Exploration of Ain Al-Harrah-Al-Lith Geothermal Field in Saudi Arabia Using EM Methods

With its 2030 vision, Saudi Arabia initiated reducing its dependence on fossil-based energy with renewable energy development, including geothermal resources, a very high priority. Previous studies have shown that Saudi Arabia has promising geothermal resources. The most prominent sites are located around Al-Lith, with four hot springs, where Ain Al-Harrah has the highest temperature and may provide the Al-Lith region with long-term electricity. Our key objective is to explore more comprehensively the prospect of geothermal resources around the Ain Al-Harrah hot spring with multi-physics. Electromagnetic (EM) methods cover a variety of applications during the energy transition and the development of renewable resources, including geothermal energy in Saudi Arabia. EM techniques are increasingly utilized to explore and characterize geothermal reservoirs for energy production or cooling/heating purposes. To achieve this goal, we are carrying out multi-physics measurements in the area and report initial results here. With the plan of drilling several wells, we initially used magnetotellurics to prepare for more detailed deep Controlled Source ElectroMagnetics later. The broadband magnetotellurics (MT) data in the period range 0.001-60 s for three different sampling frequencies were acquired using KMS-820 acquisition systems. Transient Electromagnetic (TEM) and Audio-Magnetotelluric (AMT) soundings were also collected to correct the possible static shift effect on the MT data. All the collected frequency and time-domain EM data were of high-quality. There are also initial 3D gravity results. Τhe 2D and 3D inversion results indicated similar results from top to bottom, five noteworthy features: (1) a near-surface low-resistivity (50-100 ohm.m) zone with an average thickness of less than 100 m, which can be interpreted as sediments fully saturated with freshwater (2) a medium to high resistivity unit (900-3000 ohm.m) appear at different depths, from 100-4000 m below the surface, representing the fractured basement, (3) a very high resistivity body (3000-7000 ohm.m) associated with the basement, (4) the low resistivity zone (60-125 ohm.m bulk resistivity) representing the geothermal fluids plume moving upward from the depth of 5-6 km below the surface, through the fractures (high permeability) zone reaching the depth of 500 m below the surface creating a convection cell, and (5) the hot-body with very low resistivities, 10-30 ohm.m, at the average depth of 6.5 km below the ground surface. Moreover, it is important that the surface manifestation of hot springs with a temperature of about 70-80^oC, also exists in this area. However, only drilling operations will reveal the geothermal potential, while the MT survey points to new drill locations. In the end, to gain deeper insight into the geothermal system, there are two main recommendations for any future research in the Al-Lith area as follows: (1) to conduct CSEM data acquisitions to gather high-resolution dense spatial data and provide an enhanced 3D subsurface image, and (2) to drill an exploratory well till the depth of 1 km to confirm the preliminary conceptual geophysical model and improve the interpretation of the collected data by applying constraint inversion.