Stability of Methanol, Propanol, and Sf6 as High-temperature Tracers

Tracers are needed for the development of high-temperature geothermal resources. Several candidate tracers have been tested for that purpose in hydrothermal autoclaves at the Energy & Geoscience Institute in Salt Lake City, Utah. One gas tracer, SF6, and two of the two-phase tracers, the straightchain alcohols, were tested. They were tested at temperatures ranging from 220 to greater than 300C, pH’s of 3 to 7, and times of up to two weeks. The data indicate that SF6 is stable at a temperature up to about 300C in a simple SF6-water system. Methanol is the most stable of the alcohols, with no decay being detected from a two-week run at 320C and a pH of 4. Propanol, in contrast, showed a 10% decay in a similar test. SF6 displays a strong vulnerability to the presence of rock that should be tested further before being used in a geothermal reservoir.