FORMATION DENSITY MEASUREMENT UTILIZING PULSED NEUTRONS

摘要

A device for measuring the density of a formation uses a high-energy pulsed neutron source which induces gamma rays in the formation, and determines a gamma diffusion length of the formation based on the attenuation of gamma rays produced by inelastic scattering of fast neutrons. The borehole tool houses the neutron source alo ng with a near gamma ray detector and a fan gamma ray detector. The gamma ray detectors are located at different distances from th e fast neutron source and spaced sufficiently from the fast neutron source such that dependence of inelastic gamma counts on fast neutro n transport and gamma production of the formation is substantially reduced. Gamma ray events can be sorted and counted in time- a nd energy-dependent bins. The present invention has several advantages over gamma-gamma logging, including deeper penetration of gamma, and is also superior over systems which measure, e.g., hydrogen-based porosity.