Characterization of sandstone by electrical spectroscopy for stratigraphical and hydrogeological investigations

Electrical spectroscopy is a development of the geophysical techniques of resistivity and induced polarization in which both the in-phase and quadrature components of conductivity are measured over a range of frequencies, in this study between 0.001 and 1000 Hz. Measurements have been made on Permo–Triassic sandstone samples taken from boreholes across the UK and saturated with a synthetic groundwater solution. Some samples were also selected for saturation with different strengths of sodium chloride solution. The lithology of the samples was examined using optical microscopy and parameters such as porosity and pore-throat size have been measured. From this it is clear that the electrical spectra are strongly influenced by many aspects of the sandstone lithology, including carbonate and quartz cementation. Grain and pore-throat size and their distribution are particularly important factors in the frequency dependence of the spectra. Pore surface area is an important influence on the magnitude of the quadrature conductivity. The information contained in the electrical spectra could be a very useful tool for future investigations in geological stratigraphy, hydrogeology and petroleum geology. Electrical spectroscopy can be used in both surface and borehole geophysical measurements.