[1] Review of the literature reveals that the nature of pore-scale interactions between gas hydrates and porous media remains a matter of controversy. To clarify the situation, nuclear magnetic resonance (NMR) measurements have been made on methane hydratebearing sandstones. The samples were synthetically prepared within the gas hydrate stability zone, at or near the seafloor in Monterey Bay, California. The method simulated natural hydrate deposition by gas flows that are not in thermodynamic equilibrium with the surrounding earth. The efficiency of hydrate production was variable, as has been observed elsewhere. When substantial hydrate saturations were achieved, NMR relaxation time measurements indicated that hydrate tended to replace water in the largest pore spaces. The relative permeability to water, as determined by an NMR-based correlation, was significantly reduced. The magnitude of this reduction was also consistent with formation of hydrate in the centers of pores, rather than with hydrate coating the grains. The growth habit suggested by these results is consistent with creation of hydrate nodules and lenses in coarse, unconsolidated sediments. It is also consistent with scenarios in which methane gas is delivered efficiently to the atmosphere as a result of seafloor slope failure, thereby strengthening global warming feedback mechanisms.INDEX TERMS: 3022 Marine Geology and Geophysics: Marine sediments-processes and transport; 3094 Marine Geology and Geophysics: Instruments and techniques; 5114 Physical Properties of Rocks: Permeability and porosity; 5194 Physical Properties of Rocks: Instruments and techniques; KEYWORDS: methane hydrate, pore geometry, growth habit, permeability, seafloor stability, climate change Citation: Kleinberg, R. L., C. Flaum, D. D. Griffin, P. G. Brewer, G. E. Malby, E. T. Peltzer, and J. P. Yesinowski, Deep sea NMR: Methane hydrate growth habit in porous media and its relationship to hydraulic permeability, deposit accumulation, and submarine slope stability,

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This study provides the first quantitative interpretation of the intensity pattern of spinning sidebands observed in the magic-angle spinning (MAS) NMR spectra of paramagnetic solids. The 200 MHz 1H MAS-NMR spectrum of copper chloride dihydrate and its deuterated analog are reported. The inhomogeneous interactions predominantly responsible for the sidebands are the magnetic dipolar couplings between the nucleus and the thermally-averaged magnetic moments due to the unpaired electrons on copper atoms. It is demonstrated that even in the presence of many such couplings to a given nucleus, a g anisotropy of the unpaired electron, and a chemical shift anisotropy of the nucleus, the net inhomogeneous interaction responsible for the sideband intensities is formally equivalent to a chemical shift tensor. However, inhomogeneous dipolar couplings to other nuclei give rise to subspectra corresponding to individual spin states of the other nucleus; the resultant composite spectrum no longer resembles that arising from a chemical shift tensor. The 1H MAS-NMR spectrum calculated using the known structure of copper chloride dihydrate correctly predicts the overall spectral width and sideband intensity pattern experimentally observed for the deuterated compound, and indicates that the unpaired electron density on the copper atom is partially delocalized (∼15%) onto the neighboring chlorine atoms. Two comparable sources of line broadening in deuterated copper chloride dihydrate are demonstrated to be the magnetic susceptibility anisotropy and T2 relaxation. The isotropic proton chemical shift is shown to be influenced by a small pseudocontact shift (∼10 ppm upfield) and a larger Fermi contact shift (∼76 ppm downfield).

wideline and magic angle spinning (MAS) NMR results are reported for water in a series of synthetic and naturally occurring silicate glasses containing from 0.04 to 9.4 wt % H20. For glasses free of paramagnetic metal ions, the absolute water contents can be accurately determined by a solid echo NMR technique with pyrophyllite, Al2Si4O10(OH)2, as an intensity reference. The MAS-NMR spectra can be interpreted as superpositions of the individual spectra of OH and anisotropically constrained H20 groups, the latter giving rise to spinning sidebands extending over ca. 100 kHz. Two methods are described to obtain percentages of OH and H20 groups from the relative intensities of the centerband and the spinning sidebands in these glasses. The MAS-NMR results are consistent with previous IR analyses indicating that low levels of water (<2-4 wt %) are mainly present as OH groups whereas at higher concentrations molecular H20 species dominate. Simulations of the MAS-NMR spectra based on the individual spectra of compounds in which the hydrogen-bearing species are structurally isolated (OH in tremolite and H20 in analcite) accurately reproduce the experimental spectra, indicating that the OH or H20 groups in the glasses are not preferentially clustered. The MAS-NMR centerband line shapes are dominated by a distribution of isotropic chemical shifts. The well-established linear dependence of chemical shifts on the O-H-O distance (a measure of the hydrogen bonding strength) leads to average distances of 290 ± 1.5 pm in all synthetic glasses except silica, 293 ± 1.5 pm in the volcanic rhyolite glasses, and 298 pm in silica glass. This value does not depend on the total water contents, indicating that the hydrogen-bonding characteristics of OH and H20 species in the glasses are similar.The wideline NMR procedure above yields underestimates of the total water content for synthetic and volcanic glasses containing ca. 1 wt % iron, presumably due to extreme signal broadening by the strong dipolar fields from the electron spins of the paramagnetic ions. These dipolar couplings also affect the line shape of the observable portion of the hydrogen resonance and produce intense spinning sidebands in the MAS-NMR spectra which invalidate determinations of OH/H20 ratios in these cases. and to Prof. J. R. Holloway (Chemistry, Arizona State University) for providing a water-containing rhyolite glass isotopically diluted with D2G.

We have used 3IP NMR magic-angle sample spinning and proton enhancement to characterize the following compounds: hydroxyapatite, Caio(OH)2(P04)6, and its nonstoichiometric forms; Can^/PO^; 38 2( 04)6•5 20; CaHP04• 2H2O; CaHP04; Ca(H2P04)2-H20; Ca(H2P04)2; and, as an example of niineralized tissue, dental enamel. The 31P isotropic chemical shifts tend to move upfield upon protonation of the phosphate. The chemical-shift anisotropy is small for P043groups, but significantly larger for HP042_ and H2P04~groups, where axially asymmetric shift tensors of a width ~100-130 ppm are observed. For Ca8H2(P04)6-5H20, an increase in the apparent shift anisotropy of the HP042_ groups at -165 °C suggests that some atomic or molecular motion is being partially frozen out. At room temperature the spectra of synthetic samples of nonstoichiometric hydroxyapatite with Ca/P as low as 1.33 closely resemble those of stoichiometric hydroxyapatite (Ca/P = 1.67). The nonstoichiometry in these samples does not result from the presence of additional compounds with Ca/P ratios less than 1.67. Rather, a scheme involving Ca2+ vacancies in a hydroxyapatite lattice with a concomitant loss of OHĩ ons and addition of protons seems most consistent with the NMR results. These additional protons do not appear to form rigid, discrete HP042~groups. Spectra obtained at -180 °C provide some evidence for motions involving the protonated phosphate in a hydroxyapatite lattice.