Geophysical coring, or borehole logs (Wireline Log) allow to obtain a continuous recording of the variations of a physical or chemical parameter of the soil as a function of depth. They are performed by lowering a special probe with a diameter of a few centimeters into a borehole or a piezometer or an existing well. A motorized winch controls the advancement of the probe and the measurements are carried out in a synchronized way.
With this technique it is possible to obtain a high resolution result (of the order of a decimetre) and in almost “undisturbed” conditions. It also allows for in situ measurement of a vast range of physical and physicochemical parameters such as temperature, soil and fluid resistivity, natural and induced radioactivity, windowed sections of a pipe, etc. The data is returned in graphical format with the depth expressed in meters on the ordinate axis and the measured parameter on the abscissa axis. The analysis of the temperature and conductivity gradients inside a borehole/well provides useful information on the circulation of the aquifers. Sonic log uses parameters of sound transmission in rock formations. An acoustic source produces a pressure pulse which is transmitted to the rock formations.
Different receivers record the arrival of the different types of waves, which allow the calculation of the propagation speed of the compression (P), shear (S) and Stoneley (St) waves.
The tool is operational within fluid-filled bores and requires centralization.
- Information on the lithology of geological formations
- Information on the permeability and porosity of geological formations
- Information on the quality of fluids contained in geological formations
- Information on lithological variations and variations in the fracturing of geological formations
- Determination of Vp and Vs of rock formations in unlined holes