An alternative methodology for the analysis of electrical resistivity data from a soil gas study

Abstract

S U M M A R YThe aim of this paper is to present an alternative method for the analysis of resistivity data. The methodology was developed during a study to evaluate if electrical resistivity can be used as a tool for analysing subsurface gas dynamics and gas emissions from landfills. The main assumption of this study was that variations in time of resistivity data correspond to variations in the relative amount of gas and water in the soil pores. Field measurements of electrical resistivity, static chamber gas flux and weather data were collected at a landfill in Helsingborg, Sweden. The resistivity survey arrangement consisted of nine lines each with 21 electrodes in an investigation area of 16 ×20 m. The ABEM Lund Imaging System provided vertical and horizontal resistivity profiles every second hour. The data were inverted in Res3Dinv using L 1 -norm-based optimization method with a standard least-squares formulation. Each horizontal soil layer was then represented as a linear interpolated raster model. Different areas underneath the gas flux measurement points were defined in the resistivity model of the uppermost soil layer, and the vertical extension of the zones could be followed at greater depths in deeper layer models. The average resistivity values of the defined areas were calculated and plotted on a time axis, to provide graphs of the variation in resistivity with time in a specific section of the ground. Residual variation of resistivity was calculated by subtracting the resistivity variations caused by the diurnal temperature variations from the measured resistivity data. The resulting residual resistivity graphs were compared with field data of soil moisture, precipitation, soil temperature and methane flux. The results of the study were qualitative, but promising indications of relationships between electrical resistivity and variations in the relative amount of gas and water in the soil pores were found. Even though more research and better data quality is necessary for verification of the results presented here, we conclude that this alternative methodology of working with resistivity data seems to be a valuable and flexible tool for this application.

Joint interpretation of geoelectrical and soil‐gas measurements for monitoring CO2 releases at a natural analogue

“…; Johansson et al . ). In these surveys, soil gas is typically sampled at the surface or in shallow soil depths (Chiodini et al .…”

“…This method allows reliable values of soil CO 2 degassing rates to be obtained, e.g. from environmental research undertaken, in geothermal and volcanic areas (Chiodini et al 1998(Chiodini et al , 2008Lewicki 2003;Carapezza et al 2009;Johansson et al 2011). In these surveys, soil gas is typically sampled at the surface or in shallow soil depths (Chiodini et al 1998;Ciotoli et al 1999;Yang et al 2003Yang et al , 2005Etiope and Lombardi 1995;Etiope et al 2005;Walia et al 2010).…”

Methane Occurrence and Quantification in a Very Shallow Water Environment: A Multidisciplinary Approach

“…Electrical resistivity data can be extremely valuable for analyzing the subsoil gas behavior and its relation to surface emissions. This is valid for hydrocarbon exploration and reservoir monitoring (Jiang et al., 2021; Senger et al., 2021), for gas hydrates studies (Coren et al., 2001; Kannberg & Constable, 2020; Weitemeyer et al., 2011) but also for evaluating other types of gas emissions, as, for example, from landfills (Johansson et al., 2011). Normally, these gas assessment studies are based on well‐logs or CSEM (marine controlled‐source electromagnetic) data.…”

Integrated earth resistivity tomography (ERT) and multilevel sampling gas: a tool to map geogenic and anthropogenic methane accumulation on brownfield sites

“…(Revil et al 2012;Ustra et al 2012;Adhikary et al 2014). This approach is often combined with other intrusive monitoring applications (Binley et al 2002;Johansson et al 2011;Schütze et al 2012). ERT employs a computer controlled data acquisition system in which a set of electrodes at the ground surface and in boreholes take resistivity measurements.…”

“…This paper presents a field study to outline the distribution of soil gas at a brownfield site with a complex history on the Tietê River plain, using direct sampling from multi-level monitoring wells and geophysical data from Earth Resistivity Tomography (ERT). ERT has been applied in many landfill studies to estimate the rate of gas emission (Georgaki et al 2008), identify fire-prone areas in municipal waste landfills (Frid et al 2009), and track methane migration from subsurface chambers until emission sites at surface (Johansson et al 2011). This study combines direct sampling with ERT imaging to get information about continuity of subsurface accumulations, which are difficult to determine by direct sampling methods only.…”