Exploring the influence of heterogeneity on hydraulic fracturing based on the combined finite–discrete method

Hydraulic fracture propagation is known to be influenced by heterogeneity; therefore, the influence of different heterogeneity characteristics on the propagation must be studied. Based on the combined finite–discrete method, hydraulic fracturing was simulated in homogeneous reservoirs as well as four types of heterogeneous reservoirs. Hydraulic fracture propagation in different models was evaluated by variations in hydraulic fracture morphology (fracture length, fracture aperture, and final fracture morphology), fluid pressure, and failure mode (scale factor). Results of the comparison between the homogeneous and Khristinaovic–Geertsma–de Klerk models demonstrate the rationality of the simulation model. The variation in the elastic modulus of one embedded block or interlayer rock affects hydraulic fracture propagation. However, when the elastic modulus of discrete embedded blocks and the number of discrete embedded fractures reach a certain degree, the hydraulic fracture propagation displays an abrupt change. This indicates that the more concentrated the heterogeneous characteristics, the more regular is the hydraulic fracture evolution. In addition, owing to the randomness of hydraulic fracture propagation under the influence of different heterogeneity characteristics, quantitative characterization methods that consider the hydraulic fracture morphology must be developed. Finally, this paper discusses the research direction of hydraulic fracture propagation in heterogeneous reservoirs.