid directors 155 may be configured to direct fluid at a different acute angle to that of the other fluid director(s) 155. The fluid directors 155 may be configured to direct fluid at a single, set angle.

Alternatively, one or more fluid directors 155 may be pivotable, thereby allowing the fluid to be directed from the fluid directors 155 at a variable angle. This angle may, for example, be adjusted to vary the dynamic pressure produced at the boundary between the heated fluid portion 145 and cold fluid portion 150.

[0113] One or more fluid directors 155 may be adapted to pivot between the required acute angle to the elongate central axis of the borehole 115 necessary for generating and maintaining the fluid exclusion barrier and a second angle directed either at about 90° to the elongate central axis or even at an angle directed towards the distal end 120 of the borehole 115 at an acute angle to an elongate central axis of the borehole 115. Allowing one or more fluid directors 155 to be pivoted down towards a distal end 120 of the borehole 115 may be advantageous, for example, in injecting fluid into the borehole 115 to cool the distal end of the rock cutting system 100 during certain operations.

[0114] In one embodiment, one or more of the fluid directors 155 may be adapted to rotate around an elongate central axis of the rock cutting system 100. This may be achieved, for example, by mounting one or more of the fluid directors 155 within a rotatable mounting element on an outer wall 135 of the distal portion 110, the rotatable mounting element being fluidically coupled to the fluid conduit(s) 160. Rotation of the fluid directors 155 may be driven by a mechanical, magnetic, electrical, and/or mechanical control system.

[0115] Alternatively, or in addition, one or more of the fluid directors 155 may be directed in a purely circumferential direction to a radial axis (i.e., angle β) or in a compound angular direction (i.e., angles a and β), thereby directing the fluid out of the fluid directors 155 and into the annulus 130 in a spiral or helical direction around the central elongate axis and

simultaneously providing a rotational thrust to the rotatable mounting element. Rotating one or more fluid directorsl55 in this manner may, in certain embodiments, create a more uniform fluid exclusion barrier than that created through stationary fluid directors 155. In one embodiment, a torque can be applied to the rock cutting system 100 to counteract a rotational torque applied to it by the rotational thrust of the fluid directors 155.

[0116] In one embodiment, a plurality of fluid directors 155 are spaced symmetrically in a ring around a circumference of the outer wall of the rock cutting system 100 at a set distance from the distal end. In an alternative embodiment, the fluid directors 155 may be

asymmetrically spaced. One embodiment of the invention may include a dynamic barrier assembly 105 having a plurality of rings of fluid directors 155 arranged on the outer wall of the rock cutting system 100 at different distances from the distal portion 110.

[0117] The rock cutting system 100 may include one or more sensors to measure various parameters of the dynamic barrier assembly 105 and/or other components of the system during operation. For example, one or more pressure sensors, flow rate sensors, temperature sensors, and/or chemical sensors may be utilized to monitor the properties of the fluid flow exiting the fluid directors 155 and/or the stability and/or effectiveness of the fluid exclusion barrier being maintained within the annulus 130. The rock cutting system 100 may include one or more control elements adapted to control one or more functions of the dynamic barrier assembly 105, and/or other components of the system. For example, control elements to control an angle of one or more fluid directors 155, control a cross- sectional area of an exit of one or more fluid directors 155, and/or control a rotation rate of one or more fluid directors 155 may be utilized. These control elements may be controlled automatically, for example in response to a reading from one or more sensors, and/or may be controlled manually from a surface location through one or more control signals sent through a connection conduit within the drill string 165. [0118] In one embodiment, the reacted fluid exits the spallation jet nozzle 125 at a temperature of about 800°C and/or a flow rate of about 70 grams/second. In operation, after spalling the rock at the distal end 120 of the borehole 115, this reacted fluid passes up through the annulus 130, carrying the spalled rock portions with it. This heated/reacted fluid passes through the fluid exclusion barrier and may then be carried up the annulus 130 to the surface. In one embodiment, the flow of the reacted fluid and/or spalled material through the fluid exclusion barrier creates an additional dynamic pressure in the annulus 130 of the borehole 115 that assists in maintaining the fluid exclusion barrier and preventing the cold fluid from passing down toward the distal end 120. In an alternative embodiment, the flow of the reacted fluid and/or spalled or drilled rock provides negligible additional pressure supporting the fluid exclusion barrier.

[0119] In one embodiment, as shown in FIG. 3, the barrier can include a mechanism 305 to selectively withdraw the low density superheated working fluid from the spalls using a filter or screen sized to reject a majority of the spalls. The filter or screen may include a plurality of layers, or may have only one layer. The filter may have mostly vertical elements supported by internal radial bands to reduce the potential for clogging of the filter. The gaps between the vertical elements sized to allow only the superheated fluid from entering.

