Abstract: Deformation or offset of well casing is an event induced by water injection, similar to induced earthquake in many aspects. Observations in Fuyu Oil Field indicate that the deformation of casing has close relationship with water injection, especially with injection pressure. The number of casing daformation increases as the injection pressure rises. The events happen mostly in the bottom part of Qinshankou mudstone (b₁) with developed bedding and nearly vertical fissures. The orudstone soaked with injected water is weakened in strength. Besides deformation in casing cross section, relative displacement in axial direction also happens, which indicates the result of shearing. A possible mechanism of slip along bedding in the orudstone is praposed in this paper to interpret the observations. The ratio of shear stress component to normal stress component on the bedding is too small as compared with frictional coefficient,therefore, if no water is injected or the injection pressure is not high enough, no slipping of rock mass occurs and no casing deformation consequently. A critical pore pressure of 66-76 bars is suggested to be the pore pressure required to initiate slipping and to cause considerable casing deformation.

摘要： 套管变形是指油水井套管的变形或错断现象,它是一种与注水有关的诱发事件,与注水诱发地腿有许多类似之处. 观测资料表明,套管变形与注水特别是注水压力有一很密切的关系,不注水不发生套变,注水压力提高时,套管变形速率随之增高,并且套管变形主要集中发生在青山口一段泥岩(b₁)的底部,该段泥岩的特点是,不仅层理发育,而且近直立的宏观裂隙的线密度也最高.进人泥岩中的高压注人水,以及它的浸水软化效应,使之成为强度上的软弱带.变形套管除其涝截面变形之外,抽线也发生了不同程度的相对位移,表明套管变形主要是受剪切作用的结果.本文提出了岩体沿上述泥岩中的层理面的滑动可能是扶余油田套管变形的一种机制,并用以对主要观测结果作了初步解释.上述层理面上的外加剪应力与正应力的比值远比摩擦系数小,所以,如果不注水甚至不高压注水岩体是不会发生滑动的,因而也就不会有套管变形问题.本文得出的使岩体开始滑动,也即大盘发生套管变形的临界孔压为66~76巴.