Laboratory Studies of the NMR Response of Unconsolidated Materials
The results of NMR logging in groundwater wells, by Schlumberger Water Services, have demonstrated that it is possible to obtain reliable measurements of NMR relaxation times in these types of aquifer materials. Questions remain, however, about the interpretation of the NMR log in near-surface, unconsolidated or weakly consolidated aquifers. Can we obtain reliable estimates of hydraulic conductivity? In this project we ask: What is the link between the observed distribution of NMR relaxation times and the true distribution of pore sizes in an unconsolidated material?
Laboratory measurements are made of well-characterized samples of sand where we can control and/or determine the important physical and chemical properties. By varying the amount of iron coating the surfaces of the sand samples we are able to vary the strength of the surface relaxation and explore the related changes in the way the NMR measurements capture the pore geometry. We are using the 2.2MHz Maran Ultra NMR Core Analyzer (Resonance Instruments), in the Environmental Geophysics Lab at Stanford.
It is commonly assumed, in the interpretation of NMR relaxation data, that one pore space is sampled in the time-scale of the experiment.
Project Publications and Presentations
- Grunewald, E. and R. Knight, Conditions leading to non-exponential T2* relaxation and implications for surface NMR measurements, Geophysics, in press.
- Grunewald, E. and R. Knight (2011) A laboratory study of NMR relaxation times in unconsolidated heterogeneous sediments, Geophysics, 76, No. 4 G73-G83, doi: 10.1190/1.3581094
- Grunewald, E. and R. Knight (2011) The effect of pore size and magnetic susceptibility on the surface NMR relaxation parameter T2*, Near Surface Geophysics, 9, No. 2, 169-178, doi:10.3997/1873-0604.2010062
- Grunewald, E and R. Knight (2009) A laboratory study of NMR relaxation times and pore coupling in heterogeneous media, Geophysics, 74, E215, doi:10.1190/1.3223712.
- Grunewald, E., and Knight, R., Estimating pore properties from NMR relaxation time measurements in heterogeneous media, Eos Trans. AGU, 89(53), Fall Meet. Suppl., POSTER, 2008. (Winner of AGU Outstanding Student Presentation Award in Near-Surface Geophysics)