| Title | First Multi-Well Vapor and Two-Phase Tracer Test in a Geothermal Reservoir, Using Perfluorocarbons and Alcohols |
|---|---|
| Authors | Paul N. Hirtz, Russell J. Kunzman, Michael C. Adams, Jeffery W. Roberts, Arias Sugandhi, Krisnendar Martiady, Purwantoko Mahagyo, Ahmad Suvian Iman |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | Tracer, Perfluorocarbon, Freon, HFC, alcohol, two-phase, injection, water saturation |
| Abstract | A new class of chemical tracers, perfluorocarbons (PFC), have been tested in the lab and evaluated in a field trial at the Darajat geothermal project, Indonesia. Liquid- and vapor-phase tracers are widely used in geothermal reservoir engineering to trace the path of water injected into the reservoir for pressure support and/or recharge. In the case of a vapor-dominated geothermal system such as Darajat, vapor- and two-phase tracers can be used to trace the amount of steam derived from water injected strategically around steam production wells. Freon compounds, such as chlorofluorocarbons (CFC) and hydrofluorocarbons (HFC), have been used routinely as vapor tracers in geothermal. However, CFC’s are no longer available due to ozone-depletion issues, and the only remaining HFC for practical use is R-134a. Sulfur hexafluoride (SF6) is not used due to concerns about possible reaction with silicate rocks in the reservoir under superheated conditions. Two PFC’s were tested for thermal and chemical stability and found to be stable to at least 280 ºC in the presence of reservoir rock and water. These compounds are very insoluble in water, so that had to be emulsified for application as “water-to-steam” tracers. Once the water boils in the reservoir they partition to the vapor phase and follow the steam path. The two PFC’s were tested along with R-134a and three light alcohols in the first multi-well, vapor and two-phase tracer test for a geothermal reservoir. The PFC’s produced similar return curves as the Freon tracer, which all partition strongly to the vapor-phase. There was no evidence of premature phase separation of PFC’s from injection water. In spite of their very low solubility, these compounds can be used as vapor-phase tracers in geothermal applications with adequate precautions in application, utilizing appropriate emulsions and controlled injection rates. The light alcohols are very soluble and considered two-phase tracers in that they partition more evenly between steam and water than the vapor tracers. By using tracers of widely differing solubility we were able to extend the range of boiling fractions that could be tagged as injectate traveled through the reservoir. An additional benefit is that the ratio of the tracers in each sample was used to calculate the fraction of boiling that volatilized the tracers from the injectate into the steam reservoir. In one case unique flow paths were identified in a well that allowed essentially complete separation of steam from early-boiling injectate. The tracer results confirm semi-permeable barriers within the reservoir, which will help design injection distribution strategies for improved injection management, Sugandhi, et al. (2009). The results will be used to develop alternative injection strategies to best manage reservoir performance and maximize heat recovery from reservoir rock. |