Estimation of soil petrophysical parameters from resistivity data: Application to oil-contaminated site characterization

Abstract

El método Sondeo Eléctrico Vertical (SEV), conocido desde 1912, ha cambiado sustancialmente durante los últimos 10años, apareciendo una nueva tecnología llamada Imagen de Resistividad (IR) con interpretación 2D de los datos de resistividad.Otra vía posible de desarrollo del método SEV es, partiendo de las relaciones existentes entre la resistividad eléctrica y losparámetros petrofísicos (PP), estimar estos últimos a partir de datos de IR. Para la realización práctica de este concepto fuedesarrollada la teoría del problema directo e inverso que relaciona la resistividad eléctrica con los PP. Cada trabajo de campodeberá incluir un levantamiento de SEV (IR), mediciones de resistividad eléctrica del agua subterránea con el objetivo dedeterminar su salinidad y la recolección de algunas muestras representativas de suelo del sitio con mediciones hechas enlaboratorio de la resistividad eléctrica como función de la salinidad del agua de poro, creando el modelo petrofísico del suelo deeste sitio. Esta tecnología puede ser utilizada tanto para la caracterización de sitios limpios como contaminados por hidrocarburos.Para el caso de sitios contaminados, los valores de los PP determinados en laboratorio, salinidad de agua y los datos de IR,permiten establecer la frontera petrofísica entre suelo limpio y contaminado, y por consiguiente, configurar la pluma contaminante.En este trabajo se incluyen, como ejemplos prácticos, los resultados de la aplicación de esta tecnología en algunos sitioscontaminados por hidrocarburos en México.

Joint interpretation of geoelectrical and volatile organic compounds data: a case study in a hydrocarbons contaminated urban site

“…Hydrocarbons are among the main factors of geological medium contamination. The effectiveness of electrical methods for the characterization, on surface and depth, of oil contaminated plumes has been reported by several authors (Vanhala, 1997;Modin et al, 1997;Atekwana et al, 2001;Osella et al, 2002;Delgado-Rodríguez et al, 2006;2006a). Just after contamination, a high resistivity anomaly delimits the contaminated zone.…”

“…Fischer et al (1996) studied a gasolinecontaminated site and they considered that VOC = 21 ± 2 ppm correspond to low contamination levels. Based on our experience (Ochoa et al, 2002;Delgado-Rodríguez et al, 2006, Mendez-Velarde et al, 2012, we had determined that in hydrocarbons contaminated sites VOC values greater than 20 ppm are associated with presence of hydrocarbons, either as free product, absorbed in the subsurface or dissolved in groundwater.…”

“…Once groundwater (or salinity) and soil resistivity are known, clay content and porosity are estimated for clean soil, and the geoelectric boundary is defined. The characteristics of the conductivity model, the procedure to determine the groundwater (from in-field measurements) and soil (from lab measurements) resistivity, and the equations for calculate the soil petrophysical parameters (including clay content and porosity) are explained in detail in Shevnin et al (2006; and Delgado-Rodríguez et al (2012).…”

Soil resistivity measurements to evaluate subsoil salinity in rice production systems in the Vietnam Mekong Delta

“…Group B is dominated by soils with high proportions of fine grain (>54%) and high moisture content (>43%) (Figures 6 and 7). Resistivity values of the samples clustered in group B are in the narrow range from 0.9 Ω m to 5.9 Ω m, which is the typical range for clay soil (Giao et al, 2003;Shevnin et al, 2006).…”

Application of Aquifer Delineation and Hydrogeophysical Techniques in Estimating Groundwater Recharge to Enhance Water Allocation in Groundwater-Dependent Areas, Northern Cape, South Africa

“…The field geophysical survey was conducted using the Geotrone electrical resistivity (ER) meter model G41 to measure the subsurface resistivity in the vertical electrical resistivity sounding using the Wenner array configuration [31]. During the investigation, the assumption was that geological sections are mainly horizontally layered (consisting of different geological layers) or pseudo-layered structures due to the influence of groundwater level and weathering [32]. This configuration was adopted due to its strongest signal strength, and greater sensitivity to vertical resistivity variation or structures lying horizontally concerning the rocks [31,33].…”