Crack Propagation From a Surface Assisted by Fluid Pressure and Cooling

Zhang, X. (CSIRO Earth Science and Resource Engineering) | Jeffrey, R.G. (CSIRO Earth Science and Resource Engineering) | Wu, B. (CSIRO Earth Science and Resource Engineering)



The propagation of a single fluid-filled fracture from the surface of a semi-infinite isotropic elastic solid, subjected to both a transient temperature field and a constant source fluid pressure that is less than the confining stress, is studied using a boundary element method. Fluid flow in fractures is described by the lubrication equation, while the local pressure is determined by the strong coupling between elastic deformation, heat conduction and fluid pressure. Numerical results show that the combination of cooling-induced tensile stress and the source pressure can enhance the propagation speed. Parametric studies are carried out for identifying speed regimes and show the importance of the initial fracture aperture. Three speed regimes are found to exist. If the fluid penetration into the fracture is heavily restricted, the fracture length grows exponentially at early time, and then it suddenly reaches a large speed and progressively decelerates in a finite transition time as fluid diffusion speed varies, but eventually it follows the exponential fracture growth curve at a higher index for stable fluid flow in high-permeability fractures. The time-dependent crack growth behavior does not show any signs of unstable growth, even in the high-speed transition regime. The predictions of crack growth kinetics show a good agreement with some published experimental results and highlight the stabilizing effect of fluid transport on crack growth.