On the collapse resistance of multilayer cemented casing in directional well under anisotropic formation

• The mechanical characteristics of a multilayer cemented casing system have been analyzed.
• The model has considered the wellbore deviation angle, azimuth angle and the formation transverse anisotropy simultaneously.
• A simplified model has been analyzed to verify the correctness of the method.
• The stress distributions of the system have been obtained.
• The influences of geometric parameters and mechanical parameters on the casing collapse resistance have been discussed.

In this paper, the mechanical characteristics of a multilayer cemented casing system in directional well under anisotropic formation have been presented to investigate the collapse resistance of casing under non-uniform in-situ stress. The model has considered the deviation angle, azimuth angle and the formation transverse anisotropy simultaneously. During analysis, the original in-situ stress tensor has been transformed into three stress tensors through the conversion of coordinate and stress decomposition based on the elastic mechanics. The formation mechanical parameters (Young's modulus and Poisson's ratio) have been taken as a function of wellbore circumferential angle during analysis procedure. In addition, a simplified model has been analyzed to verify the correctness of the method proposed in this paper. Subsequently, the stress distributions of the system have been obtained through solving the governing equations. On this basis, the influences of geometric parameters and mechanical parameters on the casing collapse resistance have been discussed to acquire a comprehensive understanding of this problem. Finally, some significant conclusions have been drawn based on the discussion mentioned above.