Millimeter-wave drilling with fluid

Abstract

A system for drilling through a ground borehole using millimeter wave (MMW) energy featuring a MMW power source configured to generate MMW energy, at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom, and an optical element coupled to a distal end of the waveguide and configured to pressure seal the waveguide and to transmit the MMW energy to the borehole bottom. The waveguide comprises a hollow waveguide body encompassing a cavity at an internal waveguide pressure. When the distal end of the waveguide is immersed in a fluid filling the borehole at a fluid pressure and a fluid density, at least in the vicinity of the bottom of the waveguide: the internal waveguide pressure is lower than the fluid pressure and / or the internal waveguide density is lower than the fluid density.

Description

[0001] MILLIMETER-WAVE DRILLING WITH FLUID

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a system and method for drilling, and more particularly to a system and method that uses millimeter wave (MMW) energy for drilling.

[0004] BACKGROUND OF THE INVENTION

[0005] Method of MMW drilling according to previous research, such as disclosed in US patent No. US-8,393,410-B2, to Woskov et al., entitled "Millimeter-Wave Drilling System" describes a system for drilling boreholes into subsurface formations. A gyrotron injects millimeter-wave radiation energy into the borehole and a pressurization apparatus is provided for pressurizing the borehole whereby a thermal melt front at the end of the borehole propagates into the subsurface formations.

[0006] SUMMARY OF THE INVENTION

[0007] According to one aspect of the invention, there is provided a system for drilling through a ground borehole using millimeter wave (MMW) energy, featuring:

[0008] (a)a MMW power source configured to generate MMW energy.

[0009] (b)at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom, the waveguide comprising a hollow waveguide body encompassing a cavity at an internal waveguide pressure. (c) an optical element coupled to a distal end of the waveguide and configured to pressure seal the waveguide and to transmit the MMW energy toward the borehole bottom, wherein when the distal end of the waveguide is immersed in a fluid filling the borehole at a fluid pressure and a fluid density, at least in the vicinity of the bottom of the waveguide: the internal waveguide pressure is lower than the fluid pressure; and / or the internal waveguide density is lower than the fluid density.

[0010] In some embodiments, the system includes a fluid flow system configured to provide a fluid flow of the fluid within the borehole outside and around the waveguide. The fluid flow system can include a fluid streamer for streaming the fluid at the fluid pressure into the borehole. The fluid flow system can include a partition wall extending along the borehole, leaving a fluid passage near the borehole bottom and separating between at least one downflow conduit and at least one upward backflow conduit, wherein the fluid streamer is operational for streaming the fluid at the fluid pressure into the at least one downward conduit.

[0011] In some embodiments, the partition wall includes a tube peripherally surrounding and spaced apart from the waveguide along the borehole to define the at least one downflow conduit, and wherein the tube is spaced apart from the wall of the borehole to define the at least one upward backflow conduit. In some embodiments, the partition wall includes at least one wall section configured for laterally extending at a peripheral edge thereof toward a sidewall of the borehole wall for sectioning the borehole into the at least one downflow conduit, and the at least one upward backflow conduit. In some embodiments, the partition wall includes a tube comprising the at least one downflow conduit, and the borehole serves as the at least one upward backflow conduit.

[0012] In some embodiments, the internal waveguide pressure is a low pressure. The low pressure can be below 100 atmospheres, around ambient atmospheric pressure, or below ambient atmospheric pressure at ground surface level.

[0013] In some embodiments, the waveguide cavity is sealed at the proximal side of the waveguide to prevent infiltration of gas therein, and escape of gas if contained therein. The waveguide cavity can be filled up with moisture-free gas, such as nitrogen, carbon dioxide (CO2), supercritical CO2 (SCCO2), and / or inert gas, such as argon.

[0014] In some embodiments, the frequency of the MMW is in the range of 1 GHz to 10 THz, which can optionally be selected to be above 6 GHz, and / or below 300GHz, and further optionally above 40 GHz and / or below 175 GHz.

[0015] In some embodiments, the MMW power source is configured to generate the continuous wave (CW) MMW energy.

[0016] In some embodiments, the MMW power source is configured to generate high-power MMW energy over 10kW, optionally over 10OkW, and further optionally over 500kW.

[0017] In some embodiments, the optical element comprises a window, and / or a diverging lens operational for directing the MMW energy to the borehole bottom according to a field of view (FOV). In some embodiments, the system includes a conduit insertion for applying a small amount of a second, MMW transparent fluid, directly to the borehole bottom.

[0018] In some embodiments, the waveguide includes a proximal waveguide bend and a main waveguide section extending from the waveguide bend downwards along the borehole.

[0019] In some embodiments, the fluid includes at least one of: colloid, liquid, gas, and supercritical fluid.

[0020] In some embodiments, the fluid density (specific gravity) of the fluid is close to the density of bedrock surrounding the borehole. The fluid density can be in the range of 0 to 4 g / cm3, 0.05 g / cm3to 4 g / cm3,0.75 g / cm3to 0.9 g / cm3, and further optionally 2.5 g / cm3to 3 g / cm3.

[0021] In some embodiments, the fluid density is close to waveguide density of the waveguide, and can equal, be greater than, or be smaller than, the waveguide density.

[0022] In some embodiments, the distal end of the waveguide is kept at an operational distance from the borehole bottom and the fluid is transparent to transmission of at least 5% of MMW energy through the operational distance, and optionally of at least 70% of MMW energy through the operational distance.

[0023] In some embodiments, the operational distance is below 200 meters, optionally in the range of 1 cm to 2 meters, and further optionally in the range of 2 cm to 30 cm from the borehole bottom.

[0024] In some embodiments, the system includes a waveguide operational distance retainer including at least one of:

[0025] (a) bars connecting the waveguide to the partition wall; and (b) ground-surface waveguide rig configured to firmly secure to the waveguide and to provide a counter push or pull force to respectively prevent overfloat or sinking of the waveguide in the fluid.

[0026] In some embodiments, the system includes at least one sensor configured to monitor one or more parameters of the drilling process, mounted near the bottom of the waveguide.

[0027] In some embodiments, the at least one sensor is configured to transmit sensor readings by electromagnetic transmission through the waveguide.

[0028] In some embodiments, the system further includes MMW energy harvesting means configured to receive MMW energy and convert the MMW energy into an electric current for powering the operation of the at least one sensor and / or other electric equipment, and / or for storing in an electric energy storage.

[0029] In some embodiments, the system is configured to drill the borehole at a borehole inclination which can be vertical, horizontal, or oblique.

[0030] In some embodiments, the waveguide includes a plurality of gimbaled bends.

[0031] According to another aspect of the invention, there is provided a method for drilling through a ground borehole using millimeter wave (MMW) energy, including the procedures of:

[0032] (a)generating MMW energy using a MMW power source;

[0033] (b)guiding to a borehole bottom the MMW energy through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and including a hollow waveguide body encompassing a cavity at an internal waveguide pressure; and (c) transmitting the MMW energy to the borehole bottom using an optical element coupled to a distal end of the waveguide and configured to pressure seal the waveguide and to transmit the MMW energy to the borehole bottom, wherein when the distal end of the waveguide is immersed in fluid filling the borehole at a fluid pressure and a fluid density, at least in the vicinity of the bottom of the waveguide: the internal waveguide pressure is lower than the fluid pressure; and / or the internal waveguide density is lower than the fluid density.

[0034] In some embodiments, the method includes filling the borehole with the fluid while keeping the waveguide immersed in the fluid at an operational distance from the borehole bottom wherein the fluid is transparent to MMW through the operational distance.

[0035] In some embodiments, a partition wall extends along the borehole and separates between at least one downflow conduit and at least one upward backflow conduit while leaving a fluid passage near the borehole bottom, and the method includes exerting a fluid flow of the fluid within the borehole outside and around the waveguide, by streaming the fluid by a fluid streamer at the fluid pressure into the at least one downward conduit.

[0036] In some embodiments, the partition wall is in the form of a tube peripherally surrounding and spaced apart from the waveguide, and extends along the borehole to define the at least one downflow conduit, and is spaced apart from the wall of the borehole to define the at least one upward backflow conduit. In some embodiments, the partition wall includes at least one wall section having a peripheral edge laterally extending toward a sidewall of the borehole wall for sectioning the borehole into the at least one downflow conduit, and the at least one upward backflow conduit.

[0037] In some embodiments, the partition wall is in the form of a tube which includes the at least one downflow conduit, and wherein the borehole serves as the at least one upward backflow conduit.

[0038] In some embodiments, the internal waveguide pressure is a low pressure below 100 atmospheres at ground surface level.

[0039] In some embodiments, the internal waveguide pressure is around ambient atmospheric pressure at ground surface level.

[0040] In some embodiments, the internal waveguide pressure at ground surface level is below ambient atmospheric pressure.

[0041] In some embodiments, the waveguide cavity is sealed at the proximal side of the waveguide to prevent infiltration of gas therein, and escape of gas if contained therein.

[0042] In some embodiments, the guiding includes filling the waveguide cavity with moisture-free gas.

[0043] In some embodiments, the moisture-free gas includes nitrogen.

[0044] In some embodiments, the moisture-free gas includes carbon dioxide (CO2) or supercritical CO2 (SCCO2).

[0045] In some embodiments, the guiding includes filling up the waveguide cavity with an inert gas.

[0046] In some embodiments, the inert gas includes argon. In some embodiments, the generating includes generating MMW in a MMW frequency in the range of 1 GHz to 10 THz.

[0047] In some embodiments, the MMW frequency is above 6 GHz.

[0048] In some embodiments, the MMW frequency is above 40 GHz.

[0049] In some embodiments, the MMW frequency is below 600 GHz.

[0050] In some embodiments, the MMW frequency is below 175 GHz.

[0051] In some embodiments, the generating includes generating continuous wave (CW) MMW energy.

[0052] In some embodiments, the generating includes generating high-power MMW energy over 10kW.

[0053] In some embodiments, the generating includes generating high-power MMW energy over 10OkW.

[0054] In some embodiments, the generating includes generating high-power MMW energy over 500kW.

[0055] In some embodiments, the optical element includes a window.

[0056] In some embodiments, the optical element includes a diverging lens operational for directing the MMW energy to the borehole bottom according to a field of view (FOV).

[0057] In some embodiments, the method includes applying, via a conduit insertion, a small amount of a second, MMW transparent fluid, directly to the borehole bottom.

[0058] In some embodiments, the waveguide includes a proximal waveguide bend and a main waveguide section extending from the waveguide bend downwards along the borehole. In some embodiments, the filling up includes filling up the borehole with a fluid including at least one of: colloid; liquid; gas or supercritical fluid (e.g., CO2).

[0059] In some embodiments, the fluid density (specific gravity) of the fluid is close to the density of bedrock surrounding the borehole.

