METHOD FOR DETECTING EXPANSIVE CLAYS IN A SEDIMENTARY BASIN BY SPECTROMETRIC MEASUREMENTS

Method for determining a risk of loss associated with a clay retraction-expansion effect in a target geographic zone in a sedimentary basin, by means of measurement of gamma rays emitted by natural radioelements, characterized in that the following steps are carried out: a calibration geographic zone for which losses associated with retraction-expansion effects are known is selected; an experimental correlation is estabilished between, on the one hand, a risk of loss associated with an expansive-clay retraction-expansion effect and, on the other hand, a first set of measurements of gamma rays emitted by the natural radioelements potassium (K) and thorium (Th) on the surface of said calibration geographic zone; at least one second set of measurements of gamma rays emitted by the natural radioelements potassium (K) and thorium (Th) are carried out on the surface of said target geographic zone; and a risk of loss associated with an expansive-clay retraction-expansion effect is determined in said target geographic zone, by means of said correlation and of the second set of measurements.