Image-based modelling of rock non-linear deformation under low stress levels

This study presents an image-based method for simulating the non-linear deformation of rocks caused by the pore-closure effect under increasing confining stress, by incorporating the partial-volume effect inherent in low-resolution digital rock images. The method first reconstructs digital rock models in which each voxel is assigned a pore fraction value between 0 and 1. Each partial-volume voxel is then treated as a two-part spring, where the compliant pore phase deforms before the stiffer solid phase. The continuous non-linear deformation process is discretised into a sequence of linear finite-element steps, each driven by a fixed macroscopic strain. The predictions of the method agree well with experimental stress–strain curves and wave velocities measured on three sandstone samples. These results demonstrate that the proposed method not only captures the macroscopic non-linear deformation but also provides direct pore-scale insight into the microstructural evolution that governs the mechanical behaviour of rocks under confinement.