In-situ Detection and Analysis of Methane in Coal Bed Methane Formations with Spectrometers

Abstract

A measuring system for in-situ measurements down a well ( 1 ) by a spectrometer ( 4 ) is provided. The spectrometer ( 4 ) includes a radiation source ( 5 ) and a detector ( 6 ). A probe ( 15 ) optically connected to the spectrometer ( 4 ) and includes an optical pathway ( 7 ) for transmission of a radiation from the radiation source ( 5 ) and at least a second optical pathway for transmission of a characteristic radiation from a sample probe ( 15 ) near a side surface ( 11 ) of the borehole ( 3 ) and to optically couple the optical pathways ( 7 ) to the side surface ( 11 ), wherein the probe ( 15 ) is traversable up and down the well ( 1 ) by way of a guide operatively connected to the probe ( 15 ) and to a fixed location at the well head. By use of the apparatus and method a concentration of methane or other substance of interest is obtained and thereby a potential production of a coal bed methane formation is obtained.

What we claim are: 
     
         1 . A measuring system for in-situ measurements down a well with a borehole by a spectrometer, comprising:
 the spectrometer including a radiation source and a detector which is situated at a location at the wellhead,   a probe being optically connected to the spectrometer and including an optical pathway for transmission of a radiation from the radiation source and at least a second optical pathway for transmission of a characteristic radiation from a sample to the detector, and   wherein the sample is located outside of the probe, and   wherein the probe is traversable up and down the well by way of a guide operatively connected to the probe and to the spectrometer.   
     
     
         2 . A measuring system according to  claim 1 , wherein the sample is a volume of water in the well at or near the depth down the well. 
     
     
         3 . A measuring system according to  claim 1 , wherein the optical pathway for transmission of the radiation from the radiation source includes at least one lens for focusing the radiation from the radiation source onto the sample. 
     
     
         4 . A measuring system according to  claim 1 , wherein the radiation source is a diode laser at a wavelength of 450 nm to 580 nm. 
     
     
         5 . A measuring system according to  claim 1 , wherein a filter is located between the radiation source and the sample to filter the radiation from the radiation source. 
     
     
         6 . A measuring system according to  claim 1 , wherein at least one filter is located between the sample and the detector to filter the characteristic radiation. 
     
     
         7 . A measuring system according to  claim 1 , wherein the probe includes a high-pressure optical window for transmission of the radiation from the radiation source onto the sample. 
     
     
         8 . A measuring system according to  claim 1 , wherein the probe is armored against pressure and sealed against liquids. 
     
     
         9 . A measuring system according to  claim 1 , wherein the probe includes a high-pressure feed-through jacket for an optical fiber wherein the optical fiber interfaces between the spectrometer and the wellbore via the high-pressure optical window of the probe. 
     
     
         10 . A measuring system according to  claim 1 , wherein an error corrector is provided to correct for inherent system noise and errors. 
     
     
         11 . A measuring system according to  claim 1 , wherein the probe is optically connected to the radiation source via at least one optical fiber. 
     
     
         12 . A measuring system according to  claim 1 , wherein the probe is optically connected to the detector via at least one optical fiber. 
     
     
         13 . A measuring system according to  claim 1 , wherein the radiation source is a UV/Vis spectrometer. 
     
     
         14 . A measuring system according to  claim 1 , wherein the radiation source is a near IR spectrometer. 
     
     
         15 . A measuring system according to  claim 1 , wherein the radiation source is a Raman spectrometer. 
     
     
         16 . A measuring system according to  claim 1 , wherein the radiation source is an infrared spectrometer. 
     
     
         17 . A measuring system according to  claim 1 , wherein the radiation source is a fluorimeter. 
     
     
         18 . A measuring system according to  claim 1 , wherein the detector is a charge-coupled device. 
     
     
         19 . A measuring system according to  claim 1 , wherein the detector includes at least one of a photomultiplier tube, a photo-diode array, an avalanche photo-diode, a charge injection device and a complimentary metal-oxide semiconductor image sensor. 
     
     
         20 . A method of measuring methane in at least one coal bed methane well, comprising:
 a) providing a spectrometer including a radiation source and a detector which is situated at a location at the wellhead   b) providing a probe being optically connected to the radiation source and detector in the spectrometer   c) lowering the probe to a depth down the coal bed methane well,   d) transmitting radiation from the radiation source along a first optical pathway to the probe,   e) irradiating the sample which is located outside the housing with radiation from the radiation source to produce the characteristic radiation from the sample,   f) transmitting the characteristic radiation to the detector along a second optical pathway from the probe, and   g) measuring a concentration of methane in the sample by detecting the characteristic radiation from the sample with the detector, transmitting a signal from the detector to a signal processor and processing the signal to calculate the concentration of the methane in the sample.   
     
     
         21 . A method of measuring according to  claim 20 , wherein the radiation source includes an optical fiber transmitting light waves from a spectrometer near a well head and connected to the probe. 
     
     
         22 . A method according to  claim 20 , further comprising:
 lowering the probe to at least a second depth down the well, and measuring a concentration of methane at the second depth, in order to obtain concentration of methane versus depth of the well.   
     
     
         23 . A method according to  claim 20 , further comprising:
 obtaining concentration of methane versus depth of at least a second well, in order to obtain a potential production of a coal formation.   
     
     
         24 . A method according to  claim 20 , wherein the probe is sealed against water and armored to withstand pressure down the well. 
     
     
         25 . A method according to  claim 20 , wherein the spectrometer includes a radiation source for supplying a radiation to irradiate the sample. 
     
     
         26 . A method according to  claim 20 , wherein the spectrometer includes the detector for detecting the characteristic radiation from the sample and transmitting the signal. 
     
     
         27 . A method according to  claim 26 , wherein the spectrometer includes the signal processor for processing the signal from the detector. 
     
     
         28 . A method according to  claim 20 , wherein the spectrometer includes a filter for filtering the radiation from the radiation source. 
     
     
         29 . A method according to  claim 20 , wherein the spectrometer includes a filter for filtering the characteristic radiation before the detector. 
     
     
         30 . A method according to  claim 20 , wherein the radiation source is a diode laser at a wavelength that minimizes a fluorescence of the coal. 
     
     
         31 . A method according to  claim 20 , wherein the depth is at a top of a water column in the well. 
     
     
         32 . A method according to  claim 20 , wherein the depth is at a top of a first coal bed. 
     
     
         33 . A method according to  claim 20 , wherein the depth is at a top of a second coal bed. 
     
     
         34 . A method according to  claim 20 , wherein the sample is water at or near the depth. 
     
     
         35 . A method according to  claim 20 , wherein the probe includes at least one window for transmitting the radiation from the radiation source and the characteristic radiation. 
     
     
         36 . A method according to  claim 35 , wherein the window is positioned next to the sample. 
     
     
         37 . A method according to  claim 20 , wherein the wavelength is selected to mitigate a radiation from entrained particle in the water. 
     
     
         38 . A method according to  claim 20 , wherein the wavelength is selected to mitigate errors due to length of optical pathways transmitting the radiation from the radiation source and the characteristic radiation.