Primary reason of the phenomena was analyzed.Corrective measures were provided for the design and use of PPI with a type of lock tile in order to avoid invalidation of oil pipes and cannula.

• 分析了造成偏载的主要原因，并提出将卡瓦与密封段反向组装和采取卡瓦表面曲率与套管内壁曲率接近的改进措施，以减少卡瓦偏载对套管的不利影响。