Nuclear magnetic resonance diffusion measurements for characterization of the near-surface
Abstract/Contents
- Abstract
- Nuclear magnetic resonance (NMR) logging tools can be used to directly measure the response of hydrogen-bearing fluids in sediments surrounding a well or borehole. To date, applications of NMR in the near-surface have relied solely on relaxation time measurements to assess hydrogeological properties. The sensitivity of the NMR measurement to the diffusivity of pore fluids can provide additional information about properties of pore fluids and the geometry of the pore space. The goal of this thesis is to evaluate the application of NMR diffusion measurements to characterize properties of the near-surface that are relevant to groundwater problems. Internal gradients, caused by magnetic susceptibility contrasts between the solid matrix and the pore fluid, are a potential source of error in NMR measurements of the apparent diffusion coefficient (D). The results from a laboratory study show that internal gradients in sediments are often large enough to significantly impact NMR logging measurements of D. It is therefore important to consider possible effects from internal gradients when interpreting D measurements. To assess the link between D measurements and pore size, a numerical modeling study was conducted for model pores with a range of magnetic susceptibilities and surface relaxivities. We see that the expected relationship between D and pore size only applies in pores with low magnetic susceptibility and low to moderate surface relaxivity. In a complementary laboratory study, we find that D in natural sediments is largely controlled by internal gradients caused by grains with high magnetic susceptibility. We conclude that internal gradients will significantly limit the ability to estimate pore size from NMR logging measurements of D. In a subsequent pair of studies, we evaluate the use of NMR diffusion and relaxation time measurements to quantify organic contaminants in sediments. A laboratory study showed that the ability to quantify contaminant when water is also present depends on the properties of the contaminant and on the properties of the sediment. The addition of the diffusion measurement increased the range of conditions where NMR measurements could be used to quantify contaminant volumes compared to relaxation time measurements alone. In a field study, we show that NMR logging measurements can be used to detect and quantify in situ petroleum contamination. Diffusion and relaxation time measurements were used together to identify and estimate the volume of contaminant in the sediments surrounding existing monitoring wells. This research shows that diffusion measurements can enhance the ability of NMR logging measurements to quantify subsurface contamination, but that internal gradients limit the applicability of diffusion measurements for estimating pore size.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2016 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Fay, Emily L |
|---|---|
| Associated with | Stanford University, Department of Geophysics. |
| Primary advisor | Knight, Rosemary (Rosemary Jane), 1953- |
| Thesis advisor | Knight, Rosemary (Rosemary Jane), 1953- |
| Thesis advisor | Mukerji, Tapan, 1965- |
| Thesis advisor | Vanorio, Tiziana |
| Advisor | Mukerji, Tapan, 1965- |
| Advisor | Vanorio, Tiziana |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Emily L. Fay. |
|---|---|
| Note | Submitted to the Department of Geophysics. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2016. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2016 by Emily Louise Fay
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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