[0060] In some embodiments, the fluid density is in the range of 0 to 4 g / cm3

[0061] In some embodiments, the fluid density is in the range of 0.05 g / cm3to 4g / cm3.

[0062] In some embodiments, the fluid density is in the range of 0.75 g / cm3to 0.9 g / cm3.

[0063] In some embodiments, the fluid density is in the range of 2.5 g / cm3to 3 g / cm3.

[0064] In some embodiments, the fluid density is close to waveguide density of the waveguide.

[0065] In some embodiments, the fluid density equals, is greater than, or is smaller than, the waveguide density.

[0066] In some embodiments, the fluid is transparent to transmission of at least 5% of MMW energy through the operational distance.

[0067] In some embodiments, the fluid is transparent to transmission of at least 70% of MMW energy through the operational distance.

[0068] In some embodiments, the keeping includes keeping the waveguide immersed in the fluid at an operational distance below 200 meters from the borehole bottom.

[0069] In some embodiments, the keeping includes keeping the waveguide immersed in the fluid at an operational distance in the range of 1 cm to 2 meters from the borehole bottom. In some embodiments, the keeping includes keeping the waveguide immersed in the fluid at an operational distance in the range of 2 cm to 30 cm from the borehole bottom.

[0070] In some embodiments, the keeping includes using a waveguide operational distance retainer including at least one of:

[0071] (a) bars connecting the waveguide to the partition wall; and

[0072] (b) ground-surface waveguide-rig configured to firmly secure to the waveguide and to provide a counter push or pull force to respectively prevent overfloat or sinking of the waveguide in the fluid.

[0073] In some embodiments, the method includes monitoring one or more parameters of the drilling process by at least one sensor by mounting the at least one sensor near the bottom of the waveguide.

[0074] In some embodiments, the method includes transmitting sensor readings by electromagnetic transmission through the waveguide.

[0075] In some embodiments, the method includes receiving and converting MMW energy, by MMW energy harvesting means configured to receive MMW energy and convert the MMW energy into an electric current, for powering the operation of at least one sensor and / or other electric equipment, and / or for storing in an electric energy storage.

[0076] In some embodiments, the method is operational for drilling the borehole at a borehole inclination selected from the list consisting of: vertical; horizontal; and oblique.

[0077] In some embodiments, the method includes lengthening and moving down the borehole a section of the waveguide using a plurality of gimbaled bends of the waveguide. According to another aspect of the invention, there is provided a system for drilling through a ground borehole using millimeter wave (MMW) energy, featuring:

[0078] (a) a MMW power source configured to generate MMW energy;

[0079] (b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom; and

[0080] (c) a diverging lens coupled with a distal end of the waveguide and operational for directing the MMW energy guided by the waveguide to the borehole bottom according to a field of view (FOV).

[0081] In some embodiments, the waveguide includes a hollow waveguide body encompassing a cavity at an internal waveguide pressure, the diverging lens is configured to pressure seal the waveguide at the distal end of the waveguide, and when the distal end of the waveguide is immersed in a fluid filling the borehole at a fluid pressure and a fluid density, at least in the vicinity of the bottom of the waveguide: the internal waveguide pressure is lower than the fluid pressure; and / or the internal waveguide density is lower than the fluid density.

[0082] According to another aspect of the invention, there is provided a method for drilling through a ground borehole using millimeter wave (MMW) energy, including the procedures of:

[0083] (a) generating MMW energy using a MMW power source; (b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and comprising a hollow waveguide body encompassing a cavity; and

[0084] (c) transmitting the MMW energy to the borehole bottom using a diverging lens coupled with a distal end of the waveguide and operational for directing the MMW energy guided by the waveguide to the borehole bottom according to a field of view (FOV).

[0085] In some embodiments the diverging lens is configured to pressure seal the waveguide at the distal end of the waveguide, and when the distal end of the waveguide is immersed in a fluid filling the borehole at a fluid pressure and a fluid density, at least in the vicinity of the bottom of the waveguide: the internal waveguide pressure is lower than the fluid pressure; and / or the internal waveguide density is lower than the fluid density.

[0086] According to another aspect of the invention, there is provided a system for drilling through a ground borehole using millimeter wave (MMW) energy including:

[0087] (a) a MMW power source configured to generate MMW energy;

[0088] (b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom; and

[0089] (c) at least one sensor mounted near the bottom of the waveguide, configured to monitor one or more parameters of the drilling process, and to transmit its readings by electromagnetic transmission through the waveguide. According to another aspect of the invention, there is provided a method for drilling through a ground borehole using millimeter wave (MMW) energy, including the procedures of:

[0090] (a) generating MMW energy using a MMW power source;

[0091] (b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and comprising a hollow waveguide body; and

[0092] (c) monitoring one or more parameters of the drilling process by at least one sensor mounted near the bottom of the waveguide, and transmitting its readings by electromagnetic transmission through the waveguide.

[0093] According to another aspect of the invention, there is provided a system for drilling through a ground borehole using millimeter wave (MMW) energy including:

[0094] (a) a MMW power source configured to generate MMW energy;

[0095] (b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom; and

[0096] (c) MMW energy harvesting means configured to receive MMW energy generated by the MMW power source and convert the MMW energy to electric energy, for powering at least one sensor monitoring one or more parameters of the drilling process, an electrically operated equipment and / or electric storage, mounted along or near the bottom of the waveguide.

[0097] In some embodiments, the MMW energy harvesting means includes: one or more antennas for receiving MMW; a converter for converting MMW into an electric current; and an electric energy storing means.

[0098] According to another aspect of the invention, there is provided a method for drilling through a ground borehole using millimeter wave (MMW) energy, including the procedures of:

[0099] (a) generating MMW energy using a MMW power source;

[0100] (b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and comprising a hollow waveguide body; and

[0101] (c) harvesting MMW energy by harvesting means mounted along or near the bottom of the waveguide and configured to receive MMW energy generated by the MMW power source and convert the MMW energy to electric energy, for powering at least one sensor monitoring one or more parameters of the drilling process, an electrically operated equipment and / or electric storage.

[0102] According to another aspect of the invention, there is provided a system for drilling through a ground borehole using millimeter wave (MMW) energy including:

[0103] (a) a static MMW power source configured to generate MMW energy; and

[0104] (b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom, wherein the waveguide comprises a plurality of gimbaled bends allowing the lengthening and moving down of a section of the waveguide.

[0105] According to another aspect of the invention, there is provided a method for drilling through a ground borehole using millimeter wave (MMW) energy, including the procedures of: (a) generating MMW energy using a static MMW power source;

[0106] (b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and comprising a hollow waveguide body; and

[0107] (c) lengthening and moving down of a section of the waveguide wherein a plurality of gimbaled bends of the waveguide.

[0108] According to another aspect of the invention, there is provided a system for drilling through a ground borehole using millimeter wave (MMW) energy comprising:

[0109] (a) a MMW power source configured to generate MMW energy;

[0110] (b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom; and

[0111] (c) at least one radar sensor mounted along or near the bottom of the waveguide, wherein the distal end of the waveguide is immersed in fluid filling the borehole; and wherein the fluid is transparent to transmission of MMW energy through the operational distance of the radar sensor.

[0112] According to another aspect of the invention, there is provided a method for drilling through a ground borehole using millimeter wave (MMW) energy, comprising the procedures of:

[0113] (a) generating MMW energy using a static MMW power source; (b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and comprising a hollow waveguide body; and

[0114] (c) operating at least one radar sensor mounted along or near the bottom of the waveguide, wherein the distal end of the waveguide is immersed in fluid filling the borehole; and wherein the fluid is transparent to transmission of MMW energy through an operational distance of the radar sensor. The foregoing general description of the illustrative embodiments and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure and are not restrictive.

[0115] BRIEF DESCRIPTION OF THE DRAWINGS

[0116] The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

[0117] Figure 1 is a cross-sectional side view of an embodiment of a millimeter wave (MMW) drilling system featuring a low pressure waveguide conducting MMW transmission, constructed and operative in accordance with the invention;

[0118] Figure 2 is a cross-sectional side view of another embodiment of a system constructed and operative in accordance with the invention, including a low pressure millimeter waveguide insertion and a conduit insertion for applying transparent MMW fluid;

[0119] Figures 3A-3G are cross-sectional top views of several embodiments exemplifying variants to the arrangement of a partition wall of systems constructed and operative in accordance with the invention. Figure 3A is a top cross-sectional view of the system of Figure 1 ; Figure 3B is a top cross-sectional view of the system of Figure 1 illustrating a reverse fluid flow configuration; Figure 3C is a top cross-sectional view of a system featuring a partition wall in the form of a tube which operates as the downflow conduit, wherein the borehole serves as upward backflow conduit; Figure 3D is a top cross-sectional view of the system of Figure 3C illustrating a reverse fluid flow configuration; Figure 3E is a top cross-sectional view of a system featuring a partition wall in the form of a flat wall configured for laterally extending at peripheral edges thereof toward the sidewall of a borehole for sectioning the borehole into a downflow conduit and an upward backflow conduit; Figure 3F is a top cross-sectional view of a system featuring the partition wall in the form of two wall sections configured for laterally extending at a peripheral edge thereof toward a sidewall of the borehole for sectioning the borehole into a downflow conduit, and an upward backflow conduit; Figure 3G is a top cross-sectional view of a system featuring the partition wall in the form of four wall sections configured for laterally extending at a peripheral edge thereof toward a sidewall of the borehole for sectioning the borehole into two downflow conduits, and two upward backflow conduits;

[0120] Figure 4 is a flow chart of a method for drilling through a ground borehole using millimeter wave (MMW) energy, operative in accordance with the invention;

[0121] Figures 5A is a lateral view of a proximal portion of a further system constructed and operative in accordance with the invention, having a waveguide including gimbaled bends;

[0122] Figure 5B is a perspective view of the system of Figure 5A; and

[0123] Figure 6 is a lateral view of a proximal portion of yet another system constructed and operative in accordance with the invention, having a waveguide including gimbaled mirror bends.

[0124] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions and / or aspect ratio of some of the elements can be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals can be repeated among the figures to indicate corresponding or analogous elements throughout the serial views. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0125] Applying millimeter-wave radiation energy into the borehole via pressurized gas may result in high attenuation of MMW energy due to the high density of gas at high pressure, thereby frustrating propagation of sufficient energy that can reach the borehole bottom, over distances beyond hundreds of meters, well before reaching desired drilling depths of thousands of meters. Moreover, such pressurized gas can often reach hundreds and thousands atmospheres, which can fracture the surrounding rock, escape into the surrounding ground, and require heavy equipment to produce and maintain the enormous pressure of the gas. In addition, it is highly complicated to extend a waveguide under such high pressures.

