Numerical Simulation Study on the Complex Network Fractures of Stratified Shale Gas Reservoirs

To perform the numerical simulation of complex network fractures in stratified shale gas reservoirs with natural fractures, a numerical model for network fractures was set up to determine interactions between hydraulic fractures and natural fractures by using universal distinct element code (UDEC) of non-continuous medium simulation based on numerical algorithms of seepage-stress coupling. The model was used to analyze the effect of the hydraulic fracture length, the natural fracture dip angle, the internal friction angle and the net treatment pressures on fracture network extension. The results showed that hydraulic fractures extend from the fracture tip near the well bore, and they experience shear failure along the strike of natural fractures. In the process, the connected area of natural fracture network would increase with the increases of hydraulic fractures length. It is more likely to form complex fractures or network fractures in the case of relatively large natural fracture dip angles. When the internal friction angle of the natural fractures is reduced, the connected area of natural fractures will increase and it is easier to form complex network fractures. Under a certain range of horizontal stress, fracture growth patterns would become more complex and it would be easier for tips near fractures to form network fractures as net pressure coefficients increase. Numerical simulation results could provide guidance for further understanding on shale gas fracturing fracture extension mechanism in areas away from wells.