Behaviour of Sulphur Hexafluoride in Water Above 210"C - Implications for Its Use as a Geothermal Tracer

Abstract

The solubility sulphur hexafluoride (SF,) has been recently measured in our laboratory between 75 "C and 230 "C. Increasing the temperatures above about 210 "C resulted in an unexpectedly rapid decrease in SF, gas partial pressure. Above this temperature departure from Henry's law was also observed. The decrease in SF, partial pressure and decrease in dissolved SF, suggests that depletion of SF, from the vapour and liquid water was occurring, perhaps to form a dense immiscible SF,-water phase. This also explains the anomalous behaviour of SF, as reported in recent tracer tests in high temperature geothermal aquifers.