Some pore pressure specialists use the minimum stress gradient as the fracture gradient, but others may use the maximum leak-off pressure gradient (fracture breakdown pressure gradient) or the fracture initiation pressure gradient as the fracture gradient.
In particular, it is shown there is an important interplay between the depth of the maximum compression, the stress gradient and the magnitude of the maximum compressive stress.
They do not use maximum stresses but evaluate the stress gradient in the notch ligament.
A design method was developed which is based on FE calculation of the maximum local stress, the appertaining stress gradient and the highly stressed material volume.
However, when we consider stress migration which is primarily driven by the hydrostatic stress gradient which typically have local maxima at the grain boundaries the polycrystalline structures might result in easier nucleation of voids along grain boundaries and also growth of voids (Yang et al. 2011; Zschech et al. 2009; Sukharev et al. 2009).
At the depth of 10,800 ft, if the minimum horizontal stress gradient σ h = 12.8 ppg, the maximum horizontal stress gradient σ H = 13.4 ppg, pore pressure gradient P p = 11 ppg, and tensile strength T 0 = 100 psi, then the breakdown pressure can be calculated from Eq. (8), i.e., the breakdown pressure gradient is P b = 14.18 ppg.
This could be due to the development of a moisture gradient during drying, that would reduce the maximum stress.
These profiles have been found to be weakly dependent on the laser pulse parameters, most notably an increase in tensile stress gradient with increasing duty cycle, but the maximum residual stresses are largely unaffected.
When n=1.8, the stress gradient was small and the lowest value of the maximum Von Mises stress was obtained.
