Numerical Models of Boiling and Mixing in Geothermal Waters

Abstract

An accurate numerical model of the chemical processes involved in boiling of geothermal waters provides a basis for understanding the compositions of gases and boiled waters and for inferring the origins of scale in wells and surface equipment. Similar models of fluid-fluid mixing are useful for deducing the role of mixing in precipitation of scale and for determining the consequences to formation permeability of re-injection of processed geothermal waters. Here we report the application of computer programs CHILLER and SOLVEQ (Reed, 1982: Reed and Spycher, 1984, 1985) to modeling of boiling and mixing in geothermal waters from the Fushime System, Kyushu, Japan (Yoshimura et al, 1985; Akaku, 1988) and to Broadlands, New Zealand (Reed and Spycher, 1985). The Fushime system is particularly interesting because it is an excellent example of a saline high-T system that is precipitating lead and zinc sulfide minerals. The purpose of modeling boiling and mixing in the Fushime system is to understand the underlying chemical causes of scale precipitation from those waters and to understand the processes of epithermal ore formation from saline geothermal waters.