Method for simultaneous measurement of borehole and formation neutron lifetimes
AssigneeHalliburton Company
InventorsHarry D. Smith, Jr., Dan M. Arnold
Life of this patent
Estimating the term…
Abstract
The present invention concerns methods for measuring simultaneously the formation and borehole components of thermal neutron lifetime as decay time. The borehole and formation are irradiated with pulsed 14 MEV neutrons. During the interval between neutron pulses the capture gamma radiation is measured in at least four, non-overlapping, contiguous time gates. A background radiation measurement is also periodically made. The background corrected capture gamma radiation measurements are combined to derive simultaneously, the formation and borehole neutron lifetime components which are then recorded as a function of borehole depth.
Claims21
A method for simultaneously measuring the thermal neutron decay time of materials in and about a well borehole, comprising the steps of:
- generating, in a well borehole, a relatively short duration discrete burst of fast neutrons which are rapidly moderated by interaction with nuclei of materials in the borehole and surrounding earth formations and slowed down to thermal energy, creating a thermal neutron population in the borehole and surrounding earth formations;
- detecting, in the borehole, radiations representative of the thermal neutron population in the borehole and surrounding earth formations, in at least four time intervals subsequent to said burst of fast neutrons and generating, at least four count signals representative of said thermal neutron population during said at least four time intervals;
- and
- combining said at least four count signals according to a predetermined relationship to simultaneously separate the borehole and formation decay components and to derive at least two measurement signals representative of the thermal neutron decay time of the borehole medium and the earth formation medium in the vicinity of the borehole.
A method for simultaneously determining the borehole component and the formation component of thermal neutron decay time of a borehole and earth formations in the vicinity of the borehole, comprising the steps of:
- repetitively emitting, in a well borehole, relatively short duration pulses of fast neutrons which are rapidly moderated by interaction with nuclei of materials in the borehole and surrounding earth formations and slowed down to thermal energy, creating repetitive bursts of thermal neutron populations in the borehole and surrounding earth formations;
- detecting, in the borehole during a time interval between said repetitive pulses of fast neutrons, radiations representative of the thermal neutron population in the borehole and surrounding earth formations, in at least four time intervals subsequent to a pulse of fast neutrons and generating at least four count signals representative of said thermal neutron population during said at least four time intervals;
- suppressing a plurality of said repetitive neutron pulses;
- detecting, during a separate time interval between said repetitive pulses, and while said pulses are suppressed, radiations attributable to a background radiation component of radiation in the borehole and generating a background count signal representative thereof;
- combining said at least four count signals and a function of said background count signal according to a predetermined relationship to simultaneously separate the borehole and formation decay components and to derive at least two measurement signals representative of the thermal neutron decay times of said borehole component and said formation component;
- and
- recording said at least two measurement signals as a function of borehole depth.
Dependencies are inferred from the claim text.