Search

Casing deformation occurs frequently in shale gas wells, resulting in the failure of some fracturing stages to complete normal operations, which seriously affects shale gas production. This paper firstly analyzes the casing deformation mechanism of shale gas wells and determines that the casing shear deformation caused by formation slip is the main factor of casing deformation. In order to solve the problem of casing shear deformation, a finite element numerical model including the formation, cement ring, and the casing is established. The casing shear deformation caused by formation slip is simulated, and the deformation results obtained are consistent with those measured in the actual wellbore. Based on the numerical model, a casing deformation governance method is proposed to optimize the wellbore trajectory and adjust the cement ring properties. It is calculated that reducing the dip angle á of the formation and casing vertical direction and reducing the formation slip is beneficial to reducing casing deformation. The use of low elastic modulus cement and uncementing operations can provide a buffer space for formation slip, effectively reduce casing deformation, and provide an effective treatment method for shear deformation of shale gas wells. [ABSTRACT FROM AUTHOR]

• Revealed the inherent mechanism of casing shear deformation. • Proposed measures to add a wellbore annulus buffer layer to reduce casing shear deformation. • Through experiments, it has been confirmed that adding a buffer layer can effectively reduce the shear deformation of the casing. • Optimized the structural parameters of the buffer layer through finite element method. In the process of exploiting shale gas, wells experience casing deformation at rates reaching 40%, leading to the failure of setting tools such as bridge plugs during completion operations. This failure results in cessation of fracturing operations, seriously affecting productivity. To reduce and reveal the mechanism of casing deformation, in this work, casing shear deformation experiments were designed and carried out simulating an 8.5-inch wellbore, which verified that the casing deformation was shear deformation caused by formation slip. Based on the mechanism of casing shear deformation, the measure of adding a wellbore annulus buffer layer to reduce casing shear deformation is proposed, and the finite-element method is used to verify that increasing the compressible space of the buffer layer and reducing the compression stiffness can further reduce the casing deformation. Finally, a casing shear deformation experiment with an added buffer layer was developed. The casing generated a few shear deformations under 40-mm formation slip, which verified the effectiveness of the measures proposed in this paper to reduce the shear deformation of the casing. [ABSTRACT FROM AUTHOR]