Effect of rock anistropy on hydraulic fracture propagation

Hydraulic fracture propagation in anisotropic mudstones has been investigated using a newly developed numerical model based on the Displacement Discontinuity Method (DDM). The effect of elastic and fracture toughness anisotropy on hydraulic fracture propagation is considered and fluid flow in fractures is fully coupled with rock deformation. Simulations of multiple hydraulic fractures are presented, and the results suggest that fracture lengths and apertures are affected by fracture orientation with respect to the directions of elastic symmetry. The spatial extent of the induced normal stresses perpendicular to the fracture surface increases when the fracture is aligned with the direction of least elastic modulus. When fracture toughness anisotropy is considered, the hydraulic fractures deviate towards the plane of least fracture toughness under low differential stress conditions. These results suggest that the completion design for optimum fracture growth in anisotropic rock is different from isotropic rock.