Pulsed neutron porosity logging system
AssigneeTexaco Inc.
InventorsHarry D. Smith, Jr., Michael P. Smith, Ward E. Schultz
Life of this patent
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Abstract
An improved pulsed neutron porosity logging system is provided in the present invention. A logging tool provided with a 14 MEV pulsed neutron source, an epithermal neutron detector, and a fast neutron detector is moved through a borehole. Repetitive bursts of neutrons irradiate the earth formations and, during the bursts, the fast neutron population is sampled. During the interval between bursts the epithermal neutron population is sampled along with background gamma radiation due to lingering thermal neutrons. The fast and epithermal neutron population measurements are combined to provide a measurement of formation porosity.
Claims8
A method for determining the porosity of earth formations in the vicinity of a cased well borehole comprising the steps of:
- repetitively irradiating earth formations in the vicinity of a cased well borehole with relatively short duration bursts of fast neutrons from a pulsed neutron source;
- detecting essentially only during said repetitive neutron bursts at a spaced distance from said neutron source, the fast neutron population in the borehole and generating signals representative thereof;
- detecting essentially only during the intervals between said neutron bursts at a spaced distance from said neutron source, the epithermal neutron population in the borehole and generating signals representative thereof;
- and
- combining said fast and epithermal neutron population representative signals to derive a measurement signal functionally related to the porosity of earth formations in the vicinity of the borehole.
Dependencies are inferred from the claim text.