James R. Bridges

A borehole corrected pulsed neutron well logging system

Abstract An improved well logging method has been developed for more accurately measuring the neutron capture cross section (Σ) of earth formations. A measurement of Σ with depth (well log) is useful in estimating hydrocarbon saturation of saline reservoirs. Gamma rays are detected following each burst of neutrons emitted by a pulsed 14 MeV neutron generator. An iterative procedure was developed to obtain borehole and formation exponential components from the measured data. This yields a formation Σ with reduced borehole dependence, particularly in high Σ formations. Accuracy of the two-exponential fitting procedure was verified by applying it to simulated data. An extensive set of test formation measurements further verified the accuracy of the two-exponential model and indicated only a small dependence on borehole conditions in the estimation of formation Σ.