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Improved imaging of a karst aquifer using focused source electromagnetic and differentially normalized method: a qualitative analysis
Author(s) -
Souza de Araújo Oziel,
Chemas Hindi Eduardo,
Rigoti Augustinho,
Rigoti Fábio Henrique
Publication year - 2019
Publication title -
geophysical prospecting
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.735
H-Index - 79
eISSN - 1365-2478
pISSN - 0016-8025
DOI - 10.1111/1365-2478.12795
Subject(s) - induced polarization , geology , aquifer , karst , economic geology , geophysics , regional geology , ground penetrating radar , hydrogeology , groundwater , engineering geology , inversion (geology) , electrical resistivity and conductivity , magnetic dipole , environmental geology , hydrocarbon exploration , polarization (electrochemistry) , soil science , seismology , dipole , radar , geotechnical engineering , tectonics , computer science , volcanism , physics , paleontology , telecommunications , quantum mechanics , chemistry
Geophysical investigations using conventional techniques applied to groundwater exploration can often present strong limitations involving high financial costs, complex acquisition logistics and high ambiguity in results. Dispersion of the electric current flow, induced polarization) effects, cultural noises and shallow lateral heterogeneities represent the main problems faced by geoelectric methods in these types of surveys. Moreover, elements such as intrusions and mineralization at different depths may be responsible for signal attenuation as well as high resistivity in unsaturated zones and complex three‐dimensional formations or clayey zones cause variations in the electric current. The focused source electromagnetic and differentially normalized method approaches can help to solve some these issues. Aiming at a higher signal‐to‐noise ratio, the focused source electromagnetic method and approaches of the differentially normalized method, first applied to petroleum exploration, are tested on a groundwater target, in a karst environment sectioned by a diabase dyke. We performed the processing and analysis on real IP resistivity profiling data acquired with two‐way dipole‐dipole array, guided by magnetic data acquired on the same profile, mapping a diabase dyke. The inversion of focused source electromagnetic method/differentially normalized method was not performed, instead that we converted the induced polarization–resistivity data to a differential signal to qualitatively prove the presence of aquifer. Joint interpretation of focused source electromagnetic method curves and inverted two‐dimensional induced polarization–resistivity sections allowed for precise delineation of a conductive zone associated with the karst aquifer, le magnetics allowed for the definition of a neighbour dyke. The techniques have great potential in the aid of groundwater exploration, contributing substantially to the reduction of interpretation ambiguity. Focused source electromagnetic method/differentially normalized method/ approaches show that a simple linear combination of the conventional geoelectric data is able to remove the geological noise and provide the vertical focusing of the electric current.