Abstract: In recent years, the sidetracking technology has been used in Bachu formation of Carboniferous or Sangtamu formation of the upper Ordovician in Tahe oil field in order to meet the requirement of avoiding water in parts of side tracked holes. However, some problems might occur, such as the mudstones are not stable and might collapse and fall off when immersed in liquid within the hole, bring about huge potential safety hazards for drilling and well completion. In this paper, the difficulties when using sidetracking technology with Φ177.8 mm casing in Tahe oil field has been summarized, and the feasibility of using three technologies to seal mudstone, including running Φ127 mm casing, expandable convoluted tubing and solid expandable tabular has been discussed.