A phase-field model of hydraulic fractures in acidized porous media with strain-softening properties

The use of preacidification to reduce fracture pressure in hydraulic fracturing is becoming increasingly common. Therefore, the crack path and fracture pressure in acidified porous media must be accurately predicted. Our experiments show that acidified rocks exhibit strain softening, as indicated by increased heterogeneity and plasticity and reduced strength. The elastoplastic constitutive equation of acidified rocks is established according to the unified strength theory, and the stresses in the strain -softening stage are solved using a stress return algorithm. Fluid flow follows Darcy ' s law and is coupled with solid deformation through Biot ' s theory. The phasefield evolution equation is derived using the total energy functional through a variational framework. The reservoir is divided into acidified and unacidified domains and simulated using phase -field models for ductile and brittle fracture, respectively. Numerical results indicate that the acidification degree is optimal when the formation fracture pressure is reduced to the level of fracture extension pressure and that acidification enhances the ability of hydraulic fractures to steer along natural fractures, resulting in more complex fractures. These conclusions can be used to guide the amount of preacid in the field.