天然裂缝对页岩储层网状诱导缝的控制作用

Formation and controlling effect of natural fractures on network induced fractures in shale reservoir

页岩地层只有借助体积改造技术形成网状裂缝系统才能实现有效开发,而网状裂缝形成的必要条件是诱导缝沿天然裂缝转向。借助RFPA2D数值仿真软件,从岩石力学角度出发开展诱导缝转向规律的机理研究。结果表明,天然裂缝的长度、走向等都会影响诱导缝转向的难易程度,裂缝长度越大、与最大主应力夹角越小,发生转向的可能性越大;其次,诱导缝起裂的角度也会影响其转向,起裂方位与最大主应力夹角越大,诱导缝沿天然裂缝转向越容易。文章还分析了复杂裂缝性地层诱导缝延伸规律,直观地再现了诱导缝依次打开天然裂缝并分叉的现象,并证明了只有诱导缝沿天然裂缝转向才可能形成复杂诱导缝体系。

The formation of network fracture system based on the volume transformation technique enhances the effective development of shale gas reservoir and the requisite condition for the formation of network induced fractures is the diversion of induced fractures along natural fractures.Mechanism of diversion regularity of induced fractures is studied through the application of RFPA2 Dnumerical simulation software and in view of the rock mechanics.It shows that the length and orientation affect the difficult level of induced fracture diversion.In fact,the longer the fracture is and the smaller the angle between the fracture and principal stress is,the more likely the diversion of fracture occurs.Meanwhile,the initiating angle of induced fractures also affects the diversion of fractures.The diversion of induced fractures along natural fractures becomes easier when the angle between initiating direction and principal stress becomes larger.The extending regularity of induced fractures in strata with complicated fractures is discussed and the phenomenon of open of natural fractures by induced fractures in forking shape is observed.It proves that the diversion of induced fracture along natural fractures leads to the formation of complex induced fracture system.