Laboratory monitoring of CO₂injection in saturated silica and carbonate sands using spectral induced polarization

Abstract

Series of experiments were performed to study the spectral induced polarization (SIP) response of sands fully saturated with water, into which gaseous CO 2 or N 2 was injected, in the frequency range 0.5 Hz-20 kHz. Three main observations were made. (1) SIP parameters were always most affected by gas injection when the frequency of the injected signal was in the intermediate range (1 < f < 20 kHz). This point emphasizes the interest of broadening the frequency range of SIP surveys toward intermediate frequencies. It also implies that more work is needed in order to understand and quantify the parasitic effects that occur at this frequency range (EM coupling and electrode polarization). (2) Through all the experiments performed, we were able to distinguish the parameters variations caused by a reduction of the water saturation level (invasion of a resistive gas phase in the porous space) from those resulting from dissolution processes (increase of the electrical conductivity of the saturating water). (3) The quadrature conductivity σ , which is mainly linked to the capacitive properties and inductive response of the media, always shows relative variations stronger than the resistivity of the media, hence demonstrating the interest of the additional information provided by the SIP method as against the classical resistivity method.

The Relative Importance of Saturated Silica Sand Interfacial and Pore Fluid Geochemistry on the Spectral Induced Polarization Response

“…Indeed, no significant differences, due to the electrodes and/or sample holder, are visible between the “water + resistance” and the water tests. The observed electrode behavior and SIP resolution agree with other recent studies where the same SIP setup (impedance meter and electrodes) was used (Abdulsamad et al, ; Kremer et al, ). Kremer et al (, their Figure 3) and Abdulsamad et al (, their Figure 5) also reported similar water test values.…”

Modelling the spectral induced polarization response of water-saturated sands in the intermediate frequency range (102–105 Hz) using mechanistic and empirical approaches

“…Measurements were realized on a range of resistors going from 30 to 660 Ohm, which corresponds to the resistance range measured during the different experiments. A detailed description of this study is given in Kremer et al (2016). To summarize, we identified that non-zero phase values were observable in the intermediate frequency range, testifying of the existence of instrumental effects, and that their magnitude increases with frequency and with the resistance value.…”

“…During this experimental campaign, we mainly investigated the influence of the saturating water EC value σ w upon the SIP response of these sands. Full details about how the experiences were conducted and how the conclusions were reached are given in Kremer et al (2016). In the end, three main observations were made.…”

“…The modelling work presented in this paper is based on an attempt to reproduce some experimental data that was acquired during a laboratory scale experimental campaign (see Kremer et al 2016). In particular, we will here focus on modelling the SIP response of unconsolidated granular media fully saturated with water of different electrical conductivity (EC) values (σ w equal to 15, 40 and 100 mS m −1 , respectively, NaCl electrolyte).…”

“…Electrodes were tested for stability and ability to inject electrical current and measure electrical potential differences. A detailed description of all the tests conducted is given in Kremer et al (2016). In particular, successive measurements were performed during 5 hr on the same kind of media than those studied during the experiments (silica sand fully saturated with water whose EC is 40 mS m −1 ).…”