Abstract: The six-section casing program is adopted in the Shunbei block, but it is disadvantageous with long large-size borehole,excessive casing sections and mud loss in igneous rocks, which lead to low-efficient drilling. Therefore, it is necessary to optimize the casing program. In this paper, three reservoir pressures were simulated by using the Drillworks Software. The distribution of fractures in igneous rocks was identified by using the image logging and SEM (scanning electron microscope). The collapse mechanisms of deep shale were investigated on the basis of its mineral composition and physical and chemical properties. The matching between nonstandard casings and drilling pipes was analyzed in terms of their strength and size. It is shown that there are four pressure systems in hole. The fractures distributed vertically in igneous rocks are 0.5~2 mm wide and the microfractures are 2~3 μm wide. The illite/smectite formation accounts for 70% of caving mudstones and its linear expansion ratio in distilled water is 40%~45%. Three plugging points and one risk point were defined. The long open-hole section was stabilized by taking mud loss remedial measures with potassium ammonium polysufide drilling fluid system. The ?139.7 mm non-standard casing was selected and the completion hole diameter was enlarged to 120.65 mm from 114.3 mm, so that the ?88.9 mm non-standard drilling pipe could be used and the casing program was optimized into four-section mode. By virtue of the new casing program, the drilling was performed efficiently, with the drilling cycle shortened by 125 d.