Schlumberger Technology Corporation

Fabien Haranger

Christian Stoller

Marie-Laure Mauborgne

James A Grau

Tong Zhou

Jeffrey Miles

Sicco Beekman

Markus Berheide

Francoise Allioli

A method for gain correcting a gamma ray spectrum includes acquiring a gamma ray spectrum including gamma ray counts distributed into a plurality of energy channels, evaluating the acquired gamma ray spectrum to determine an energy of a calibration feature therein, comparing the energy of the calibration feature in the acquired spectrum to a standard spectral energy to determine a deviation between the energy of the calibration feature and the standard spectral energy, and adjusting the acquired spectrum so that the energy of the calibration feature is equal to the standard spectral energy to obtain a gain calibrated spectrum.

Spectral alignment method for induced gamma ray logging

A method for making natural gamma ray measurements includes deploying a logging while drilling tool including an electrical neutron output of the electrical neutron source is modulated and the natural gamma ray sensor is used to make a corresponding gamma ray measurement during at least a portion of the modulation. The gamma ray measurement is processed to obtain a corrected total natural gamma ray measurement of the subterranean formation.

Drilling fluid activation correction via neutron generator modulation

The disclosure relates to a method for correcting a downhole natural gamma-ray measurement performed in a wellbore. A gamma-ray measurement including at least a gamma-ray count rate is obtained by a gamma-ray detector disposed in a bottom hole assembly having a mud channel inside of the assembly, such that mud flows downwards in the mud channel and upwards outside of the assembly and a neutron source situated above the gamma-ray detector and activating the mud. The method includes:

Method and system for correcting a natural gamma-ray measurement performed in a wellbore

Composition-matched downhole tools and methods for using such tools are provided. One such method includes emitting neutrons using a neutron source in the downhole tool to generate formation gamma rays in a surrounding formation. At the same time, however, some of the neutrons may interact with different parts of the downhole tool to form tool gamma rays. The gamma ray spectra of at least some of the formation gamma rays and the tool gamma rays may be detected using a gamma ray detector. The tool gamma rays from the different parts of the tool may have a substantially similar spectral shape. As such, a processor may be used to analyze the spectra of the tool gamma rays using a single tool background standard, thereby simplifying the analysis and improving the precision of the results.

Composition-matched inelastic or capture spectroscopy tool

Methods and systems to determine and regulate the gain of gamma-ray detectors in tools equipped with neutron sources are provided. Gain regulation may be based on the gamma ray background generated in the tool by interaction of neutrons with the nuclei of some elements constituting the tool structure. Some chemical elements that are used in construction of the tool's mechanical parts and structure result in characteristic gamma ray lines in a measured energy spectrum. These lines can be used to calibrate the energy scale of the response of the detector, without any added calibration radio isotopic source.

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Princeton, NJ, United States of America

Fabien Haranger