--> ABSTRACT: Shale Compaction in the Overpressured Beaufort-Mackenzie Basin, Canada, by Dale R. Issler, T. John Katsube, John Bloch; #91020 (1995).

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Shale Compaction in the Overpressured Beaufort-Mackenzie Basin, Canada

Dale R. Issler, T. John Katsube, John Bloch

The Beaufort-Mackenzie Basin (BMB) is a natural laboratory for studying shale compaction and overpressure generation. It is characterized by extreme lateral and temporal variations in sedimentation rate which correlate with distinct compaction and pore pressure trends. Well log interpretation is enhanced by the relatively uniform composition of this shale dominated succession and by the availability of core material and pore pressure data (approximately 1500 pressure measurements from over 110 wells) for log calibration. Five major compaction zones have been previously mapped using sonic log data from more than 110 BMB wells. Forty-one shale core samples from 9 wells were selected for petrophysical and chemical property measurements to confirm the log-based studies and to obtain data for constraining compaction models.

Compositional data confirm the relative homogeneity of BMB shales and indicate that the variability in mineral composition is largely depositional in origin with minimal diagenetic effects. The samples contain less than 2% Total Organic Carbon of Type III. I/S and quartz are the most abundant minerals (30 to 55% and 25 to 58%, respectively) and show no depth-related trends. Measured core (effective) porosity varies between 5% and 39% and mean pore-size ranges between 9 and 330 nm in samples recovered from the depth range, 1 to 4.9 km. Measured permeabilities are in the nano-darcy range. The trend of decreasing mean pore-size and porosity with depth is drastically reduced or reversed within overpressured zones, particularly at depths > 2.4-3.4 km. Core porosity measurements are in g od agreement with previous sonic log porosity determinations, confirming the relationship between undercompaction, overpressure and high sedimentation rate, as inferred from well log analysis.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995