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TitleNMR logging in deglacial sediments of the Ottawa Valley
AuthorCrow, HORCID logo; Paradis, DORCID logo; Griffiths, MORCID logo; Liang, X X
SourceSymposium on the Application of Geophysics to Engineering and Environmental Problems 2021; 2021 p. 255-257,
Alt SeriesNatural Resources Canada, Contribution Series 20200057
PublisherEnvironmental & Engineering Geophysical Society
MeetingSAGEEP 2021 - Symposium on the Application of Geophysics to Environmental and Engineering Problems (SAGEEP); Denver, Colorado; US; March 29 - April 2, 2020
Mediapaper; on-line; digital
File formatpdf
Lat/Long WENS -75.5000 -75.0000 45.5000 45.2500
Subjectssurficial geology/geomorphology; geophysics; mineralogy; hydrogeology; Science and Technology; Nature and Environment; deglaciation; glacial deposits; eskers; sands; gravels; silts; clays; geophysical logging; magnetic susceptibility; boreholes; depositional environment; porosity; scanning electron microscope analyses; provenance; hydraulic conductivity; Canadian Shield; Phanerozoic; Cenozoic; Quaternary
Illustrationsgeophysical logs; profiles
ProgramGroundwater Geoscience Aquifer Assessment & support to mapping
Released2021 01 01
AbstractIn July 2018, borehole nuclear magnetic resonance (NMR) technology was applied in three GSC calibration boreholes intersecting deglacial sediments of the Ottawa Valley, near Embrun, ON (Crow et al., 2020a). Sediments in the study area range in texture from a coarse-grained sand and gravel esker, to fine-grained, geotechnically sensitive, silty clays (Cummings et al., 2011). The silt and clay-sized particles flocculated is a proglacial sea to produce a loose sediment framework with elevated porosities, reaching 74 porosity units (pu) in the study area. Scanning electron microscopy from other sites in the region has shown the clay-sized fraction consists of aggregated mineral grains separated by a network of small pores approximately 0.5 - 1 micron in size (Delage et al., 1982). Mineralogy of the fine-grained sediments largely reflect a provenance from the Canadian Shield (Crow et al., 2017). Magnetic susceptibility logs indicate magnetic minerals can be present in Shield-derived sands in relatively elevated and variable levels. This geological setting was expected to challenge NMR technology due to small pores, high water contents, and magnetic mineral content. The study objective was therefore to evaluate the performance of newly-developed slim-hole NMR tools in this environment. Measurement of in situ water content is important in eastern Canada for geohazard studies of sediment response to earthquake shaking (e.g. retrogressive failure of 'quick clays', liquefaction potential), and for aquifer/aquitard characterization.
Two NMR instruments were deployed with diameters of investigation (doi) ranging from 14.0 to 30.5 cm, and echo spacings of 0.5 ms and 1.0 ms. In the silty clays, qualitative results indicate the NMR responses correctly identified formation fluid as predominantly clay-bound. Quantitative comparisons of NMR porosities to core porosities were typically within ±5 pu (range of ±10 pu), but deviated in some intervals where the mineralogy and concentration of magnetic particles changed from silt and clay-size detrital grains to nanoparticles. Very short T2 times (<2 ms) were recorded, indicating the importance of a short echo spacing to reduce uncertainty in measured water contents. In these sensitive sediments, drilling caused intervals of water-filled voids or sediment disturbance behind casings. The tools' larger doi's were needed to reach undisturbed conditions, but the narrower doi's permitted a useful assessment of borehole completion, which improved interpretation of other geophysical logs and guided optimal packer placement in wells during subsequent hydraulic testing (Crow et al., 2020b).
In the sandy eskers, qualitative results indicate NMR responses are identifying predominantly free water, despite intervals of relatively elevated magnetic susceptibilities. Quantitative results in the sands are a topic of ongoing study. Preliminary lab NMR tests on esker sands revealed shortened T2 times, an effect also observed in downhole NMR responses where magnetic susceptibilities were relatively elevated. Hydraulic conductivities (K) derived from NMR data are being compared to K values estimated from packer tests in the esker sands to provide a more quantitative indication of magnetite influence. Results of this study highlight the benefits of a geophysical log suite, especially magnetic susceptibility, for NMR log interpretation in settings with magnetic geology (Figure 1).
Summary(Plain Language Summary, not published)
The same technology used for magnetic resonance imaging (MRI) in medical applications is being used to image the amount of groundwater in rocks and sediment. This technology is called borehole magnetic resonance (BMR) imaging in geological settings, and is helping us understand groundwater storage. While BMR has been used in large-diameter oil and gas industry wells since the 1990's, it has only been recently adapted for logging in narrow-diameter water wells and shallow geotechnical boreholes. This makes BMR a valuable new technology to integrate into the group of borehole instruments LMS already uses to study rock, sediment, and groundwater. A study was undertaken to look at a new BMR tool in four LMS research boreholes that were drilled into sediments prone to landsliding. The study concluded that the new BMR tool has many practical applications in landslide and groundwater protection studies - topics of ongoing research in LMS Programs.

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