含薄夹层盐岩地层套管等效应力分析

Analysis of Casing Equivalent Stress in Rock Salt Formation with Thin Interlayer

采用FLAC3D三维有限差分软件,建立了套管-水泥环-层状地层三维有限差分模型,分别研究了泥岩夹层弹性参数、厚度对含薄夹层盐岩地层界面处以及层内套管等效应力的影响。夹层厚度对上下岩层中的套管等效应力都有影响,泥岩和盐岩力学特性上的不匹配导致二者界面附近套管受力不均衡;夹层较厚时,套管等效应力相对较小;与泥岩相比,盐岩中套管等效应力较大,套管更容易发生屈服;夹层弹性参数不同时,夹层弹性模量越低,界面处以及夹层层内套管等效应力越大。该研究为含薄夹层盐岩地层套管设计和井筒安全性评价提供了理论依据。

A 3D model with casing,cement and salt formation was established by using finite-difference software FLAC3D.The effects of elastic parameters and thickness of mudstone interlayer on casing equivalent stress of interface and interlayer in rock salt formation with thin interlayer were analyzed.The thickness of mudstone interlayer had an impact on casing equivalent stress of both upper and lower strata,and the mismatch of mechanical behavior between rock salt and mudstone could lead to casing stress unbalance.For big thickness of mudstone interlayer,casing equivalent stress was relatively small,compared with mudstone interlayer,casing equivalent stress is relatively big in rock salt and the casing is more prone to yield.When elastic parameters of mudstone interlayer are different,the lower the elastic modulus is at the interface,the greater the casing equivalent stress is on the interface and in the interlayer.This study could provide a theoretical basis for the casing design and wellbore safety evaluation in rock salt formation with thin interlayer.