International Geologiical Congress - Oslo 2008

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GAH-01 Gas hydrates in oceanic and permafrost environments ? importance for energy, climate and geohazards

 

A basin modeling approach on gas hydrate formation assessment - Mackenzie basin, Canada

 

Karsten Kroeger, GeoForschungsZentrum Potsdam (Germany)
Rolando di Primio, GeoForschungsZentrum Potsdam (Germany)
Brian Horsfield, GeoForschungsZentrum Potsdam (Germany)
 

 

Quantification of gas hydrates has so far been based chiefly on well log and seismic data assessment and results have been extrapolated based on gas hydrate stability field models and lithological properties. However, more detailed studies, e.g. from the Mallik 5L-38 gas hydrate research well have shown that gas hydrate distribution is highly discontinuous and all estimates are therefore subject to large errors. On a global scale, the more recent gas hydrate estimates vary by the factor 10. It is therefore necessary to work out additional constraints on gas hydrate quantities.
The Mackenzie Basin in northwestern arctic Canada is characterized by up to 700 m thick permafrost, extending the stability field of gas hydrates down to more than 1200 m. We have chosen this region to assess methane fluxes on a basin scale since the geology of the basin is well known after 40 years of conventional hydrocarbon exploration. In this area, no BSRs, which indicate free gas below gas hydrate layers have been identified. This indicates that gas hydrate formation may have been inhibited due to limited availability of methane. According to results of numerical basin modeling using the program Petromod and available geochemical data a considerable part of hydrocarbons was generated from the lower Eocene to Paleocene part of the up to 10 km thick Tertiary deltaic succession. However, generation from these sources came to an end in most parts of the basin in the late Miocene due to uplift of the basin. Therefore leakage from reservoirs is proposed to be a main source for gas in sub-permafrost gas hydrates which, according to δ13C measurements are mainly fed by thermogenic methane. The specific burial and hydrocarbon generation history of the Mackenzie Basin makes the area an ideal natural laboratory to experiment on factors controlling natural gas emission from the subsurface and provides a unique opportunity to study formation capacities of gas hydrates.

 

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