[0120] In one embodiment, the spall size to be rejected by the screen is in the range of greater than about 20 microns. In an alternative embodiment, the screen may be adapted to reject larger or smaller spall sizes. Rejected spalls, along with a smaller portion of the superheated fluid, may continue up the annular region but intersect a flexible physical barrier 306 which causes the spalls to clump in a manner that restricts downward movement of coolant fluid. These collected spalls may continue to move up more slowly and eventually intersect the coolant flow jets 307 where they are swept into the flow and carried upstream. Another feature of this design is that some of the up flowing fluid may also be used to help preheat the reaction chamber prior to fluids entering the combustion reaction chamber 112.

[0121] One embodiment of the invention includes a rock cutting system, for example a thermal spallation cutting system 100, having a dynamic barrier assembly 105 including one or more barrier supporting structures 400 (e.g., shims or brushes) to assist in maintaining a fluid exclusion barrier preventing fluid from flowing from the cold fluid portion 150 to the heated fluid portion 145 of the annulus 130, as shown in FIGS. 4A and 4B. The barrier supporting structure 400 may include, or consist essentially of, one or more shims and/or brushes. The shims and/or brushes may be constructed, for example, from a material (such as, but not limited to, a metal, a ceramic, and/or a plastic) that is flexible enough to bend and fit through various size boreholes but robust enough to withstand the hot corrosive environment therein. Example metals include, but are not limited to, aluminum, stainless steel, and/or a super alloy. Example super alloys may include nickel-chromium-iron-molybdenum alloys such as those

manufactured under the trade name Hastelloy^® X. In one example embodiment, the barrier supporting structure 400 includes shims constructed from thin sheets (e.g., about 0.040" thick) stainless steel or a super alloy. In alternative embodiments, shims of differing thickness and/or structure may be used. In another example embodiment, the barrier supporting structure 400 includes brushes manufactured from one or more ceramic fibers and/or braided metal wires.

[0122] The barrier supporting structure(s) 400 may be positioned above, below, and/or at substantially the same distance from the distal end as the fluid directors 155. Such barrier supporting structure(s) 400 may be advantageous, for example, when the diameter of a borehole is too large for the high velocity fluid directors 155 to create sufficient dynamic pressure to prevent cold section fluid from entering the heated fluid portion 145 at the bottom of the borehole 115.

[0123] The barrier supporting structure(s) 400 may be of any appropriate longitudinal length and extend out to any appropriate distance from the outer wall of the rock cutting system. For example, an example barrier supporting structure 400 includes brushes formed from a plurality of braided wires extending, for example, up to twelve inches or more from the outer wall of the rock cutting system. In alternative embodiments, shorter or longer brushes or shims may be used, as required.

[0124] In operation, the barrier supporting structure 400 provides a fluid exclusion physical obstruction within the annulus 130 which provides an additional element hindering the flow of cold fluid through the fluid exclusion barrier and into the heated fluid portion 145. In one embodiment, the barrier supporting structure 400 includes one or more bypass slots or local openings 405 to provide a low resistance passageway for the hot spalling fluid and

spalls/cuttings to pass through the fluid exclusion barrier and into the cold fluid portion 150, so that they can be lifted up the borehole by cooling water. In one example embodiment, the bypass slots 405 include, or consist essentially of, one or more helical groves, similar in form, for example, to a drill string centralizer. [0125] In one embodiment, the barrier supporting structure(s) 400 may rotate along with, or separate from, the fluid directors 155. In various embodiments, the barrier supporting structure(s) 400 may be shims that include, or consist essentially of, one or more hydraulically activated metal bladders. Alternatively, or in addition, the shims may be formed as one or more flapper element, with downflowing fluid providing a force to open flappers (thereby preventing fluid downflow), while upflowing fluid closes the flappers against the outer wall of the rock cutting system, thereby allowing the upflowing fluid to flow around the flappers. In one embodiment, a sheath can slide over the barrier supporting structure(s) 400 to protect it during insertion into and/or removal from the borehole.

[0126] One embodiment of the invention includes a thermal spallation cutting system 100, having a dynamic barrier assembly 105 including a stabilizer 450 with one or more flutes 455 therein, as shown in FIGS. 4C and 4D. In operation, the flutes 455 accelerate the fluid from the distal end 120 of the borehole 115 through the dynamic barrier assembly 105 to reduce the Raleigh-Taylor instability.

[0127] The stabilizer 450 can, in one embodiment, serve as a bore wall wiper to scrape off wall jet softened formation that is inside the specified hole diameter and/or serve as a no-go if the drill advances too fast before the hole is spalled to the required minimum hole diameter. The vertical position of the bottom of blades may serve as a standoff contact with the idea that a constant, very low, weight on bit will advance the stabilizer 450 and scrape the soft wall to shape a round hole and at the same time produce the near-optimum nozzle standoff at the bottom of the hole.

