The Impacts of Bedding Strength Parameters on the Micro-Cracking Morphology in Laminated Shale under Uniaxial Compression

Featured Application The micro-cracking morphology and rock strength of laminated shale could be used to judge whether the shale gas formation is suitable for hydraulic fracturing or not. The micro-cracking morphology in laminated shale formation plays a critical role in the enhancement of shale gas production, but the impacts of bedding strength parameters on micro-cracking morphology have not been well understood in laminated shale formation. This paper numerically investigated the initiation and evolution of micro-cracking morphology with bedding strength parameters in laminated shale under uniaxial compression. First, a two-dimensional particle flow model (PFC2D) was established for laminated shale. Then, the micro-mechanical parameters of this model were calibrated using stress-strain curves and final fracture morphology measured in the laboratory. Finally, the impacts of bedding strength parameters on the uniaxial compressive strength (UCS), crack type and the complexity of fracture network were analyzed quantitatively. Numerical simulation results indicate that the UCS of shale varies linearly with the bedding strength, especially when the shear failure of beddings is dominant. Matrix cracks mainly depend on bedding strength, while the generation of tensile cracks is determined by the shear-to-tensile strength ratio of beddings (STR). The shale with a higher STR is likely to produce a more complex fracture network. Therefore, the bedding strength parameters should be carefully evaluated when the initiation and evolution of micro-cracking morphology in laminated shale formation are simulated.