Casing string excessive design could lead to the increase of well construction cost.Especially in southwest oil and gas field,the number of shale gas wells is huge,therefore casing string excessive design could cause unnecessary material consumption,and increase the development cost of shale gas resources.According to the design method in SY/T 5724-2008"Design for Casing String Structure and Strength",the surface and intermediate casing string of typical deep shale gas wells in southwest China are checked and analyzed.On the basis of casing design principle and wellhead specification,the optimal design scheme is put forward,and the cost is analyzed.Moreover,with reference to the casing string design principles of large energy enterprises in the world,the differences and optimization directions of casing string design methods in deep shale gas wells in southwest China are determined.The results show that the procurement cost of casing can be greatly reduced after optimization while the casing strings still satisfy the requirements of strength and well control.The research re-sults provide a theoretical basis for the optimal design of casing string in deep shale gas wells.
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