水平井平行裂缝间诱导应力干扰机制的数值模拟研究

水平井平行裂缝间的诱导应力场相互叠加，造缝机理复杂化。应用数值模拟方法，对多平行裂缝诱导应力相互干扰的机制进行研究。首先对预制单裂缝在垂直和平行裂缝方向上诱导应力的数值解和解析解进行对比，结果表明垂直裂缝表面方向的诱导应力相对平行裂缝表面的诱导应力要大。其次对2条预制平行裂缝及2条同步扩展裂缝周边的诱导应力变化规律进行研究，结果表明小裂缝间距、长裂缝和小主应力差更有利于主应力反转和网状裂缝的形成。最后研究了3条同步扩展的平行裂缝的几何形态，研究表明较小缝间距和较大的水平应力差异系数会造成中间裂缝很难起裂或起裂后迅速止裂，不易形成有效裂缝。较小的主应力比值有利于裂缝转向，产生沿原始最小主应力方向的分支裂缝，更有利于在页岩储层中形成复杂裂缝网络。在合适的地应力条件和缝间距下，中间裂缝能突破“扩展抑制期”而进入“二次扩展期”。

Numerical simulation research on mechanism of induced stressperturbation between parallel fractures in horizontal wells

The stress fields induced by parallel fractures of horizontal wells overlap on each other,making the initiation and extension of fractures more complicated.A numerical simulation is carried out to study the mechanism of induced stress perturbation between multiple parallel fractures.A comparison of the theoretical solution and numerical results of the induced stress both parallel and normal to the fracture is made firstly.The calculated results indicate that the additional stress is always higher in the direction perpendicular to the fracture than in the direction parallel to the fracture.Secondly,the stress distribution of two prefabricated fractures and two synchronously extended fractures is discussed.It is found that the small fracture spacing,long fracture length and small principal stress difference are conducive to the appearance of stress-reversal region and complex hydraulic fracture network.Lastly,the geometry of three synchronously extended fractures is analyzed,and the results show that in the case of small fracture spacing and big horizontal stress difference coefficient,the middle fracture propagates more difficultly or even stop propagating soon after initiation.The small principal stress ratio is advantageous to the appearance of branching cracks parallel to the direction of original minimum principal stress direction,thus the possibility of complex fractures in the reservoir formation by the subsequent hydraulic fracturing is greater.Under appropriate fracture spacing and in-situ stress condition,the middle fracture can overcome the “extension inhibition period” and step into the “secondary extension period”.