Abstract
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.
Highlights
The initiation and evolution of micro-cracking morphology in a shale gas reservoir depends on the hydraulic treatments and on the mechanical properties of the rock matrix and beddings.Being different from isotropic rock, finely bedded internal structures in shale formation may result in much more complex anisotropic characteristics and may induce different fracturing morphologies.Previous investigations found that laminated structures could affect rock anisotropy
Cracks and tensile at different angles. These results clearly demonstrate with a higher contribute morecracks significantly to thedip complexity of micro-cracking morphology
A numerical model is established for the uniaxial compression of laminated shale formation
Summary
The initiation and evolution of micro-cracking morphology in a shale gas reservoir depends on the hydraulic treatments and on the mechanical properties of the rock matrix and beddings. The impacts of the tensile and shear strength of beddings on the uniaxial compression morphology in shale formations These results are helpful in understanding the relationship between strength, crack types and crack fractal dimension of shale specimens are investigated under bedding strength and the evolution a fracture network in shale gas formations. The numerical simulationsofreveal the role of bedding strength parameters inIt makestensile it possible to predict the complexity of the shale fracture network based on the final fracture cracking and micro-cracking morphology in shale formations These results are helpful in morphology of shalethe under uniaxialbetween compression, canparameters be used toand optimize hydro-fracturing understanding relationship beddingwhich strength the evolution of a designfracture siting. It makes it possible to predict the complexity of the shale fracture network based on the final fracture morphology of shale under uniaxial compression, which can be used to optimizeShale hydro-fracturing siting
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