The initial forces on isolation system were determined and analyzed by researching the well construction and hydrating and hardening process of slurry. It is indicated that there are initial forces on isolation system while cementing operation is completed. The initial forces include: The ground stress, formed by redistribution of ground stress after drilled, acts on formation near borehole. The hydrostatic pressure of fluid in casing acts on casing. The cement sheath applies compressive force on casing and undertakes reacting force at cement-casing interface, which is less than pore pressure of formation at cement-casing interface. The cement sheath also applies compressive force on formation and endures reacting force at cementformation interface, which is equal to pore pressure of formation at cement-formation interface. The initial forces at cementcasing interface and cement-formation interface are formed by gradually transferred pore pressure through slurry on hardening process of slurry. The field data proves the initial forces at cement-casing interface and cement-formation interface. The change of initial forces can seriously influence the isolation ability of isolation system.%结合建井过程和水泥浆的水化硬化过程对封固系统初始作用力进行分析.结果表明:固井作业完成时封固系统受到初始作用力的作用,初始作用力包括井眼附近地层承担的钻开井眼后重新分布的地应力、套管内部流体对套管的静液柱压力、一界面处水泥环对套管的挤压力及其反作用力、二界面处水泥环对地层的挤压力及其反作用力,作用在一界面处的初始作用力形成的初始应力稍小于地层孔隙压力;作用在二界面处的初始作用力形成的初始应力与地层孔隙压力相等;一、二界面处的初始作用力是水泥浆水化直至形成水泥石的过程中逐渐传递地层孔隙压力的结果.现场测量数据验证了一、二界面处初始作用力的存在.封固系统初始作用力的变化会对封固系统产生重要影响.
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