Some Understandings and Enlightenment on the Failure of Fishing and Dropping Drilling Tools in a Highly Deviated Well of East China Sea

A highly deviated well-Well A1 in East China Sea had a stuck-pipe after its ϕ311.15 mm borehole was drilled. After an explosion, a sidetrack operation was made in the upper casing. After the sidetrack borehole was drilled, the drill string was broken. Many times of fishing ended in failure. From the aspects of fishing assembly, operation parameters and software simulation, this paper briefly describes the process of fishing operation after drill string breakage, and analyzes the causes of fishing failure. Some reasonable suggestions are put forward for the drilling operation, the accident prevention and treatment of similar wells in this region. It can give some inspiration and reference for drilling operation, well condition treatment, fishing tools and fishing method selection in similar formations.