--> Abstract: Shale Compaction and Illite/Smectite Diagenesis, Beaufort-Mackenzie Basin, Arctic Canada, by J. Ko and R. Hesse; #91012 (1992).

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ABSTRACT: Shale Compaction and Illite/Smectite Diagenesis, Beaufort-Mackenzie Basin, Arctic Canada

KO, J., and R. HESSE, McGill University, Montreal, Quebec, Canada

The burial trends of I/S mixed-layer clays in the Beaufort-Mackenzie basin were established on the basis of detailed mineralogical studies of 213 core and drill-cutting samples from 22 wells onshore and offshore. Shale compaction appears to play an important role in I/S diagenesis. Illitization in overpressured shales is faster and

more advanced than in normally compacted sections. For instance, relatively low I-content and composition gradients are observed in the normally pressured zone sandwiched between two geopressure zones in Reindeer D-27. Illitization in Taglu G-33 and Mallik A-06 is relatively advanced compared to Taglu C-42 where the top of the overpressured shale section is about 400 m deeper than in G-33 and A-06. Accelerated illitization in overpressure environments is probably due to higher water/particle ratios compared to normally compacted sections (c.f. Whitney, 1990). Hydrocarbons in the Beaufort-Mackenzie basin are found above, within and below overpressure zones. However, relative to the zone of I/S diagenesis they appear to occur always above or in the top portion of the active illitization zone, i.e., above the first occurrence of ordered I/S. Where illitization begins at relatively great depth (e.g., Taglu, Mallik), hydrocarbon occurrences are also deep. Where the apparent depth of illitization is shallow because of uplift caused by growth faults, diapirs, or tectonics, hydrocarbons also occur at shallow depth (e.g., Reindeer). In offshore wells where the depth of illitization is 1 to 1.5 km shallower than onshore, most hydrocarbon discoveries were made at depths of 1-2 km.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)