关键词: CT扫描, 微观孔隙结构, 离散元, 岩石力学特性, 裂缝扩展

Abstract: Reservoir rock is a type of heterogeneous material, which has pore structure with complex geometry, and microstructure affects the macro-mechanical properties and fracture characteristics of rocks. Therefore, understanding of reservoir rock micro-pore structure and its influence on rock mechanics is of great significance to oil and gas exploitation and reservoir transformation. For this reason, micro-pore structure of tight sandstone is quantitatively characterized by CT scanning experiment and digital image processing technology, and a discrete element model with pore structure is established. The micro-parameters of the model are calibrated by uniaxial compression experiment. The influence of pore structure on rock mechanical properties and crack propagation is analyzed by uniaxial compression simulation in PFC3D. The results show that the probability distribution of micro-pore structure of tight sandstone satisfies the lognormal distribution. The geometry and distribution of micro-pore structure are complex and have fractal features. Existence of micro-pore structure results in decrease of uniaxial compressive strength. The larger the fractal dimension is, the smaller the uniaxial compressive strength is, and the relationship is approximately linear. The micro-pore structure plays a decisive role in crack initiation position, propagation and penetration direction. Cracks initially appear at the tip of the pores. In the plane parallel to the loading direction, the cracks propagate along the 30° direction of the tip of the pore and parallel to the loading direction. In the plane perpendicular to the loading direction, the crack in the XY plane extends along the axis of the fracture or causes the hole diameter to increase. Cracks are likely to cause penetration between pores during loading.

Key words: CT scanning, micro-pore structure, discrete element, rock mechanical properties, crack propagation