Penetration Rate / Depth Monitor for Drilling with Millimeter-Wave Beamforming

Abstract

Describes an apparatus and method for drilling deep boreholes in earth materials with millimeter-wave radiation to access deep resources such as geothermal. The borehole depth and temperature at the bottom of the borehole can be monitored with a probe signal and / or radiation emission from the bottom of the borehole.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of priority of U.S. Application No. 63 / 291,731, filed Dec. 20, 2021, titled “Rate of Penetration / Depth Monitor for a Millimeter-Wave Beam Made Hole”, which is incorporated herein by reference in its entirety.

[0003] Government Support

[0004] This invention was made with government support under Contract No. DE-AR0001051 awarded by the U.S. Department of Energy. The government has certain rights in the invention. BACKGROUND OF THE INVENTION

[0005] A high-power millimeter-wave beam generated by a vibratory gyrotron can form a borehole in rock by melting and / or vaporizing the rock. The borehole opening process operates at temperatures greater than the melting temperature and vaporization temperature of the rock, which are 1000° C. and 3000° C., respectively. Conventional sensors for monitoring the borehole of a mechanical drill require physical contact with the bottom of the borehole and cannot survive at these temperatures. SUMMARY OF THE INVENTION

[0006] This technology can be used to form deep boreholes in rock with a high-power millimeter-wave beam and to monitor the bottom of the borehole. The monitoring equipment can be kept on the ground at ambient temperature and pressure, regardless of the borehole depth or temperature.

[0007] This technology includes a method of measuring the depth and / or rate of penetration of a borehole drilled with a millimeter-wave drilling beam, the millimeter-wave drilling beam being guided to the bottom of the borehole by a transmission line. The method includes coupling a probe signal into the transmission line. The transmission guides the probe signal to the bottom of the borehole, and at least a portion of the probe signal is reflected and / or scattered from the bottom of the borehole as a return beam. The transmission line guides the return beam from the bottom of the borehole. The return beam is coupled out of the transmission line and mixed with a local oscillator to produce an intermediate-frequency beam, the amplitude and / or frequency of the intermediate-frequency beam being used to determine the depth and / or rate of penetration of the borehole.

[0008] In some cases, the amplitude of the detection signal is modulated, in which case the depth and / or penetration rate of the borehole can be based on the amplitude of the intermediate frequency beam. In other cases, the frequency of the detection signal is modulated, in which case the depth and / or penetration rate of the borehole is based on the frequency of the intermediate frequency beam. Additionally, in still other cases, the detection signal includes pulses, and the depth and / or penetration rate of the borehole is based on the flight time of the pulses.

[0009] The detection signal can be generated at a frequency different from the frequency of the millimeter wave drilling beam or can be picked up from the millimeter wave drilling beam.

[0010] If desired, a temperature signal at a temperature signal frequency different from the frequency of the millimeter wave drilling beam (and different from the detection frequency) can be coupled with the detection signal into the transmission line to determine the temperature at the bottom of the borehole.

[0011] Other embodiments of the present technology include a system for drilling a borehole with a source, a transmission line, a depth / penetration rate monitor, and a beam combiner. In operation, the source generates a millimeter wave drilling beam. The transmission line coupled to the source guides the millimeter wave drilling beam to the bottom of the borehole. The depth / penetration rate monitor also coupled to the transmission line monitors the depth and / or penetration rate of the borehole. And the beam combiner coupled to the transmission line and the depth / penetration rate monitor couples the detection signal into the transmission line for transmission to the bottom of the borehole and couples the return beam generated by reflecting and / or scattering the detection signal from the bottom of the borehole from the transmission line to the depth / penetration rate monitor.

[0012] The depth / penetration rate monitor can be configured to operate as a reflectometer, a frequency modulated radar, or a pulse modulated time of flight radar. The depth / penetration rate monitor can generate the detection signal at a frequency different from the frequency of the millimeter wave drilling beam. In other cases, the beam combiner guides a portion of the millimeter wave drilling beam returning from the bottom of the borehole as the return beam to the depth / penetration rate monitor.

[0013] The beam combiner can include a bevel mirror that is used to reflect the millimeter wave drilling beam around a bend in the transmission line. There can be a hole in the bevel mirror to transmit radiation at the detection frequency and reject radiation at the frequency of the millimeter wave drilling beam.

[0014] The system can further include a temperature monitor that is used to receive a temperature signal to monitor the temperature of the borehole at a temperature signal frequency different from the frequency of the millimeter wave drilling beam and different from the detection frequency. And it can include a small signal beam combiner that is coupled to the depth / penetration rate monitor, the temperature monitor, and the beam combiner to couple the temperature signal with the detection signal.

[0015] All combinations of the foregoing concepts and additional concepts discussed in greater detail below, provided that such concepts are not mutually inconsistent, are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of the claimed subject matter that appear at the end of this disclosure are considered to be part of the inventive subject matter disclosed herein. Terms explicitly used herein may also appear in any disclosure incorporated by reference and shall be given the meaning most consistent with the particular concepts disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings are for illustrative purposes only and are not intended to limit the scope of the inventive subject matter. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be exaggerated or enlarged in the drawings to assist in understanding different features. In the drawings, like reference symbols generally refer to like features (e.g., elements that are functionally and / or structurally similar).

[0017] Figure 1A Shown is a directed energy millimeter wave (MMW) drilling system that uses a high-power drilling beam to drill a borehole and monitors the rate of penetration (ROP) and / or depth of the borehole using at least one collinear small-signal detection signal at a frequency different from that of the high-power drilling beam.

[0018] Figure 1B Shown is an embodiment of an MMW drilling system that uses a high-power drilling beam to drill a borehole and also monitors the rate of penetration (ROP) and / or depth of the borehole.

[0019] Figure 1C Depicted are details of a ROP / depth monitor that can be implemented with an isolator and a detector and that can use MMW radiation to drill a borehole.

[0020] Figure 2A Shown is an embodiment of a beam combiner for combining a high-power heating beam with one or more higher-frequency detection signals in a directed energy MMW drilling system for Figure 1A .

[0021] Figure 2B Shown is another embodiment of a beam combiner for combining a high-power heating beam with one or more lower-frequency detection signals in a directed energy MMW drilling system similar to that shown in Figure 1A .

[0022] Figure 3 is Figure 1APhoto of the portion of the MMW drilling system that includes the small-signal combiner that combines the 94 GHz beam for monitoring drill hole ROP / depth and the 137 GHz beam for monitoring drill hole temperature, where the 28 GHz high-power heating beam propagates through a high-power bevel bend on a 28 GHz overmode waveguide (e.g., as schematically shown in Figure 2A ).

[0023] Figure 4 A circuit for generating a 94 GHz probing signal for monitoring drill hole ROP / depth using reflectometry or frequency modulation (FM) radar techniques is shown. The circuit is shown to have an optional small-signal combiner for accessing the 137 GHz temperature signal.

[0024] Figure 5 The connection of the drill hole ROP / depth monitor to other electronics for operation as a reflectometer is shown.

[0025] Figure 6 The connection of the drill hole ROP / depth monitor to other electronics for operation as an FM radar is shown.

[0026] Figure 7 Is a graph of the signal generated by probing a flat lead target that is moving uniformly away from the monitor at a starting distance of approximately 18 cm and a speed of 0.5 mm / min with the 94 GHz ROP / depth monitor beam.

