Progress Report on Multiphase Geothermal Modeling

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.