FROZEN HEAT | Volume 2

the Gulf of Mexico (Frye et al. 2008), and the eastern Nankai Trough (Fujii et al. 2008) provide insight into the resources that might be available as sand-hosted gas hydrates. These studies informed a recent global review by Johnson (2011), which pro- vides a rough first-order estimate of the share of global in-place resources of gas hydrates that could occur in sand reservoirs (Figure 2.4). The estimate suggests significant potential tech- nically recoverable resource (TRR) of gas hydrates in every re-

gion of the globe, with a cumulative mean estimate of in-place resources within sand reservoirs of more than 1 217 trillion cubic metres of gas. That value represents roughly 5 per cent of the typical mid-range estimate for global gas hydrate in-place resources. However, these estimates are highly speculative and require significant field confirmation. The following sections review a range of the best-studied occurrences of gas hydrates in both coarse-grained and fine-grained reservoirs.

Estimates of the methane held in hydrates worldwide Estimates of the methane held in hydrates orld ide

Figure 2.4-b: Gas hydrates resource potential by global regions. Estimates of the methane held in hydrates worldwide. Early estimates for marine hydrates (encompassed by the green region), made before hydrate had been recovered in the marine environment, are high because they assume gas hydrates exist in essentially all the world’s oceanic sediments. Subsequent estimates are lower, but remain widely scattered (encompassed by the blue region) because of continued uncertainty in the non- uniform, heterogeneous distribution of organic carbon from which the methane in hydrate is generated, as well as uncertainties in the efficiency with which that methane is produced and then captured in gas hydrate. Nonetheless, marine hydrates are expected to contain one to two orders of magnitude more methane than exists in natural gas reserves worldwide (brown square) (U.S. Energy Information Administration 2010). Continental hydrate mass estimates (encompassed by the pink region) tend to be about 1 per cent of the marine estimates (Figure modified from Boswell and Collett (2011)). Estimates are given in Gigatonnes of carbon (GtC) for comparison with other organic hydrocarbon reservoirs. At standard temperature and pressure, 1 GtC (Gigatonnes of carbon) represents 1.9 Tcm (trillion cubic meters) of methane which has an energy equivalent of approximately 74 EJ (exajoules).

Gigatonnes carbon Gigatonnes carbon

10 7 10 7

First observation of marine hydrate Methane in marine hydrates (based only on the pressure and temperature requirements for hydrate stability) First observation of marine hydrate Methane in marine hydrates (based only on the pressure and temperature requirements for hydrate stability)

10 6 10 6

10 5 10 5

Methane in marine gas hydrates Methane in marine gas hydrates

10 4 10 4

10 3 10 3

10 2 10 2

Methane in permafrost gas hydrates Methane in permafrost gas hydrates

Global natural gas reserves (conventional) Global natural gas reserves (conventional)

10 10

1 1

1970 1975 1980 1985 1990 1995 2000 2005 2010 1970 1975 1980 1985 1990 1995 2000 2005 2010

A GLOBAL OUTLOOK ON METHANE GAS HYDRATES 39