ABSTRACT

Natural gas hydrates may contribute to both future energy supplies and to the increase of atmospheric greenhouse gases. Evaluation of the importance of gas hydrates requires an improved knowledge of the preset hydrate distribution. Analysis of thermal and geophysical logs from 369 wells in the Canadian Arctic Islands and the Beaufort SeaMackenzie Delta regions indicates that a maximum of 1900 to 3900 Gt of methane may be stored as hydrate in this region. Consideration of the recent geological and climatic history of the area demonstrates that the volume of hydrate is variable with time_ Decomposition of hydrates is possibly occurring beneath approximately 73,000 km2 of the Canadian Beaufort Shelf. Approximately 105 m3 hydrate/km2 may become unstable over a 100 year period due to marine transgression. In contrast, cooling of sediments and hydrate formation is occurring In the Arctic Islands as new land emerges from the ocean in response to isostatic rebound.

INTRODUCTION

Natural gas hydrates consist of gas molecules such as methane enclosed in the cage-like structure of water molecules (Davidson, 1973). Gas hydrates are stable under certain pressure and temperature conditions, such as those found in sediments beneath permafrost and ice-sheets in the cold regions and beneath the seafloor at water depths greater than about 200m. Recently, a great deal of attention has been focused on natural gas hydrates as they may contribute to future energy supplies. Gas hydrates also represent a significant source of greenhouse gas (methane) which may be released to the atmosphere as hydrates in the lithosphere decompose in response to climate warming. It is important, therefore, to improve our knowledge of the hydrate distribution in order to evaluate their overall importance. The volume of hydrate in the earth's sediments is not constant and varies over time as subsurface temperature and pressure conditions change.

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