Recoil analysis of deepwater drilling riser after emergency disconnection

Abstract

In this paper, the mechanical model and governing equations for the recoil response of deepwater drilling riser are established based on the mass-spring-damping system with three degrees of freedom. The direct acting tensioner (DAT) and axial elongation of riser before disconnection the are taken as the boundary condition and initial condition of the mechanical model, respectively. The model can consider the influence of frictional resistance induced by drilling mud discharge and elastic potential energy due to axial elongation on the recoil response. The clearance between the Low Marine Riser Package (LMRP) and the blowout preventer (BOP) after disconnection is figured out through solving the governing equations. Then, the parameter sensitivity analysis is given to present a comprehensive understanding of the recoil response. Analysis results show that the phase difference has a significant influence on the recoil response. The most favorable phase difference is 60°. The possibility of collision between the LMRP and the BOP increases with water depth and amplitude of the DAT. The top tensioner has an optimal heave motion frequency, which is the most advantageous for implementing riser emergency disconnection. Corresponding measures should be taken to prevent spring stiffness of the DAT from decreasing. Besides, riser with large diameter and wall thickness is conducive to a safe disconnection.