| 摘要 |
In the illustrative embodiments of the invention disclosed, a more accurate elemental analysis of an earth formation surrounding a borehole is achieved by comparing a gamma ray energy spectrum measured in the borehole, following irradiation of the borehole and the surrounding earth formation with high-energy neutrons, with a composite spectrum made up of a combination of weighted standard spectra of elements postulated to have contributed significantly to the borehole spectrum, wherein the standard spectra include a tool background spectrum that accounts for the spectral contribution due to neutron interactions with the tool constituents. The tool background spectrum is derived by isolating the tool contribution to one or more of the elemental standard spectra, and by using one or a combination of such isolated tool contribution spectra as the tool background spectrum. In the case of thermal neutron capture gamma ray spectra, the tool background spectrum is also preferably stripped from certain of the raw elemental standard spectra to arrive at the final elemental standard spectra for inclusion in the composite spectrum compared with the borehole spectrum. In addition to an improved elemental analysis, information is also obtained as to the borehole fluid salinity and/or the formation fluid salinity from a determination of the capture tool background yield.
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