[0128] In one embodiment, flow ports inside the body of the stabilizer connect the bottom of the cooling water shroud annulus to jets in the center of the flutes 455 that produce an atomized spray of a small fraction of the total cooling water onto the hot wall of the recently spalled hole to quench the spallation process and flash to produce a large volume flow from a small mass flow of cooling water. The high pressure inlet pressure of quench jets is recovered in the jet stagnation zone to produce the driving force to force the super heater fluids to flow both up and down flutes and spill over onto the surface of the blades to produce the hot/cold flow separation between the cooling water circulation above the moving annular barrier/seal and the hot returns flow below the barrier. Jets pointed at an acute angle relative to an elongate central axis, exiting the tool above an upset in the tool outer diameter (such as from a stabilizer 450) can have synergistic effects. [0129] It should be noted that the dynamic pressure "q" of the fluid exiting the fluid directors is given by the equation:

where is the fluid density and " v " is the fluid velocity. Dynamic pressure is closely related to the kinetic energy of a fluid particle, since both quantities are proportional to the particle's mass (through the density, in the case of dynamic pressure) and square of the velocity.

Dynamic pressure is, in fact, one of the terms of Bernoulli's equation, which is essentially an equation of energy conservation for a fluid in motion. The dynamic pressure is equal to the difference between the stagnation pressure and the static pressure.

[0130] The dynamic pressure of the spalling fluid flowing up the borehole annulus changes as a function of pressure and depth. As the pressure increases the density of the spalling fluid increases, thereby causing a reduction in velocity and in turn a reduction in dynamic pressure.

A plot showing the relationship between the dynamic pressure of a spalling fluid (in this case

800°C steam at 70g/sec) in an annulus having a 4 inch outer diameter and 3.5 inch inner diameter to the changing borehole pressure (which increases with depth) is shown in FIG. 5.

As a result, the maximum depth at which a set dynamic pressure will support the formation of a fluid exclusion barrier for any given borehole can be calculated.

[0131] For example, from the borehole calculations of the graph in FIG. 5, for an embodiment where the minimum dynamic pressure required to support the cooling water is 50 Pa, the system described herein reaches this minimum dynamic pressure at a borehole pressure of 82.7xl0⁶Pa, which corresponds to a depth of approximately 8500 meters, assuming the borehole is filled with clear water (density = 1000 kg/m ).

Example Test Systems

[0132] An example test cell for a dynamic barrier assembly 105 for use with a thermal spallation cutting system is shown in FIGS. 6 A to 7B. The system tested the use of a thermal spallation cutting system capable of forming a borehole diameter of at least 4 inches. The tool body had a body diameter of 3.5 inches and the system was tested in 4 inch and 5 inch diameter boreholes. The borehole was constructed from clear PVC tubing.

[0133] The drill string 165 was coupled, at a proximal end, to a surface mounting system 600 located at the top of the test cell. The surface mounting system 600 included a cooling water inlet 605 for injection of one or more fluids (such as, but not limited to, water) into a first fluid conduit 610 that is fluidically coupled to a plurality of fluid directors 155 (i.e., jet nozzles). The first fluid conduit 610 was coupled to a pumping system adapted to pump fluid to the fluid directors 155 at any required flow rate and pressure. A second inlet 615 was coupled to a second fluid conduit 620 within the drill string 165 to provide a fluid conduit for the simulated spallation working fluid (i.e., air) for the spallation rock cutting system 100. A pressure tap 625 was used to monitor the pressure within the borehole upstream of the fluid directors 155 during operation. A borehole outlet 630 provided an outlet for removal of fluid from the annulus.

[0134] The system used high pressure air in the second fluid conduit 620 to simulate the steam or super critical spalling fluid used for thermal spallation at different depths. The following calculations outline the experimental conditions using air, and comparable conditions for steam in a 600 foot deep water filled borehole:

For Air:

Pressure, P_a = 32 psi_g (46.7 psi_a)

Temperature, T_a = 20°C

Density, /¾ = 3.829 kg/m³

Comparable values for steam at 800°C at 259.4 psi:

Density, p_s = 3.82 kg/m³

[0135] As shown, careful selection of pressurized air characteristics provided a spallation fluid flow having a substantially similar density to that of steam at working borehole depths.

[0136] Drilling mud (in this case cooling water), was used as the fluid ejected from the fluid directors 155. The water was pumped down the first conduit 160 toward the distal portion of the system where it was caused to reverse direction and was ejected from eight

symmetrically positioned fluid directors 155 at a set distance upstream of the bottom of the borehole. The fluid directors 155 redirected the water upward at an angle a of approximately 20°. The diameter of each fluid director 155 at the exit was 0.302 inches and the corresponding fluid velocity at the exit of the fluid directors 155 was 6.3 m/s.

