Influence of rock heterogeneity on hydraulic fracturing: A parametric study using the combined finite-discrete element method

Hydraulic fracturing has proven to be an efficient technique to enhance production in unconventional reservoirs. Since heterogeneity is commonplace in reservoir rocks, it is vital to investigate the influence of rock heterogeneity on hydraulic fracture propagation. Here, based on the combined finite-discrete element method (FDEM) and cohesive zone model, two series of numerical models with uniformly distributed and Weibull-distributed elastic modulus of rock are assembled, respectively. The comparison with the theoretical solution demonstrates the reliability of the simulation models in both the toughness-dominated regime (TDR) and viscosity-dominated regime (VDR). The parameter analysis demonstrates the rationality of parameters for cohesive elements. The results show that the previous theoretical equations can be used as a preliminary evaluation of simulation parameters. The effects of different parameters such as element size, Weibull distribution type, and far-field stress on hydraulic fracture length, fluid pressure, maximum fracture aperture, and the final fracture morphology are evaluated. The results demonstrate that the distribution type of rock elastic modulus has a significant impact on the hydraulic fracture propagation in both TDR and VDR. The “jump” phenomena have been observed in TDR caused by high fracture toughness. The displacement of fracture location and asymmetrically dynamic propagation are affected by the distribution of rock elastic modulus. Besides, the hydraulic fracture propagation in TDR is more susceptible to element size, the distribution of rock elastic modulus, and far-field stress than that in VDR. This research may shed light on the development of hydraulic fracturing technology in tight reservoirs.