Abstract: After years of production, part of oil reservoirs in the mature oilfield has entered the ultra-high water cut development stage. The remaining oil occurrence is highly dispersed, and it is hard to maintain stable production. Meanwhile, multiple re-perforating and plugging-perforating operations have been performed in oil wells along the vertical profile of oil layers, which results in complex wellbore conditions and failure to meet the requirements of well treatment. This severely impacts the reconstruction performance of well patterns. To improve wellbore conditions and meet the treatment requirements of gradually producing layers from bottom to top, such as CO₂ synergistic cyclic injection and the combination of profile control, plugging, and cyclic injection, the field testing of small casing secondary well completion in directional wells was performed. To overcome the difficulties in casing running and ensuring cementing quality, the directional well small casing secondary well completion technical series was formed, which consists of high-efficiency channel milling, hydraulic rolling casing swage, and small casing cementing techniques. The presented technique series delivers the wellbore reconstruction, characterized by the long-interval sealing of complex wells, resistance to CO₂ corrosion, and high pressure-bearing capacity, and provides technical support for well pattern improvement and increasing recoverable reserves in mature oilfields.