SEM imaging of gas hydrate formation processes and growth textures, and comparison to natural hydrates of marine and permafrost origin

Cryogenic scanning electron microscopy provides an excellent means for examining grain morphologies, grain contacts, phase distributions, and pore characteristics within gas-hydrate-bearing samples of both natural and laboratory origin. Here, we use SEM to observe a variety of laboratory-synthesized sI and sII gas hydrates of known composition and pressure-temperature histories. We show images that convey the diversity of textures observed at various extents of hydrate growth in single-phase gas hydrate systems and hydrate/sediment assemblages, including transient morphologies that are limited primarily to early-to-mid stages of reaction. The resulting textures of fully reacted and/or annealed samples are then followed through increasingly complex laboratory or ocean-floor processes, including compaction, compression, partial dissociation, or partial dissolution. Lastly, we compare the observed features to those developed within natural gas-hydrate-bearing samples recovered from both marine and permafrost settings. We find that lab-synthesized samples can be produced to yield remarkably similar textures, phase distributions, and grain contacts to those found in some hydrate-bearing materials recovered from natural settings.