Evaluation of resistivity anisotropy parameters in the Eastern Mitidja basin, Algeria, using azimuthal electrical resistivity tomography

Abstract

We study electrical anisotropy using azimuthal electrical resistivity tomography (A‐ERT) for identifying geological layers and determining the preferential aquifer flow direction. The work presented in this paper aims at calculating the anisotropy coefficient from the inverted resistivity measurements, relating the geophysical results to the site geology and water flow direction, and comparing the results with those obtained from prior studies using hydrogeological approaches. The study area is located in the Eastern Mitidja basin, about 15 km east of Algiers. The work carried out includes three measurement points, totalling 24 ERT profiles. For each point, eight A‐ERT profiles, using Wenner–Schlumberger array configuration, were performed every 22.5° around a fixed central point. The data processing includes two‐dimensional inversion of each profile, representation of the inverted resistivities at the central points as a function of the azimuth in polar diagrams, and implementation of an inversion program to determine the best fitting azimuthal anisotropy parameters. The origin of electrical anisotropy is probably due to grain alignment, which is often observed in fine‐grained sediments such as clays and some sands. This alignment creates a higher electrical resistivity perpendicular to the alignment than parallel to it, which is an indicator for higher hydraulic permeability in the minimum resistivity direction, which corresponds to the preferential groundwater flow direction.

The effect of near‐surface azimuthal anisotropy on a joint interpretation of seismic and electrical resistivity data

“…Aissaoui et al . (2019) evaluated the electrical resistivity anisotropy with azimuthal electrical‐resistivity tomography. Furthermore, it was used to determine the direction of groundwater flow.…”

“…To study fracture systems in the near-surface, Taylor and Fleming (1988) apply azimuthal observations to characterize fracture systems. Aissaoui et al (2019) evaluated the electrical resistivity anisotropy with azimuthal electrical-resistivity tomography. Furthermore, it was used to determine the direction of groundwater flow.…”