Numerical simulation of hydraulic fracturing process with consideration of fluid–solid interaction in shale rock

Abstract

As a critical technology for the efficient exploitation of shale gas, hydraulic fracturing is a two-way fluid-solid coupling interaction process of water-rock. The accurate water pressure calculation in single shale rock fracture during hydraulic fracturing is critical to the fluid-solid coupling analysis. This paper selected the fractured shale rock from the shale reservoir for analysis based on the Saint-Venant principle. Moreover, the water pressure in a single shale rock fracture was calculated by solving the Navier-Stokes equations. Meanwhile, a fluid-solid coupling model of fractured shale rock during hydraulic fracturing was established and evaluated the changing process of hydraulic fracturing. Our results show that in the hydraulic fracturing process, the changing process of water pressure in a single shale fracture with or without fluid-solid coupling is similar, and both have a water hammer effect. Single shale rock fracture opened instantly in an elliptical shape. The maximum instantaneous water pressure at the fracture tip considering fluid-solid coupling was 3.01 times the initial water pressure. The Mises stress at the fracture tip caused by the maximum instantaneous water pressure was 2.97 times the Mises stress at the fracture tip caused by the water pressure in the fracture after stable water pressure change. Mode Ⅰ fracture occurred in the fractured shale rock when high-pressure water rapidly invaded 2/3 of the length of the fracture. The findings in this study may help to understand the hydraulic fracturing mechanism in shale rock.