Abstract

Arctic gas hydrates (GH) sequester large volumes of natural gases. New Beaufort Sea-Mackenzie Delta Basin (BMB) permafrost and geothermal gradient maps motivate the revision of the gas hydrate stability zone (GHSZ) and re-evaluation of BMB GH resources using two independent, petroleum system-based resource models. The first model is both deterministic and spatial, and it is based on the quantitative analysis of both GH occurrences and reservoir characteristics. In addition, a spatial density of structural elements parameter that is well correlated to GH occurrences is used as a proxy for petroleum migration into the GH stability zone for the purpose of guiding the interpolation of GH occurrences between wells. The second GH resource model is probabilistic. Like the deterministic resource model, it permits regional resource characterization as a function of reservoir parameters that are potential proxies for technological and economic supply requirements. The total resource potential mapped deterministically is 8.82 × 10¹²m³ raw initial natural gas in place (GIP). Geographic resource variations are illustrated by GHs maps exceeding specified characteristics as illustrated by GH saturation (S_gh), which is a potential proxy for reservoir energy. If the average S_gh is either >30% or >50%, then the inferred GH resource volumes are 6.40 × 10¹² m³ and 4.59 × 10¹² m³ GIP, respectively. The probabilistic GH resource appraisal predicts an expected total resource = 10.23 × 10¹² m³ GIP. Similarly, if the average S_gh is either >30% or >50%, then the respective GH resource volumes inferred probabilistically are expected to be 6.93 × 10¹² m³ and 4.20 × 10¹² m³ GIP, respectively, which is comparable to the deterministically mapped estimates. Methane sequestered in GHs constrains regional, long-term, geologically-sourced methane flux rates. The BMB long-term regional methane flux sequestered in GHs is certainly <4.20 mg/m²/d and more likely not >0.12 mg/m²/d, whereas a single active thermogenic natural gas seep has a discharge of approximately 3.9 × 10³ mg/m²/d. Although additional study is required before the atmospheric contribution from BMB geologically-sourced methane can be assessed, it is clear that:

1) much more thermogenic methane migrates into the GHSZ, or higher, than is trapped in the conventional resource;

2) the current atmospheric natural gas flux at point seeps can exceed greatly the long-term regional flux sequestered in the GHSZ, and;

3) the GHSZ is an imperfect trap.