Geophysical Exploration of the Western Saudi Arabian Geothermal Province: First Results from the Al-Lith Area

Abstract

Hot spring with temperatures around 96°C and 56°C are located in the Ain Al-Harrah and Wadi Markub sites (Al-Lith province, Western Saudi Arabia). They are part of a number of surface geothermal evidences spread in the southwestern part of Saudi Arabia. Based on recent geological and geochemical surveys, a geophysical data acquisition was completed in the area in 2013, encompassing MT and seismic reflection. The main objective of this geophysical work is imaging of the local structural setting, with particular reference to fracture/fault systems that may enhance porosity/permeability of the granite rocks in place and let the hot water escape from the reservoir through the hot springs. Geochemical analysis indicates that meteoric water is heated at rather shallow depth in the area of study. Geochemical indications and logistic constraints drove the design of a high resolution geophysical survey that utilized a 96-channel seismograph and a 100 kg weight drop seismic source to complete 16 seismic profiles in the area centered about one of the hot springs. MT measurements were performed (16 stations) on a 12 hours time span. The results show a clear resistivity anomaly located around 2500 m from topographic surface. Several fractures are further observed in the imaged volume up to an approximate depth of 800 m. Surface geology and geophysical data provide information that is compatible with a circulation of fluids in a complex system of fracture related to at least two principal directions (i.e. N and NW-SE trending). Local conditions (temperature, flow rate, structural setting) encourage an extension of the geophysical work done to date for the reconstruction of the regional geothermal conditions in the perspective of direct uses and electricity generation.