Structural, Mineralogical, and Rheological Properties of Methane Hydrates in Smectite Clays

Abstract

Smectite clays are widely dispersed in deep ocean sediments and can be subdivided into two representative clay types, Cheto- and Wyoming-montmorillonites. In this study, we measured the thermodynamic phase behavior of methane hydrates intercalated at various concentrations of these clays and found the relatively weak promotion tendency when compared to that of pure methane hydrate stability. The structure and morphology of intercalated methane hydrate (IMH) samples were analyzed using the MAS NMR, RAMAN, LT-XRD, and Cryo-FE-SEM. The (27)Al and (29)Si solid-state MAS NMR spectra of IMH Cheto and Otay clays represent that the structural stability is preserved during the IMH formation, which is also indicated with the XRD pattern showing no structural transformation but different d-spacing values due to clay-water suspension and IMH. In addition, Cryo-SEM images of IMH samples show that IMH Otay clays provide well-developed methane hydrate (MH) morphology, compared to the IMH Cheto clay.