3D hydrogeological parametrization using sparse piezometric data

Abstract. When modelling contamination transport in the subsurface and aquifers, it is crucial to assess the heterogeneities of the porous medium, including the vertical distribution of the aquifer parameter. This issue is generally addressed thanks to geophysical investigations.

As an alternative, a method is proposed using inversion data from a 2D calibrated flow model (solely reliant on piezometric series) as parameterization constraints for a 3D hydrogeological model. The methodology is tested via a synthetic model, ensuring full knowledge and control of its structure. The synthetic aquifer is composed of five lithofacies, distributed according to a sedimentary pattern, and functions in an unconfined regime. The level of heterogeneity for hydraulic conductivity spans three orders of magnitude. It provides the piezometric chronicles used to inverse 2D flow parameter fields and the lithological logs used to interpolate the 3D lithological model. Finally, the parameters of each facies (hydraulic conductivity and porosity) are obtained through an optimization loop, that minimizes the difference between the 2D calibrated transmissivity and the transmissivity computed with the estimated 3D facies parameters.

The method estimate parameters close to the known initial parameters, even with sparse piezometric and lithological data sampling. The maximal discrepancy is 61 % of the initial value for the permeability and 16 % for the porosity (mean error 18 % and 4 %, respectively). Although the methodology does not prevent interpolation error, it succeeds in reconstructing flow and transport dynamics close to the control data. Due to the inherent limitations of the 2D inversion approach, the method only applies to the saturated zone at this point.