[0126] Another approach may involve working with low pressure (i.e., below 100 atm) gas which is used to fill up the entirety of the borehole, but this approach does not solve the borehole stability problem - as the borehole wall tends to collapse under the surrounding high ambient pressure at depths such as deeper than 3km. This low gaseous pressure in the borehole renders the technique inapplicable for use in pressurized gaseous, or liquid pockets, as it may blowout the waveguide and significantly reduce safety.

[0127] Furthermore, regarding both approaches, holding a waveguide in a gaseous medium imposes severe structural loads on the waveguide, which tends to break up and renders the task of reaching depths above 10 km an insurmountable challenge.

[0128] The present invention overcomes the attenuation deficiency and the other drawbacks by providing a low pressure waveguide, or a waveguide containing matter at a low density. Low pressure or low density inside the waveguide (herein: “internal waveguide pressure”, “internal waveguide density”, e.g., pressure and density of gas filling the waveguide cavity), lower the loss of MMW energy along the waveguide. Pressure or density within the waveguide which is lower than that of surrounding fluid also increases the buoyancy of the waveguide in the fluid. The waveguide may be immersed in a fluid filling or filling up the borehole, and which is streaming there through. The streamed fluid is operational to carry debris of ground or molten or vaporized rock and any released earth fluids, or other system fluids, to cool down the waveguide and borehole, seal the borehole against leakage into or out of the borehole, stabilize the borehole from collapse, and keep acceptable temperature of optical elements and sensitive electronics which are disposed near the bottom of the borehole. The waveguide is sealed at its distal end by an optical element. Sealing the waveguide at its distal end allows keeping the internal pressure of the waveguide, lower than fluid pressure at the distal end of the waveguide. The term “optical element” in this context refers to microwave optics, namely, an element which serves to transmit (or reflect) electromagnetic MMW. The optical element may be or may include, for example, a window or a lens. For example, the low pressure within the waveguide can be selected such that the attenuation along the waveguide to its very bottom is less than 50%. For example, 100 atmospheres can be low enough although much lower pressures, such as ambient atmospheric pressure or even induced vacuum can be applicable. In terms of low density, this is typically equivalent to densities lower than 200g per liter. The waveguide can be filled up with nitrogen, argon, carbon dioxide (CO2), supercritical CO2 (SCCO2), or any other gas, preferably moisture-free and / or inert gas. The internal pressure in the waveguide can be regulated by providing an opening at the top of the waveguide to the atmosphere, or by hermetically sealing the waveguide to allow maintaining a desired pressure, including depressurizing gas, up to “vacuum” pressure. The sealed waveguide is immersed in a higher pressure fluid within the borehole. The fluid can include gas, liquid, colloid (mud), supercritical fluid (e.g., CO2) or any combination thereof. The low pressure waveguide allows MMW beam energy to reach the bottom of the borehole without significant attenuation, without compromising preservation of borehole stability by virtue of the surrounding fluid which also serves to efficiently remove melted or vaporized rock from the bottom and to cool down the wellbore and reduce the structural stress on the waveguide. The fluid can include a novel colloid composition that is highly transparent to MMW energy for allowing passage of the MMW energy along the operational distance, namely - from the bottom waveguide window toward the rock at the bottom of the well, typically distanced below 2 meter from the optical element (the operational distance can be greater, e.g., 200 meters, depending on the fluid properties, such as liquid or gaseous physical state and composition of the fluid). The term “operational distance” (or “operational working distance”), as referred to herein, relates to the distance the MMW may travel from the bottom waveguide optical element to a target, e.g., the bottom of the borehole, and remain productive or effective at achieving its task, e.g., drilling. Operational distance depends on the optical element. For example, a diverging lens decreases the operational working distance, while a window may have only a minor influence on the operational working distance. Decreasing the operational working distance serves to decrease the attenuation of the MMW energy throughout this operational distance and thereby to increase the rate of MMW eventually reaching the bottom of the borehole and the efficiency of MMW drilling. Decreasing the operational working distance also serves to more efficient circulation of fluids within this distance, which continuously remove fresh deposits of melted rock particles from the borehole bottom generated by the drilling melting action. A large operational distance (e.g., above 0.3 meter) can lead the fluid to divert upwards, without reaching the bottom of the borehole. Thus, compromising extracting melted rock particles and maintenance of MMW fluid transparency within the operational working distance.

[0129] In addition, the fluid composition influences the buoyancy of the waveguide within the fluid, thereby facilitating manufacture of a waveguide by available inexpensive materials (e.g., steel or aluminum), which together with low pressure gas inside the waveguide, render the specific mass density of the hollow waveguide similar or slightly higher than that of the surrounding fluid, without incurring limitation to the waveguide length beyond any required drilling lengths (e.g., up to 30 km). Buoyancy of the waveguide can reduce rig size and hook load capacity. Furthermore, the disclosed pressure sealing by an optical element coupled to a distal end of the waveguide may facilitate or allow the buoyancy and drilling to greater lengths.

[0130] In some embodiments, the disclosed system may include a fluid source, e.g., a pump, configured to fill or fill up the borehole with a fluid as described hereinabove. In some embodiments, the disclosed system may be coupled with such a fluid source.

[0131] It is noted that the present invention is described with respect to vertical borehole drilling, but is also readily directed and applicable to horizontal borehole drilling (or any inclined or oblique drill direction). Accordingly, the terms “up”, “down”, “upward”, “downward” and the like should be regarded as relative to a vertically inclined borehole, and should be interpreted as rotated in accordance with the inclination of the borehole, e.g., “up” should be understood as proximally oriented and “down” should be understood as distally oriented, e.g., with respect to an operator of the system or with respect to the MMW power source of the system. Additionally, or when applicable, “proximal” should be interpreted at relating to the beginning of the borehole while “distal” should be interpreted as relating to the end of the borehole or the bottom of the borehole.

[0132] According to a broad aspect of the invention, the invention includes a system for drilling through a ground borehole using millimeter wave (MMW) energy, featuring:

[0133] (a)a MMW power source configured to generate MMW energy.

[0134] (b)at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom, the waveguide comprising a hollow waveguide body encompassing a cavity at an internal waveguide pressure.

[0135] (c) an optical element coupled to a distal end of the waveguide and configured to pressure seal the waveguide and to transmit the MMW energy toward the borehole bottom, wherein when the distal end of the waveguide is immersed in a fluid filling the borehole at a fluid pressure and a fluid density, at least in the vicinity of the bottom of the waveguide: the internal waveguide pressure is lower than the fluid pressure; and / or the internal waveguide density is lower than the fluid density. In some embodiments, the system includes a fluid flow system configured to provide a fluid flow of the fluid within the borehole outside and around the waveguide. The fluid flow system includes or integrates the fluid source. The fluid flow system can include a fluid streamer for streaming the fluid at the fluid pressure into the borehole. The fluid flow system can include a partition wall extending along the borehole, leaving a fluid passage near the borehole bottom and separating between at least one downflow conduit and at least one upward backflow conduit, wherein the fluid streamer is operational for streaming the fluid at the fluid pressure into the at least one downward conduit.

[0136] In some embodiments, the partition wall includes a tube peripherally surrounding and spaced apart from the waveguide along the borehole to define the at least one downflow conduit, and wherein the tube is spaced apart from the wall of the borehole to define the at least one upward backflow conduit. In some embodiments, the partition wall includes at least one wall section configured for laterally extending at a peripheral edge thereof toward a sidewall of the borehole wall for sectioning the borehole into the at least one downflow conduit, and the at least one upward backflow conduit. In some embodiments, the partition wall includes a tube comprising the at least one downflow conduit, and the borehole serves as the at least one upward backflow conduit.

[0137] In some embodiments, the internal waveguide pressure is a low pressure. The low pressure can be below 100 atmospheres, around ambient atmospheric pressure, or below ambient atmospheric pressure at ground surface level.

[0138] In some embodiments, the waveguide cavity is sealed at the proximal side of the waveguide to prevent infiltration of gas therein, and escape of gas if contained therein. The waveguide cavity can be filled up with moisture-free gas, such as nitrogen, carbon dioxide (CO2), supercritical CO2 (SCCO2), and / or inert gas, such as argon.

[0139] In some embodiments, the frequency of the MMW is in the range of 1 GHz to 10 THz, which can optionally be selected to be above 6 GHz, and / or below 300GHz, and further optionally above 40 GHz and / or below 175 GHz.

[0140] In some embodiments, the MMW power source is configured to generate the continuous wave (CW) MMW energy.

[0141] In some embodiments, the MMW power source is configured to generate high-power MMW energy over 10kW, optionally over 10OkW, and further optionally over 500kW.

[0142] In some embodiments, the optical element comprises a window, and / or a diverging lens operational for directing the MMW energy to the borehole bottom according to a field of view (FOV). A diverging lens decreases the operational working distance, and thus reduces MMW energy losses due to absorption in fluid. Furthermore, the diverging lens also facilitates or allows the fluid to carry up the molten rock particles more efficiently to the surface. Long operational distance does not allow the fluid to reach the bottom of the borehole effectively (the flow is diverted upwards before reaching the borehole bottom as noted above.

[0143] In some embodiments, the system includes a conduit insertion for applying a small amount of a second, MMW transparent fluid, directly to the borehole bottom.

[0144] In some embodiments, the waveguide includes a proximal waveguide bend and a main waveguide section extending from the waveguide bend downwards along the borehole. In some embodiments, the fluid includes at least one of: colloid, liquid, gas or supercritical fluid (e.g., CO2).

[0145] In some embodiments, the fluid density (specific gravity) of the fluid is close to the density of bedrock surrounding the borehole. The fluid density can be in the range of 0 to 4 g / cm3,0.05 g / cm3to 4 g / cm3, 0.75 g / cm3to 0.9 g / cm3, and further optionally 2.5 g / cm3to 3 g / cm3.

[0146] In some embodiments, the fluid density is close to waveguide density of the waveguide, and can equal, be greater than, or be smaller than, the waveguide density. In this context, waveguide density is the product of the combined weighted densities of the waveguide housing and the gas-filled waveguide cavity 111 (and any further element of the waveguide or contained therein). According to some aspects, the fluid density is equal up to ±1 % of the waveguide density.

[0147] In some embodiments, the distal end of the waveguide is kept at an operational distance from the borehole bottom and the fluid is transparent to transmission of at least 5% of MMW energy through the operational distance, and optionally of at least 70% of MMW energy through the operational distance. The higher the transmission is, the faster the drilling process is.

[0148] In some embodiments, the operational distance is below 200 meters, optionally in the range of 1 cm to 2 meters, and further optionally in the range of 2 cm to 30 cm from the borehole bottom.

[0149] In some embodiments, the system includes a waveguide operational distance retainer including at least one of:

[0150] (a) bars connecting the waveguide to the partition wall; and (b) ground-surface waveguide rig configured to firmly secure to the waveguide and to provide a counter push or pull force to respectively prevent overfloat or sinking of the waveguide in the fluid.

