Great variability of lithology and permeability

low porosity

poor connectivity

complex pore structure and serious heterogeneity are the common characteristics of glutenite reservoir. Therefore it is difficult to control crack propagation form of hydraulic fractures

and undertake a large-scale reconstruction. Based on the characteristics of a typical glutenite reservoir in China

the propagating mechanism of hydraulic fractures is investigated by using numerical method. Numerical simulation results show that the hydraulic fracturing is more complex due to the existing of gravels and there are four fracturing modes: terminations

deflections

penetrations and attractions. The primary fractures are strictly dependent on the difference of the maximum and minimum stress. With the increasing of principal stress difference

fractures are selected to cut through gravels rather than propagate around gravels. Consequently the propagation of primary fractures appears discrepancy and a lower breakdown pressure is needed. The higher the gravel volume content is

the worse the heterogeneity is. With the increasing of gravel volume content

the interaction between gravels and fractures is more evident. The higher gravel volume content needs a higher breakdown pressure. For the cases with a constant gravel volume content

the fracture initiation is mainly influenced by the stochastic distributing of gravels

consequently a gently higher breakdown pressure is required for the larger gravels.