A continuum damage failure model for hydraulic fracturing of porous rocks

A continuum damage mechanics (CDM) based constitutive model has been developed to describe elastic, plastic and damage behavior of porous rocks. The pressure sensitive inelastic deformation of porous rocks together with their damage mechanisms are studied for drained and undrained conditions. Fracture mechanics of microcrack and micro-void nucleation and their coalescence are incorporated into the formulation of the CDM models to accurately capture different failure modes of rocks. A fracture mechanics based failure criterion is also incorporated to accurately capture the post fracture crack advances in the case of progressive failures. The performance of the developed elastoplastic and CDM models are compared with the available experimental data and then the models are introduced into a commercial software package through user-defined subroutines. The hydraulic fractures growth in a reservoir rock is then investigated; in which the effect of injection pressure is studied and the simulations are compared with the available solutions in the literature. The developed CDM model outperforms the traditional fracture mechanics approaches by removing stress singularities at the fracture tips and simulation of progressive fractures without any essential need for remeshing. This model would provide a robust tool for modeling hydraulic fracture growth using conventional elements of FEA with a computational cost less than similar computational techniques like cohesive element methods.