Supercritical geothermal reservoir revealed by a granite–porphyry system. (September 2016)

• Record Type: Journal Article
• Authors: Tsuchiya, Noriyoshi; Yamada, Ryoichi; Uno, Masaoki
• Is Part Of: Geothermics. Volume 63(2016:Sep.)
• Page Start: 182
• Page End: 194
• Publication Date: 2016-09
• Subjects: Supercritical geothermal reservoir -- Porphyry copper mineralization -- Granite–porphyry system -- Mineral filling veins -- Geofluids; Hydrogeology -- Periodicals; Geothermal resources -- Periodicals; Énergie géothermique -- Périodiques; GEOTHERMAL ENGINEERING; GEOTHERMAL ENERGY; GEOTHERMAL EXPLORATION; Geothermal resources; Hydrogeology; Periodicals; Electronic journals; 621.44
• DOI: 10.1016/j.geothermics.2015.12.011
• Languages: English
• ISSNs: 0375-6505

Abstract

Highlights: A granite-porphyry system was studied as a natural analog of a supercritical geothermal reservoir. Veinlet systems (quartz veins, hydrothermal breccia veins and glassy veins) provide important information on supercritical geofluids and their evolution to subcritical conditions. The glassy veins form at 500–550 °C under lithostatic pressure. The change from lithostatic pressure to hydrostatic pressure was sudden resulting in hydrothermal breccia veins. A geologic model for "beyond brittle" and "Supercritical" geothermal reservoir was revealed. Abstract: To understand the geological properties of a supercritical geothermal reservoir, we investigated a granite–porphyry system as a natural analog. Quartz veins, hydrothermal breccia veins, and glassy veins are present in Neogene granitoids in NE Japan. The glassy veins formed at 500–550 °C under lithostatic pressures, and then pressures dropped drastically. The solubility of silica also dropped, resulting in formation of quartz veins under a hydrostatic pressure regime. Connections between the lithostatic and hydrostatic pressure regimes were key to the formation of the hydrothermal breccia veins, and the granite–porphyry system provides useful information for creation of fracture clouds in supercritical geothermal reservoirs.