Regional assessment of geothermal energy resources in Saudi Arabia

This dissertation evaluates the potential for geothermal energy throughout Saudi Arabia, including the Quaternary volcanic fields, sedimentary basins, and hot springs. The study concludes that there is significant untapped potential to extract geothermal energy from deep hot sedimentary aquifers (HSA) in the greater Arabian and Red Sea Basins. However, previous studies overestimated the geothermal potential in volcanic fields and hot springs. The critical success factors in volcanic fields are (1) evidence of Holocene volcanism, (2) presence of shallow magma chambers, and (3) presence of groundwater aquifers. However, evidence indicates that most of the basalt fields lack shallow magma chambers and were fed by dikes directly from the mantle. Furthermore, volcanic fields over the Arabian Shield lack underlying aquifers. The only potential is in the lava fields north of the Shield, which are underlain by Paleozoic aquifers. This study reveals that the hot springs in the Proterozoic basement near Al-Lith, Jizan and Hajjah (Yemen) discharge artesian groundwaters that were heated by the continental geothermal gradient. They are recharged by rainwater infiltration through the uplifted basement in the Asir highlands. They have no potential as sources of geothermal energy due to low temperatures, low fracture porosity, and permeability in the basement. In a desert setting, hot saline waters (>100 °C) from deep hot sedimentary aquifers (HSA) are suitable for direct use in cooling (e.g., using absorption chillers), as an energy source for desalination of seawater or brackish groundwaters inland, and for heating in industrial applications. The hot waters can be circulated between producer and injector wells to maintain reservoir pressure. This untapped source of low enthalpy geothermal energy has large potential in Saudi Arabia, where the subsurface geology is well known. In the greater Arabian Basin, where the geothermal gradient is 22-35 °C/km, there are prolific aquifers at depths of 2-3 km whose temperatures exceed 100 °C. These aquifers include the Saq-Sarah aquifers in the shallower western parts of the basin, Minjur further east, and the Arab-D and Sulaiy-Buwaib aquifers along the east coast. The favorable areas are extensive, broad synclinal lows between the narrow hydrocarbon-bearing anticlinal structures. The Red Sea Basin also contains HSA at depth, but practical extraction is limited to the onshore coastal basins. These basins contain two geothermal plays: (1) deep siliciclastic aquifers of the Al Wajh and Barqan Formations, which fill the Miocene half grabens, and (2) post-salt sandstones in the Ghawwas Formation. The latter play is particularly prospective along the coast near Jizan, where the geothermal gradients are high > 45 °C/km. In both plays, the main challenge is finding porous and permeable aquifers at depth.