Fracture-mechanics analysis of the breakdown process in minifracture or leakoff test

The breakdown pressure - the peak pressure that is reached during pressurization of the wellbore - is interpreted in this paper to correspond to a condition of unstable crack propagation. It is shown that the classical Hubbert and Willis¹⁴ and Haimson and Fairhurst⁹ breakdown criteria represent a condition of fracture initiation in the limiting case of fast and slow pressurization rate, respectively; and that the breakdown pressure, p_b, could be either equal to or larger than the fracture-initiation pressure, p_i.