Patent ID: 9746582
Date: 2017-08-29
CPC Classifications: G01V

Claim:
1. A method for determining a composition of a subsurface formation, comprising: characterizing by energy detected gamma rays resulting from interaction of neutrons that have been generated from a chemical isotope source or an electrically operated neutron source and have irradiated the formation, the detection performed at at least one spaced apart position from a position of the irradiation; determining elemental yields by spectrally analyzing the energy characterized gamma rays; selecting a subset of the elemental yields as background yields and filtering the background yields; calculating an apparent contribution of the filtered background yields to the characterized gamma rays; determining foreground elemental yields of the formation by spectrally analyzing the characterized gamma rays having the apparent contribution removed; wherein the spectrally analyzing comprises determining a sum of products of elemental yields for a plurality of elements with a standard gamma ray spectrum for each of the plurality of elements.