[0027] Figure 8 A graph of the signals generated by the 94 GHz ROP / depth monitoring beam (right axis) and the 28 GHz drilling beam (left axis) is shown, both used to simultaneously detect the formation of a melt pit in the surface of basalt rock as the drilling beam removes the rock.

[0028] Figure 9 Is a photo of a cracked cross-section of a MMW beam melt pit in basalt rock. Detailed Description

[0029] Figure 1A A high-power directed energy millimeter wave (MMW) drilling system 100 is shown that has at least one monitor 160 for sensing the rate of penetration (ROP) and / or depth of a drill hole 110 made by the system in a material 150 such as earth materials. The system 100 may also include one or more auxiliary monitors 170 to monitor one or more conditions at the bottom of the drill hole 110, such as temperature, surface emissivity ε, and melt turbulence, as well as other properties. The drilling system 100 uses a high-power MMW drilling beam 105 to "drill" the drill hole 110 into the material 150. Drilling may include melting, evaporating, and / or ablating the material as the drill hole is deepened.

[0030] High-power MMW radiation 103 from high-power source 120 can be coupled into high-power transmission line 130 (which can be implemented as a waveguide) and delivered to the bottom of borehole 110. At the bottom of the borehole, high-power MMW radiation 103 can exit the distal end 138 of transmission line 130 and form a drilling beam 105 that interacts with the material in its path. According to some embodiments, drilling beam 105 has sufficient power to melt, for example, granite. High-power source 120, such as a gyrotron, can generate MMW radiation 103 at a frequency in the range of approximately or exactly 30 GHz to approximately or exactly 300 GHz, where the average power is in the range of approximately or exactly 100,000 watts to approximately or exactly 2,000,000 watts. MMW radiation 103 at these power levels can be continuous wave or can be pulsed to produce higher instantaneous power levels.

[0031] When system 100 is drilling borehole 110, the power and frequency of MMW radiation 103 from high-power source 120 can be constant over time. For example, when drilling a borehole, the power and frequency can remain constant for seconds, minutes, dozens of minutes, or even over an hour. In some cases, when system 100 is drilling borehole 110, one or both of the power and frequency of MMW radiation 103 from high-power source 120 can vary within the above frequency range and power range. For example, when encountering different materials, the frequency and / or power can be changed to improve energy coupling with different materials and heating of different materials.

[0032] Detection signals 108, 109 from monitors 160, 170 can be radiatively coupled into and out of high-power transmission line 130 using one or more combiners 140, 142. The (one or more) detection signals 108, 109 can be at one or more frequencies different from the frequency of high-power drilling beam 105 to sense the (one or more) conditions at the bottom of borehole 110. Additionally, the detection signal 108 from the ROP / depth monitor 160 can be at a frequency different from the one or more frequencies used for the (one or more) auxiliary monitors 170. For example, the frequency for the ROP / depth monitor can be in the range of 10 GHz to 300 GHz. In some cases, the frequency for the ROP / depth monitor can be in the range of 10 GHz to 1 THz. The frequency for the (one or more) auxiliary monitors can also be in the range of 10 GHz to 300 GHz. In some cases, the frequency for the (one or more) auxiliary monitors can be in the range of 10 GHz to 1 THz. The power level of the detection signal can be in the range of 0.1 watt to 100 watts, or in some cases can be an even higher power level. When detecting thermal emissions from the bottom of borehole 110, the power level of the received detection signal 109 can be less than 0.1 watt. The phrase “detection signal” is used herein to refer to a signal transmitted into the borehole by the ROP / depth monitor 160 or auxiliary monitor 170 and used to measure the characteristics of borehole 110. In some cases, an auxiliary monitor (such as a temperature radiometer) can receive and monitor the radiative emissions (e.g., blackbody radiation) from the borehole without transmitting a detection signal. Conditions that the ROP / depth monitor 160 and the (one or more) auxiliary monitors can sense include, but are not limited to: the penetration rate of the borehole while drilling borehole 110, the depth of borehole 110, the surface emissivity ε of the earth material, and the temperature of the earth material 150 while drilling borehole 110. The depth of borehole 110 can be measured or not measured while actively drilling the borehole.

[0033] High-power transmission line 130 guides high-power MMW radiation 103 from high-power source 120 to the bottom of the borehole, where drilling beam 105 can vaporize rock and other materials. High-power transmission line 130 is typically hollow and has a size with a diameter exceeding one wavelength (overmode) such that it can handle high power. It is configured to reduce or minimize mode conversion so that the most efficient fundamental mode can propagate with minimum loss. There may be some intentional mode conversion for special applications emitted from the distal end 138 or for more efficiently negotiating bends, but mainly, the MMW radiation 103 propagates through high-power transmission line 130 in a single mode for efficient long-distance transmission. Linear polarization HE 11The mode is the most efficient mode in the circular high-power transmission line 130, which has corrugations inside and has a good conductor metal surface, such as copper. Other suitable modes include azimuthally polarized TE in a smooth-wall metal waveguide 01 mode. This has 69% of the efficiency of the HE 11 mode in a circular waveguide with corrugations inside. The HE 11 mode can also be guided by the borehole 110, which acts as a dielectric waveguide, such as a hollow fiber optic cable. For example, the drilling beam 105 can vitrify the walls of the borehole as the borehole 110 advances, thus forming a hollow circular dielectric waveguide.

[0034] The MMW drilling system 100 may include a ROP / depth monitor 160 that is radiatively coupled to the high-power transmission line 130. The ROP / depth monitor 160 generates a small-signal probe signal (also referred to as the probe signal 108 or the probe beam), which may be at a different frequency from the drilling beam 105 for sensing the ROP and / or depth of the borehole. For example, the probe signal 108 may be centered at a probe frequency within a frequency range of 30 GHz to 1 THz, with a bandwidth of up to 5 GHz. In some cases, the frequency of the probe signal 108 may vary at a frequency within this frequency range when measurements are being made. Preferably, the probe signal 108 may be guided by the same high-power transmission line 130 that guides the drilling beam 105. When measurements are being made, the average probe signal power may be in the range of 0.01 watt to 10 watts and may be constant or vary over a range of power levels within this range.

[0035] One or more auxiliary monitors 170 may generate and / or receive one or more other small-signal probe signals 109 at other frequencies for detecting or monitoring other parameters associated with the drill borehole 110 and the MMW drilling system 100. In some cases, the auxiliary monitor 170 receives radiation emissions from the borehole for analysis. For example, the auxiliary monitor 170 may monitor borehole temperature by radiometry and / or monitor waveguide / borehole fill composition by millimeter wave or terahertz spectroscopy. In some embodiments, the temperature may be monitored by millimeter wave thermal emissions from the bottom of the borehole 110, which are coupled into the transmission line 130 and propagated back to the auxiliary monitor 170. The radiometer antenna pattern defined by the high-power transmission lines 130 and 138 selects the size of the observed spot of the returned temperature signal. (Thermal emissions occur in all modes where the receiver antenna pattern selects the mode(s) that will propagate along the high-power transmission line 130 and be detected by the auxiliary monitor 170. Thus, the returned thermal signal 109 has a nature that is at least partially defined by the radiometer field of view.) In some cases, the fill composition may be monitored by millimeter wave or terahertz spectral emission or absorption. The spectroscopy performed by the auxiliary monitor 170 may be passive by using a thermal blackbody emission background or local plasma excitation emission, or active by utilizing a frequency-scanned probe signal. For passive spectroscopy, the receiving antenna (essentially the high-power transmission line 130) essentially defines the returned signal, as is the case for the returned temperature signal. For active probing, the high-power waveguide defines and guides the probe signal. These auxiliary probe signals may have an average power level in the range of 0.1 watt to 100 watts and may operate at one or more frequencies in the range of 30 GHz to 1 THz.

