Sensitivity analysis on the effect of natural fractures and injected fluid on hydraulic fracture propagation in a fractured reservoir

• A 3D DFN model coupling different kinds of natural fractures is built. • Propagation of hydraulic fractures in the DFN model is modeled. • Influence of natural discontinuities on hydraulic fracturing effectiveness is studied. In this work, a series of numerical simulations based on an outcrop-data-based discrete fracture network (DFN) model of the shale reservoir in the Ordos Basin, China are conducted, trying to determine the dependence of hydraulic fracturing on the properties of natural fractures and injected fluid. The accuracy of the method is verified through the PKN solution for a homogeneous rock model and a laboratory test for a shale sample obtained from the study area. Parametric studies are performed for different field parameters, including natural fracture aperture, natural fracture frictional coefficient, fluid injection rate and fluid viscosity. The results suggest that the level of fracture complexity decreases as the aperture of natural fractures increase, and increasing the frictional coefficient of natural fractures can improve the hydraulic fracturing efficiency. Higher injection rates could translate into higher injection pressure and more energy available for rock failure near the wellbore, and therefore improve the fracture complexity. However, higher fluid viscosity leads to higher resistance to fracture propagation, and thus reduces the hydraulic fracturing efficiency.