[0137] As shown in FIGS. 7 A and 7B, operating the dynamic barrier assembly 105 with the described parameters in a four inch borehole produced operating conditions with no drilling mud (i.e., water) observable in the bottom of the borehole. The system was tested further by changing various parameters, such as the flow rate of the simulated spallation fluid from the spallation jet nozzle, the flow rate of the fluid from the fluid directors 155, and the size of the annulus, to determine respective parameters contribution to the effectiveness of the fluid exclusion barrier in preventing drilling mud from falling to the bottom of the borehole.

[0138] A modified example test cell modeling a dynamic barrier assembly 105 for use with a thermal spallation cutting system in a borehole having a surface roughness substantially equivalent to that in an actual borehole 115 is shown in FIGS. 8A to 8B. A coating of a bonding material (e.g., putty) and sand was applied to a 5 inch diameter borehole in order to simulate surface roughness of an actual borehole wall. As shown in FIG. 8B, the dynamic barrier assembly 105 was effective in preventing drilling mud from falling to the bottom of the borehole, even for boreholes having a roughened wall surface.

[0139] FIG. 9 shows a spallation hole opening system 101 with two horizontally oriented spallation jet nozzles 125 impinging on a hole opening region surface 121. As shown, the hole opening is taking place in the immediate vicinity of a fracture 700. The fluid directors 155 are shown located in the narrow wellbore 115 above an enlarged region 117 of the wellbore where the velocity of upward flowing gasses may be higher and more likely to entrain liquids. In some cases, the hole opening may not occur at the bottom of the well, such that there is an additional lower wellbore 116 below the enlarged region 117. This lower wellbore 116 may be filled with a substance, such as sand, or may serve to collect liquid or spalls if left open. As shown, the enlarged region 117 can be quite irregular depending on the size and nature of the heated fluid portion 145 of the wellbore. No (or relatively little) spallation may occur in the cold fluid portion 150 since it is typically below the spallation temperature.

[0140] In one embodiment, shown in FIGS. 10A to IOC, shims 410 which make up the barrier supporting structure 400 can be moved into or out of a sealing position by an actuation mechanism assembly 460. This assembly may include an actuator piston 470, depicted in the FIG. 10B as a piston which can be moved by the application of fluid pressure on one side. The supporting structure 400 can be returned to its collapsed position by a return spring 475. Such a configuration means that the barrier support structure 400 may default to the collapsed position in case of a failure of the actuating fluid. The actuation assembly may be designed with an internal opening 465 to allow for the passage of fluids, electronics, or other components necessary or desirable for rock cutting. The barrier supporting structure 400 may include a plurality of individual shims 410. The individual shims 410 may be affixed by a hinge 430 which allows them to be rotated between the expanded sealing position and the collapsed position. A hinge 430 can reduce the amount of force required to move the shim 410 into position and impose a minimal amount of bending stresses in the shim material. In the collapsed position, the individual shims 410 may not extend beyond the outer diameter of the outer wall 135 of the drill string to avoid damage to the barrier support structure 400 when the spallation rock cutting system is being run into position or pulled out of the borehole 115.

[0141] As shown in FIGS. 11A to 11C, the barrier supporting structure 400 may be comprised of a plurality of individual braided wires 415. A fluid, such as water, can be introduced into the inside of these individual braided wires 415 from one end through a fluid inlet 416. This cooling fluid may serve to reduce the temperature of the individual braided wire 415 in order to improve its strength, springiness, and durability. The design may also allow for the seepage of the cooling fluid into the annulus 130 in order to cool the upward flow from the heated fluid portion 145. The barrier supporting structure 400 may be activated by

compression or by rotation using the drilling fluid as a pressure source or by electrical driven motors.

[0142] As shown in FIGS. 12A and 12B, the barrier supporting structure 400 may be constructed from individual shims 410 which are moved into position via linear translation. FIG. 12A depicts the barrier supporting structure in the expanded sealing position, as it would be while rock cutting or spalling. FIG. 12B depicts the collapsed position, as it would be for movement into and out of the borehole 115. In the embodiment depicted, the individual shims 410 are flexible and can be forced into the expanded position without requiring a hinge and do not protrude beyond the outer wall 135 of the drill when in the collapsed position. The movement of the barrier support structure 400 is achieved by the actuation mechanism assembly 460, which may be comprised of an actuator piston 470 and a return spring 475. Fluid pressure may be applied to the actuator piston 470 via the actuator inlet 471. The embodiment is depicted with an internal opening 465 to allow for the passage of fluids, electronics, or other components necessary or desirable for rock cutting.

