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US 4,409,481 AGranted
Method for simultaneous measurement of thermal neutron decay components
AssigneeHalliburton Company
InventorsHarry D. Smith, Jr., Ward E. Schultz, Jerry L. Verbout
Life of this patent
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Abstract
A method is disclosed for simultaneous determination of borehole and formation thermal neutron decay time components. The methods employ pulsed high energy neutron sources and time gated dual spaced detectors. Exponential decay curves are assumed for each of the components and iterative least squares fitting employing rapid convergence techniques are utilized.
Claims49
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 population 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 subintervals subsequent to a pulse of fast neutrons and generating at least four count rate signals representative of said thermal neutron populations during said at least four time subintervals;
- detecting, during a separate time interval between said repetitive bursts of fast neutrons, radiations attributable to a background radiation component of radiation and generating a background count signal representative thereof;
- correcting said at least four count rate signals for the presence of said background radiation component to provide at least four background corrected count rate signals;
- combining said at least four background corrected count rate signals according to an iterative fitting technique in which exponential relationships are assumed to exist for a borehole and a formation component of thermal neutron decay time to simultaneously obtain two measurement signals representative of the borehole component and the formation component of thermal neutron decay times;
- and
- recording said measurement signals as a function of borehole depth.
4 more elements
A method for simultaneously measuring the borehole component and the formation component of thermal neutron decay times of a borehole and earth formation 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 population in the borehole and surrounding earth formations;
- detecting at least at two different longitudinally spaced locations in the borehole during a time interval between said repetitive pulses of fast neutrons, radiations repesentative of the thermal neutron population in the borehole and surrounding earth formations, in at least four time subintervals subsequent to a pulse of fast neutrons and generating, at each of said at least two longitudinally spaced locations in the borehole, at least four count rate signals representative of said thermal neutron populations during said at least four time subintervals;
- combining said at least four count rate signals at each of said at least two differently longitudinally spaced locations in the borehole according to an iterative fitting technique in which exponential relationships are assumed to exist for a borehole component and a formation component of thermal neutron decay time to simultaneously obtain two measurement signals at each of said at least two longitudinally spaced locations representative of the borehole component and the formation component of thermal neutron decay times at said longitudinal locations;
- and
- recording said measurement signals as a function of borehole depth.
2 more elements
A method for simultaneously measuring the borehole and formation components 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 population 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 subintervals subsequent to a pulse of fast neutrons and generating at least four count rate signals representative of said thermal neutron populations during said at least four time subintervals;
- combining said at least four count rate signals according to a predetermined relationship in which exponential relationships are assumed to exist for a borehole and a formation component of thermal neutron decay time to simultaneously obtain two measurement signals representative of the borehole component and the formation component of thermal neutron decay time;
- and
- recording said measurement signals as a function of borehole depth.
2 more elements
Dependencies are inferred from the claim text.