TY - JOUR

T1 - Analysis of time-lapse data error in complex conductivity imaging to alleviate anthropogenic noise for site characterization

AU - Flores Orozco, A.

AU - Kemna, A.

AU - Binley, A.

AU - Cassiani, G.

N1 - © 2019 Society of Exploration Geophysicists. Use is subject to SEG terms of use and conditions

PY - 2019/3/5

Y1 - 2019/3/5

N2 - Previous studies have demonstrated the potential benefits of the complex conductivity (CC) imaging over electrical resistivity tomography for an improved delineation of hydrocarbonimpacted sites and accompanying biogeochemical processes. However, time-lapse CC field applications are still rare, in particular for measurements performed near anthropogenic structures such as buried pipes or tanks, which are typically present at contaminated sites. To fill this gap, we have developed CC imaging (CCI) results for monitoring data collected in Trecate (northwest Italy), a site impacted by a crude oil spill. Initial imaging results reveal only a poor correlation with seasonal variations of the groundwater table at the site (approximately 6 m). However, it is not clear to which extend such results are affected by anthropogenic structures present at the site. To address this, we performed a detailed analysis of the misfit between direct and reciprocal time-lapse differences. Based on this analysis, we were able to discriminate spatial and temporal sources of systematic errors, with the latter commonly affecting measurements collected near anthropogenic structures. Following our approach, CC images reveal that temporal changes in the electrical properties correlate well with seasonal fluctuations in the groundwater level for areas free of contaminants, whereas contaminated areas exhibit a constant response over time characterized by a relatively high electrical conductivity and a negligible polarization effect. In accordance with a recent mechanistic model, such a response can be explained by the presence of immiscible fluids (oil and air) forming a continuous film through the micro and macropores, hindering the development of ion-selective membranes and membrane polarization. Our results demonstrate the applicability of CCI for an improved characterization of hydrocarboncontaminated areas, even in areas affected by cultural noise.

AB - Previous studies have demonstrated the potential benefits of the complex conductivity (CC) imaging over electrical resistivity tomography for an improved delineation of hydrocarbonimpacted sites and accompanying biogeochemical processes. However, time-lapse CC field applications are still rare, in particular for measurements performed near anthropogenic structures such as buried pipes or tanks, which are typically present at contaminated sites. To fill this gap, we have developed CC imaging (CCI) results for monitoring data collected in Trecate (northwest Italy), a site impacted by a crude oil spill. Initial imaging results reveal only a poor correlation with seasonal variations of the groundwater table at the site (approximately 6 m). However, it is not clear to which extend such results are affected by anthropogenic structures present at the site. To address this, we performed a detailed analysis of the misfit between direct and reciprocal time-lapse differences. Based on this analysis, we were able to discriminate spatial and temporal sources of systematic errors, with the latter commonly affecting measurements collected near anthropogenic structures. Following our approach, CC images reveal that temporal changes in the electrical properties correlate well with seasonal fluctuations in the groundwater level for areas free of contaminants, whereas contaminated areas exhibit a constant response over time characterized by a relatively high electrical conductivity and a negligible polarization effect. In accordance with a recent mechanistic model, such a response can be explained by the presence of immiscible fluids (oil and air) forming a continuous film through the micro and macropores, hindering the development of ion-selective membranes and membrane polarization. Our results demonstrate the applicability of CCI for an improved characterization of hydrocarboncontaminated areas, even in areas affected by cultural noise.

KW - Air

KW - Crude oil

KW - Electric conductivity

KW - Groundwater

KW - Groundwater pollution

KW - Oil spills

KW - Polarization

KW - Systematic errors

KW - Biogeochemical process

KW - Complex conductivity

KW - Electrical resistivity tomography

KW - High electrical conductivity

KW - Mechanistic modeling

KW - Membrane polarization

KW - Seasonal fluctuations

KW - Site characterization

KW - Ion selective membranes

U2 - 10.1190/GEO2017-0755.1

DO - 10.1190/GEO2017-0755.1

M3 - Journal article

VL - 84

SP - B181-B193

JO - Geophysics

JF - Geophysics

SN - 0016-8033

IS - 2

ER -