On April 13, 2011, at the Changqing Oilfield of PetroChina in the Wushenqi block, the Su Dong 15-36H well was treated as an accident well. The well collapsed at a depth of 3286 meters, and the casing deformed, making it impossible to continue construction. A new side-drilling window was opened to salvage the accident. Due to the severe deformation of the casing at this window location, the well inclination reached 76.44 degrees, which is an extremely high inclination, and there have been no successful cases of opening windows under such well conditions in the country. The company developed a dual-cylinder variable-diameter directional tool specifically for this uniqueness, successfully solving technical challenges such as inconsistent inner diameter of the deformed casing and extremely high well inclination. The success of this window opening case has significantly enhanced the company's reputation in the northwest oilfield market.