| 摘要 |
<p>A method and an apparatus for correcting nuclear measurements performed in a borehole traversing earth formation, for the effect of said borehole, wherein the formation is irradiated with high energy neutrons source and the gamma rays resulting from the capture of neutrons with atoms of the formation and the borehole are detected and processed so as to generate two energy spectra representative of gamma rays coming from two respective zones radially spaced from the neutron source; from each spectrum is derived a response of atoms of a same element located at the respective zones, a first response being mainly representative of the borehole and a second response being mainly representative of the formation; from a predetermined relationship between the responses and from calibration a corrective factor for borehole effects is obtained. Each response comprises the elemental yield of a single element, such as hydrogen for porosity measurements, or chlorine for salinity measurements, or iron for lithology measurements. Elemental yields are derived from gamma rays either detected at two time gates following each a burst, or by using two different detectors longitudinally spaced from said neutron source. <IMAGE></p> |
