Correlation of vertical electrical sounding and borehole-log data for delineation of saltwater and freshwater aquifers

Abstract

In a case history from the Mahanadi basin (India), we demonstrate the use of resistivity data from electric-log soundings and from borehole logs to discriminate between saltwater and freshwater aquifers. We use interpreted data from eight surface-based vertical electrical soundings (VES) and electric well logs from three boreholes in this study. We establish a quantitative relation among longitudinal unit conductance S (obtained from VES), water resistivity [Formula: see text], and layer thickness h. We show that ambiguities in resistivity data interpretation limit its ability to distinguish between freshwater and saltwater aquifers. Electric well-log data interpretation is much more accurate but requires boreholes, which are not cost effective when exploring for groundwater. Integrating well-log-based estimates of [Formula: see text] into resistivity interpretation of surface-based soundings improves its ability to discriminate freshwater aquifers while maintaining cost-effective exploration.

Evaluation of DC, FDEM and IP resistivity methods for imaging perched saltwater and a shallow channel within coastal tidal flat sediments

“…Through these surveys, the applied methods were assessed to characterize and image the shallow sediments within the tidal flat deposits. Schlumberger electrical soundings are usually designed to discriminate between electrical resistivities associated with lithological and/or hydrological characteristics (Hodlur et al, 2006). Their inherent capability is to detect changes in the electrical conductivity of the subsurface layers that reflect the fluid content of such layers (Hwang et al, 2004).…”

Correlation of vertical electrical sounding and electrical borehole log data for groundwater exploration

“…The resistivity of formation water R w can also be estimated by using the empirical formula, obtained by correlating CL and 1/ R w . The relation between CL and R w is given by the following equation (Hodlur et al 2006): where CL is the longitudinal unit conductance in Siemens (S) and R w is the resistivity of formation water in Ωm.…”

“…Due to the above factors, the electrical borehole record is more realistic. The surface electrical sounding data interpretation becomes more realistic when they compare well with electrical borehole data interpretation (Steeple 2005;Hodlur, Dhakate and Andrade 2006;Mark et al 2007). If a quantitative relation between the borehole geophysical parameters like R t and F and the surface resistivity sounding parameter (namely the longitu-dinal unit conductance CL) exists, the interpreted electrical sounding data can be easily translated into electrical borehole log data for some parameters like formation resistivity R t and formation resistivity factor F. We have successfully attempted to retrieve electrical borehole log parameters like true formation resistivity R t and formation resistivity factor F from longitudinal unit conductance obtained from interpreted vertical electrical sounding data.…”

Resolution of freshwater and saline water aquifers by composite geophysical data analysis methods

“…In other regions, unsaturated zones, brackish water saturated zones and freshwater zones recorded resistivities <5 m, by virtue of the principle of equivalence. Hodlur et al (2006) established an empirical relationship between longitudinal unit conductance and water resistivity and used this relation for the identification of fresh and saline water zones. Interpreted geophysical data of vertical electrical soundings clustering around electrically log boreholes were used for correlation.…”