[0036] In some embodiments, temperature monitoring may include the auxiliary monitor 170 emitting a temperature probe signal into the drill borehole 110. The temperature probe signal may be used to determine the surface emissivity ε at the bottom of the borehole. Generally, the radiation emission from the bottom of the borehole (and detected by the temperature radiometer) is the product of the surface emissivity and the temperature (εT). The emissivity may have a value in the range of 0 to 1. Knowing the surface emissivity can provide a more accurate determination of the temperature of the earth material 150 at the bottom of the drill borehole 110. The emissivity may be measured by measuring the reflectivity of the surface with the temperature probe signal. For an opaque surface, the emissivity may be obtained from the expression ε = 1 - r, where r is the surface reflectance.

[0037] Temperature monitoring can be useful for two reasons. First, the temperature of earth materials can be monitored during drilling to improve removal efficiency. For example, a certain temperature can be maintained during drilling (e.g., using a feedback loop that receives a signal indicative of temperature from the drilling area and adjusts the delivered power accordingly). The maintained temperature can be a temperature that causes the earth materials to evaporate or ablate them primarily into microparticles that can be ejected from the borehole using high-pressure gas. The pressurized gas can be pumped downward along the transmission line 130 and pressurized by the energy from the drilling beam 105, which increases the temperature of the materials in the confined borehole volume as described by the ideal and real gas laws, while the vapor and / or microparticles are ejected upward outside of the transmission line.

[0038] Second, for geothermal harvesting, temperature monitoring is also useful when drilling has stopped and allows the earth materials to cool to a lower temperature or their steady-state temperature. In this case, temperature monitoring can determine when sufficient depth has been reached to harvest geothermal energy. For example, the temperature can drop to its steady-state temperature, which can be measured by a temperature monitor. Alternatively, when the temperature drops to its steady-state temperature, at least one lower temperature can be measured. The steady-state temperature (at which geothermal energy can be harnessed and no further drilling is required) can be in the range of 50 °C to 500 °C. An exponential or functional fit to the decreasing temperature can be used to determine the final steady-state temperature at the bottom of the borehole.

[0039] One or more auxiliary detection signals 109 from the auxiliary monitor(s) 170 can be combined by the small-signal combiner 142 with the detection signal 108 from the ROP / depth monitor 160 onto a common small-signal transmission line 133, which carries the detection signals 108, 109 to and from the power combiner 140, as Figure 1A depicted. The power combiner 140 couples the combined small-signal detection signals 108, 109 from the small-signal transmission line 133 to the high-power transmission line 130, which also directs the high-power MMW radiation 103 to the bottom of the borehole 110. At the bottom of the borehole 110, the detection signals 108, 109 can leave and / or enter the distal end 138 of the transmission line 130 to sense physical properties (e.g., penetration rate, temperature, depth of the borehole, material composition, melt turbulence, etc.). Blackbody radiation emissions from the heated earth materials 150 can also enter the distal end 138 of the transmission line 130 for transmission to the auxiliary monitor 170.

[0040] The small signal detection signals 108, 109 can return from the bottom of the borehole 110 and can be guided back to the power combiner 140 by the high power transmission line 130. The power combiner couples the returned small signal detection signals 108, 109 to the small signal combiner 142 via the small signal transmission line 133. The small signal combiner 142 directs the different small signal detection signals 108, 109 and / or radiation emissions to the respective monitors 160, 170. The return signals can be divided and sent to the respective monitors using frequency, polarization, or time to demultiplex the signal at the small signal combiner 142. The monitors 160, 170 measure the amplitude, frequency, and / or phase of their respective received detection signals to derive some information about the conditions at the bottom of the borehole 110, such as the penetration rate of the drilling beam, the borehole depth, the surface emissivity, the melt turbulence, and / or the temperature, as well as other characteristics. Since the monitors 160, 170 derive information from the returned detection signals 108, 109 and / or radiation emissions, they can be kept on the ground, away from the bottom of the borehole 110 that is heated to extreme temperatures. Thus, for example, the monitors do not have to be as rugged as downhole monitors used to monitor mechanical drills. They can also monitor conditions at the bottom of the borehole 110 that are more extreme (e.g., hotter) than the conditions at the bottom of a borehole made with a mechanical drill.

[0041] Evaluating melt turbulence can be beneficial for drilling deep boreholes. Melt turbulence can indicate the viscosity level of the molten earth material 150. For some drilling applications, once the appropriate viscosity is reached, the molten earth material 150 can be displaced to the walls of the borehole, where the molten earth material will cool to form a solid shell that lines the borehole 110. This self-forming shell can stabilize the borehole 110 and, in some cases, can be strong enough to prevent borehole collapse.

[0042] Figure 1B and Figure 1C An alternative high power directed energy MMW drilling system 102 is shown. This system 102 can use a portion of the high power MMW radiation instead of the detection signals 108 at different frequencies to monitor the penetration rate and / or depth of the borehole. As in Figure 1AIn this case, a vibrating gyroscope or other high-power MMW source 120 generates high-power MMW radiation 103, and the high-power MMW radiation is guided to the bottom of the borehole by a high-power waveguide or transmission line 130. However, in this case, the penetration rate / depth monitor does not generate and transmit a detection signal at a frequency different from the frequency of the high-power MMW radiation 103 forming the drilling beam 105. Instead, a small portion of the forward high-power MMW radiation 103 picked up by the isolator 180 is coupled to the vibrating gyroscope frequency detector 184 at one of the beam traps via the beam traps 181, 182. Additionally, the reflected power isolator 180 simultaneously couples a portion of the high-power MMW radiation 103 returning from the bottom of the borehole 110 to the detector 184. The returned MMW radiation 103 can be coupled from the reflected power beam trap 182 via the small-signal transmission line 186.

[0043] Figure 1C Further details of the isolator 180 and the detector 184 are depicted, and the isolator and the detector can be part of another embodiment of the ROP / depth monitor 162. More specifically, the reflected power isolator 180 can include a polarizer grating 183 of copper wire at a 45-degree angle to the axis of the high-power transmission line 130. There can be two beam traps 181, 182 opposite each other on each side of the polarizer grating 183. The MMW radiation 103 is linearly polarized mainly in the HE 11 mode, which passes through the polarizer grating of the power isolator 180, but there is usually an undesired small-power component that does not pass through the polarizer in the wrong polarization. The power isolator 180 filters out and / or reflects other polarization components of the MMW radiation 103 according to the traveling direction of the MMW radiation 103 to the side beam traps 181, 182. One forward beam trap 181 can absorb the filtered forward power, and the second reflected power beam trap 182 can absorb the returned reflected power. In some cases, the beam traps 181, 182 are not perfect and can scatter power to each other. In this case, the small-signal waveguide 186 may not be required. The polarizer grating 183 reflects the power returned from the target at the bottom of the borehole 110 into the reflected power beam trap 182. The polarization of this returned reflected power is flipped 90 degrees by a circular polarizer in the bevel elbow, which is part of the small-signal and high-power beam combiner 140, as Figure 2AAs shown. The circular polarizer has grooves in its surface that circularly polarize an incident linearly polarized beam and repolarize the returning reflection into the orthogonal linear polarization of the incident beam. A detector 184 (e.g., a 28 GHz diode) positioned off-center on the forward beam trap 81 picks up these signals rejected by the polarizer grating. The forward and returning signal components coherently interfere in the diode detector to produce a detected signal amplitude that depends on the relative phase of the forward reflection signal, which in turn depends on the distance to the rock melt surface. The isolator 180 and the detector 184 can be used to implement a second ROP / depth monitor 162, which can be used alone or in addition to the ROP / depth monitor 160 (which can operate at a different frequency) to improve the reliability and accuracy of distance measurements.

