Method for simultaneous measurement of borehole and formation neutron decay-times employing iterative fitting

摘要

A borehole and earth formations in its vicinity, are repetitively irradiated with pulsed fast neutrons, and during the intervals between pulses, capture gamma radiation is measured in at least four, non-overlapping, contiguous time intervals. A background radiation measurement is made between successive pulses and used to correct count-rates representative of thermal neutron populations in the borehole and the formations, the count-rates being generated during each of the at least four time intervals. The background- corrected count-rate measurements are iteratively fitted to exponential curves using a least squares technique to simultaneously derive signals representing borehole component and formation component of the thermal neutron decay time. The signals are recorded as a function of borehole depth.