US 10,520,641 B2 · Gamma calibration

Abstract

Estimating parameters of interest of a formation, including density, porosity, and fluid saturation. Methods relate to gamma ray energy spectra calibration for a radiation detector including generating a calibration radiation spectrum using measurements of radiation with the detector in a time interval wherein the radiation comprises predominantly gamma rays emitted by decay of radionuclides produced by neutron activation reactions resulting from neutron irradiation, the time interval following a prior time interval corresponding to thermal neutrons produced from the irradiation; making at least one other radiation measurement with the detector outside the time interval; and producing a calibrated radiation measurement from the at least one other radiation measurement using the calibration radiation spectrum. The measurements may be taken in the time interval by conveying the radiation detector in the borehole at high speed and using a background gate of the detector.

Claims20

Dependent claims

A method of gamma ray energy spectra calibration for a radiation detector in a borehole intersecting a volume of an earth formation, comprising:

irradiating the earth formation with a neutron pulse produced by a pulsed neutron source disposed in the borehole to produce gamma-rays;
generating a calibration radiation spectrum using measurements of radiation with the detector in a time interval, wherein the radiation of the measurements consists of gamma rays emitted by decay of radionuclides produced by neutron activation reactions resulting from the irradiation, the time interval following a prior time interval, wherein the prior time interval corresponds with thermal neutrons produced from the irradiation and begins with the cessation of the neutron pulse;
making at least one other radiation measurement with the detector outside the time interval;
and
producing a calibrated radiation measurement from the at least one other radiation measurement using the calibration radiation spectrum.

2 more elements

An apparatus for gamma ray energy spectra calibration for at least one radiation detector for use in a borehole intersecting a volume of an earth formation, comprising:

at least one radiation detector configured for conveyance by a carrier and configured to generate information representative of nuclear radiation from the formation;
and
an information processing device configured to:
generate a calibration radiation spectrum using measurements of radiation with the detector in a time interval, wherein the radiation of the measurements consists of gamma rays emitted by decay of radionuclides produced by neutron activation reactions resulting from irradiation of the earth formation with a neutron pulse, the time interval following a prior time interval, wherein the prior time interval corresponds with thermal neutrons produced from the irradiation and begins with the cessation of the neutron pulse;
make at least one other radiation measurement with the detector outside the time interval;
and
produce a calibrated radiation measurement from the at least one other radiation measurement using the calibration radiation spectrum.

4 more elements

Dependencies are inferred from the claim text.

Gamma calibration

Life of this patent

Gamma calibration

Life of this patent

Abstract

Claims20