The fracture interventions were operated in 144 segments of 24 wells in CNPC Changning and Weiyuan shale gas fields. Among these fracture interventions, 10 wells happened different degree of casing deformations, and one well had casing connection jump-out. So the casing failure rate reached 45.8%. The casing failure modes included casing deformations in reservoir fracturing sections which occurred following hydraulic fracturing, blockage during drifting and bridge plug process, casing connection jump-out, and annulus pressure buildup between casing and tubing during well shut-in. A comparative study was performed on the geological conditions, well completions, and fracturing pressure for the shale gas fields between China and North America. The study shows significant challenges for shale gas exploration in China, with severe conditions such as high reservoir temperature at 150 °C, high gas pressure at 60MPa, and discontinued in-situ stress in the faults where the maximum horizontal stress is significantly higher than the overburden pressure and the minimum horizontal stress. Standard T&C connections were used for casing strings. Based on analysis of casing installation, fracturing and production process, it was concluded that the conventional tubular design approach could not be applicable for the shale gas applications in China. The primary cause for local casing deformation can be related to the formation shear loading, resulting from multi-layer fracturing process. Casing joint used premium connection of gas-seal. API Spec 5CT (2010) material transverse impact toughness couldn't meet fracturing needs in practice. Coupling often cracks and then jumps out. This paper presents Finite Element Analysis (FEA) of casing strings subjected to shear loading and transverse impact toughness of resistance to crack initiation on fracturing. Based on the FEA study, the performance requirements and evaluation criteria for shale gas production casing were developed. This paper also presents an example where the proposed methodology was used to analyze and evaluate casing performance, and ensure the safety of the well operation.

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