| 摘要 |
The composition of an earth formation is investigated by repetitively irradiating the formation with bursts of fast neutrons and generating 56 an energy spectrum of the gamma rays resulting from the in elastic scattering of such neutrons by nuclei of the formation. This spectrum is analyzed by comparing it 70 with a composite spectrum, made up of standard spectra 68 of constituents postulated to comprise the formation to determine the proportions in the formation of the postulated constituents. The composite spectrum includes one or more standard spectrum derived 62 from a background energy spectrum generated 58 from gamma rays detected during periods between neutron bursts. The standard background spectrum or spectra are preferably updated repetitively to reflect the current background component in the detected inelastic scattering gamma ray spectrum. More reliable information is thereby obtained of the presence of oil in the formation through the derivation of such indicators as the carbon/oxygen ratio, calcium/silicon ratio and the like. The detected background gamma ray spectrum may also be analysed to determine the proportions of the formation constituents contributing to such spectrum; and the standards for the most significant background contributors, or the composite spectrum produced by such standard spectra, may be used among the standard spectra for the inelastic scattering spectrum analysis in lieu of the standardized detected background spectrum itself. <IMAGE> |