[0143] FIGS. 13A and 13B depict a flexible membrane 420 which can serve as the barrier supporting structure 400. FIG. 13A depicts the expanded sealing position while FIG. 13B depicts the collapsed position. In this embodiment, the membrane 420 may be stretched. In other embodiments, an inelastic membrane may be used, such as a folded or pleated membrane. The membrane 420 may be expanded using a fluid, such as cooling water, flowing into the interior of the membrane via fluid directors 155. This fluid can also serve to reduce the operating temperature of the membrane 420 in order to improve its strength and durability. When collapsed, the membrane 420 may fall within the outer wall of the tool 135 to avoid damage when running the tool into or pulling the tool out of the borehole 115.

[0144] As shown in FIGS. 14A to 14C, the barrier support structure 400 may have a flexible membrane 420 which expands an array of individual shims 410. The use of the shims 410 may improve the ability of the barrier support structure 400 to move past protrusions from the inside of the borehole 115 and protect the membrane 420 from wear. The membrane 420 may be expanded by introducing a fluid, such as cooling water, through the fluid directors 155. The fluid can serve to cool an inner surface 421 of the flexible membrane 420. If the membrane material has a relatively low thermal conductivity or is relatively thick, an outer surface 422 may be subjected to excessive temperatures. To counter this problem, small perforations 425 can be introduced into the surface of the membrane 420 such that some portion of the fluid will be transferred to the outside surface where it can absorb some heat and reduce the temperature of the membrane 420. The individual shims 410 can be rotated about a hinge 430, or can be designed such that they are flexible enough to move into the expanded position while affixed at the base. In this embodiment, a retracting spring 475 is used to pull the flexible membrane 420 back into the collapsed position once fluid pressure is no longer being applied

[0145] FIG. 15 shows a moveable packer 500 which is placed into position such that it forms an outer seal 515 against the wall 140 of the borehole. This outer seal 515 may be impermeable to liquids, solids, and/or gasses, or it may be configured such that only a partial seal is formed and the upward velocity of gasses, such as those generated from a spallation jet, are sufficient to prevent liquids from moving down past the seal 515. Additionally, the moveable packer 500 may have an inner seal 510 to allow for movement of the spallation rock cutting system 100. Similarly, this seal 510 can be impermeable or semi-permeable and reliant on the upward flow velocity to maintain liquid exclusion. In this embodiment, the moveable packer 500 is shown with bypass holes 406 which allow for the passage of upward flowing gasses and cuttings and are similar in function to the bypass slots 405 shown in FIG. 4B. These bypass holes 405 may not be necessary if the outer seal 515 or inner seal 510, or both, are semipermeable and allow for the passage of upward flowing gasses and cuttings. The moveable packer 500 may need to be repositioned in the borehole 115 as the drilling or hole opening progresses. The movable packer 500 may be made of elastomers, plastics, drillable ceramics, metal or other materials that can survive the operation conditions, either with circulation of coolant externally or through internal passages to prevent damage from the high temperature or without coolant, where they are exposed to the high temperature fluid.

[0146] As shown in FIGS. 16A and 16B, some portion of the hot working fluid returning up the annulus can be extracted and re -pressurized using rotating blades 350. The re- pressurized annular fluid 355 can be mixed with the superheated fluid coming down from the combustor 360 prior to flowing out through the spallation jet nozzle 125. The annular fluid may first be strained through a mechanism 305 to selectively withdraw the low density superheated working fluid from the spalls and/ or any liquid present. This may be used in conjunction with other dynamic barriers such as brushes and actuated shims to limit the intrusion of coolant.

[0147] FIGS. 17 A to 17C show a barrier supporting structure 400 which has a plurality of individual shims 410 which are designed to overlap. FIG. 17A depicts the expanded sealing position, while FIG. 17B depicts the collapsed position. The individual shims 410 may be comprised of an overlapping portion 412 which overlap other shims 410 when the barrier is in the collapsed position and a non-overlapping portion 411 which never overlaps the other shims 410. This design allows for full coverage in the expanded position where gaps between individual shims 410 might be exposed as they move into the expanded position due to the increased seal length along the circumference. In this embodiment, the individual shims 410 are connected via hinges 430 to allow for relative movement between the parts. Alternatively, the individual shims 410 could be made flexible enough to allow them to move between the expanded and collapsed position so that only some or none of the hinges 430 would be required.

