SGP-TR-99 Chelated Indium Activable Tracers for Geothermal Reservoirs Constantinos V. Chrysikopoulos Paul Kruger June 1986 Financial support was provided through the Stanford Geothermal Program under Department of Energy Coi ktraat No. DE-AT03-80SF11459 and by the Department of Civil Engineering, Stanford University Stanford Geothermal Program Interdisciplinary Research in Engineering and Earth Sciences STANFORD UNIVERSITY Stanford, California ACKNOWLEDGEMENTS The authors acknowledge Mike Thompson of U. S. Geological Survey (USGS), Menlo Park, for many stimulating discussions and permission to the high-temperature laboratory facilities; as well as Don Busick and Gary Warren of Hcalth Physics, Stan- ford Linear Accelerator Center (SLAC), for providing the califclmiurh-252 neutron source. Appreciation is extended to Lew Semprini, Evangelos Vcludriqs and Yathrib Al-Riyami, for their friendly assistances to our research efforts. This investigation was made possible by U. S. Department of Energy Grant DE-ATO3-8OS1:114$9. iii ABSTRACT Sensitivity calculations for several potential activable tracers fcilr geothermal fluids based on a 10-minute irradiation in a thermal flux of 2xl06n/cm'sec and 30-minute delay time till measurement were performed. Indium was se1ecti:d to be the most promising activable tracer. The thermal stability of indium tracer chelated with organic ligands ethylenediaminetetraacetic acid (EDTA) and nitrilotriacedc acid (NTA) was measured at several temperatures in the temperature range of 1;eothermal interest. Measurement of the soluble indium concentration was made as a f'unction of time by neutron activation analysis. From the data, thermal decomposition rates were estimated. The results indicated that the ability of EDTA to enhance indium solubility at elevated temperatures is superior compared to the ability of NTA. Adsorption experiments at geothermal reservoir temperatures were run to exanine the effects of adsorbate concentration, rock size, and temperature on the tracer adsoqjtion and ther- mal degradation. The rock employed for these measurements was gragwacke, a prek valent rock type at The Geysers, California geothermal field. The re:sults indicated that significant adsorption of InEDTA did not occur at temperatures up to 200°C. At higher temperatures a sharp reduction in soluble indium concentraltion was observed. The change in temperature behavior was caused by the thermal (degradation of the organic ligand. The experimental results indicate that InEDTA and InNTA are excel- lent activable tracers for surface water and ground water systems, whila InEDTA can be used effectively in geothermal reservoirs with temperatures up to 200°C V 1 I . TABLE OF CONTENTS Page ... Aknowledgements...................................................................................................... 111 Abstract ...................................................................................................................... v List of Illustrations .................................................................................................... ix List of Tables ............................................................................................................. x Nomenclature ............................................................................................................ .xi Chapter 1. INTRODUCTION ................................................................................ 1 1.1. Overview ...................................................................................... 1 1.2. Conventional Tracers................................................................... 2 Internal Tracers ........................................................................... 3 Chemical Tracers ........................................................................ 3 Radioactive Tracers .................................................................... 4 Activable Tracers ........................................................................ 5 1.3. Neutron Activation Analysis ....................................................... 5 1.4. Activable Tracer Requirements ................................................... 8 1.5. Objectives of the Study ............................................................... 9 Chapter 2 . LITERATURE REVIEW ..................................................................... 11 2.1. Chemical Nature of Geothermal Systems ................................. 11 2.2. The Sensitivity Calculation ......................................................... 15 2.3. Indium .......................................................................................... 19 Occurrence and Geochemistry.................................................... 19 Uses ............................................................................................. 22 Chemical Properties and Aqueous Chemistry ........................... 22 Liquid-Liquid Extraction ............................................................ 29 Ion Exchange Behavior .............................................................. 30 Detection Methods ....................................................................... 32 Nuclear Properties........................................................................ 32 2.4. Chelates ........................................................................................ 35 Ethylenediaminetetraacetic Acid ................................................ 36 Nitrilotriacetic Acid .................................................................... 41 Chapter 3 . EXPERIMENTAL PROCEDURES..................................................... 45 3.1. General Considerations................................................................ 45 Vii Reagent Preparation .................................................................... 45 Glassware Cleaning .................................................................... 45 3.2. Activation Facilities..................................................................... 46 Counting Apparatus .................................................................... 47 Gamma-Ray Scintillation Detector Calibrations........................ 48 3.3. Statistical Considerations of Radioactivity Measurcmeats ........50 3.4. Concentration Determination ..................................................... 53 Irradiation and Counting Procedures .......................................... 53 3.5. Tracer Stability Studies ............................................................... 55 Air Bath ....................................................................................... 55 Pressure Vessels .......................................................................... 56 Experimental Design .................................................................. 57 3.6. Tracer Adsorption Studies ........................................................... 57 Rock Properties .......................................................................... 58 .. Crushing and Sieving................................................................. 59 Specific Surface Area ................................................................. 60 Experimental Design ................................................................... 61 Chapter 4 . RESULTS AND DISCUSSION ...................................... .......,...........63 4.1. Tracer Stability Results .............................................................. 64 Time Function of Tracer Solubility .......................................... 64 Thermal Stability Behavior ....................................................... 64 4.2. Tracer Adsorption Results .......................................................... 69 Tracer Adsorption Evaluation at Room Temperatue ...............69 Effect of Temperature ................................................................. 71 Chapter 5 . CONCLUSIONS AND RECOMMENDATIONS............................... 75 5.1. Conclusions .................................................................................. 75 5.2. Recommendations ........................................................................ 76 APPENDICES A . Derivation of Radioactivity Correction Factors for Decay During Counting .......................................................................................... 77 B . Data Listings - Stability Experiments .......................................................... 81 C . Data Listings - Adsorption Experiments ..................................................... 83 D . Rate Constant Calculation............................................................................ 85 REFERENCES .......................................................................................................... 87 ... Vlll LIST OF ILLUSTRATIONS Figure Page I Distribution Diagram of Indium Hydrolysis ................................................ 26 I1 Precipitation Region of In+3........................................................................... 26 III Predominance Diagram for III+~-OH-CLSpecies ........................................... 28 IV Gamma Spectra of Indium- 116m ................................................................. 34 V palpH Diagram for EDTA ........................................................................... 38 VI Indium-EDTA Complex Formation ..............................................................38 VI1 Thermal Decomposition Mechanism of EDTA ........................................... 41 VI11 palpH Diagram for