地下储气库井筒水泥环的弹塑性分析

Analysis on the elastoplastic of cement sheath in underground gas storage wellbore

为了分析连续注采工况下地下储气库井筒水泥环的受力与变形规律,基于弹塑性力学的基本原理,以套管-水泥环-围岩组合体为研究对象,结合温度、孔隙压力及地层远场应力等影响因素,推导出注采工况下受内外压作用的水泥环的弹塑性应力和位移的解析解。实例计算表明:注气中水泥环会发生塑性变形,内外壁面径向接触应力随内压非线性增加;注采中的井筒温度和孔隙压力变化是影响水泥环受力的重要因素;水泥环弹性极限内压随温度的降低和孔隙压力的增大而增大;水泥环与套管、围岩的径向接触应力随温度的升高和孔隙压力的增大而增大。研究成果为优化储气库运行参数、控制"微环空"的产生提供了技术支持。

In this paper, the casing-cement sheath-surrounding rock assembly was taken as the study object to reveal the stress and deformation of cement sheath in underground gas storage wellbore in the case of continuous injection and production. The analytical solutions to the elastoplastic stress and displacement of cement sheath subjected to internal and external pressure in the working conditions of injection and production were derived based on the basic principles of elastoplastic theory combined with the influential factors, e.g. temperature, pore pressure and far-field in-situ stress. The calculation examples show that in the process of gas injection, the cement sheath may deform plastically and the radial contact stress on the inner and outer wall increases nonlinearly with the increase of internal pressure. The variation of temperature and pore pressure during gas injection and production has significant effect on the stress of cement sheath. The elastic limit internal pressure of cement sheath increases with the increasing of pore pressure and the decreasing of temperature. As temperature and pore pressure increase, the radial contact stress of cement sheath on the casing and surrounding rock increases. The research results provide the technological support for optimizing underground gas storage operating parameters and preventing the formation of micro-annulus. （10 Figures, 21 References）