Articles | Volume 20, issue 5
Research article
12 May 2016
Research article |  | 12 May 2016

Travel-time-based thermal tracer tomography

Márk Somogyvári, Peter Bayer, and Ralf Brauchler

Abstract. Active thermal tracer testing is a technique to get information about the flow and transport properties of an aquifer. In this paper we propose an innovative methodology using active thermal tracers in a tomographic setup to reconstruct cross-well hydraulic conductivity profiles. This is facilitated by assuming that the propagation of the injected thermal tracer is mainly controlled by advection. To reduce the effects of density and viscosity changes and thermal diffusion, early-time diagnostics are used and specific travel times of the tracer breakthrough curves are extracted. These travel times are inverted with an eikonal solver using the staggered grid method to reduce constraints from the pre-defined grid geometry and to improve the resolution. Finally, non-reliable pixels are removed from the derived hydraulic conductivity tomograms. The method is applied to successfully reconstruct cross-well profiles as well as a 3-D block of a high-resolution fluvio-aeolian aquifer analog data set. Sensitivity analysis reveals a negligible role of the injection temperature, but more attention has to be drawn to other technical parameters such as the injection rate. This is investigated in more detail through model-based testing using diverse hydraulic and thermal conditions in order to delineate the feasible range of applications for the new tomographic approach.

Short summary
A new innovative method of aquifer characterization is presented, using tomographic thermal tracer tests to map the hydraulic conductivity distribution. The travel times of the heated water between different sources and receivers are used in the inversion process following an analog procedure with hydraulic tomography. The developed method is a fast and robust alternative of model calibration. The method is tested on a virtual aquifer and shows applicability under a broad range of conditions.