A New Quantitative Approach to Predicting Physical Property Changes During Diagenesis of Mudstones

Abstract

We developed a new technique for quantifying the amount of porosity loss during silica diagenesis. The technique is based on 3-D seismic data from offshore Norway, where the biosiliceous mudstones of the Kai and Brygge Formations are deformed by a polygonal fault system. Evidence is shown that the dip of the polygonal fault planes reduces abruptly across the opal-A to opal-CT diagenetic boundary, suggesting that the fault planes were passively rotated into shallower dips due to diagenesis. The reduction of fault plane dip was used to quantify the vertical compaction strain due to diagenesis. Using an independent assessment of the magnitude of the porosity loss, we are able to validate the method based on fault planes dip, and also to evaluate whether the porosity loss results in an exclusively vertical strain. We also investigate the impact of the silica diagenesis on the shear strength of the sediments and fault growth.