Model Studies on Some Aspects of Resistivity and Membrane Polarization Behaviour Over a Layered Earth*

Abstract

Electrolytic model tank experiments to study resistivity and time domain induced polarization (IP) response over layered earth models were initiated primarily to facilitate the understanding of field results. Alternate layers of clay and sand (or clay‐coated sand) with, in some cases, a surficial layer of water were assembled in the tank and resistivity and IP measurements made for a range of electrode spacings using the Wenner configuration. Graphite and silver‐silver chloride electrodes were used as current and potential electrodes respectively. Clay‐coated (3% by weight) sand was found to generate stronger polarization than either clay or sand alone. Apparent chargeability ma was observed to be positive for a nonpolarizable surface layer. For a polarizable surface layer, the sign of IP was controlled by the polarizability, the thickness of the second layer, and the spacing of the electrode spreads. The apparent chargeability ma can theoretically change sign from positive to negative and vice versa with a gradual increase in electrode spacing, and such negative IP effects were obtained in a few observations. A simultaneous decrease in IP and an increase in resistivity, which is a qualitative diagnostic feature for the occurrence of clean freshwater sand aquifers, could also be generated in the model tank experiment. Combined resistivity and IP soundings were carried out near Fredericton Junction and Tracy, New Brunswick, Canada. Field curves are presented along with the model curves for qualitative comparison and understanding of IP behaviour over a layered earth. Twenty‐five out of twenty‐seven soundings show only positive apparent chargeabilities, whereas two show chargeability sign changes (positive/negative/positive). The model study gives reason to believe that surface soils and Quaternary gravel boulder deposits near Fredericton Junction are relatively non‐polarizable. As an auxiliary experiment, sand and clay were taken in different proportions by weight and mixed thoroughly with water in a cement mixer. The mixtures were then compressed with a suitable die and plunger under 3.6 Pa pressure to prepare cylindrical samples of height 18 cm and diameter 15.5 cm. IP measurements were done on the flat faces using the Wenner configuration with a= 2 cm. Chargeability was found to be negative for 100 and 90% clay mixtures. It reached a positive maximum for an 80% clay‐20% sand mixture and then decreased gradually with increasing sand and decreasing clay content.

Grey wolf optimisation for inversion of layered earth geophysical datasets

“…The resistivity and MT data were inverted individually. Whereas IP data have been inverted simultaneously with resistivity data, doing so reduces ambiguity significantly (Roy and Elliot ; Olorunfemi ). Furthermore, DC resistivity data are a byproduct without any additional further cost of IP survey.…”

“…The field data of apparent resistivity (Figure (a)) and apparent chargeability (Figure (a)) analysed here have been adapted from Roy and Elliot (). Both apparent resistivity and apparent chargeability were acquired for hydrogeological studies in the Chatham area of New Brunswick, Canada, using Schlumberger array.…”

Induced polarization effect in reservoir rocks and its modeling based on generalized effective-medium theory

“…Vacquier et al (1957) [1] and Marshall and Madden (1959) [2] described, respectively, the time domain IP measurements on artificial clay and sand mixtures and a theoretical model for membrane (clay) polarization. Ogilvy and Kuzmina (1972) [11] described additional time domain measurements on artificial mixtures, while Roy and Elliot (1980) [12] used horizontal layers of varying clay-sand composition to model negative apparent chargeabilities due to geometric effects. Vanhala and Soininen (1995) [13] carried out laboratory measurements using spectral IP on soil samples in order to assess the effect of mineralogy, grain size distribution, moisture content, and electrolyte composition on the resistivity of soil material.…”

An efficient non‐linear least‐squares 1D inversion scheme for resistivity and IP sounding data

“…Many workers have indicated that by interpreting IP sounding (IPS) data together with DC resistivity measurements, the ambiguity in interpretation is significantly reduced. IPS curves often offer better resolution in delineating a layered structure than that of resistivity alone (Roy and Elliot 1980;Olorunfemi 1985). Note that the IP observables such as chargeability, frequency effect and phase are equivalent (Hohmann 1990).…”