Characterizing unconsolidated sediments using the spectral induced polarization (SIP) method

Spectral induced polarization measurements (i.e. complex resistivity or conductivity measurements in the frequency range from 1 mHz to 1 kHz) can be used to obtain electrical parameters by fitting of an function (e.g. the Cole-Cole model) to the complex resistivities. The dc bulk resistivity and the frequency dependence of the complex resistivity is represented by these parameters (according to the used model). In terms of rock properties the electrical parameters depend on the pore-space geometry and the microstructure of the internal rock boundary layer. The crux is the relationship between electrical parameters and rock properties. Such a relationship is urgently required for a quantitative interpretation of SIP data. Own laboratory investigations of unconsolidated sediments are compared with equations proposed in literature which relates electrical parameters to rock properties. The investigations are mainly focused on the relation of the electrical parameters to the specific surface area (related to the pore space) or to the grain size (distribution) respectively. The specific surface area is derived by moisture analyzing (evaporation measurements at a constant temperature) and pulsed field gradient NMR measurements. Grain size distribution is obtained by sieve analysis. The derivation of specific surface area or grain size from electrical measurements yield an improved characterization of unconsolidated sediments, which is independent of the conductivity of the pore water, and enables the prediction of the hydraulic permeability from measured electrical data. To evaluate the permeability predictions from electrical measurements, we will perform simultanous hydraulical conductivity and streaming potential measurements, as well as complex electrical measurements in the laboratory.