Analytical interpretation of hydraulic fracturing initiation pressure and breakdown pressure

The rock collapse during Hydraulic Fracturing (HF) is the result of the accumulation of rock damage to a certain extent. That means there are two key pressure values: the fracture initiation pressure (FIP) and the breakdown pressure (FBP), which characterize the micro damage initiation and the macroscopic fracture stable expansion respectively. However, various conventional analytical breakdown pressure models cannot clearly distinguish and quantitatively characterize the difference between FIP and FBP. This paper presents a combined model. The fracture initiation is defined to start when the stress intensity factor at some point inside the rock reaches the fracture toughness. The breakdown is defined as the derivative of stress intensity factor versus radius is positive, not only as the onset of fracture initiation. According to the comparison and analysis of the actual fracturing experiments, this combined model makes it possible to accurate predict the FIP and the FBP respectively.