Oil and gas development in certain harsh environments, such as extreme storm prone areas or arctic regions, may require the floating production platform to be designed to enable it to be released from its risers and moorings and moved out of the way of the approaching threat. Such floating platforms generally employ an underwater disconnectable buoy to support the moorings and risers after the main platform is moved away. For a deep draft floating structure, the risers can be released from their support near the top of the platform and lowered through the hull to a disconnectable buoy. In such a case, the risers can be routed through I-tubes and lowered in a controlled manner using rigging during a normal release operation. However, an emergency disconnection may require lowering of the risers without guidance of rigging. To avoid damage to the risers and the buoy during the emergency disconnection, risers can be fitted with passive damping devices to limit the lowering riser speed. This paper presents the numerical efforts to define the emergency riser release and lowering procedure. CFD simulations were performed to evaluate the hydrodynamic behavior of a disconnected riser in a flooded I-tube with the controlling devices attached to the risers. Applying the CFD results, riser lowering performance was computed using finite element analysis method. Primary parameters that affect flexible riser behavior, including stress level and curvature, are identified and sensitivity study results are presented. This paper concludes that a safe and controlled riser release procedure and system is achievable.

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