Study on Propagation and Diversion Characteristics of Hydraulic Fractures in Vuggy Carbonate Reservoirs

Hydraulic fractures generated in the stimulation of vuggy carbonate reservoirs feature complex propagation as they do not necessarily propagate along the prospected path. In view of this, vuggy carbonate rock samples were prepared based on the analysis of the vuggy characteristics of carbonate reservoirs. With test results of true triaxial hydraulic fracturing, the interference of cavities in the propagation of hydraulic fractures under different horizontal principal stress differences was investigated. Moreover, the extended numerical finite element method was used to analyze the factors affecting the propagation of hydraulic fractures in vuggy carbonate reservoirs and their propagation paths. The results revealed that non-planar propagation would occur when hydraulic fractures encountered cavities when the difference coefficient of the horizontal principal stress was below 0.15, and smaller horizontal principal stress was accompanied by a larger diversion propagation distance and more complex fracture pattern. When the coefficient was between 0.15 and 0.36, hydraulic fractures would overcome the stress concentration of cavities for planar propagation, but they would be captured by cavities encountered along the propagation path. When the coefficient was no less than 0.36, hydraulic fractures would overcome the stress concentration of cavities and penetrate cavities for planar propagation. In addition, the fracturing pressure would decrease as the stress difference increased. The research results can provide a reference for hydraulic fracturing design for vuggy carbonate reservoirs.