On April 13, 2011, in the Wushenqi block of CNPC Changqing Oilfield, Well Sudong 15-36H was an accident well. The well collapsed at 3286 meters and the casing deformed and the construction could not be continued. A new side-drilling window was used to save the accident. Due to the serious casing deformation at the opening position, the well inclination reaches 76.44 degrees, and there is no case of successful opening of such wells in China. Based on this particularity, the company specially developed a double-cylinder variable diameter guide, which successfully solved the technical problems of inconsistent casing deformation and large well deviation. The successful case of this window opening has improved the company's visibility in the Northwest Oilfield market.