An integrated study on physical properties of a KTB gneiss sample and marble from Portugal: Pressure dependence of the permeability and frequency dependence of the complex electrical impedance

• Published in: Pure and Applied Geophysics Vol. 160; no. 5-6; pp. 929 - 936
• Main Authors: HEIKAMP, Stephanie, NOVER, Georg
• Format: Conference Proceeding Journal Article
• Language: English
• Published: Basel Springer 01-05-2003; Springer Nature B.V
• Subjects: Analytical methods; Aspect ratio; Conductivity; Cracks; Crystalline rocks; Earth sciences; Earth, ocean, space; Electrical conductivity; Electrical impedance; Electrical resistivity; Electrochemistry; Engineering and environment geology. Geothermics; Engineering geology; Exact sciences and technology; Frequencies; Frequency dependence; Geometry; Gneiss; Hydrostatic pressure; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Impedance; Impedance spectroscopy; Marble; Permeability; Physical properties; Porosity; Pressure; Pressure dependence; Pressure gauges; Resistivity; Spectroscopy; Spectrum analysis; Iberian Peninsula; Southern Europe; Central Europe; Portugal; Germany; pore geometry; physical properties; gneisses; Europe; porosity; deep drilling; permeability; pore fluid; impedance; least-squares; hydrostatic pressure; metamorphic rocks; Pressure; saturation; interpretation; spectroscopy; marbles; KTB; geometry; electrical conductivity; dispersion; fractures; dimensions; laboratory studies
• ISSN: 0033-4553; 1420-9136
• DOI: 10.1007/PL00012573

-- Pressure-induced variations in pore geometry were studied on dry- and fluid- saturated samples by means of electrical impedance spectroscopy and permeability measurements. Hydrostatic pressures (up to 120 MPa) and uniaxial pressures (up to failure) were applied. Hydrostatic pressures reduce the aspect ratio of cracks and thus cause a decrease of permeability and electrical bulk conductivity. The opposite was observed in uniaxial pressure experiments where new cracks were formed and consequently permeability and electrical conductivity were increased. More specific informations of these generated observations were derived from the interpretation of the frequency dispersion of the complex electrical conductivity. This least-squares-refinement considers electrochemical interactions between the fluid pore electrolyte and the inner surface of the sample, thus providing informations on the pore geometry and pressure-induced variations. Consequently changes in aspect ratio, size and geometry of the pore system can be detected by means of impedance spectroscopy.