Laboratory study of methane hydrate formation kinetics and structural stability in sediments

- Comparison of hydrate kinetics & yield in Stöber silica, bentonite clay and pure hydrate.
- Particle size plays a crucial role in kinetics and hydrate yield.
- Raman spectroscopy reveals that the hydrates are in sI.
- Hydration number using Raman spectroscopy estimated as 5.93-6.12.

The natural gas hydrate deposits in the offshore of India are embedded in different sediments, namely clay rich silts and sands, coarse grain sand and volcanic fly ash. The variations in gas hydrate concentrations at different geological locations shows dependency on sediment mineralogy. It is also known that the particle size of the sediments plays an important role in hydrate formation and gas hydrate concentrations in sediments. We carried out systematic studies on the methane hydrate formation kinetics and methane hydrate volumetric yields, in stirred reactor experiments, using suspensions of synthetic silica and natural sediment from Krishna-Godavari (KG) Basin. The hydrate formation behavior in silica and KG basin sediment is also compared with the formation of methane hydrates in a “pure system” without sediment or added silica grains. Our results show that the hydrate formation kinetics is faster in 50 μm silica system followed by that in natural marine sediment. Observed methane hydrate yield in the laboratory is higher (∼39%) in both the pure (no sediment) and 1 μm silica suspensions. The gas intake is much quicker (∼375 min) in the suspension of 50 μm silica system, while the hydrate yield is noticeably less (∼29.38%). The methane hydrates are characterized by Raman spectroscopy and they show characteristic structure I (sI) methane hydrate signatures, with a hydration number in the range 5.93-6.12.