Abstract
Previous studies on hydraulic fracturing mainly focus on the effects of the in-situ stress state, permeability, fracturing fluids, and approach angle in homogeneous rocks, but the impacts of joint mechanical properties in laminated shale reservoirs on the propagation and formation of the fracture network are still unclear. In this study, a coupled fluid-mechanical model was developed to investigate the impacts of joint mechanical properties on hydraulic fracture propagation. Then, this model was validated with Blanton’s criterion and some experimental observations on fracture morphology. Finally, a series of numerical simulations were conducted to comparatively analyze the impacts of joint mechanical properties on the total crack number, the percentage and distribution of each fracture type, the process of crack propagation, and the final fracture morphology. Numerical results show that the cracking behaviors induced by joint mechanical properties vary with the approach angle. Joint strength has a significant influence on the generation of matrix tensile cracks. The tensile-to-shear strength ratio plays an even more important role in the shear slips of bedding planes and is conducive to the formation of complex fracture morphology.
Highlights
The huge demand for unconventional natural gas has stimulated the exploration and exploitation of shale gas reservoirs
Because shale gas reservoirs have extremely low permeability and porosity, the gas production from a shale reservoir is usually enhanced by a horizontal well plus staged hydraulic fracturing [1,2,3,4,5]
In order to better investigate the influences of the joint strength and tensile-to-shear strength ratio on hydraulic fracture propagation, we study the relationship between the fracture type and crack aperture
Summary
The huge demand for unconventional natural gas has stimulated the exploration and exploitation of shale gas reservoirs. Most of the previous investigations only considered one or two main preexisting fractures in their model, while the shale gas reservoir as a sedimentary formation has massive layered structures In this sense, a particle-based numerical method is a good choice when the interaction between induced and natural fractures is to be captured under various geological and environmental conditions. A coupled fluid-mechanical model was established based on PFC2D and validated by Blanton’s criterion This model was used to comparatively study the influence of the joint strength and tensile-to-shear strength ratio on the crack propagation as well as hydraulic fracture morphology under different approach angles.
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