层理性页岩气储层复杂网络裂缝数值模拟研究

在考虑天然裂缝的条件下，为了更好地对层理性页岩气储层的复杂网络裂缝进行数值模拟，采用模拟非连续介质的通用离散元程序（UDEC），基于渗流-应力耦合数值算法，建立了人工水力裂缝与天然裂缝相互作用的网络裂缝数值计算模型，并利用该模型分析了水力裂缝长度、天然裂缝倾角、内摩擦角及施工净压力对缝网扩展的影响。结果表明:水力裂缝从近井筒处裂缝尖端起裂扩展，并沿着天然裂缝的走向发生剪切破坏，且随水力裂缝长度增长，天然裂缝网络连通面积增大；天然裂缝倾角较大，形成复杂缝或网络缝的概率也相对较大；天然裂缝内摩擦角越小，天然裂缝连通面积越大，越易形成复杂网络裂缝；水平地应力差在一定范围内，净压力系数越大，裂缝的扩展形态越复杂，相邻裂缝的尖端越易连通形成网络裂缝。数值模拟研究结果可为进一步认识远井地带页岩气压裂裂缝扩展机理提供指导。 

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.