Ability of Thermo-Sensitive Tracers for Precisely Estimating System Temperatures in Column Experiments with Thermal Gradient

摘要

For a sustainable reservoir management, the proper knowledge of the reservoir temperatures is an important prerequisite. Common practice in geothermal energy generation is the reinjection of driving fluids. While the temperature of the produced and/or injected fluids can be measured downhole the occurring thermal drawdown in the exploited reservoir, including its spatial and temporal distribution, cannot be determined directly. In the mid 1980s, thermo-sensitive tracers were mentioned first as a potential tool to measure and detect reservoir temperatures and temperature distributions in-situ. Currently, the renaissance of research on thermo-sensitive tracers can be observed. Recently published results from isothermal experiments in static and dynamic systems are promising and the successful applicability of thermo-sensitive tracers in non-isothermal systems can be expected. Therefore, this work focuses on the application of thermo-sensitive tracers in systems with thermal gradient. It verifies the underlying theory in experiments and shows the possibility for estimating accurate system temperatures from thermo-sensitive tracers. To investigate the contributing processes, the experiments were performed under controlled and well defined laboratory conditions. The used thermo-sensitive tracers follow a pseudo-first-order hydrolysis reaction. Furthermore, the inert tracers and the decay products from hydrolysis can be measured online by fluorescence spectroscopy. As a consequence thereof, the applied thermo-sensitive tracers are able to detect the system temperature with an accuracy of a few degrees Kelvin from a single measurement by knowing solely the input and output concentrations as well as the experiment duration. Beside the general verification of the underlying theory and the ability of the tested thermo-sensitive tracers to give precise system temperature estimates in lab experiments, preliminary results from more elaborated injection schemes, e.g. tracer pulse injections, push-pull tracer tests and a virtually moving thermal front are presented.