注水油田剪切套损机理研究与数值模拟

Mechanism analysis and numerical simulation of casing's shear failure in water injection oilfield

油田注水开发过程中,一旦注入水进入泥页岩夹层或断层带,将诱发大面积岩石顺层滑动,造成成片的套管变形或错断。渗流对油藏地应力场的影响在于一方面孔隙压力作为渗透力作用于岩体,另一方面表现为泥页岩的水化作用。基于Mohr-Coulomb准则和有效应力原理分析断层交界面岩石滑动机理,得到界面滑动时孔隙压力极值的估算方法。建立空间三维计算模型,并在泥岩夹层与砂岩储层中间加设一层接触单元,通过数值模拟得到注水压力对交界面岩层滑动及套管Mises应力的影响规律,为油田开采过程中防止剪切套损提供理论依据及合理计算方法。

During the oil field waterflooding process, bedding slip will happen if high pressure injection water cuts into the mudstone and shale interlayers, and regional casing impairment will be induced. The influence of seepage field on the stress field includes two aspects： on one hand, pore pressure is assumed as a body force and applied to the rock mass; on the other hand, the hydration of mudstone and shale is obvious, which will decrease rock mechanical properties. Based on the Mohr-Coulomb theory and effective stress principle, the sliding mechanism of interface rock is analyzed, and also the maximum of pore pressure can be given. The three dimension model is built, and contact element is used to simulate the interface between mudstone interlayer and sandstone reservoir. The numerical simulation results show that with the increase of pore pressure, the sliding displacement and the Mises stress of casing has increased. The numerical simulation analysis provides theoretical basis and effective methods of water injection to reduce casing damage during the oil production process.