Mechanism and Controlling Method for Casing Deformation in Shale Gas Wells

Casing deformation problem caused by hydraulic fracturing treatments has seriously reduced the number of fracturing stages. A well understanding of the mechanism and controlling method for this problem is very necessary. Based on the detected results, shear deformation is the main type of casing deformation in Weirong shale gas field, Sichuan province of China. According to the analysis on the special geological condition in this area, the reactivation and slip of natural fractures in shale gas formation are treated as the main reason for causing deformation in shale gas well. Model for calculating fracture reactivation and slippage are established. The shear reactivity trend factors in different condition are calculated to judge the reactivation of fractures. Based on the slippage calculation model, the slippages of fractures in four shale gas wells are calculated. Compared with the geological conditions and hydraulic fracturing treatment in Fuling and Yongchuan shale gas field with no casing deformation in China, the existence of dominant natural fracture is one of the most important factors for casing deformation. The results coincide with the field detected casing deformation incidents which certifies the theory that reactivation and slip of dominant fractures induced the casing deformation. In the end, the useful methods for controlling casing deformation in shale gas wells, including temporary plugging, fracture identification, and changing casing size are proposed. The research in this paper provides reference values for controlling casing deformation in exploiting unconventional oil and gas with hydraulic fracturing treatment and reservoirs contains plenty of activated dominant natural fractures.