A new porosity evaluation parameter based on neutron porosity logging

Abstract

The neutron porosity logging is one of the main methods for measuring the formation porosity. However, for the formation with complex mineral compositions and fluid properties, it is difficult to calculate the formation porosity accurately by the neutron porosity logging. In this paper, the relationship between the neutron slowing-down length and the neutron diffusion length and the formation hydrogen index is studied. Based on the thermal-neutron flux formula, a new parameter, apparent formation hydrogen index, is constructed by the neutron counting ratio and the formation density and the capture cross section. The apparent formation hydrogen index is close to the formation hydrogen index and is not affected by the excavation effect. The response characteristic of the apparent formation hydrogen index is more consistent with the volume physical model. The porosity calculated by the new parameter is closer to the formation porosity, especially in the gas-bearing formation.