The Optimal Design of a Casing Program for Ultra-Deep Wells in the Tahe Oilfield and Its Periphery

With the expansion and extension of exploration and development in the Tahe Oilfield and its periphery, the original casing program revealed it had limitations in the deeper reservoir, affecting drilling speed and safety. For specific formations, based on the bottom-up and top-down casing program design methods, and considering the formation pressure distribution and setting position, the size and running depth of surface, intermediate and production casings were determined.The original four-stage casing program was simplified to a three-stage one. Specifically, by optimizing φ177.8 mm casing to φ193.7 mm, a new three-stage casing program was designed for high-efficient drilling of ultra-deep wells in areas in simple geological conditions, such as the non-salt area in the Tahe Oilfield. Using φ265.1 mm or φ206.4 mm casing to isolate salt-gypsum layer, a casing program of long open hole through salt-gypsum layer and special casing sealing salt-gypsum layer was designed for fast drilling of ultra-deep wells in salt areas in the Tahe Oilfield. With unconventional casings of φ273.1 mm(for φ311.1 mm hole)and φ206.4 mm (for φ241.3 mm or φ215.9 mm hole), a casing program was designed for the safe drilling of ultra-deep wells in areas under complex conditions.By simplifying casing program and optimizing the size and running depth of casing, the drilling speed and efficiency could be improved in areas with relatively simple geological conditions.By optimizing the unconventional casing program, safe drilling could be conducted in areas with complex geological conditions.