Multi-scale Discontinuities Due to Differential Stress Around a Pressurized Borehole
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Most fracture propagation models do not properly represent smaller-scale discontinuities in the process zone. This paper reviews the different modeling strategies available to date to model crack propagation at microscopic, mesoscopic, and macroscopic scales. The differential stress induced damage (DSID) model recently proposed by the authors is then used to simulate fracture propagation around a pressurized borehole with the finite element method. In a pristine rock mass, the damage zone presents several symmetries in three dimensions, which are in agreement with the definition of the damage-driving force controlling the initiation and propagation of damage. If hydraulic fracturing is enhanced by the presence of initial cracks, the propagation of the damage zone depends on the geometry of the initial defects. It is found that simulating rock initial texture by a smeared damaged zone provides good analogs to the viscosity-dominated and toughness-dominated fracture propagation regimes expected during hydraulic fracturing. Future work will be dedicated to the fully coupled formulation of a hydro-mechanical model of damage around hydraulic fractures.