[0044] In the second ROP / depth monitor 162, the reflected signal from the polarization grating is coherently mixed with a portion of the forward-propagating high-power MMW radiation 103 coupled to the ROP / depth monitor 162 to serve as a local oscillator. The ROP / depth monitor 160 can have its own frequency source that provides a local oscillator signal for the monitor, and the frequency of this local oscillator signal can be different from the frequency of the MMW radiation 103. The ROP / depth monitors 160, 162 detect their beat frequencies or intermediate frequencies caused by mixing their respective local oscillator signals with the reflected signals received from the borehole 110, and they process their respective detected beat signals to determine the ROP or depth of the borehole 110. If the MMW radiation 103 and the drilling beam 105 are at a constant frequency, the penetration rate / depth monitor 162 acts as a reflectometer, where the digital representation of the amplitude maxima and minima indicates the depth of the borehole, as described below. If the frequencies of the MMW radiation 103 and the drilling beam 105 are chirped or scanned, the penetration rate / depth monitor 162 acts as a frequency-modulated (FM) radar, where the phase or frequency of the beat indicates the depth of the borehole, as described below. Similarly, the frequency source of the ROP / depth monitor 160 can be fixed or scanned to operate the ROP / depth monitor as a reflectometer or an FM radar, respectively.

[0045] 1. Combine the frequency-multiplexed probe signal with the guided high-power MMW radiation

[0046] In some instances, the high-power MMW radiation 103, the small-signal detection signals 108, 109, and the radiation emission of interest from the bottom of the borehole 110 are at different frequencies such that they can be frequency multiplexed and demultiplexed using the small-signal combiner 142 and the power combiner 140. The small-signal monitors 160, 170 can be radiatively coupled to the high-power transmission line 130 by using fundamental-mode microwave / millimeter-wave waveguide components such as signal splitters, directional couplers, or frequency multiplexers. (Waveguides that support only the fundamental mode have a cross-section that is less than one wavelength or approximately half a wavelength of the radiation used by the small-signal monitors 160 or 170.) The detection signals 108, 109 of the monitors can be coupled to the high-power transmission line 130 using the configuration described in Figure 2A and Figure 2B . The high-power transmission line 130 can be overmoded for the detection signals (e.g., the waveguide diameter for the transmission line 130 can be much larger than the wavelength of the radiation for the detection signals 108, 109).

[0047] Figure 2A and Figure 2B depict examples of the power combiners 140a, 140b that can radiatively couple the small-signal detection signals 108, 109 propagating to and from the monitors 160, 170 onto the high-power transmission line 130 and radiatively couple the small-signal detection signals from the high-power transmission line that carries the high-power MMW radiation 103 to the bottom of the borehole 110. The configuration of the power combiner depends on the relative frequencies of the small-signal detection signals 108, 109, the radiation emission of interest, and the high-power MMW radiation 103. Figure 2A The power combiner 140a in Figure 2B can combine the higher-frequency small-signal detection signal with the lower-frequency high-power MMW radiation 103 traveling along the transmission line 130. The power combiner 140b in

[0048] Figure 2A can combine the lower-frequency small-signal detection signal 108 and / or detection signal 109 with the higher-frequency high-power drilling beam.

[0048] In the Figure 2A beam combiner, the small coupling hole 205 in the bevel mirror 210 mounted at the bend in the high-power transmission line 130 can be used to access the (one or more) higher-frequency detection signals 108, 109 and the lower-frequency MMW radiation 103 without disturbing the drilling beam 105. The high-power MMW radiation 103 is reflected from the bevel mirror 210, e.g., as in Figure 1AReflect downward toward the bottom of the borehole 110. Meanwhile, the small signal detection signals 108, 109 from the monitors 160, 170 propagate through the coupling holes 205 in the bevel mirror 210 and travel downward to the bottom of the borehole. The returned small signal detection signals 108, 109 and / or the radiation emissions travel upward through the holes 205 in the bevel mirror 210 to the monitors 160, 170. The diameter of the coupling holes 205 and / or the inner diameter of the small signal transmission line 133 are less than half the wavelength of the high-power MMW radiation 103 to prevent the MMW radiation 103 from propagating toward the monitors 160, 170. In other words, the coupling holes 205 in the bevel mirror 210 and / or the small signal transmission line 133 only allow the MMW radiation 103 to propagate briefly toward the monitors 160, 170 and effectively act as a low-frequency cut-off or high-pass filter. The mode conversion losses in the coupling between the small signal transmission line 133 and the high-power transmission line 130 can be calibrated out.

[0049] In Figure 2B the power combiner 140b, the dichroic or polarization-dependent filter 220 in the high-power transmission line 130 passes the high-power MMW radiation 103 at a higher frequency and reflects the small signal detection signals 108, 109 at a lower frequency and / or the radiation emissions from the bottom of the borehole 110. More specifically, the polarization-dependent filter 220 can be implemented as a wire grid or mesh with low-density wires. For example, a wire grid (including straight parallel conductive wires or conductive traces) can transmit a first linearly polarized wave and reflect a second linearly polarized wave whose polarization orientation is orthogonal to the first polarized wave. As another example, a dielectric window mounted at an appropriate angle or thickness can be used as the frequency-selective filter 220 to separate the radiation at two different frequencies. The filter 220 is configured to transmit the high-power MMW radiation 103 downward toward the bottom of the borehole 110. The dichroic or polarization-dependent filter 220 also reflects the detection signals 108, 109 from the monitors 160, 170 downward toward the bottom of the borehole 110 via the high-power transmission line 130 and reflects the returned detection signals 108, 109 and / or the radiation emissions of interest toward the monitors 160, 170 via the small signal transmission line 133.

