Continuous emissions monitor for directed-energy borehole drilling
Apparatus and methods for monitoring emissions from a borehole to determine the composition of earthen material removed from the borehole are described. Monitoring can be done in real time as the borehole is being deepened with a millimeter-wave drilling beam. The present technology can monitor in real-time the elemental composition of the earthen materials (e.g., rock, minerals, crystals, metals, etc.) in a borehole created by a directed-energy beam that melts and vaporizes the earthen material materials in its path. Using a continuous emissions monitor (CEM) in combination with directed-energy excavation of a borehole enables rapid surveying of the subsurface for precious and commercial metals.
1 . A method of monitoring emissions from a borehole drilled with a millimeter-wave directed-energy drilling beam, the method comprising:
receiving, in a plasma chamber, exhaust gas created by vaporizing earthen material with the millimeter-wave directed-energy drilling beam;
in the plasma chamber, heating the exhaust gas with electromagnetic radiation to produce a plasma and optical emissions from the plasma;
making a spectroscopic measurement of the optical emissions with a spectrometer; and
determining a composition of the exhaust gas based on the spectroscopic measurement of the optical emissions.
2 . The method of claim 1 , further comprising:
receiving, in the plasma chamber, a portion of millimeter-wave radiation used to make the millimeter-wave directed-energy drilling beam; and
focusing the portion of millimeter-wave radiation to provide the electromagnetic radiation that produces the plasma.
3 . The method of claim 2 , further comprising:
picking off the portion of the millimeter-wave radiation returned from a reflection of the millimeter-wave directed-energy drilling beam from a bottom of the borehole.
4 . The method of claim 1 , further comprising calibrating the spectrometer.
5 . The method of claim 4 , wherein calibrating the spectrometer comprises:
introducing an aerosol from a calibration source into the plasma chamber, wherein the aerosol supplies a known amount of an element from the calibration source to the plasma;
measuring optical emission levels from the plasma while the aerosol is present in the plasma, the optical emission levels indicating an amount of the element; and
determining, from the optical emission levels, an amount of the element in the exhaust gas.
6 . The method of claim 1 , wherein receiving the exhaust gas created by vaporizing earthen material comprises receiving particulates from the borehole into a sample tube connected to the plasma chamber with a gas flow.
7 . A system for monitoring the composition of earthen material in a borehole created by a millimeter-wave directed-energy drilling beam, the system comprising:
a plasma chamber to receive exhaust gas from the borehole and to receive a portion of millimeter-wave radiation that is used to make the millimeter-wave directed-energy drilling beam, wherein the plasma chamber is configured to heat the exhaust gas with the portion of the millimeter-wave radiation to create a plasma emitting optical emissions; and
a spectrometer, in electromagnetic communication with the plasma chamber, to measure a spectrum of the optical emissions from the plasma, the spectrum indicating the composition of the earthen material in the borehole.
8 . The system of claim 7 , further comprising:
a sample tube or sample port connected to the plasma chamber to receive the exhaust gas from the borehole; and
an exhaust tube or exhaust port connected to the plasma chamber to exhaust at least the exhaust gas from the plasma chamber.
9 . The system of claim 8 , wherein the sample tube or sample port is made of a material to withstand temperatures of at least 800° C.
10 . The system of claim 7 , wherein the spectrometer is a grating spectrometer configured to monitor, with a spectral resolution of 0.02 nm or finer, at least one band with a bandwidth of 20 nm and a center wavelength in a range from 200 nm to 800 nm.
11 . The system of claim 7 , further comprising:
a mirror, disposed in the plasma chamber, to focus the portion of the millimeter-wave radiation to a spot; and
a sample tube, extending into the plasma chamber, to discharge the exhaust gas from the borehole into the plasma chamber near the spot.
12 . The system of claim 11 , further comprising:
a fiber optic cable connected to the plasma chamber and arranged to receive the optical emissions from the spot and guide the optical emissions to the spectrometer.
13 . The system of claim 7 , further comprising:
a calibration source, in fluid communication with the plasma chamber, to provide an aerosol for calibration of the spectrometer to the plasma chamber.
14 . The system of claim 7 , further comprising:
a reflected power isolator, in electromagnetic communication with the plasma chamber, to couple the portion of the millimeter-wave radiation out of a transmission line that guides the millimeter-wave radiation to a bottom of the borehole to form the millimeter-wave directed-energy drilling beam.
15 . A system for drilling a borehole and monitoring emissions from the borehole, the system comprising:
a high-power millimeter-wave (MMW) source;
a waveguide to carry MMW radiation from the MMW source to the borehole;
exhaust piping to seal the borehole and capture exhaust gas from the borehole while the borehole is being deepened with a MMW drilling beam formed from the MMW radiation;
a plasma chamber in fluid communication with the exhaust piping to receive an exhaust slip stream picked off from the exhaust gas;
a spectrometer in electromagnetic communication with the plasma chamber to detect emissions from a plasma formed in the plasma chamber from the exhaust slip stream; and
a reflected power isolator, in electromagnetic communication with the plasma chamber, to couple a portion of the MMW radiation produced by the MMW source to the plasma chamber.
16 . The system of claim 15 , further comprising:
a mirror, disposed in the plasma chamber, to focus the portion of the MMW radiation to a spot inside the plasma chamber; and
a sample tube, extending into the plasma chamber, to discharge the exhaust slip stream into the plasma chamber near the spot.
17 . The system of claim 16 , further comprising:
a fiber optic cable connected to the plasma chamber and arranged to receive optical emissions from the spot and guide the optical emissions to the spectrometer.
18 . The system of claim 15 , wherein the spectrometer is a grating spectrometer configured to monitor, with a spectral resolution of 0.02 nm or finer, at least one band with a bandwidth of 20 nm and a center wavelength in a range from 200 nm to 800 nm.
19 . The system of claim 15 , further comprising:
a calibration source, in fluid communication with the plasma chamber, to provide an aerosol for calibration of the spectrometer to the plasma chamber.
20 . A system for drilling a borehole and monitoring emissions from the borehole, the system comprising:
a high-power millimeter-wave (MMW) source;
a waveguide to carry MMW radiation from the MMW source to the borehole;
exhaust piping to seal the borehole and capture exhaust gas from the borehole while the borehole is being deepened with a MMW drilling beam formed from the MMW radiation;
a plasma chamber in fluid communication with the exhaust piping to receive an exhaust slip stream picked off from the exhaust gas;
a spectrometer in electromagnetic communication with the plasma chamber to detect emissions from a plasma formed in the plasma chamber from the exhaust slip stream; and
a calibration source, in fluid communication with the plasma chamber, to provide an aerosol for calibration of the spectrometer to the plasma chamber.