Abstract: Carbonate reservoirs in ordovician strata of Tahe Oilfield are rich in hydrocarbon resources. With the extension of production cycle and the increase of oil production, the cost of development increases accordingly. Sidetracking technique on old wells is one of the most effective ways to reduce the cost of oil and gas development. However, window milling and sidetracking in Tahe Oilfield is difficult, because of the limited hole size, water avoidance requirement, unstable mudstone and complicated pressure system, etc. In view of expandable tubular technology has advantage in dealing with complex formation and pressure system and reducing casing program, it has been deployed on three pilot wells in Tahe field with success. The paper analyzed the casing program, hole trajectory, casing window, reaming method, drilling assembly and drilling parameter of three pilot wells. The tests show that the expandable tubular technology can solve the difficulties in this area, and has great significance for old well reformation. But the research of supporting tools should be enhanced to further improve the economical efficiency.