[0148] FIGS. 18A and 18B compare drilling and hole opening technologies and illustrate some of the dimensional parameters associated with each one. FIG. 18A shows a spallation hole opening system 101 with a horizontally-oriented spallation jet nozzle 125 located such that the jet impinges on the surface 121 of the enlarged region 117. FIG. 18B shows a spallation drilling system 100 with a downward facing spallation jet nozzle 125 located such that the jet impinges on the distal end 120 of the borehole. The nozzle to wall distance 220 is measured from the spallation jet nozzle 125 to the hole opening region surface 121 or distal end 120 of the borehole. The barrier to nozzle distance 245 is measured from the barrier supporting structure 400 to the spallation jet nozzle 125. The borehole to drill string distance 230 is measured from the wall 140 of the borehole to the outer wall 135 of the drill string. Some of the proposed designs for the barrier supporting structure 400 are designed to span this distance. If the drill string is centered in the borehole, the distance may be half of the difference between the inside diameter 240 of the borehole 140 tool outside diameter 235 of the outer wall 135 of the drill string. If the tool is off-centered, the bore hole to drill string distance 230 may be greater in some areas and lesser in others.

[0149] The specific setpoints for various hole size, tool size, annular gap, ROP, cuttings load, working fluid and jet properties, first fluid and second fluid properties, and other appropriate properties of the system may be determined, in one embodiment, through, computational fluid dynamics (CFD) modeling and/or experimental testing of the system for a specific set of parameters, depending upon the required properties and performance

characteristics of the borehole being created or enlarged. In certain embodiments, such as water-filled boreholes, these parameters, as may be determined by CFD and experimentation, may fall within the ranges indicated in Table 1 in FIG. 19. For example, various thermal spallation rock cutting system parameters may include a gap size ranging from between about 0.1 and 4.5 in., an open area ranging from between about 0.0001 and 0.07 m (e.g., about

0.0684 m ), a fluid barrier distance from spalling fluid outlet ranging from between about 0.001 and 650 m (e.g., about 0.00254m or 609.6m), a dynamic pressure of between about 60 and 30,000 Pa, a dynamic pressure / open area of between about 1,000 and 2,800,000 Pa/m , a dynamic pressure / hydraulic diameter of between about 2,000 and 1,300,000 Pa/m, and a dynamic pressure / gap size of between about 4,000 and 2,600,000 Pa/m. One embodiment of a thermal rock cutting system at 10,000 ft depth in a water filled borehole operating at 5 MWt thermal output for spalling is also provided. In other embodiments, such as gas, steam, or foam filled boreholes, the values in the chart may fall outside of these ranges. In other embodiments, products, ratios or other relationships between the parameters may be required for the fluid exclusion barrier to function.

[0150] It should be understood that alternative embodiments, and/or materials used in the construction of embodiments, or alternative embodiments, are applicable to all other embodiments described herein.

[0151] The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments, therefore, are to be considered in all respects illustrative rather than limiting the invention described herein. Scope of the invention is thus indicated by the appended claims, rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.

[0152] What is claimed is:

Claims

1. A method of providing a fluid exclusion barrier between fluid regions in a borehole, comprising:

directing a thermal rock cutting system having a distal portion down a borehole; and isolating a first fluid within a proximal portion of an annulus formed between the rock cutting system and a wall of the borehole by generating a fluid exclusion barrier within the annulus upstream of the distal portion of the rock cutting system while substantially preventing flow of the first fluid through the fluid exclusion barrier toward the distal end of the borehole.

2. The method of claim 1 further comprising directing substantially all material from a distal end of the borehole to pass through the fluid exclusion barrier towards a proximal end of the borehole.

3. The method of claim 1, wherein the thermal rock cutting system comprises a rock cutting system.

4. The method of claim 1, wherein the thermal rock cutting system comprises a hole opening system.

5. The method of claim 1, wherein the thermal rock cutting system comprises an air-based thermal spallation system.

6. The method of claim 1, wherein the first fluid comprises at least one of drilling mud, aerated foam, water, air, steam and a combination thereof.

7. The method of claim 1, wherein means for generating the fluid exclusion barrier comprises at least one fluid outlet for directing a second fluid from the rock cutting system into the annulus.

8. The method of claim 7, wherein the at least one fluid outlet is located substantially flush with an outer wall of the rock cutting system.

9. The method of claim 7, wherein the fluid outlet comprises at least one of a fluid directing jet nozzle and a fluid directing slot.

10. The method of claim 9, wherein the second fluid exits the at least one fluid directing jet nozzle at a flow rate of at least about 37 gallons/minute.

11. The method of claim 7, wherein the at least one fluid outlet is adapted to direct the second fluid from the outer wall of the rock cutting system towards a proximal end of the borehole at an acute angle to an elongate central axis of the borehole.

12. The method of claim 11, wherein the acute angle comprises an angle between about 5° and about 60°.

13. The method of claim 11, wherein the acute angle comprises an angle between about 10° and about 45°.

14. The method of claim 11, wherein the at least one fluid outlet is adapted to direct adjustably the second fluid from the outer wall of the rock cutting system.

15. The method of claim 7, wherein the means for generating a fluid exclusion barrier comprises a plurality of fluid outlets arranged symmetrically around the outer wall of the rock cutting system upstream of the distal portion thereof.