[0050] A transition region including a section of the tapered waveguide 230 can be located between the small-signal transmission line 133 and the high-power transmission line 130, and can be located near the dichroic or polarization-dependent filter 220 (e.g., within 10 cm of the mirror). The tapered waveguide 230 can transform the transverse mode from the small-signal transmission line 133 to better match the mode supported by the high-power transmission line 130 and vice versa, in order to reduce the mode-coupling loss between the two transmission lines. In some cases, even though the wavelength(s) of the probe signal(s) can be longer than the wavelength of the high-power MMW radiation 103, the diameter of the small-signal transmission line 133 can be much smaller than the diameter of the high-power transmission line 130. The tapered waveguide 230 helps couple the probe signals 108, 109 propagating in the small-signal transmission line 133 to the larger high-power transmission line 130 and vice versa. The taper of the tapered waveguide 230 can be linear or parabolic and should be long enough to reduce or minimize the mode-conversion loss (e.g., below 10 dB). The parabolic taper is typically shorter than the linear taper. The inner surface of the tapered waveguide 230 preferably matches the inner surface of the transmission line to which the tapered waveguide 230 is connected. For example, when the transmission lines 130, 133 to which the tapered waveguide 230 is connected are implemented as waveguides with a corrugated inner surface, it can have a corrugated inner surface to efficiently transmit the HE 11 mode. The end-width (diameter) dimension of the tapered waveguide 230 is sized to match the width (diameter) of the transmission line to which that end is connected. A high-power vibratory gyro frequency notch filter can also be added to the small-signal monitoring waveguide to further reject any stray or scattered high-power vibratory gyro electromagnetic radiation.

[0051] An example of a high-power dielectric component that can be used in the power combiner 140b is a diamond slab oriented at the Brewster angle, which is 67 degrees for diamond in air at one atmosphere. The diamond slab combines and separates beams with orthogonal linear polarizations. At the Brewster angle, the polarization in the plane of incidence (the plane containing the incident and reflected beam vectors and the normal to the slab) is transmitted without loss (except for extremely small slab absorption), and the beam with perpendicular polarization to the plane of incidence is highly reflected. The transmitted beam will be the high-power MMW radiation 103 propagating along the high-power transmission line 130, and the reflected beam will be the probe signal 108 and / or the probe signal 109.

[0052] Figure 3 is a photograph of a part of the directed-energy MMW drilling system and shows it connected to the Figure 2AA small-signal beam combiner 142 similar to the power combiner shown in FIG. The small-signal beam combiner 142 decouples the 135-139 GHz radiation emission or temperature signal 109 received from the borehole 110 for temperature radiation measurement and decouples the detection signal 108 of the 94 GHz ROP / depth return from the small-signal transmission line 133 (implemented as a rectangular waveguide, a circular-to-rectangular transition, and a circular waveguide), and the small-signal transmission line is bent 90 degrees towards the high-power bevel mirror 210. The temperature radiometer is used as the auxiliary monitor 170. The hole in the bevel mirror 210 radiatively couples the collinear, combined returned detection signal 108 and temperature signal from the larger-diameter high-power transmission line (not visible in the photo) below the bevel mirror 210 to the monitors 160, 170, such that the detection signal 108 and temperature signal propagate along the high-power transmission line, where 28 GHz high-power radiation is used to form the drilling beam 105. In Figure 3 The top of the copper bevel mirror 210 mounted on the 28 GHz high-power transmission line with a 3-inch (76 mm) inner diameter is shown in the lower right of FIG. The small-signal transmission line 133 includes a copper circular waveguide with a 0.097-inch (2.5 mm) inner diameter, which has a vertical portion attached to the bevel mirror 210 and aligned with a hole of the same diameter in the center of the bevel mirror, and the hole introduces the detection signal 108 into the high-power transmission line to propagate collinearly with the high-power MMW radiation.

[0053] Continuing from Figure 3 upward from the bevel mirror 210 in the exemplary system of FIG., a circular-to-rectangular waveguide transition of the wr-8 band (90-140 GHz) is attached, followed by an E-plane bend. The E-plane bend is attached to a horizontally oriented 3 dB wr-8 directional coupler, which separates the combined returned detection signal 108 and temperature signal between the two monitors 160, 170. The returned detection signal 108 for the 94 GHz ROP / depth monitor 160 and the temperature signal for the GHz temperature radiometer 109 are separated by the directional coupler to the wr-8 to wr-6 (110-170 GHz) waveguide transition of the auxiliary monitor 170 and to the wr-8 to wr-10 (75-110 GHz) transition (partially visible) of the ROP / depth monitor 160. The wr-6 to wr-8 waveguide transition prevents the ROP / depth detection signal from interfering with the received temperature signal of the radiometer because 94 GHz cannot propagate in the wr-6 waveguide. Similarly, the 28 GHz high-power drilling beam cannot propagate in the 0.097-inch diameter waveguide, shielding the monitors while enabling them to fully monitor the borehole target surface with the higher-frequency beam.

[0054] 2. Penetration Rate / Depth Monitoring Instrument

[0055] The ROP / Depth Monitor 160 can operate as a reflectometer (reflective interferometer), a frequency modulated (FM) radar, or a pulsed time-of-flight radar. In the reflectometer configuration, the frequency of the small signal ROP / Depth Probe Signal 108 (also referred to as the probe frequency) is fixed. The returned probe signal 108 is mixed with its untransmitted portion to produce a DC signal, the amplitude of which depends on the round-trip return phase of the returned probe signal 108 relative to its pre-transmission condition. Since the depth change is equal to one quarter of the wavelength at the probe frequency, the detected signal amplitude should vary from a maximum to a minimum and vice versa. In other words, in the reflectometer configuration, the ROP / Depth Monitor 160 has a depth resolution Δz, which can be written as:

[0056]

[0057] where λ is the wavelength at the probe frequency. The ROP is determined by measuring the rate at which the signal changes from a maximum to a minimum, and the depth is determined by counting the number of maximum-to-minimum changes over time from the start or reference phase of the probe transmission.

[0058] In the FM radar configuration, the probe frequency is scanned over a bandwidth Δf at a certain modulation frequency f m . When the untransmitted copy of the ROP / Depth Probe Signal 108 is detected in the mixer, the round-trip reflected phase shift produces a tone at an intermediate beat frequency f B that is proportional to the depth Z. The depth is given by:

[0059]

[0060] where c is the propagation speed of the MMW in the high-pressure fill of the high-power MMW transmission line 130. In some embodiments, gas can be forced down along the transmission line 130 to help remove evaporative and / or particulate material from the bottom of the borehole 110 to deepen the borehole. The resolution of the depth depends on the bandwidth of the frequency scan:

[0061]

[0062] The relative advantages of the reflectometer and FM radar configurations can be understood by considering exemplary frequencies. At 94 GHz (λ = 3.19 mm) and a 1 GHz tuning bandwidth typically available for commercial Gunn oscillators, the depth resolution of the reflectometer would be 0.8 mm (Equation 1), and the depth resolution of the FM radar would be 150 mm (Equation 3). The reflectometer is more suitable for shallow boreholes (e.g., laboratory boreholes) where the depth is less than a few times the resolution of the FM radar, while the FM radar is more suitable for deep boreholes in the field. Additionally, for deep boreholes, the measurement of frequency is more reliable than the amplitude variation that may vary due to reasons other than phase changes.

[0063] In a time-of-flight configuration, short electromagnetic pulses (full-width at half maximum pulse duration of τ) are transmitted towards the bottom of the borehole. The round-trip time delay for the pulses to return to the surface electronics can be used to determine the distance to the bottom of the borehole. This relationship is given by:

[0064] Z = cΔt / 2 (4)

[0065] where c is the velocity of the transmitted pulse, and Δt is the round-trip delay time. The spatial resolution depends on the pulse length τ and the velocity of the transmitted pulse:

[0066] Δz = cτ (5)

[0067] In air at atmospheric pressure, the propagation velocity is the speed of light. For a 1 ns pulse corresponding to available 1 GHz electronics, the resolution would be 300 mm.

