Study on Riser System in Hang-Off Configuration for Deep-Sea Mining

For Deep Sea Mining (DSM), the current concept for the Vertical Transport System (VTS) has multiple lines for the return of water to the sea bottom. Such VTS resembles a drilling riser, which is a field-proven technology. Our objective is to compare a drilling riser with different boundary conditions, including hang-off configuration. Numerical simulation was calculated using commercial software for dynamic analysis of riser systems. The simulation included a 1, 500m long riser, sea current, irregular waves, and the platform motion calculated using Response Amplitude Operator. For the top tensioned configuration, the tensioning system is required to avoid the riser pipe's buckling and the Mathieu Instability at the bottom portion of the riser. On the other hand, the same phenomenon did not occur in the hang-off configuration. The LMRP and BOP attached to the bottom end kept the riser pipe tensioned during the whole simulation. Therefore, the hang-off configuration is an important alternative for DSM riser. Besides, a tensioning system shall be mandatory for VTS when supported or attached to the seafloor.