某井φ177.8 mm偏梯形螺纹接头套管发生脱扣事故，通过分析下套管、固井注水泥及钻塞过程和井下返出的套管残片的理化检验结果找出了套管脱扣的原因。结果表明：该套管接箍工厂上扣端脱扣发生于固井水泥凝固期间；造斜井段全角变化率过大、井眼不规则、套管引鞋下面没有预留口袋使得套管承受异常载荷出现松动，最终发生脱扣失效。

The φ177.8 mm casing with buttress thread connection in an oil well had a pulling out accident. Found out the causes of casing pulling out through by analysis on the process of casing running, cementing, drilling cementation plug and physical testing and chemical analysis of casing remains from well bottom. The results show that pulling out of casing joint from mill end occurred during cement solidification. The casing loosed under abnormal load because of severe dogleg severity of kick-off section, borehole irregularity and no pocket under casing guide, which finally led to the polling out of casing.