Neutron Porosity Based On One Or More Gamma Ray Detectors And A Pulsed Neutron Source

摘要

A method for pulsed neutron well logging of a subsurface formation, includes irradiating the formation with a plurality of bursts of neutrons of a group of selected durations; detecting gamma rays resulting from interaction of the neutrons during a group of selected time gates which contains at least some early and late gamma ray counts. The gamma rays are detected at at least two axially spaced apart locations from a position of the irradiating. In a computer, a ratio TRat is determined between the sum of detected gamma rays at a first axial spacing to the sum at a second axial spacing. A borehole correction is performed according to a function related to the ratio TRat before converting the ratio TRat to a hydrogen index or porosity of the subsurface formation.

主权项

1. A method for pulsed neutron well logging of a subsurface formation, comprising:
irradiating the formation with a plurality of bursts of neutrons of a group of selected durations; detecting gamma rays resulting from interaction of the neutrons during a group of selected time gates, the gamma rays detected at at least two axially spaced apart locations from a position of the irradiating; in a computer, determining a ratio TRat of the sum of detected gamma rays at a first axial spacing to the sum at a second axial spacing; and in the computer, performing a borehole correction according to a function related to the ratio TRat before converting the ratio TRat to a hydrogen index or porosity of the subsurface formation.