On the interaction between severe slug buildup and dynamic response of a submerged top-tensioned riser

Severe slugging in deepwater flowlines and risers systems is one of the flow assurance problems that interrupts the steadily flow of reservoir fluids, most severely in offshore oilfields with undulated seabed terrain. This flow regime threatens the structural integrity of subsea production systems due to its fatigue loading behaviour which prompts the need to investigate its impact on the riser stability. A mathematical model which based on a modified Euler-Bernoulli beam theory and plug flow is presented to analyse the dynamic response of a riser during severe slug buildup. Solution for the transverse deflections of the riser in space and time was sought through finite difference approximations with implicit space and explicit time discretization scheme implemented in Matlab, with an adaptive algorithm that computes the changing hydrostatic pressure in the riser due to the severe slug buildup. The dynamic response of the riser was observed to be undergoing a damped vibration with decaying amplitude. Accuracy of the solution was verified with a coupled fluid-structure interaction simulation in Abaqus. Parametric studies on velocity variations and riser responses were conducted. The mathematical solution presented in this paper has opened a new idea for riser pipe analysis with respect to severe slug flow.