Deep Geothermal Reservoirs with Fluid at Supercritical Conditions

Abstract

The temperature gradient between the core and the surface of the Earth results from a continuous flow of natural heat. This gradient embraces a wide range of thermal energy sources, which occupy different vertical spatial intervals. These resources can go from shallow depths (102 m), to medium depths (103 m), and to even deeper depths (104 m), reaching the immense temperatures of molten rocks. During the span of human life, deep geothermal energy, represents practically an infinite potential. Warm aquifers below oil reservoirs, hot dry rock, submarine reservoirs, and engineered geothermal reservoirs are examples of profound geothermal systems. The fluids contained in these systems could be found at supercritical thermodynamic conditions, at more than 374°C and pressures larger than 220 bar. These fluids have a higher density, contain more volumetric enthalpy and exergy, and could provide twenty times as much power, per unit fluid volume, as the normal geothermal fluids used today. The aim of this paper is to provide a brief description of water at supercritical conditions and of the power it contains.