空心微珠水泥在盐膏层蠕变环境下的套管防护性能研究

Casing Protection Performance Research on Hollow Microbead Cement under Evaporite Bed Creep Condition

  • 摘要: 盐膏层在含油气盆地中分布较广,其蠕变特性会对套管产生持续挤压,导致套管变形甚至破坏,严重影响油气井的寿命和生产安全。为有效缓解盐膏层蠕变对套管的破坏,基于空心微珠水泥浆体系,利用微珠破碎起到的应力释放作用,降低套管/水泥环界面应力,吸收盐膏层蠕变位移,为盐膏层套管防护提供了一种“以空间换时间”的缓冲设计方案。通过室内蠕变环境下管柱变形评价试验,研究了水泥中空心微珠加量和粒径对套管变形的影响。结果显示,盐膏层蠕变初期,水泥中的空心微珠通过破碎吸收盐膏蠕变位移,阻止套管变形;当蠕变量超过临界值后,套管开始变形,且变形量随蠕变量增加而增大。增大水泥中空心微珠的加量和粒径,可以显著提高其吸收临界盐膏层蠕变位移的能力,有效缓冲地层蠕变初期对套管的挤压,保证套管形变前井筒内工具的通过性。该研究成果为盐膏层井筒完整性设计提供了新的理论依据与技术途径。

     

    Abstract: Evaporite beds are widely distributed in oil and gas-bearing basins. Their creep characteristics exert continuous compressive forces on casing, leading to casing deformation and even failure which severely affects the lifespan and production safety of oil and gas wells. To effectively mitigate the damage to casing caused by evaporite bed creep, based on a hollow microbead cement slurry system, a buffering design scheme of “trading space for time” was proposed for casing protection in evaporite beds by utilizing the stress-relieving effect of microbead fragmentation to reduce the casing/cement sheath interfacial stress and absorb the evaporite bed creep displacement. Through laboratory evaluation tests of string deformation under a creep condition, the influence of cement with different hollow microbead contents and particle sizes on casing deformation was investigated. The results indicate that during the initial stage of evaporite bed creep, the hollow microbeads in the cement absorb formation creep displacement through fragmentation, preventing casing deformation; when the creep displacement exceeds a critical value, the casing begins to deform, and the deformation increases with the increase of creep displacement. Increasing the content and particle size of hollow microbeads in the cement can significantly enhance its ability to absorb critical evaporite bed creep displacement, effectively buffer the compression on the casing during the initial stage of formation creep, and ensure the runability of downhole tools in the wellbore before casing deformation. The research results provide a new theoretical basis and technical approach for wellbore integrity design in evaporite beds.

     

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