International Geologiical Congress - Oslo 2008

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GDP-08 Basin subsidence and mantle dynamics

 

The hydrocarbon budget of the Mackenzie Basin (Canada): Generation, migration and surface losses

 

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

 

The carbon budget of sedimentary basins is of ongoing interest, not only for resource exploration and management. It becomes more and more apparent that thermal cracking of organic material within sediment basins also contributes significantly to the greenhouse gas budget by methane and CO2 exhalation. Gas hydrates have been put forward to play the role of a capacitor, storing high amounts of methane and releasing them during periods of climatic warming. In this study, the Mackenzie Basin in northwestern arctic Canada serves as an example of factors controlling hydrocarbon flow in a sediment basin.

In order to address all issues of hydrocarbon flow budgets, a detailed and comprehensive study of the Mackenzie Basin has been carried out. The Mackenzie is characterized by high rates of subsidence and filled by up to 10 km thick Tertiary deltaic sediments. Source rocks are of Eocene, Paleocene and Cretaceous age and, due to the complex basin history, each have experienced a specific maturation process. Late Miocene uplift and erosion together with arctic surface conditions have terminated most of the hydrocarbon generation in the basin. The structural complexity of the basin and the time relationship between generation from specific source rocks and the formation of reservoirs constrains possible source reservoir relationships. This is especially evident if generation from Paleocene and Cretaceous sources is considered which occurred before the formation of large offshore reservoir structures such as the large Amauligak field. Model results indicate that 90% of all hydrocarbons generated and expelled from the source rock are lost in the process of migration and, at least in part, are spilled at the seafloor and exhalated to the atmosphere. Timing of reservoir formation, spill from reservoirs and leakage are factors that contribute to this huge loss. These results are an example of how important a role natural gas release from sedimentary basins may have played in earth's climatic history and how important it is to consider this in future resource assessments.

 

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