Electromagnetic Insights: 3D Subsurface Modeling of Al-Hassa, Saudi Arabia

Al-Hassa area features Saudi Arabia's largest oasis and one of the world's largest naturally irrigated land. Moreover, Al-Hassa area is very close to Ghawar, known as the largest conventional oil-field in the world. Additionally, more than 280 natural springs used in the past to water the farmland where the water in some of the springs, is used to be warm. The quality of water also exhibits spatial variations, hinting at a complex subsurface that must be characterized. Finally, the available geological information from outcrops, are very limited, since the majority of the study area is covered by a sand-layer. Based on the above, it seems that this important for its natural resources (oil gas, groundwater, low-enthalpy geothermy) area is partly unexplored or the data are not available. The purpose of this work is to reconstruct the 3D subsurface geophysical structure of the study area by combining different geophysical electromagnetic (EM) methods. Thus, three EM geophysical methods to construct a detailed 3D model of the subsurface were applied. Specifically, 46 magnetotelluric (MT) stations, 6 audio magnetotelluric (AMT) stations, and 35 transient electromagnetic (TEM) stations were acquired within Al-Hassa National Park. The data from all these EM soundings were processed and integrated to achieve the highest resolution from the surface to the maximum depth of investigation. 2D and 3D processing, and joint interpretation was applied to all EM data. The EM findings were confirmed by gravity measurement conducted in the same area. The integration of various geophysical data sets, including TEM, MT, AMT and gravity data, uncovers lateral discontinuities in resistivity, a complex structure, and fracture zones acting as pathways or barriers to groundwater flow. This comprehensive modelling approach offers invaluable insights into the subsurface dynamics, enhancing our understanding for the complexity of the study area.