Compaction behavior of argillaceous sediments as function of diagenesis

Abstract

The paper presents the results of laboratory compaction tests on samples of Kimmeridge clay taken from two different locations in the UK. The main objective of the laboratory tests is to determine how diagenesis affects the hydro-mechanical properties and compaction behavior of argillaceous sediments. The two Kimmeridge clays used in the tests are essentially from the same parent material but have undergone different degrees of mechanical and chemical diagenesis. The laboratory tests are designed to determine the effects of mechanical loading and chemical processes on changes in porosity, permeability, compressibility, strength and effective horizontal stress in argillaceous materials. Another objective of the study is to investigate the adequacy of soil mechanical constitutive models in predicting the response of argillaceous materials to conditions corresponding to burial depths in sedimentary basins. The tests on Kimmeridge clay are carried out to as high as 150 MPa effective vertical stress corresponding to about 9 km in burial. The results indicate that mechanical compaction and burial depth cannot explain the differences in the hydro-mechanical behavior of the tested materials. The differences in hydro-mechanical response are attributed to chemical diagenesis by precipitation of minerals in the pores of the sediment. Other observed effects of chemical diagenesis on hydro-mechanical behavior of lithified sediments are: (1) increase in apparent pre-consolidation stress; (2) decrease in compressibility; (3) decrease in permeability; and (4) decrease in effective horizontal stress. Implications of the results to fluid flow and overpressure development in sedimentary basins are discussed.