DAGE Method (Detection of Geoelectrical Anomalies) applied to electrical resistivity: overcoming challenges in the location of boreholes in crystalline environments

Abstract

This study presents the development of the DAGE method (Detection of Geoelectrical
Anomalies), an innovative approach to enhance the accuracy of tubular well siting in crystalline rock environments. Prior to DAGE, there was no established methodology linking geophysical
studies to drilling efficiency in this type of terrain. The method is based on the geometric
analysis of geoelectrical anomaly curves, apparent resistivity values, and lithotype and
productivity data from 30 wells in the municipality of Iracema, Ceará, Brazil. The research
identified two geoelectrical curve patterns: the "U" shape, characterized by broad anomalies with two or more low resistivity values (<200 Ωm), commonly associated with fractured gneissic rocks, and the "V" shape, associated with narrow anomalies with low to moderate resistivity (200-400 Ωm), typical of granitic rocks. The application of DAGE achieved an 80% success rate in well siting, with 24 productive wells and an average yield of 3.56 m³/h, 78% higher than the regional average of 2.0 m³/h in the crystalline basement of Ceará. DAGE stands out as a
significant technical-scientific contribution, substantially reducing the number of dry wells in crystalline terrains. The greater the extent of "U"-shaped geoelectrical anomaly curves detected using DAGE, the higher the probability of productivity for the located well, making this method
applicable to any crystalline context (igneous and metamorphic rocks).