3D thermobaric modelling of the gas hydrate stability zone onshore central Spitsbergen, Arctic Norway

Abstract

Dissociation of onshore natural gas hydrates (NGHs) could lead to the release of methane directly to the atmosphere, especially in Arctic regions such as Svalbard, where enhanced climate warming has the capacity to promote rapid methane evasion to the atmosphere following the decay of permafrost and glacier ice. Here we present the first assessment of the NGH stability zone (GHSZ) in central Spitsbergen, a climate-sensitive part of Svalbard where thermobaric conditions appear favourable for onshore NGH formation. We developed an approach incorporating regionally constrained 3-dimensional parameterisation of temperature, pressure and phase boundary (93% methane, 7% ethane, 35 ppt salinity) to define the GHSZ. This resulted in an up to 650 m thick (mean: 308 m) GHSZ covering 74.8% of the study area, thickening significantly in the east where the climate is colder. Perturbation of the base case parameters was undertaken to quantify the sensitivity of the GHSZ to the variation in environmental conditions across the study area. We present 26 examples of these deterministic scenarios and show that the largest changes in the GHSZ were observed when either the ethane content (to 20%) or the regional pore water pressure (to 125% hydrostatic) were increased. The GHSZ also increased markedly when the geothermal gradient was reduced from 33 to 26 °C km−1, but was almost completely inhibited by a dry gas (100% methane), greater salinity (50 ppt), or exposure to an increase in surface temperatures relative to the mean annual air temperature (e.g., by 2 °C). Most parameters affected both the upper and the lower stability boundary of the GHSZ, with the exception of the geothermal gradient, which impacted primarily upon the latter. Given that Svalbard is host to a proven petroleum system, we conclude that NGHs almost certainly exist onshore Svalbard.