[0068] In pulsed operation, the peak pulse power level can be as high as 100 kW. High power and lower spatial resolution with a time-of-flight configuration would be suitable for the deepest boreholes drilled.

[0069] Figure 4 Details of the circuitry of the 94 GHz ROP / depth monitor 160 are shown, which can operate as a reflectometer or as an FM radar. The circuitry is constructed from wr-10 waveguide components for the 75 - 110 GHz band. The voltage-tuned 94 GHz ±0.5 GHz Gunn oscillator 410 is driven by an 8 V, 800 mA power supply 405 and is connected via an isolator 412 to a 10 dB directional coupler 415, which protects the Gunn oscillator from reflected backscatter. The directional coupler directs 10% of the Gunn oscillator output to a bias mixer 418 as a local oscillator for depth determination, which is powered by a 12 V, 20 mA power supply 420. The directional coupler directs the remaining 90% of the Gunn oscillator output to a three-port circulator 425 as a small-signal ROP / depth probing signal. The three-port circulator 425 directs this probing signal from port 1 to port 2, which is coupled to a solid-state single-pole double-throw (SPDT) PIN switch 430, which is powered by a ±5 V, 20 mA power supply 440 and is controlled by a transistor-transistor logic (TTL) signal set on a control input 435. One output of the PIN switch 430 is connected to a load 432, and the other output is connected via waveguide components to a small-signal combiner 142, as Figure 3As shown and described above. The small-signal combiner 142 combines the 94 GHz ROP / depth sounding signal onto the high-power transmission line 130 that travels down the borehole. The small-signal combiner 142 may also direct the radiation measurement signal from the borehole and the high-power transmission line 130 to a bolometer for temperature monitoring. The combiner 142 also directs the returned sounding signal from the borehole to port 2 of the three-port circulator 425, which outputs the returned sounding signal via port 3 to the bias mixer 418 for detection. Then, the returned signal from the bias mixer may go to a reflectometer or FM radar electronics for processing and determining the depth of the borehole.

[0070] Figure 4 The circuitry can operate as an FM radar when a swept voltage is applied to the Gunn oscillator and the PIN switch is set to continuously transmit and receive signals. The PIN switch 430 can also be removed from the circuit to reduce transmission and signal loss due to absorption in the switch. Figure 5 Shown is the ROP / depth monitor 160 connected to a lock-in amplifier 510, a TTL signal generator 520, and data acquisition electronics 530 to operate as a reflectometer. The TTL generator provides a 5 V square wave to the control input 435 ( Figure 4 ) of the PIN switch at a frequency typically exceeding 100 Hz to alternately direct the sounding signal to the target or load 432, which modulates the sounding signal sent down the borehole from the ROP / depth monitor 160. The returned amplitude-modulated (AM; on / off) reflectometer signal is acquired by the lock-in amplifier 510 using the signal from the TTL generator 520 as a reference. Using the lock-in amplifier 510 allows for the detection of extremely weak signals. The output of the lock-in amplifier 510 is directed to a data acquisition system that can process, store, and / or display the signal from the lock-in amplifier.

[0071] Figure 6 Shown is the ROP / depth monitor 160 connected to a voltage sweep generator 610, a frequency-to-voltage converter 620, and data acquisition electronics 530 to operate as an FM radar. A swept voltage is applied to the Gunn oscillator 410 ( Figure 4)The output from the sweep voltage generator 610 is applied to modulate the detection frequency (e.g., the frequency of its linear sweep or chirp detection signal). The bias mixer 418 mixes the resulting returned detection signal with a local oscillator copy of the non-transmitted swept detection signal to produce a tone at the intermediate frequency (IF) port of the mixer, the beat frequency of which is proportional to the distance to the target (the bottom of the borehole). This beat frequency can be directly acquired by the data acquisition electronics 530 for further processing, or can be converted to a voltage by the frequency-voltage converter 620 and provided to the data acquisition electronics 530. The received data can be processed, displayed, and / or stored by the data acquisition electronics 530. When the ROP / depth monitor is configured for FM radar operation, the PIN switch 430 is maintained in a position where it continuously transmits and receives signals (e.g., no switching signal to the load 432). In some embodiments, the PIN switch 430 can be removed from the circuit to increase signal strength.

[0072] Figure 7 An example of a signal detected by the ROP / depth monitor 160 when operating as a reflectometer is shown. In this case, the target is a flat lead brick on a motorized translation stage located approximately 18 cm from the transmitting horn connected to the output of the wr-10 waveguide of the reflectometer (e.g., the output from the PIN switch 430), which is typically coupled to the small signal combiner 142, as Figure 4 shown. The target is translated in depth at a uniform rate of 0.5 mm / hr. The signal moves through a peak (maximum - minimum - maximum) for every half-wavelength of 1.6 mm. Figure 7 A total of six such edges crossing a total distance of 9.6 mm are shown. In an actual drilling application on the melt surface target, the edges may be non-uniform due to an uneven fluctuating surface and / or non-uniform penetration rate. For example, if the height of a portion of the surface at the bottom of the borehole varies by about 1 / 4 wavelength or more of the detection frequency, it can reflect a portion of the detection signal in a direction opposite to the rest of the detection signal, thereby reducing the edge peak signal strength (and edge contrast).

[0073] Figure 8 A reflectometer signal from a melt pit melted into the basalt rock surface by a 28 GHz drilling beam is shown, which has a power of approximately 4.5 kW in a diameter of approximately 40 mm incident on the basalt surface. This system uses two reflectometer beams at different frequencies: one at the drilling beam frequency of 28 GHz picked up from the radiation of the returned drilling beam, and a separate 94 GHz monitoring beam (e.g., Figure 1A and Figure 1B both together). The top curve is the reflectometer signal from the 94 GHz monitor 160, and the bottom curve is from the coupled to the reflected power isolator 180 (Figure 1B ) of the reflectometer signal of the 28 GHz Schottky diode detector / mixer 184, which also samples the forward high power MMW radiation. The edge peaks are not as ideal as shown in laboratory tests from a flat solid surface. These curves show approximately six 94 GHz peaks to approximately two 28 GHz peaks that are proportional to the ratio of the probe signal wavelengths used to form a melt pit approximately 10 mm deep.

[0074] Figure 9 Shows a cross-section of a basalt melt pit 910 formed by exposing a solid basalt rock 920 to a drilling beam, as described in conjunction with Figure 8 that. The melt pit depth is approximately 10 mm. The molten rock pools and solidifies in the melt pit, thus filling a large portion of the drilling area. Having different reflectometer probe signals at different frequencies can reduce the uncertainty of monitoring non-ideal reflectometer signals. For example, detecting peaks based on the ratio of the probe wavelengths of different probe signals and cross-correlating the number of detected peaks can increase the certainty of depth measurement.

[0075] Devices for measuring the depth or penetration rate of a borehole drilled with a millimeter-wave directed energy drilling beam can be implemented and / or included in a drilling system in various configurations. Exemplary configurations are listed below. Corresponding methods for measuring depth or penetration rate can also be implemented.

