Complete composition and density correlated sampling in the specific purpose Monte Carlo codes McPNL and McDNL for simulating pulsed neutron and neutron porosity logging tools

A very unique feature of the specific purpose Monte Carlo codes McPNL and McDNL for simulating pulsed neutron and neutron porosity logging tools, respectively, is the complete composition and density correlated sampling approach that is possible and that has been incorporated in these codes. The rules, requirements and procedures used for this approach are described and sample results are given for a number of practical cases. This approach is particularly useful for providing corrections to the log responses for almost all variations caused by composition and/or density variations. The standard deviations of the ratios of the responses from the correlated samples to the reference sample responses (the relative standard deviations) are usually two or more orders of magnitude less than the absolute standard deviation of the reference sample. Computation time is increased only by about 10% for ten additional correlated samples over that of the reference sample by itself. (author)