| Title | Coupled Iodine-125 and 2NSA Reservoir Tracer Testing at the Rotokawa Geothermal Field, New Zealand |
|---|---|
| Authors | Jeffrey WINICK, Farrell SIEGA, Simon ADDISON, Ian RICHARDSON, Bruce MOUNTAIN, Bernard BARRY |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | Rotokawa, tracers, naphthalene, iodine-125 |
| Abstract | In 2011 a reservoir tracer test was conducted at the Rotokawa geothermal field to better understand the reservoir response to increased production following commissioning of the newly constructed 138 MWe Nga Awa Purua power station. The test used four types of naphthalene disulfonate tracer (1,5- 1,6- 2,6- and 2,7NDS) to trace the injection fluid movements. After more than one year of monitoring, no returns of injected NDS tracers were detected in any production wells. Following an extensive laboratory testing program in 2012, it was determined that these NDS tracers are not conservative at Rotokawa injection reservoir temperatures. Based on tracer stability experiments, a series of naphthalene based breakdown products and reaction pathways were hypothesized which led to the conclusion that 2-naphthalene sulfonic acid (2NSA) is a likely byproduct of NDS thermal breakdown, and is potentially the most stable of the available naphthalene tracers. Tracer samples from the 2011 test were re-analyzed and small quantities of 2NSA were confirmed in a number of key production wells. Based on these results, a new reservoir tracer test was planned and executed in 2013 which coupled radioactive iodine-125 (125I) and 2NSA in an effort to benchmark the performance of 2NSA against a known, conservative, and thermally stable tracer. Results from this test have demonstrated detectable returns of both 125I and 2NSA, though the response times and magnitudes are significantly different. These data have identified key limitations in the use of naphthalene tracers in high-temperature geothermal environments. When integrated with other resource monitoring information, the test results have helped identify important reservoir processes responsible for observed field changes. |