Reserve evaluation of a fault-conditioned aquifer: the Barreiras Aquifer in the coastal region of NE Brazil

Abstract

Saturated thickness is a vital parameter in the assessment of hydrogeological reserves. By considering thickness variations associated with faults, the present study aimed to evaluate the water reserves of an unconfined aquifer. The study area was the Barreiras Aquifer in the lower course of the Maxaranguape River in Brazil. The methodology involved morphotectonic and lithostratigraphic analysis, well profile correlation, and hydrogeological and geoelectrical analysis (vertical electrical sounding, VES). The morphotectonic analysis employed topographical (Shuttle Radar Topography Mission) and hydrographical data to support the structural characterization, considering the lack of outcrops with specific features in the area. The results of these assessments enabled the creation of a morphotectonic lineament map, highlighting the prevailing NE and NW directions. The hydrogeophysical cross sections obtained from geoelectrical inverse models and well data reveal saturated thickness values ranging from 19 to 66 m, featuring some lineaments as faults. The hydrogeological reserve was calculated based on 18 subareas associated with blocks resulting from structural compartmentalization. Based on an area of approximately 250 km², the average saturated thickness for each subarea, and an average effective porosity of 7.6%, the saturated reserve is estimated to be 8.7 × 10⁸ m³.

Keywords:
Hydrogeological reserves; faults; morphotectonic analysis; geoelectrical models; Barreiras Aquifer