Stress-induced deformation of sandstone monitored in X-ray microscopy and its influence on permeability evolution

In recent years, various digital cores have been constructed to depict the microstructure of rock. However, how to reveal the evolution of microstructure and fluid flow in the process of mechanical damage is a big challenge. In this paper, based on in-situ uniaxial compression in three-dimensional (3D) X-ray microscopy, the Es-3 sandstone was used to study the stress-induced structure deformation and its influence on permeability at pore scale. Both two-dimensional (2D) images and 3D digital cores were reconstructed at different stress stages. During the progressive deformation process of rock, porosity, effective porosity, pore size distribution, pore shape distribution, tortuosity and fractal dimension were obtained. Based on digital cores, the permeability was calculated and seepage path was simulated under different axial stresses. This work revealed that the distribution of pores and effective pores in sandstone is microscopically heterogeneous. In compaction stage, the pores shrank and micro cracks closed, consequently the permeability decreased. In fracturing process, the pores expanded and new cracks were generated, as a result, the permeability significantly increased.