Study of thermal neutron time-spectrum of PNN logging based on multiscale filtering

Pulsed neutron-neutron logging is applied to calculate the formation macroscopic capture cross section through thermal neutron time-spectrum recorded by He-3 neutron detector. On the basis of filtering of time-spectrum, the effective formation macroscopic capture cross section can be obtained. As a case study, effective solutions for selecting optimized wavelet basis and threshold quantization are investigated from the characteristics of thermal neutron time-spectrum, and further the method of multiscale filtering based on threshold shrinkage is applied to filtering of thermal neutron time-spectrum of X well by longitudinal depth and transversal time respectively. The results indicate thermal neutron count decays as an exponential function of time. The research provide a new method to the filtering of thermal neutron time-spectrum of Pulsed neutron-neutron logging. (authors)