Comparison of nuclear well logging data with the results of core analysis: the significance of nuclear well logging in geological exploration

It is possible to consider the results of a geophysical assay of a formation statistically. In this case the geological formation in question is considered as a field for the regionalized variable. The regionalized variable itself (in the sense of Matheron's theory of geostatistics) is defined on some geometrical support being equal to the volume of the sample. In this case the results, or rather their scattering around the mean value, depend on the volume of the sample. This leads to some discrepancies between the results of the geological assay (on the core samples) and the geophysical data. By using the concept of the absolute dispersion coefficient in the de Wijs scheme, it is possible to obtain a new approach to the problem of how to construct the calibration curves for the nuclear probes on the basis of the field borehole logging and the laboratory measurements on the core samples. The method seems to be very interesting for many practical purposes in the evaluation of geological formations for oil and for solid mineral exploration. (author)