A NEW EFFECTIVE MONTE-CARLO MIDWAY COUPLING METHOD IN MCNP APPLIED TOA WELL LOGGING PROBLEM

The background of the Midway forward-adjoint coupling method including the black absorber technique for efficient Monte Carlo determination of radiation detector responses is described. The method is implemente d in the general purpose MCNP Monte Carlo code. The utilization of the method is fairly straightforward and does not require any substantial extra expertise. The method was applied to a standard neutron well lo gging porosity tool problem. The results exhibit reliability and high efficiency of the Midway method. For the studied problem the efficienc y gain is considerably higher than for a normal forward calculation, w hich is already strongly optimized by weight-windows. No additional ef fort is required to adjust the Midway model if the position of the det ector or the porosity of the formation is changed. Additionally, the M idway method can be used with other variance reduction techniques if e xtra gain in efficiency is desired. (C) 1998 Elsevier Science Ltd. All rights reserved.