某超深复杂井二开套管井下泄漏原因分析

完井深度8024m的某超深复杂井,在完井测试过程中,二开套管在2964.6m处发生泄漏。通过调查和理论计算发现,导致二开套管泄漏的原因主要是:二开套管固井质量不好,形成超长的水泥空段,套管柱坐挂吨位偏低,导致水泥空段套管在井下发生弯曲失稳;三开钻井周期过长,进尺缓慢,且频繁起下钻作业,导致钻具不断磨损套管内壁,当磨损导致套管的剩余壁厚无法承受井内载荷,套管发生泄漏失效。

Investigation of Reasons for In-well Leakage of Secondary-drilling Casing as Used in a Certain Extra-deep Complicated Well

During the well completion testing to a certain extra-deep complicated well with 8 024 m completion depth,leakage takes place with the secondary drilling case at the point of 2 964.6 m. Based on relevant investigation and theoretic calculation, the reasons for the said leakage are indentified as follows. Due to poor cementation quality of the casing,there exist cement-free sections,and this causes low sitting/hanging tonnage of the casing string,and thus leads to the casing in the cement-free section bends,and gets unstable. And because of rather long third drilling period,slow drilling footage and over frequent drill up-and-down operations, the drilling tool constantly abrades the inner surface of the casing,and once the casing is worn to be too thin to bear the load in the well,leakage failure eventually takes place.