[0151] In some embodiments, the system includes at least one sensor or a sensor unit including the least one sensor configured to monitor one or more parameters of the drilling process, mounted near the bottom of the waveguide, e.g., near a distal end of the waveguide or along the bottom or distal half of the waveguide.

[0152] In some embodiments, the at least one sensor or the sensor unit is configured to transmit sensor readings by electromagnetic transmission through the waveguide.

[0153] In some embodiments, the system further includes MMW energy harvesting means configured to receive MMW energy and convert the MMW energy into an electric current for powering the operation of the at least one sensor and / or other electric equipment, and / or for storing in an electric energy storage.

[0154] In some embodiments, the system is configured to drill the borehole at a borehole inclination which can be vertical, horizontal, or oblique. In some embodiments, the system may include integrated sensor configured to be inserted to the borehole to acquire azimuth and inclination data. The drilling direction may be then adjusted accordingly, e.g., using steering motors or optical correction mechanisms such as additional prism.

[0155] In some embodiments, the waveguide includes a plurality of gimbaled bends. In accordance with another broad aspect of the invention, the invention includes a method for drilling through a ground borehole using millimeter wave (MMW) energy, including the procedures of:

[0156] (a)generating MMW energy using a MMW power source;

[0157] (b)guiding to a borehole bottom the MMW energy through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and including a hollow waveguide body encompassing a cavity at an internal waveguide pressure; and

[0158] (c) transmitting the MMW energy to the borehole bottom using an optical element coupled to a distal end of the waveguide and configured to pressure seal the waveguide and to transmit the MMW energy to the borehole bottom, wherein when the distal end of the waveguide is immersed in fluid filling the borehole at a fluid pressure and a fluid density, at least in the vicinity of the bottom of the waveguide: the internal waveguide pressure is lower than the fluid pressure; and / or the internal waveguide density is lower than the fluid density.

[0159] In some embodiments, the method includes filling or filling up the borehole with the fluid while keeping the waveguide immersed in the fluid at an operational distance from the borehole bottom wherein the fluid is transparent to MMW through the operational distance.

[0160] In some embodiments, a partition wall extends along the borehole and separates between at least one downflow conduit and at least one upward backflow conduit while leaving a fluid passage near the borehole bottom, and the method includes exerting a fluid flow of the fluid within the borehole outside and around the waveguide, by streaming the fluid by a fluid streamer at the fluid pressure into the at least one downward conduit.

[0161] In some embodiments, the partition wall is in the form of a tube deploying includes peripherally surrounding and spaced apart from the waveguide, and extends along the borehole to define the at least one downflow conduit, and is spaced apart from the wall of the borehole to define the at least one upward backflow conduit.

[0162] In some embodiments, the partition wall includes at least one wall section having a peripheral edge laterally extending toward a sidewall of the borehole wall for sectioning the borehole into the at least one downflow conduit, and the at least one upward backflow conduit.

[0163] In some embodiments, the partition wall is in the form of a tube which includes the at least one downflow conduit, and wherein the borehole serves as the at least one upward backflow conduit.

[0164] In some embodiments, the internal waveguide pressure is a low pressure below 100 atmospheres at ground surface level.

[0165] In some embodiments, the internal waveguide pressure is around ambient atmospheric pressure at ground surface level.

[0166] In some embodiments, the internal waveguide pressure at ground surface level is below ambient atmospheric pressure.

[0167] In some embodiments, the waveguide cavity is sealed at the proximal side of the waveguide to prevent infiltration of gas therein, and escape of gas if contained therein.

[0168] In some embodiments, the guiding includes filling or filling up the waveguide cavity with moisture-free gas. In some embodiments, the moisture-free gas includes nitrogen.

[0169] In some embodiments, the moisture-free gas includes carbon dioxide (CO2) or supercritical CO2 (SCCO2).

[0170] In some embodiments, the guiding includes filling or filling up the waveguide cavity with an inert gas.

[0171] In some embodiments, the inert gas includes argon.

[0172] In some embodiments, the generating includes generating MMW in a MMW frequency in the range of 1 GHz to 10 THz.

[0173] In some embodiments, the MMW frequency is above 6 GHz.

[0174] In some embodiments, the MMW frequency is above 40 GHz.

[0175] In some embodiments, the MMW frequency is below 600 GHz.

[0176] In some embodiments, the MMW frequency is below 175 GHz.

[0177] In some embodiments, the generating includes generating continuous wave (CW) MMW energy.

[0178] In some embodiments, the generating includes generating high-power MMW energy over 10kW.

[0179] In some embodiments, the generating includes generating high-power MMW energy over 10OkW.

[0180] In some embodiments, the generating includes generating high-power MMW energy over 500kW.

[0181] In some embodiments, the optical element includes a window.

[0182] In some embodiments, the optical element includes a diverging lens operational for directing the MMW energy to the borehole bottom according to a field of view (FOV). In some embodiments, the method includes applying, via a conduit insertion, a small amount of a second, MMW transparent fluid, directly to the borehole bottom.

[0183] In some embodiments, the waveguide includes a proximal waveguide bend and a main waveguide section extending from the waveguide bend downwards along the borehole.

[0184] In some embodiments, the filling or filling up includes filling or filling up the borehole with a fluid including at least one of: colloid; liquid; gas or supercritical fluid (e.g., CO2).

[0185] In some embodiments, the fluid density (specific gravity) of the fluid is close to the density of bedrock surrounding the borehole.

[0186] In some embodiments, the fluid density is in the range of 0 to 4 g / cm3

[0187] In some embodiments, the fluid density is in the range of 0.05 g / cm3to 4 g / cm3.

[0188] In some embodiments, the fluid density is in the range of 0.75 g / cm3to 0.9 g / cm3.

[0189] In some embodiments, the fluid density is in the range of 2.5 g / cm3to 3 g / cm3.

[0190] In some embodiments, the fluid density is close to waveguide density of the waveguide.

[0191] In some embodiments, the fluid density equals, is greater than, or is smaller than, the waveguide density.

[0192] In some embodiments, the fluid is transparent to transmission of at least 5% of MMW energy through the operational distance. In some embodiments, the fluid is transparent to transmission of at least 70% of MMW energy through the operational distance.

[0193] In some embodiments, the keeping includes keeping the waveguide immersed in the fluid at an operational distance below 200 meters from the borehole bottom.

[0194] In some embodiments, the keeping includes keeping the waveguide immersed in the fluid at an operational distance in the range of 1 cm to 2 meters from the borehole bottom.

[0195] In some embodiments, the keeping includes keeping the waveguide immersed in the fluid at an operational distance in the range of 2 cm to 30 cm from the borehole bottom.

[0196] In some embodiments, the keeping includes using a waveguide operational distance retainer including at least one of:

[0197] (a) bars connecting the waveguide to the partition wall; and

[0198] (b) ground-surface waveguide-rig configured to firmly secure to the waveguide and to provide a counter push or pull force to respectively prevent overfloat or sinking of the waveguide in the fluid.

[0199] In some embodiments, the method includes monitoring one or more parameters of the drilling process by at least one sensor by mounting the at least one sensor near the bottom of the waveguide.

[0200] In some embodiments, the method includes transmitting sensor readings by electromagnetic transmission through the waveguide.

[0201] In some embodiments, the method includes receiving and converting MMW energy, by MMW energy harvesting means configured to receive MMW energy and to convert the MMW energy into an electric current, for powering the operation of at least one sensor, and / or other electric equipment, and / or for storing in an electric energy storage.

[0202] In some embodiments, the method is operational for drilling the borehole at a borehole inclination selected from the list consisting of: vertical; horizontal; and oblique.

[0203] In some embodiments, the method includes lengthening and moving down the borehole a section of the waveguide using a plurality of gimbaled bends of the waveguide.

[0204] According to another aspect of the invention, there is provided a system for drilling through a ground borehole using millimeter wave (MMW) energy, featuring:

[0205] (a) a MMW power source configured to generate MMW energy;

[0206] (b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom; and

[0207] (c) a diverging lens coupled with a distal end of the waveguide operational for directing the MMW energy guided by the waveguide to the borehole bottom according to a field of view (FOV).

[0208] In some embodiments, the waveguide includes a hollow waveguide body encompassing a cavity at an internal waveguide pressure, the diverging lens is configured to pressure seal the waveguide at the distal end of the waveguide, and when the distal end of the waveguide is immersed in a fluid filling the borehole at a fluid pressure and a fluid density, at least in the vicinity of the bottom of the waveguide: the internal waveguide pressure is lower than the fluid pressure; and / or the internal waveguide density is lower than the fluid density.

[0209] According to another aspect of the invention, there is provided a method for drilling through a ground borehole using millimeter wave (MMW) energy, including the procedures of:

[0210] (a) generating MMW energy using a MMW power source;

[0211] (b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and comprising a hollow waveguide body encompassing a cavity; and

[0212] (c) transmitting the MMW energy to the borehole bottom using a diverging lens coupled with a distal end of the waveguide and operational for directing the MMW energy guided by the waveguide to the borehole bottom according to a field of view (FOV).

[0213] In some embodiments the diverging lens is configured to pressure seal the waveguide at the distal end of the waveguide, and when the distal end of the waveguide is immersed in a fluid filling the borehole at a fluid pressure and a fluid density, at least in the vicinity of the bottom of the waveguide: the internal waveguide pressure is lower than the fluid pressure; and / or the internal waveguide density is lower than the fluid density.

[0214] According to another aspect of the invention, there is provided a system for drilling through a ground borehole using millimeter wave (MMW) energy including:

[0215] (a) a MMW power source configured to generate MMW energy; (b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom of the borehole; and

[0216] (c) at least one sensor mounted near the bottom of the waveguide, configured to monitor one or more parameters of the drilling process, and to transmit its readings by electromagnetic transmission through the waveguide.

[0217] According to another aspect of the invention, there is provided a method for drilling through a ground borehole using millimeter wave (MMW) energy, including the procedures of:

[0218] (a) generating MMW energy using a MMW power source;

[0219] (b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and comprising a hollow waveguide body; and

[0220] (c) monitoring one or more parameters of the drilling process by at least one sensor mounted near the bottom of the waveguide, and transmitting its readings by electromagnetic transmission through the waveguide.

[0221] According to another aspect of the invention, there is provided a system for drilling through a ground borehole using millimeter wave (MMW) energy including:

[0222] (a) a MMW power source configured to generate MMW energy;

[0223] (b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom; and

[0224] (c) MMW energy harvesting means configured to receive MMW energy generated by the MMW power source and convert the MMW energy to electric energy, for powering at least one sensor monitoring one or more parameters of the drilling process, an electrically operated equipment and / or electric storage, mounted along or near the bottom of the waveguide.

[0225] In some embodiments, the MMW energy harvesting means includes: one or more antennas for receiving MMW; a converter for converting MMW into an electric current (e.g. , rectennas that combine a rectifier and antenna / s are applicable); and an electric energy storing means.

