Nuclear-Magnetic-Resonance (NMR) Quantitative-Relaxation-Tomography (QRT) is proposed for use with available 11-cm cores of the top meter of ocean bottom sediments in order to determine porosity and pore-size distributions as functions of position within a core without disturbing the material. This information, with cm or mm resolution, is relevant to the understanding of acoustic properties of ocean bottom sediments, which affect sonar and echo sounding. The feasibility of the method is shown by QRT on samples up to 8 cm in diameter of glass beads ranging from 0.3 to 16 mm in diameter and also of small 2-mm plastic cylinders. Three kinds of maps are produced for each section, with 0.70.7 mm pixel size and 5 mm slice thickness: Proton Density maps, T1 maps and T2 maps. For each voxel the relaxation data are fitted to single exponential functions, giving values of T1, T2 and also of extrapolated signal, giving voxel porosity. Since the tomograph has a minimum echo time of 10 ms, any part of the signal having T2<10 ms is not seen. In the systems tested, the NMR porosity Φnmr is, for this reason, approximately 4 percentage porosity units less than the porosity Φ measured destructively by wet and dry weight differences.
V. Bortolotti, M. Gombia, F. Cernich, E. Michelozzi, P. Fantazzini (2006). A study to apply nuclear magnetic resonance porosity measurements to seabed sediments. MARINE GEOLOGY, 230, 21-27 [10.1016/j.margeo.2006.03.014].
A study to apply nuclear magnetic resonance porosity measurements to seabed sediments
BORTOLOTTI, VILLIAM;GOMBIA, MIRKO;FANTAZZINI, PAOLA
2006
Abstract
Nuclear-Magnetic-Resonance (NMR) Quantitative-Relaxation-Tomography (QRT) is proposed for use with available 11-cm cores of the top meter of ocean bottom sediments in order to determine porosity and pore-size distributions as functions of position within a core without disturbing the material. This information, with cm or mm resolution, is relevant to the understanding of acoustic properties of ocean bottom sediments, which affect sonar and echo sounding. The feasibility of the method is shown by QRT on samples up to 8 cm in diameter of glass beads ranging from 0.3 to 16 mm in diameter and also of small 2-mm plastic cylinders. Three kinds of maps are produced for each section, with 0.70.7 mm pixel size and 5 mm slice thickness: Proton Density maps, T1 maps and T2 maps. For each voxel the relaxation data are fitted to single exponential functions, giving values of T1, T2 and also of extrapolated signal, giving voxel porosity. Since the tomograph has a minimum echo time of 10 ms, any part of the signal having T2<10 ms is not seen. In the systems tested, the NMR porosity Φnmr is, for this reason, approximately 4 percentage porosity units less than the porosity Φ measured destructively by wet and dry weight differences.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
