An integrated geophysical study for inferring the subsurface setting of water-bearing aquifers: case study at Wadi al-Dawasir area, Saudi Arabia

Abstract

Wadi al-Dawasir area is very important province in Saudi Arabia. It contains the main water aquifer that stores a proven groundwater reserve (Wajid aquifer). This study aims to investigate the subsurface features of this aquifer (thickness, depth to basement and the structural elements) using an integrated gravity (2D profiles) and aeromagnetic data interpretation (RTP, low-pass and high-pass maps). Gravity data are measured in the field using CG-5 AutoGrav, while magnetic data are taken from a survey made by Saudi Geological Survey. The interpretation of aeromagnetic data revealed presence of interesting structural elements trending toward N–S, NNE–SSW, WNW and NNW–SSE directions. Positive magnetic anomalies are found indicating the presence of anticlinal blocks and strike-slip fault patterns. These structural elements are associated with the prevailing Najd fault and the transform fault systems. Gravity data showed that the depth to basement vary from 600 to 1150 m, giving rise to local basins with a considerable range of aquifer thicknesses (250–700 m). Finally, a basement relief map is conducted based on an integrated interpretation of the magnetic, gravity and seismic outputs. It shows an increase in depth (aquifer thickness) from south to north. The petrophysical analysis of the Wajid Formation assigns good aquifer properties in the upper section. In terms of subsurface features determinations, the concluded results (top of basement, thickness of aquifer and the prevailing structural elements) are matched with the interpreted seismic section, indicating a good compatibility of data.