[0226] According to another aspect of the invention, there is provided a method for drilling through a ground borehole using millimeter wave (MMW) energy, including the procedures of:

[0227] (a) generating MMW energy using a MMW power source;

[0228] (b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and comprising a hollow waveguide body; and

[0229] (c) harvesting MMW energy by harvesting means mounted along or near the bottom of the waveguide and configured to receive MMW energy generated by the MMW power source and convert the MMW energy to electric energy, for powering at least one sensor monitoring one or more parameters of the drilling process, an electrically operated equipment and / or electric storage.

[0230] According to another aspect of the invention, there is provided a system for drilling through a ground borehole using millimeter wave (MMW) energy including:

[0231] (a) a static MMW power source configured to generate MMW energy; and (b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide down the MMW energy to a borehole bottom of the borehole, wherein the waveguide comprises a plurality of gimbaled bends allowing the lengthening and moving down of a section of the waveguide.

[0232] According to another aspect of the invention, there is provided a method for drilling through a ground borehole using millimeter wave (MMW) energy, including the procedures of:

[0233] (a) generating MMW energy using a static MMW power source;

[0234] (b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and comprising a hollow waveguide body; and

[0235] (c) lengthening and moving down of a section of the waveguide wherein a plurality of gimbaled bends of the waveguide.

[0236] According to another aspect of the invention, there is provided a system for drilling through a ground borehole using millimeter wave (MMW) energy comprising:

[0237] (a) a MMW power source configured to generate MMW energy;

[0238] (b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom; and

[0239] (c) at least one radar sensor mounted along or near the bottom of the waveguide, wherein the distal end of the waveguide is immersed in fluid filling the borehole; and wherein the fluid is transparent to transmission of MMW energy through the operational distance of the radar sensor.

[0240] According to another aspect of the invention, there is provided a method for drilling through a ground borehole using millimeter wave (MMW) energy, comprising the procedures of:

[0241] (a) generating MMW energy using a static MMW power source;

[0242] (b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and comprising a hollow waveguide body; and

[0243] (c) operating at least one radar sensor mounted along or near the bottom of the waveguide, wherein the distal end of the waveguide is immersed in fluid filling the borehole; and wherein the fluid is transparent to transmission of MMW energy through an operational distance of the radar sensor.

[0244] Reference is now made to Figure 1 , which is a cross-sectional side view of an embodiment of millimeter wave (MMW) drilling system 100 which includes low pressure waveguide 110, which is configured to conduct MMW transmission, constructed and operative in accordance with the invention. Low pressure waveguide 110 includes an elongated body 113 having two ends 113a and 113b, which enables and directs the propagation of the MMWs from one end of waveguide 110, e.g., end 113a (or proximal end 113a), at which the MMWs enter waveguide 110, to the other end of waveguide 110, e.g., end 113b (or distal end 113b), at which the MMWs exit waveguide 110. Low pressure waveguide 110 may be, for example, a corrugated waveguide. Proximal end 113a of waveguide 110 may be open, e.g., when located above ground, or closed or sealed. System 100 is directed to drill through ground 104 along wellbore or borehole 102, which can be initially drilled by conventional methods, or generated by the present method from the beginning. System 100 includes MMW power source 106 configured to generate MMW energy in the range of 1 GHz to 10 THz, optionally in the range of 6 GHz to 300 GHz, and further optionally in the range of 40-175 GHz. Power source 106 can feature a high-power source, generating MMW energy over 10kW, optionally over 100kW, e.g., 500kW. The MMW can be generated as a continuous wave (CW), although pulse patterns may also be applicable. Power source 106 can feature a Gyrotron, a Klystron, multiple traveling wave tubes (TWTs) or any other MMW source. Output MMW beam 108 is guided within waveguide cavity 111 , by hollow waveguide 110 which has a waveguide bend 112. Thereafter, beam 108 is redirected to waveguide section 114, which is configured to lengthen and be pushed down as the borehole deepens, e.g., by adding waveguide segments at the top of section 114. This redirection can also be achieved through several gimbaled bends, so that the power source 106 will be static while section 114 is lengthened and moved down, as the borehole deepens.

[0245] Reference is now made to Figures 5A, 5B and 6 which exemplify a gimbaled waveguide. Figures 5A shows a lateral view of a proximal portion of a system 700 which includes a waveguide 110’ featuring gimbaled bends. Figure 5B shows a perspective view of the proximal portion of system 700. In this example, waveguide 110’ includes bends 112a-112e, which are gimbaled by virtue of gimbals (rotational joints) 147a, 147b, and 147c. Waveguide 110’ in Figures 5A, 5B exemplifies optional configurations of waveguide 110 of Figures 1 -2.

[0246] The proximal portion of system 700 includes a static power source 106 positioned on or above ground 104 connected to waveguide 110’. Waveguide 110’ is composed of a plurality of linked elongated waveguide sections or segments. The proximal portion of waveguide 110’ includes waveguide sections 110a, 110b, and 110c and the distal portion of waveguide 110’ includes section 110d which is connected to waveguide 114 by joint 160. Section 110a is connected to power source 106. Waveguide 110’ features gimbaled bends 112a to 112e, which allow relative rotations of sections 110a to 110d. Waveguide section 110a is connected to power source 106 at one (proximal) end and at its other (distal) end - to waveguide section 110b by gimbal 147a. Waveguide section 110b is connected at its other (distal) end to waveguide section 110c by gimbal 147b. Waveguide section 110c is connected at its other (distal) end to waveguide section 110d by gimbal 147c. Waveguide section 110b features bends or bend corners 112a and 112b. Waveguide section 110c features bends or bend comers 112c and 112d. Waveguide section 110d features bend or bend corner 112e. Bends 112a to 112e feature an L-shaped (90 degrees) corner.

[0247] Gimbaled bends 112a to 112e include each a fixed mirror 148. Fixed mirrors 148 are mounted in a fixed manner within the respective waveguide section and configured to direct, e.g., bend, the M MW waves generated by power source 106 along waveguide 110’. Gimbals 147a, 147b and 147c allow the respective waveguide sections to axially rotate about axes 149a, 149b and 149c, respectively. For example, gimbal bend 112a can rotate about axis 149a relative to section 110a (denoted by arrow 152a), gimbal bends 112b-112c can rotate relative to each other about axis 149b (denoted by arrows 152b), and gimbal bends 112d-112e can rotate relative to each other about axis 149c (denoted by arrows 152c). This configuration allows the direction and pushing down or raising (arrow 154) of waveguide section 114, which is configured to lengthen, through a borehole in ground 104 as the borehole deepens, e.g., by adding waveguide sections at the top of section 114. Gimbaled bends 112a to 112e allow power source 106 to be static while waveguide section 114 is lengthened and moved down, as the borehole deepens. According to some aspects, system 700 may further include a rig 132 configured to move waveguide section 114 downwards (or upwards). This motion passively rotates gimbal bends 112a to 112e and thus these gimbaled bends are not required to be equipped with motors.

[0248] Reference is now made to Figure 6 which shows a lateral view of a proximal portion of MMW beam 108 generated and directed via a system 800, which includes a waveguide including gimbaled mirror bends 155a, 155b and 155c, where the gimbals include movable mirrors 145a-145c, respectively.

[0249] System 800 includes a static power source 106 and a waveguide (spanning along the contour lines of beam 108, which can be spaced apart to encircle beam 108) configured to direct MMW beam 108 generated by power source 106. Beam 108 is composed of a plurality of beam sections or segments 108a, 108b, 108c and 108d which are connected by gimbaled mirror bends 155a, 155b, and 155c.

[0250] Gimbaled mirror bends 112a, 112b and 112c are mounted within the waveguide and configured to move in accordance with the bending of the waveguide to allow the redirection of beam 108 in accordance with the redirection of the waveguide. Thus, gimbaled mirror bends 155a, 155b and 155c may direct beam 108 to a bottom of a borehole in the ground to allow system 800 to drill and deepen the borehole according to the disclosure while allowing power source 106 to be statically positioned above the ground.

[0251] Referring again to Figures 1 - 2, as is conventionally known, the inner wall of MMW waveguides can be corrugated for better transmission efficiency. The pressure inside waveguide 110 (110 in this context includes section 114) can be 1 atm in the borehole top, allowing exposure of the void within waveguide 110 to ambient atmosphere, but can be lower (up to vacuum conditions) or somewhat higher, e.g., up to 100 atm. Waveguide 110 can consist of multiple segments (e.g., 9 meter long as is common in conventional drilling), and extend in a length up to 30,000 meters. Optical Element 116 serves two main functions: to pressure seal waveguide 110; and optionally to direct energy according to field of view (FOV) 118 (which extends along the operational distance within the fluid, e.g., the distance from optical element 116 to bottom 120) toward bottom 120 of wellbore 102, using for example a diverging lens structure. In some embodiments, the optical element pressure seals the waveguide such that no fluid from the borehole can enter the waveguide, e.g., through its bottom end 113b, while the waveguide is located in the borehole, e.g., when immersed in fluid filling or filling up the borehole. The MMW energy emitted through window 116 melts or evaporates the rock at wellbore bottom 120, so at least for some time, melted rock lingers in a melted form 122 on borehole bottom 120. The operational distance from window 116 and borehole bottom 120 should normally be below 2 meters, and optimally in the range of 2-30cm, but can be somewhat larger (e.g., in some cases, up to 200m). Borehole 102, outside waveguide section 114, is filled up with fluid (comprising colloid, mud, liquid, pressurized gas, supercritical fluid (e.g., CO2) or any combination thereof), and will be referenced herein for simplicity as “fluid”.

[0252] System 100 includes a fluid partition wall in the form of tube 124, peripherally surrounding waveguide section 114, and spaced apart therefrom for leaving a cavity 126, which can serve as a down flow conduit (or alternatively - as an upward backflow conduit). Tube 124 can consist of several segments. If desired tube 124 can be fixed to waveguide section 114, e.g., by bars such as exemplary bar 128, which can serve as holding means or retainers that keep waveguide section 114 at a constant positioning relative to tube 124, which may be significant to prevent over-floating or sinking of waveguide section 114 in the fluid. Accordingly, segments of tube 124 can be formed together with segments of waveguide section 114 and added together to simultaneously extend tube 124 and waveguide section 1 as wellbore 102 deepens. Rig 130 is disposed at the top of borehole 102 and holds in place tube 124 which is firmly secured thereto and is configured to holding tube 124 through the process of tube lengthening and downward pushing as the borehole deepens. Waveguide section 114 is firmly held in place by waveguide rig 132, as known to a person skilled in the art. Alternatively, both tube 124 and waveguide section 114 are held by a single rig, such as rig 130, and in addition tube 124 and waveguide section 114 can be fixed to each other by bars 126 as noted above.

