Methods and apparatus for borehole-corrected spectral analysis of earth formations

A method is described for analyzing an earth formation traversed by a borehole, comprising: moving a logging tool, including a pulsed high-energy neutron source and a gamma ray detector, through the borehole, irradiating the borehole/formation environment with pulses of high-energy neutrons from the source; detecting gamma rays with the detector which result from the capture of thermal neutrons by chemical elements of the borehole and formation constituents; determining from the detected gamma rays elemental gamma ray yields, Y/sub E/, indicative of the presence of specific chemical elements, E, in the borehole/formation measurement environment; determining sensitivity factors, S/sub E,M/, representative of the efficiency of detecting the chemical elements, E, in predetermined borehole and formation constituents, M; and deriving for each of predetermined constituent regions, R, in the borehole/formation measurement environment which contains a chemical element, E