威荣区块深层页岩气井套管变形失效分析

Analysis on Casing Deformation Failure in Deep Shale Gas Wells in Weirong Shale Gas Play

在深层页岩气水平井分段多级压裂过程中,出现越来越多的套管变形损坏的现象。套管变形导致后续压裂施工段无法进行,严重影响压裂施工效果。统计分析威远荣县地区套管损坏特征,得出导致套管变形的主控因素。针对不同压裂顺序,运用有限元软件对页岩气井压裂过程中近井筒地应力变化进行对比研究。研究结果表明,威远区块深层页岩气井套管变形主要出现在水平段中间及跟端附近,类型主要为剪切变形;在非均质深层页岩中,多级水力裂缝起裂与扩展导致井筒周围地应力非均匀累加,诱发天然裂缝滑移,进而造成套管的剪切与挤毁;随着井筒与裂缝的距离增大,套管受到的压缩应力逐渐降低;避开裂缝发育区域压裂以及合理减小压裂规模可以降低套管失效风险。本研究进一步揭示了深层页岩气多级压裂过程中套管损坏机理,并提出了基于套管保护的压裂措施,对于预防压裂过程中套管损坏有一定的借鉴意义。

Casing deformation in shale gas wells during multi-fracturing has seriously affected the efficiency and safety of shale gas production in China.Casing deformation leads to the failure of subsequent fracturing construction,which seriously affects the fracturing construction effect.The characteristics of casing deformation in Weiyuan and Rongxian shale gas field were statistically analyzed,and the main influence factors were obtained.According to different fracturing sequences,the finite element software was used to compare the stress changes of the near wellbore during the fracturing process of shale gas wells.The results show that the casing deformation in shale gas wells mainly occurs near the heel of the horizontal section,and shear failure is the main type of casing deformation in Weiyuan shale gas field;in heterogeneous deep shale,the multi-stage hydraulic crack initiation and expansion leads to non-uniform accumulation of ground stress around the wellbore,which induces natural crack slippage,which in turn causes shearing and collapse of the casing,and as the distance between the wellbore and the crack increases,the compressive stress of the casing is gradually reduced.Avoiding fractures in the fracture development zone and reducing the scale of the fracturing can reduce the risk of casing failure.This study further reveals the mechanism of casing deformation during multi-fracturing in shale gas wells,and proposes fracturing measures for casing integrity.The results demonstrated in this paper can provide the theoretical basis for preventing casing deformation during fracturing in shale gas wells.