In-situ 3D high-spatial resolution aquifer characterization with hydraulic parameter distribution at decameter scale

Abstract:

Currently, a major challenge in aquifer characterization is the determination of hydraulic parameters with high-spatial resolution. Since the mid-90’s, various working groups have developed numerical evaluation approaches for hydraulic tomography: the inversion of hydraulic tests that have been recorded using tomographic arrangements. The practical application is often associated with long test times, complex evaluations, and prolonged computation times.

In our study, a hydraulic tomographical data set consisted of 450 drawdown curves produced by a series of short term pumping tests conducted over 4 working days. Data was collected by two scientists without a technical staff. The tests were performed at the test site “Stegemühle”, Göttingen, Germany in a confined sand and gravel aquifer with a thickness of 2-3 m.

For the inversion, an approach has been used, which is based on the transformation of the groundwater flow equation into a form of Eikonal equation (Vasco et al., 2000). Utilizing this approach, the hydraulic data can be inverted using an Eikonal solver e.g. SIRT. This Eikonal solver is considerably computationally efficient and allows hundreds of draw down curves to be inverted on a standard laptop within minutes. Following the methodology described in Brauchler et al. 2013, 3D distribution of diffusivity and specific storage were directly reconstructed, and subsequently their product: the hydraulic conductivity.

This study exemplifies that the required data can be recorded and analyzed efficiently in the field, which is a vital precondition for the in-situ field aquifer characterization with hydraulic tomography.

Literature

Vasco, D.W., Keers, H., Karasaki, K. (2000) Estimation of reservoir properties using transient pressure data: An asymptotic approach. Water Resour. Res. 36(12), 3447-3465
Brauchler, R., Hu, R., Hu, L., Jimenéz, S., Bayer, P., Ptak, T. (2013) Rapid field application of hydraulic tomography for resolving aquifer heterogeneity in unconsolidated sediments, Water Resour. Res., (49), 1-12