The vapor-dominated reservoirs of Larderello, Italy, The Geysers, California, and Matsukawa, Japan, have been under exploitation for several decades. Much geological, geophysical, geochemical, and reservoir engineering information on these systems has been published in the technical literature. Conceptual models have been developed which explain important physical and chemical conditions and processes in these systems (Ferrara et al., 1970; Sestini, 1970; White et al. 1971; Truesdell and White, 1973; Weres et al., 1977; DíAmore and Truesdell, 1979; Pruess and Narasimhan, 1982). Vapor-dominated reservoirs are overlain by a caprock of generally low permeability, in which heat transfer occurs mainly by conduction. In the main vapor-dominated zone vertical gradients of temperature and pressure are small, so that conductive heat flow is negligibly small. Heat transfer in these zones occurs by means of a vapor-liquid counterflow process known as ìheat pipeî (White et al., 1971; Martin et al., 1976; Straus and Schubert, 1981; Pruess, 1985). Vapor originates at depth from boiling of liquid. It rises to shallower horizons where it condenses, depositing its large latent heat of vaporization. The condensate then returns to depth driven by gravity force. Little is known about fluid and heat transfer processes, and thermodynamic conditions of formation fluids beneath the main permeable zones of vapor-dominated systems. Systematic long-term increases in production temperatures with strong superheating have been reported for Larderello (Sestini, 1970). These observations suggested that fluids with very high enthalpy can be delivered from greater depths (2-4 km). In recent years a programme of deep exploration has been carried out at Larderello by the Ente Nazionale per IíEnergia Elettrica (ENEL), results of which have been presented by Cappetti et al.. (1985). Several wells have been drilled to depths of 3000 m and more, and temperatures in excess of 300?C have been observed. More recently, similarly high temperatures and high-enthalpy fluids have been reported for a deep well at The Geysers (Drenick, 1986). In this paper we present temperature data for deep horizons at Larderello, and we attempt to analyze the data with a view on identifying reservoir conditions and processes at depth. Of particular interest are the mechanisms and rates of fluid and heat flow in the natural state and in response to exploitation.

Press the Back button in your browser, or search again.

Copyright 1987, Stanford Geothermal Program: Readers who download papers from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the original publisher.