A HOT DRY ROCK GEOTHERMAL ENERGY CONCEPT UTILIZING SUPERCRITICAL CO2 INSTEAD OF WATER

摘要

A novel renewable energy concept -- heat mining using supercritical CO_2 (SCCO_2) for both reservoir creation and heat extraction -- is here proposed. This concept builds on the earlier, very extensive Hot Dry Rock (HDR) research and development effort conducted by Los Alamos National Laboratory at Fenton Hill, NM. This previous field testing very convincingly demonstrated the viability of the HDR concept based on the results obtained from the production testing of two separate confined reservoirs for almost a year each. However, using SCCO_2 instead of water in a closedloop HDR system offers three significant advantages over the original Los Alamos concept: 1. The very significant wellbore density difference between the cold SCCO_2 in the injection well (about 0.96 g/cc) and the hot SCCO_2 in the production wells (about 0.39 g/cc) would provide a very large buoyant drive (i.e., thermal siphoning), markedly reducing the circulating pumping power requirements over those of a comparable water-based HDR system. 2. The inability of SCCO2 to dissolve and transport mineral species from the geothermal reservoir to the surface would eliminate scaling in the surface piping, heat exchangers, and other surface equipment. 3. HDR reservoirs at temperatures in excess of 374 deg C (the critical temperature for water) could be developed without the problems associated with silica dissolution in water-based systems, potentially providing increased thermodynamic efficiency.