The Use of N-Propanol as a Tracer at the Site of the Coso Engineered Geothermal System

Abstract

In order to better characterize fluid-flow pathways in two-phase Engineered Geothermal Systems (EGS), two-phase tracers are needed. Short-chain aliphatic alcohols are excellent candidates for tracing injection fluids in such reservoirs based on thermal stability, vapor-liquid partitioning, and cost. Previous tests using alcohol tracers were conducted with some success (Fukuda 2005, Adams 2004). The detection limits for these tests were typically in the range of 30 parts per billion (ppb) to several hundred ppb, requiring the use of prohibitively large quantities of alcohol tracer. In this study, a method was developed that demonstrates a detection-limit reduction by a factor greater than 30. This approach, which combines Solid Phase Microextraction (SPME) with gas chromatography (GC), resulted in a limit of detection of approximately 1 ppb for n-propanol. The amount of tracer needed to conduct a tracer test is likewise reduced with the detection limit. A test using a reduced volume of n-propanol and a liquid-phase tracer was conducted at the site of the EGS project at the Coso geothermal field.