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Status of Modeling Efforts for the Wairakei Geothermal Field

Description: The theoretical model used in this study is based on an approach that combines the mass, momentum and energy balances for steam and water into two partial differential equations in terms of the dependent variables, pressure and enthalpy. The assumptions used in this formulation and the detailed development of the equations are presented in Faust (1976). The resulting two- and three-dimensional equations are approximated by finite-difference expressions, and are solved using either direct or iterative matrix techniques. Our conceptual model of the Wairakei system is basically the same as that outlined in Mercer, Pinder and Donaldson (1975), with the exception that we now allow for mass leakage through the bottom of the reservoir. The Wairakei hydrothermal system is considered to have been at steady state prior to exploitation. The first step in modeling the Wairakei field is therefore the reproduction of the observed virgin or steady state conditions. The results of the steady state simulation are used as initial conditions for the transient model of exploitation. This modeling effort represents an ongoing project, and the results to be presented will describe the current status of our Wairakei simulation. 4 refs.
Date: December 1, 1976
Creator: Mercer, James W. & Faust, Charles R.
Partner: UNT Libraries Government Documents Department

Progress Report on Multiphase Geothermal Modeling

Description: Work over the past year has concentrated on three areas: 1) to implement a concept of vertical equilibrium in geothermal modeling, 2) to improve the matrix equation solution technique for both two- and three-dimensional models, which improvements this report describes in detail, and 3) to apply a vertical equilibrium, areal model to the Wairakei, New Zealand geothermal field. The steady-state modeling indicates that large regions in the reservoir probably had a small steam cap prior to exploitation. Furthermore, transient simulations indicate that leakage into the reservoir is significant; that is, the Wairakei reservoir is not a closed system. The most difficult part of history matching at Wairakei is adjusting permeabilities in order to remove enough mass from storage (as opposed to leakage) and reproduce the observed pressure decline trends. 5 refs.
Date: December 14, 1977
Creator: Mercer, James W. & Faust, Charles R.
Partner: UNT Libraries Government Documents Department