Investigation on crack initiation and propagation in hydraulic fracturing of bedded shale by hybrid phase-field modeling

摘要

The physical, mechanical, and hydraulic properties of shales with continuous bedding plane vary with bedding orientation significantly. Thus, understanding and predicting crack initiation and propagation in hydraulic fracturing of bedded shale are crucial in terms of reservoir reconstruction. In this paper, a hybrid phase-field method is proposed to investigate the hydraulic fracturing behaviour in bedded shale with pre-existing crack subjected to fluid injection. First, the Terzaghi and Mandel problems are carried out to validate the fully coupled hydro-mechanical model. The hybrid phase-field model applying to hydraulic fracturing treatment in the porous media is validated by the experiment of the plaster with a circular hole and two symmetric pre-existing cracks subjected to internal pressurization. Then, the numerical investigations of hydraulic fracturing behaviour in bedded shale specimen containing prefabricated cracks and varying bedding angles are implemented by employing the hybrid phase-field model. Moreover, the fluid pressure, damage region area and injection time responses are numerically investigated. Finally, the interaction of hydraulic fractures and two pre-existing natural cracks in bedded shale is presented. The hybrid phase-field modeling results show that the crack propagation paths and fluid pressure of bedded shale specimens depend on the pre-existing crack configuration, bedding angle and the mechanical and seepage properties of the bedding plane.