Numerous investigators have pursued development of large-scale two-phase digital simulation models of vapor-dominated geothermal systems. These represent significant advances in the capability to numerically simulate complex systems. However, the basic physical phenomena which are being modeled are still under investigation. The purpose of this discussion is to present the results of a numerical study in which some of the physical phenomena which may occur in vapordominated geothermal reservoirs are examined. These phenomena include: (1) superheating of discharging steam, (2) energy changes due to compressible work, (3) conductive heat transport, and (4) gravitational effects of the steam column. Further details pertaining to this study are available in a report by Moench (1976).

The numerical model used in this study draws upon the concepts of White and others (1971) for a vapor-dominated geothermal system, though of necessity some simplifications have been made. The physical system is idealized as a one-dimensional column of porous or highly fractured rock filled with a mixture of steam and liquid water under high pressure. This reservoir is overlaid by a "cap rock" that has low permeability. At the bottom of the reservoir there is a zone where liquid water saturates the pores. Heat is supplied by a magma chamber at depth and transferred upward through the liquid-saturated zone by conduction and convection. The primary mechanisms for heat transfer through the vapor-dominated zone are vaporization and condensation. Figure 1 illustrates the distributions of temperature and pressure to be expected in this idealized natural system.

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Copyright 1976, 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.