A study of uncertainties in the prediction of neutron porosity logging-tool responses

The prediction of logging-tool responses suffers from both systematic and random sources of error of which only the latter can be treated in a scientifically objective manner. The use of a point-energy Monte Carlo code with a versatile modelling package essentially eliminates systematic errors and in this paper a detailed discussion of all sources of random uncertainty is given with particular reference to the responses of a dual-spaced neutron porosity tool in both water and sandstone. Sensitivity analysis is employed to identify the principal contributors to the total calculational uncertainty, and the statistical credibility of the comparison between measurements and calculations is discussed. (author)