3D thermo-baric modeling of the gas hydrate stability zone of central Spitsbergen, Arctic Norway

Dissociation of onshore natural gas hydrates could lead to the release of methane directly to the atmosphere. This is particularly alarming in the Arctic that experiences enhanced warming compared to more temperate latitudes. The Norwegian high-Arctic Svalbard archipelago offers 1) the presence of relatively thick permafrost giving suitable thermo-baric conditions within the gas hydrate stability zone (GHSZ) and 2) an active petroleum system. The recent discovery of natural gas in direct association with permafrost in Adventdalen provides clear evidence for recent gas migration, and motivated us to consider whether some of this gas could also occur as natural gas hydrates. We thus present a comprehensive assessment of the GHSZ in central Spitsbergen spanning the onshore and near-shore (fjords) settings. We utilize a novel approach incorporating 3-dimensional parameterization of temperature, pressure and the gas hydrate phase boundary. Our base case model employed a constant geothermal gradient of 33°C km^-1 with a laterally varying surface temperature, a 93:7 methane-ethane mixture and a pore water salinity equivalent to sea water. This resulted in an up to 650 m thick (mean: 308 m) GHSZ covering 74.8% of the study area and thickening significantly to the east where the climate is colder. We quantify the uncertainty range of the GHSZ maps by perturbing base case parameters with data-driven constraints. The largest changes in the GHSZ were observed when either the ethane content or the regional pore water over-pressure were increased (to 20% and to 125% hydrostatic pressure, respectively), or when the geothermal gradient was reduced to 26°C km^-1. The GHSZ was almost completely inhibited (by ca. 98%) in the presence of a dry gas (100% methane), greater salinity (50 ppt), or an increase in subsurface temperatures relative to the mean annual air temperature (e.g. by 2°C). While deep burial greatly reduced overall reservoir properties, fractured sandstones of Paleogene, Cretaceous and Late Triassic-Middle Jurassic age all lie partly within the GHSZ and may represent possible reservoirs. We conclude that there is high potential for natural gas hydrate in central Spitsbergen and a dedicated exploration effort is needed to find and characterize natural hydrate deposits onshore Spitsbergen.