[0076] (1) A system for drilling a borehole, the system comprising: a source configured to generate millimeter-wave radiation; a transmission line coupled to the source to direct the millimeter-wave radiation to the bottom of the borehole and form a millimeter-wave drilling beam in an area at the distal end of the transmission line; a penetration rate / depth monitor coupled to the transmission line to monitor the depth and / or penetration rate of the borehole; and a beam combiner coupled to the transmission line and the penetration rate / depth monitor to couple a probe signal into the transmission line for transmission to the bottom of the borehole and couple a returned probe signal generated by reflecting and / or scattering the probe signal from the bottom of the borehole from the transmission line to the penetration rate / depth monitor.

[0077] (2) The system according to configuration (1), wherein the penetration rate / depth monitor is configured to operate as a reflectometer.

[0078] (3) The system according to configuration (1), wherein the penetration rate / depth monitor is configured to operate as a frequency-modulated radar.

[0079] (4) The system according to configuration (1), wherein the penetration rate / depth monitor is configured to operate as a pulsed-modulated time-of-flight radar.

[0080] (5) The system according to any one of configurations (1) to (4), wherein the penetration rate / depth monitor is configured to generate the detection signal at a frequency different from the frequency of the millimeter-wave radiation.

[0081] (6) The system according to any one of configurations (1) to (5), wherein the beam combiner is configured to direct a portion of the millimeter-wave radiation returned from the bottom of the borehole to the penetration rate / depth monitor as the returned detection signal.

[0082] (7) The system according to any one of configurations (1) to (6), wherein the beam combiner includes an inclined mirror that is configured to reflect the millimeter-wave radiation around a bend in the transmission line and has a hole therein to transmit the detection signal.

[0083] (8) The system according to any one of configurations (1) to (7) further includes: a temperature monitor configured to receive radiation indicative of the temperature of the borehole; and a small-signal beam combiner coupled to the transmission line to couple radiation from the transmission line, wherein the radiation propagates along the transmission line together with the returned detection signal.

[0084] (9) A method of measuring the depth and / or penetration rate of a borehole drilled with millimeter-wave radiation, the millimeter-wave radiation being guided by a transmission line to the bottom of the borehole and formed into a millimeter-wave drilling beam, the method comprising: coupling a detection signal into the transmission line; guiding the detection signal to the bottom of the borehole with the transmission line, at least a portion of the detection signal being reflected and / or scattered from the bottom of the borehole as a returned detection signal; guiding the returned detection signal from the bottom of the borehole with the transmission line; coupling the returned detection signal out of the transmission line; mixing the returned detection signal with a local oscillator to produce an intermediate-frequency signal; and determining the depth and / or penetration rate of the borehole based on the amplitude and / or frequency of the intermediate-frequency signal.

[0085] (10) The method according to (9) further comprising modulating the amplitude of the detection signal and determining the depth and / or penetration rate of the borehole based on the amplitude of the intermediate-frequency signal.

[0086] (11) The method according to (9) further comprising modulating the frequency of the detection signal and determining the depth and / or penetration rate of the borehole based on the frequency of the intermediate-frequency signal.

[0087] (12) The method according to (9) further includes: forming the detection signal into at least one pulse; and determining the depth and / or penetration rate of the borehole based on the flight time of the at least one pulse.

[0088] (13) The method according to any one of (9) to (12) further includes generating the detection signal at a frequency different from the frequency of the millimeter-wave radiation.

[0089] (14) The method according to any one of (9) to (12) further includes forming the detection signal from a portion of the millimeter-wave radiation.

[0090] (15) The method according to any one of (9) to (14) further includes receiving, via the transmission line, radiation indicating the temperature at the bottom of the borehole.

[0091] (16) A method of forming a borehole with a millimeter-wave drilling beam and determining the depth and / or penetration rate of the borehole, the method including: coupling millimeter-wave radiation into a transmission line; coupling a detection signal into the transmission line; guiding, with the transmission line, the millimeter-wave radiation and the detection signal to the bottom of the borehole; forming the millimeter-wave drilling beam at a distal end of the transmission line; increasing the depth of the borehole with the millimeter-wave drilling beam; guiding, with the transmission line, a returned detection signal from the bottom of the borehole, the returned detection signal being at least a portion of the detection signal reflected and / or scattered from the bottom of the borehole; coupling the returned detection signal outside the transmission line; mixing the returned detection signal with a local oscillator to generate an intermediate-frequency signal; and determining the depth and / or penetration rate of the borehole based on the amplitude and / or frequency of the intermediate-frequency signal.

[0092] (17) The method according to (16) further includes modulating the amplitude or frequency of the detection signal, and determining the depth and / or penetration rate of the borehole based on the amplitude of the intermediate-frequency signal.

[0093] (18) The method according to (16) further includes: forming the detection signal into at least one pulse; and determining the depth and / or penetration rate of the borehole based on the flight time of the at least one pulse.

[0094] (19) The method according to any one of (16) to (18) further includes: coupling a first temperature signal emitted from the bottom of the borehole into the transmission line when drilling with the millimeter-wave drilling beam; coupling the first temperature signal from the transmission line to a temperature monitor; determining a first temperature with the temperature monitor; adjusting the amount of power in the millimeter-wave radiation based on the first temperature; stopping guiding the millimeter-wave radiation to the bottom of the borehole; allowing the bottom of the borehole to reach a lower temperature; coupling at least a second temperature signal emitted from the bottom of the borehole into the transmission line; coupling at least the second temperature signal from the transmission line to a temperature monitor; determining at least a second temperature with the temperature monitor; and determining whether the drilling has reached a sufficient depth to obtain geothermal energy based on at least the second temperature.

[0095] 4. Summary

[0096] All parameters, dimensions, materials, and configurations described herein are intended to be exemplary, and the actual parameters, dimensions, materials, and / or configurations will depend on one or more specific applications for which the teachings of the present invention are used. It should be understood that the foregoing embodiments are presented primarily by way of example, and within the scope of the appended claims and their equivalents, embodiments of the present invention may be practiced in a manner different from the specifically described and claimed manner. Embodiments of the invention disclosed herein relate to each individual feature, system, article, material, kit, and / or method described herein. Additionally, any combination of two or more such features, systems, articles, materials, kits, and / or methods that are not mutually contradictory is included within the scope of the invention disclosed herein.

[0097] Additionally, various inventive concepts may be embodied as one or more methods for which at least one example has been provided. In some cases, the actions performed as part of the method may be ordered differently. Accordingly, in some embodiments of the present invention, the corresponding actions of a given method may be performed in an order different from the specifically shown order, which may include performing some actions simultaneously (even if those actions are shown as sequential actions in the illustrative embodiments).

[0098] All publications, patent applications, patents, and other references mentioned herein are hereby incorporated by reference in their entirety.

[0099] All definitions defined and used herein should be understood to be based on dictionary definitions, definitions in documents incorporated by reference, and / or the ordinary meaning of the defined terms.

[0100] Unless explicitly stated to the contrary, the indefinite articles "a" and "an" as used herein in the specification and claims should be understood to mean "at least one (kind)".

[0101] As used herein in the specification and claims, the phrase "and / or" shall be understood to mean "any one or both" of the elements so combined, i.e., elements that exist conjointly in some cases and separately in other cases. Multiple elements listed with "and / or" shall be construed in the same manner, i.e., "one or more" of the elements so combined. Other elements may optionally exist, whether related or unrelated to those specifically identified, in addition to the elements specifically identified by the "and / or" clause. Thus, as a non-limiting example, in one embodiment, when used in conjunction with open-ended language such as "comprising", a reference to "A and / or B" may refer only to A (optionally including elements other than B); in another embodiment, only to B (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); and so on.

