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.

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.

Abstract: A method of identifying barite in a subterranean annulus that surrounds a wellbore, where the method includes detecting gamma rays in the wellbore that are generated from the annulus, obtaining a count rate of the detected gamma rays, comparing the count rate with reference data, and determining the presence of barite in the wellbore based on the comparison. The count rate can be a ratio of counts of detected gamma rays obtained from spaced apart receivers on a downhole tool, or a ratio of detected inelastic and capture gamma rays. The reference data is obtained by using a simulation algorithm.

Abstract: A method of identifying barite in a subterranean annulus that surrounds a wellbore, where the method includes detecting gamma rays in the wellbore that are generated from the annulus, obtaining a count rate of the detected gamma rays, comparing the count rate with reference data, and determining the presence of barite in the wellbore based on the comparison. The count rate can be a ratio of counts of detected gamma rays obtained from spaced apart receivers on a downhole tool, or a ratio of detected inelastic and capture gamma rays. The reference data is obtained by using a simulation algorithm.