On determining uncertainties of magnetic resonance sounding estimated transmissivities for groundwater modeling

Abstract

The nuclear magnetic resonance sounding (MRS) method is used increasingly as a tool for hydrological investigations. Compared to other geophysical methods, the advantage of MRS is that it is directly sensitive to the presence of water in the subsurface. Data interpretations can also be used to get information about the subsurface pore structures, which under special conditions can be related to hydraulic properties such as aquifer transmissivity. However, to broaden the usage of this information in hydrological modeling, the uncertainties related to these transmissivity estimates must be determined. Otherwise, properly balanced weights cannot be given to the prior information obtained from MRS transmissivity estimates as compared to the hydrological data sets when used for groundwater model calibration. We have developed a methodology to estimate the uncertainties of MRS-based transmissivity estimates. Compared to previous studies, the methodology is well defined, and it takes into account important factors such as the uncertainties of the hydraulically estimated transmissivities, the uncertainty of the correlation factor in the petrophysical relation, and the uncertainties and correlations of the geophysically estimated parameters. We have determined the correlations and uncertainties of the geophysical parameters using a linear and a nonlinear method, and we find that the results are comparable.

Investigating the impact of artificial environmental watering on a semi‐arid, highly saline floodplain using electromagnetics and surface nuclear magnetic resonance

“…Therefore we have assumed that our study area is weakly magnetic, the T 2IH −1 term is small, and T 2 * is similar to T 2 . This approach has been used in other studies, such as Gunther and Muller‐Petke () and Vilhelmsen et al (). This assumption allows us to estimate hydraulic conductivity through equations such as the Sum‐of‐echoes equation (Allen et al, ).…”

“…The initial signal amplitude is related to water content, which is a proxy for porosity in the saturated zone, and a relaxation time constant T 2 * can be estimated from the signal envelope to inform the pore size (Legchenko, Baltassat, Beauce, & Bernard, 2002). The use of surface NMR to estimate permeability has been demonstrated in a number of studies, such as Gunther and Muller-Petke (2012) and Vilhelmsen, Christensen, and Auken (2016). This is achieved by applying permeability models, such as the Schlumberger Doll Research equation (Kenyon, Day, Straley, & Willemsen, 1988) and the Sum-of-echoes equation (Allen et al, 2000), to relate NMR parameters to permeability.…”

Anthropogenic wetlands due to over-irrigation of desert areas: a challenging hydrogeological investigation with extensive geophysical input from TEM and MRS measurements

“…The method is well established for nearsurface characterization (Chalikakis et al, 2008;Günther and Müller-Petke, 2012;Knight et al, 2012). Different studies have also dealt with estimating hydrogeological parameters from MRS and have found good correlation between MRSderived parameters and those from borehole aquifer tests (Boucher et al, 2009;Herckenrath et al, 2012;Plata and Rubio, 2008;Vilhelmsen et al, 2014Vilhelmsen et al, , 2016Vouillamoz et al, 2012Vouillamoz et al, , 2015.…”

“…This local scale coincides with the area where hydrogeophysical surveys have led to an in-depth understanding of the geologic setting. The US Geological Survey SUTRA code (Voss and Provost, 2002), which can handle density-dependent flows under saturated-unsaturated conditions, was used to simulate a number of scenarios of artificial aquifer recharge. Based on the hydrogeological set- ting of the study area, the limestone unit identified in the depth range between 0 and −100 m a.m.s.l.…”

Feasibility study on prepolarized surface nuclear magnetic resonance for soil moisture measurements

“…The method of surface nuclear magnetic resonance (SNMR) and in particular its specific applications for one-dimensional investigations, also called magnetic resonance sounding (MRS), are mainly developed and established for groundwater exploration and noninvasive aquifer characterization (Costabel et al, 2017;Legchenko et al, 2004;Müller-Petke & Yaramanci, 2015;Vilhelmsen et al, 2016). Their general benefit is Abbreviations: DC, direct current; FID, free induction decay; MRS, magnetic resonance sounding; PP, prepolarization; NMR, nuclear magnetic resonance; RTD, relaxation time distribution; Rx, surface receiver; SNMR, surface nuclear magnetic resonance; TDR, time domain reflectometry; Tx, surface transmitter; Tx-pulse, transmit or excitation pulse.…”