| Title | Experimental Determination of Rate Constants for the Breakdown of the Organic Tracers 2-NSA, 2,6-NDS, 2,7-NDS, 1,5-NDS and 1,6-NDS Under Geothermal Conditions |
|---|---|
| Authors | L. Sajkowski, B.W. Mountain and T.M. Seward |
| Year | 2020 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | tracer studies, naphthalene disulfonic acid, naphthalene sulfonic acid, NDS, NSA, experimental geochemistry |
| Abstract | Naphthalene sulfonates are widely used in the geothermal industry as tracers. Experimental results show, however, that these compounds do have their temperature limits. Knowledge of the rate of thermal breakdown is essential to ensure successful tracer tests. In addition, information on the breakdown products could be useful in interpreting fluid temperature history. The main goal of this project is to broaden the understanding of the processes taking place when these tracers are exposed to conditions found in geothermal environments. The experiments were conducted to measure the rate of the thermal breakdown reactions. Five polyaromatic (di)sulfonates: 1,5-naphthalene disulfonate (1,5-NDS), 1,6-naphthalene disulfonate (1,6-NDS), 2,6-naphthalene disulfonate (2,6-NDS), 2,7-naphthalene disulfonate (2,7-NDS) and 2-naphthalene sulfonate (2-NSA) were studied. Aqueous solutions containing NDS/NSA were sealed inside glass ampoules using an oxy-acetylene torch and placed in cold-seal pressure vessels. These were exposed to between 200°C and 330°C for different times from 20 hours to 3 months. The experimental solution consisted 0.05M NaCl at neutral pH. The various naphthalene sulfonates were analysed by high performance liquid chromatography (HPLC) using fluorescence detection. The rate constants were estimated by least squares fitting of the results. These show that NDS breakdown rates are temperature dependent. Stability increased as follow: 1,5-NDS<1,6-NDS<2,6-NDS/2,7NDS <2-NSA. Additionally, 2-NSA and 1-NSA were detected as breakdown products of naphthalene disulfonates. 2-NSA and 1-NSA were not stable at 300˚C. |