Abstract: Well P-1 in the East China Sea develops marginal oil and gas reservoirs with sidetrack drilling from the old well. It has the characteristics of ultra-deep, large horizontal displacement and long slope stability. In the process of well completion, the well bore has large friction and is difficult to clean up, difficulty of perforation correctionand high construction risk. The conventional tubing structure design is difficult to meet the requirements of safe and reliable operation. Therefore, through the research of wellbore cleaning technology, efficient lubrication technology, perforation depth correction technology and tubing structure optimization, it can effectively clean the well bore, reduce the friction resistance, solve the problem of perforation depth correction, and realize the seal evaluation of the gas well tubing structure. The field application shows that the ultra-deep and extended-reach well completion technology is feasible, and the low-cost development of marginal oil and gas fields is realized.