Burial/Compaction and Seismic Anisotropy in Shaly Formations

The major trends in the relation between seismic anisotropy and compaction/diagenesis in shaly formations have been recently analyzed from two databases. Unfortunately many of the data of one of the databases correspond to other lithologies than shales, even in a broad sense, which tends to weaken the reached conclusions. In the present study we re-iterate the analysis on two carefully selected and actualized large databases (typically more than 800 samples). Our results confirm that burial/compaction can be excluded as a major cause of seismic anisotropy in shaly formations. Also clay platelet alignment can explain most of the anisotropy measurements of both databases. As a consequence, burial and/or compaction has generally no first order effect on clay platelet alignment. We suggest that the condition of deposition of the sediments is the major factor for the alignment of the clay platelets. At last, we propose simple plots for straightforwardly quantifying the Orientation Distribution Function coefficients W_200 and W_400 of the clay platelet alignment from the measurement of seismic anisotropy parameters.