Mechanistic Explanation of the Impact of Pore Pressure on Hydraulic Fracture Propagation

The effect of non-uniform pore pressure field and saturation on fracture propagation is investigated using a peridynamics-based hydraulic fracturing simulator. The model solves for rock displacement, fluid saturation, and fluid pressure both inside and outside the fracture in a fully-coupled manner. When fractures initiate from multiple injection points, they can propagate towards each other by opening against the maximum stress. Laboratory experiments conducted on synthetic rock samples show that saturating a porous rock with fluid before fracturing it decreases the breakdown pressure. Under low far-field stresses in the laboratory, fractures are attracted towards the high pore pressure region. The strength of this attraction depends on both the magnitude of the pressure and the pressure gradients. The simulation results are completely consistent with experiments and show why this effect is observed in the lab. These results highlight the importance of poroelasticity and non-planar fracture growth behavior in hydraulic fracture modeling.