Corrections of fast neutron inelastic scattering effects on D-T neutron porosity logging

Abstract

With the continuous development of logging tools with controllable neutron sources, improving the processing method to make their measurements more consistent with those obtained by chemical sources has become a development trend in well logging based on controllable sources. To study the correction method that is not constrained by other parameters and does not require chemical sources, the reasons for the differences in the neutron porosity responses of D-T and chemical sources are theoretically analyzed. Then the fast neutron slowing-down process is divided into two stages depending on neutron energy. A method to correct the effects of inelastic scattering in D-T neutron porosity is established through the derivation of the theoretical relationship. Finally, the effectiveness of the correction method is verified using the simulation and measured data. The results show that after inelastic scattering correction, the measurement results of neutron porosity logging with controllable and chemical sources are highly consistent, and there is a close correspondence between the two types of sources in terms of measured data. Therefore, the proposed inelastic scattering correction method can effectively replace density correction to make the measurement results of the D-T neutron source more consistent with those of chemical sources. This study is of great significance for the wide application of neutron porosity measurement with controllable neutron sources and the replacement of radioactive sources in logging tools in the future.