INFERENTIAL MEASUREMENT OF PHOTOELECTRIC ABSORPTION CROSS-SECTION OF GEOLOGIC FORMATIONS FROM NEUTRON-INDUCED, GAMMA-RAY SPECTROSCOPY

摘要

A method for inferring the photoelectric absorption of a formation by directly mapping spectroscopic measurements of gamma rays induced in the formation using a fast neutron source. The mapping is accomplished by creating a polynomial function based on counts of gamma-ray events in the gamma-ray energy spectrum; the coefficients of the polynomial function are determined in known calibration environments, and the value of the polynomial is the inferred photoelectric absorption parameter. The spectroscopic measurements are preferably generated by sorting gamma-ray counts of the gamma-ray spectrum into a plurality of energy-dependent channels, and measuring these gamma-ray energy distributions during different portions of the firing cycle where different types of dominant gamma-ray production reactions occur.