[0253] Fluid flow within cavity 126 (or 140 if the flow direction is reversed) is generated in downward direction 134 by pump module 136. Pump module 136 is an example of a fluid streamer, which can feature fluid pumping into the inlet of cavity 126 (or 140), or fluid suction from the outlet of cavity 140 (or 126), or alternative components such as evaporation apparatus that depletes fluid at the outlet of cavity 126 or 140 (wherein fresh fluid fills up the borehole through the inlet of the other cavity, to replace the missing evaporated fluid). The fluid flow is directed down toward melted rock 122 and is diverted to flow back in direction 138 through an upward backflow conduit defined by space 140 which is enclosed between tube 124 and the sidewall of bore 102, with the assistance of optional diverter 142. Diverter 142 assists in generating flow of fluid at the bottom of borehole 102 for maintaining fluid flow required for sweeping and carrying up the drill debris and fallout material (molten rock, solid rock particles and gas or liquids (water, oil)) which is released as a result of the drilling at the bottom 120 of borehole 102, and for preventing liquid and molten rock deposit accumulation at the walls of borehole 102. As the flowing “dirty” fluid carrying up the debris and drill fallout reaches the top of borehole 102, pump module 136 is optionally configured to recirculate this dirty fluid by filtering out the drill debris and fallout material to leave clean fluid ready for pumping down and thereby save the need to continuously supply fresh fluid.

[0254] System 100 can advantageously include sensors disposed near the bottom of borehole 102, as represented by sensors housing 144. Housing 144 can be installed either on waveguide 110, tube 124, or optical element 116. The sensors can include temperature sensors, a camera, radar or sonar, that can monitor rock cracks, fractures, presence of oil, water and gas, and further parameters. Specifically, the very use of MMW transparent fluid, allows for the use of a radar sensor during the drilling process to determine rock material, gas / water pockets, and the like, which can be essential for drilling progress decisions. These sensors can operate within the environment at the bottom of borehole 102 due to the cooling effect induced by virtue of the fluid flow, which can maintain a temperature of about 100-150 degrees centigrade, well below 250 degrees centigrade beyond which electrical equipment ceases to operate, and thus allow operation of electric equipment. In addition, the fluid can be selected to be transparent to MMW, to allow better penetration of the MMW energy emitted from optical element 116, and better penetration of the radar signal.

[0255] Reference is now also made to Figure 2 which is a cross-sectional side view of another embodiment constructed and operative in accordance with the invention, of system 200, which features the low pressure millimeter waveguide 110 of system 100 of Figure 1 , and further includes conduit insertion 150 for applying transparent MMW fluid. As the fluid is required to provide the sweeping action along borehole 102 on the one hand and inherit MMW transparency at the small FOV area 118 along the operational distance above bottom of wellbore 102 on the other hand, and considering higher price of MMW transparent fluid, two distinct fluid compositions may be required. The cooling and sweeping fluid can be conducted downward in large quantities through tube 124, while a small quantity of particularly MMW transparent (and thermally isolative) fluid (e.g., at least two times less than the quantity of the cooling and sweeping fluid or at least 50 times less or at least 90 times less than the quantity of the cooling and sweeping fluid) can be supplied directly to FOV area 118 via pipe 150, which can be disposed within cavity 126 or cavity 140. Once released around area 118 and functioning to facilitate effective propagation of MMW energy from optical element 116 toward bottom 120, the small mass of this transparent fluid is eventually absorbed by the much larger mass of the cooling fluid and then swept away upwards. Referring also to Figure 1 , examples of possible components of MMW transparent fluid, particularly colloid (mud), include silica, zirconia, alumina particles, mineral oil, and any combination thereof. In this context, the terms “transparent” and “transparency", refer to MMW energy transmission along the operational distance above 5%, and optionally above 70%. The density (specific gravity) of the fluid can be selected to be in the range of 0 to 4g / cm3,0.05g / cm3to 4g / cm3, 0.75 g / cm3to 0.9 g / cm3, 2.5g / cm3to 3g / cm3, close to or in conformity with the density of bedrock (basement rock, such as granite, and basalt), which is effective for balancing lithostatic pressures all along the borehole, and avoiding stress loads on the borehole wall. The density (specific gravity) of the fluid and the density of the waveguide can be designed to match each other or to be close to each other, for reducing structural load on the waveguide. It is noted that waveguide density results from the combined weighted densities of the waveguide housing and the gas-filled waveguide cavity 111. In this context, the term ‘internal waveguide density’ references the density of the gas inside cavity 111. Fluid density which is somewhat greater than the waveguide density, will exert a floating push on the waveguide.

[0256] In addition, as waveguide 110 is already designed to conduct electromagnetic energy with minimal attenuation, the sensor readings can be easily transmitted through waveguide 110 back to the surface of borehole 102, e.g., by simple RF transmission, as depicted by arrow 146 (which is a low energy transmission which does not interfere with the high energy incoming MMW energy to the extent of substantially attenuating the transmission signal). System 100 may include a power source for powering the sensors, which can feature electric batteries, which should suffice for the operation throughout the drilling, and which can also serve to power any other electrically operated equipment disposed at the bottom or along waveguide 110, such as mechanical drilling tools and fluid pumps for facilitating the fluid turbulence and flow. Optionally, system 100 can be equipped with adequate antennas, converters (e.g., rectennas), and electric energy storing means (e.g., rechargeable batteries and charging circuitry) configured to receive and harvest MMW energy (which is already transmitted for the drilling process), to convert the MMW energy into an electric current and thereby supply the power to the operation of the sensors, as well of other electric equipment that can be installed at the bottom of wellbore 102, such as mechanical drilling tools and fluid pumps, or for storing in an electric energy storage.

[0257] It is noted that system 100 can be operational in some instances to drill right from the surface of ground 104, and in other cases - the upper part of the borehole can be drilled by other conventional methods. In addition, system 100 allows drilling through liquid and gas and as such is adequate for oil, gas, and water exploration and harvesting in addition to geothermal energy drills.

[0258] Reference is now made to Figures 3A-3G, which present cross- sectional top views of several embodiments exemplifying variants to the arrangement of a partition wall of systems constructed and operative in accordance with the invention. Figure 3A is a top cross-sectional view of system 100 of Figure 1 , wherein cavity 126 serves as a downflow conduit and cavity 140 serves as an upward backflow conduit. Figure 3B is a top cross-sectional view of system 100 illustrating a reverse fluid flow configuration, wherein cavity 126 serves as an upward backflow conduit and cavity 140 serves as a downflow conduit. Figure 3C is a top cross-sectional view of system 300 featuring partition wall 124 in the form of a tube which operates as downflow conduit 126, wherein borehole 102 serves as upward backflow conduit 140. Figure 3D is a top cross- sectional view of system 300 illustrating a reverse fluid flow configuration wherein partition wall 124 is in the form of a tube which operates as upward backflow conduit 140, wherein borehole 102 serves as downflow conduit 126. Figure 3E is a top cross-sectional view of system 400 featuring partition wall 124 in the form of a flat wall configured for longitudinally attaching at peripheral edges thereof to the sidewall of borehole 102 for sectioning borehole 102 into a downflow conduit 126 and an upward backflow conduit 140. It is noted that partition wall 124 extends at its peripheral edges toward the sidewall of borehole 102 to the extent of close proximity, e.g., distanced a few centimeters away from the sidewall, and hermetical sealing or attaching between wall 124 and the sidewall of borehole 102 is not essential for effective separation between the upstream and downstream conduits.

[0259] The direction of the flow can be reversed to exchange conduits 126 and 140. Figure 3F is a top cross-sectional view of system 500 featuring partition wall 124 in the form of two wall sections configured for longitudinally attaching at a peripheral edge thereof to a sidewall of borehole 102 for sectioning the borehole into downflow conduit 126, and an upward backflow conduit 140. The direction of the flow can be reversed to exchange conduits 126 and 140. Figure 3G is a top cross-sectional view of system 600 featuring partition wall 124 in the form of four wall sections configured for longitudinally attaching at a peripheral edge thereof to the sidewall of borehole 102 for sectioning borehole 102 into two downflow conduits 126, and two upward backflow conduits 140. The direction of the flow can be reversed to exchange conduits 126 and 140. Reference is now made to Figure 4, which is a flow chart of method 1000 for drilling through a ground borehole using millimeter wave (MMW) energy, operative in accordance with the invention. Method 1000 includes procedure 1002 of generating MMW energy using a MMW power source.

[0260] Method 1000 includes procedure 1004 of guiding down the MMW energy to a borehole bottom of the borehole through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and including a hollow waveguide body encompassing a cavity at an internal waveguide pressure.

[0261] Method 1000 includes procedure 1006 of transm itting the MMW energy to the borehole bottom using an optical element coupled to a distal end of the waveguide and configured to pressure seal the waveguide and to transmit the MMW energy to the borehole bottom. When the distal end of the waveguide is immersed in fluid filling the borehole at a fluid pressure, the internal waveguide pressure is lower than the fluid pressure.

[0262] Method 1000 includes optional procedure 1008 of filling, or filling up, the borehole with a fluid at a fluid pressure which, at least in the vicinity of the bottom of the waveguide, is higher than the internal waveguide pressure, while keeping the waveguide immersed in the fluid at an operational distance from the borehole bottom, wherein the fluid is transparent to MMW through the operational distance.

[0263] Method 1000 can include optional procedure 1010 of exerting a fluid flow of the fluid within the borehole outside and around the waveguide.

[0264] Procedure 1010 includes sub-procedure 1012 of deploying a partition wall extending along the borehole and separating between at least one downflow conduit and at least one upward backflow conduit while leaving a fluid passage near the borehole bottom.

[0265] Procedure 1010 further includes sub-procedure 1014 of streaming the fluid by a fluid streamer at the fluid pressure into the at least one downward conduit.

[0266] Procedure 1012 of deploying may include peripherally surrounding and spacing apart from the waveguide the partition wall in the form of a tube, extending the tube along the borehole to define the at least one downflow conduit, and spacing apart the tube from the wall of the borehole to define the at least one upward backflow conduit. Procedure 1012 of deploying may include deploying at least one wall section of the partition wall while laterally extending a peripheral edge thereof toward a sidewall of the borehole wall for sectioning the borehole into the at least one downflow conduit, and the at least one upward backflow conduit. Procedure 1012 of deploying may include deploying a partition wall in the form of a tube which includes the at least one downflow conduit, and wherein the borehole serves as the at least one upward backflow conduit.

[0267] The internal waveguide pressure may be a low pressure, e.g., below 100 atmospheres, around ambient atmospheric pressure, or below ambient atmospheric pressure, at ground surface level.

