The specific purpose Monte Carlo code McENL for simulating the response of epithermal neutron lifetime tools

A specific-purpose Monte Carlo code, called McENL, for modeling the time response of epithermal lifetime tools is described. The code was developed primarily for the Monte Carlo neophyte and requires a minimum amount of input preparation. The weight windows technique, using an automated importance function based on the solution of an adjoint diffusion model, is used to improve the efficiency of the calculation. Complete composition and density correlated sampling is also included in the code and is used to study the effect on tool response of small variations in the formation, borehole, or logging tool composition and density. McENL was benchmarked against test-pit data for the Mobil pulsed neutron porosity tool. Results of the experimental validation and details of code performance are presented