页岩膨胀应变及固井质量对套管变形的影响研究

Study on the Effect of Shale Expansion Strain and Cementing Quality on Casing Deformation

威荣地区页岩气井套管变形问题突出,但目前引发该区域套管变形的机理尚不明确。该文基于页岩理化性质,分析了页岩膨胀应变对套管应力的影响,研究了考虑页岩膨胀应变条件下的固井质量与套管变形的关系。研究表明:威荣地区页岩呈硬脆性,力学强度高,水化后强度变化不明显;页岩膨胀应变及固井质量的综合作用对套管应力有明显影响,当水泥环缺失及存在微环隙时,能为膨胀应力提供足够的释放空间,降低套管应力,当膨胀应力不能被充分释放时,需尽量保证井筒组合体结构的完整性。高密度射孔对膨胀应力的释放具有积极效果,在合理的射孔参数条件下开展高密度射孔作业是预防套管变形的有效措施之一。该研究为同类页岩气藏套管变形机理研究提供了参考。

The casing deformation in shale gas wells in Weirong area is a prominent problem,but the mechanism that causes casing deformation in this area is still unclear.In this paper,based on the physical and chemical properties of shale,the effect of shale expansion strain on casing stress was analyzed,and the relationship between cementing quality and casing deformation under the consideration of shale expansion strain was studied.It was found in the study that the shale in the Weirong area was hard and brittle,with high mechanical strength and insignificant strength changes after hydration and the combined action of shale expansion strain and cementing quality exerted a significant effect on the casing stress.When cement sheath was missing and micro-annulus existed,there was sufficient space for releasing expansion strain to reduce casing stress.When the expansion stress could not be released completely,it was necessary to ensure the structural integrity of wellbore assembly.High-density perforation had a positive effect on the release of expansion strain.High-density perforation based on reasonable perforation parameters was one of the effective measures to prevent casing deformation.This study provides a reference for the study of casing deformation mechanism in similar shale gas reservoir.