[0268] The waveguide cavity may be sealed at the proximal side of the waveguide to prevent infiltration of gas therein, and escape of gas if contained therein. Procedure 1004 of guiding may include filling or filling up the waveguide cavity with moisture-free gas, such as nitrogen, carbon dioxide (CO2), supercritical CO2 (SCCO2), or with an inert gas, such as argon. Procedure 1002 of generating may include generating MMW in a MMW frequency in the range of 1 GHz to 10 THz. Optionally, this frequency may be above 6 GHz, above 40 GHz, below 600 GHz, and / or below 175 GHz. Procedure 1002 of generating may include generating continuous wave (CW) MMW energy. Procedure 1002 of generating may include generating high-power MMW energy, e.g., over 10kW, over 100kW, or over 500kW.

[0269] The optical element may include a window, and / or a diverging lens which is operational for directing the MMW energy to the borehole bottom according to a field of view (FOV).

[0270] Method 1000 may include a procedure of applying, via a conduit insertion, a small amount of a second, MMW transparent fluid, directly to the borehole bottom.

[0271] The waveguide may include a proximal waveguide bend and a main waveguide section extending from the waveguide bend downwards along borehole.

[0272] Procedure 1008 of filling or filling up may include filling or filling up the borehole with a fluid including at least one of: colloid; liquid; gas or supercritical fluid (e.g., CO2). The fluid density (specific gravity) of the fluid may be close to the density of bedrock surrounding the borehole, e.g., in the range of 0 to 4 g / cm3,0.05 g / cm3to 4 g / cm3, 0.75 g / cm3to 0.9 g / cm3, and further optionally 2.5 g / cm3to 3 g / cm3. The fluid density may be close to the waveguide density of the waveguide, e.g., equal to, greater than, or smaller than, the waveguide density.

[0273] The fluid may be transparent to transmission of MMW energy through the operational distance, e.g., of at least 5% of MMW energy through the operational distance, or of at least 70% of MMW energy through the operational distance.

[0274] The keeping in procedure 1008 of filling or filling up may include keeping the waveguide immersed in the fluid at an operational distance below 200 meters from the borehole bottom, in the range of 1 cm to 2 meters from the borehole bottom, or in the range of 2 cm to 30 cm from the borehole bottom. Accordingly, the keeping may include using a waveguide operational distance retainer which includes at least one of:

[0275] (a) bars connecting the waveguide to the partition wall; and

[0276] (b) ground-surface waveguide-rig configured to firmly secure to the waveguide and to provide a counter push or pull force to respectively prevent overfloat or sinking of the waveguide in the fluid.

[0277] Method 1000 may include a procedure of monitoring one or more parameters of the drilling process by at least one sensor, by mounting the at least one sensor near the bottom of the waveguide. Method 1000 may include a procedure of transmitting sensor readings by electromagnetic transmission through the waveguide. Method 1000 may include a procedure of receiving and converting MMW energy, by adequate MMW energy harvesting means configured to receive MMW energy and convert the MMW energy into an electric current, for powering the operation of at least one sensor and / or other electric equipment, and / or for storing in an electric energy storage.

[0278] Method 1000 may be operational for drilling the borehole at a borehole inclination selected from the list consisting of: vertical; horizontal; and oblique.

[0279] The illustrated components of the drawings are exemplary and variations are contemplated to be within the scope of the present disclosure. For example, the numbers of components may be greater or fewer than as described and the types of components may be different than as described. Other variations and applications are contemplated to be within the scope of the present disclosure.

[0280] Accordingly, systems, apparatuses, devices, and methods have been described herein. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of aspects of the disclosed technology. However, it is apparent to one skilled in the art that the disclosed technology can be practiced without using every aspect presented herein.

[0281] Different aspects are disclosed herein. Features of certain aspects can be combined with features of other aspects, thus certain aspects can be combinations of features of multiple aspects.

[0282] While several embodiments of the disclosure have been described herein and / or shown in the drawings, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.

Claims

CLAIMS1. A system for drilling through a ground borehole using millimeter wave (MMW) energy comprising:(a) a MMW power source configured to generate MMW energy;(b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom, the waveguide comprising a hollow waveguide body encompassing a cavity at an internal waveguide pressure; and(c) an optical element coupled to a distal end of the waveguide and configured to pressure seal the waveguide and to transmit the MMW energy to the borehole bottom, wherein when the distal end of the waveguide is immersed in a fluid filling the borehole at a fluid pressure and a fluid density, at least in the vicinity of the bottom of the waveguide: the internal waveguide pressure is lower than the fluid pressure; and / or the internal waveguide density is lower than the fluid density.

2. The system of claim 1 , comprising a fluid flow system configured to provide a fluid flow of the fluid within the borehole outside and around the waveguide, the fluid flow system comprising a fluid streamer for streaming the fluid at the fluid pressure into the borehole.

3. The system of claim 2, wherein the fluid flow system comprises a partition wall extending along the borehole, leaving a fluid passage near theborehole bottom and separating between at least one downflow conduit and at least one upward backflow conduit, wherein the fluid streamer is operational for streaming the fluid at the fluid pressure into the at least one downward conduit.

4. The system of claim 3, wherein the partition wall comprises a tube peripherally surrounding and spaced apart from the waveguide along the borehole to define the at least one downflow conduit, and wherein the tube is spaced apart from the wall of the borehole to define the at least one upward backflow conduit.

5. The system of claim 3, wherein the partition wall comprises at least one wall section configured for laterally extending at a peripheral edge thereof toward a sidewall of the borehole wall for sectioning the borehole into the at least one downflow conduit, and the at least one upward backflow conduit.

6. The system of claim 3, wherein the partition wall comprises a tube comprising the at least one downflow conduit, and the borehole serves as the at least one upward backflow conduit.

7. The system of claim 1 , wherein the internal waveguide pressure is a low pressure below 100 atmospheres at ground surface level.

8. The system of claim 7, wherein the internal waveguide pressure is around ambient atmospheric pressure at ground surface level.

9. The system of claim 7, wherein the internal waveguide pressure at ground surface level is below ambient atmospheric pressure.

10. The system of claim 1 , wherein the waveguide cavity is sealed at the proximal side of the waveguide to prevent infiltration of gas therein, and escape of gas if contained therein.

11. The system of claim 10, wherein the waveguide cavity is filled up with moisture-free gas.

12. The system of claim 11 , wherein the moisture-free gas comprises nitrogen.

13. The system of claim 11 , wherein the moisture-free gas comprises carbon dioxide (CO2) or supercritical CO2 (SCCO2).

14. The system of claim 10, wherein the waveguide cavity is filled up with an inert gas.

15. The system of claim 1 , wherein the MMW frequency of the MMW is in the range of 1 GHz to 10 THz.

16. The system of claim 15, wherein the MMW frequency is above 6 GHz.

17. The system of claim 15, wherein the MMW frequency is above 40 GHz.

18. The system of claim 15, wherein the MMW frequency is below 600 GHz.

19. The system of claim 15, wherein the MMW frequency is below 175 GHz.

20. The system of claim 1 , wherein the MMW power source is configured to generate continuous wave (CW) MMW energy.

21. The system of claim 1 , wherein the MMW power source is configured to generate high-power MMW energy over 10kW.

22. The system of claim 1 , wherein the MMW power source is configured to generate high-power MMW energy over 100kW.

23. The system of claim 1 , wherein the MMW power source is configured to generate high-power MMW energy over 500kW.

24. The system of claim 1 , wherein the optical element comprises a window.

25. The system of claim 1 , wherein the optical element comprises a diverging lens operational for directing the MMW energy to the borehole bottom according to a field of view (FOV).

26. The system of claim 1 , comprising a conduit insertion for applying a small amount of a second, MMW transparent fluid, directly to the borehole bottom.

27. The system of claim 1 , wherein the waveguide comprises a proximal waveguide bend and a main waveguide section extending from the waveguide bend downwards along the borehole.

28. The system of claim 1 , wherein the fluid comprises at least one of: colloid; liquid;gas; or supercritical fluid.

29. The system of claim 1 , wherein fluid density (specific gravity) of the fluid is close to the density of bedrock surrounding the borehole.

30. The system of claim 29, wherein the fluid density is in the range of 0 to 4 g / cm3.31 . The system of claim 30, wherein the fluid density is in the range of 0.05 g / cm3to 4 g / cm3.

32. The system of claim 31 , wherein the fluid density is in the range of 0.75 g / cm3to 0.9 g / cm3.

33. The system of claim 31 , wherein the fluid density is in the range of 2.5 g / cm3to 3 g / cm3.

34. The system of claim 1 , wherein fluid density of the fluid is close to waveguide density of the waveguide.

35. The system of claim 34, wherein the fluid density equals or is smaller than, the waveguide density.

36. The system of claim 1 , wherein the distal end of the waveguide is kept at an operational distance from the borehole bottom, and wherein the fluid is transparent to transmission of at least 5% of MMW energy through the operational distance.

37. The system of claim 36, wherein the fluid is transparent to transmission of at least 70% of MMW energy through the operational distance.

38. The system of claim 1 , wherein the distal end of the waveguide is kept at an operational distance from the borehole bottom, and wherein the operational distance is below 200 meters from the borehole bottom.

39. The system of claim 38, wherein the operational distance is in the range of 1 cm to 2 meters.

40. The system of claim 39, wherein the operational distance is in the range of 2 cm to 30 cm.

41. The system of claim 38, comprising a waveguide operational distance retainer comprising at least one of:(a) bars connecting the waveguide to the partition wall; and(b) ground-surface waveguide rig configured to firmly secure to the waveguide and to provide a counter push or pull force to respectively prevent overfloat or sinking of the waveguide in the fluid.

42. The system of claim 1 , comprising at least one sensor configured to monitor one or more parameters of the drilling process, mounted near the bottom of the waveguide.

43. The system of claim 42, wherein the at least one sensor is configured to transmit sensor readings by electromagnetic transmission through the waveguide.

44. The system of claim 1 , further comprising MMW energy harvesting means configured to receive MMW energy and convert the MMW energy into an electric current for powering the operation of at least one sensor and / or other electric equipment, and / or for storing in an electric energy storage.

45. The system of claim 1 , configured to drill the borehole at a borehole inclination selected from the list consisting of: vertical; horizontal; and oblique.

46. The system according to claim 1 , wherein the waveguide comprises a plurality of gimbaled bends.

47. A method for drilling through a ground borehole using millimeter wave (MMW) energy, comprising the procedures of:(a) generating MMW energy using a MMW power source;(b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and comprising a hollow waveguide body encompassing a cavity at an internal waveguide pressure; and(c) transmitting the MMW energy to the borehole bottom using an optical element coupled to a distal end of the waveguide and configured to pressure seal the waveguide and to transmit the MMW energy to the borehole bottom,wherein when the distal end of the waveguide is immersed in a fluid filling the borehole at a fluid pressure and a fluid density, at least in the vicinity of the bottom of the waveguide: the internal waveguide pressure is lower than the fluid pressure; and / or the internal waveguide density is lower than the fluid density.

