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Basic: Spectral Gamma


XRF analysis measures the elemental concentrations of K, U and Th by weight in a given rock sample. These amounts are then converted to a synthetic total gamma.  Wireline and MWD tools measure the emission of natural gamma rays from rock in-situ in order to back calculate how much K, U and Th are present in a volume of rock or the total natural gamma ray reading.  By comparing the results of XRF and wireline or MWD, cuttings or core can be depth shifted if necessary to their correct locations of origin.  In horizontal wells, the XRF can provide a spectral gamma to compliment MWD data.   Figure A shows a spectral gamma plots for a vertical oil sands core from the McMurray Formation, while Figure B displays spectral gamma analysis for a horizontal well from the Duvernay Formation.


Figure A. XRF Spectral Gamma Analysis from a Vertical Well in the McMurray Formation. 


Figure B. XRF Spectral Gamma Analysis from a Horizontal Well in the Duvernay Formation.