Compaction, strain, and stress anisotropy in porous rocks

Compaction in sedimentary basins is usually addressed as one dimensional process that ignores inelastic strain changes in the directions orthogonal to active load. In this study, we present new experiments of Sheshminskaya sandstone demonstrating the role of three dimensional inelastic compaction under true-triaxial load. We extend Athy’s law to three dimensional tensorial formulation of the compaction model and show that compaction in one direction is associated with decompaction in the orthogonal directions. Compaction begins with the onset of load with no yield criterion. The three dimensional compaction model accurately simulates the measured compaction values of the Sheshminskaya sandstone under sequential loading in three different directions. We apply the new compaction model to study the effects of vertical compaction on horizontal stress and overall compaction in sedimentary basins. We show that the vertical to horizontal stress ratio in sedimentary basins is controlled by the rock properties defined in this study. These properties are calibrated in laboratory experiments. Connecting the compaction and permeability tensors predicts that the three dimensional inelastic compaction causes significant anisotropy in the permeability even for homogeneous aquifers. Article highlights New true-triaxial experiments show that compaction in one direction is associated with decoThe black dashed line inmpaction in the orthogonal directions. We introduce a compaction-strain tensor that extends the isotropic Athy’s law. We show that the compaction-strain tensor is responsible for the stress and material anisotropy in sedimentary basins.