Geological logging system using gamma radiation

摘要

A method of determining physical parameters of geological formations by using a sonde lowered down a borehole at the end of a cable and including a source 80 of gamma radiation, a very near detector 83, a near detector 81, and a far detector 82, comprises, for each of a series of energy windows, a model is created characteristic of the response of each detector; a "low resolution" value of a looked-for parameter is determined which, when applied to the model, gives rise to a theoretical measurement that is substantially equal to the "low resolution" real measurement obtained by combining the measurements from all three detectors; the measurements from the two detectors 81, 83 nearest the source are combined to constitute a "high resolution" real measurement; and a "high resolution" value of the parameter is determined which, when applied to the model, gives rise to a theoretical value that is substantially equal to the "high resolution" real measurement, the determination being performed on the basis of the "high resolution" real measurement and of the "low resolution" value of the parameter. IMAGE