A Tool for Thermo-sensitive Tracer Selection and Evaluation in Field Experiments

Abstract

The proper knowledge of the reservoir temperature distribution and precise prediction of the thermal breakthrough is essential for efficient energy yield and sustainable reservoir management. Recently, a number of hydrolyzable compounds with different kinetic properties, i.e., esters and amides, were proposed as thermo-sensitive tracers (TSTs) for characterizing the thermal state of geothermal reservoirs. Despite their coverage of wide ranges of temperatures and residence times, the practical application is still limited to lab scale. The required set of Arrhenius parameters for different compound classes is available from previous studies, but there is still no dimensioning tool that allows the characterization and evaluation of the tracer behavior at larger scale. In order to conduct a successful field tracer test, a comprehensive reservoir model, which is able to capture the tracer reaction and its compound-specific sensitivity for different temperature settings and residence time distributions (e.g., due to aquifer heterogeneities) is needed. In this study, a very flexible numerical tracer transport model is introduced that supports the tracer selection as well as the dimensioning and optimization of the test setup according to the prevailing reservoir conditions. The model results and limitations of thermo-sensitive tracers are presented for selected cases of high practical relevance.