Dynamic fracture evolution of tight sandstone under uniaxial compression in high resolution 3D X-ray microscopy

Abstract

Stress-induced fracture evolution in tight sandstone reservoir is of great significance in hydraulic fracturing treatment and borehole stability. The meso scale fracture mechanism needs to be well understood. In this work, the smaller-sized tight sandstone specimens (4 mm in diameter and 8 mm in height) from Bashijiqike formation were studied under uniaxial compression in high resolution three dimensional (3D) X-ray microscopy (XRM). Using high-resolution XRM, 2D slices and 3D digital cores with real pore structure characteristics were reconstructed at different stages of uniaxial compression. During the uniaxial loading process, porosity and diameter distribution of the voids were obtained to analyze the progressive deformation of rock, and then the complexity and heterogeneity of the cracks were quantified by applying fractal analysis. The results show that the fracture evolution of tight sandstone at meso scale could be divided into compaction stage, linear elastic behavior stage, non-linear deformation stage and residual deformation stage. The mineral composition and meso structure of tight sandstone have significant effects to its mechanical properties, fracture pattern and crack morphology under uniaxial compression. The propagation direction of secondary cracks tends to parallel to the direction of axial stress, revealed by higher resolution of region of interest (ROI) imaging.