Geysers and Larderello: a geochemical comparison of steam systems
The Geysers are currently the largest exploited geothermal field in the world with electrical production of approximately 1800 MW. Produced fluid is entirely saturated or slightly superheated steam, although production volumes require mainly liquid water (by weight) in the reservoir. The production mechanism of vapor-dominated geothermal reservoirs exemplified by the Geysers and Larderello, as studied geochemically and by simulation, consists of in-situ vaporization of relatively immobile liquid water on surfaces and small fractures to form highly mobile steam that moves along large fractures and possibly solution cavities to wells. Workers have suggested that, in the natural state, steam moved up and laterally away from boiling centers through a two-phase liquid-vapor zone toward near-surface and distal zones of conductive heat loss and steam condensation. Condensed liquid water flowed slowly down through the two-phase zone to deep, liquid-saturated zones where it flowed back to the boiling centers. Geochemical evidence of this subsurface hydrologic cycle is found at Larderello in lateral variations in steam chemistry produced by partial condensation of laterally flowing steam and in sequential three-part steam sources: condensate, two-phase, and deep brine. Although similar lateral variations in steam chemistry across parts of the Geysers indicate that lateral flow and partial condensation were active in the natural state, there is little evidence at the Geysers for the sequential production of sources seen in Larderello. However, large variations in steam chemistry across the Geysers may indicate that different sources of steam exist concurrently. Production-related changes in steam chemistry can be caused by accelerated vaporization, the development of pressure gradients, changing sources of steam, the presence or absence of recharge, and even well-bore effects.
- Research Organization:
- Geological Survey, Menlo Park, CA
- OSTI ID:
- 5055331
- Report Number(s):
- CONF-8608105-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 70:7; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
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