Electrical Resistivity Characterization of Anisotropy in the Biscayne Aquifer

Abstract

Electrical anisotropy occurs when electric current flow varies with azimuth. In porous media, this may correspond to anisotropy in the hydraulic conductivity resulting from sedimentary fabric, fractures, or dissolution. In this study, a 28-electrode resistivity imaging system was used to investigate electrical anisotropy at 13 sites in the Biscayne Aquifer of SE Florida using the rotated square array method. The measured coefficient of electrical anisotropy generally ranged from 1.01 to 1.12 with values as high as 1.36 found at one site. The observed electrical anisotropy was used to estimate hydraulic anisotropy (ratio of maximum to minimum hydraulic conductivity) which ranged from 1.18 to 2.83. The largest values generally were located on the Atlantic Coastal Ridge while the lowest values were in low elevation areas on the margin of the Everglades to the west. The higher values of anisotropy found on the ridge may be due to increased dissolution rates of the oolitic facies of the Miami formation limestone compared with the bryozoan facies to the west. The predominate trend of minimum resistivity and maximum hydraulic conductivity was E-W/SE-NW beneath the ridge and E-W/SW-NE farther west. The anisotropy directions are similar to the predevelopment groundwater flow direction as indicated in published studies. This suggests that the observed anisotropy is related to the paleo-groundwater flow in the Biscayne Aquifer.

Comparison of REV size and tensor characteristics for the electrical and hydraulic conductivities in fractured rock

“…method is of particular interest because (i) numerous field, laboratory and theoretical studies have demonstrated that geoelectrical data are significantly affected by the presence and characteristics of fractures such as density, orientation and aperture (Taylor & Fleming 1988;Jinsong et al 2009); (ii) ER measurements can be acquired using a variety of electrode configurations and spacings, thereby offering the potential to obtain information on subsurface properties over a wide range of spatial scales (Telford et al 1990;Everett 2013); and (iii) strong analogies between fluid and electric current flow in fractured media suggest that geoelectrical data may contain important information regarding the corresponding hydrogeological properties (Brown 1989;Van Siclen 2002). As a result, ER studies in fractured rock have been widespread and include the development and application of anisotropic tomographic methods (Pain et al 2003;Herwanger et al 2004a,b;Li & Spitzer 2005;Greenhalgh et al 2009); the use of azimuthal resistivity surveys to estimate predominant fracture orientations (Taylor & Fleming 1988;Al Hagrey 1994;Lane et al 1995;Busby 2000) along with, in many cases, properties of the hydraulic conductivity tensor (Ritzi & Andolsek 1992;Skjernaa & Jørgensen 1994;Steinich & Marin 1996;Skinner & Heinson 2004;Boadu et al 2005;Boadu et al 2008;Yeboah-Forson & Whitman 2014) and the acquisition of surface-based electrical resistivity tomography (ERT) profiles for the identification and characterization of fracture zones (Porsani et al 2005;Sharma & Baranwal 2005;Yadav & Singh 2007;Robert et al 2011Robert et al , 2012.…”

Imageamento Elétrico Como Ferramenta De Monitoramento Do Comportamento Da Água No Solo

“…Dentre os métodos geofísicos, o método elétrico de corrente contínua, baseado na medição da resistividade elétrica, permite o monitoramento da umidade do solo e a identificação do nível da água em aquíferos (Fetter, 1994). Esse método representa uma alternativa barata, não invasiva e simples de monitoramento geoelétrico da subsuperfície rasa (Loke, 2001;Ren e Tang, 2014;Yeboah-Forson et al, 2014).…”

Seismic Refraction and Electrical Resistivity Tests for Fracture Induced Anisotropy in a Mountain Watershed

“…Geophysical methods help us better understand fracture induced azimuthal anisotropy, specifically, 2D seismic refraction, and ER methods (Yeboah-Forson and Whitman, 2014;Busby, 2000;Zhu et al, 2012;Holbrook et al, 2014;Befus et al, 2011;Babcock et al, 2015;Greenhalgh et al, 2009;Matias, 2002;Li and Uren, 1997). Fracture presence introduces seismic azimuthal anisotropy (Tsvankin and Grechka, 2011;Lynn and Michelena, 2011;Burns et al, 2007;Crampin, 1985), and electrical azimuthal anisotropy (Berryman and Hoversten, 2013;Greenhalgh et al, 2010;Yeboah-Forson and Whitman, 2014;Taylor and Fleming, 1989).…”

“…Fracture presence introduces seismic azimuthal anisotropy (Tsvankin and Grechka, 2011;Lynn and Michelena, 2011;Burns et al, 2007;Crampin, 1985), and electrical azimuthal anisotropy (Berryman and Hoversten, 2013;Greenhalgh et al, 2010;Yeboah-Forson and Whitman, 2014;Taylor and Fleming, 1989). If hydraulic anisotropy exists in the subsurface, but is not taken into account, geophysical measurements can be interpreted incorrectly.…”

“…Some studies have resulted on measurements of electrical anisotropy coefficients (Yeboah-Forson and Whitman, 2014;Busby, 2000;Zhu et al, 2012). It has been suggested that most cases of anisotropy reported in the literature have been most likely misinterpretations (Greenhalgh, 2008).…”