| Titre | NMR logging in deglacial sediments of the Ottawa Valley |
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| Auteur | Crow, H ; Paradis,
D; Griffiths, M; Liang, X X |
| Source | Symposium on the Application of Geophysics to Engineering and Environmental Problems 2021; 2021 p. 255-257, https://doi.org/10.4133/sageep.33-138 |
| Image |  |
| Année | 2021 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20200057 |
| Éditeur | Environmental & Engineering Geophysical Society |
| Réunion | SAGEEP 2021 - Symposium on the Application of Geophysics to Environmental and Engineering Problems (SAGEEP); Denver, Colorado; US; mars 29 - avril 2, 2020 |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.4133/sageep.33-138 |
| Media | papier; en ligne; numérique |
| Formats | pdf |
| Province | Ontario |
| SNRC | 31G/06 |
| Région | Embrun |
| Lat/Long OENS | -75.5000 -75.0000 45.5000 45.2500 |
| Sujets | déglaciation; dépôts glaciaires; eskers; sables; graviers; silts; argiles; diagraphie géophysique; susceptibilité magnétique; trous de mine; milieu sédimentaire; porosité; analyses au microscope
électronique à balayage; origine; conductivité hydraulique; Bouclier Canadien; géologie des dépôts meubles/géomorphologie; géophysique; minéralogie; hydrogéologie; Sciences et technologie; Nature et environnement; Phanérozoïque; Cénozoïque;
Quaternaire |
| Illustrations | diagraphies géophysiques; profils |
| Programme | Géoscience des eaux souterraines Caractéristiques d'aquifères et support cartographique |
| Diffusé | 2021 01 01 |
| Résumé | (disponible en anglais seulement)
In 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). |
| Sommaire | (Résumé en langage clair et simple, non publié)
La même technologie utilisée pour l'imagerie par résonance magnétique (IRM) dans les applications médicales est utilisée pour imager la quantité
d'eau souterraine dans les roches et les sédiments. Cette technologie, appelée imagerie par résonance magnétique de forage (RMF) dans les milieux géologiques, nous aide à comprendre le stockage des eaux souterraines. Bien que la RMF soit utilisée
dans les puits de pétrole et de gaz de grand diamètre depuis les années 1990, elle n'a été adaptée que récemment pour l'exploitation de puits d'eau de faible diamètre et de forages géotechniques peu profonds. Cela fait de la RMF une nouvelle
technologie importante à intégrer dans le groupe d'instruments que le STM utilise déjà pour étudier la roche, les sédiments et les eaux souterraines. Une étude a été entreprise pour examiner un nouvel outil de RMF dans quatre forages de recherche STM
qui ont été forés dans des sédiments sujets aux glissements de terrain. L'étude a conclu que le nouvel outil RMF a de nombreuses applications pratiques dans les études de protection contre les glissements de terrain et les eaux souterraines - sujets
de recherche en cours dans les programmes STM. |
| GEOSCAN ID | 326104 |
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