Conservative Solute Versus Heat Transport in Porous Media During Push-pull Tests

Abstract

Both heat and solute transport in porous media are described by partial differential equations of similar form. Nevertheless, observing these phenomena in the field on the scale of well tests clearly indicates dissimilar behaviour. This article studies the aforementioned transport processes by interpreting two push-pull tests of different duration. In both tests, chloride is applied as a conservative tracer and lower temperature water is injected in higher temperature pristine water at different flow rates. Simulation and interpretation of the tests are performed by means of ReacTrans, a two-dimensional, axially symmetric, finite-difference, solute and heat transport model. Since conflicting views exist in literature on the relation between solute and thermal dispersivity, analysis of field observations focuses on parameters which describe aquifer characteristics affecting these processes. Parameter estimation is conducted through sensitivity analysis and collinear diagnosis in order to identify derivable parameters. It is concluded that longitudinal solute dispersivity and thermal diffusivity could be inferred accurately from chloride and temperature data sampled from the injection/extraction well respectively. Involving supplementary data sampled from an observation well enables derivation of effective porosity from chloride data and thermal retardation from temperature data. Moreover, it is inferred that longitudinal solute dispersivity is scale dependent. Thermal diffusivity, however, seems not to be. This points to dissimilar development of transition zones during solute and heat transport. It is concluded that conductive transport of heat is much more important than effects of velocity variations through the pore space.