FROZEN HEAT | Volume 1

Silt and Sand-rich Host Sediments

Thinly interbedded (Nankai Trough; Gulf of Mexico GC955)

Without Gas Hydrate Porosity: 30-45%

Permeabilitiy 500-2000 md Mechanical Strength: Low

With Gas Hydrate Porosity: 10-15% Permeability; 0.1 - 0.5 md Gas Hydrate Saturation: 50-90%

Massively-bedded (Gulf of MexicoWR313; Mallik)

100 microns

Clay-rich Host Sediments

Grain-displacing in disrupted, deformed sediments (KG Basin, Ulleung Basin)

Pore-filling in undisrupted sediments (Blake Ridge)

Without Gas Hydrate Porosity: 50-70% Permeability: Diminishes with Depth

With Gas Hydrate Porosity: 45-60%

Permeability: Nil (0.0001 md) Gas Hydrate Saturation: 5-40%

to very low values (0.0001 md) Mechanical Strength: Very Low

With Gas Hydrate Porosity: 45-60%

100 microns

Permeability: Nil (0.0001 md) Gas Hydrate Saturation: 1-10%

100 microns

Massive Occurrences (no host sediment)

Consolidated host sediments (rock) (Messoyahki, Barrow (AK), Qilian Mtns (Tibet))

(Gulf of Mexico, Cascadia, others)

Variety of Lithologies Porosity: Reduced due to grain compaction, cementation Permeabilitiy: Reduced 500-2000 md Mechanical Strength: Very high

Figure 1.9: Summary of how the host sediment controls the form of gas hydrate occurrence. Gas hydrates are primarily found in unconsolidated sands (upper row) or clays (centre row). Hydrates also commonly occur in thin, hydrate-bearing sand layers separated by fine-grained sediment (upper right), and can even form in sands that have themselves been consolidated, or packed more tightly together, to form a rock (lower right). In clays, gas hydrates can exist in low concentrations in the small pores between grains (centre left). Gas hydrates in higher concentrations tend to displace grains to form veins, lenses, and nodules (centre right), and those veins, lenses or nodules can occasionally grow large enough to appear as a massive hydrate occurrences (lower left) (adapted from Boswell et al. 2011).

FROZEN HEAT 24