FORMATION DENSITY MEASUREMENT UTILIZING PULSED NEUTRONS

摘要

A device for measuring the density of a formation uses a high-energy pulsedneutron source which induces gamma rays in theformation, and determines a gamma diffusion length of the formation based onthe attenuation of gamma rays produced by inelasticscattering of fast neutrons. The borehole tool houses the neutron source alongwith a near gamma ray detector and a fan gamma raydetector. The gamma ray detectors are located at different distances from thefast neutron source and spaced sufficiently from the fastneutron source such that dependence of inelastic gamma counts on fast neutrontransport and gamma production of the formation issubstantially reduced. Gamma ray events can be sorted and counted in time- andenergy-dependent bins. The present invention has severaladvantages over gamma-gamma logging, including deeper penetration of gamma,and is also superior over systems which measure, e.g.,hydrogen-based porosity.