Riser Recoil During Unscheduled Lower Marine Riser Package Disconnects

Abstract

Abstract In the event of a deep water emergency disconnection, the sudden release of the Lower Marine Riser Package (LMRP) connector can cause the riser string to reach destructive velocities and displacements. Impact between the outer barrel of the telescoping joint and the diverter housing must be avoided. Likewise, the LMRP assembly must lift a sufficient distance from the BOP stack to avoid impact due to oscillatory displacements caused by rig motion. The objectives that must be met by any riser recoil system are to reduce the risk of damage to the LMRP, BOP stack, riser string, and substructure (with associated equipment), so that when the conditions that forced the emergency disconnect sequence no longer exist, operations may resume without delay. This paper illustrates some of the significant variables affecting the velocity and displacement of the riser string and LMRP during an emergency disconnect sequence. The methods of controlling the emergency-disconnection process are reviewed. Correct modeling of physical forces at work can assist in applying control mechanisms to increase the envelope of safe operation of a tensioner system equipped with a riser recoil system (Fig. 1). A riser recoil test was conducted on an deepwater offshore drilling ship to test the effectiveness of the riser recoil control equipment, and to verify the model. P. 33