ABSTRACT: Evolution of Shale Petrophysical Properties with Compaction in the Overpressured Zone of the Beaufort-McKenzie Basin

KATSUBE, T. J., Geological Survey of Canada, Ottawa, Ontario, Canada, D. R. ISSLER, Institute of Sedimentary and Petroleum Geology, Calgary, Alberta, Canada, M. A. WILLIAMSON, Geological Survey of Canada, Atlantic Geoscience Centre, Dartmouth, Nova Scotia, Canada, and M. E. BEST, Geological Survey of Canada, Pacific Geoscience Centre, Sidney, British Columbia, Canada

The effect of compaction on porosity, pore structure and pore-size distribution of shales has been investigated for a suite of 10 samples from a depth of 1000-4100 m in the Beaufort-McKenzie Basin offshore northern Canada. This is part of a comprehensive petrophysical study of shales and compaction processes that aims to fill the gap in our knowledge of shale properties. Information on permeability and porosity evolution of shales with compaction is required for models that attempt to reconstruct fluid migration pathways over geologic time.

Measured porosity varies between 30% at 1000 m and 5-10% at depths of 2500 m to 4000 m, depending on lateral position in the basin. These results support earlier work that defined shale compaction zones on the basis of sonic log data calibrated to shale core measurements. The pore-structure generally shows a unimodal pore-size distribution, with modes at approximately 200 nm at 1000 m, decreasing to 10-20 nm at greater depths. Permeabilities are within the range 10-14-10-11 sq. meters near the seafloor and decrease to approximately 10-22-10-26 at greater depth, a 6-10 order of magnitude decrease due to burial. With increasing depth, diagenetic and overpressure effects on pore structure become significant.

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