Effect of the bore hole on nuclear logging measurements

Abstract

An analytical study with sand representing an ore was undertaken to find whether the ratio of the characteristic gamma-ray flux to thermal neutron flux in a bore hole can be reliably used as a measure of the characteristic element particularly if the water content of the ore is unknown. Both Monte Carlo and two-dimensional transport theory methods were used and found to be in good agreement but the use of two-dimensional transport theory is preferred for speed. A homogeneous analysis which ignores the effect of the bore hole and probe is compared to the detailed representation. It is shown that when the bore and probe are represented in the analysis there is a significant variation with water content of the ratio of the characteristic gamma-ray flux to the thermal neutron flux. This variation is not accurately predicted by the homogeneous model which is therefore inadequate.