Rate of penetration/depth monitor for a borehole formed with millimeter-wave beam
Apparatus and methods are described for drilling deep boreholes with millimeter-wave radiation in earthen materials to access deep resources such as geothermal heat. Borehole depth and temperature at the bottom of the borehole can be monitored with probe signals and/or radiative emission from the bottom of the borehole.
1 . A system for drilling a borehole, the system comprising:
a source to generate a millimeter-wave radiation;
a transmission line, coupled to the source, to guide the millimeter-wave radiation to a bottom of the borehole and to form a millimeter-wave drilling beam in a region at a distal end of the transmission line;
a rate-of-penetration/depth monitor, coupled to the transmission line, to monitor a depth and/or a rate-of-penetration of the borehole; and
a beam combiner, coupled to the transmission line and to the rate-of-penetration/depth monitor, to guide a probe signal into the transmission line for transmission to the bottom of the borehole and to guide a returned probe signal, generated by reflection and/or scattering of the probe signal from the bottom of the borehole, from the transmission line to the rate-of-penetration/depth monitor.
2 . The system of claim 1 , wherein the rate-of-penetration/depth monitor is configured to operate as a reflectometer.
3 . The system of claim 1 , wherein the rate-of-penetration/depth monitor is configured to operate as a frequency-modulated radar.
4 . The system of claim 1 , wherein the rate-of-penetration/depth monitor is configured to operate as a pulse-modulated time-of-flight radar.
5 . The system of claim 1 , wherein the rate-of-penetration/depth monitor is configured to generate the probe signal at a frequency different than a frequency of the millimeter-wave radiation.
6 . The system of claim 1 , wherein the beam combiner is configured to direct a portion of the millimeter-wave radiation returned from the bottom of the borehole to the rate-of-penetration/depth monitor as the returned probe signal.
7 . The system of claim 1 , wherein the beam combiner comprises a miter mirror to reflect the millimeter-wave radiation around a bend of the transmission line and having a hole therein to pass the probe signal.
8 . The system of claim 1 , further comprising:
a temperature monitor to receive radiation indicative of a temperature of the borehole; and
a small-signal beam combiner, coupled to the transmission line, to guide the radiation from the transmission line, wherein the radiation propagates along the transmission line with the returned probe signal.
9 . A method of measuring a depth and/or a rate of penetration of a borehole drilled with millimeter-wave radiation guided by a transmission line to a bottom of the borehole and formed into a millimeter-wave drilling beam, the method comprising:
guiding a probe signal into the transmission line;
guiding the probe signal to the bottom of the borehole with the transmission line, at least a portion of the probe signal reflecting and/or scattering from the bottom of the borehole as a returned probe signal;
guiding the returned probe signal from the bottom of the borehole with the transmission line;
guiding the returned probe signal out of the transmission line;
mixing the returned probe signal with a local oscillator signal to produce an intermediate frequency signal; and
determining the depth and/or the rate of penetration of the borehole from an amplitude and/or a frequency of the intermediate frequency signal.
10 . The method of claim 9 , further comprising:
modulating an amplitude of the probe signal.
11 . The method of claim 9 , further comprising:
modulating a frequency of the probe signal.
12 . The method of claim 9 , further comprising:
forming the probe signal into at least one pulse; and
determining the depth and/or the rate of penetration of the borehole based on a time of flight of the at least one pulse.
13 . The method of claim 9 , further comprising:
generating the probe signal at a frequency that is different than a frequency of the millimeter-wave radiation.
14 . The method of claim 9 , further comprising forming the probe signal from a portion of the millimeter-wave radiation.
15 . The method of claim 9 , further comprising:
receiving radiation indicative of a temperature of the bottom of the borehole via the transmission line.
16 . A method of forming a borehole with a millimeter-wave drilling beam and determining a depth and/or a rate of penetration of the borehole, the method comprising:
guiding millimeter-wave radiation into a transmission line;
guiding a probe signal into the transmission line;
guiding the millimeter-wave radiation and the probe signal to a bottom of the borehole with the transmission line;
forming the millimeter-wave drilling beam at a distal end of the transmission line;
increasing a depth of the borehole with the millimeter-wave drilling beam;
guiding a returned probe signal from the bottom of the borehole with the transmission line, the returned probe signal being at least a portion of the probe signal reflecting and/or scattering from the bottom of the borehole;
guiding the returned probe signal out of the transmission line;
mixing the returned probe signal with a local oscillator signal to produce an intermediate frequency signal; and
determining the depth and/or the rate of penetration of the borehole from an amplitude and/or a frequency of the intermediate frequency signal.
17 . The method of claim 16 , further comprising:
modulating an amplitude or frequency of the probe signal.
18 . The method of claim 16 , further comprising:
forming the probe signal into at least one pulse; and
determining the depth and/or the rate of penetration of the borehole based on a time of flight of the at least one pulse.
19 . The method of claim 16 , further comprising:
guiding a first temperature signal that is emitted from the bottom of the borehole into the transmission line while drilling with the millimeter-wave drilling beam;
guiding the first temperature signal from the transmission line to a temperature monitor;
determining a first temperature with the temperature monitor;
adjusting an amount of power in the millimeter wave radiation based on the first temperature;
ceasing the guiding of the millimeter-wave radiation to the bottom of the borehole;
allowing the bottom of the borehole to reach a lower temperature;
guiding at least a second temperature signal that is emitted from the bottom of the borehole into the transmission line;
guiding 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 access geothermal heat based on at least the second temperature.