Optical feedback to monitor and control laser rock removal

Abstract

Methods, systems, and devices related to downhole wellbore operations such as drilling and completing wells in an earth formation that include a laser device. The method includes lasing a rock and detecting an optical response of the lased rock. It can be determined from the optical response whether the lased rock is responding as specified (e.g. spalling, melting, etc.) If the lased rock is not responding as specified, one or more laser parameters are adjusted to achieve the specified response. Spalling is determined by the detection of sparks, or other light that erratically changes in intensity over time, by an optical detector. The detection of steady light may indicate other types of rock removal mechanisms, such as melt or dissociation.

What is claimed is: 
     
         1 . A method for removing subterranean rock with a laser, the method comprising:
 from inside a well bore, lasing subterranean rock around the well bore;   detecting emissions from the lased rock;   determining whether the detected emissions from the lased rock indicate a specified material removal mechanism; and   if the detected emissions do not indicate the specified material removal mechanism, adjusting one or more laser cutting parameters until emissions detected from the lased rock indicates the specified material removal mechanism.   
     
     
         2 . The method of  claim 1 , further comprising assessing an optical profile of the emissions detected from the lased rock for characteristic properties of the specified material removal mechanisms. 
     
     
         3 . The method of  claim 2 , wherein a characteristic property of a specified material removal mechanism comprises a detection of a rapidly time-varying emissions. 
     
     
         4 . The method of  claim 2 , wherein a characteristic property of a material removal mechanism comprises a detection of steady emissions. 
     
     
         5 . The method of  claim 1 , wherein the detected emissions indicate that the lased rock is spalling. 
     
     
         6 . The method of  claim 1 , wherein the emission intensity indicate a specified material removal mechanism if the emissions fluctuate with a frequency above a specified threshold value. 
     
     
         7 . The method of  claim 1 , wherein adjusting the one or more laser parameters comprises, in response to the emissions detected from the lased rock, changing one or more of beam irradiance of the laser, laser power, laser spot size, laser on time, purge time, or delay time between laser shut-off and purge turn-on. 
     
     
         8 . The method of  claim 1 , wherein detecting emissions from the lased rock comprises receiving light from the lased rock for a period of time. 
     
     
         9 . The method of  claim 1 , wherein detecting emissions from the lased rock comprises detecting a steady emission intensity, the method further comprising determining that the lased rock is not spalling based on detecting the steady emission intensity. 
     
     
         10 . The method of  claim 9 , further comprising determining that the rock is melting based on detecting the steady emissions. 
     
     
         11 . The method of  claim 10 , further comprising determining that the rock is dissociating based on detecting the steady emissions. 
     
     
         12 . The method of  claim 1 , where lasing subterranean rock comprises perforating a sidewall of the well bore. 
     
     
         13 . The method of  claim 1 , where lasing subterranean rock comprises drilling the well bore. 
     
     
         14 . A well apparatus for rock removal, comprising:
 a laser tool configured for insertion into the well and to direct laser energy onto rock;   a detector configured for insertion into the well and to detect emissions emitted from the rock; and   a controller configured to adjust power of a laser based on emissions detected from the rock.   
     
     
         15 . The apparatus of  claim 14 , wherein the controller comprises a processor communicatively coupled to the controller and configured to receive signals from the detector and output emissions information to the controller. 
     
     
         16 . The apparatus of  claim 14 , wherein, when the detected emissions from the rock indicate that the rock is not responding as specified, the controller is configured to automatically adjust one or more of an irradiance of the laser energy, laser power, laser spot size, laser on time, purge time, or delay time between laser shut-off and purge turn-on. 
     
     
         17 . The apparatus of  claim 16 , wherein the detected emissions from the rock indicates that the rock is not spalling when the emissions have a varying intensity with respect to time below a threshold value. 
     
     
         18 . The apparatus of  claim 14 , wherein the controller is configured to maintain the power of the laser when the emissions detected from the rock indicate that the rock is spalling. 
     
     
         19 . The apparatus of  claim 14 , wherein the controller is configured to determine that the rock is spalling when emission intensity detected has varying intensities with respect to time, the variations in intensities occurring with a frequency above a threshold value. 
     
     
         20 . The apparatus of  claim 14 , further comprising a reflector configured to reflect a laser beam towards the rock and to reflect the emission from the rock to the detector. 
     
     
         21 . The apparatus of  claim 14 , further comprising a dichroic reflector, the dichroic reflector configured to reflect a laser beam towards the rock and to transmit the light emitted from the rock to the detector. 
     
     
         22 . The apparatus of  claim 14 , further wherein the detector comprises one of an optical spot detector, an optical line detector, or a two-dimensional array detector. 
     
     
         23 . A well laser system for use in a subterranean well comprising:
 a laser apparatus configured to:
 produce a laser beam, and 
 direct the laser beam towards a subterranean rock; 
   an optical detector configured to detect light emitted from the rock; and   a controller communicatively coupled to the optical detector, the controller configured to:
 receive a signal from the optical detector, 
 determine from the signal whether the rock is responding as specified; and 
 adjust a parameter of the laser if the rock is not responding as specified. 
   
     
     
         24 . The system of  claim 23 , wherein the controller comprises a processor configured to receive signals from the optical detector and output instructions to the controller to adjust the power of the laser if the rock is not responding as specified. 
     
     
         25 . The system of  claim 23 , wherein the controller is configured to automatically adjust the power of the laser when the light detected from the rock indicates that the rock is not spalling. 
     
     
         26 . The system of  claim 25 , wherein the controller determines that the rock is not spalling when no sparks are detected by the optical detector. 
     
     
         27 . The system of  claim 26 , wherein the controller further determines that the rock is dissociating when the light detected is a steady glow. 
     
     
         28 . The system of  claim 26 , wherein the controller further determines that the rock is melting when the light detected is a steady glow. 
     
     
         29 . The system of  claim 23 , wherein the controller is configured to maintain the power of the laser when sparks are detected by the optical detector. 
     
     
         30 . The system of  claim 23 , wherein the laser apparatus further comprises a dichroic reflector, the dichroic reflector configured to reflect a laser beam towards the rock and to transmit the light emitted from the rock to the optical detector. 
     
     
         31 . The system of  claim 23 , wherein the optical detector comprises a spot detector. 
     
     
         32 . The system of  claim 23 , wherein the optical detector comprises a line detector. 
     
     
         33 . The system of  claim 23 , wherein the optical detector comprises a two-dimensional detector array.