48. The method of claim 47, comprising filling the borehole with the fluid while keeping the waveguide immersed in the fluid at an operational distance from the borehole bottom, wherein the fluid is transparent to MMW through the operational distance.

49. The method of claim 48, wherein a partition wall extends along the borehole and separates between at least one downflow conduit and at least one upward backflow conduit while leaving a fluid passage near the borehole bottom, the method comprising exerting a fluid flow of the fluid within the borehole outside and around the waveguide, by streaming the fluid by a fluid streamer at the fluid pressure into the at least one downward conduit.

50. The method of claim 49, wherein: the partition wall is in the form of a tube peripherally surrounding and spaced apart from the waveguide, is extending along the borehole to define the at least one downflow conduit, and is spaced apart from the wall of the borehole to define the at least one upward backflow conduit.51 . The method of claim 49, wherein the partition wall comprises at least one wall section having a peripheral edge laterally extending toward a sidewall ofthe borehole wall for sectioning the borehole into the at least one downflow conduit, and the at least one upward backflow conduit.

52. The method of claim 49, wherein a partition wall in the form of a tube comprises the at least one downflow conduit, and wherein the borehole serves as the at least one upward backflow conduit.

53. The method of claim 47, wherein the internal waveguide pressure is a low pressure below 100 atmospheres at ground surface level.

54. The method of claim 53, wherein the internal waveguide pressure is around ambient atmospheric pressure at ground surface level.

55. The method of claim 53, wherein the internal waveguide pressure at ground surface level is below ambient atmospheric pressure.

56. The method of claim 47, wherein the waveguide cavity is sealed at the proximal side of the waveguide to prevent infiltration of gas therein, and escape of gas if contained therein.

57. The method of claim 56, wherein the guiding comprises filling the waveguide cavity with moisture-free gas.

58. The method of claim 57, wherein the moisture-free gas comprises nitrogen.

59. The method of claim 57, wherein the moisture-free gas comprises carbon dioxide (CO2) or supercritical CO2 (SCCO2).

60. The method of claim 56, wherein the guiding comprises filling the waveguide cavity with an inert gas.

61. The method of claim 47, wherein the generating comprises generating MMW in a MMW frequency in the range of 1 GHz to 10 THz.

62. The method of claim 61 , wherein the MMW frequency is above 6 GHz.

63. The method of claim 61 , wherein the MMW frequency is above 40 GHz.

64. The method of claim 61 , wherein the MMW frequency is below 600 GHz.

65. The method of claim 64, wherein the MMW frequency is below 175 GHz.

66. The method of claim 47, wherein the generating comprises generating continuous wave (CW) MMW energy.

67. The method of claim 47, wherein the generating comprises generating high-power MMW energy over 10kW.

68. The method of claim 67, wherein the generating comprises generating high-power MMW energy over 100kW.

69. The method of claim 68, wherein the generating comprises generating high-power MMW energy over 500kW.

70. The method of claim 47, wherein the optical element comprises a window.

71. The method of claim 47, wherein the optical element comprises a diverging lens operational for directing the MMW energy to the borehole bottom according to a field of view (FOV).

72. The method of claim 47, comprising applying, via a conduit insertion, a small amount of a second, MMW transparent fluid, directly to the borehole bottom.

73. The method of claim 47, wherein the waveguide comprises a proximal waveguide bend and a main waveguide section extending from the waveguide bend downwards along the borehole.

74. The method of claim 48, wherein the filling comprises filling the borehole with a fluid comprising at least one of: colloid; liquid; gas; or supercritical fluid.

75. The method of claim 48, wherein fluid density (specific gravity) of the fluid is close to the density of bedrock surrounding the borehole.

76. The method of claim 75, wherein the fluid density is in the range of 0 to 4g / cm3.

77. The method of claim 76, wherein the fluid density is in the range of 0.05 g / cm3to 4 g / cm3.

78. The method of claim 77, wherein the fluid density is in the range of 0.75 g / cm3to 0.9 g / cm3.

79. The method of claim 77, wherein the fluid density is in the range of 2.5 g / cm3to 3 g / cm3.

80. The method of claim 47, wherein fluid density of the fluid is close to waveguide density of the waveguide.

81. The method of claim 80, wherein the fluid density equals, or is smaller than, the waveguide density.

82. The method of claim 48, wherein the fluid is transparent to transmission of at least 5% of MMW energy through the operational distance.

83. The method of claim 82, wherein the fluid is transparent to transmission of at least 70% of MMW energy through the operational distance.

84. The method of claim 48, wherein the keeping comprises keeping the waveguide immersed in the fluid at an operational distance below 200 meters from the borehole bottom.

85. The method of claim 84, wherein the keeping comprises keeping the waveguide immersed in the fluid at an operational distance in the range of 1 cm to 2 meters from the borehole bottom.

86. The method of claim 85, wherein the keeping comprises keeping the waveguide immersed in the fluid at an operational distance in the range of 2 cm to 30 cm from the borehole bottom.

87. The method of claim 84, wherein the keeping comprises using a waveguide operational distance retainer comprising at least one of:(a) bars connecting the waveguide to the partition wall; and(b) ground-surface waveguide rig configured to firmly secure to the waveguide and to provide a counter push or pull force to respectively prevent overfloat or sinking of the waveguide in the fluid.

88. The method of claim 47, comprising monitoring one or more parameters of the drilling process by at least one sensor mounted near the bottom of the waveguide.

89. The method of claim 47, comprising transmitting sensor readings by electromagnetic transmission through the waveguide.

90. The method of claim 47, comprising receiving and converting MMW energy, by MMW energy harvesting means configured to receive MMW energy and convert the MMW energy into an electric current, for powering the operation of at least one sensor and / or other electric equipment, and / or for storing in an electric energy storage.

91. The method of claim 47, operational for drilling the borehole at a borehole inclination selected from the list consisting of: vertical; horizontal; andoblique.

92. The method of claim 47, comprising lengthening and moving down the borehole a section of the waveguide using a plurality of gimbaled bends of the waveguide.

93. A system for drilling through a ground borehole using millimeter wave (MMW) energy comprising:(a) a MMW power source configured to generate MMW energy;(b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole; and(c) a diverging lens coupled with a distal end of the waveguide and operational for directing the MMW energy guided by the waveguide to the borehole bottom according to a field of view (FOV).

94. The system of claim 93, wherein: the waveguide comprises a hollow waveguide body encompassing a cavity at an internal waveguide pressure; the diverging lens is configured to pressure seal the waveguide at the distal end of the waveguide; and when the distal end of the waveguide is immersed in a fluid filling the borehole at a fluid pressure and a fluid density, at least in the vicinity of the bottom of the waveguide: the internal waveguide pressure is lower than the fluid pressure; and / or the internal waveguide density is lower than the fluid density.

95. A method for drilling through a ground borehole using millimeter wave (MMW) energy, comprising the procedures of:(a) generating MMW energy using a MMW power source;(b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and comprising a hollow waveguide body encompassing a cavity; and(c) transmitting the MMW energy to the borehole bottom using a diverging lens coupled with a distal end of the waveguide and operational for directing the MMW energy guided down by the waveguide to the borehole bottom according to a field of view (FOV).

96. The method of claim 95, wherein: the diverging lens is configured to pressure seal the waveguide at the distal end of the waveguide; and when the distal end of the waveguide is immersed in a fluid filling the borehole at a fluid pressure and a fluid density, at least in the vicinity of the bottom of the waveguide: the internal waveguide pressure is lower than the fluid pressure; and / or the internal waveguide density is lower than the fluid density.

97. A system for drilling through a ground borehole using millimeter wave (MMW) energy comprising:(a) a MMW power source configured to generate MMW energy;(b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom; and(c) at least one sensor mounted near the bottom of the waveguide, configured to monitor one or more parameters of the drilling process, and to transmit its readings by electromagnetic transmission through the waveguide.

98. A method for drilling through a ground borehole using millimeter wave (MMW) energy, comprising the procedures of:(a) generating MMW energy using a MMW power source;(b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and comprising a hollow waveguide body; and(c) monitoring one or more parameters of the drilling process by at least one sensor mounted near the bottom of the waveguide, and transmitting its readings by electromagnetic transmission through the waveguide.

99. A system for drilling through a ground borehole using millimeter wave (MMW) energy comprising:(a) a MMW power source configured to generate MMW energy;(b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom; and(c) MMW energy harvesting means configured to receive MMW energy generated by the MMW power source and convert the MMW energy to electric energy, for powering at least one sensor monitoring one or more parameters ofthe drilling process, an electrically operated equipment and / or electric storage, mounted along or near the bottom of the waveguide.

100. The system of claim 99, wherein the MMW energy harvesting means comprises: one or more antennas for receiving MMW; a converter for converting MMW into an electric current; and an electric energy storing means.

101. A method for drilling through a ground borehole using millimeter wave (MMW) energy, comprising the procedures of:(a) generating MMW energy using a MMW power source;(b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and comprising a hollow waveguide body; and(c) harvesting MMW energy by harvesting means mounted along or near the bottom of the waveguide and configured to receive MMW energy generated by the MMW power source and convert the MMW energy to electric energy, for powering at least one sensor monitoring one or more parameters of the drilling process, an electrically operated equipment and / or electric storage.

102. A system for drilling through a ground borehole using millimeter wave (MMW) energy comprising:(a) a static MMW power source configured to generate MMW energy; and(b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to aborehole bottom, wherein the waveguide comprises a plurality of gimbaled bends allowing the lengthening and moving down of a section of the waveguide.

103. A method for drilling through a ground borehole using millimeter wave (MMW) energy, comprising the procedures of:(a) generating MMW energy using a static MMW power source;(b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source; and(c) lengthening and moving down of a section of the waveguide wherein a plurality of gimbaled bends of the waveguide.

104. A system for drilling through a ground borehole using millimeter wave (MMW) energy comprising:(a) a MMW power source configured to generate MMW energy;(b) at least one waveguide coupled to the MMW power source and configured to deploy along the borehole and to guide the MMW energy to a borehole bottom; and(c) at least one radar sensor mounted along or near the bottom of the waveguide, wherein the distal end of the waveguide is immersed in fluid filling the borehole; and wherein the fluid is transparent to transmission of MMW energy through an operational distance of the radar sensor.

105. A method for drilling through a ground borehole using millimeter wave (MMW) energy, comprising the procedures of:(a) generating MMW energy using a static MMW power source;(b) guiding the MMW energy to a borehole bottom through at least one waveguide which is deployed along the borehole, coupled to the MMW power source, and comprising a hollow waveguide body; and (c) operating at least one radar sensor mounted along or near the bottom of the waveguide, wherein the distal end of the waveguide is immersed in fluid filling the borehole; and wherein the fluid is transparent to transmission of MMW energy through an operational distance of the radar sensor.

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