292 Geophysics in Geothermal Exploration • Geothermal Heat Pumps (GHPs): GHPs leverage stable ground temperatures (10–16 °C) found a few meters below the surface to provide efficient heating and cooling for buildings. This technology is widely applicable and doesn’t require high temperatures. Classifying by geological settings: • Shallow Geothermal Systems: This involves tapping into the moderate temperatures found at shallow depths, typically up to a few hundred meters, to power geothermal heat pumps. • Sedimentary Basin Systems: In regions with porous/fractured/karstified sedimentary layers, geothermal reservoirs of hot water can be found at moderate depths, often used for direct heating or low-temperature electricity production. • Volcanic Systems: High-temperature geothermal reservoirs in volcanic regions are ideal for electricity generation. Countries like Indonesia and New Zealand are renowned for tapping volcanic geothermal resources for power. • Rift and Fault Zones: In areas where tectonic plates pull apart or fracture, crust is thinner, and heat flow is higher than usual promoting geothermal reservoir development in conjunction with volcanic activity. • Fractured Granite and Crystalline Rock: Some geothermal resources are found in fractured hard rock, where engineered geothermal systems (EGS) create or enhance pathways for water to circulate and absorb heat. Conventional and non-conventional geothermal resources: • Conventional Hydrothermal Systems: These systems involve naturally occurring hot water or steam reservoirs. They are typically used in volcanic or highgeothermal-gradient areas and are well-suited for electricity generation. • Non-Conventional Systems (Enhanced Geothermal Systems and Closed Loop). In regions lacking natural hydrothermal reservoirs, EGS can artificially create or enhance pathways in hot dry rock/low permeability rocks for water to circulate, picking up heat for use at the surface. Closed-loop systems involve circulating a working fluid through pipes underground without any interaction with natural groundwater, making them potentially viable and after a complete economic assessment in a broad range of geological environments. These advancements allow us to make use of geothermal energy far beyond natural manifestations, making it a sustainable and reliable source of heat and power. The need to characterize subsurface is critical and require the use of geophysical techniques. A range of geophysical techniques Historically, geophysical methods have played a pivotal role in the exploration of oil, gas, and minerals, serving as the backbone of resource discovery for decades. There are various geophysical methods, each based on distinct theoretical principles, that
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