Low‐Field Borehole NMR Applications in the Near‐Surface Environment

Abstract

The inherent heterogeneity of the near subsurface (<200 m below the ground surface) presents challenges for agricultural water management, hydrogeologic characterization, and engineering, among other fields. Borehole nuclear magnetic resonance (NMR) has the potential not only to describe this heterogeneity in space nondestructively but also to monitor physical and chemical changes in the subsurface with time. Nuclear magnetic resonance is sensitive to parameters of interest like porosity and permeability, saturation, fluid viscosity, and formation mineralogy. Borehole NMR tools have been used to measure soil moisture in model soils, and recent advances in lowfield borehole NMR instrumentation allow estimation of hydraulic properties of unconsolidated aquifers. We also demonstrate the potential for low-field borehole NMR tools to monitor field-relevant biogeochemical processes like biofilm accumulation and microbially induced calcite precipitation at laboratory and field scales. Finally, we address some remaining challenges and areas of future research, as well as other possible applications where borehole NMR could provide valuable complementary data.Abbreviations: DP, direct push; MICP, microbially induced calcite precipitation; NMR, nuclear magnetic resonance; rf, radio frequency; PVC, polyvinyl chloride; RWTH, Rheinisch-Westfälische Technische Hochschule. Core Ideas• Low-field borehole NMR characterizes subsurface heterogeneities from pore to macro scales. • Borehole NMR is sensitive to biogeochemical processes and conversions in the subsurface. • Development of borehole NMR benefits hydrogeology, soil management, and engineering.

Nuclear magnetic resonance logging: Example applications of an emerging tool for environmental investigations

“…Concurrent with instrument development, numerous theoretical, empirical, and field studies have demonstrated robust correlations between the measured NMR response and key hydraulic parameters including fluid‐filled porosity (Timur, ), pore size distribution (Gallegos & Smith, ), permeability (Kenyon, Day, Straley, & Willemsen, ; Seevers, ; Shikhov, d'Eurydice, Arns, & Arns, ), and a number of researchers have presented specific applications in unconsolidated media, including both the saturated and vadose zones (e.g., Behroozmand, Keating, & Auken, ; Costabel & Günther, 2014; Costabel & Yaramanci, ; Dlubac et al., ; Falzone & Keating, ; Keating & Falzone, ; Kirkland & Codd, ; Knight et al., ; Merz, Pohlmeier, Vanderborght, Van Dusschoten, & Vereecken, ; Parsekian et al., ). The physical principle of NMR logging is the same principle underlying magnetic resonance imaging technology used in medicine and NMR spectroscopy in chemistry; specifically, NMR methods utilize a quantum physical property associated with hydrogen atoms known as the nuclear spin angular momentum, where the NMR tool measures the response of the hydrogen spins to a magnetic field perturbation (Dunn, Bergman, & Latorraca, ).…”

“…NMR could be used in the future at this site to monitor changes in water content distribution over time. Kirkland and Codd () provide further discussion on additional time‐lapse monitoring applications for NMR.…”

Noninvasive Imaging of Processes in Natural Porous Media: From Pore to Field Scale

“…Such dedicated equipment has been historically developed by the petroleum industry for well‐logging purposes (Coates et al, 1999), and during the past few years it has been adopted for hydrological purposes (Kirkland et al, 2015; Sucre et al, 2011). Using a small‐scale instrument, Kirkland and Codd (2018) demonstrated the usefulness of a mobile NMR borehole device to quantify the soil moisture distribution as well as biofilm and precipitate formation at the field scale. By analysis of one‐dimensional resolved NMR relaxation data, they were able to derive hydraulic conductivity profiles from the surface to a depth of 10 m.…”

Hydraulic Conductivity from Nuclear Magnetic Resonance Logs in Sediments with Elevated Magnetic Susceptibilities

“…The typical time constraints associated with traditional hydraulic tests, particularly in complex heterogeneous systems, can impede the acquisition of detailed and extensive datasets needed for comprehensive investigations (e.g., Paradis et al 2014). The recent development of small‐diameter borehole nuclear magnetic resonance (NMR) tools (e.g., Sucre et al 2011; Walsh et al 2013; Hopper et al 2017), slimmed down from petroleum industry models, allows for the continuous measurement of volumetric water content and estimations of pore size distributions and K in near‐surface groundwater studies (e.g., Dlubac et al 2013; Johnson et al 2014; Parsekian et al 2015; Knight et al 2016; Kirkland and Codd 2018; Ren et al 2019; Spurlin et al 2019).…”