Abstract: Addressing the difficulties associated with the newly-explored/exploited blocks of Keshen Gas Field like Keshen 3, including deep reservoir, high pressure of the stratum, and so high a shut-in pressure as up to 110 MPa, the design for optimization of the casing string structure of the hole geometry of Well TabiaoⅡis made.Accordingly the Φ206.38 mm×17.25 mm hi-strength, hi-toughness and hi-air tightness non-API BG140V BGT2 casing is developed.The optimized casing string can not only meet the high shut-in pressure requirement, but also satisfy the requirement for hanging load of the drilling rig rotary hook.Relevant evaluation test result shows that the newly designed and developed Φ206.38 mm×17.25 mm BG140V BGT2 casing is capable of meeting the complicated service conditions of the newly-explored blocks of Keshen Oilfield, and that the FATT of the casing material is under-74℃, which meansthat safety for construction and gas production under thelimitingambient temperatureof-38℃shall be ensured.