Investigation Of The Multi-Scale Analysis And Multi-Exponential Inversion Algorithm Of PNN Logging Time Spectrum

Pulsed neutron-neutron logging is a method that can determine watersaturation by means of the formation macroscopic absorption cross section according to thermal neutron time spectrum by using two different He-3 neutron detector. In order to improve the reliability of logging data applied to the evaluation of strata, the means of extracting the essential features of strata and establishing the corresponding relationships between PNN logging data and the strata is applied in this paper.From the theory of multi-scale analysis of wavelet, the multi-scale analysis based on threshold shrink of logging curve are studied systematically on the basis of the optimum wavelet base selected by means of correlation coefficient. The selection and quantification of threshold shrink is discussed. The PNN logging curve through the multi-scale analysis is studied. The analysis indicates that the thermal neutron count ratio attenuats as time goes on. The conclusion is satisfied with the post processing of time spectrum.Levenberg-Marquardt is implemented by means of programming. The algorithm is verified through single-exponential inversion, double-exponential inversion and multi -exponential inversion. And the effection of noise and the number of arrangement points is analyzed. Using a damp least-squares inversion algorithm, thermal neutron time spectrum can be invesed. According to multi-exponential inversion algorithm, the smooth and sucessive thermal neutron life spectrum(τspectrum) is developed.Firstly, theτspectrum is studied by simulation data to analyze the effect of formation water salinity, porosity, oil saturation and distance on the eigen value of thermal neutron life. Simulations results show that the double-peak ofτspectrum reveals the ability of the wellbore and the formation to capture thermal neutron; and the appearance of single-peak or double-peak forτspectrum depends on the time chosing. The research shows that the application ofτspectrum to actual logging data may identify oil and water zone.Secondly, theτspectrum is studied by actual logging data, the effect of strata and cased well is analyzed. The research shows that the application ofτspectrum to actual logging data may identify oil and water zone. Therefore this method may ameliorate logging interpretation of neutron life and improve market value.By means of upper research, theτspectrum with more logging information is recognized clearly, then more technical support will be provided for neutron life logging.