A two-dimensional coupled hydro-mechanical finite-discrete model considering porous media flow for simulating hydraulic fracturing

• Development of a fluid-solid coupling model considering rock matrix permeability for hydraulic fracturing.
• Using a simple pure fracture seepage to characterise porous media flow and fracture seepage.
• A calibration approach for rock macroscopic permeability is recommended.
• Influence of pore pressure and fluid viscosity on hydraulic fracturing is studied.
• The distribution of stress and fluid pressure, and crack extensions in hydraulic fracturing can be reproduced.

In this study, we propose a new coupled hydro-mechanical model considering porous media flow (FDEM-flow) for simulating hydraulic fracturing, which makes full use of the unique topological connection between joint elements and solid elements in the combined finite-discrete element method (FDEM). The joint elements form the flow channel for fluid, through which flow obeys the cubic law. In addition, viscous forces of fluid are taken into account in FDEM-flow. A simple example with analytical solution is given to verify the model. Then, the effects of fluid viscosity on hydraulic fracturing are investigated by this model. The simulated results show that when a low viscosity fluid is injected, the fluid infiltrates the fracture rapidly. The initiation pressure is lower than the theoretical value and the breakdown pressure is slightly larger than the initiation pressure. When high viscosity fluid is injected, fluid infiltrate into the cracks very slowly. The initiation pressure is close to the theoretical value and the breakdown pressure is much larger than the initiation pressure.