Thermal Neutron Cross Section Logging based on compensated neutron logging.

ABSTRACT

In this paper, the compensated neutron logging is transformed into the Thermal Neutron Cross Section Logging (TNXS) to improve the application effect. Because the compensated neutron logging measures the neutron count, TNXS cannot be directly measured by the compensated neutron logging tool. Moreover, the thermal neutron ratio cannot be directly converted into the TNXS due to the influence of lithology and fluid. The ratio of thermal neutron count is related not only to the formation hydrogen index, but also to the formation density and the formation capture cross section. The density and the capture cross section of formations can be used to reduce the influence of lithology and fluid. Therefore, the thermal neutron counting ratio can be converted into the TNXS by density and the capture cross section of formations. The accuracy of the porosity calculated by the TNXS is studied based on the Monte Carlo method. The results show that the thermal neutron counting ratio can be accurately converted to the TNXS by density and the capture cross section of formations. The porosity calculated by TNXS is closer to the formation porosity than that calculated by the compensated neutron logging, especially in gas-bearing formations and complex lithologic formations.