HGS Research Highlight - Heat tracer test in an alluvial aquifer: field experiment and inverse modelling

Heat tracer test in an alluvial aquifer: field experiment and inverse modelling

Authors:Maria Klepikova, Samuel Wildemeersch, Pierre Jamin, Philippe Orban, Thomas Hermans, Frederic Nguyen, Serge Brouyère, Alain Dassargues

Characterization and predictive modelling of transport in heterogeneous aquifers is of great interest to groundwater contamination prevention as well as geothermal reservoir exploitation and heat storage that still provides many challenges.  In this study, we investigate the potential of using heat as a tracer for characterization of transport in a shallow alluvial aquifer. A thermal tracer test was conducted in the alluvial aquifer of the Meuse River, Belgium. In order to understand and analyze the observed complex behavior of the heat plume, a three-dimensional groundwater flow and heat transport model was developed using the HydroGeosphere code (HGS).

Two-dimensional K (m/s) tomogram for the lower (a) and upper (b) parts of the aquifer obtained from the inversion of transient temperature responses.

Heat plume movement in the aquifer.

The HGS simulations performed in this study takes advantage of the key features of HGS including numerical simulation of variable-density groundwater flow, coupled groundwater flow and heat transport, and linkage of HGS and the parameter estimation software PEST in three dimensions, including pilot points as spatial regularization scheme.

By inversion of temperature breakthrough curves measured in observation boreholes, valuable insights in the 3D characteristics of the heat transport mechanisms were obtained. The observed complex behavior of the heat plume was explained by high lateral and vertical heterogeneity of the hydraulic conductivity field combined to the groundwater flow gradient on the site. Additionally, a clear temperature-induced water density effect was detected. By using the pilot-point based inversion approach, the main preferential paths were characterized as providing a reasonably good fit to all observed thermal breakthrough curves.

Finally, this study considers heat transport processes playing a predominant role in heat storage projects, open shallow and low temperature geothermal projects. Our results indicate that the actual efficiency of these projects will be strongly affected by the heterogeneity of the K-field. Heat tracer tests, combined with detailed inversion procedures could be a useful approach for constraining groundwater flow and heat transport models used for assessing low temperature geothermal systems as well as of many similar projected geothermal systems efficiency in urban zones.

Full article can be accessed here.