--> Abstract: Physical Properties in Shales and Mudstones Versus Depth and their Implications for Basin Analysis; #90063 (2007)

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Physical Properties in Shales and Mudstones Versus Depth and their Implications for Basin Analysis

 

Øyvind, Marcussen1, Christer B. Peltonen1, Nazmul Haque Mondol1, Knut Bjørlykke1, Jens Jahren1 (1) University of Oslo, Oslo, Norway

 

Changes in physical properties of fine-grained sediments during burial are the result of complex compaction processes. Well log data from the Norwegian continental shelf, together with mineralogical and geochemical data, have been used to study the compaction behaviour for shales and mudstones with different composition. In the North Sea, smectite rich mudstones of Eocene and Oligocene age have lower velocities and bulk densities compared to mudstones consisting mostly of kaolinite, chlorite and mica. The difference in velocities can be in the order of 500-700 m/s at a burial depth less than 2 km. This is consistent with results from experimentally compacted clay minerals which show that smectitic clays have a low compressibility compared to kaolinitic clays. The low velocities and densities in smectitic rich sediments may also partly be due to a reduced effective stress caused by overpressure in the low permeability smectitic clays. In basin analysis simple exponential or linear compaction curves are often applied for shales. Well log data from the Norwegian continental shelf show that shales and mudstones are as different as sandstones with respect to their physical properties during burial. Changes in lithology and mineralogy can be related to provenance and sedimentary facies also for mudstones. Different types of shales and mudstones have different compaction trends. Using simple standard exponential curves may introduce large errors in basin analysis and seismic interpretation.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California