Modeling the phase partitioning behavior of gas tracers under geothermal reservoir conditions

A model of the liquid-vapor phase partitioning behavior of low concentratio ns of gas tracers in water at geothermal temperatures and pressures is pres ented. This model uses Henry's coefficient to describe the variation of the gas tracer solubility with temperature and pressure. A new method is descr ibed for the determination and representation of Henry's coefficients. The method uses experimentally determined values of Henry's coefficient and a t heoretically predicted value of behavior at the critical point of water to provide data that can be fitted by a semi-empirical correlation. No assumpt ions regarding ideal behavior are necessary. The semiempirical correlation is a modified version of that presented by Harvey, A. (1996. Semiempirical correlation for Henry's constants over large temperature ranges. American I nstitute of Chemical Engineers Journal 42(5), 1491-1494) and better account s for high temperature and non-ideal behavior. Sets of model coefficients a re given for a range of possible gas tracers. The resulting phase partition ing model is simple and may be easily implemented in a numerical geothermal simulator. The use and behavior of the model is illustrated by its applica tion to a number of idealised test problems. (C) 2001 CNR. Published by Els evier Science Ltd. All rights reserved.