Monte Carlo Simulating of Three Detector Density Logging

Abstract

AbstractTo amend the defects of traditional litho‐density logging tool, the paper advances the scheme of three‐detector density logging tool, that is, add a backscatter detector in negative spacing range on the basis of traditional dual‐detector density tool. With Monte Carlo general program MCNP (3B), the paper, which starts from the mechanism of the interaction between photon and formation, calculates various responses of backscatter detector, long spacing detector and short spacing detector, gains photon flux spectrum distribution, the change rules of photon flux with spacing, the relationships between photon flux and formation density, the relationships between spacing and detecting depth, count window and so on. Results reveal that the responses to formation of long or short spacing detector of three‐detector density tool are same as these of traditional dual‐detector density tool. Backscatter detector has high count rate and clear responses to formation, which is almost reverse to these of long or short spacing detector. Therefore, it is feasible to put the third detector in negative spacing range, which will improve measuring precision and vertical resolution. At the same time, it indicates that Monte Carlo method is effective in the early research of nuclear logging tool, and can direct tool design.