[0102] As used herein in the specification and claims, "or" shall be understood to have the same meaning as "and / or" as defined above. For example, when separating items in a list, "or" or "and / or" shall be interpreted inclusively, i.e., including at least one, but also including more than one of the elements or items in the list, as well as (optionally) other unlisted items. Merely clear contrary language, such as "only one of..." or "exactly one of..." or when used in a claim "consisting of..." will refer to including exactly one element of a plurality of elements or items in the list. In general, the term "or" as used herein shall be interpreted only as indicating exclusive alternatives (i.e., "one or the other, but not both") when preceded by exclusive terms such as "any one", "one of...", "only one of...", or "exactly one of...". When used in a claim, "consisting essentially of..." shall have the ordinary meaning as used in the field of patent law.

[0103] As used herein in the specification and claims, the phrase "at least one" with respect to a list of one or more elements should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each specifically listed element within the list of elements, and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally exist in addition to those specifically identified within the list of elements referred to in the phrase "at least one", whether related or unrelated to those specifically identified. Thus, as a non-limiting example, in one embodiment, "at least one of A and B" (or equivalently, "at least one of A or B", or equivalently "at least one of A and / or B") can mean at least one that optionally includes more than one A, no B (and optionally includes elements other than B); in another embodiment, it can mean at least one that optionally includes more than one B, no A (and optionally includes elements other than A); in yet another embodiment, it can mean at least one that optionally includes more than one A, and at least one that optionally includes more than one B (and optionally includes other elements); and so on.

[0104] In the claims as well as in the above specification, all transitional phrases such as "comprising", "including", "carrying", "having", "containing", "involving", "holding", "consisting of", etc. should be understood to be open-ended, i.e., meaning including but not limited to. Only the transitional phrases "consisting of" and "consisting essentially of" should be closed or semi-closed transitional phrases, respectively, as set forth in section 2111.03 of the Patent Examination Procedure Manual of the United States Patent and Trademark Office.

Claims

1. A system for drilling a borehole, the system comprising: a source configured to generate millimeter wave radiation; a transmission line coupled to the source to direct the millimeter wave radiation to the bottom of the borehole and to form a millimeter wave drilling beam in a region at the distal end of the transmission line; a penetration rate / depth monitor coupled to the transmission line to monitor the depth and / or penetration rate of the borehole; and a beam combiner coupled to the transmission line and the penetration rate / depth monitor to couple a probe signal into the transmission line for transmission to the bottom of the borehole and to couple a returned probe signal generated by reflecting and / or scattering the probe signal from the bottom of the borehole from the transmission line into the penetration rate / depth monitor.

2. The system according to claim 1, wherein the penetration rate / depth monitor is configured to operate as a reflectometer.

3. The system according to claim 1, wherein the penetration rate / depth monitor is configured to operate as a frequency modulated radar.

4. The system according to claim 1, wherein the penetration rate / depth monitor is configured to operate as a pulse modulated time of flight radar.

5. The system according to claim 1, wherein the penetration rate / depth monitor is configured to generate the probe signal at a frequency different from the frequency of the millimeter wave radiation.

6. The system according to claim 1, wherein the beam combiner is configured to direct a portion of the millimeter wave radiation returned from the bottom of the borehole as the returned probe signal to the penetration rate / depth monitor.

7. The system according to claim 1, wherein the beam combiner includes a bevel mirror configured to reflect the millimeter wave radiation around a bend in the transmission line and having an aperture therein to pass the probe signal.

8. The system according to claim 1, further comprising: a temperature monitor configured to receive radiation indicative of the temperature of the borehole; and a small signal beam combiner coupled to the transmission line to couple radiation from the transmission line, wherein the radiation propagates along the transmission line together with the returned probe signal.

9. A method of measuring the depth and / or penetration rate of a borehole drilled with millimeter wave radiation directed by a transmission line to the bottom of the borehole and formed into a millimeter wave drilling beam, the method comprising: coupling a probe signal into the transmission line; directing the probe signal to the bottom of the borehole with the transmission line, at least a portion of the probe signal being reflected and / or scattered from the bottom of the borehole as a returned probe signal; directing the returned probe signal from the bottom of the borehole with the transmission line; coupling the returned probe signal out of the transmission line; mixing the returned probe signal with a local oscillator to generate an intermediate frequency signal; and determining the depth and / or penetration rate of the borehole based on the amplitude and / or frequency of the intermediate frequency signal.

10. The method according to claim 9 further comprises: modulating the amplitude of the detection signal and determining the depth and / or penetration rate of the borehole based on the amplitude of the intermediate frequency signal.

11. The method according to claim 9 further comprises: modulating the frequency of the detection signal and determining the depth and / or penetration rate of the borehole based on the frequency of the intermediate frequency signal.

12. The method according to claim 9 further comprises: forming the detection signal into at least one pulse; and determining the depth and / or penetration rate of the borehole based on the flight time of the at least one pulse.

13. The method according to claim 9 further comprises: generating the detection signal at a frequency different from the frequency of the millimeter wave radiation.

14. The method according to claim 9 further comprises forming the detection signal from a portion of the millimeter wave radiation.

15. The method according to claim 9 further comprises: receiving, via the transmission line, radiation indicative of the temperature at the bottom of the borehole.

16. A method of forming a borehole with a millimeter wave drilling beam and determining the depth and / or penetration rate of the borehole, the method comprising: coupling millimeter wave radiation into a transmission line; coupling a detection signal into the transmission line; guiding, with the transmission line, the millimeter wave radiation and the detection signal to the bottom of the borehole; forming the millimeter wave drilling beam at a distal end of the transmission line; increasing the depth of the borehole with the millimeter wave drilling beam; guiding, with the transmission line, a returned detection signal from the bottom of the borehole, the returned detection signal being at least a portion of the detection signal reflected and / or scattered from the bottom of the borehole; coupling the returned detection signal out of the transmission line; mixing the returned detection signal with a local oscillator to generate an intermediate frequency signal; and determining the depth and / or penetration rate of the borehole based on the amplitude and / or frequency of the intermediate frequency signal.

17. The method according to claim 16 further comprises: modulating the amplitude or frequency of the detection signal and determining the depth and / or penetration rate of the borehole based on the amplitude of the intermediate frequency signal.

18. The method according to claim 16 further comprises: forming the detection signal into at least one pulse; and determining the depth and / or penetration rate of the borehole based on the flight time of the at least one pulse.

19. The method according to claim 16 further comprises: coupling a first temperature signal emitted from the bottom of the borehole into the transmission line while drilling with the millimeter wave drilling beam; coupling the first temperature signal from the transmission line to a temperature monitor; determining a first temperature with the temperature monitor; adjusting the amount of power in the millimeter wave radiation based on the first temperature; stopping guiding the millimeter wave radiation to the bottom of the borehole; allowing the bottom of the borehole to reach a lower temperature; coupling at least a second temperature signal emitted from the bottom of the borehole into the transmission line; coupling at least the second temperature signal from the transmission line to a temperature monitor; determining at least a second temperature with the temperature monitor; and Determine whether the drilling has reached a sufficient depth to obtain geothermal energy based on at least the second temperature.

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