废弃井中水泥塞性能参数优化

Optimizing Cement Plug Performances in the Abandoned Well

确保废弃井中水泥塞不发生破坏是能够长期埋存地下二氧化碳的关键。在非均匀地应力条件下,废弃井中水泥塞的弹性模量、泊松比等性能参数是影响其完整性的重要因素。本文通过建立非均匀地应力条件下地层-水泥环-套管-水泥塞组合力学模型,利用有限元方法,数值模拟计算得到了不同因素下保证水泥环发生破坏的临界值:地应力组合σx=30MPa,σy=40MPa条件下,不同泊松比水泥塞所对应的临界弹性模量为:32.8、29.2、25.5、22.0、19.1GPa;20GPa和30GPa弹性模量水泥塞所对应的临界泊松比为:0.16和0.19;水泥塞弹性模量为20GPa条件下,不同泊松比水泥塞对应的临界地应力σy值分别为:51、49、46、42.5和39MPa。研究结果表明,水泥塞性能参数小于其临界值时才能确保水泥塞不发生破坏,为废弃井中水泥塞性能参数的设计提供了一定的理论指导。

That the cement plug in the abandoned well is integrated is the key to bury CO2 in the formation effectively for a long time. Under the circumstance of inhomogeneous formation stress, the elastic modulus and Poisson＇s ratio are the very important factors to affect integrity of the cement plug. This pa- per set up the mechanical model of formation--cement sheath--casing- cement plug and calculated the critical value of destruction though the finite element analysis. Under the formation stress σx= 30MPa, σy = 40MPa, the critical elastic modulus of different Poisson＇s ratio are 32.8, 29.2, 25.5, 22.0 and 19. 1GPa ; When the elastic modulus of the cement plug are 20GPa and 30GPa, the critical Poisson＇s ratios are shown to be 0.16 and 0.19 ; And when the elastic modulus of the cement plug is 20GPa, the critical formation stress of different Poisson＇s ratio are 51, 49, 46, 42.5 and 39MPa. The research result shows that only if the performance parameters are less than critical value can the cement plug keep integrated and this can give some advice to the design of the cement plug.