The impact of conductive layers on depth of investigation estimation in 2D geoelectrical imaging: A case study of West Bani Mazar, El Minia, Egypt

Abstract

The appearing of clay (conductive) layer(s) at different depths of the lithological succession has been widely observed in the Upper Egypt district. This phenomenon has dramatic effects on the resultant depth of investigation of any geoelectrical survey of such environment. Study the effect of such layers on estimating Depth of Investigation (DOI) is the main goal of this article. Because the reliability of the Two Dimensional Electrical Resistivity Imaging (2DERI) models alters rapidly with changing conductive layers depths as well as noisy data ratios, an accurate estimation of DOI is critical to help geophysists determining the optimum hydrogeophysical survey design in clayey environments. The modified depth of investigation method which mainly depends on the statistical method is applied to estimate the DOI. In this article, the study is based on synthetic and field data sets. Wenner (W), Wenner Schlumberger (WSC) and Dipole-Dipole (DD) electrode arrays were chosen to clarify which electrode gives larger DOI in the conceptual models (presence conductive layer at 0, 50 and 100 m depths) from the ground surface. Moreover, the study will include a test for the effect of adding 10% noise to synthetic data sets on DOI estimation.It is well known that Wenner array better matches with layer-like targets, DD with 3D horizontally limited ones. Based on these results, there is a relationship between DOI and depth of the conductive layer [larger DOI is recorded when conductive layer exists at deeper depths and vice versa].This could be related to the existence of a conductive layer in the lithology succession that can limit the current to flow vertically and subsequently, affects DOI estimation. 2D ERI field data from West Bani Mazar, El Minia is used to support the supposed first conceptual model on DOI estimation.