Spatial Heterodyne Integrated Computational Element (SH-ICE) Spectrometer

Abstract

A spatial heterodyne spectrometer may employ an integrated computational element (ICE) to obtain a measure of one or more fluid properties without requiring any moving parts, making it particularly suitable for use in a downhole environment. One illustrative method embodiment includes: directing light from a light source to illuminate a sample; transforming light from the sample into spatial fringe patterns using a dispersive two-beam interferometer; adjusting a spectral weighting of the spatial fringe patterns using, an integrated computation element (ICE); focusing spectral-weight-adjusted spatial fringe patterns into combined fringe intensities; detecting the combined fringe intensities; and deriving at least one property of the sample.

1 . A spectral analysis tool that comprises:
 a light source that illuminates a sample;   a detector;   an optical path that couples light that has interacted with the sample to the detector;   and   an integrated computational element (ICE) that adjusts a spectral weighting of light propagating along the optical path.   
     
     
         2 . The tool of  claim 1 , wherein the ICE has a programmable wavelength dependent attenuation. 
     
     
         3 . The tool of  claim 1 , wherein the ICE employs spatially-dependent masking to adjust the spectral weighting based on a spatial dependence of spatial fringe patterns. 
     
     
         4 . The tool of  claim 3 , wherein the ICE has a programmable spatial dependence. 
     
     
         5 . The tool of  claim 3 , wherein the ICE further employs wavelength dependent masking. 
     
     
         6 . The tool of  claim 5 , wherein the wavelength dependence is programmable. 
     
     
         7 . The tool of  claim 3 , wherein the ICE is a multiplex device employing multiple different row-oriented spectral weighting regions to provide multiple adjustments to the spectral weighting. 
     
     
         8 . The tool of  claim 1 , wherein the ICE employs multiple different row-oriented spectral weighting regions to provide multiplex adjustments to the spectral weighting. 
     
     
         9 . The tool of  claim 29 , further comprising a focusing element that recombines one or more rows of spatial fringe pattern information at row-associated points. 
     
     
         10 . The tool of  claim 9 , wherein the detector comprises an array of detectors that capture row-associated combined intensity measurements at the row-associated points. 
     
     
         11 . The tool of  claim 29 , wherein the detector acquires a two-dimensional image of spectral-weight-adjusted spatial fringe patterns, and wherein row-oriented spatial fringe pattern information is combined electronically. 
     
     
         12 . The tool in  claim 29 , wherein detector acquires a two-dimensional image of spectral-weight-adjusted spatial fringe patterns, and wherein row-oriented spatial fringe pattern information is Fourier transformed electronically. 
     
     
         13 . The tool of  claim 1 , wherein the spectral analysis tool is integrated into a downhole wireline or logging-while-drilling instrument package. 
     
     
         14 . The tool of  claim 13 , wherein the sample includes fluid drawn from a formation. 
     
     
         15 . The tool of  claim 13 , wherein the sample includes a portion of a borehole wall. 
     
     
         16 . The tool of  claim 13 , wherein the sample includes fluid from a borehole. 
     
     
         17 . A spectral analysis method that comprises:
 directing light from a light source to illuminate a sample;   transforming light from the sample into spatial fringe patterns using a dispersive two-beam interferometer; and   adjusting a spectral weighting of the spatial fringe patterns using an integrated computation element (ICE);   
     
     
         18 . The method of  claim 30 , wherein said detecting includes focusing spectral-weight-adjusted spatial fringe patterns into combined fringe intensities. 
     
     
         19 . The method of  claim 17 , wherein said operations of directing, transforming, and adjusting are performed in a downhole tool. 
     
     
         20 . The method of  claim 19 , further comprising modifying operation of the downhole tool based on at least one derived property of the sample. 
     
     
         21 . The method of  claim 17 , wherein said adjusting includes applying a spatially-dependent mask to the spatial fringe patterns. 
     
     
         22 . The method of  claim 21 , wherein the spatially-dependent mask further applies a wavelength-dependent attenuation. 
     
     
         23 . The method of  claim 17 , wherein said adjusting includes applying different masks in multiple row-oriented regions. 
     
     
         24 . The method of  claim 30 , wherein said detecting includes:
 sensing spectral-weight-adjusted spatial fringe patterns with a two-dimensional array of detectors; and   electronically combining measurements along a row dimension to obtain the combined fringe intensities.   
     
     
         25 . The method of  claim 24 , further comprising applying a spatial Fourier transform to the sensed spectral-weight-adjusted spatial fringe patterns. 
     
     
         26 . The method of  claim 17 , wherein the sample is a fluid drawn from a port seated against a borehole wall. 
     
     
         27 . The method of  claim 17 , wherein the sample is a borehole fluid or a portion of a borehole wall. 
     
     
         28 . The method of  claim 30 , wherein the property is at least one of: a contamination level, a quantity of at least one fluid type, and a concentration of at least one substance. 
     
     
         29 . A spectral analysis tool that comprises:
 a light source that illuminates a sample;   a detector;   an optical path that couples light that has interacted with the sample to the detector; and   a dispersive two-beam interferometer that transforms light propagating along the path into spatial fringe patterns associated with corresponding wavelengths.   
     
     
         30 . The method of  claim 17 , further comprising:
 detecting combined fringe intensities derived from spectral-weight-adjusted spatial fringe patterns; and   deriving at least one property of the sample.