16. The method of claim 15, wherein the plurality of fluid outlets are adapted to rotate around an elongate central axis of the rock cutting system.

17. The method of claim 7, wherein the second fluid is selected from the group consisting of a drilling mud, aerated foam, water, air, and a combination thereof.

18. The method of claim 17, wherein the second fluid further comprises at least one of a chemical additive, a thermally-sensitive foaming agent, a buffer, and a base.

19. The method of claim 7, further comprising pumping the second fluid through at least one fluid conduit in the rock cutting system to the at least one fluid outlet.

20. The method of claim 7, further comprising controlling a volumetric flow rate of the second fluid.

21. The method of claim 7, wherein the fluid exclusion barrier has a dynamic pressure that is greater than the Raleigh-Taylor instability at the fluid exclusion barrier.

22. The method of claim 7, wherein the fluid exclusion barrier has a dynamic pressure of at least about 50 Pa.

23. The method of claim 1, wherein the distal portion of the rock cutting system comprises at least one thermal spallation jet nozzle.

24. The method of claim 23, wherein the material directed to pass through the fluid exclusion barrier comprises at least one of an output of the thermal spallation jet nozzle and material excavated from the distal end of the borehole.

25. The method of claim 24, wherein the output of the thermal spallation jet nozzle comprises a reacted fluid.

26. The method of claim 25, wherein the reacted fluid comprises steam or supercritical water.

27. The method of claim 26, wherein the reacted fluid further comprises combustion gases.

28. The method of claim 26, wherein the reacted fluid further comprises at least one of a particle and a base.

29. The method of claim 25, wherein the reacted fluid exits the thermal spallation jet nozzle at a temperature of up to about 800°C.

30. The method of claim 25, wherein the reacted fluid exits the thermal spallation jet nozzle at a flow rate of up to about 70 grams/second.

31. The method of claim 24, wherein at least one of the output of the thermal spallation jet nozzle and the material excavated from the distal end of the borehole creates a dynamic pressure in the annulus between the rock cutting system and the wall of the borehole that assists in maintaining the fluid exclusion barrier.

32. The method of claim 1, wherein the fluid exclusion barrier comprises at least one of a filter or screen.

33. The method of claim 32, wherein the filter or screen comprises a plurality of layers.

34. The method of claim 32, wherein the filter or screen is adapted to prevent spalls of greater than about 20 microns from passing therethrough.

35. The method of claim 1, wherein the fluid exclusion barrier comprises at least one stabilizer with at least one flute therein.

36. The method of claim 35, wherein the flute is adapted to accelerate fluid from the distal end through the fluid exclusion barrier to reduce the Raleigh-Taylor instability.

37. The method of claim 1, wherein the fluid exclusion barrier comprises at least one of a brush and a shim.

38. The method of claim 37, wherein the fluid exclusion barrier forms a bypass path adapted to allow material from the distal end of the borehole to pass therethrough.

39. The method of claim 37, wherein the shim comprises a hydraulically activated bladder.

40. The method of claim 37, wherein the shim comprises a pressure or flow actuated flapper.

41. The method of claim 37, wherein the brush comprises a plurality of elements.

42. The method of claim 41, wherein the plurality of elements is selected from the group consisting of high temperature or corrosion resistant metal wires, ceramic fibers, braided wires, and combinations thereof.

43. An apparatus for providing a fluid exclusion barrier between fluid regions in a borehole, comprising:

a rock cutting system having a distal portion adapted for insertion down a borehole; and means for generating a fluid exclusion barrier within an annulus formed between the rock cutting system and a wall of the borehole, when inserted, upstream of the distal portion of the rock cutting system, adapted to substantially prevent the flow of a first fluid through the fluid exclusion fluidic barrier toward the distal end of the borehole.

44. The apparatus of claim 43, wherein the fluid exclusion barrier is adapted to allow substantially all material from the distal end of the borehole to be directed through the fluid exclusion barrier toward a proximal end of the borehole.

45. The apparatus of claim 43, wherein the rock cutting system comprises a rock cutting system.

46. The apparatus of claim 43, wherein the rock cutting system comprises a hole opening system.

47. The apparatus of claim 43, wherein the rock cutting system comprises an air-based thermal spallation system.

48. The apparatus of claim 43, wherein the first fluid comprises at least one of drilling mud, aerated foam, water, air, steam and a combination thereof.

49. The apparatus of claim 43, wherein means for generating the fluid exclusion barrier comprises at least one fluid outlet for directing a second fluid within the rock cutting system into the annulus.

50. The apparatus of claim 49, wherein the at least one fluid outlet is located substantially flush with an outer wall of the rock cutting system.

51. The apparatus of claim 49, wherein the fluid outlet comprises at least one of a fluid directing jet nozzle and a fluid directing slot.

