Propagation and geometry of multi-stage hydraulic fractures in anisotropic shales

Abstract

We analyze the efficiency of hydraulic fracturing operations by modeling reservoirs undergoing one and three hydraulic fracturing stages under various far-field stresses and injection rates using the eXtended finite element method. The reservoir is vertical transversely isotropic (VTI), and the effect of the degree of anisotropy on fracture propagation is analyzed. The numerical models are validated using the KGD model and experimental studies. We calculate the permeability of the fractured medium using the Gueguen and Dienes model, enhanced to account for the proppants' presence within the fractures. Our results show that the cracks expand towards the maximum principal stress in isotropic formations and kink towards the weakest plane in VTI formations as the mechanical contrast increases. This behavior tends to close the cracks and leads to a higher compressive load on the proppants. Moreover, cracks grow independently when the distance between cracks exceeds 12 m, and a planar propagation is observed for a distance above 20 m. The results also show that the fractured area and the resulting permeability are larger for close cluster spacing (< 12 m). This work allows the identification of the best fracturing scenario to optimally enhance the permeability of anisotropic unconventional reservoirs under different hydro-mechanical conditions. © 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.