Theory and numerical analysis for two-dimensional recoil of deepwater drilling riser after emergency disconnection

Abstract

Riser systems usually encounter large offset and huge environmental loads when emergency disconnection. However, the two-dimensional recoil theory and research still lack. This paper consequently establishes the two-dimensional riser recoil dynamics theory and two-dimensional mud discharge theory. The interaction mechanism between the riser and discharged mud is discussed, and the types of discharged load and the contribution of internal fluid (FI) to the riser finite element matrix are clarified. Combining the method of integration and coordinates reconstruction, the actual ordinate of the riser and elongation of the tensioner are retrieved. Numerical analysis results show the FI mass and gravity should not be included in the axial part of the riser element matrix during recoiling. The additional inertial load of FI due to the movement of the riser element influences the transverse displacement. The extremums of VM and bending moment appear at two ends of the riser system during early recoil stage. Transverse deformation of the riser system significantly affects the longitudinal displacement, which cannot be ignored. The dynamic responses of recoil in different two-dimensional scenarios are explored, including in different wave and current environments, at different vessel offset points, and with different vessel transverse velocities.