52. The apparatus of claim 51, wherein the at least one fluid directing jet nozzle is adapted to direct the second fluid at a flow rate of at least about 37 gallons/minute.

53. The apparatus of claim 49, wherein the at least one fluid outlet is adapted to direct a second fluid from the outer wall of the rock cutting system towards a proximal end of the borehole at an acute angle to an elongate central axis of the distal end of the rock cutting system.

54. The apparatus of claim 53, wherein the acute angle comprises an angle between about 5° and about 60°.

55. The apparatus of claim 53, wherein the acute angle comprises an angle between about 10° and about 45°.

56. The apparatus of claim 53, wherein the at least one fluid outlet is adapted to direct adjustably the second fluid from the outer wall of the rock cutting system.

57. The apparatus of claim 56, wherein the fluid outlet is adapted to direct the second fluid from the outer wall of the rock cutting system towards a bottom of the borehole at an acute angle to an elongate central axis of the distal end of the rock cutting system to cool the spallation jet during certain operations.

58. The apparatus of claim 49, comprising a plurality of fluid outlets arranged

symmetrically around the outer wall of the rock cutting system upstream of the distal portion thereof.

59. The apparatus of claim 58, wherein the plurality of fluid outlets are adapted to rotate around an elongate central axis of the rock cutting system.

60. The apparatus of claim 49, wherein the second fluid is selected from the group consisting of a drilling mud, water, and a combination thereof.

61. The apparatus of claim 60, wherein the second fluid further comprises at least one of a chemical additive, a thermally-sensitive foaming agent, a buffer, and a base.

62. The apparatus of claim 49, further comprising means for pumping the second fluid through at least one fluid conduit in the rock cutting system to the at least one fluid outlet.

63. The apparatus of claim 49, further comprising means for controlling a volumetric flow rate of the second fluid.

64. The apparatus of claim 49, wherein the fluid exclusion barrier has a dynamic pressure that is greater than the Raleigh-Taylor instability at the fluid exclusion barrier.

65. The apparatus of claim 49, wherein the fluid exclusion barrier has a dynamic pressure of at least about 50 Pa.

66. The apparatus of claim 43, wherein the distal end of the rock cutting system comprises at least one thermal spallation jet nozzle.

67. The apparatus of claim 66, wherein the material directed to pass through the fluid exclusion barrier comprises at least one of an output of the thermal spallation jet nozzle and material excavated from the distal end of the borehole.

68. The apparatus of claim 67, wherein the output of the thermal spallation jet nozzle comprises a reacted fluid.

69. The apparatus of claim 68, wherein the reacted fluid comprises steam or supercritical fluids.

70. The apparatus of claim 68, wherein the reacted fluid exits the thermal spallation jet nozzle at a temperature of up to about 800°C.

71. The apparatus of claim 68, wherein the reacted fluid exits the thermal spallation jet nozzle at a flow rate of up to about 70 grams/second.

72. The apparatus of claim 67, wherein at least one of the output of the thermal spallation jet nozzle and the material excavated from the distal end of the borehole creates a dynamic pressure in the annulus between the rock cutting system and the wall of the borehole that assists in maintaining the fluid exclusion barrier.

73. The apparatus of claim 43, wherein the fluid exclusion barrier comprises at least one of a filter or screen.

74. The apparatus of claim 73, wherein the filter or screen comprises a plurality of layers.

75. The apparatus of claim 73, wherein the filter or screen is adapted to prevent spalls of greater than about 20 microns from passing therethrough.

76. The apparatus of claim 43, wherein the fluid exclusion barrier comprises at least one stabilizer with at least one flute therein.

77. The apparatus of claim 76, wherein the flute is adapted to accelerate fluid from the distal end through the fluid exclusion barrier to reduce the Raleigh-Taylor instability.

78. The apparatus of claim 43, wherein the fluid exclusion barrier comprises at least one of a brush and a shim.

79. The apparatus of claim 78, wherein the fluid exclusion barrier forms a bypass path adapted to allow material from the distal end of the borehole to pass therethrough.

80. The apparatus of claim 78, wherein the shim comprises a hydraulically activated bladder.

81. The apparatus of claim 78, wherein the shim comprises a pressure or flow actuated flapper.

82. The apparatus of claim 78, wherein the brush comprises a plurality of elements.

83. The apparatus of claim 82, wherein the plurality of elements are arranged in rows or randomly.

84. The apparatus of claim 82, wherein the plurality of elements is selected from the group consisting of ceramic fibers, braided wires, and combinations thereof.

85. The apparatus of claim 43, wherein the rock cutting system comprises at least one of a thermo-mechanical rock cutting system, a thermochemical rock cutting system, a borehole shaping system, a reaming system, a slotting system, a perforating system, and a side-tracking system.