Casing deformation mechanisms of horizontal wells in seismically active zones: a comprehensive analysis

The Sichuan basin's shale gas fields demonstrate elevated seismic activity, which poses a significant challenge in the development of shale gas. Besides, casing deformation emerges as a prominent concern, leading to substantial disruptions in shale gas production operations. In order to address the issue of casing deformation in seismically active areas, an analysis was conducted on the seismicity and casing deformation. Subsequently, a three-dimensional finite element model was developed to represent the casing-cement sheath-fault-formation assembly. A study was conducted to investigate the mechanism of casing shear deformation caused by fault slip, as well as the corresponding mechanical response of the casing. An investigation was conducted to analyze the influence of drilling and fracturing parameters on casing shear deformation. Additionally, strategies to effectively manage casing shear deformation were proposed. Furthermore, a novel approach to designing casing strength was introduced. The analysis of the data reveals that the Weiyuan, Changning, and Zhaotong shale gas fields exhibit high levels of tectonic stress, notable disparities in horizontal stress, and well-developed fault systems. The aforementioned factors are responsible for an increased occurrence of casing shear deformation and a greater probability of triggering earthquakes. The occurrence of fault slip results in the escalation of casing deformation and stress within a 1-meter vicinity of the fault. The casing Mises stress surpasses the yield strength with relative ease. The inclusion of casing deformation quantity in casing strength design can significantly reduce downhole incidents resulting from casing shear deformation during hydraulic fracturing operations.