Movement optimization of freely-hanging deepwater risers in reentry

• The movement of riser upper end causes the oscillation of riser lower end.
• The oscillation of riser lower end brings about the connection difficulty.
• Movement optimization via ACO algorithm endeavors to reduce the oscillation.
• Tank experiment of a riser model confirms good efficiency of the optimized movement.
• Numerical analysis of a 1500 m flexible riser shows good efficiency of the optimized movement also.

Due to the complexity of riser dynamic behavior in various sea conditions, the reentry of the deepwater drilling riser to the seabed wellhead is difficult to perform. To facilitate reentry operation, Ant Colony Optimization (ACO) algorithm is adopted to optimize the movement of the riser upper end. Under optimized movement, the distance between the riser lower end and the seabed wellhead is shortened, and the oscillation of the riser lower end is damped quickly. To test the efficiency of reentry motion optimization, the water-tank experiments are carried out. The experimental results show the good efficiency of the movement optimization. For a 1500 m riser in deepwater drilling, the numerical simulations of ordinary and optimized reentry motions are shown also.