ERT monitoring of gas injection into water saturated sands: Modelling and inversion of cross-hole laboratory data

Abstract

A set of laboratory experiments were performed in order to investigate the capacity of the electrical resistivity tomography method to detect and monitor the circulation of gaseous CO 2 into geological media. The experiments consisted of injecting reactive (CO 2) or inert (N 2) gases into reactive (carbonate) or inert (silica) sands saturated with water. The laboratory setup was a metric-scale cylindrical tank instrumented with electrodes placed on vertical rods, hence simulating a borehole to borehole monitoring network. The results demonstrated that the ERT method can efficiently detect, locate and image gas circulation plumes. Two main behaviors were identified: either an increase of the medium resistivity due to the invasion of the porous space by an electrically insulating gas phase, or a resistivity decrease induced by dissolution processes that enhance ionic concentrations in the saturating water. The observed anomalies showed varying geometric shapes depending on which type of sand was used. A 3D cellular automaton model was built and managed to reproduce different gas plumes circulation patterns and the electrical resistivity response associated. This modeling work confirmed the link existing between the shapes of the resistivity anomalies, the gas plumes geometry and the particle size distribution of the sand. Through a numerical sensitivity analysis, several measuring protocols were tested and developed in order to improve the imaging capacity of the electrical resistivity method. Results demonstrated that the most efficient protocol was different depending on the shape of the gas plume, thus stressing the importance of having a priori knowledge on the geological, lithological and hydraulic characteristics of the subsurface, in order to correctly assess the most likely gas plume geometry and hence design the most adapted monitoring protocol.

Geophysical response to simulated methane migration in groundwater based on a controlled injection experiment in a sandy unconfined aquifer

“…Our numerical simulations show that ERT is effective at monitoring macroscale gas accumulation primarily around an injector where gas accumulation would be most significant, which is consistent with recent laboratory experiments using ERT to image CO 2 and N 2 gas circulation (e.g., Kremer et al, 2018). However, our results also indicate that the ERT method will be much less effective at resolving thin pools of gas extending beyond the main bulb.…”

Three‐Dimensional Time‐Lapse Geoelectrical Monitoring of Water Infiltration in an Experimental Mine Waste Rock Pile

“…Despite these recent successful applications, qualitative and quantitative interpretation of ERT datasets in terms of hydrogeological properties remain very challenging, especially when both moisture content and groundwater ionic content may change simultaneously (Kemna et al, 2002; Koestel et al, 2008; Singha and Gorelick, 2005). This issue has been addressed for laboratory studies where one (or several) physical parameters can be controlled and the medium is usually homogeneous (Bechtold et al, 2012; Binley et al, 1996; Garré et al, 2010; Koestel et al, 2008; Kremer et al, 2018; Slater et al, 2000). Large‐scale field studies usually assume that either solute conductivity or volumetric water content is constant over time to provide quantitative hydrogeological results by using empirical or laboratory petrophysical relationships (Clément et al, 2014; Dimech et al, 2018; Dumont et al, 2018; Hübner et al, 2017; Jayawickreme et al, 2008; Kuras et al, 2009; Uhlemann et al, 2017).…”