Comparison of Two Ensemble-Kalman Filter Based Methods for Estimating Aquifer Parameters from Real 3-D Hydraulic and Tracer Tomographic Tests

Abstract

Pumping and tracer tests are site-investigation techniques frequently used to determine hydraulic conductivity. Tomographic test layouts, in which multiple tests with different combinations of injection and observation wells are performed, gain a better insight into spatial variability. While hydraulic tomography has repeatedly been applied in the field, tracer tomography lags behind. In a previous publication, we presented a synthetic study to investigate whether the ensemble Kalman Filter (EnKF) or the Kalman Ensemble Generator (KEG) performs better in inverting hydraulic- and tracer-tomographic data. In this work, we develop an experimental method for solute-tracer tomography using fluorescein as a conservative tracer. We performed hydraulic- and tracer-tomographic tests at the Lauswiesen site in Germany. We analyzed transient drawdown and concentration data with the EnKF and steady-state hydraulic heads and mean tracer arrival times with the KEG, obtaining more stable results with the KEG at lower computational costs. The spatial distribution of the estimated hydraulic conductivity field agreed with earlier descriptions of the aquifer at the site. This study narrows the gap between numerical studies and field applications for aquifer characterization at high resolution, showing the potential of combining ensemble-Kalman filter based methods with data collected from hydraulic and solute-tracer tomographic experiments.

Fiber Optic Pressure Measurements Open Up New Experimental Possibilities in Hydrogeology

“…Besides the advantages of an optimized measurement range, the small dimensions of FO transducers and cables allow their use in different types of wells and piezometers. They can be installed easily with dedicated small-diameter access tubes in isolated zones of packer systems (e.g., Figure 1c), in continuous multichannel tubing (CMT, e.g., Einarson and Cherry 2002;Hochstetler et al 2016;Sánchez-León et al 2020), and other small-diameter observation wells which can be installed efficiently with Direct Push techniques (e.g., Dietrich and Leven 2006;Leven et al 2011). Additional logistical benefits include: availability of FO extension cables at custom lengths (up to 150 m) to allow greater distances between wells and a DAQ station; easy coiling-uncoiling of FO cables to avoid the need for reels; and smaller volume and weight per transducer and cable to reduce storage, transport, shipping space and costs-and to allow small footprints at the interface of many transducers plugged into modular, expandable light/signal conditioning units at one DAQ system (Figure 2c).…”

Stochastic Inversion of Three‐Dimensional Discrete Fracture Network Structure With Hydraulic Tomography

“…The underlying principle of tomographic methods is the application and combined interpretation of signals sent from different sources and/or recorded at different nearby receivers. Hydraulic tomography, for instance, is commonly based on multilevel pumping or slug tests with pressure signals recorded in cross‐borehole test configurations (Berg & Illman, 2011; Brauchler et al., 2003, 2013; Cardiff & Barrash, 2011; Cardiff et al., 2013, 2020; Hu et al., 2011; Illman, 2014; Illman et al., 2009; Klepikova et al., 2020; Laloy et al., 2018; Poduri et al., 2021; Sánchez‐León et al., 2020a, 2020b; Sharmeen et al., 2012; Tiedeman & Barrash, 2020; Wang et al., 2017; Yeh & Liu, 2000; Zha et al., 2015; Zhao et al., 2019; Zhao & Illman, 2017). This facilitates spatial resolution of aquifer heterogeneity by inversion procedures and further use of reconstructed permeability patterns in flow models.…”

“…Three‐dimensional (3D) inversion problems applying data from tomographic experiments are more challenging and have been handled primarily by continuous inversion methods. These provide tomograms of continuous hydraulic conductivity distributions (Cardiff & Barrash, 2011; Cardiff et al., 2013, 2020; Tiedeman & Barrash, 2020) and hydraulic conductivity together with storativity distributions (Berg & Illman, 2011; Illman et al., 2009; Sánchez‐León et al., 2020b; Zha et al., 2015; Zhao et al., 2019; Zhao & Illman, 2017). Promising alternatives rely on the simplification of the inversion problem by prescribing selected characteristics of the main flow paths between two boreholes (Klepikova et al., 2020); they focus on critical hydraulic aspects such as the role of a leakage interface (Wu et al., 2020) or the aperture distribution (Wu et al., 2021).…”