Patent Document ID: 3946226
Application ID: 05448091
Patent Flag: 1

Claim One:
1. A method of investigating subsurface earth formations traversed by a borehole comprising the steps of: repetitively irradiating earth formations in the vicinity of a borehole with pulses of fast neutrons which engage in inelastic scattering interactions with formation nuclei and which are thereafter slowed to thermal energy and engage in further neutron capture interactions with formation nuclei; detecting, during a first discrete time interval associated with said fast neutron pulses, energy dependent distributions of gamma radiations attributable to the inelastic scattering of fast neutrons by the elements carbon and oxygen in the formations and generating signals representative of carbon inelastic gamma rays and oxygen inelastic gamma rays; detecting, during a second, later discrete time interval, energy dependent distribution of gamma radiations attributable to the capture of thermal neutrons by the elements calcium and silicon in the formations and generating signals representative of calcium capture gamma rays and silicon capture gamma rays; generating a first ratio signal comprising a ratio of said carbon and oxygen inelastic gamma ray representative signals; generating a second ratio signal comprising a ratio of said calcium and silicon capture gamma ray representative signals; and recording said first and second ratio signals as a function of borehole depth.