CONTAMINATION INDICATIONS DERIVED FROM ELECTRICAL PROPERTIES IN THE LOW FREQUENCY RANGE¹

Abstract

BORNER, F., GRUHNE, M. and SCHON, J. 1993. Contamination indications derived from electrical properties in the low frequency range. Geophysical Prospecting 41,83-98.Electrical measurements are an important and integrated component of geophysical investigations connected with environmental problems. As a result of an analysis of the electrical conductivity, basic experiments on sandstones at frequencies below 10 kHz show that the complex behaviour of conductivity is caused exclusively by a complex interface conductivity. Its value is determined mainly by the internal rock interface to porosity ratio, the composition of the pore fluid and connected matrix-water interactions resulting in a specific microstructure of the interface. Therefore, it can be expected that the interface region of a soil or rock material is very sensitive to changes in composition caused by contamination. Contaminated sandstone and clay samples were investigated using a low-frequency measurement system. The investigations are directed at the influence of different contaminants and their concentration. Results show that the complex electrical conductivity (real and imaginary parts) is influenced by properties of the pore-filling contaminant. This influence results in a change of the level of both parts and the shape of their frequency dependence. The imaginary part in particular seems to provide important secondary information ; in some cases this part alone allows a differentiation of the various contaminants. The different behaviour of various rock types shows that the effects observed are the result of interactions between pore fluid properties and the internal pore surface structure.

Influence of pore fluid chemistry on the complex conductivity and induced polarization responses of Berea sandstone

“…IP methods are often an effective means of mapping subsurface contamination in cases where dc resistivity methods are ineffective [Sadowski, 1988;Cahyna et al, 1990;B6rner et al, 1993]. Furthermore, IP methods can also be used to predict the hydraulic properties of subsurface formations In this investigation we measure the time domain and broadband frequency domain IP responses of Berea sandstone as a function of the bulk solution ionic strength and pH.…”

Multi-parameter petrophysical characterization of Variscan greisen rocks from the Southern Bohemian Batholith (Austria) and the Eastern Erzgebirge Volcano-Plutonic Complex (Germany)

“…Further data of kaolinite-bearing shaly sandstone samples (Börner, 1992) also plot in the clay-dominated region and support this assumption. Three clay samples (88% montmorillonite, 87% Kaolinite and 11% illite, and 43% kaolinite and 24% illite, respectively) from Börner et al (1993) also plot close to the region where the clayey crystalline rocks and sandstones are found but with significantly higher values of σ', which can be explained by their high absolute content of clay minerals. This may be due to their extremely high clay content or the different properties of illite or montmorillonite as compared to kaolinite.…”

Electrical impedance tomography of the 1995 OGI gasoline release

“…Figure 5 is only the second time that dispersion and reactance of the subsurface have been imaged (see Daily and Ramirez, 1996). These results are important because of the recent reports by Olheoft (1986), Borner et al (1993) and Vanhala (1996) The baseline images of 512 Hz resistivity magnitude are included for reference.…”