dependent on the particular reservoir characteristics. Many of the known marine deposits are probably unfeasible for hydrate production. Te candidates that are currently being explored are high concentration accumulations in coarse- grained sand environments with high porosity and permeability.
8.3.3 Global GHSZ Thicknesses
Burwicz et al. (2011) have calculated GHSZ thicknesses based on the global bathymetry, salinity, bottom water temperature, and heat flow (as a proxy to geothermal gradients as they are not globally available). GHSZ thicknesses can be considered
a proxy for potential hydrate deposits distribution but not necessarily for the real volume of hydrate-bearing sediments. Te formation of hydrates is mainly controlled by methane supply either through the direct degradation of organic matter within the GHSZ or through an upward flux of deeper biogenic and thermogenic methane. Global estimates of methane fluxes from deep sediments are poorly constrained.
Figure 8.20: Predicted thickness of the global GHSZ. The thickest zones (600–800m) are mainly situated in high-latitude regions (Arctic and Antarctic) due to low bottom water temperatures which maintain conditions required for hydrate formation. Extended GHSZs are also observed along continental margins (>500m) where thick sedimentary sequences are deposited. In these settings the extent of the GHSZ is not limited by sediment thickness so that free gas can accumulate in sediments below it. Note that this definition of the global GHSZ gives an upper limit to possible gas hydrate occurrences.
Figure 8.21: Gas hydrate saturation of the pore space, modified from Klauda & Sandler (2005).
